Tuning the fuzzy damping controller for UPFC through genetic algorithm with comparison to the gradient descent training

The unified power flow controller (UPFC) is the most versatile device in the flexible ac transmission systems (FACTS) which can provide superior power flow and voltage control through its main control. It can also improve power system dynamic performance through its supplementary control. In this paper, a fuzzy supplementary controller is designed for the UPFC to damp tie line power oscillation in the interconnected power systems. The parameters of the fuzzy damping controller (FDC) are optimized using the gradient descent training method and the genetic algorithm, respectively. The UPFC power frequency model, its main and supplementary control block diagrams and the formulation for the FDC parameter optimization are presented. Time simulation on a multi-machine inter-connected power system shows that the two optimization methods converge very well and yield very close FDC parameters and the designed FDC performs well in damping the tie line power oscillation under large disturbances. Computer simulation results also show that the FDC has better robustness under different system operation conditions than its conventional counterpart.