Enhancing power system transient stability using optimal unified power flow controller based on Lyapunov control strategy

This paper presents a new control strategy for an Optimal Unified Power Flow Controller (OUPFC) through a Lyapunov energy function in terms of local parameters to improve the transient stability of a power system. The OUPFC is a hybrid configuration of Flexible AC Transmission System (FACTS) devices, i.e. an arrangement of small-sized Unified Power Flow Controller (UPFC) and a full-scale Phase Shifting Transformer (PST). In this study, a new term of OUPFC's energy function and its injection model in a simplified structure preserving model is developed and implemented in a two-machine power system using MATLAB/Simpower. The ability of the OUPFC controller to enhance the transient stability is compared to that of UPFC. The results show that using the proposed control strategy for OUPFC leads to more abatement of the first swing oscillations and enlargement of stability margin. It is concluded that compensation of UPFC's angle displacement may come true using OUPFC with appropriate angles in proper locations. So, compared to UPFC, OUPFC enjoys another degree of freedom. (C) 2017 Sharif University of Technology. All rights reserved.