Active Current Transferring Modular Multilevel Converter With DC Fault Blocking Capacity

The rapid blocking of DC fault is the bottleneck problem in DC transmission/distribution technology development. Aiming at the problems that high cost and/or high losses issue arises with using of DC circuit breaker or modular multilevel converter (MMC) based on improved DC-blocking submodule when clearing faults, an active-current-transferring MMC with the ability of blocking DC fault is proposed in this paper. A current breaking branch, an arm blocking branch and an energy absorption branch are introduced to the conventional MMC topology. After the DC fault occurs, the fault current is actively transferred by disconnecting the current breaking branch and the redirection of the bridge arm current is realized, and then the half-bridge submodule is used to absorb the internal fault energy of MMC. Meanwhile, the additional full-bridge submodules in the energy absorption branch are used to absorb the fault energy on the line side during blocking period, thereby achieving fast blocking of short circuit fault. Finally, the simulation results verify the feasibility of the proposed topology.