Operation and Modulation of a Hybrid Submodule Alternate Arm Converter

This paper presents the Alternating Arm Converter(AAC) with hybrid sub-module(H-AAC), which combines full-bridge sub-modules(FBSMs) and half-bridge submodules(HBSMs). When the AAC operates in “sweet-spot”, the FBSMs are only required during over-modulation, while the HBSMs can replace the remaining FBSMs. First, a new modulation strategy is proposed to ensure capacitor voltage balancing between the FBSMs and the HBSMs. Then, the design criteria and operation performance of the H-AAC are analyzed and presented. Compared to the half-bridge modular multilevel converter(HB-MMC), the proposed H-AAC reduces approximately $\mathbf{4 5 \%}$ of SMs, $\mathbf{9 \%}$ of power devices, and $\mathbf{6 0 \%}$ of capacitance in the SMs. Owing to the hybrid sub-module, the operating losses of H-AAC are lower than those of the HB-MMC. Finally, the effectiveness is verified by the simulation.