Active Power Enhancement Control Strategy of Grid-Forming Inverters Under Asymmetrical Grid Faults

Due to the simple implementation and good dynamic response, the current-limiting gain control strategy (CLGCS) is widely utilized to limit the overcurrent of grid-forming inverters under asymmetrical grid faults. However, it will curtail the transmission capability of the active power (AP), which has not been investigated in detail before. In this article, its AP curtailment issue is first elaborated based on sequence networks. To enhance the transmission capability of the AP and ride-through asymmetrical grid faults simultaneously, an AP enhancement control strategy (APECS), including the proposed voltage-limiting gain control strategy (VLGCS) plus negative-sequence current feedback-based voltage compensation (NSCFVC) and the CLGCS, is proposed. The inverter output overvoltage and overcurrent are automatically limited by the proposed VLGCS and CLGCS without any fault detection. The transmission capability of the AP is enhanced with the proposed NSCFVC by eliminating negative-sequence fault currents. Consequently, the maximum inverter output phase voltage and current as well as the AP with both the CLGCS and the proposed APECS are comparatively analyzed based on sequence networks. The fault ride-through ability and enhanced transmission capability of the AP with the proposed APECS are verified by theoretical and experimental results.