中文摘要：

直流故障穿越是柔性直流输电（voltage sourced converter based high voltage direct current transmission,VSCHVDC）技术面临的重要问题之一。全桥型模块化多电平换流器（full bridge modular multilevel converter,FBMMC）能够快速清除直流侧故障,是实现直流故障穿越的理想拓扑。该文首先分析现有换流阀闭锁保护策略下电容放电阶段和换流阀闭锁阶段的等效电路,推导电容电压和电流的解析式。针对实际工程中功率模块具有恒功率负载特性,换流站闭锁期间功率模块电容电压逐渐发散并最终导致交流断路器跳闸的问题,提出一种FBMMC-HVDC的故障穿越控制保护策略。在故障穿越期间,换流器处于可控状态,能够避免电容电压发散,无需切断交直流系统连接;在故障清除后能够立即恢复正常运行,具备暂时性和永久性直流故障穿越能力。在PSCAD/EMTDC软件中构建了FBMMC-HVDC仿真模型,对比上述两种保护策略,分析两种策略各自的优缺点。

英文摘要：

DC short-circuit fault ride through capability is one of main issues in applications of voltage sourced converter based high voltage direct current（VSC-HVDC） transmission systems. Benefit from the capability of quick fault elimination, full bridge modular multilevel converter（FBMMC） is suitable for dc fault ride through. The equivalent circuit models in different phases of the valve block strategy were analyzed and the analytic solutions for capacitor voltage and current were deduced. According to the constant load characteristic of power modules, the mechanism of capacitor voltages divergence was explored. A dc short-circuit fault ride through control strategy for FBMMC-HVDC was proposed, with the converter remaining controllable during the fault clearance. The advantages include avoiding capacitor voltages divergence, no need to cut off ac system and quickly restart of system following clearance of temporary or permanent dc fault. The proposed fault ride through control strategy is demonstrated on simulation model in PSCAD/EMTDC. The advantages and disadvantage of both strategies are contrasted with simulation results.