SSR Analysis of DFIG-based Series-compensated System Based on Complex Torque Analysis Method

DFIG-based series-compensated can increase the capacity of wind power transmission, but it can also cause the sub-synchronous resonance (SSR) problem. There are some SSR analysis methods will be explained, including complex torque analysis method, eigenvalue analysis method and impedance analysis method. Impedance analysis is used to determine the stability of the system by establishing a small signal frequency domain impedance model of power electronic devices, utilizing the Nyquist criterion or generalized Nyquist criterion. Previous studies have not considered the effect of the grid-side converter (GSC) side current on the sub-synchronous resonance characteristics of the system. In this paper, the influence of GSC side current and GSC control parameters on the damping characteristics of the system sub-synchronous resonance is analyzed in detail. The results show that the GSC side current has a positive damping effect on the stator torque. Considering the GSC side current, the phase margin between the stator torque and the rotational speed is changed from 359° to 229°, and the effect on the SSR is changed from negative to positive damping. The positive damping effect will increase with larger controller gain or lower connection inductance.