Series capacitor compensation is used for increasing transmission capacity in long-distance power transmission, which may cause sub-synchronous resonance (SSR) without damping strategy. In this paper, model of the system that a doubly-fed induction generator (DFIG)-based wind farm connected to series compensated line is built, which is based on IEEE first benchmark model. According to the eigenvalue analysis, SSR arises when the system operates with a high series compensation level and/or low wind speed. Therefore, a combined control strategy to mitigate SSR is proposed, which is based on virtual impedance method and SSR damping controller(SSDC). It inserts an additional virtual impedance at rotor side converter, and add a SSDC to the grid side converter, which can provide extra electrical damping to mitigate SSR. The simulation results in MATLAB/Simulink show that the combined SSR-damping control strategy can effectively mitigate SSR.

sub-synchronous resonance,DFIG,virtual impedance method,SSR damping controller