A Modulation Method for Three-Phase Dual-Active-Bridge Converters in Battery Charging Applications

The Three-phase Dual-Active-Bridge (DAB3) converters are a common choice for quick charging stations for batteries in electric vehicles due to their high power density, versatility, and galvanic isolation capability. However, the DAB3 topology has limited soft-switching range, particularly under light load conditions when the voltage conversion ratio differs significantly from unity, resulting in hard switching, increased loss, and higher electromagnetic interference. To address these issues, various techniques have been proposed, but they often lead to other problems such as higher current ripple or unbalanced thermal distribution. In this paper, a new modulation scheme, called symmetric duty-cycle control (SDM), is proposed for DAB3 converters to overcome these issues. A multiaspect comparison of SDM was conducted against two existing techniques, SPS and ADCC, and its superiority was validated through simulation and experimental results. Our proposed SDM scheme provides a current ripple within 10% to 15% of the average current and enables zero current switching for the whole voltage and power ranges. Additionally, a modified version of SDM can even improve overall efficiency by 7% compared to the conventional SPS technique.