Active Current-Limiting Control Based DC Fault Ride-Through of Full-Bridge MMC

Most of existing current protection strategies of flexible DC systems mainly rely on fault identification, and then block the converter through the action of the protection system. In this paper, a novel DC voltage with active current-limiting capability has been proposed for DC fault ride-through (DC-FRT) of full-bridge modular multilevel converter (FB-MMC). With this method, the output of DC voltage control has been directly used as the zero-axis component of final modulation signals of FB-MMC, to control the number of positive or negative insertions of the full-bridge sub-modules (FB-SMs), with the final purpose for current-limiting in DC-FRT. In addition, a simple DC voltage feedforward control has been adopted to improve DC voltage dynamic, to reduce the peak value of the transient fault current. The PSCAD/EMTDC simulation results show that the proposed control can effectively limit the peak fault current and provide a stable steady-state fault current without relying on fault detection.