Dual-Sequence Synchronization Stability Analysis and Control of Multi-Paralleled Wind Farms during Asymmetrical Grid Faults

This paper proposes a simplified equivalent model of multi-paralleled wind farms is established based on the symmetrical components method to deal with the problem of dual-sequence synchronization stability during asymmetrical grid faults. Based on the model, the effects of multiple coupling characteristics such as sequence coupling and mutual coupling of wind farms on the stability of dual-sequence synchronization are studied in detail. Then, an assessment method is proposed to evaluate the dual-sequence synchronization stability of multi-paralleled wind farms under various asymmetrical grid faults. This assessment method can judge whether there are positive-sequence (PS) and negative-sequence (NS) steady-state equilibrium points for each wind farm in the system, and identify the wind farms that are instability due to the lack of a PS/NS equilibrium point. In addition, a current control strategy is derived to maximize the stability margin of dual-sequence synchronization. This strategy can ensure that each wind farm in the system has equilibrium point.

Keywords: Asymmetrical grid faults, multi-paralleled wind farms, synchronization stability, equilibrium points, low voltage ride-through (LVRT), synchronization stability assessment method.