Practical application considerations for power system stabilizer (PSS) controls

The basic function of the PSS is to apply a signal to the excitation system, creating electrical torques that damp out power oscillations. There is a significant body of literature about the design, tuning and performance of PSS controls. In some cases this previous work has not fully considered some important practical aspects that can affect the way the PSS controls influence the unit response. Although the primary function of the PSS is to supply positive damping torque contributions, experience indicates that it can impact the generator-power system transient performance under certain conditions. The various aspects of the PSS performance considered in this paper can be summarized in four areas: (1) the effect of PSS on system volt/VAr swings; (2) the interaction of the PSS with governor action during slow frequency regulation, or unit loading/unloading; (3) the interaction of the PSS with other controls such as UEL, VAr controllers, and HVDC, SVC, or TCSC devices; and (4) the possible interaction of the PSS with the turbine generator shaft torsional dynamics. These issues are the focus of this paper. Test results and computer simulations are shown to illustrate the concepts, and guidelines are presented to provide a unified tuning.