Design of a hierarchical fuzzy logic PSS for a multi-machine power system

The performance of fuzzy-logic power system stabilizer (FPSS), which is tuned automatically as the operating conditions of power system change, is investigated by applying it to a multi-machine power system. FPSS is developed using speed deviation and the derivative of speed deviation as the controller inputs variables. Two scaling parameters are introduced to tune the FPSS. These scaling parameters are the output of another fuzzy-logic system (FLS), which gets its inputs from the operating condition of the power system. The proposed scheme is referred to as the self tuning fuzzy power system stabilizer (TFPSS). This mechanism of tuning the FPSS makes it adaptive to changes in the operating condition. The response of the system with three power system stabilizers (PSSs), namely CPSS, FPSS and self tuned FPSS, are compared. It is shown that the tuned FPSS is superior to both CPSS and fixed-parameter FPSS. The effect of the defuzzification methods on the on the control signal response is also shown in this paper.