A Modular Multilevel Converter (MMC) Based Solid-State Transformer (SST) Topology With Simplified Energy Conversion Process and Magnetic Integration

This article proposes a solid-state transformer (SST) topology based on modular multilevel converter (MMC) with high integration structure. By integrating the medium frequency (MF) transformer into the MMC leg and applying the mixed-frequency modulation on the half-bridge submodules, the line frequency ac to MF-ac conversion is realized directly without intermediate dc link. The proposed SST simplifies the energy conversion process, reduces the total amount of active components and magnetic components, and thus, can increase the power density of the system and reduce the manufacturing cost. Operation principle and design considerations are given in this article. In addition, simulation and experimental results are demonstrated to verify the validation of the proposed topology.