DC Faults Ride-Through and Fast Recovery of MVDC System Based on Improved HB-MMC

According to existing methods of dealing with dc faults in a medium-voltage direct current (MVDC) distribution system based on a modular multi-level converter (MMC), there is a direct contradiction between the fault current elimination speed and the economic performance. To relieve this contradiction, a method based on an improved half-bridge submodule (HBSM) that could withstand bidirectional voltages is proposed in this paper to realize the dc faults ride-through and the fast recovery of the system. The working principle of fault current elimination and the fast recovery of the system based on the improved HB-MMC are analyzed, respectively. Then, the simulation model is established in PSCAD, and simulation results show that the fault current could be eliminated within 20ms and the system could be recovered rapidly without vulnerable devices in the converter suffering from surge current again. Finally, comparisons between the improved HBSM and existing SMs are made, and it is proved that among these SMs, the fault current elimination speed of the improved HBSM is the second fast, but the additional cost and operating losses of improved HBSM are the smallest, meaning the comprehensive performance of the improved HBSM is the best.