Is lead compensation appropriate to PSS design?

In power system studies, it has been long recognized that power system stabilizer (PSS) aims to provide appropriate phase lead in order to compensate the phase lag of generator excitation system. Therefore, lead compensation prevails in almost all stability studies and the effectiveness of PSSs with lead compensation was demonstrated by eigenvalue and swing plots, to confirm that their PSS designs can enhance the system damping under both small and large disturbances. The present paper will (a) explore whether the lead compensation of PSS has provided the correct phase compensation even with substantial improvements of system damping, and (b) highlight the risks due to lead compensation. A systematic technique based on eigenvalue sensitivity is recommended to effectively provide correct phase compensation and to suppress the risks in PSS tuning.