Rapid protection strategy with reduced fault currents for the MMC-HVDC grids under DC short-circuit fault

The DC short-circuit fault occurring on the overhead line endangers the modular multilevel converter based high voltage direct current (MMC-HVDC) grids. An optimized protection coordination (OPC) strategy with a global fault current limiting control is proposed to limit the DC fault current in this article, which can suppress the rising rate of the global fault current, and at the same time, the fault area can be identified quickly and the relevant DC circuit breakers can be pre-operated. To realize the OPC strategy, a rapid fault identification method based on the current change rate and Pearson correlation coefficient is designed. The proposed rapid protection strategy can decrease the peak value of DC fault current by reducing the rising rate of current and shortening the protection time. Simulation and experimental results verify the effectiveness of the proposed strategy under both balanced and unbalanced grid-side voltage conditions. The adoption of the proposed control is beneficial for MMCs to safely ride through DC short-circuit fault in a continuous operation manner.