Analysis and optimisation of modulation strategy based on dual-phase-shift for modular multilevel high-frequency-link DC transformer in medium-voltage DC distribution network

DC/DC converters are crucial in DC distribution networks for converting voltage and interconnecting different voltage links. The modular multilevel high-frequency-link DC transformer (MDCT), which employs multiplex conversion principle and provides many advantages, realises voltage conversion, power transfer and electrical isolation between links in medium-voltage DC distribution networks. To improve the performance of MDCT, this study investigates the modulation with the phase-shift strategy and its influence on current stress, power characteristic and efficiency characteristic of MDCT. Besides, to simultaneously achieve an optimal solution for both current stress and efficiency characteristics of MDCT, an optimal modulation strategy based on dual-phase-shift is proposed. Finally, an MDCT prototype is constructed and experimental results verify the correctness and effectiveness of the analysis and proposed scheme.