Study on a New Type MMC Hybrid Double Sub-Module Topology and Control Strategy

To solve the problem of the DC fault in the modular multilevel converter (MMC), a new topology of self-blocking sub-module is proposed in the paper-hybrid double sub-module (HDSM), which results in lower cost with the capacity of blocking the DC fault current, comparing with the full bridge sub-module. Comparing with clamp double sub-module, it can meet the reactive power requirement of the AC system without blocking action during the fault ride-through period. Besides, a voltage balancing strategy for the MMC based on the HDSM is proposed to keep the voltage of the sub-module balancing. Finally, simulation results show that the novel topology of sub-modules are valid and feasible.