基于选相投旁通对的LCC-HVDC系统逆变侧换流变故障性涌流主动抑制策略

当高压直流输电系统换流变阀侧发生单相接地故障，由于换流阀的单向导通性，阀侧故障电流中含有较大的直流分量，流入换流变可能导致换流变饱和并产生“故障性涌流”。与传统三大涌流不同，故障性涌流由阀侧单相接地故障诱发并受直流控制与保护系统的影响。计及直流控保系统的影响，分析了逆变侧换流变发生阀侧单相接地故障时，换流变故障性涌流的产生机理及其对换流变差动保护的影响。针对换流变保护区内阀侧单相接地故障场景下，故障性涌流可能导致差动保护误闭锁的问题，提出了一种基于选相投旁通对的故障性涌流主动抑制策略，可以从根本上避免差动保护误闭锁问题。基于PSCAD/EMTDC的仿真实验验证了所提方案的有效性。

Faulty-phase bypass-pair-based mitigation strategy for fault-induced inrush currents in LCC-HVDC inverter-side converter transformers

When a single-phase-to-ground fault occurs on the valve-side of the converter transformer in the line- commutated converter high-voltage direct current system, then because of the forward-bias characteristics of converter valves, the valve-side fault currents contain large DC components. These flow into the converter transformer, resulting in the saturation of the converter transformer and fault-induced inrush current (FIIC). The FIIC, different from the traditional inrush currents, is induced by the valve-side grounding fault and affected by DC control and the protection system. Considering their influence, the generation mechanism and characteristics of FIIC on the inverter side are analyzed, and the influence of FIIC on converter differential protection is analyzed. Given the problem that the FIIC may lead to the mal-block of differential protection when the single-phase grounding fault occurs in the case of an internal fault, a protection strategy based on phase selection and triggering the bypass-pairs is proposed to actively suppress the FIIC and fundamentally avoid the mal-block of differential protection. Finally, simulation experiments based on PSCAD/EMTDC have been conducted to verify the effectiveness of the proposed strategy. This work is supported by the Natural Science Foundation of Ningxia Hui Autonomous Region (No. 2021AAC03497).