AC voltage and reactive power control in DFIG-based wind farms: A comparative study for mitigating sub-synchronous resonance in compensated and weak networks

Integrating Doubly-Fed Induction Generator (DFIG)-based wind farms into weak and series-compensated systems may introduce significant subsynchronous resonance (SSR) risks, compromising system stability. This paper presents a detailed comparative analysis of two control strategies, reactive power control, and AC voltage control, implemented in the outer control loops related to the grid side converter (GSC) to mitigate SSR in DFIG-based systems. The comparisons are based on modal analysis, and the dynamic risk of SSR is investigated by evaluating several operating conditions and key control parameters. This includes different levels of series compensation, weakness, phase-locked loop (PLL) bandwidth, and current control parameters associated with the rotor-side converter (RSC). The results demonstrate that AC voltage control provides superior dynamic performance and less SSR risk damping, especially in highly compensated grids where reactive power control is unstable. Furthermore, sensitivity analysis highlights the critical role of RSC tuning and PLL bandwidth in maintaining system stability to avoid SSR risks. These findings offer practical insights for control design strategies in DFIG-based wind farms, particularly for applications in weak and compensated grids, enhancing grid reliability and reducing the risk of SSR.