Parameterization of robust three-term power system stabilizers

This paper addresses the problem of determining robust three-term output-feedback power system stabilizers (PSSs) (C1(s) = (x1s + x2 + x3/s) ; C2(s) = x1(1 + x2s)/(1 + x3s)) which can function properly over wide range of operating conditions. Necessary and sufficient constraints that characterize the admissible set of PSSs parameters are derived firstly by applying Routh-Hurwitz (RH) criterion to the characteristic polynomial of the generalized plant model. The complete set of stabilizing PSSs for any operating point is therefore determined in the controller parameter space [x1, x2, x3] by plotting RH constraints at this point. Since the design parameters are load-dependent and have to be adjusted at each operating condition, an interval plant is developed to describe uncertainties in the model parameters imposed by continuous variation in load patterns. Necessary and sufficient constraints for Hurwitz stability of such interval plant are derived using Kharitonov's theorem where robust PSS design is reduced to simultaneous stabilization of finite number of vertex/segment plants. The stability region for each of these plants is plotted using RH constraints where the intersection of the resulting stability regions yields the set of parameters that guarantee Hurwitz stability of the considered interval plant. Simulation results of an applicant PSS confirm the effectiveness of the proposed design approach.