A Combinational Power Circuit-based Submodule Topology for MMC With Shoot-through and Selfbalancing Capability

The upper and lower power switches of sub modules (SMs) in Modular Multilevel Converter (MMC) could be switched on simultaneously by disturbances which could destroy the SM circuit and cause damage to MMC. To improve reliability, this paper proposes a novel SM topology based on the combinational power circuit. It consists of three circuits: the half-bridge circuit, clamping circuit and energy-transfer circuit. It overcomes the shoot-through problem using the impedance-source network. The fluctuation of SM capacitor voltages can be controlled by the hysteresis control strategy in each SM. The SMs are self-balanced by making the fluctuation of each SM capacitor voltage consistent. The circulating harmonic current can be small even without any circulating current suppression strategy (CCSS). Without the need for voltage balancing control and CCSS, it greatly reduces the computation load. Finally, a five-level single-phase experimental platform is established to verify the feasibility of MMC based on the proposed SM topology.