PHASE PLANE METHOD STABILITY ANALYSIS OF FUZZY LOGIC PSS

Abstract

This paper presents a novel approach to investigate the stability of fuzzy logic based power system stabilizers using phase plane method and limit cycle analysis. Fuzzy logic controller (FLC) is highly non-linear and eigen values of the system cannot be obtained. The phase plane method is utilized for the stability analysis of fuzzy controller and for the development of effective rule base of the fuzzy power system stabilizers (PSSs). The limit cycles with definite area and trajectory in the phase-plane plot not converging towards the origin, is the unstable fuzzy stabilizer. Modifying the linguistic variables in the non-converging region of limit cycle by an opposite linguistic variables (e.g. NS to PS), the unstable fuzzy controller can be converted into a stable fuzzy controller. The effect of fired rules on stability and minimization of non-converging areas of the limit cycles is illustrated and tested for Multi Machine Power System (MMPS).