A Modular Multilevel DC-Link Front-to-Front DC Solid-State Transformer Based on High-Frequency Dual Active Phase Shift for HVDC Grid Integration

This paper proposes a modular multilevel dclink dc solid-state transformer (MADCT) based on high-frequency dual active phase shift for HVDC grid integration. The proposed MADCT employs one arm of modular multilevel converter as HVDC active front-end interface and dual active bridge as high-frequency power transfer link, which brings many advantages and makes the operation of MADCT quiet different with traditional dc transformers. Compared with the traditional dc transformer schemes, the MADCT not only has good modularity and flexibility but also has good fault handling capacity. Especially, the performances of current stress, power transfer capacitor, and efficiency are improved. The topology, operation principle, voltage, current, power performances, and control and parameter design are presented and analyzed comprehensively in this paper. At last, a MADCT prototype is built and the experimental results verify the correctness and effectively of the proposed solution.