Mitigation of Subsynchronous Control Interaction in DFIG-Based Wind Farm Using Repetitive-PI

The subsynchronous interaction between the wind farm’s grid-side converter and the series-compensated transmission line can trigger subsynchronous oscillations (SSO). The wind power system oscillation frequency depends on the actual operational conditions. This paper proposes a repetitive-PI control strategy to mitigate oscillations under various conditions. The repetitive-PI control offers fast dynamic performance and high steady-state accuracy, which can eliminate steady-state errors and improve the system’s robustness. Firstly, the repetitive-PI composite controller is derived based on the frequency domain expansion of the repetition controller. Then, the stability of the repetitive-PI composite controller is analyzed, and its main parameters of it are designed. Finally, to demonstrate the efficacy of the proposed suppression technique for SSO, simulations are conducted under different wind speeds, series compensation levels, and numbers of operating wind turbines. The time-domain simulation results and impedance model-based analysis demonstrate that the proposed repetitive-PI control strategy enhances the system’s damping performance and improves its disturbance resistance.