Mechanism and Characteristics analysis of Ultra-low Frequency Oscillation phenomenon in a Power Grid with a High Proportion of Hydropower

In a power grid with a high proportion of hydropower, a ultra-low frequency oscillation (ULFO) phenomenon usually appears at around 0.05 Hz along with extremely low damping, which may greatly influences the security and stability of the grid’s operation. Preliminary operation experiences and study show that the ULFO can be affected by changing the parameters of the speed-regulating system of the hydraulic generator unites, however, it is not clear how much contribution of each parameter to the ULFO or whether there exists other factors that may impact the ULFO. This study analyzes the mechanism of ULFO by taking into consideration of a variety of factors including the speed governor model, hydraulic turbine model, generator model, excitation system model, and load model. The linearized state-space equations of a loaded power grid with double hydraulic generator units are deduced. The characteristics of oscillation modes are investigated through eigenvalue analysis and the participation factors of each state variable are calculated. Conclusions regarding the impacts of parameters on the frequency and damping of the ULFO are drawn and validated using simulations of a 10-generator 39-node sample system.