Novel Submodule Topology with Large Current Operation and DC-Fault Blocking Capability for MMC-HVDC

High-voltage direct-current system based on modular multilevel converter (MMC-HVDC) is widely expected to plays a significant role in promoting the development of large-scale offshore wind power. The maximum current limit of insulated-gate bipolar transistor (IGBT) is the main constrain for MMC-HVDC to operate in large current operation, while DC-fault blocking ability and economy are the two important concerns of MMC-HVDC. This paper proposes a novel parallel multiple submodule (PM-SM) topology to realize parallel output of submodule currents, which make MMC capable of large current operation and have filtering effect on high frequency harmonics. Combining with carrier phase-shift modulation or nearest level modulation, the frequency multiplication of bridge arm current of MMC can be realized to further improve the power quality of the system. Considering the demand of DC-fault blocking ability, simplified full-bridge double submodule (S-FBDSM) is also proposed as an economical option to compose PM-SM. It can provide double the reverse capacitance voltages in the arm current path regardless of a positive or negative arm fault current. The economic analysis is conducted to demonstrate the advantage of S-FBDSM. Simulation results and experiment results verify the feasibility and superiority of PM-SM composed of S-FBDSM.