A Novel Three-level Submodule for Modular Multilevel Converter with DC Fault Blocking Capability

Modular Multilevel Converter (MMC) has proven to be the most viable and promising candidates for high power applications. However, half bridge submodule, the most commonly used cells in MMC, possess limited two-level output voltage and inability to block dc fault current, consequently restricting the application of MMC in high power situations. A novel structure of submodule with three-level output voltage and dc fault blocking capability relying on antiparallel insulated-gate bipolar transistors used in MMC is presented in this paper. Compared with other submodules with the same function, the new-model submodule has additional benefits of less diodes and semiconductor switching devices, lower conducting losses, and faster speed of dc fault current blocking. To stabilize the capacitors voltage, a control method based on neighboring number sorting is proposed according to the structure characteristics of this new-model three-level MMC (3L-MMC). The feasibility and validity of the proposed converter under the fault condition is demonstrated by simulations in MATLAB/Simulink.