Real-time identification of subsynchronous oscillation modal parameters based on dynamic characteristics of generator rotors under ambient excitation

Through the real-time measurement of rotor speed of a running generator unit, which was a weak response signal excited by power grid load fluctuations and noises, the generator-grid oscillation modal parameters (modal frequecies, dampings and amplitudes) were recognized online. The random decrement characteristic signal including free damped response components of the generator-grid system structure oscillation was obtained through the application of random decrement technique (RDT) to the processing of the rotor angular displacement differential signal under ambient excitation. The time-domain attenuation characteristic curves of subsynchro- nous oscillation (SSO) components were obtained from the random decrement characteristic signal through the application of the narrow band pass filter algorithm, and then the vibration modal dampings at the specified frequencies under the current operation condition were calculated. This new scheme was used to analyze the measured data of a 1 000 MW generator unit in Suizhong power plant and identified the SSO modal parameters of the Suizhong power plant and Gaoling HVDC power grid effectively. Real-time subsynchronous oscillation safety monitoring can be realized based on this method.