Transient stability assessment of systems comprising phase-shifting FACTS devices by direct methods

Abstract

In this paper the concept of a control Lyapunov function is used to develop control strategies for thyristor-controlled phase-shifting transformers (TCPSTs). Two typical representatives of TCPSTs were chosen for consideration: a Quadrature Boosting Transformer (QBT) and a Phase Angle Regulator (PAR). For the case of the QBT we showed that the proposed control law can significantly improve the large signal stability in comparison to the control-law-based on the traditionally used injection model proposed in various references. Even if the system parameters are estimated very roughly, our proposed strategy gives better results than the ‘traditional’ strategy. Also, some novel energy functions, which consider the action of an optimally controlled TCPST in a single-machine infinite-bus (SMIB) system, are presented and validated by a numerical example.