A Novel Fault Current Limiting Control for Half-Bridge MMC

A novel fault current limiting control for half-bridge modular multilevel converters (MMC) is proposed in this paper. This control scheme is able to limit the fault current without implementing extra devices. It will be triggered automatically once DC faults occur and can suppress the fault current by reducing the output DC voltages of MMCs. Compared with the existing fault current limiting methods, the proposed fault current limiting control has a better performance on fault current limiting, since it only depends on the real-time current characteristics and no fault detection delay is imposed. Firstly, the principle of the proposed novel fault current limiting control is introduced. Then, the mathematical analysis of this control scheme is disclosed. Finally, this control scheme is simulated in a four-terminal HVDC grid model to demonstrate its effectiveness. The simulation results show that the proposed fault current limiting control can reduce the interrupted current and energy absorption of a DCCB from 10.39 kA and 38.24 MJ to 4.25 kA and 6.79 MJ, respectively.