A Modular Multilevel Converter With Novel Double Reverse Blocking Sub-Modules for DC Fault Current Blocking Capability

The half bridge sub-module (HBSM)-based modular multilevel converter (MMC) is widely used in high voltage direct current (HVDC) transmission systems. However, it cannot block the dc fault current due to the uncontrolled freewheeling diodes in IGBT modules. The existing sub-modules with inherent dc fault current blocking capability still suffer from large power device amounts and complex control schemes. To solve these issues, this brief proposed a novel double reverse blocking sub-module (DRBSM), which has the fewer power devices than the existing sub-modules. With the same output voltage level, DRBSM has the same dc fault current blocking capability as full bridge sub-module (FBSM) and the same control logic circuit as HBSM. In order to further reduce the amount of power devices, a hybrid MMC based on HBSM and DRBSM is also proposed and the design principle is given in detail. Two study cases are built in simulation to verify the proposed DRBSM-based MMC and hybrid MMC well.