Design of Robust Type-2 Fuzzy Logic Power System Stabilizer Using Hopf Bifurcations

A power system shifts to a state outside the stability boundary encountered by unstable limit cycles, at this point it will not return to the stable operating point. This resembles an increasing oscillatory behaviour in a nonlinear continuous time dynamic systems. Locating the unstable limit cycles and enhancing the stability margin is a difficult task. The effective devices for damping these oscillations are Power System Stabilizers (PSSs). The conventional power system stabilizer (CPSS) considered is lead-lag PSS. The conventional power system stabilizer enhances the stability margin of the power system. The dynamic stability margin of power system is evaluated by finding the loading condition that result in Hopf bifurcations. At this load the power system exhibits a pair of purely imaginary eigenvalues. Literature shows that a Fuzzy Logic Power System Stabilizer (FLPSS) is a controller to cover a wider range of operating conditions. In the present paper a type-2 fuzzy logic power system stabilizer is used to damp the power system oscillations. The parameters of the stabilizer are designed for the loading condition resulting in Hopf bifurcations of power system with CPSS. To obtain the best damping characteristics, speed deviation ( ), derivative of speed deviation ( ) and power angle ( ) are taken as input to type-2 fuzzy logic power system stabilizer. The proposed controller is included in the small signal model of the power system. The performance of the proposed controller is tested over varied operating conditions. The efficacy of the proposed controller is compared to Convectional Power System Stabilizer.