Robust power system stabiliser

Power system stabilisers (PSS) are usually implemented by feeding a speed signal through a supplementary loop that comprises a proper phase lead. The design parameters of this loop are load dependent. Thus, they have to be adjusted at each operating condition. A simple robust PSS is designed that can properly function over a wide range of operating conditions and extend the machine loadability. The lead compensator design is achieved by drawing the root loci for a finite number of extreme characteristic polynomials. Such polynomials are obtained, using the Kharitonov theorem, to reflect wide loading conditions on characteristic equation coefficients. For this purpose the explicit analytical forms for the coefficients of the system transfer functions are derived. Simulation results illustrate the effectiveness of the proposed stabiliser as it is applied to the original nonlinear differential equations describing system dynamics under wide loading conditions at lagging and leading power factors.