Reactive Components Analysis and Efficiency-Oriented Control for DAB Converters Under Variable Duty-Cycle Phase-Shift Modulation

The dual active bridge (DAB) bidirectional DC–DC converter is critical in modern power conversion, requiring high efficiency across the entire power transmission range. Since reactive power does not transfer energy and only contributes to power loss, prior studies have proposed various reactive power minimization strategies to improve efficiency. However, most studies focus solely on the primary side and rely on fixed-duty-cycle phase-shift modulation, leaving the influence of the secondary side unclear and the potential of variable-duty-cycle phase-shift modulation (5DoF) unexplored. To address these gaps, this study analyzes both active and reactive power on both primary and secondary sides. Based on the analysis, under 5DoF modulation, a composite power factor maximization strategy, which simultaneously accounts for both sides, is proposed and validated through theoretical analysis and experimental comparison with existing methods. Compared with primary-side power factor maximization, the composite power factor maximization achieves lower RMS current, a wider zero voltage switching (ZVS) region, and maintains high efficiency across the entire operating range, as verified by experimental results. At heavy load (normalized transmission power Ptn = 0.8), the proposed method achieves maximum 96.0% efficiency, comparable to existing approaches, while at light load (Ptn = 0.1), it improves efficiency from 85.5% to 88.2%, thereby surpassing state-of-the-art techniques.