Mechanistic Analysis of Ultra-Low-Frequency Oscillation Accompanied by Low-Frequency Oscillation in Hydropower System

The Proportional-Integral-Derivative (PID) parameter settings of the hydroelectric unit governor can induce both ultra-low frequency oscillation (ULFO) and low-frequency oscillation (LFO). The occurrence of ULFO accompanied by LFO poses a serious threat to the safe and stable operation of the power system. Understanding the influence of governor PID parameters on ULFO and LFO is crucial for configuring PID parameters to ensure the safe and stable operation of the power system. In this paper, the damping torque method is used to study the evolution of the damping torque in the prime mover system of a hydroelectric unit under varying PID parameters. The parameters and their influence mechanisms on the stability of ULFO and LFO are clarified. Among them, increasing the proportional and differential coefficients has a greater impact on the stability of the speed control system in the low-frequency band, which can super-produce LFO. The simulation results validate the accuracy of the analysis.