A Self Blocking Hybrid Submodule With Capacitor Voltage Self-balancing Capability

Modular multilevel converter based on half bridge submodules has been widely used in HVDC transmission and power conversion, but it has the problem of DC side fault suppression. In this regard, firstly, based on the analysis of the working mechanism of the existing blocking submodule topologies and combining with the clamping circuit, this paper proposes a self-blocking hybrid submodule, which has the ability of capacitor voltage self-balancing and DC fault blocking. Secondly, a capacitor voltage self-balancing strategy is proposed, which can reduce the complexity of the sorting algorithm. Additionally, the economy of different topologies is compared, which demonstrates the economic advantage of the proposed topology. Finally, simulation model and small capacity physical experiment system are built. The results show that the proposed submodule can realize the functions of DC fault suppression and capacitor voltage self-balancing.