Control Strategy of Hybrid HVDC System Based on LCC and Hybrid MMC

The Hybrid high voltage direct current (HVDC) system combines the advantages of both line commutated converter (LCC) and modular multilever converter (MMC). However, when it is applied to large-capacity overhead line transmission, there are two key problems: DC side fault self-clearance and the maintenance of power transmission after a fault occurred in AC system of rectifier side. The hybrid HVDC system, which adopts LCCs in rectifier station and hybrid MMCs in inverter station, can solve these two problems. Firstly, the operation principle of hybrid MMC is introduced, and the relationship between DC operating range and full-bridge sub module proportion is described in detail. Then control strategy and feasible DC fault clearance strategy for hybrid HVDC are introduced. Finally, a bipolar hybrid DC transmission system is built in PSCAD /EMTDC. The simulation results indicate that the proposed control strategy can effectively deal with DC side faults and the rectifier side AC system faults.