Small-Signal Stability and Dynamic Behaviors of a Hydropower Plant With an Upstream Surge Tank Using Different PID Parameters

This paper used the state space method to establish a stability analysis model of a hydroturbine governing system (HTGS) coupled with a water diversion system. The stability characteristics of different regulating regions (RRs) were studied according to the eigenvalues of the system, and they were verified by numerical simulations in the time domain. The dynamic system responses and dominating factors were analyzed for governor parameters selected in different domains of the RRs. In addition, an intermediate unstable RR was discovered and its influencing factors were investigated. The results show that the unstable RR occurs because of the interaction between the oscillations in the HTGS and surge tanks and indicate that the system performance varies in different domains of the RR, with better performance observed in domain II. Then, a comprehensive critical stable area is observed in the surge tank based on the effect of the turbine, governor and water inertia, and a specific instance of the traditional Thoma stable area is observed in the proposed area. Either reducing the cross-sectional area of the surge tank and head loss coefficients of the headrace tunnel or increasing the water inertia of the water diversion system can increase the unstable RRs.