Reverse blocking sub-module based modular multilevel converter with DC fault ride-through capability

Modular multilevel converter (MMC) is one of the promising voltage source converter topologies in the field of high voltage direct current (HVDC) transmission system. Based on analysis of the existing sub-module topologies, an improved half-bridge sub-module topology based on reverse blocking IGBTs (RB-HBSM) was proposed for solving the fault ride through issues. In this paper, the fault current blocking mechanism and the electrical stress of the main power switches are studied firstly in detail. Then the fault control flow chart is presented. Feasibility of the proposed sub-module topology and the fault protection theory are verified by simulation. The proposed RB-HBSM-MMC topology is able to block the fault current without changing the original control and modulation strategies compared with the conventional MMC, thus it further reduces the complicity of industry design.