Abstract: The new-generation power systems mainly relies on a high proportion of new energy grid connection. DC transformers is an important energy management unit in new-generation power systems, need to have higher performance and conversion efficiency. In order to reduce current effective value of the DC transformer and improve the control flexibility, this paper proposes a combined dual active bridge converter based on modulated coupled inductor. The proposed converter controls the equivalent inductance of the modulated coupled inductor by modulating pulse-width-modulation signals, without any additional auxiliary circuits. In order to reduce the current effective value of the converter, when the converter operates at light load and the voltage does not match, the coupled inductor can be modulated and controlled to a larger equivalent inductance. When the converter operates at heavy load, the coupled inductor can be modulated and controlled to a smaller equivalent inductance. Meanwhile, a hybrid modulation strategy for the converter is proposed based on the working principle of the modulated coupled inductor, and a minimum current compliance control law is designed. Finally, the proposed converter is validated through experiments, and the results show the effectiveness of the proposed method.

Key words: new-generation power systems, DC transformer, dual-active-bridge converters, modulated coupled inductor