中文摘要：

难于阻断直流侧故障电流是典型半桥模块化多电平换流器（halfbridgesubmodulebasedmodularmultilevelconverter，HBSM-MMC）的固有缺陷，严重影响该类型换流器在直流电网中的应用，因此开展具有直流故障电流阻断能力的MMC拓扑及控制技术研究意义重大。首先介绍典型HBSM-MMC的拓扑结构及工作原理，阐述其直流侧故障特性及影响机理，对比分析现阶段存在的直流侧故障清除方法及优缺点，指出基于换流器拓扑的自清除方法是解决直流侧故障电流阻断问题的最有效方法之一；通过对国内外MMC拓扑的调研，分别详细研究3类MMC优化拓扑结构及其直流故障隔离和电流阻断机理，对比分析3类优化拓扑的各项参数和功能实现的优缺点，为后续MMC技术在多端直流输电系统和多电压等级直流电网中的应用提供技术参考。

英文摘要：

Incapability of blocking DC fault current is an inherent defect of typical half bridge sub module based modular multilevel converter （HBSM-MMC）, which seriously affects its application in DC grid. Thus, the study on the topology and control technology of MMC with DC fault current blocking capacity is of great significance. This paper first introduced the topology and operation principle of typical HBSM-MMC, described the fault characteristics of its DC side and influence mechanism, analyzed the existing DC side fault clearing methods at present and their advantages and disadvantages, and pointed out that self-clearing by converter based on its topology is an effective method to solve this problem. Through technical survey, this paper studied and presented three types of optimized MMC topology and their DC fault isolation and current blocking mechanism, then compared the indexes of them and analyzed their merits and drawbacks of function realization, thus it provides technical reference for further study and application of MMC technology in multi-terminal DC transmission system and DC grid with multi voltage levels.