Mechanism Analysis and Application of PSS4B to Suppress Ultra Low Frequency Oscillation in Power Grid With High Shares of Hydropower

Yunnan power grid is a typical hydropower grid in China, which may be the main cause for ultra-low frequency power oscillation in Yunnan power grid in recent years according to some research results. An effective solution to suppress ultra-low frequency oscillation is to add PSS control to the excitation system of hydropower units. Compared with the conventional single-band PSS, PSS4B has higher order and control freedom with three independently adjustable phase compensation branches for low, medium and high frequency bands. Firstly, this paper analyzes the negative damping characteristics of the hydropower in the low frequency and reproduces the ultra-low frequency oscillation phenomenon based on RTDS real-time simulation. Then the mechanism of PSS4B to suppress the ULF(ultra-Iow frequency) oscillation is analyzed. The parameters of PSS4B are adjusted and PSS4B is applied to the main hydropower unit (NZD plant) of Yunnan Power Grid. The ULF oscillation is successfully suppressed, which verifies the correctness of the theoretical analysis.