Semi-global stabilization by output feedback is studied for a class of nonuniformly observable and nonsmoothly stabilizable nonlinear systems. The contribution of this paper is to point out that most of the restrictive growth conditions required in the previous work can be relaxed or removed if a less demanding control objective, namely, semi-global instead of global stabilization is sought. In particular, it is proved that without imposing restrictive conditions, semi-global stabilization by nonsmooth output feedback can be achieved for a chain of odd power integrators perturbed by a smooth triangular vector field, although it is neither smoothly stabilizable nor uniformly observable. Extensions to nonstrictly triangular systems are also discussed in the two-dimensional case. Several examples are provided to illustrate the key features of the proposed semi-global output feedback controllers. Copyright © 2013 John Wiley & Sons, Ltd.

This paper studies an optimal state estimation (Kalman filtering) problem under the assumption that output measurements are subject to random time delays caused by network transmissions without time stamping. We first propose a random time delay model which mimics many practical digital network systems. We then study the so-called unbiased, uniformly bounded linear state estimators and show that the estimator structure is given based on the average of all received measurements at each time for different maximum time delays. The estimator gains can be derived by solving a set of recursive discrete-time Riccati equations. The estimator is guaranteed to be optimal in the sense that it is unbiased with uniformly bounded estimation error covariance. A simulation example shows the effectiveness of the proposed algorithm.Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, we introduce an online algorithm that uses integral reinforcement knowledge for learning the continuous-time optimal control solution for nonlinear systems with infinite horizon costs and partial knowledge of the system dynamics. This algorithm is a data-based approach to the solution of the Hamilton–Jacobi–Bellman equation, and it does not require explicit knowledge on the system's drift dynamics. A novel adaptive control algorithm is given that is based on policy iteration and implemented using an actor/critic structure having two adaptive approximator structures. Both actor and critic approximation networks are adapted simultaneously. A persistence of excitation condition is required to guarantee convergence of the critic to the actual optimal value function. Novel adaptive control tuning algorithms are given for both critic and actor networks, with extra terms in the actor tuning law being required to guarantee closed loop dynamical stability. The approximate convergence to the optimal controller is proven, and stability of the system is also guaranteed. Simulation examples support the theoretical result. Copyright © 2013 John Wiley & Sons, Ltd.

This paper deals with the consensus problem of second-order multi-agent systems with sampled data. Because of the unavailable velocity information, consensus problem is studied only by using the sampled position information. The final consensus states of multi-agent system are given. And a necessary and sufficient consensus condition is provided, which depends on the parameters of sampling interval, eigenvalues of Laplacian matrix, and coupling strengths. Then, the case that both the sampled position and velocity information can be obtained is discussed. On the basis of introducing a time-varying piecewise-continuous delay and proposing a novel time-dependent Lyapunov functional, the sufficient consensus condition is presented, and the upper bound of sampling interval can be estimated. Simulation examples are provided finally to demonstrate the effectiveness of the proposed design methods. Copyright © 2013 John Wiley & Sons, Ltd.

Anti-windup systems are modified control structures, which are designed to compensate against the detrimental effects of saturations. This manuscript considers primarily the stability robustness of two well-known anti-windup structures. Sufficient conditions for the stability robustness of the anti-windup structures and optimal robustness against structured norm-bounded plant uncertainty are found. A saturated loop is said to be optimally robust if the constrained loop is as robust as its unconstrained counterpart. The robustness condition is shown to be less conservative than existing results on additive uncertainty. Although it is known that the conventional internal model control provides optimal robustness against additive unstructured uncertainty, this is not the case against the more general uncertainty structure. Copyright © 2013 John Wiley & Sons, Ltd.

This paper is concerned with the problem of stabilizing a linear system with input delay. Motivated by the first-order truncated predictor feedback (TPF) approach recently developed by the authors, a general higher-order TPF controller that contains higher-order terms of the nominal feedback gains is proposed. It is shown that this higher-order TPF can also globally and semi-globally stabilize the concerned time-delay systems in the absence and in the presence of input saturation, respectively. Safe implementation via numerical approximation of this higher-order TPF is also established. However, in spite of the fact that the higher-order TPF utilizes more information of the state, numerical examples have demonstrated that the first-order TPF outperforms the higher-order TPF, indicating that the intuition of higher-order approximation leading to better results is incorrect in this case.Copyright © 2013 John Wiley & Sons, Ltd.

This paper presents a robust fault detection and isolation scheme using a sliding mode observer based on a linear parameter varying system, with fault reconstruction capability. Both actuator and sensor fault reconstruction schemes are considered that possess robustness against a certain class of uncertainty and corrupted measurements. For actuator fault reconstruction, the input distribution matrix (associated with the actuators being monitored) is factorized into fixed and varying components. LMIs are used to design the key observer parameters in order to minimize the effect of uncertainty and measurement corruption on the fault reconstruction signal. The faults are reconstructed using the output error injection signal associated with the nonlinear term of the sliding mode observer. For sensor fault reconstruction, the idea is to reformulate the problem into an actuator fault reconstruction scenario so that the same design procedure can be applied. This is achieved by augmenting the original system with the filtered sensors being monitored. Simulations using a full nonlinear model of a large transport aircraft are presented and show good fault reconstruction performance. Copyright © 2013 John Wiley & Sons, Ltd.

Observability is a basic, yet challenging, issue when studying Boolean control networks (BCNs). Recently, a criterion for observability of controllable BCNs was proposed by using the algebraic representation of logical dynamics based on the technique of the semi-tensor product of matrices. In this paper, we present new necessary and sufficient conditions guaranteeing observability of a BCN without preassuming its controllability. The conditions are hence more general. Some examples are worked out to illustrate the obtained results. Copyright © 2013 John Wiley & Sons, Ltd.

A multiple-model adaptive control methodology is proposed that is able to provide stability and performance guarantees, for uncertain linear parameter-varying plants. The identification problem is addressed by taking advantage of recent advances in model falsification using set-valued observers (SVOs). These SVOs provide set-valued estimates of the state of the system, according to its dynamic model. If such estimate is the empty set, the underlying dynamic model is invalidated, and a different controller is connected to the loop. The behavior of the proposed control algorithm is demonstrated in simulation, by resorting to a mass–spring–dashpot system. As a caveat, the computational burden associated with the SVOs can be prohibitive under some circumstances. Copyright © 2013 John Wiley & Sons, Ltd.

This study is concerned with the problem of robust delay-probability-distribution-dependent stability of uncertain stochastic genetic regulatory networks with mixed time-varying delays. The parameter uncertainties are modeled as having a structured linear fractional form. Besides, we consider that the derivatives of the discrete time delays have different upper bounds in various delay intervals. Moreover, less conservative conditions are obtained by choosing an augmented novel Lyapunov–Krasovskii functional and using the lower bound lemma together with the Jensen inequality lemma. Furthermore, the criteria can be applicable to both fast and slow time-varying delays. Finally, numerical examples are presented to illustrate the effectiveness of the theoretical results. Copyright © 2013 John Wiley & Sons, Ltd.

Without assuming that the mobile agents can communicate with their neighbors all the time, the consensus problem of multi-agent systems with general linear node dynamics and a fixed directed topology is investigated. To achieve consensus, a new class of distributed protocols designed based only on the intermittent relative information are presented. By using tools from matrix analysis and switching systems theory, it is theoretically shown that the consensus in multi-agent systems with a periodic intermittent communication and directed topology containing a spanning tree can be cast into the stability of a set of low-dimensional switching systems. It is proved that there exists a protocol guaranteeing consensus if each agent is stabilizable and the communication rate is larger than a threshold value. Furthermore, a multi-step intermittent consensus protocol design procedure is provided. The consensus algorithm is then extended to solve the formation control problem of linear multi-agent systems with intermittent communication constraints as well as the consensus tracking problem with switching directed topologies. Finally, some numerical simulations are provided to verify the effectiveness of the theoretical results. Copyright © 2013 John Wiley & Sons, Ltd.

This paper is concerned with the decentralized stabilization problem for a class of large-scale feedforward nonlinear time-delay systems. The uncertain nonlinearities involved in the systems are assumed to be bounded by continuous functions of the inputs and delayed inputs multiplied by unmeasured states and delayed states. An observer-based decentralized output feedback control scheme is proposed by using the dynamic gain control design approach. On the basis of the Lyapunov–Krasovskii stability theory, the global asymptotic stability of the closed-loop control system is proved. Contrary to many existing control designs for feedforward nonlinear systems, the celebrated forwarding design and saturation design are not utilized here. An example is finally given to demonstrate the effectiveness of the proposed design procedure. Copyright © 2013 John Wiley & Sons, Ltd.

This paper proposes an improvement to the delay-dependent stability of discrete systems with time-varying delays. The approach is based on the observation that the positive definiteness of a chosen Lyapunov–Krasovskii functional does not necessarily require all the involved symmetric matrices to be positive definite, which has been overlooked in the literature. The derived delay-dependent stability conditions are in terms of linear matrix inequalities. It is theoretically proved that our results are less conservative than the corresponding ones obtained by requiring the positive definiteness of all the symmetric matrices in a chosen Lyapunov–Krasovskii functional. The importance of the present approach is that a great number of delay-dependent analysis and synthesis results obtained by the aforementioned requirement in the literature can be improved by the present approach without introducing any new decision variables. Copyright © 2013 John Wiley & Sons, Ltd.

This paper introduces a novel solution for the multi-input multi-output (MIMO) quantitative feedback theory control design problem with tracking error specifications. Looking for a minimum controller overdesign, the technique finds new controller quantitative feedback theory bounds based on necessary and sufficient conditions for the existence of suitable associated prefilter matrix elements. It improves previous approaches to the subject and includes (i) the possibility of a free selection of the nominal plant, (ii) a less conservative application of the Schwartz inequality to decisively reduce the potential controller overdesign, (iii) a methodology to design independently the elements of the prefilter matrix, and (iv) a scope of application to both sequential and nonsequential MIMO controller design methods. The benefits of the new control design technique are illustrated by means of two examples. The first one, a standard 2 × 2 MIMO problem, is provided for comparison purposes with previous approaches. The second example, included as a major control challenge, deals with a well-known demanding distillation column benchmark problem. Copyright © 2013 John Wiley & Sons, Ltd.

Many well studied classes of dynamical systems such as actuator-constrained linear systems and dynamic artificial neural networks can be written as discrete-time Luré systems with sector-bounded and/or slope-restricted nonlinearities. Two types of observer-based output feedback control design methods are presented, compared, and analyzed with regard to robustness to model uncertainties and insensitivity to output disturbances. The controller designs are formulated in terms of LMIs that are solvable with standard software. The design equations are illustrated in numerical examples.Copyright © 2013 John Wiley & Sons, Ltd.

This paper investigates the problems of stability analysis and stabilization for stochastic time-delay systems. Firstly, this paper uses the martingale theory to investigate expectations of stochastic cross terms containing the Itô integral. On the basis of this, an improved delay-dependent stability criterion is derived for stochastic delay systems. In the derivation process, the mathematical development avoids bounding stochastic cross terms, and neither model transformation method nor free-weighting-matrix method is used. Thus, the method leads to a simple criterion and shows less conservatism. Secondly, on the basis of this stability result, this paper further proposes a state-feedback controller that exponentially stabilizes the stochastic delay system by a strict LMI. Therefore, unlike previous results, it is not necessary to transform the nonlinear matrix inequalities into LMIs by the cone complementarity linearization method or parameter-tuning method, which always yield a suboptimal solution. Finally, examples are provided to demonstrate the reduced conservatism of the proposed conditions.Copyright © 2013 John Wiley & Sons, Ltd.

This paper studies finite-time coordinated tracking problem for multiple double integrator systems with a time-varying leader's velocity and bounded external disturbances. We consider the dynamic feedback designs for two different cases. In the first case, the velocities of the followers and the leader are assumed to be unavailable, and the communication topology is assumed to be undirected and fixed. In the second case, the velocities of the followers and the leader are assumed to be available, and the communication topology is assumed to be directed and switching. Distributed finite-time observers are designed, respectively, to obtain the velocity information in the first case and the relative state information in the second case. The states of these observers are then used to design control inputs that achieve finite time robust coordinated tracking of multiple double integrator systems in the presence of bounded disturbances for these two cases. Simulation results are provided to validate the effectiveness of these theoretical results. Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, we present an invariant-set-based method for actuator and sensor fault detection and isolation in Lure systems. The Lure plant is controlled by an observer-based feedback tracking controller, designed for the nominal (fault-free) system. Suitable residual signals are constructed from measurable system outputs and estimates associated with the nominal observer. Faults are diagnosed by online contrasting the residual signal trajectories against sets of values that the residuals are shown to attain under healthy or faulty operation. These values are obtained via set-invariance analysis of the system closed-loop trajectories. Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, multi surface sliding cooperative control scheme is presented and new multiple sliding surfaces are proposed. It is proven that, for the setup that each agent is described by a chain of integrators, where the last integrator is perturbed by a bounded disturbance, leader–follower consensus can be achieved on these sliding surfaces if the communication graph has a directed spanning tree. Also, sliding variables can be driven to the sliding surfaces in fast finite time by the nonsmooth control law. The fast finite-time Lyapunov stability theorem, the terminal sliding control technique, and the adding a power integrator design approach are used in our proposed control. Simulation results demonstrate the effectiveness of the proposed scheme.Copyright © 2013 John Wiley & Sons, Ltd.

This paper addresses the finite horizon H_∞ control problem for a class of discrete-time nonlinear Markov jump systems with multiplicative noise and nonlinear feedback device. The system nonlinearity occurs in a random way specified by a Bernoulli process, whereas the actuator and sensor nonlinearities are restricted to a sector region. Both the state and the dynamic output feedback H_∞ controllers are devised in terms of difference LMIs. The proposed approach not only allows the resulting system to achieve a prescribed disturbance attenuation level, but also enables the output of actuator/sensor to meet the designated sector condition. Moreover, it is also shown that our approach is well-adapted for dealing with the discrete-time Markov jump systems with saturated actuator and sensor. Finally, a backward iterative algorithm is provided to solve the obtained difference LMIs and a numerical example is presented to verify the efficiency of the theoretical results.Copyright © 2013 John Wiley & Sons, Ltd.

In this brief, we extend the existing results on fault tolerant control via virtual actuator approach to a class of systems with Lipschitz nonlinearities to maintain the closed-loop stability after actuator faults. This generalization is established by relying on the input-to-state stability properties of cascaded systems. The virtual actuator block, placed between faulty plant and nominal controller, generates useful input signals for faulty plant by using output signals of the nominal controller to guarantee the closed-loop stability in the presence of actuator faults. This design problem is reduced to a matrix inequality that can be turned to an LMI by fixing a variable to a constant value and solving the resulting LMI feasibility problem. The proposed fault tolerant control method is successfully evaluated using a nonlinear system. Copyright © 2013 John Wiley & Sons, Ltd.

This paper discusses the problem of output feedback stabilization for a more general class of stochastic high-order nonlinear systems with time-varying delays. On the basis of a subtle homogeneous observer and controller construction, and the homogeneous domination approach, the closed-loop system is globally asymptotically stable in probability, by choosing an appropriate Lyapunov–Krasovskii functional. An example is given to illustrate the effectiveness of the proposed design procedure. Copyright © 2013 John Wiley & Sons, Ltd.

The problem of fault-tolerant control (FTC) for a class of uncertain nonlinear systems with actuator faults is discussed, and an observer-based FTC scheme is proposed. Adaptive fuzzy observers are designed to provide a bank of residuals for fault detection and isolation. Using a backstepping approach, we proposed a novel fault diagnosis algorithm, which removes the classical assumption that the time derivative of the output error should be known. Further, an accommodation scheme is proposed to compensate for the effect of the fault, where it is not needed to know the bounds of the time derivative of the fault. The proposed controller guarantees that all signals of the closed-loop system are semi-globally uniformly ultimately bounded and converge to a small neighborhood of the origin by appropriately choosing designed parameters. In addition, a sufficient condition for the existence of an fault detection and isolation observer is derived using Lyapunov stability theory. Finally, a numerical example and a practical aircraft longitudinal motion dynamics are used to demonstrate the effectiveness of the proposed FTC approach. Copyright © 2013 John Wiley & Sons, Ltd.

This paper describes a method for designing discrete time static output feedback sliding mode tracking controllers for uncertain systems that are not necessarily minimum phase or of relative degree one. In this work, a procedure for realizing discrete time controllers via a particular set of extended outputs is presented for systems with uncertainties. The conditions for existence of a sliding manifold guaranteeing a stable sliding motion are given. A procedure to synthesize a control law that minimizes the effect of the disturbance on the sliding mode dynamics and the augmented outputs is given. The proposed control law is then applied to a benchmark aircraft problem taken from the literature that represents the lateral dynamics of a F-14 aircraft under powered approach. Copyright © 2013 John Wiley & Sons, Ltd.

Synthesis of an observer-based linear parameter-varying controller is considered for a general linear parameter-varying plant. The parameter vector and its derivative are both assumed to take values in known bounded domains, whereas only the parameter vector is assumed to be measurable during online operation. The synthesis problem is considered for -gain and -type performance objectives. Potentially conservative parameter-dependent linear matrix inequality conditions are derived for the solvability of these two problems. To facilitate the reduction of conservatism, the conditions are expressed in a way to have bilinear dependence on an arbitrary positive scalar. In addition to employing a suitable relaxation scheme to reduce these conditions into finitely many constraints, a line search hence needs to be performed over the positive scalar to obtain the best achievable performance with an observer-based controller. The online implementation of the observer-based controller is relatively simpler if compared with a controller of unrestricted structure. Moreover, the observer-based controller will have no dependence on the parameter derivatives irrespective of the choices of the design variables. Copyright © 2013 John Wiley & Sons, Ltd.

The paper concerns the control of vertical take-off and landing (VTOL) underactuated aerial vehicles (UAVs) in hover flight, on the basis of measurements provided by an onboard video camera. The objective is to stabilize the vehicle to the equilibrium pose associated with an image of a planar target, using a minimal sensor suite and poor knowledge of the environment. By using the homography matrix computed from the camera measurements of the target, stabilizing feedback laws are derived on the basis of the visual data and gyrometer measurements only. Explicit stability conditions on the control parameters are provided, showing that a proper tuning of the control parameters ensures a large robustness margin with only planar target and visibility assumptions, although the target size and orientation, the UAV position, linear velocity and orientation are unknown. Additional issues, such as the use of accelerometers to improve the UAV's positioning in the case of unmodeled dynamics (such as wind), are also considered. Copyright © 2013 John Wiley & Sons, Ltd.

This paper describes the design of an active fault-tolerant control scheme that is applied to the actuator of a wind turbine benchmark. The methodology is based on adaptive filters obtained via the nonlinear geometric approach, which allows to obtain interesting decoupling property with respect to uncertainty affecting the wind turbine system. The controller accommodation scheme exploits the on-line estimate of the actuator fault signal generated by the adaptive filters. The nonlinearity of the wind turbine model is described by the mapping to the power conversion ratio from tip-speed ratio and blade pitch angles. This mapping represents the aerodynamic uncertainty, and usually is not known in analytical form, but in general represented by approximated two-dimensional maps (i.e. look-up tables). Therefore, this paper suggests a scheme to estimate this power conversion ratio in an analytical form by means of a two-dimensional polynomial, which is subsequently used for designing the active fault-tolerant control scheme. The wind turbine power generating unit of a grid is considered as a benchmark to show the design procedure, including the aspects of the nonlinear disturbance decoupling method, as well as the viability of the proposed approach. Extensive simulations of the benchmark process are practical tools for assessing experimentally the features of the developed actuator fault-tolerant control scheme, in the presence of modelling and measurement errors. Comparisons with different fault-tolerant schemes serve to highlight the advantages and drawbacks of the proposed methodology. Copyright © 2013 John Wiley & Sons, Ltd.

The problem of infinite-horizon H_∞ state-feedback tracking control for linear continuous time-invariant retarded systems with stochastic parameter uncertainties is investigated. Two tracking patterns are considered depending on the nature of the reference signal; that is, whether it is measured online or previewed in a fixed time-interval ahead. The stochastic uncertainties appear in the dynamics matrices for both the retarded and the non-retarded states of the system. The delayed system is transformed via the input–output approach, to an uncertain norm-bounded system. A new method that efficiently yields a min–max strategy to the solution of each of the aforementioned two cases is suggested where, given a specific reference signal, the controller plays against nature, which chooses the maximizing energy-bounded disturbance. The theoretical results are demonstrated by two examples that show the impact of the delay length and the preview length on the system performance. Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, we consider the problem of coordinating a collection of autonomous unmanned vehicles while guaranteeing collision avoidance. Each vehicle is regulated by a local controller that ensures stability and provides desired path tracking performance in the absence of constraints. The fulfillment of coordination tasks (e.g., collision avoidance) and local constraints (e.g., input saturation constraints) is achieved through a command governor (CG) strategy that, whenever necessary, modifies the nominal paths of the vehicles. First, a centralized CG approach is proposed and fully analyzed. Then, a more interesting distributed implementation requiring low communication rates is discussed. Both approaches make use of a receding horizon strategy and require the on-line solution of mixed-integer optimization programs. Finally, an example is given for illustration purposes.Copyright © 2013 John Wiley & Sons, Ltd.

This paper is concerned with the decentralized H_∞ controller synthesis problem for discrete-time LTI systems. Despite of intensive research efforts over the last several decades, this problem is believed to be nonconvex and still outstanding in general. Therefore, most of existing approaches resort to heuristic optimization algorithms that do not allow us to draw any definite conclusion on the quality of the designed controllers. To get around this difficulty, in this paper, we propose convex optimization procedures for computing lower bounds of the H_∞ performance that is achievable via decentralized LTI controllers of any order. In particular, we will show that sharpened lower bounds can be obtained by making good use of structures of the LTI plant typically observed in the decentralized control setting. We illustrate via numerical examples that these lower bounds are indeed useful to ensure the good quality of decentralized controllers designed by a heuristic optimization. Copyright © 2013 John Wiley & Sons, Ltd.

This paper develops a backstepping controller synthesis methodology for piecewise polynomial (PWP) systems in strict form. The main contribution of the paper is to formulate sufficient conditions for controller design for PWP systems in strict form as a sum of squares feasibility problem under the assumption that an initial control Lyapunov function exists to start the iterative backstepping procedure. This problem can then be translated into a convex SDP problem and solved by available software packages. The controller synthesis problem for PWP systems in strict feedback form is divided into two cases. The first case consists of the construction of a sum of squares polynomial control Lyapunov function for PWP systems with discontinuous vector fields. The second case addresses the construction of a PWP control Lyapunov function for PWP systems with continuous vector fields. One major advantage of the proposed method is the fact that it can handle systems with discontinuous vector fields and sliding modes. The new synthesis method is applied to several numerical examples. One of these examples offers the first convex optimization solution to piecewise affine (PWA) control of a benchmark circuit system addressed before in the literature using non-convex PWA control solutions. Copyright © 2013 John Wiley & Sons, Ltd.

The problem of designing a globally exponentially convergent observer for a class of (linear in transport and nonlinear in generation) semi-linear parabolic distributed systems is addressed within a matrix inequality framework, yielding (i) sufficient convergence conditions with physical meaning and (ii) the weight of a Lyapunov functional as design degree of freedom. The proposed approach is illustrated and tested with a representative case example in chemical reaction engineering. Copyright © 2013 John Wiley & Sons, Ltd.

This paper proposes a novel islanding fault detection method for distributed generation systems. Islanding fault detection of distributed generation systems in microgrids and smart grids is an essential security technology. The existing methods for islanding fault detection can be classified as passive methods (such as under/over voltage detection, under/over frequency detection, and voltage phase jump detection, based on natural effects of islanding) and active methods (impedance measurement, slip mode frequency shift, Sandia frequency shift and so on). Once the power consumed by a local load matches the power generated by a local inverter, the islanding phenomenon will be not obvious, and traditional passive methods may fail. In contrast, the active methods can overcome this disadvantage. However, active methods create extra disturbances that may degrade the quality of power generated by the inverter. By reducing the harmonics of the inverter output, coupled with the use of a novel filtering method, the proposed approach can be achieved without additional disturbance and does no nondetection zone islanding detection. In this paper, current harmonic compensation is applied to inverter control to minimize the inverter output harmonics, highlighting on the grid harmonics. Set-membership filter is developed to estimate the voltage harmonics. Islanding condition is detected by the changes of the specific order harmonics. The effectiveness of the proposed method is demonstrated by simulations. A Kalman filter contrast experiment is presented to confirm that the set-membership filter can more effectively detect islanding. Copyright © 2013 John Wiley & Sons, Ltd.

The asymptotic rejection of spacecraft systems under multi-tone sinusoidal disturbances has been studied recently for the case where the frequencies of the disturbance are known. In this paper, we further consider the case where the frequencies of the disturbance are unknown. We show that this case can be solved by an adaptive regulation technique. We also present some analysis on the convergence issue of the estimated frequencies to unknown frequencies. Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, we consider the estimation problem of a class of single-input–single-output nonlinear Lipschitz systems with nonmatching uncertainty or disturbance, where the distribution vector may include the unknown states. A hybrid nonlinear observer structure that combines a high-gain feedback with higher order sliding mode term is proposed. The high-gain feedback works to constrain the estimation error to within an invariant set, and the sliding mode term will asymptotically track the uncertainty if the system satisfies strict structure assumptions. Furthermore, with the higher order sliding mode, the chattering effect will be effectively attenuated without sacrificing robustness, and the system uncertainty can be recovered without filtering effect. Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, passive and active approaches for the design of fault-tolerant controllers (FTCs) are presented. The FTCs are used to improve the damping of inter-area oscillations in a power grid. The effectiveness of using a combination of local and remote (wide area) feedback signals is first demonstrated. The challenge is then to guarantee a minimum level of dynamic performance following a loss of remote signals. The designs are based on regional pole placement using linear matrix inequalities. First, a passive FTC is proposed. It is shown that the computation of the controller reduces to the solution of bilinear matrix inequalities. An iterative procedure is then used to design the controller. Next, as an alternative to active, time-varying controllers, one for each fault scenario, we propose an approach for the design of a ‘minimal switching’ FTC in which only one controller is designed, but where a simple switch is incorporated into the controller structure. A case study in a linear and nonlinear Nordic equivalent system is presented to show that the closed-loop response using a conventional control design could deteriorate the performance or even destabilize the system if the remote signals are lost and to demonstrate the effectiveness of the proposed FTC designs. Copyright © 2013 John Wiley & Sons, Ltd.

This paper presents a new nonlinear polynomial controller for wind turbines that assures stability and maximizes the energy produced while imposing a bound in the generated power derivative in normal operation (guarantees a smooth operation against wind turbulence). The proposed controller structure also allows eventually producing a transient power increase to provide grid support, in response to a demand from a frequency controller. The controller design uses new optimization over polynomials techniques, leading to a tractable semidefinite programming problem.

The ability of the wind turbine to increase its power under partial load operation has been analysed. The aforementioned optimization techniques have allowed quantifying the maximum transient overproduction that can be demanded to the wind turbine without violating minimum speed constraints (that could lead to unstable behaviour), as well as the total generated energy loss. The ability to evaluate this shortfall has permitted the development of an optimization procedure in which wind farm overproduction requirements are divided into individual turbines, assuring that the total energy loss in the wind farm is minimum, while complying with the maximum demanded power constraints. Copyright © 2013 John Wiley & Sons, Ltd.

This paper proposes a robust H_∞-based adaptive backstepping control scheme for the output stabilization of a special class of cascaded nonlinear systems. This kind of systems possess the feature that the first sub-equation is a linear perturbed system, whereas the rest ones perform a general semi-strict feedback form. Different from the conventional backstepping design approach, the special cascaded structure ensures to introduce the H_∞ technique to the backstepping procedure such that both the robust performance and the robust stability can be simultaneously guaranteed. Within the Lyapunov framework, the proposed control scheme is proved to guarantee (i) the uniformly ultimate boundedness of the system signals with a bound that can be made arbitrarily small by suitably choosing control parameters; (ii) asymptotic output stabilization as long as the uncertain nonlinearities and external disturbances vanish; and (iii) -performance of the closed-loop system. A space interception scenario is utilized to demonstrate the effectiveness of the proposed control scheme. Copyright © 2013 John Wiley & Sons, Ltd.

This paper presents a fault detection approach for discrete-time affine linear parameter varying systems with additive faults. A finite horizon input-output linear parameter varying model is used to obtain a linear in the model parameter regression residual form. The bias in the residual term vanishes because of quadratic stability of an underlying observer. The new methodology avoids projecting the residual onto a parity space, which in real time requires at least quadratic computational complexity. When neglecting the bias, the fault detection is carried out by an χ² hypothesis test. Finally, the algorithm uses model parameters that can be identified prior to the on-line fault detection with linear least squares. A realtime experiment is carried out to demonstrate the viability of the proposed method. Copyright © 2013 John Wiley & Sons, Ltd.

The paper is devoted to investigating sliding mode control for a class of nonlinear uncertain stochastic systems with input nonlinearity and Markovian switching. A nonfragile observer subjected to the transition rates of the modes is designed. By some specified matrices, the connections among the designed sliding surfaces corresponding to every mode are established. The state estimation-based sliding mode control law is derived to guarantee the reachability of the sliding surface in finite time interval. The sufficient conditions on asymptotically stochastic stability of the error system and sliding mode dynamics with a given disturbance attenuation level are derived in terms of linear matrix inequalities. Finally, an example is provided to illustrate the efficiency of the proposed method. Copyright © 2013 John Wiley & Sons, Ltd.

This paper considers the problem of reliable decentralized stabilization with multicontroller configurations when some of the controllers are faulty in the sense that they fail to act optimally or do not function in the way that they were originally intended to function. Specifically, we introduce a solution concept that requires controllers to respond optimally (i.e. in the sense of best-response correspondences) to the nonfaulty controllers regardless of the identity or actions of the faulty controllers. At any time, we assume that the nonfaulty controllers know only that there can be at most one faulty controller in the system, but they know neither the identity of the faulty controller nor how this faulty controller behaves. We present a design framework using an extended linear matrix inequality technique for deriving reliable stabilizing state-feedback gains; whereas a set of filters whose estimation-error dynamics satisfy certain quadratic integral constraints is used as decentralized observers within the subsystems for extending the result to the output-feedback case. Moreover, a sufficient condition for solvability of the problem is provided in terms of the minimum-phase condition of the subsystems. We also present an application of the results to a power system problem. Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, we are concerned with the boundary stabilization of a one-dimensional anti-stable Schrödinger equation subject to boundary control matched disturbance. We apply both the sliding mode control (SMC) and the active disturbance rejection control (ADRC) to deal with the disturbance. By the SMC approach, the disturbance is supposed to be bounded only. The existence and uniqueness of the solution for the closed-loop system is proved and the ‘reaching condition’ is obtained. Considering the SMC usually requires the large control gain and may exhibit chattering behavior, we develop the ADRC to attenuate the disturbance for which the derivative is also supposed to be bounded. Compared with the SMC, the advantage of the ADRC is not only using the continuous control but also giving an online estimation of the disturbance. It is shown that the resulting closed-loop system can reach any arbitrary given vicinity of zero as time goes to infinity and high gain tuning parameter goes to zero.Copyright © 2013 John Wiley & Sons, Ltd.

This paper presents a functional observer scheme using two sliding mode observers in cascade. A coordinate transformation is performed on the system such that existing sliding mode observer theory can be directly applied to achieve functional state estimation. The necessary and sufficient existence conditions for the scheme (in terms of the original system matrices) are also investigated, and they are found to be less stringent than earlier work on functional state estimation using one sliding mode observer; this could have benefits in terms of cost and simplicity. A numerical example verifies the effectiveness of the scheme. Copyright © 2013 John Wiley & Sons, Ltd.

Preserving Order Observers provide an estimation that is always above or below the true variable, and in the absence of uncertainties/perturbations, the estimation converges asymptotically to the true value of the variable. In this paper, we propose a novel methodology to design preserving order observers for a class of nonlinear systems in the nominal case or when perturbations/uncertainties are present. This objective is achieved by combining two important systemic properties: dissipativity and cooperativity. Dissipativity is used to guarantee the convergence of the estimation error dynamics, whereas cooperativity of the error dynamics assures the order-preserving properties of the observer. The use of dissipativity for observer design offers a big flexibility in the class of nonlinearities that can be considered while keeping the design simple: it leads in many situations to the solution of a linear matrix inequality (LMI). Cooperativity of the observer leads to an LMI. When both properties are considered simultaneously, the design of the observer can be reduced, in most cases, to the solution of both a bilinear matrix inequality and an LMI. Because a couple of preserving order observers, one above and one below, provide an interval observer, the proposed methodology unifies several interval observers design methods. The design methodology has been validated experimentally in a three-tanks system, and it has also been tested numerically and compared with an example from the literature.Copyright © 2013 John Wiley & Sons, Ltd.

This paper considers the problem of observer-based H_∞ controller design for a class of discrete-time nonhomogeneous Markov jump systems with nonlinear input. Actuator saturation is considered to be a nonlinear input of such system and the time-varying transition probability matrix in the system is described as a polytope set. Furthermore, a mode-dependent and parameter-dependent Lyapunov function is investigated, and a sufficient condition is derived to design observer-based controllers such that the resulting error dynamical system is stochastically stable and a prescribed H_∞ performance is achieved. Finally, estimation of attraction domain of such nonhomogeneous Markov jump systems is also made. A simulation example shows the effectiveness of developed techniques. Copyright © 2013 John Wiley & Sons, Ltd.

This paper investigates the problem of global disturbance rejection for switched nonlinear systems in strict-feedback form with unknown exosystem where the solvability of the disturbance rejection problem for subsystems is not assumed. First, a sufficient condition for the solvability of the global disturbance rejection problem is given. As an extension of the classic concept of internal model for non-switched systems, a new concept of switched internal model is proposed. Second, in order to solve the problem in question, a constructive adaptive control methodology is established on the basis of the multiple Lyapunov functions method, backstepping, and the changing supply functions technique. Finally, an example is provided to demonstrate the effectiveness of the proposed approach. Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, we consider the output synchronization problem for heterogeneous networks of right-invertible linear agents. We assume that all the agents are introspective, meaning that they have access to their own local measurements. Under this assumption, we then propose a decentralized control scheme for solving the output synchronization problem for a set of network topologies. The proposed scheme can also be applied to solve the output formation problem with arbitrary formation vectors. We also consider the regulation of output synchronization problem, where the output of each agent has to track an a priori specified reference trajectory, generated by an exosystem. In this case, we assume that the root agent has access to its own output relative to the reference trajectory.Copyright © 2013 John Wiley & Sons, Ltd.

We consider the problem of output feedback robust stabilization of a ducted-fan aerial vehicle in which high-gain observers are used to overtake the knowledge of the linear and angular velocities of the vehicle in the control law. The proposed result is semiglobal in the attitude dynamics and in the estimation error, and global in the position variables. It is shown how the high-gain control structure is effective notwithstanding the nonminimum-phase behavior of the considered class of systems, provided that the airframe fulfills some geometric properties. The controller relies upon the use of nested saturations and high-gain control laws. Although the theory is specified for a force-torque generation mechanism of a ducted-fan aerial vehicle, the results can be simply extended to the output feedback of many other under-actuated rotorcrafts, such as helicopters. Experimental results are also proposed showing the effectiveness of the control law. Copyright © 2013 John Wiley & Sons, Ltd.

External forces affect the dynamics of load-carrying robot devices. The knowledge of such disturbances is generally needed for control purposes. However, direct disturbance measurement using force sensors is not always possible. This paper introduces a force estimator for force-sensor-less robotic manipulators. The algorithm is based on the knowledge of the dynamics of the robotic device, whereas mass of the load is typically unknown. Using this algorithm, low-frequency external forces can be estimated robustly even for quasi-statically time-varying and uncertain loads. Experiments validate the proposed strategy in practice. Moreover, the applicability of the estimation algorithm is further illustrated by using it in a human–robot comanipulation setup in which the robot is providing additional coordinated forcing to alleviate human effort needed to manipulate the robot. Copyright © 2013 John Wiley & Sons, Ltd.

We study the local asymptotic stability of undirected formations of single-integrator and double-integrator modeled agents based on interagent distance control. First, we show that n-dimensional undirected formations of single-integrator modeled agents are locally asymptotically stable under a gradient control law. The stability analysis in this paper reveals that the local asymptotic stability does not require the infinitesimal rigidity of the formations. Second, on the basis of the topological equivalence of a dissipative Hamiltonian system and a gradient system, we show that the local asymptotic stability of undirected formations of double-integrator modeled agents in n-dimensional space is achieved under a gradient-like control law. Simulation results support the validity of the stability analysis. Copyright © 2013 John Wiley & Sons, Ltd.

This paper is concerned with the distributed filtering problem for a class of nonlinear systems with randomly occurring sensor saturations (ROSS) and successive packet dropouts in sensor networks. The issue of ROSS is brought up to account for the random nature of sensor saturations in a networked environment of sensors, and accordingly, a novel sensor model is proposed to describe both the ROSS and successive packet dropouts within a unified framework. Two sets of Bernoulli distributed white sequences are introduced to govern the random occurrences of the sensor saturations and successive packet dropouts. Through available output measurements from not only the individual sensor but also its neighboring sensors, a sufficient condition is established for the desired distributed filter to ensure that the filtering dynamics is exponentially mean-square stable and the prescribed performance constraint is satisfied. The solution of the distributed filter gains is characterized by solving an auxiliary convex optimization problem. Finally, a simulation example is provided to show the effectiveness of the proposed filtering scheme. Copyright © 2013 John Wiley & Sons, Ltd.

This paper investigates robust consensus for multi-agent systems with discrete-time dynamics affected by uncertainty. In particular, the paper considers multi-agent systems with single and double integrators, where the weighted adjacency matrix is a polynomial function of uncertain parameters constrained into a semialgebraic set. Firstly, necessary and sufficient conditions are provided for robust consensus based on the existence of a Lyapunov function polynomially dependent on the uncertainty. In particular, an upper bound on the degree required for achieving necessity is provided. Secondly, a necessary and sufficient condition is provided for robust consensus with single integrator and nonnegative weighted adjacency matrices based on the zeros of a polynomial. Lastly, it is shown how these conditions can be investigated through convex programming by exploiting linear matrix inequalities and sums of squares of polynomials. Some numerical examples illustrate the proposed results.Copyright © 2013 John Wiley & Sons, Ltd.

We propose an output feedback controller for a class of feedforward nonlinear systems under sensor noise. The sensor noise is any signal whose DC component is finite, which covers not only deterministic signals but also random signals including many practical noises. We introduce a notion of virtual state, then propose a measurement output feedback controller that utilizes a gain scaling factor. The gain scaling factor is commonly employed by the observer and controller. Through analysis, we show that all system states and output remain to be bounded in the presence of sensor noise, and the bound of states except output can be made arbitrarily small. Moreover, if the DC component of sensor noise is zero, the ultimate bound of the states and output can be made arbitrarily small by increasing the gain scaling factor in the presence of sensor noise.Copyright © 2013 John Wiley & Sons, Ltd.

Hybrid Petri nets represent a powerful modeling formalism that offers the possibility of integrating, in a natural way, continuous and discrete dynamics in a single net model. Usual control approaches for hybrid nets can be divided into discrete-time and continuous-time approaches. Continuous-time approaches are usually more precise, but can be computationally prohibitive. Discrete-time approaches are less complex, but can entail mode-mismatch errors due to fixed time discretization. This work proposes an optimization-based event-driven control approach that applies on continuous time models and where the control actions change when discrete events occur. Such an approach is computationally feasible for systems of interest in practice and avoids mode-mismatch errors. In order to handle modelling errors and exogenous disturbances, the proposed approach is implemented in a closed-loop strategy based on event-driven model predictive control.Copyright © 2013 John Wiley & Sons, Ltd.

Exponential necessary stability conditions for linear systems with multiple delays are presented. The originality of these conditions is that, in analogy with the case of delay free systems, they depend on the Lyapunov matrix function of the delay system. They are validated by examples for which the analytic characterization of the stability region is known. Copyright © 2013 John Wiley & Sons, Ltd.

Building an appropriate mathematical model that describes the system behaviour with a certain degree of satisfaction is quite challenging owing to the uncertain and volatile nature of thermodynamic constants and geometric parameters. In this paper, we present a technique to approximate and validate the dynamic behaviour of the Aström–Bell boiler-turbine power plant based on an RBFNN over a large operating range. The proposed RBFNN is applied to solve the parametric identification problem for nonlinear and complex systems using an optimiser based on a hybrid genetic algorithm. This optimiser is composed of the gradient descent optimiser and a genetic algorithm for fast convergence. Two simulations were performed to show the effectiveness of the proposed technique under different situations with several boiler-turbine input variables. The optimal structure and parameters of the obtained RBFNN-based model emulates well the dynamic behaviour of the Aström–Bell boiler-turbine system.Copyright © 2013 John Wiley & Sons, Ltd.

To improve the transient response of an electric power transmission system, a hybrid adaptive robust control method is proposed in this paper for the static var compensator by incorporating the immersion and invariance adaptive (I&I adaptive) and L₂-gain control. In contrast to the standard I&I adaptive control algorithm, establishing a target system is not required in constructing the robust control law with the proposed method. Thus, the procedure of solving PDEs to satisfy the immersion condition can be avoided. In addition, both parametric and non-parametric uncertainties, which commonly exist in electric power transmission systems, are considered. The parametric uncertainty induced by the damping coefficient of the system is estimated by the designed adaptive law, which is constructed by ensuring the estimation error converges to zero. The non-parametric uncertainty is caused by external disturbances and approximation errors in modeling the uncertain structure. By assuming that the L₂-gain of the system to the non-parametric uncertainties satisfies a dissipation inequality, we found that the robustness of the controller can be guaranteed. It is proved that all the system states are globally bounded and converge to a new stable equilibrium. Simulation results are also presented to show the effectiveness of the proposed control method in improving the transient response of the system and the convergence speed of the system states. Copyright © 2013 John Wiley & Sons, Ltd.

Optimal control problems for switched nonlinear systems are investigated. We propose an alternative approach for solving the optimal control problem for a nonlinear switched system based on the theory of moments. The essence of this method is the transformation of a nonlinear, nonconvex optimal control problem, that is, the switched system, into an equivalent optimal control problem with linear and convex structure, which allows us to obtain an equivalent convex formulation more appropriate to be solved by high-performance numerical computing. Consequently, we propose to convexify the control variables by means of the method of moments obtaining semidefinite programs. Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, the problem of fault detection for continuous-time switched systems under asynchronous switching is investigated. The designed fault detection filter is assumed to be asynchronous with the original systems. Attention is focused on designing a fault detection filter such that the estimation error between the residual and the fault is minimized in the sense of H_∞ norm. By employing piecewise Lyapunov function and average dwell time techniques, a sufficient condition for the existence of such a filter is exploited in terms of certain linear matrix inequalities. Finally, an example of a switched electrical circuit is provided to illustrate the effectiveness of the proposed approach.Copyright © 2013 John Wiley & Sons, Ltd.

We study the problem of designing state-feedback controllers to track time-varying state trajectories that may exhibit jumps. Both plants and controllers considered are modeled as hybrid dynamical systems, which are systems with both continuous and discrete dynamics, given in terms of a flow set, a flow map, a jump set, and a jump map. Using recently developed tools for the study of stability in hybrid systems, we recast the tracking problem as the task of asymptotically stabilizing a set, the tracking set, and derive conditions for the design of state-feedback tracking controllers with the property that the jump times of the plant coincide with those of the given reference trajectories. The resulting tracking controllers guarantee that solutions of the plant starting close to the reference trajectory stay close to it and that the difference between each solution of the controlled plant and the reference trajectory converges to zero asymptotically. Constructive conditions for tracking control design in terms of LMIs are proposed for a class of hybrid systems with linear maps and input-triggered jumps. The results are illustrated by various examples. Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, a trajectory planning approach is proposed for underactuated overhead cranes. Different from existing trajectory planning methods, the presented approach generates trajectory commands online without the necessity of iterative optimization, which is convenient for practical implementation. We demonstrate the performance of the proposed method, including swing elimination and precise trolley positioning, with rigorous Lyapunov-based mathematical analysis. Both numerical simulation and experimental results suggest that the presented method is feasible and efficient for practical applications. Copyright © 2013 John Wiley & Sons, Ltd.

The theory of H_∞ control of switched systems is extended to stochastic systems with state-multiplicative noise. Sufficient conditions are obtained for the mean square stability of these systems where dwell time constraint is imposed on the switching. Both nominal and uncertain polytopic systems are considered. A Lyapunov function, in a quadratic form, is assigned to each subsystem that is nonincreasing at the switching instants. During the dwell time, this function varies piecewise linearly in time following the last switch, and it becomes time invariant afterwards. Asymptotic stochastic stability of the set of subsystems is thus ensured by requiring the expected value of the infinitesimal generator of this function to be negative between switchings, resulting in conditions for stability in the form of LMIs. These conditions are extended to the case where the subsystems encounter polytopic-type parameter uncertainties. The method proposed is applied to the problem of finding an upper bound on the stochastic L₂-gain of the system. A solution to the robust state-feedback control problem is then derived, which is based on a modification of the L₂-gain bound result. Two examples are given that demonstrate the applicability of the proposed theory.Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, the problem of non-fragile observer-based H_∞ control for discrete-time switched delay systems is investigated. Both data missing and time delays are taken into account in the links from sensors to observers and from controllers to actuators. Because data missing satisfies the Bernoulli distribution, such problem is transformed into an H_∞ control problem for stochastic switched delay systems. Average dwell time approach is used to obtain sufficient conditions on the solvability of such problems. A numerical example and a real example for water quality control are provided to illustrate the effectiveness and potential applications of the proposed techniques. Copyright © 2013 John Wiley & Sons, Ltd.

This paper considers the problem of stabilizing a single-input single-output linear time varying system using a low order controller and a reference model. The closed loop is a linear singularly perturbed system with uniform asymptotic stability behavior. We calculate bounds ϵ ∈ (0,ϵ^*) as in Kokotović's book, such that the uniform asymptotic stability of the singularly perturbed system is guaranteed. We show how to design a control law such that the system dynamics is assigned by a Hurwitz polynomial with constant coefficients.Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, adaptive NN control is proposed for bilateral teleoperation system with dynamic uncertainties, unknown external disturbances, and unsymmetrical stochastic delays in communication channel to achieve transparency and robust stability. Compared with previous passivity-based teleoperation framework, the communication delays are unsymmetrical and stochastic. By partial feedback linearization using nominal dynamics, the nonlinear dynamics of the teleoperation system are transformed into two subsystems: local master/slave dynamics control and time-delay motion tracking. By integrating Markov jump systems and adaptive parameters updating, adaptive NN control strategy is developed. The stability of the closed-loop system and the boundedness of tracking errors are proved using Lyapunov–Krasovskii functional synthesis under specific linear matrix inequalities conditions. The proposed adaptive NN control is robust against motion disturbances, parametric uncertainties, and unsymmetrical stochastic delay, which effectiveness is validated by extensive simulation studies.Copyright © 2013 John Wiley & Sons, Ltd.

In this work, stability analysis is performed for a cyclic dynamical model of gene regulatory networks involving time delays, under negative feedback. The model considered has nonlinearities with negative Schwarzian derivatives. Sufficient conditions implying global stability of these types of GRNs are obtained. The special case of homogenous gene regulatory networks is also studied; in this case, the proposed stability conditions depend only on the parameters of the nonlinearity function. Illustrative numerical examples complete the presentation.Copyright © 2013 John Wiley & Sons, Ltd.

This paper is devoted to the attitude control of a quaternion missile model, which is nonlinear in aerodynamics with atmospheric moment uncertainties, inertia uncertainties, bounded disturbances and actuator failures. By employing the back-stepping technique, the corresponding sliding mode controller is designed to guarantee the state variables of the closed loop system to converge to a small region of the reference states with the help of the adaptive law by estimating the total uncertainties, and be chatter-free. Also, simulation results are presented to illustrate the effectiveness of the control strategy. Copyright © 2013 John Wiley & Sons, Ltd.

The discrete-time and continuous-time fuzzy systems with quantization and packet dropout are considered in this paper. The quantizer used here is a uniform one with arbitrary quantization regions, and the packet dropout process is modeled as a time-homogenous Markov process. Because of the properties of packet dropout process, the fuzzy systems considered here are seen as Markov jump fuzzy systems, and the theories of Markov jump system are used to discuss the mean square stability of the closed-loop systems. On the basis of the zoom strategy and Lyapunov theory, for the given failure rate and recovery rate, sufficient conditions are given for the closed-loop fuzzy systems to be mean square stable, and the feedback controllers are designed to ensure the stability of fuzzy systems. A single link direct joint driven manipulator model is presented to show the effectiveness of the main results.Copyright © 2013 John Wiley & Sons, Ltd.

This paper is concerned with the stabilization problem for a class of state-constrained switched nonlinear system in p-normal form in a domain. A key point in the backstepping design procedure is to find a common stabilizing function at each step. A barrier Lyapunov function, which grows to infinity when its arguments approach some limits, is introduced to ensure that the state constraint is not violated at any time. Bounded state feedback controllers of individual subsystems and a common Lyapunov function are explicitly constructed to asymptotically stabilize the closed-loop system under arbitrary switchings. An example is given to show the effectiveness of the proposed method.Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, we study the problem of control of discrete-time linear time varying systems over uncertain channels. The uncertainty in the channels is modeled as a stochastic random variable. We use exponential mean square stability of the closed-loop system as a stability criterion. We show that fundamental limitations arise for the mean square exponential stabilization for the closed-loop system expressed in terms of statistics of channel uncertainty and the positive Lyapunov exponent of the open-loop uncontrolled system. Our results generalize the existing results known in the case of linear time invariant systems, where Lyapunov exponents are shown to emerge as the generalization of eigenvalues from linear time invariant systems to linear time varying systems. Simulation results are presented to verify the main results of this paper.Copyright © 2012 John Wiley & Sons, Ltd.

This paper studies the multi-equilibrium property of the multiple substrates and multiple products with no inhibition (MMN) module. On the basis of the topological structure, a model for such module is established in the form of a set of nonlinear ordinary differential equations. It is shown that the injectivity of the MMN module is equivalent to the nonsingularity of Jacobian matrix of its rate function, and a necessary and sufficient condition for the injectivity is obtained by using the Hadamard product. For non-injective MMN module, a sufficient condition for existence of multiple positive equilibria is provided by introducing the concept of input-matrix. For a type of commonly encountered MMN module— -MMN module—a structure-oriented criterion for judging its injectivity is given. For -MMN modules with some special structure, it is shown that there does not exist multiply equilibria and the equilibrium (if exists) is asymptotically stable. Examples and simulations are given to illustrate the results obtained. Copyright © 2012 John Wiley & Sons, Ltd.

The problem of stabilizing networks of interconnected dynamical systems (NDS) in a scalable fashion is considered. As the first contribution, a generalized lemma and example network are provided to demonstrate that state-of-the-art, tractable dissipation-based NDS stabilization methods can fail even for simple unconstrained, linear, and time-invariant dynamics. Then, a solution to this issue is proposed, in which controller synthesis is decentralized via a set of parameterized storage functions. The corresponding stability conditions allow for max-type construction of a trajectory-specific Lyapunov function for the full closed-loop network, whereas neither of the local storage functions is required to be monotonically converging. The provided approach is indicated to be nonconservative in the sense that it can generate converging closed-loop trajectories for the motivating example network and a prescribed set of initial conditions. For input-affine NDS and quadratic parameterized storage functions, the synthesis scheme can be formulated as a set of low-complexity semidefinite programs that are solved online, in a receding horizon fashion. Moreover, for linear and time-invariant networks, an even simpler, explicit control scheme is derived by interpolating a collection of a priori generated converging state and control trajectories in a distributed fashion. Copyright © 2012 John Wiley & Sons, Ltd.

This paper provides a deep insight into the saturated PID control of a double integrator with bounded disturbance. On the basis of the nested saturation functions, a simple PID-like controller is proposed. The main difficulty in saturation control with bounded disturbances is to prove that the unsaturated regions are invariant. By phase plane and singular perturbation analysis, we prove that the saturation restrictions on the controller can be removed one by one in finite time, and the closed-loop system can be finally reduced to a nonsaturated PID controlled double integrator. The sufficient conditions for the stability of the closed loop with disturbance are also derived. Finally, numerical simulations are conducted to validate the effectiveness of the proposed control scheme.Copyright © 2012 John Wiley & Sons, Ltd.

This paper investigates the problem of adaptive neural control design for a class of single-input single-output strict-feedback stochastic nonlinear systems whose output is an known linear function. The radial basis function neural networks are used to approximate the nonlinearities, and adaptive backstepping technique is employed to construct controllers. It is shown that the proposed controller ensures that all signals of the closed-loop system remain bounded in probability, and the tracking error converges to an arbitrarily small neighborhood around the origin in the sense of mean quartic value. The salient property of the proposed scheme is that only one adaptive parameter is needed to be tuned online. So, the computational burden is considerably alleviated. Finally, two numerical examples are used to demonstrate the effectiveness of the proposed approach.Copyright © 2012 John Wiley & Sons, Ltd.

This paper addresses exponential stability of linear networked control systems. More specifically, the paper considers a continuous-time linear plant in feedback with a linear sampled-data controller with an unknown time varying sampling rate, the possibility of data packet dropout, and an uncertain time varying delay. The main contribution of this paper is the derivation of new sufficient stability conditions for linear networked control systems taking into account all of these factors. The stability conditions are based on a modified Lyapunov–Krasovskii functional. The stability results are also applied to the case where limited information on the delay bounds is available. The case of linear sampled-data systems is studied as a corollary of the networked control case. Furthermore, the paper also formulates the problem of finding a lower bound on the maximum network-induced delay that preserves exponential stability as a convex optimization program in terms of linear matrix inequalities. This problem can be solved efficiently from both practical and theoretical points of view. Finally, as a comparison, we show that the stability conditions proposed in this paper compare favorably with the ones available in the open literature for different benchmark problems. Copyright © 2012 John Wiley & Sons, Ltd.

Designing an interval observer with stability properties for nonlinear systems, which are not cooperative and not globally Lipschitz, is an open problem. This paper studies a general canonical structure for which interval observers with input to state stability (ISS) properties can be derived. This canonical block triangular nonlinear structure is rather general and may result from a change of coordinates or an output injection. We provide a general method for explicitly constructing framers for systems for which can be given such a structure. We also construct ISS interval observers when additional properties are satisfied. The systems we consider are in general not cooperative and not globally Lipschitz. We illustrate the constructions by designing a framer and an ISS interval observer for two models of bioreactors. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents an alternative method of designing a guidance controller for a small unmanned aerial vehicle (UAV) so as to perform path following under wind disturbances. The wind effects acting on UAVs need to be taken into account and eventually eliminated. To solve this problem, we adopted a disturbance observer-based control approach. The wind information is first estimated by a nonlinear disturbance observer, then it is incorporated into the nominal path following controller to formulate a composite controller that is able to compensate wind influences. The globally asymptotic stability of the composite controller is illustrated through theoretical analysis, whereas its performance is evaluated by various simulations including the one with software-in-the-loop. Initial flight tests using a small fixed-wing UAV are carried out to demonstrate its actual performance. Copyright © 2012 John Wiley & Sons, Ltd.

Like feedback strategy, coding scheme is an important part of networked control system design as well. On the basis of spherical polar coordinate, a novel coding scheme is proposed for stabilization problem of discrete linear time invariant system subject to packet erasure channel with feedback. The coding scheme uses encoder without access to control inputs. In the case that a decoder does not use control inputs, a definite relation between the quantized data and the corresponding quantization error is established, which helps to analyze the stability of system, and a selective quantization method is adopted, by which finite data rate is obtained. In the case that a decoder uses control inputs, instead of quantizing the system state at each time step as usual, the encoder quantizes the initial state all the time by updating quantizer. Sufficient conditions guaranteeing the system stable are presented for two cases, respectively, and the corresponding design methods for coding schemes are given.Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, an adaptive fuzzy decentralized output feedback control approach is presented for a class of uncertain nonlinear pure-feedback large-scale systems with immeasurable states. Fuzzy logic systems are utilized to approximate the unknown nonlinear functions, and a fuzzy state observer is designed to estimate the immeasurable states. On the basis of the adaptive backstepping recursive design technique, an adaptive fuzzy decentralized output feedback is developed. It is proved that the proposed control approach can guarantee that all the signals of the resulting closed-loop system are semiglobally uniformly ultimately bounded (SUUB), and that the observer and tracking errors converge to a small neighborhood of the origin by appropriate choice of the design parameters. Simulation studies are included to illustrate the effectiveness of the proposed approach. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, the design of an interval observer with an adaptive dynamical gain is presented. The observer is formulated in the framework of robust state estimation of uncertain dynamical systems, where an interval that encloses the unknown state variables is provided. For a specific type of interval observer design, an optimal gain could provide the narrowest interval. Because this gain depends on the (unknown) state, it can however not be determined, and only intervals for this optimal gain can be estimated. Here, we propose a strategy to track, with a high gain observer, the optimal gain together with the computation of its derivative. The observer performance is first illustrated with the simple case of an uncertain bioreactor model. Then, we propose the real case of the estimation of microalgal oil in the framework of biofuel production. The proposed observer design, when applied to experimental data of Isochrysis affinis galbana, appears to be a suitable robust estimation technique. Copyright © 2012 John Wiley & Sons, Ltd.

We address the problem of regulating a subset of outputs of a linear time-invariant plant with multi-rate measurements so as to achieve asymptotic tracking of an exogenous signal generated by the free motion of a linear time-invariant system, denoted by exosystem. A solution to this problem is required to yield closed-loop stability and should be such that output regulation is achieved even in the presence of small plant uncertainties and exogenous disturbances also generated by the exosystem. Contrarily to previous works, we propose a solution to the general case where the plant may have more measured outputs than inputs. We show that this solution allows us to solve simultaneous stabilization and output regulation problems that are not possible to solve through the previous works. Besides incorporating an internal model of the exosystem, the key feature of our proposed controller is that it includes a system that blocks signals generated by the exosystem arriving to the controller from the non-regulated outputs. Copyright © 2012 John Wiley & Sons, Ltd.

A periodic adaptive control approach is proposed for a class of nonlinear sampled-time systems with varying parametric uncertainties that are periodic with respect to angular displacement, and the only prior knowledge is the periodicity. The new adaptive controller updates the parameters and the control signal periodically in a pointwise manner between two consecutive spatial cycles and in the sequel achieves the asymptotic tracking convergence. Rigorous analysis are presented along with a numerical example to show the effectiveness of the proposed controller.Copyright © 2012 John Wiley & Sons, Ltd.

This paper is concerned with the transient performance improvement in tracking control problems for linear multivariable discrete-time singular systems subject to actuators saturation. A composite nonlinear feedback control strategy is considered, and the resulting controller consists of a linear feedback law and a nonlinear feedback law without any switching element. The nonlinear term leads to a varying damping ratio of the closed-loop system and yields a small overshoot as the output approaches the target reference, whereas the linear component is designed to achieve a quick response of the closed-loop system. Two composite nonlinear feedback control laws by both state feedback and measurement output feedback are addressed. An illustrative example is included to show the validity of the obtained results. Copyright © 2012 John Wiley & Sons, Ltd.

Containment analysis and design problems for high-order linear time-invariant singular swarm systems on directed graphs with time delays are investigated. To eliminate impulse terms in singular swarm systems and ensure that the singular swarm systems can achieve containment, time-delayed protocols are presented for leaders and followers, respectively. By model transformation, containment problems of singular swarm systems are converted into stability problems of multiple low-dimensional time-delayed systems. In terms of linear matrix inequality, sufficient conditions are presented for time-delayed singular swarm systems to achieve containment, which are independent of the number of agents. By using the method of changing variables, an approach is provided to determine the gain matrices in the protocols. Numerical simulations are shown to demonstrate theoretical results. Copyright © 2012 John Wiley & Sons, Ltd.

Stability and performance features of linear PI compensation for continuous bioreactors are studied in this paper. First, it is established that conventional PI control can be represented as the combination of an I/O inverse dynamics feedback with a modeling error dynamic estimator. Then, the analysis of the closed-loop dynamics carried out with singular perturbation tools shows that PI control can recover the stability and performance induced by exact I/O inverse dynamics feedback controller. The theoretical results are illustrated via a typical numerical example. Copyright © 2012 John Wiley & Sons, Ltd.

Tunnel passing is a pattern formation of multiple robots, an outcome of formation control which is the general problem of controlling a large number of robots required to move as a group. Tunnel passing deals with the task of driving a team of robots from arbitrary initial positions through a tunnel of given geometry. This paper proposes a decentralized planner that guarantees collision-free tunnel passing maneuvers of a team of nonholonomic car-like robots fixed in a prescribed formation, while considering all the practical limitations and constraints due to nonholonomy, tunnel geometry, and the formation specifications. Although solutions in literature are restricted to tunnels with linear segments, this paper introduces piecewise tunnel walls with straight and curved segments. The motion planner, derived from the Lyapunov-based control scheme works within an overarching leader-follower framework to generate either split/rejoin or expansion/contraction of the formation, as feasible solutions. Results from simulating virtual scenarios demonstrated the effectiveness of the proposed nonlinear controllers.Copyright © 2012 John Wiley & Sons, Ltd.

This paper addresses the controller synthesis problem of linear time-delay systems subjected to saturating control. Delay-dependent regional stabilization criteria are derived based on Lyapunov–Krasovskii approach by using both the polytopic or dead-zone representation of the saturation function. The main contribution of the paper lies in developing less conservative convex criterion in terms of LMIs to obtain superior results. On the basis of the derived stabilization criterion, an optimization problem is defined to compute the stabilizing state feedback gains with an aim to maximize the stabilizing region while guaranteeing the asymptotic stability of the closed-loop system. Considering three numerical examples, an assessment of the polytopic and dead-zone nonlinearity approaches is made.Copyright © 2012 John Wiley & Sons, Ltd.

This paper is concerned with the problem of control with -stability constraint for a class of switched positive linear systems. The -stability means that all the poles of each subsystem of the resultant closed-loop system belong to a prescribed disk in the complex plane. A sufficient condition is derived for the existence of a set of state-feedback controllers, which guarantees that the closed-loop system is not only positive and exponentially stable with each subsystem -stable but also has a weighted performance for a class of switching signals with average dwell time greater than a certain positive constant. Both continuous-time and discrete-time cases are considered, and all of the obtained conditions are formulated in terms of linear matrix inequalities, whose solution also yields the desired controller gains and the corresponding minimal average dwell time. Numerical examples are given to illustrate the effectiveness of the presented approach.Copyright © 2012 John Wiley & Sons, Ltd.

The problem of fault tolerant attitude stabilization with finite-time convergence is investigated for spacecraft with redundant actuators. On the basis of the sliding mode control technique, a robust controller is derived with uncertain inertia parameters, actuator faults, and external disturbances explicitly addressed. It is shown that finite-time reachability into the small neighborhood of sliding surface, and faster time convergence of attitude orientation are achieved. To address actuator input constraints, an adaptive fault tolerant controller is further proposed. One feature of the proposed strategy is that the design of the fault tolerant control does not require any fault detection and isolation mechanism to detect, separate, and identify actuator faults. The attitude stabilization performance using the controller is evaluated through a numerical example. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we consider robust output regulation of distributed parameter systems with infinite-dimensional exosystems capable of generating polynomially growing signals. We design an observer-based error feedback controller solving the control problem. The controller is chosen in such a way that it incorporates an internal model of the infinite-dimensional exosystem. The remaining parameters of the controller are chosen to stabilize the closed-loop system strongly. We also analyze the classes of signals generated by the exosystem. In particular, we explore the connection between the smoothness properties of the reference and disturbance signals and the strictness of the conditions required for the existence of a controller solving the robust output regulation problem. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents a new sporadic control approach to the tracking problem for MIMO closed-loop systems. An LTI sampled data plant with unmeasurable state affected by external unknown disturbances is considered. The plant is interconnected to an event-based digital dynamic output-feedback controller via a network. Both the external reference and the unknown disturbance are assumed to be generated as the free output response of unstable LTI systems. The main feature of the new event-driven communication logic (CL) is that it works without the strict requirement of a state vector available for measurement. The purpose of the CL is to reduce as much as possible the number of triggered messages along the feedback and feedforward paths with respect to periodic sampling, still preserving internal stability and without appreciably degrading the control system tracking capability.

The proposed event-driven CL is composed of a sensor CL (SCL) and of a controller CL (CCL). The SCL is based on the computation of a quadratic functional of the tracking error and of a corresponding suitably computed time-varying threshold: a network message from the sensor to the controller is triggered only if the functional equals or exceeds the current value of the threshold. The CCL is directly driven by the SCL: the dynamic output controller sends a feedforward message to the plant only if it has received a message from the sensor at the previous sampled instant. Formulation of the controller in discrete-time form facilitates its implementation and provides a minimum inter-event time given by the sampling period. An example taken from the related literature shows the effectiveness of the new approach. The focus of this paper is on the stability and performance loss problems relative to the sporadic nature of the control law. Other topics such as network delay or packets dropout are not considered. Copyright © 2012 John Wiley & Sons, Ltd.

A system is considered underactuated if the number of the actuator inputs is less than the number of degrees of freedom for the system. Sliding mode control for underactuated systems has been shown to be an effective way to achieve system stabilization. It involves exponentially stable sliding surfaces so that when the closed-loop system trajectory reaches the surface, it moves along the surface while converging to the origin. In this paper, a general framework that provides sufficient conditions for asymptotic stabilization of underactuated nonlinear systems using sliding mode control in the presence of system uncertainties is presented. Specifically, it is shown that the closed-loop system trajectories reach the sliding surface in finite time, and a constructive methodology to determine exponential stability of the closed-loop system on the sliding surface is developed, which ensures asymptotic stability of the overall closed-loop system. Furthermore, the aforementioned framework provides the basis to determine an estimate of the domain of attraction for the closed-loop system with uncertainties. Finally, the results developed in the paper are experimentally validated using a linear inverted pendulum testbed to show a good match between the actual domain of attraction of the upward equilibrium state of the pendulum and its analytical estimate.Copyright © 2012 John Wiley & Sons, Ltd.

A systematic approach for the design of multirate controllers resulting in closed loops free of intersample ripple is proposed. The approach is particularly suited for design frameworks such as optimal control for which previous proposed conditions to eliminate intersample ripple cannot be readily incorporated. It is based on transforming the control inputs in the lifted transfer matrix of the design plant in a manner that stabilizing controllers for the transformed plant are in one-to-one correspondence with stabilizing ripple-free controllers for the original plant. Thus, no solutions are lost in the process of this transformation and a general stability result is obtained that can be also used in other multirate controller design methodologies to achieve ripple-free response. The results do not require that the plant should be open-loop stable and in particular can contain integrating instabilities. Copyright © 2012 John Wiley & Sons, Ltd.

This paper focuses on the problem of static anti-windup design for a class of multivariable nonlinear systems subject to actuator saturation. The considered class regards all systems that are rational on the states or that can be conveniently represented by a rational system with algebraic constraints considering some variable changes. More precisely, a method is proposed to compute a static anti-windup gain which ensures regional stability for the closed-loop system assuming that a dynamic output feedback controller is previously designed to stabilize the nonlinear system. The results are based on a differential algebraic representation of rational systems. The control saturation effects are taken into account by the application of a generalized sector bound condition. From these elements, LMI-based conditions are devised to compute an anti-windup gain with the aim of enlarging the closed-loop region of attraction. Several numerical examples are provided to illustrate the application of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.

The insensitive multi-objective H_∞ control synthesis problem via dynamic output feedback for linear delta operator systems with insensitivity to sampling time jitter is investigated in the case of small sampling times. The delta-domain model instead of the standard shift-domain model is used to avoid the inherent numerical ill-condition resulting from using the latter model at high sampling rates. Parameter sensitivity function of the transfer function with respect to sampling time is defined to mitigate the effect of sampling time jitter because it may cause significant degradation of the overall system performance. It is worth pointing out that a novel bounded real lemma for delta operator allowing extra degree of freedom for multi-objective control design is presented by using the well-known projection lemma. Then, from this new lemma, a two-step design procedure based on LMI is presented to design insensitive dynamic output feedback controllers such that the resulting closed-loop system is asymptotically stable and meets the requirement of sensitivity specification. A numerical example is also presented to show the effectiveness of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.

A solution to the longstanding problem of sensorless control of an electrical machine is provided in this paper. That is, the construction of an asymptotically stable controller that regulates the mechanical speed of the motor, measuring only the electrical coordinates. The result is presented for a non-salient permanent magnet synchronous motor perturbed by an unknown constant load torque. The proposed scheme is a fourth order nonlinear observer-based controller that does not rely on—intrinsically nonrobust—operations like open-loop integration of the systems dynamical model nor signal differentiation and can be easily implemented in real time. The controller is easy to commission, with the tuning gains directly determining the convergence rates of the position, speed, and load torque observers. Simulation and experimental results are presented. In particular, a comparison with a sensorless field-oriented controller, recently proposed in the drives literature, is carried out. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we consider the observer design problem for a class of observable linear systems perturbed by nonlinear, time-varying terms. Our design methodology is based on a canonical form, similar to canonical forms used elsewhere in the literature, that allows the nonlinearities to be dominated using high gain. We show that linear state and output transformations to this canonical form exist if, and only if, the data of the system satisfies a certain admissibility property. Moreover, the appropriate transformations can easily be constructed using available tools. We furthermore show that, if a system does not satisfy the admissibility property, it may be possible to extend it with an invertible output filter that makes the data of the extended system admissible. We refer to the problem of constructing such a filter as the output shaping problem and introduce an algorithm that solves the problem whenever it is solvable.Copyright © 2012 John Wiley & Sons, Ltd.

In many applicative fields, there is the need to model and design complex systems having a mixed discrete and continuous behavior that cannot be characterized faithfully using either discrete or continuous models only. Such systems consist of a discrete control part that operates in a continuous environment and are named hybrid systems because of their mixed nature. Unfortunately, most of the verification problems for hybrid systems, like reachability analysis, turn out to be undecidable. Because of this, many approximation techniques and tools to estimate the reachable set have been proposed in the literature. However, most of the tools are unable to handle nonlinear dynamics and constraints and have restrictive licenses. To overcome these limitations, we recently proposed an open-source framework for hybrid system verification, called Ariadne, which exploits approximation techniques based on the theory of computable analysis for implementing formal verification algorithms. In this paper, we will show how the approximation capabilities of Ariadne can be used to verify complex hybrid systems, adopting an assume–guarantee reasoning approach. Copyright © 2012 John Wiley & Sons, Ltd.

The authors propose a robust nonlinear controller based on a block control linearization technique combined with a second order sliding mode super-twisting algorithm for controlling the rotor speed of single-phase induction motors. The block control approach is used to design a sliding manifold in terms of the stator current and its desired value. The super-twisting sliding mode algorithm is applied then to render the designed manifold be attractive. A nonlinear observer is designed to estimate the unmeasured variables (rotor flux linkages and torque load). Copyright © 2012 John Wiley & Sons, Ltd.

The issue of exponential stability analysis of continuous-time switched singular systems consisting of a family of stable and unstable subsystems with time-varying delay is investigated in this paper. It is very difficult to analyze the stability of such systems because of the existence of time-delay and unstable subsystems. In this regard, on the basis of the free-weighting matrix approach, by constructing the new Lyapunov-like Krasovskii functional, and using the average dwell-time approach, delay-dependent sufficient conditions are derived and formulated in terms of LMIs to check the exponential stability of such systems. This paper also highlights the relationship between the average dwell-time of the switched singular time-delay system, its stability, exponential convergence rate of differential states, and algebraic states. Finally, a numerical example is given to confirm the analytical results and illustrate the effectiveness of the proposed strategy.Copyright © 2012 John Wiley & Sons, Ltd.

The problem of group consensus is investigated in this paper, where all agents possess double-integrator dynamics. Two different kinds of consensus protocols are proposed for networks with fixed communication topology to reach group consensus for the agents’ positions and velocities. Convergence analysis is discussed, and necessary and/or sufficient conditions are presented for multiagent systems to achieve group consensus. The first protocol leads to dynamic consensus where positions of all agents reach time-varying consensus values. By applying the second protocol, both the agents’ positions and their velocities reach constant consensus values. That is, static consensus is achieved. Simulation examples are given to show the effectiveness of the theoretical results.Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, a hybrid adaptive observer is designed for a class of nonlinear sampled-data systems with constant unknown parameters. The proposed observer uses a predictor of the output between the sampling times. This predictor is re-initialized at each sampling time. This observer is very simple to implement and converges exponentially under some sufficient conditions. An explicit relation between the bound of the maximum allowable sampling time (τ_MASP) and the parameters of the observer is also given. Copyright © 2012 John Wiley & Sons, Ltd.

The present paper proposes a switching control scheme for a plant with multiple sensor–estimator/control–actuator pairs. The scheme is shown to handle the specific stability problems originated by the switching between the different feedback loops and accommodate to faults in the measurement (sensors) channels. The main contribution is a fault tolerant switching scheme with stability guarantees assured by a pre-imposed dwell time. The detection and the fault tolerance capabilities are achieved through the separation of sets associated with suitable residual signals corresponding to healthy and faulty functioning. Another contribution of the paper resides in a recovery technique for the post-fault reintegration of the biased estimations. This technique makes use of a virtual sensor whose associated estimation, based on an optimization procedure, minimizes the recovery time. Copyright © 2012 John Wiley & Sons, Ltd.

In this work, we consider a class of control systems governed by the stochastic nonlinear third-order dispersion equation in Hilbert spaces. We first prove the existence of mild solutions of stochastic nonlinear third-order dispersion equation by using fixed point theory, infinite dimensional semigroup properties, stochastic analysis techniques, and then a new set of sufficient conditions are formulated which guarantees the approximate controllability of the main problem. Finally, an example is provided to illustrate the application of the obtained results.Copyright © 2012 John Wiley & Sons, Ltd.

This paper investigates the problem of exponential H_∞ filtering for stochastic systems with time delays and Markovian jumping parameters. On the basis of Lyapunov–Krasovskii functional theory and generalized Finsler lemma, a delay-dependent bounded real lemma is established without using any model transformations, bounding techniques for cross terms, or additional free matrix variables. The obtained bounded real lemma guarantees that the filtering error system is both mean-square exponentially stable and almost surely exponentially stable with a prescribed H_∞ noise attenuation level. Then an exponential H_∞ filter is designed for stochastic retarded Markovian jump systems in terms of a set of LMIs. Meanwhile, the mathematical equivalence of the proposed method to one recent method is presented, but our proposed method is more computationally efficient with fewer matrix variables than that recent method. The validity of the method is verified by a numerical example.Copyright © 2012 John Wiley & Sons, Ltd.

A non-smooth optimization technique to directly compute a lower bound on the skew structured singular value ν is developed. As corroborated by several real-world challenging applications, the proposed technique can provide tighter lower bounds when compared with currently available techniques. Moreover, in many cases, the determined lower bound equals the true value of ν. Thanks to the efficiency of the non-smooth technique, the algorithm can be applied to problems involving even a significant number of uncertain parameters. Another appealing feature of the proposed non-smooth approach is that the dimension of repeated scalar uncertainties in the overall structured uncertainty matrix has little impact on the computational time. The technique can be used to compute a lower bound on the structured singular value μ as well. Copyright © 2012 John Wiley & Sons, Ltd.

This paper addresses the distributed observer-based consensus problem of second-order multi-agent systems via sampled data. Firstly, for the case of fixed topology, a velocity-independent distributed control law is proposed by designing a distributed observer to estimate the unavailable velocity, then a sufficient and necessary condition of consensus on design parameters and sampling period is obtained by using the matrix analysis method. Secondly, for the case of stochastically switching topology, a sufficient and necessary condition of mean square consensus is also proposed and proven, and an algorithm is provided to design the parameters in the consensus protocol. Two simulation examples are given to illustrate the effectiveness of the proposed consensus algorithms. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents some further results on adaptive sliding mode control (ASMC) for a class of nonlinear systems with bounded uncertain parameters. Given a large initial tracking error, current ASMC design generally produces an unnecessarily large switching gain, consequently leading to a serious chattering problem or a large-amplitude control jump for the continuous counterpart. To solve such an overadaptation problem, the switching gain adaptation mechanism is first analyzed in this paper, and the adaptation induced by the initial tracking error is suggested to be removed. Then, by exploiting the global sliding mode feature of time-varying sliding mode control and integral sliding mode control, we present two effective methodologies for ASMC design. The proposed ASMC algorithms ensure that there is no overestimation of the switching gain and the system response is not slowed down when a small switching gain is generated. The validity of the proposed methods is verified by both theoretical analysis and simulation results. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents a sufficient condition for observability of continuous-time switched nonlinear systems that also involve state jumps. Without the assumption of observability of individual modes, the sufficient condition is based on gathering partial information from each mode so that the state is completely recovered after several switchings. Based on the sufficient condition, a hybrid-type observer is designed, which comprises a copy of the actual plant and an error correction scheme at discrete time instants. In order to execute the proposed design, the observable component of the state at each mode needs to be estimated without transients or ‘peaking’ (caused by high-gain observers), and this motivates us to introduce a back-and-forth estimation technique. Under the assumption of persistent switching, analysis shows that the estimate thus generated converges asymptotically to the actual state of the system. Simulation results validate the utility of the proposed algorithm. Copyright © 2012 John Wiley & Sons, Ltd.

The fault detection and isolation (FDI) problem with finite frequency specifications is addressed in this paper under the framework of geometric approach for networked control systems subject to communication constraints and packet losses. The considered communication constraint is that only one of the transmission nodes is allowed to gain access to the shared channel. Also, those transmission nodes are scheduled to transmit data according to a specified stochastic protocol. Then by virtues of the common unobservable subspace and the finite frequency stochastic H₋ index, a novel FDI scheme is developed in which a set of FDI filters that perform the FDI task with only partially available measurements are designed such that each residual is only sensitive to one fault in certain frequency domain and decoupled from the others. Further, less conservative conditions including some previous existing results have been presented to construct the FDI filters. Finally, an example is given to illustrate the effectiveness of the proposed method.Copyright © 2012 John Wiley & Sons, Ltd.

This paper describes a scheme based on high-gain observers to detect and locate leaks in subterranean pipelines of liquefied petroleum gas (LPG). In fact, sub-observers connected in cascade are used to generate residuals that allow to detect when a leak occurs and, above all, to isolate the region of the pipeline where the leak is located. Once the region is identified, a dedicated observer is employed to more precisely estimate the leak position as well as its coefficient. The approach is validated with data from a real industrial LPG pipeline.Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we consider the semi-global regulation of output synchronization problem for heterogeneous networks of invertible linear agents subject to actuator saturation. That is, we regulate the output of each agent according to an a priori specified reference model. The network communication infrastructure provides each agent with a linear combination of its own output relative to that of neighboring agents, and it allows the agents to exchange information about their own internal observer estimates while some agents have access to their own outputs relative to the reference trajectory.Copyright © 2012 John Wiley & Sons, Ltd.

Based on recent papers that have demonstrated that robust iterative learning control can be based on parameter optimization using either the inverse plant or gradient concepts, this paper presents a unification of these ideas for discrete-time systems that not only retains the convergence properties and the robustness properties derived in previous papers but also permits the inclusion of filters in the input update formula and a detailed analysis of the effect of non-minimum-phase dynamics on algorithm performance in terms of a ‘plateauing’ or ‘flat-lining’ effect in the error norm evolution. Although the analysis is in the time domain, the robustness conditions are expressed as frequency domain inequalities. The special case of a version of the inverse algorithm that can be used to construct a robust stable anti-causal inverse non-minimum-phase plant is presented and analysed in detail.Copyright © 2012 John Wiley & Sons, Ltd.

This paper addresses a robust control approach for a class of input–output linearizable nonlinear systems with uncertainties and modeling errors considered as unknown inputs. As known, the exact feedback linearization method can be applied to control input–output linearizable nonlinear systems, if all the states are available and modeling errors are negligible. The mentioned two prerequisites denote important problems in the field of classical nonlinear control. The solution approach developed in this contribution is using disturbance rejection by applying feedback of the uncertainties and modeling errors estimated by a specific high-gain disturbance observer as unknown inputs. At the same time, the nonmeasured states can be calculated from the estimation of the transformed system states. The feasibility and conditions for the application of the approach on mechanical systems are discussed. A nonlinear multi-input multi-output mechanical system is taken as a simulation example to illustrate the application. The results show the robustness of the control design and plausible estimations of full-rank disturbances.Copyright © 2012 John Wiley & Sons, Ltd.

This work considers linear systems with input constraints with the objective of designing a controller that guarantees stability from all initial conditions in the null-controllable region (the set of initial conditions from where the system can be stabilized). To this end, a recently developed procedure for construction of constrained control Lyapunov functions is utilized within a Lyapunov-based model predictive controller coupled with an auxiliary control design to achieve stabilization from all initial conditions in the null-controllable region. Illustrative simulation results as well as an application to a nonlinear chemical process example is presented to demonstrate the efficacy of the results.Copyright © 2012 John Wiley & Sons, Ltd.

This paper addresses the distributed control by input–output linearization of a nonlinear diffusion equation that describes a particular but important class of distributed parameter systems. Both manipulated and controlled variables are assumed to be distributed in space. The control law is designed using the concept of characteristic index from geometric control by using directly the PDE model without any approximation or reduction. The main idea consists in the control design in assuming an equivalent linear diffusion equation obtained by use of the Cole–Hopf transformation. This framework helps to demonstrate the closed-loop stability using some concepts from the powerful semigroup theory. The performance of the proposed controller is successfully tested, through simulation, by considering a nonlinear heat conduction problem concerning the control of the temperature of a steel plate modeled by a nonlinear heat equation with Dirichlet boundary conditions. Copyright © 2012 John Wiley & Sons, Ltd.

This paper addresses the problem of how to achieve superior performance by adaptively and distributively adjusting control gains of a cooperative control system. It is shown that according to distributed observations of changing network topologies and on the basis of online estimation of network connectivity, cooperative controls with adaptive gains can be synthesized to making the time derivative of the cooperative control Lyapunov function more negative and hence to improve stability and convergence of the overall system. For undirected networks, the proposed adaptive design reduces to improving the Fiedler eigenvalue (algebraic connectivity) as well as other eigenvalues. On the other hand, connectivity of a directed network is characterized by the property of the first left eigenvector(s) associated with its dominant eigenvalue, and in this paper, a distributed high-gain observer design is proposed for each of the networked systems to utilize the same communication network among the systems. It is shown that even in the presence of transmission delays, the distributed estimators converge fast to the first left eigenvector(s) of the network. In addition, the expected consensus value(s) of the overall cooperative system under control is also estimated in a distributive manner. Rigorous analysis is carried out on estimation convergence and observer gain selection. It is shown that the proposed estimation and adaptive control designs are fully distributed, have guaranteed performance for all possible varying topologies as long as their dwelling times are bounded away from zero, and are robust with respect to excessively fast topology changes. Simulation results are included to demonstrate effectiveness of the proposed estimation and control schemes. Copyright © 2012 John Wiley & Sons, Ltd.

In this article, the concept of dual observer-based compensators is extended from linear to nonlinear systems. It is shown that a dual observer-based compensator achieves stabilization by rendering an invariant manifold attractive in which desired dynamics can be assigned. The design of these compensators for nonlinear systems is considerably simple if a flat output of the system to be controlled is known which is illustrated by means of a simple example. Copyright © 2012 John Wiley & Sons, Ltd.

In a traditional anti-windup design, the anti-windup mechanism is set to be activated as soon as the control signal saturates the actuator. A recent innovation of delaying the activation of the anti-windup mechanism, both static and dynamic, until the saturation reaches a certain level of severity has led to a performance improvement of the resulting closed-loop system. It has been shown that significant further performance improvements can be obtained by activating a static anti-windup mechanism in anticipation of actuator saturation, instead of immediate or delayed activation. This paper demonstrates that anticipatory activation of a dynamic anti-windup mechanism would also lead to significant performance improvements over both the immediate and delayed activation schemes.Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents a new method to synthesize a decentralized state feedback robust H^∞ controller for a class of large-scale linear uncertain systems satisfying integral quadratic constraints. The decentralized controller is constructed by taking only block-diagonal elements of a nondecentralized state feedback controller and treating neglected off-diagonal blocks as uncertainties. A solution to this controller synthesis problem is given in terms of a stabilizing solution to a parametrized algebraic Riccati equation where the parameters are obtained using a differential evolution algorithm.Copyright © 2012 John Wiley & Sons, Ltd.

We consider the use of quadratic approximate value functions for stochastic control problems with input-affine dynamics and convex stage cost and constraints. Evaluating the approximate dynamic programming policy in such cases requires the solution of an explicit convex optimization problem, such as a quadratic program, which can be carried out efficiently. We describe a simple and general method for approximate value iteration that also relies on our ability to solve convex optimization problems, in this case, typically a semidefinite program. Although we have no theoretical guarantee on the performance attained using our method, we observe that very good performance can be obtained in practice.Copyright © 2012 John Wiley & Sons, Ltd.

General nonlinear time-varying differential systems are considered. An explicit criterion for exponential stability is presented. Furthermore, an explicit robust stability bound for systems subjected to nonlinear time-varying perturbations is given. In particular, it is shown that the generalized Aizerman conjecture holds for positive linear systems. Some examples are given to illustrate obtained results.Copyright © 2012 John Wiley & Sons, Ltd.

Anti-disturbance control and estimation problem is introduced for a class of nonlinear system subject to disturbances. The adaptive disturbance observers are constructed separately from the controller design to estimate the disturbance with partial known information. By integrating disturbance-observer-based control with fuzzy control, a novel type of composite hierarchical anti-disturbance control scheme is presented for a class of nonlinear system with unknown nonlinear dynamics. Simulations for a flight control system are given to demonstrate the effectiveness of the results compared with the previous schemes.Copyright © 2012 John Wiley & Sons, Ltd.

This paper deals with formation control problems for multi-agent systems by using iterative learning control (ILC) design approaches. Distributed formation ILC algorithms are presented to enable all agents in directed graphs to achieve the desired relative formations perfectly over a finite-time interval. It is shown that not only asymptotic stability but also monotonic convergence of multi-agent formation ILC can be accomplished, and the convergence conditions in terms of linear matrix inequalities can be simultaneously established. The derived results are also applicable to multi-agent systems that are subject to stochastic disturbances and model uncertainties. Furthermore, the feasibility of convergence conditions and the effect of communication delays are discussed for the proposed multi-agent formation ILC algorithms. Simulation results are given for uncertain multi-agent systems to verify the theoretical study. Copyright © 2012 John Wiley & Sons, Ltd.

This paper addresses analysis and switching control problems of continuous/discrete-time switched linear systems. A particular class of matrix inequalities, the so-called Lyapunov–Metzler inequalities, will be modified to provide conditions for stability analysis and output feedback control synthesis under a relaxed min-switching logic. The switching rule combined with switching output feedback controllers will be designed to stabilize the switched system and satisfy a prespecified gain performance. The proposed analysis and switching control approach could refrain frequent switches commonly observed in min-switching based designs. The effectiveness of the proposed approach will be illustrated through numerical examples. Copyright © 2012 John Wiley & Sons, Ltd.

The aim of the present paper was to increase the efficiency of self-tuning minimum variance (MV) control of linear systems followed by the so-called hard nonlinearities. To this end, an approach based on reordering of observations to be processed for the reconstruction of an unmeasurable internal intermediate signal, which acts between a linear dynamic time-invariant (LTI) system and a static nonlinear block of the closed loop Wiener system with a saturation nonlinearity in an output, has been developed. The technique based on the ordinary least squares and on data partition is used for the internal signal extraction. The results of numerical simulation, identification, and self-tuning MV control as well as generalized MV control of the second-order discrete-time closed loop LTI system with the saturation nonlinearity are given by the computer. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents a new method to construct a decentralized nonlinear robust H^∞ controller for a class of large-scale nonlinear uncertain systems. The admissible uncertainties and nonlinearities in the system satisfy integral quadratic constraints and global Lipschitz conditions, respectively. The decentralized controller, which is required to be stable, is capable of exploiting known nonlinearities and interconnections between subsystems without treating them as uncertainties. Instead, additional uncertainties are introduced because of the discrepancies between nondecentralized and decentralized nonlinear output feedback controllers. The H^∞ control objective is to achieve an absolutely stable closed-loop system with a specified disturbance attenuation level. A solution to this control problem involves stabilizing solutions to algebraic Riccati equations parametrized by scaling constants corresponding to the uncertainties and nonlinearities. This formulation is nonconvex; hence, an evolutionary optimization method is applied to solve the control problem considered. Copyright © 2012 John Wiley & Sons, Ltd.

This paper is concerned with the quantized output feedback stabilization problem for a class of uncertain systems with nonsmooth nonlinearities in the actuator device via sliding mode control schemes. It is assumed that system signals are quantized before being transmitted through communication channels. First, a dynamical compensator is developed to estimate unmeasurable system state. Then a sliding surface, in the augmented space using the system output and the estimated state, is proposed, and an adaptive sliding mode control scheme with a static adjustment law of the quantization parameter is established. It is shown that the proposed quantized feedback control strategy is able to tackle parameter uncertainty, external disturbances, and nonsymmetric input nonlinearity simultaneously and guarantees the reachability of the sliding modes of the uncertain system. Finally, an example is given to verify the validity of the theoretical results. Copyright © 2012 John Wiley & Sons, Ltd.

This paper considers finite-time formation control problem for a group of nonholonomic mobile robots. The desired formation trajectory is represented by a virtual dynamic leader whose states are available to only a subset of the followers and the followers have only local interaction. First of all, a continuous distributed finite-time observer is proposed for each follower to estimate the leader's states in a finite time. Then, a continuous distributed cooperative finite-time tracking control law is designed for each mobile robot. Rigorous proof shows that the group of mobile robots converge to the desired geometric formation pattern in finite time. At the same time, all the robots can track the desired formation trajectory in finite time. Simulation example illustrates the effectiveness of our method. Copyright © 2012 John Wiley & Sons, Ltd.

This paper studies the stability problem of a class of linear switched systems with time-varying delay in the sense of Hurwitz convex combination. By designing a parameter-dependent switching law and using a new convex combination technique to deal with delay terms, a new stability criterion is established in terms of LMIs, which is dependent on the parameters of Hurwitz convex combination. The advantage of the new criterion lies in its less conservatism and simplicity. Numerical examples are given to illustrate the effectiveness and the less conservatism of the proposed method.Copyright © 2012 John Wiley & Sons, Ltd.

This paper is concerned with the problem of the fault detection filter design for discrete-time switched linear systems with average dwell-time. The designed fault detection filters are also switched systems, which are assumed to be asynchronously switched with the original switched systems. Improved results on the weighted l₂ performance and the H₋ performance are first given, and the multiple Lyaounov-like functions during matched period and unmatched period for the running time of one subsystem are used. By the aid of multiple Lyapunov-like functions combined with Projection Lemma, the FD filters are designed such that the augmented systems under asynchronous switching are exponentially stable, and the residual signal generated by the filters achieves the weighted l₂-gain for disturbances and guarantees the H₋ performance for faults. Sufficient conditions are formulated by linear matrix inequalities, and the filter gains are characterized in terms of the solution of a convex optimization problem. Finally, examples are provided to demonstrate the effectiveness of the proposed design method.Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we present a mechanism, called oscillation killer, intended to eliminate limit cycles that may occur as a consequence of unexpected external disturbances, interactions with the environment, changes in systems set-points, physical parameters, and so on. Examples range from controlled systems with friction to electrical networks with varying loads and impedances. The proposed mechanisms is shown to be particulary appropriate for nonlinear systems displaying a locally asymptotically equilibrium point surrounded by a locally asymptotically stable limit set outside this local domain.Copyright © 2012 John Wiley & Sons, Ltd.

A new approach to design a Nonlinear Model Predictive Control law that employs an approximate model, derived directly from data, is introduced. The main advantage of using such models lies in the possibility to obtain a finite computable bound on the worst-case model error. Such a bound can be exploited to analyze the robust convergence of the system trajectories to a neighborhood of the origin. The effectiveness of the proposed approach, named Set Membership Predictive Control, is shown in a vehicle lateral stability control problem, through numerical simulations of harsh maneuvers. Copyright © 2012 John Wiley & Sons, Ltd.

A periodic adaptive control approach is proposed for a class of nonlinear discrete-time systems with time-varying parametric uncertainties which are almost periodic, and the only prior knowledge is the periodicity. The new adaptive controller updates the parameters and the control signal periodically in a pointwise manner over one entire period, in the sequel that achieves a bounded tracking convergence. The result is further extended to scenarios with unknown input gain, higher order dynamics, and tracking. Copyright © 2012 John Wiley & Sons, Ltd.

This paper studies the input-to-state stability (ISS) of descriptor systems with exogenous disturbances. on the basis of the ISS theory of standard state-space nonlinear systems, a sufficient condition for a class of nonlinear descriptor system to be ISS is proved. Furthermore, a design method of the state feedback controllers is given to make the closed-loop system ISS. A numerical example is given to illustrate the effectiveness of the controller design.Copyright © 2012 John Wiley & Sons, Ltd.

We study the stability and robustness of a large platoon of vehicles, where each vehicle is modeled as a double integrator, for two decentralized control architectures: predecessor following and symmetric bidirectional. In the predecessor-following architecture, the control action on each agent only depends on the information from its immediate front neighbor, whereas in the symmetric bidirectional architecture, it depends equally on the information from both its immediate front neighbor and back neighbor. We prove asymptotic stability of the formation for a class of nonlinear controllers with sector nonlinearity, with the linear controller as a special case. We show that the convergence rate of the predecessor-following architecture is much faster than that of the symmetric bidirectional architecture. However, the predecessor-following architecture suffers high algebraic growth of initial errors. We also establish scaling laws (with N) of certain H_∞ norms of the formation that measure its robustness to external disturbances for the linear case. It is shown that the robustness performance grows geometrically in N for predecessor-following architecture but only polynomially in N for symmetric-bidirectional architecture. Extensive numerical simulations are conducted to verify the predictions for the linear case and empirically estimate the corresponding performance metrics for a saturation-type nonlinear controller. On the basis of the analytical and numerical results, it is seen that the symmetric bidirectional architecture outperforms the predecessor-following architecture in all measures of performance. Within the predecessor-following architecture, the nonlinear controller is seen to perform better in general than the linear one. A number of design guidelines are provided on the basis of these conclusions. Copyright © 2012 John Wiley & Sons, Ltd.

This paper investigates the global asymptotic synchronization in an array of coupled neural networks with random coupling strengths, probabilistic interval time-varying coupling delays as well as unbounded distributed delays (mixed delays). Two important integral inequalities that include the Jensen's inequality as a special case are developed. On the basis of the developed inequalities, the properties of random variables and Lyapunov functional method, several delay-dependent sufficient synchronization criteria are derived for the considered model. The derived synchronization criteria are formulated by linear matrix inequalities (LMIs) and can be easily verified by using MATLAB LMI Toolbox. Some existing results are improved and extended by taking different values of parameters of the obtained results. Numerical simulations are finally given to demonstrate the effectiveness of the theoretical results.Copyright © 2012 John Wiley & Sons, Ltd.

This paper is concerned with the state estimation problem for two-dimensional (2D) complex networks with randomly occurring nonlinearities and randomly varying sensor delays. To describe the fact that measurement delays may occur in a probabilistic way, the randomly varying sensor delays are introduced in the delayed sensor measurements. The randomly occurring nonlinearity, on the other hand, is included to account for the phenomenon of nonlinear disturbances appearing in a random fashion that is governed by a Bernoulli distributed white sequence with known conditional probability. The stochastic Brownian motions are also considered, which enter into not only the coupling terms of the complex networks but also the measurements of the output systems. Through available actual network measurements, a state estimator is designed to estimate the true states of the considered 2D complex networks. By utilizing an energy-like function, the Kronecker product and some stochastic analysis techniques, several sufficient criteria are established in terms of matrix inequalities under which the 2D estimation error dynamics is globally asymptotically stable in the mean square. Furthermore, the explicit expression of the estimator gains is also characterized. Finally, a numerical example is provided to demonstrate the effectiveness of the design method proposed in this paper. Copyright © 2012 John Wiley & Sons, Ltd.

This brief paper addresses the finite-time stability problem of switched positive linear systems. First, the concept of finite-time stability is extended to positive linear systems and switched positive linear systems. Then, by using the state transition matrix of the system and copositive Lyapunov function, we present a necessary and sufficient condition and a sufficient condition for finite-time stability of positive linear systems. Furthermore, two sufficient conditions for finite-time stability of switched positive linear systems are given by using the common copositive Lyapunov function and multiple copositive Lyapunov functions, a class of switching signals with average dwell time is designed to stabilize the system, and a computational method for vector functions used to construct the Lyapunov function of systems is proposed. Finally, a concrete application is provided to demonstrate the effectiveness of the proposed method.Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we are concerned with the boundary stabilization of a one-dimensional anti-stable wave equation with the boundary external disturbance. The backstepping method is first applied to transform the anti-stability from the free end to the control end. A variable structure feedback stabilizing controller is designed by the Lyapunov function approach. It is shown that the resulting closed-loop system is associated with a nonlinear semigroup and is asymptotically stable. In addition, we show that this controller is robust to the external disturbance in the sense that the vibrating energy of the closed-loop system is also convergent to zero as time goes to infinity in the presence of bounded deterministic disturbance at the control end. The existence and uniqueness of the solution are also developed by the Galerkin approximation scheme. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, a real-time algorithm is proposed for nonlinear infinite horizon optimal control. The time axis transformation of the horizon is combined with receding horizon control to realize state feedback by numerical optimization over an infinite horizon. Moreover, a descriptor equation is utilized in place of a state equation to avoid the numerical difficulty due to the infinite horizon. Then a nonlinear equation is obtained to determine the trajectories of the state, costate, and control input over the transformed horizon. The nonlinear equation is solved at each sampling time by a continuation method to trace a time-varying solution. The proposed algorithm is applied to nonlinear systems to evaluate its accuracy and effectiveness. Copyright © 2012 John Wiley & Sons, Ltd.

This paper is concerned with the H_∞ filtering problem for two-dimensional T-S fuzzy systems. Sufficient conditions for the solvability of this problem are obtained by using basis-dependent Lyapunov functions. By considering the measured output as an independent variable with respect to the state variable and the disturbance input, a new method for designing two-dimensional H_∞ filters is presented. Moreover, it has been shown that the proposed method is equivalent to the conventional one. Therefore, the proposed method does not lead to any conservativeness that may be caused by separately considering the measured output, the state variable, and the disturbance input. In converting the parameterized linear matrix inequalities (PLMI) into LMI constraints, attention is focused on the reduction of the number of LMI-based conditions. On the basis of the proposed theorem, the number of LMI-based conditions is reduced to r³ from r³(r + 1)² ∕ 4 by the conventional method. Thus, the computational advantage is obvious for fuzzy systems with large number of fuzzy rules. Simulation results have demonstrated the effectiveness of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.

In this study, the reliable control for time-varying systems with random actuator faults and probabilistic nonlinearities is investigated. The system under consideration has the following main features: (1) nonlinearities with new characters. The probability information of nonlinearities belonging to different varying bounds is used; (2) its multi-actuators are subject to various possible faults/failures, and failure rates can vary in some measure; and (3) there are uncertainties in the plant model parameters. Covering these features, a comprehensive model is developed for uncertain time-varying delay systems. By employing the Lyapunov functional method, free-weighting matrix method, and the linear matrix inequality technique, we can obtain several delay-distribution-dependent sufficient conditions to ensure the exponentially mean square stability of the system. Those conditions are characterized in terms of linear matrix inequalities, and the reliable controller feedback gain can be solved by the standard numerical software. A simulation example is presented to show the effectiveness and applicability of the results. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we present a robust actuator fault-tolerant control strategy for constrained linear systems in the presence of bounded state and input disturbances. The scheme is based on a bank of state estimators that match different fault situations that can occur in the system. A fault detection and isolation unit verifies that suitable residual variables lie inside pre-computed sets and selects the estimate that matches the current plant behaviour. A bank of robustly stabilizing tube-based model predictive control laws is designed, each associated to a fault scenario, and the appropriate controller is selected among them by using the information provided by the fault detection and isolation module. By means of ‘tubes’ of trajectories, we ensure robust closed-loop exponential stability of the constrained system and good performance in the fault-free case and under the occurrence of abrupt actuator faults, including actuator outage and loss of effectiveness by an unknown amount. Copyright © 2012 John Wiley & Sons, Ltd.

A rotor speed estimation algorithm in a direct vector controlled permanent magnet synchronous generator wind energy conversion system is proposed. The proposed method is based on a simple equation obtained from the flux model of the machine and contains only stator flux and current. Constant gain recursive least squares estimator is used for implementing the speed estimation algorithm. Rotor position information used for coordinate transformation is computed using the estimated speed. Stator flux information required by the speed estimator is obtained using the stator voltage equation by implementing a programmable low pass filter. The estimated speed is used as the feedback signal for the speed control loop of the vector controlled machine side converter control system whose command speed is obtained from a wind speed sensorless maximum power point tracking controller, thus, we obtain a complete rotor speed and wind speed sensorless permanent magnet synchronous generator wind energy conversion system. Simulation is carried out to validate the performance of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.

This paper is devoted to output-feedback adaptive control for a class of multivariable nonlinear systems with both unknown parameters and unknown nonlinear functions. Under the Hurwitz condition for the high-frequency gain matrix, a robust adaptive backstepping control scheme is proposed, which is able to guarantee the tracking performance and needs only one parameter to be updated online regardless of the system order and input–output dimension. To cope with the unknown nonlinear functions and improve the tracking performance, a kind of high-gain K-filters is introduced. It is proved that all signals of the closed-loop system are globally uniformly bounded. Simulation results on coupled inverted double pendulums are presented to illustrate the effectiveness of the proposed scheme. Copyright © 2012 John Wiley & Sons, Ltd.

In this work, a class of switching systems known as integrator is studied. Such systems have the feature of being very simple and allow us to gain insight on the effect that the switching sequence has on system stability. Three problems are analyzed. First, the practical stabilizability problem under system uncertainty is studied. Confinement regions are explicitly computed, and switching sequences based on the nominal behavior of the systems are derived. Second, the practical stabilizability problem using output feedback is solved; in this case, sufficient conditions are proposed. Finally, by joining both results, sufficient conditions for practical stabilizability of uncertain systems under output feedback are given. The results are illustrated with examples and some extensions for uncertain linear system and event-based switching are given. Copyright © 2012 John Wiley & Sons, Ltd.

Stable-protocol (SP) output consensus analysis and design for high-order linear time-invariant swarm systems with switching topologies are dealt with. Firstly, on the basis of observability decomposition, a dynamic output feedback consensus protocol with switching topologies is given. Then, a necessary and sufficient condition for SP output consensus is shown, and an explicit expression of the output consensus function is presented, which is independent of switching topologies. Furthermore, necessary and/or sufficient conditions for SP output consensualization, which are independent of the number of agents, are shown respectively. Finally, a numerical example is shown to demonstrate theoretical results.Copyright © 2012 John Wiley & Sons, Ltd.

Stabilization of a reaction–diffusion equation, in which the heat source depends on the temperature of the whole space, is considered by using boundary control. A new backstepping transformation is introduced, in which there are two kernels. Through a series of mathematical tricks, the exact solutions of kernels are obtained, and a control law is obtained specifically. The inverse transformation is derived, and stability of the closed loop system established. Simulation results show that the closed loop system is stable. Copyright © 2012 John Wiley & Sons, Ltd.

We consider the multi-agent optimization problem where multiple agents try to cooperatively optimize the sum of their local convex objective functions, subject to global inequality constraints and a convex constraint set over a network. Through characterizing the primal and dual optimal solutions as the saddle points of the associated Lagrangian function, which can be evaluated with stochastic errors, we propose the distributed primal–dual stochastic subgradient algorithms for two cases: (i) the time model is synchronous and (ii) the time model is asynchronous. In the first case, we obtain bounds on the convergence properties of the algorithm for a diminishing step size. In the second case, for a constant step size, we establish some error bounds on the algorithm's performance. In particular, we prove that the error bounds scale as in the number of n agents. Copyright © 2012 John Wiley & Sons, Ltd.

This paper proves a new property of the nonlinear regulators that proposed in two previous papers by the second author with co-workers. In both papers, the steady-state control is immersed into a linear internal model. In general, the model produces the sinusoidal signals generated by an exosystem, as well as a number of their harmonics, which are induced by the system's nonlinearities. When the internal model does not account for all harmonics or when the model's characteristic frequencies are not exactly those of the exosystem, there will be an error between the steady-state control needed to achieve zero steady-state regulation error and the steady-state control produced by the internal model. If the norm of this error is bounded by a constant δ, it has been shown that the steady-state regulation error will be of the order O(δ). In this paper, we prove a shaper result where the steady-state regulation error is shown to be of the order O(μδ), where μ is a design parameter of a continuously implemented sliding mode controller. Therefore, the regulation error can be reduced by decreasing μ. This result allows us to trade off the accuracy of the internal model versus the value of μ as means of reducing the regulation error.Copyright © 2012 John Wiley & Sons, Ltd.

The semi-Markov jump linear system (S-MJLS) is more general than the Markov jump linear system (MJLS) in modeling some practical systems. Unlike the constant transition rates in the MJLS, the transition rates of the S-MJLS are time varying. This paper focuses on the robust stochastic stability condition and the robust control design problem for the S-MJLS with norm-bounded uncertainties. The infinitesimal generator for the constructed Lyapunov function is first derived. Numerically solvable sufficient conditions for the stochastic stability of S-MJLSs are then established in terms of linear matrix inequalities. To reduce the conservativeness of the stability conditions, we propose to incorporate the upper and lower bounds of the transition rate and meanwhile apply a new partition scheme. The robust state feedback controller is accordingly developed. Simulation studies and comparisons demonstrate the effectiveness and advantages of the proposed methods. Copyright © 2012 John Wiley & Sons, Ltd.

The main contribution of this paper is to completely characterize the dynamic behavior of the discrete-time double integrator with a saturated locally stabilizing linear state feedback law. In continuous-time setting, any linear state feedback control law that locally stabilizes the double integrator also globally stabilizes the system in the presence of actuator saturation. In discrete-time setting, the equivalent of the double integrator does not have the same property. In this paper, we completely characterize the global behavior of saturated locally stabilizing linear state feedback laws for the discrete-time double integrator. Copyright © 2012 John Wiley & Sons, Ltd.

Copositive linear Lyapunov functions are used along with dissipativity theory for stability analysis and control of uncertain linear positive systems. Unlike usual results on linear systems, linear supply rates are employed here for robustness and performance analysis using L₁-gain and L_∞-gain. Robust stability analysis is performed using integral linear constraints for which several classes of uncertainties are discussed. The approach is then extended to robust stabilization and performance optimization. The obtained results are expressed in terms of robust linear programming problems that are equivalently turned into finite dimensional ones using Handelman's theorem. Several examples are provided for illustration. Copyright © 2012 John Wiley & Sons, Ltd.

This paper investigates the problem of an integrated fault detection system design for linear discrete time-varying systems with bounded power disturbances. In the integrated design of residual generator and evaluator, an approximated energy constraint is first imposed on the bounded power disturbances, and then selected by solving a min–max problem to achieve minimal-size set of undetectable faults under the condition of zero false alarms. To tackle the problem that the computational burden involved in solving the min–max optimization grows with time, the moving horizon method is proposed. The proposed approach in this paper has two advantages: (i) the approximated energy constraint on bounded power disturbances is explicitly selected as a min–max solution in the integrated design to improve fault detection rate; by contrast, when directly applying any existing fault detection method to the case of bounded power disturbances, a predefined approximated energy constraint is implicitly introduced without considering fault detection performance; (ii) the design objective of the proposed approach can choose to consider faults only in the recent time horizon rather than faults in the complete time horizon; this strategy enhances detection performance of recent faults and benefits early fault detection, but has not been considered by existing fault detection methods.Copyright © 2012 John Wiley & Sons, Ltd.

Recently, a model for flocking was introduced by Cucker and Smale together with a proof of convergence. This proof established unconditional convergence to flocking (i.e., to a common velocity), provided the interaction between agents was strong enough and conditional convergence otherwise. The strength of the interaction is measured by a parameter β, and the critical value at which unconditional convergence stops holding is β = 1 ∕ 2. This model was extended by Shen to allow for a hierarchical leadership structure among the agents, and similar convergence results were proved. But, for discrete time, convergence result was only for the flock with an overall leader moving with a constant velocity. In this note, we establish convergence result for the flock with a free-will leader. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we investigate the relationship between stability and internal stability of nonlinear systems. It is shown that under certain conditions, stability implies attractivity of the equilibrium and that local stability with finite gain implies local asymptotic stability of the origin. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents an approach to discrete-time robust H^∞ control for a class of nonlinear uncertain systems on the basis of the use of Sum Quadratic Constraints. The approach involves controllers, which include copies of the system nonlinearities in the controller. The nonlinearities being considered are those that satisfy a certain global Lipschitz condition. The linear part of the controller is synthesized using linear robust H^∞ control theory, and this leads to a nonlinear controller, which gives an upper bound on the attainable disturbance attenuation level. Copyright © 2012 John Wiley & Sons, Ltd.

This paper deals with the H_∞ filtering problem for a class of discrete time-varying systems with state saturations, randomly occurring nonlinearities as well as successive packet dropouts. Two mutually independent sequences of random variables that obey the Bernoulli distribution are employed to describe the random occurrence of the nonlinearities and packet dropouts. The purpose of the addressed problem is to design a time-varying filter such that the H_∞ disturbance attenuation level is guaranteed, over a given finite-horizon, for the filtering error dynamics in the presence of saturated states, randomly occurring nonlinearities, and successive packet dropouts. By introducing a free matrix with its infinity norm less than or equal to 1, the error state is bounded by a convex hull so that some sufficient conditions obtained via solving a certain set of recursive nonlinear matrix inequalities. Furthermore, the obtained results are extended to the case when state saturations are partial. Two numerical simulation examples are provided to demonstrate the effectiveness and applicability of the proposed filter design approach. Copyright © 2012 John Wiley & Sons, Ltd.

Finite-time formation control of multiple second-order agents via dynamic output feedback is investigated in this paper. Under the assumption that the velocities of all agents cannot be measured, a continuous consensus algorithm is first proposed such that the states of all agents will reach an agreement in finite time. Then, the consensus algorithm is applied to the finite-time formation control, including stationary formation and moving formation, respectively. Rigorous proof shows that all agents will converge to the desired formation pattern in finite time. Finally, an example is given to verify the efficiency of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.

This paper proposes and develops a generalized sector-bound approach to feedback stabilization of nonlinear control systems described by state–space models. This approach is inherited from the methodology of the sector-bounded or passive nonlinearities and influenced by the concept of absolute and quadratic stability. It aims not only to regionally stabilize the nonlinear dynamics asymptotically but also to maximize the estimated region of quadratic attraction and to ensure nominal performance at each equilibrium. More importantly, it has a close connection to gain scheduling and switching control. A path of equilibria is programmed on the basis of the assumption of centered- ε-cover, which leads to a sequence of linear controllers that regionally stabilize the desired equilibrium asymptotically. Simulation results are worked out to illustrate our proposed design method. Copyright © 2012 John Wiley & Sons, Ltd.

Convergence property of the iterative algorithm for Hammerstein or Wiener systems is generally hard to establish because of the existence the unmeasurable internal variables in such systems. In this paper, a fixed-point iteration is introduced to identifying both Hammerstein and Wiener systems with a unified algorithm. This newly proposed estimation algorithm gives consistent estimates under arbitrary nonzero initial conditions. In addition, the errors of the estimates are established as functions of the noise variance, and thus how the noise affects the quality of parameter estimates for a finite number of data points is made clear.Copyright © 2012 John Wiley & Sons, Ltd.

This paper is concerned with the stability and stabilization problems for a class of time-delayed systems, whose time-varying delays are studied via Markovian approach. By separating the delay interval into several subintervals and by considering the inherent distribution of time-varying delay, a new model is firstly developed. On the basis of the established model, a novel Lyapunov functional, which makes full use of each subinterval's delay bounds and the randomicity of time-varying delay, is constructed to drive less conservative stability criteria. Especially sufficient conditions for the existence of stabilizing controllers are obtained as linear matrix inequalities, which are further used to deal with networked control systems. Finally, numerical examples are used to demonstrate the effectiveness of the proposed methods. Copyright © 2012 John Wiley & Sons, Ltd.

This paper proposes an improved zonotopic method to set membership state estimation for nonlinear discrete-time systems with a bounded description of noise and parameters. According to the previous method, a zonotope containing the uncertain trajectory of the system is computed using interval arithmetic in the time update. In the observation update, an improved intersection algorithm of zonotope and strip is used to obtain a zonotope bounding the intersection of the uncertain trajectory with the region of the state space consistent with the observed output. This obtained zonotope is used to describe the feasible solution set of state. It is proven that the zonotope obtained by the improved algorithm can be tighter than the one obtained by the previous algorithm. Simulation experiments are conducted showing the performance of the improved state estimation method as compared with the previous one. Two types of noise distribution are considered. The results expose the weakness of the previous method and illustrate the effectiveness of the improvement. Copyright © 2012 John Wiley & Sons, Ltd.

A kind of real-time Kalman filtering problem is discussed for systems with distributed multichannel measurements. Recursive filters are presented for two cases with correlated and uncorrelated measurement noises. An optimal algorithm is constructed using projection theory in Hilbert space according to a first-come-first-served scheme. An update is generated whenever a new measurement arrives at a central unit. Therefore, the algorithm has the practical advantages of flexibility and the easiness for real-time implementation.Copyright © 2012 John Wiley & Sons, Ltd.

This paper investigates the design of distributed observers for agents with identical linear discrete-time state-space dynamics networked on a directed graph interaction topology. The digraph is assumed to have fixed topology and contain a spanning tree. Cooperative observer design guaranteeing convergence of the estimates of all agents to their actual states is proposed. The notion of convergence region for distributed observers on graphs is introduced. It is shown that the proposed cooperative observer design has a robustness property. Application of cooperative observers is made to the synchronization problem. A command trajectory generator and pinning control are employed for synchronizing all the agents to a desired trajectory. Complete knowledge about the agent's state is not assumed. A duality principle is shown for observers and state feedback for distributed discrete-time systems on graph topologies. Three different observer/controller architectures are proposed for dynamic output feedback regulator design, and they are shown to guarantee convergence of the estimate to the true state and synchronization of all the agents' states to the command state trajectory. This provides design methods for cooperative regulators based on a separation principle. It is shown that the observer convergence region and feedback control synchronizing region for discrete-time systems are inherently bounded, so that the conditions for observer convergence and state synchronization are stricter than the results for the continuous-time counterparts. This is in part remedied by using weighting of different feedback coupling gains for every agent. Copyright © 2012 John Wiley & Sons, Ltd.

A three-time scale singular perturbation control law is designed for a nonlinear helicopter model in vertical flight. The proposed control law is based on time scale decomposition and is able to achieve the desired altitude by selecting a desired angular velocity and the associated collective pitch angle of the blades. The stability of the system is performed by presenting a stability analysis for generic three-time scale singularly perturbed systems, which allows to construct a composite Lyapunov function for the resultant closed-loop system by using time scale separation and also providing mathematical expressions for the upper bounds of the singularly perturbed parameters that define the three-time scale. Numerical results on both, the singular perturbation control strategy and the stability analysis, are also presented for the studied nonlinear highly coupled helicopter model. Copyright © 2012 John Wiley & Sons, Ltd.

For complex dynamic systems, a modular control design process is often employed, wherein the overall design is partitioned into smaller modules. This paper considers a particular inner-loop/outer-loop modular control strategy in which the designer of the outer-loop module does not know the specifics of the inner loop but instead possesses a reference model that captures the ideal inner-loop input–output behavior. In the first part of this paper, we establish analytical properties of the modular reference-model-based design. In the second part, we introduce a novel mechanism, referred to as the modular control error compensation, which mitigates the performance loss that arises when the inner-loop reference model is not matched. We propose an iterative algorithm, using μ synthesis, to design this compensator to reduce performance loss on the basis of two concrete worst-case performance metrics. The effectiveness of the modular control strategy with the modular control error compensation is demonstrated through experimental results on an automotive system. Copyright © 2012 John Wiley & Sons, Ltd.

We give sufficient conditions for the exponential stability of a class of perturbed time-varying difference equations with multiple delays and slowly varying coefficients. Under appropriate growth conditions on the perturbations, combined with the ‘freezing’ technique, we establish explicit conditions for global exponential stability. Copyright © 2012 John Wiley & Sons, Ltd.

This paper addresses the design of low-level controllers for leader–follower formations of nonholonomic vehicles in the presence of bounded measurement delays. The concept of input-to-state stability is extended to encompass the effect of bounded delays and restrictions on the input. A method is proposed to integrate a Smith predictor in a backstepping design on the basis of nested saturations and nonlinear small-gain assignment, which allows for time delays in the feedback loop. Robustness analysis under uncertain bounded time delays is provided, and design tradeoffs resulting from the use of bounded controls are discussed. Illustrative simulations are shown to validate the design and robustness analysis in the context of a simple leader–follower trailing control problem. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, robust adaptive output feedback control is studied for a class of discrete-time nonlinear systems with functional nonlinear uncertainties of the Lipschitz type and unknown control directions. In order to construct an output feedback control, the system is transformed into the form of a nonlinear autoregressive moving average with eXogenous inputs (NARMAX) model. In order to avoid the noncausal problem in the control design, future output prediction laws and parameter update laws with the dead-zone technique are constructed on the basis of the NARMAX model. With the employment of the predicted future outputs, a constructive output feedback adaptive control is proposed, where the discrete Nussbaum gain technique and the dead-zone technique are used in parameter update laws. The effect of the functional nonlinear uncertainties is compensated for, such that an asymptotic tracking performance is achieved, whereas other signals in the closed-loop systems are guaranteed to be bounded. Simulation studies are performed to demonstrate the effectiveness of the proposed approach. Copyright © 2012 John Wiley & Sons, Ltd.

This paper investigates the consensus problem for multi-agent systems and presents a class of nonlinear consensus protocols. First, we reveal some structure property of the corresponding Laplacian matrix by decomposing the interaction graph into strongly connected components. Then, by means of the input-to-state stability and algebraic graph theory, we propose a framework to prove consensus for multi-agent systems with nonlinear protocols. In particular, we prove that consensus can be always reached in systems of single-integrator agents with a directed communication topology containing a spanning tree, provided the nonlinear protocol is an odd and increasing function. The nonlinear consensus protocols proposed in this paper include the classical linear consensus protocol as a special case, and may have a wide range of applications, including consensus with faster convergence rates and with bounded control inputs. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, the problems of exponential stability and -gain analysis of event-triggered networked control systems (NCSs) with network-induced delays are studied. We first propose event-triggering conditions in the sensor side and controller side, respectively. Because the implementation of our event-triggering scheme only needs periodic supervision of the system state at the constant sampling instants, instead of being monitored continuously, it is expected that the scheme will improve the resource utilization. Taking the network-induced delays into account and using delay system approach, we constructed a unified model of NCSs with hybrid event-triggering schemes. On the basis of this model, sufficient conditions for the exponential stability and -gain analysis are developed in the form of LMIs by using a discontinuous Lyapunov–Krasovskii functional approach. Moreover, the corresponding results can be further extended to more general cases, where the system matrices of the considered plant contain parameter uncertainties, represented in either polytopic or norm-bounded frameworks. In addition, as a special case, we also present the exponential stability, -gain analysis, and the control feedback gain design of event-triggered NCSs without considering the effects of network-induced delays and event-triggering condition in the controller side. Finally, a simulation example is provided to illustrate the usefulness and effectiveness of the proposed hybrid event-triggering schemes.Copyright © 2012 John Wiley & Sons, Ltd.

This paper studies the problem of designing the static output feedback controller for the positive linear continuous-time systems. On the basis of a system augmentation approach, a novel characterization on the stable condition of the closed-loop system is firstly established. Then, a necessary and sufficient condition is given to ensure the existence of the desired static output feedback controller, and an iterative linear matrix inequality algorithm is presented to compute the feedback gain matrix. Finally, a numerical example is provided to illustrate the effectiveness of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.

This paper proposes a linear matrix inequality based method for the estimation of domain of attraction for a class of discrete-time nonlinear systems subject to uncertain constant parameters. Recursive algebraic representations of the system dynamics and of the Lyapunov stability conditions are applied to obtain convex conditions which guarantee the system robust local stability while providing an estimate of the domain of attraction. A large class of discrete-time nonlinear systems and of Lyapunov functions can be embedded in the proposed methodology including the whole class of regular rational functions of the system state variable and uncertain parameters. Numerical examples illustrate the application of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.

This paper studies the stability of linear systems with interval time-varying delays. By constructing a new Lyapunov–Krasovskii functional, two delay-derivative-dependent stability criteria are formulated by incorporating with two different bounding techniques to estimate some integral terms appearing in the derivative of the Lyapunov–Krasovskii functional. The first stability criterion is derived by using a generalized integral inequality, and the second stability criterion is obtained by employing a reciprocally convex approach. When applying these two stability criteria to check the stability of a linear system with an interval time-varying delay, it is shown through some numerical examples that the first stability criterion can provide a larger upper bound of the time-varying delay than the second stability criterion.Copyright © 2012 John Wiley & Sons, Ltd.

This paper discusses the exponential stability and stabilization for nonlinear descriptor systems with discrete and distributed delays. In terms of the Lyapunov method, the exponential stability of the slow subsystem is firstly obtained. Then, a new homotopy-based approach is proposed to investigate the exponential stability of the fast subsystem. By an estimate of the weighted matrix norm for a nonlinear mapping, the exponential stability of the fast subsystem and thus delay-dependent sufficient conditions for the exponential stability of the systems are obtained. In addition, a state feedback controller is designed for the stabilization of the nonlinear descriptor systems. Finally, the effectiveness of the proposed approach is illustrated by numerical examples. Copyright © 2012 John Wiley & Sons, Ltd.

This paper considers a class of Lur'e descriptor systems (LDS) subject to exogenous disturbances. The concept of input-to-state stability (ISS) is generalized to descriptor systems. Such a notion characterizes the robust stability of the full state of the systems. Based on the conventional ISS theory, a sufficient condition expressed by linear matrix inequalities (LMIs) for the LDS to be ISS is derived. It is further shown that this condition also guarantees a special class of LDS to be of index one. Then, a state feedback controller is designed to make the closed-loop system ISS. Finally, an example is given to illustrate the obtained results. Copyright © 2012 John Wiley & Sons, Ltd.

We generalize the J-spectral factorization of para-Hermitian proper rational matrix in the case when it has no constant inertia on the imaginary axis. This result and the presented numerical algorithm are based on a canonical form of para-Hermitian matrix pencils. We apply the new spectral factorization to the optimal control of the proper plant by dynamic measurement feedback over a frequency region. Copyright © 2012 John Wiley & Sons, Ltd.

We propose a measurement feedback controller for a class of feedforward nonlinear systems under sensor noise. The sensor noise has unknown magnitude, frequency, and phase. Our proposed controller is coupled with a low-pass filter in such a way that the sensor noise is attenuated. We show that the controlled system results in bounded states whose ultimate bounds are inversely proportional to the minimum frequency of the sensor noise. Our result is further generalized to work in a case where the sensor noise is only required to have a Fourier transform with finite energy. Moreover, if the sensor noise enters only at partial states, depending on the location of the sensor noise, the ultimate bounds of the particular states can be made arbitrarily small via the gain factor of the controller. Copyright © 2012 John Wiley & Sons, Ltd.

This work deals with the closed-loop robust stability of nonlinear model predictive control (NMPC) coupled with an extended Kalman filter (EKF). First, we point out the gaps between the practical formulations and theoretical research. Then, we show that the estimation error dynamics of an EKF are input-to-state stable (ISS) in the presence of nonvanishing perturbations. Moreover, a target setting optimization problem is proposed to solve the target state corresponding to the desired set points, which are used in the objective function in NMPC formulation. Thus, the objective function is a Lyapunov function candidate, and the input-to-state practical stability (ISpS) of the closed-loop system can be established. Moreover, we see that the stability property deteriorates because of the estimation error. Simulation results of the proposed scheme are presented.Copyright © 2012 John Wiley & Sons, Ltd.

We consider a class of neutral stochastic systems with time-varying delay and study the exponential stability in the mean square sense. We derive sufficient stability conditions via applying Lyapunov functional method along with some practical techniques. Firstly, in computing the constructed Lyapunov functional, we make use of some basic rules of Itô calculus to reduce the conservatism produced by noise because it, in principle, plays a negative role for preserving stability in the mean square sense. Also, it is an important observation that, using some slack matrices, we can create convex conditions to accommodate the computation to time-varying delay. In the sequel, we use a perturbation approach to estimate the decay rate of state and come to the conclusion of stability. Finally, we include an example to demonstrate the effectiveness of the method. Copyright © 2012 John Wiley & Sons, Ltd.

This paper addresses attitude synchronization and tracking problems in spacecraft formation in the presence of model uncertainties and external disturbances. A decentralized adaptive sliding mode control law is proposed using undirected interspacecraft communication topology and analyzed based on algebraic graph theory. A multispacecraft sliding manifold is derived, on which each spacecraft approaches desired time-varying attitude and angular velocity while maintaining attitude synchronization with the other spacecraft in the formation. A control law is then developed to ensure convergence to the sliding manifold. The stability of the resulting closed-loop system is proved by application of Barbalat's Lemma. Simulation results demonstrate the effectiveness of the proposed attitude synchronization and tracking methodology. Copyright © 2012 John Wiley & Sons, Ltd.

This paper addresses the problem of adaptive neural control for a class of uncertain stochastic pure-feedback nonlinear systems with time-varying delays. Major technical difficulties for this class of systems lie in: (1) the unknown control direction embedded in the unknown control gain function; and (2) the unknown system functions with unknown time-varying delays. Based on a novel combination of the Razumikhin–Nussbaum lemma, the backstepping technique and the NN parameterization, an adaptive neural control scheme, which contains only one adaptive parameter is presented for this class of systems. All closed-loop signals are shown to be 4-Moment semi-globally uniformly ultimately bounded in a compact set, and the tracking error converges to a small neighborhood of the origin. Finally, two simulation examples are given to demonstrate the effectiveness of the proposed control schemes. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we develop a nonlinear controller to achieve output tracking for a nonminimum phase vertical take-off and landing aircraft without velocity measurements. To attenuate the effects of input disturbances and unmatched uncertainties, auxiliary control inputs are introduced in the state observer. Then by taking the aircraft lateral movement into consideration, a control law is proposed to force the vertical take-off and landing aircraft to asymptotically track the desired trajectories even in the presence of unexpected changes of the trajectories, while driving the unstable internal dynamics to follow the bounded and causal ideal internal dynamics via the stable system center method. Numerical simulation results illustrate the effectiveness and robustness of the proposed controller.Copyright © 2012 John Wiley & Sons, Ltd.

The stabilization properties of derivative control for chemical reactor stabilization have been rarely studied in the literature. In a pioneering work, Aris and coworkers (Chem. Eng. Sci. 1959; 11:199–206.) used linear analysis to show that derivative control offers greater stabilization flexibility than proportional control. The aim of this work is to show that mixed derivative and proportional control can yield global stabilization for a large class of continuously stirred tank reactors (CSTR) characterized by having stable isothermical dynamics. The stability proof exploits the structure of CSTR models where the nonlinearity is concentrated in the chemical reaction kinetics. It is shown that the proportional mode is a type of energy shaping to induce a unique equilibrium point, while the derivative mode can be interpreted as a global damping injection to reduce undesired transient effects, such as temperature overshooting and oscillations. A numerical example is used to illustrate the different features of mixed proportional and derivative control in chemical reactor dynamics. Copyright © 2011 John Wiley & Sons, Ltd.

This paper considers autonomous robotic sensor networks taking measurements of a physical process for predictive purposes. The physical process is modeled as a spatiotemporal random field. The network objective is to take samples at locations that maximize the information content of the data. The combination of information-based optimization and distributed control presents difficult technical challenges as standard measures of information are not distributed in nature. Moreover, the lack of prior knowledge on the statistical structure of the field can make the problem arbitrarily difficult. Assuming the mean of the field is an unknown linear combination of known functions and its covariance structure is determined by a function known up to an unknown parameter, we provide a novel distributed method for performing sequential optimal design by a network comprised static and mobile devices. We characterize the correctness of the proposed algorithm and examine in detail the time, communication, and space complexities required for its implementation. Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, we propose a tracking control law for a linear dynamical system under time-varying input constraints. The proposed control law consists of a dual-mode model predictive control (MPC) law and a target recalculation mechanism. As the terminal controller of the dual-mode MPC, we propose a saturation-level-dependent gain-scheduled feedback control law that ensures closed-loop stability against arbitrary change of the position limit of the actuators. We also present conditions that guarantee feasibility and stability of the control algorithm under time-varying input constraints. The control algorithm is reduced to an online optimization problem under linear matrix inequality constraints. Copyright © 2012 John Wiley & Sons, Ltd.

This paper deals with convex relaxations for quadratic distance problems, a class of optimization problems relevant to several important topics in the analysis and synthesis of robust control systems. Some classes of convex relaxations are investigated using the sum of squares paradigm for the representation of positive polynomials. The main contribution is to show that two different relaxations, based respectively on the Positivstellensatz and on properties of homogeneous polynomial forms, are equivalent. Relationships among the considered relaxations are discussed and numerical comparisons are presented, highlighting their degree of conservatism. Copyright © 2012 John Wiley & Sons, Ltd.

This paper is concerned with the second-order consensus problem of multi-agent systems with a virtual leader, where all agents and the virtual leader share the same intrinsic dynamics with a locally Lipschitz condition. It is assumed that only a small fraction of agents in the group are informed about the position and velocity of the virtual leader. A connectivity-preserving adaptive controller is proposed to ensure the consensus of multi-agent systems, wherein no information about the nonlinear dynamics is needed. Moreover, it is proved that the consensus can be reached globally with the proposed control strategy if the degree of the nonlinear dynamics is smaller than some analytical value. Numerical simulations are further provided to illustrate the theoretical results. Copyright © 2012 John Wiley & Sons, Ltd.

The main bottleneck for the application of H_∞ control theory on practical nonlinear systems is the need to solve the Hamilton–Jacobi–Isaacs (HJI) equation. The HJI equation is a nonlinear partial differential equation (PDE) that has proven to be impossible to solve analytically, even the approximate solution is still difficult to obtain. In this paper, we propose a simultaneous policy update algorithm (SPUA), in which the nonlinear HJI equation is solved by iteratively solving a sequence of Lyapunov function equations that are linear PDEs. By constructing a fixed point equation, the convergence of the SPUA is established rigorously by proving that it is essentially a Newton's iteration method for finding the fixed point. Subsequently, a computationally efficient SPUA (CESPUA) based on Galerkin's method, is developed to solve Lyapunov function equations in each iterative step of SPUA. The CESPUA is simple for implementation because only one iterative loop is included. Through the simulation studies on three examples, the results demonstrate that the proposed CESPUA is valid and efficient. Copyright © 2012 John Wiley & Sons, Ltd.

We consider the problem of asymptotic rejection of exogenous harmonic inputs having unknown amplitudes, phases, and frequencies on the output for a class of uncertain and nonminimum-phase linear systems. Special emphasis is given to the case in which the controlled system has multiple zeros at the origin. It is shown how the method recently proposed to design internal models by means of regression arguments, combined with control strategies based on the redesign of the zero dynamics of the system through redefinition of the output, can be successfully used to solve the problem in presence of plant parameter uncertainties.Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we provide a proof of almost sure exponential convergence to consensus for a general class of ergodic edge selection processes. The proof is based on the multiplicative ergodic theorem of Oseledec and also applies to continuous time gossip algorithms. An example of exponential convergence in a non ergodic case is also discussed. Copyright © 2012 John Wiley & Sons, Ltd.

The solution to the nonlinear output regulation problem requires one to solve a first-order partial differential equation, known as the Francis–Byrnes–Isidori equations. In this paper, we propose a method to compute approximate solutions to the Francis–Byrnes–Isidori equations when the zero dynamics of the plant are hyperbolic and the exosystem is two dimensional. With our method, we are able to produce approximations that converge uniformly to the true solution. Our method relies on the periodic nature of two-dimensional analytic center manifolds. Copyright © 2012 John Wiley & Sons, Ltd.