Analysis of Ultra-Low Frequency Oscillation in Hydro-Dominant Power System and Suppression Strategy by GPSS

After asynchronous operation, the Southwest Power Grid in China has the risk of ultra-low frequency oscillation, which seriously threatens the stable operation of the power grid. Based on the hydropower single-unit with load system, the extend Philips-Heffron model is built considering PSS/GPSS (Governor Power System Stabilizer). Then, the damping torque analysis is carried out in both prime mover and excitation side. The negative damping in the prime mover side is prominent in the ultra-low frequency band and the effect of damping ratio increase by PSS and GPSS is compared. After that, the small signal analysis of the whole system is conducted, the participation factors of the ULFO mode shows the high participation and controllability by GPSS control. At last, the proper GPSS parameters configured by small signal analysis are equipped in the hydro unit of asynchronous four-machine two-area system which reveals an obvious ULFO suppression effect. Furthermore, the practical ULFO identification algorithm based on feature points extraction and analysis which crossing the PFC (Primary Frequency Control) dead zone (49.95–50.05 Hz) is proposed, the GPSS control cubicle which embedded the practical ULFO identification algorithm is developed and the semi-physical simulation is conducted to verify the real ULFO suppression effect by GPSS control.