Stability Analysis and Improved Oscillation Suppression Strategy for Grid-Connected VSG-DFIG

Doubly-fed induction generator (DFIG) employing virtual synchronous generator (VSG) control can exhibit external characteristics similar to synchronous machines, endowing DFIGs with voltage and frequency support capabilities. However, when DFIGs are grid-connected via series-compensated transmission lines, they are prone to sub-synchronous oscillation (SSO) incidents that threaten power system security and stability. Therefore, it is crucial to investigate the grid-connected stability of VSG-DFIG under series compensation conditions. Focusing on the grid-connected stability of indirect voltage-type VSG-DFIG with series compensation, this study establishes a state-space model incorporating the angular deviation between the grid voltage angle and the VSG control outer-loop output angle for stability analysis. The impacts of grid parameters and control parameters on system stability are systematically revealed. Building upon these findings, an additional damping control strategy integrated into the stator voltage loop is proposed to suppress sub-synchronous oscillations, with simulation results validating the effectiveness of the proposed approach.