A Compact AC/DC Converter Based on MMC for Medium/Low-Voltage Grid Interconnection

To address the issues of high cost, low efficiency, and low power density in existing AC/DC interconnection converters, this paper proposes a compact AC/DC interconnection converter topology based on mixed-frequency decoupling modulation. By embedding a high-frequency intermediate submodule (ISM) at the midpoint of the arm of a traditional modular multilevel converter (MMC), the topology directly constructs a medium-voltage high-frequency port. Through decoupling modulation of half-bridge submodules, it achieves power decoupling control among medium-voltage DC, medium-voltage AC, and low-voltage DC ports. This topology simplifies the energy conversion process and reduces the number of passive components and medium-frequency transformers, thereby enhancing the system’s power density and lowering costs. Additionally, the paper presents a detailed analysis of the topology’s equivalent circuit, energy fluctuation mechanism of the intermediate submodule, and overall control strategy of the converter. Finally, the effectiveness of the topology and control strategy is verified via a MATLAB/Simulink simulation model.