Application of the direct Lyapunov method to improve damping of power swings by control of UPFC

Large interconnected power systems often suffer from weakly damped swings between synchronous generators and subsystems. This paper presents an approach, based on the use of the nonlinear system model and application of the direct Lyapunov method, to improve damping of power swings using the unified power flow controller (UPFC). A state-variable control strategy has been derived as well as its implementation using locally available signals of real and reactive power. The results of simulation tests, undertaken using a small multi-machine system model, have been presented.