Clarification on power system stabiliser design

The application of power system stabiliser (PSS) since 1960s has exerted a great effect on improving power system dynamic stability and has become a very important auxiliary excitation control measure to deal with low frequency oscillation. The common design approach is to compensate for the phase lag caused by the excitation system, and thereby increase damping of the system. Is that the real key in stabilising the system? This study clarifies the damping torque concept and analyses the flaws of the damping torque-based PSS design theory. The key parameters in PSS design to stabilise the power system are fully investigated, based on which the study reveals the real nature of the PSS working mechanism. It has been shown in the study that phase compensation is not the necessary condition in stabilising the system; stabiliser gain is very important for controller design. Case studies in the real power system validate the analysis results.