Coprime factorization approach to multi-input PSS design for damping SSR and local modes

This paper illustrates the application of Glover-McFarlane´s H_∞ loop-shaping technique to design a dual-input power system stabilizer (PSS). The PSS stabilizes one key sub-synchronous (SSR) mode and a local mode contributing to critical electromechanical oscillations involving turbine-generators and electrical network. The IEEE first benchmark model (FBM) for the analysis of SSR phenomena has been considered in this study. A linearized model of the system is pre- and post-compensated using loop-shaping approach. The problem of robust stabilization of a normalized coprime factor plant description is formulated into a generalized H_∞ problem and the solution are obtained analytically. Stability of the system is discussed through eigenvalue analysis. The controller has ensured good damping to subsynchronous modes which were otherwise very poorly damped or undamped depending upon operating conditions.