An Improved LVRT Strategy for Overvoltage Supression of Sending-End Grid-Forming Converter Station

As large-scale clean energy bases continue to be planned and constructed, the control strategies for their transmission via VSC-HVDC systems have emerged as a significant focus of contemporary research. Given that the strength of the sending-end power grid is typically weak, the grid-forming (GFM) converter station at the sending end is often utilized as the primary voltage source to ensure voltage safety and stability. This paper presents an enhanced low voltage ride-through (LVRT) control strategy for the GFM converter station at the sending end, aimed at mitigating overvoltage during the voltage recovery phase. First, this study analyzes the mechanisms leading to overvoltage on the sending-end AC bus following fault clearance, in conjunction with existing VSC-HVDC LVRT control strategies. Then, an segmented AC voltage recovery strategy is proposed to effectively suppress AC overvoltage. Finally, the efficacy of the proposed method is validated using DIgSILENT PowerFactory.