Design of fuzzy damping controller of UPFC through genetic algorithm

The addition of a PSS-like supplementary controller to the UPFC main control can provide effective damping to the low frequency oscillation on the heavily loaded tie lines of interconnected power systems. However, the conventional controller designed based on a linearized model cannot provide satisfactory performance over a wide range of operation point and under large disturbances. In this paper, the design of a fuzzy damping controller (FDC) for UPFC as a substitute of the conventional supplementary controller is presented. Scaling factors are inserted to the membership functions of both inputs and output for easy design of fuzzifier and defuzzifier. A genetic algorithm (GA) is applied to optimize the performance of the FDC through fine-tuning of the scaling factors. A 4-machine interconnected power system is used as the test system with a UPFC installed in one of the tie lines. Comparisons between the performances of both the fuzzy and the conventional supplementary controllers are studied. Computer test results show that FDC is very effective in damping the oscillation and in the meantime has a better robustness as compared with its conventional counterpart.