中文摘要：

模块化多电平换流器（modular multi-level converter,MMC）是柔性直流输电系统中的关键设施,其可靠性关系到整个输电系统的安全稳定运行。该文基于拓扑分析,综合考虑子模块、控制保护系统及阀冷系统等部件,建立了详细的MMC可靠性模型,并利用k/n（G）模型和伽玛（Gamma）分布分别构建MMC在两种备用策略下的可靠度函数。基于所建立的可靠性模型,定量分析了元件冗余及其冗余度、子模块备用策略对MMC可靠性的影响,分析结果可为MMC拓扑设计和备用安排提供必要的信息。

英文摘要：

The modular multi-level converter（MMC） is one of the significant facilities in the voltage source converter based high voltage direct current（VSC-HVDC） transmission system, and its reliability plays a key role in the reliable and continuous operation of the HVDC system. A detailed reliability model of the MMC was proposed with the consideration of sub-modules, the control/protection system and the cooling system. Reliability functions of MMCs with two redundancy strategies were presented by the k-out-of-n： G model and the Gamma distribution respectively. Based on the proposed reliability models, a quantitative assessment of the relative merits of MMCs with different redundant components, different redundancy rates and different redundancy strategies was undertaken, which could provide essential data for the decision-making in topology design and redundancy arrangement.