An investigation of variable power collective pitch control for load mitigation of floating offshore wind turbines
Article first published online: 10 MAY 2012
Copyright © 2012 John Wiley & Sons, Ltd.
Volume 16, Issue 4, pages 519–528, May 2013
How to Cite
Lackner, M. A. (2013), An investigation of variable power collective pitch control for load mitigation of floating offshore wind turbines. Wind Energ., 16: 519–528. doi: 10.1002/we.1500
- Issue published online: 16 MAY 2013
- Article first published online: 10 MAY 2012
- Manuscript Accepted: 17 JAN 2012
- Manuscript Revised: 13 JAN 2012
- Manuscript Received: 30 JUN 2009
This paper investigates the loads on offshore floating wind turbines and a new control method that can be used to reduce these loads. In this variable power collective pitch control method, the rated generator speed, which is the set point that the collective pitch control attempts to drive the actual generator speed towards, is no longer a constant value but instead a variable that depends on the platform pitch velocity. At a basic physical level, this controller achieves the following: as the rotor of a floating turbine pitches upwind, the controller adjusts so as to extract more energy from the wind by increasing the rated generator speed and thus damps the motion; as the rotor pitches downwind, less energy is extracted because the controller reduces the rated generator speed and again damps the motion. This method is applied to the NREL 5 MW wind turbine model, in above-rated conditions where the platform motion is most problematic. The results indicate significant load reductions on key structural components, at the expense of minor increases in power and speed variability. The loads on the blades and tower are investigated more generally, and simple dynamic models are used to gain insight into the behavior of floating wind turbine systems. It is clear that for this particular design, aerodynamic methods for reducing platform motion and tower loads are likely inadequate to allow for a viable design, and so new designs or possibly new control degrees of freedom are needed. Copyright © 2012 John Wiley & Sons, Ltd.