Compared to traditional Modular Multilevel Converter（MMC）

Hybrid Modular Multilevel Converter is a newer DC converter topology. The topology includes both full bridge sub-modules and half bridge sub-modules. Consequently

the advantages of the full bridge sub-module isolation DC side bipolar short-circuit fault and the economics of the half-bridge sub-module are simultaneously achieved. We studied the isolating DC side short-circuit faults ability of hybrid MMC with different full bridge sub-modules’ proportions. The fault isolation voltage value of the full bridge sub-module capacitor was derived by analyzing the equivalent circuit diagram under the short-circuit fault state. Thereby

the formula for calculating the full bridge sub-modules’ proportion critical value of the hybrid MMC which can effectively isolate the DC side bipolar short-circuit fault was derived. Finally

the above analysis results were confirmed by PSCAD simulation. It can be concluded that the proportion of the full bridge sub-module which is designed reasonably has practical significances for saving the cost of the hybrid MMC and improving its ability to isolate DC faults.