Instantaneous Start-Up and Shutdown Method for Three-Phase Dual-Active Bridge DC-DC Converters

Abstract

The three-phase Dual-Active Bridge (DAB3) dc-dc converter benefits from inherent soft-switching operation over a wide power and voltage range using the conventional Single Phase-Shift modulation (SPS). However, it is hard-switched at light load and considerably deviating input and output voltages. Several modulation schemes have been proposed to overcome this disadvantage and to extend the soft-switching range of the converter. An immediate start-up and shutdown method for the DAB3 in SPS operation can be used to switch between different modulation schemes. Those methods must be fully soft-switched to maintain the advantages of the mentioned modulation strategies. In this paper, we propose a soft-switched control scheme to start up and shut down the three-phase Dual-Active Bridge converter from or to zero transformer currents with energized input and output capacitors. Both, start-up and shutdown happen in less than one switching period without causing imbalances or oscillations of transformer phase and magnetizing currents. The soft-switching behavior of the proposed methods is analyzed in detail. Their effectiveness is proven mathematically and demonstrated with the aid of simulation results.