Mechanism analysis and suppression method of ultra-low-frequency oscillations caused by hydropower units

The ultra-low-frequency oscillation (ULFO) occurred in the hydro-dominant Yunnan power grid during its asynchronous interconnection with the China southern power grid in 2016, with the oscillation frequency at about 0.05 Hz. In view of this practical engineering problem, this paper analyzes the mechanism of this problem and puts forward the corresponding suppression measures. First, this paper utilizes the classical control theory to reveal the mechanism of the ULFO and analyze the effect of the governor parameters on the ULFO. According to the analysis, the ULFO will occur when the installed capacity of the hydro-power units is too large and the ratio of the hydro-power governor's proportional parameter to the integral parameter is too small. Secondly, a new method to tune the governor parameters is proposed, the parameters tuned by this method can avoid the recurrence of the ULFO under different operation conditions. Finally, simulation verifications are run in a three-machine system and the Yunnan power grid using PSS/E (Power System Simulator/Engineering). The simulation results verify the effectiveness of the analysis and the measure.