A Multiport Three-stage Power Electronic Transformer

The four-stage PETs have been wildly used in the application for locomotive traction and DC distribution. However, the four-stage PETs have complex structure and low efficiency, because of the multiple power conversion stages. Therefore, a three-stage PET based on modular multilevel converter (MMC) with multiple ports is proposed. A fundamental modulation signal with an injected medium frequency modulation signal consist of the modulation signal for MMC, where the power conversion stages of PET can be reduced. In addition, the equivalent circuit analysis and design procedure are provided. The simplified structure of PET is validated by simulation results, where the proposed PET has four interfaces.