A Reverse-blocking Hybrid Topology with DC Fault Blocking Capability of Modular Multilevel Converter

The occurrence of DC-side bipolar short-circuit faults in flexible DC transmission systems is a serious problem at present. In order to achieve fault clearing, an improved reverse-blocking hybrid submodule (RB-Hybrid-SM) topology of modular multilevel converter with DC-side fault current clearing capability is presented. All submodule (SM) capacitances of the proposed topology are series into the fault circuit and provide back electromotive force (back EMF) with converter valve blocking to clear the fault current. Then the fault clearing mechanism is analyzed, and the fault current analysis expression is pushed according to fault equivalent circuit. Finally, using this topology as an example, an improved reverse-blocking hybrid SM modular multilevel converter (RB-Hybrid-SM-MMC) simulation model was built in the PSCAD/EMTDC software are carried out to verify its effectiveness and feasibility. The simulation results show that the new SM topology proposed in this paper can quickly block the fault current, and always provide 2U(C) back EMF during the fault blocking process.