Suppression of Autoparametric Resonance in Longitudinal Power Systems

Abstract

Autoparametric resonance is a phenomenon in which one oscillation mode gets unstable through interaction with another mode. There is a possibility that a low-frequency oscillation gets unstable because of the resonance in longitudinal power systems. The physical cause of the resonance is load, and the resonance gets stronger as load increases. Damping torques of generators are effective to suppress the resonance. We show that if there is certain amount of damping torque, a longitudinal system gets stable irrespective of the number and capacity of generators. Since the interaction between the modes arises from voltage deviation at load buses, it is useful to make the voltage deviation small. We clarify how automatic voltage regulators (AVR) mitigate the resonance. The AVRs reduce the strength of the resonance to one tenth of that for the system where the internal voltages are assumed constant. High gain AVRs make the mode unstable, however. Power system stabilizers (PSS) stabilize the mode, and simultaneously provide some damping necessary to suppress the resonance. Lastly, we verify through simulations that AVRs and PSSs really stabilize the system.