Modulated Coupled Inductor for Input-Serial–Output-Parallel Dual-Active-Bridge Converter

In this letter, a solution to achieve changeable inductance without any other auxiliary circuit based on pulsewidth modulation (PWM) for the coupled inductor is proposed to reduce the circulating current at the steady state and limit the inrush current during startup for the input-serial–output-parallel dual-active-bridge converter in the solid-state-transformer applications. By modulating the PWM signals, the equivalent inductance of the coupled inductor can be changed without any other auxiliary circuit. The smaller equivalent inductance is adopted in the steady state to reduce the circulating current and increase the power transfer capability. And the larger equivalent inductance is used to limit the inrush current during the startup. The analysis based on the modulated coupled inductor for the steady state and the startup process is given. The design consideration for the coupling coefficient is introduced according to the optimization of the leakage inductor root-mean-square current, the inrush current, and the filter capacitance. Finally, the comparison of experimental results between the proposed solution and the conventional method for a 1600 W/250 kHz prototype verifies the effectiveness.