Current-Fed Dual Active Bridge Converter With Asymmetric Three-Phase Transformer

This paper proposes a current-fed dual active bridge (DAB) converter with an asymmetric three-phase transformer, aiming to achieve high efficiency over a wide operating range. In the proposed converter, the neutral point (junction) of the three-phase transformer is clamped by the DC power supply on the primary side and by a capacitor on the secondary side, decoupling each phase of the transformer. This configuration enables transformers with different turn ratios, allowing for the selection of energizing phases according to the circuit condition. In order to show the effectiveness of the proposed converter, this paper models the power losses of the proposed converter and shows its efficiency characteristics through theoretical analysis. Furthermore, the efficient operating modes corresponding to the circuit and load conditions are indicated based on the theoretical analysis. Experiments using a 1 kW prototype demonstrate the validity of the theoretical analysis. Consequently, the efficiency characteristics obtained experimentally indicate similar trends from the theoretical analysis, confirming that the proposed converter operates efficiently over a wide range. Additionally, the proposed converter is compared using the analytical models to a DAB converter with a symmetric three-phase transformer. As a result, it is shown that the proposed converter can achieve an efficiency improvement of more than five percentage points (% points) under light loads, and the efficiency drop in specific operating points can be capped by 1.25% points.