A robust power system stabiliser for an overseas application

This paper presents a method of designing robust power system stabilisers (PSS) for damping low frequency electromechanical oscillations. The technique uses a quadratic cost function for specifying the closed loop performance and H_∞ constraints for the closed loop robustness. The structure of the controller can be selected by the engineer thus allowing robust tuning of existing PSS. In addition, the upper and lower limits of the PSS are incorporated thus ensuring that the recommended parameter values can be implemented. A sequential quadratic algorithm is used to solve the optimisation problem. The method is implemented on an equivalent of the Eskom network and the results are discussed. The proposed method of tuning the PSS is shown to be superior to the conventional techniques both in performance and robustness properties. An important consequence of the approach is that existing PSS can simply be retuned for optimal robust performance without replacement of the generator excitation control equipment