A restart/reclose method based on low current injection for MMC based DC grid

The current fault restart/reclose method for flexible direct current (DC) grid is to see whether the DC voltage can be established when the converter is unlocked again. This method will cause secondary damage to the grid once restarting with the permanent fault. Due to the problem of fault restart/reclose of modular multilevel converter (MMC)-based DC grid, A restart/reclose method based on low current injection is studied in this paper. The low current can be injected by the full bridge (FB) MMC or the transfer branch of DC breaker. If the fault disappears, the low current can lead to full voltage, otherwise, the voltage is still low. builds the low current injection control strategy for FB-MMC and the DC breaker with transfer branch is built in PSCAD simulation system. The proposed method can also judge the fault type by the highest voltage raised by the low current. The simulation verifies the effectiveness of the proposed restart/reclose method.