• transient stability;
  • direct method;
  • BCU method;
  • dynamic security assessment;
  • energy function


Despite possible changes in energy sources, the importance of maintaining the stability of interconnected power systems will not change. Technologies for maintaining power system stability must evolve with renewable energy technology. As renewable energy increases, analysis and control methods for transient stability assessment must be reexamined and improved. This paper presents an overview of on-line dynamic security assessment (DSA) systems and related direct methods. The controlling unstable equilibrium point (UEP) method and the boundary of the stability-region-based controlling UEP (BCU) method are briefly described in order to provide a framework of understanding the concept of a transient stability-screening program for DSA systems. The integrated package TEPCO-BCU, a very advanced practical program based on the theory of the controlling UEP method, BCU method, energy function method, and BCU-guided time-domain method, is described from the viewpoint of on-line performance. Finally, the importance of validating the assessment results of the BCU method is discussed. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.