The resonance mechanism low frequency oscillations induced by nonlinear governor system

Many low frequency oscillation phenomenons cannot be interpreted by negative damping theory and the An-Bao line low frequency oscillation is one of them. The oscillation mode of An-Bao line is local mode of Shang-An power plant through analyzing by Prony and eigen-value method separately. So single-machine infinite bus system with PSS and AVR was set up using MATLAB to analyze the An-Bao line low frequency oscillation. Simulation results indicate that the An-Bao line low frequency oscillation cannot be reproduced by adjusting damping. Consequently, the resonance mechanism of low frequency oscillation was put up. When the disturbance frequency of prime mover power is near to natural frequency of power system, constant amplitude power oscillation will occur even if the damping is big enough. Finally, the cause of power disturbance is analyzed from the governor system of steam turbine. If the speed-droop of governing system is nonlinear in some running point, small speed deviation may result in high-level control valve oscillation that can arouse low frequency oscillation of resonance mechanism.