A new topology of sub-modules with DC fault current blocking capability and a new type of hybrid MMC converter

To solve the problem that traditional MMC based on half-bridge sub-module being incapable of isolating dc fault current, a new topology of self-blocking sub-module is proposed in this paper. Four types of self-blocking sub-modules that require simultaneously blocking the IGBTs are firstly proposed. To eliminate the requirements on simultaneously blocking, two types of enhanced self-blocking sub-modules are further proposed. To further reduce the used power electronic devices, a hybrid converter combines enhanced self-blocking sub-modules with traditional half bridge sub-modules is then proposed. Feasibility of the proposed sub modules and hybrid converter are verified by simulations in PSCAD/EMTDC. The proposed hybrid converter is able to isolate dc fault current with only 25% increase of the used power electronic device compared with traditional half-bridge cell MMC which is not able to isolate dc fault current. © 2014 Chinese Society for Electrical Engineering.