Mode Identification and Damping Torque Analysis of Ultra-Low Frequency Oscillations

After the asynchronous interconnection of Yunnan and South China Power Grid, a long period of ultra-low frequency oscillation occurred, which seriously affected the safe and stable operation of the system. This paper presents the damping analysis of hydraulic turbine governing systems under ultra-low frequency oscillations. A transfer function identification method is proposed combined with damping torque analysis (DTA) method to accurately capture the damping characteristics of governing systems. Total least square estimation of signal parameters via rotational invariance techniques (TLS-ESPRIT) algorithm, a mode identification method, is used to verify the damping torque analysis. From the analysis and simulations, high hydro penetration and large Tw which worsen the damping of system may be the reason for ultra-low frequency oscillation occurrence in Yunnan Power Grid.