Research on Frequency Stability of Islanded Hydroelectric DC Sending System

In this paper, a resonance function to simulate pulsating situation of the tail pipe pulsation based on the linear turbine model is designed, and a novel water turbine model that considers the tail pipe water pressure pulsation as well as the elastic water column is built. By using time domain simulation method, the accuracy of the turbine model is verified, and the influence of the parameters of hydraulic system and the governor on frequency vibration in sending-end of islanded DC system is analyzed. Simulation results show that such parameters as the hydraulic startup time (T_w) and governor parameter (K_D) have great impact on frequency vibration in sending-end of islanded DC system with the exception of elastic time (T_e). Moreover, DC frequency limiter model is modified to restrain from frequency oscillation by using secondary low-pass filter instead of linear low-pass filter and regulating PI parameters. The results show that the frequency in sending-end will be controlled to about 50Hz, which verifies the validity of modified DC frequency limiter.