Abstract: Aiming at ultra-low frequency oscillation in power system caused by hydraulic turbine governing

system，an additional damping control strategy for governing side was developed. Firstly，according to the damping torque method，the negative damping generated by the hydraulic turbine governing system was regarded as the main reason for the ultra-low frequency oscillation of the power system. Secondly，the damping torque coefficient expression of the speed regulation system was derived，which proves that the coefficient is closely related to the time constant of water hammer effect and the PID parameters of the governor. Besides，based on the additional damping control strategy，the positive damping compensation was introduced in the speed control side of the system. The grey wolf optimization（GWO）algorithm was applied to optimize the PID parameters to further

improve the damping characteristics of the system. Finally，simulation verification in a single-machine system and a

four-machine two-area system was executed through Matlab/Simulink. The results illustrate that the proposed

control strategy can significantly enhance the damping characteristics of the speed control system and effectively

suppress ultra-low frequency oscillation.

      Key words: ultra-low frequency oscillation；hydraulic turbine governing system；additional damping control；

damping torque method；parameter tuning