Abstract When a fault occurs on the line equipped with Unified Power Flow Controller (UPFC) based on Modular Multilevel Converter (MMC), it may cause the blocking of MMCs and then make UPFC out of operation. To avoid the non-function of UPFC under the condition of external fault, a UPFC fault ride through (FRT) strategy, which can convert UPFC to Static Synchronous Compensator (STATCOM), is proposed. The FRT strategy is realized by connecting the Current Limiting Reactor (CLR) on the DC bus to limit the fault current flowing through the DC bus, which is good for the shunt side MMC being unblocked. On the other hand, the FRT strategy may cause the series side MMC be unblocked under some fault cases, which has adverse effects on the distance protection due to the vibration of the measured impedance. To solve this problem, the coordination of the FRT strategy of UPFC with the distance protection is provided, the High Voltage Breaker (HVB) across the series transformer of UPFC is forced to close if the series side MMC is unblocked during FRT, thus the performance of the distance relay is guaranteed. Simulation results based on PSCAD/EMTDC verify the proposed FRT strategy and coordinationi scheme.

中文翻译：

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统一潮流控制器的故障穿越策略及其与保护的协调

摘要 当装有基于模块化多电平转换器（MMC）的统一潮流控制器（UPFC）的线路发生故障时，可能会导致MMC闭锁，进而导致UPFC停止运行。为避免UPFC在外部故障条件下无法正常工作，提出了一种UPFC故障穿越（FRT）策略，将UPFC转换为静态同步补偿器（STATCOM）。FRT策略是通过在直流母线上连接限流电抗器（CLR）来限制流过直流母线的故障电流，有利于并联侧MMC的畅通。另一方面，FRT策略在某些故障情况下可能会导致串联侧MMC不阻塞，由于被测阻抗的振动而对距离保护产生不利影响。为了解决这个问题，提供了UPFC的FRT策略与距离保护的协调，如果FRT期间串联侧MMC不阻塞，则UPFC串联变压器两端的高压断路器（HVB）强制闭合，从而距离继电器的性能保证。基于 PSCAD/EMTDC 的仿真结果验证了所提出的 FRT 策略和协调方案。