Closed-Form Asymmetrical Duty-Cycle Control to Extend the Soft-Switching Range of Three-Phase Dual-Active Bridge Converters
Jingxin Hu, Zhiqing Yang, Shenghui Cui, Rik W. De Doncker, IEEE Transactions on Power Electronics, 28 January 2021.
The three-phase dual-active bridge (DAB) converter is a promising topology for high-power dc-dc conversions in dc grids and industrial applications. However, the conventional single phase-shift modulation shows a limited soft-switching range and large reactive currents in the light-load operation especially with large voltage variations. This paper proposes an asymmetrical duty-cycle control (ADCC) method for the three-phase DAB to extend the soft-switching range and reduce reactive currents by realizing three-phase triangular- and trapezoidal-current-mode operation. Closed-form solutions of the proposed modulation schemes are derived that enables a simple online calculation of the control parameters. The proposed modulation schemes can substantially reduce losses of both power semiconductor devices and the medium-frequency transformer. Thus, the three-phase DAB converter can realize high efficiency over a wide operation range, especially for the light-load conditions. Considering the practical implementation, a compensation method is presented to correct the distorted current waveforms caused by the dead time, and ensure the desired soft-switching operation. Besides, the power loss imbalance between switches induced by the asymmetrical duty cycle is addressed by an active thermal balancing strategy. The effectiveness of the proposed method is validated by simulation results and experiments on a down-scaled converter prototype.