Abstract: Frequency oscillations tend to occur in a hydropower units-dominated primary frequency regulating system. In setting PID parameters of the turbine governor, small disturbances in the stability of frequency is often taken as the objective of optimization. This paper presents an analysis of the influence of PID parameters on frequency oscillation torque and low-frequency oscillation torque using a damped torque method. To suppress the frequency oscillations, adjusting PID parameters was found aggravate low-frequency oscillations in the system, which was verified using a four-machine two-zone system. Finally, a parameter tuning method was developed for hydropower dominant systems that can improve the frequency stability of the systems without deteriorating weakly-damped low-frequency oscillation modes.

Key words: hydropower dominant system, damping torque, frequency oscillation, low-frequency oscillation, PID parameter setting method