Soft-Switching Modulation for Dual Active Bridge Converters with Unified DC and AC Bus Integration

This article presents a soft-switching modulation technique for dual active bridge (DAB) converters with unified DC and AC bus integration for both DC–DC and DC– AC applications. The core idea involves using a single control variable that maintains a proportional and linear relationship between the input and output current. The proposed modulation, referred to as triangular current modulation (TCM), achieves soft-switching independently of the control variable and the converter's voltage gain within the designed limits, enhancing adaptability across applications. In AC mode, it facilitates nearunity power factor operation without requiring a phase-locked loop, while in DC mode, it enables the converter to deliver both positive and negative pole voltages. The technique ensures zerocurrent switching (ZCS) turn-on and turn-off for the low-voltage bridge and achieves soft-switching for the high-voltage bridge: zero-voltage switching (ZVS) turn-on and ZCS turn-off for one arm, and ZVS/ZCS turn-on with ZCS turn-off for the other. The effectiveness of the approach is validated through experimental testing on a 400 W scaled-down prototype of a matrix-type bidirectional DC–AC converter, achieving a peak efficiency of 94.6%.