Oscillatory Stability Analysis for Wind Power Systems Based on Operating-Condition Dependent Impedance Model

The large-scale integration of wind generators into power grid has caused severe sub-synchronous oscillation (SSO) issues, which threaten the stability of the system. Since the characteristics of SSO highly depend on system status, it is of significance to quantify the oscillatory stability of wind power systems under various operating conditions. To address this issue, operating-condition dependent impedance model is established first for each system component with the consideration of frequency coupling effects. Then the frequency-coupled impedance network model (INM) of the system is formed and its transfer function matrix is obtained. Next, the INM is simplified into an aggregated impedance, of which the frequency response is used to quantify the system stability. Finally, the proposed method is applied to a wind power system in China where actual SSOs once happened. The oscillation frequency and damping of SSO under different operating conditions are calculated and the analytic results are verified with EMT simulations.