Asymmetrical duty-cycle control of three-phase dual-active bridge converter for soft-switching range extension

The three-phase dual-active bridge (DAB3) converter is a promising topology for high-power conversion in future dc grids due to bidirectional power flow, inherent soft-switching capability and reduced filter size. However, the conventional single phase-shift control (SPS) does not allow the soft-switching operation with large voltage variations in light load conditions. This paper proposes an asymmetrical duty-cycle control (ADCC) method for the DAB3 to extend the soft-switching range by realizing zero-current switching (ZCS). Three triangular and trapezoidal current modes are introduced, analyzed and seamlessly combined. It is established through loss analysis that the proposed modulation schemes reduce both the semiconductor and transformer losses substantially in light load conditions. By employing ADCC, the DAB3 can achieve high efficiency even under low load conditions. The proposed method has been validated by experimental results.