An Asymmetrical DAB Converter Modulation and Control Systems to Extend the ZVS Range and Improve Efficiency

This article presents a new optimized hybrid modulation and control systems based on symmetrical and asymmetrical operations of a dual-active-bridge converter to minimize the transformer root-mean-square (RMS) current and extend the zero-voltage-switching (ZVS) range. Various modulation modes are analyzed, and their corresponding power, RMS current equations, and soft-switching conditions are derived. The RMS equations are minimized using the multivariable optimization method, and the corresponding parametric equations are obtained. A hybrid control system has been proposed to regulate the battery current, to ensure smooth inductor current transients, and eliminate the need for a blocking capacitor on the low-voltage side. Using asymmetrical-extended-phase-shift and conventional symmetrical modes, a wider ZVS range is achieved compared to advanced modulations, such as triple phase shift. Moreover, in the low-power region, an optimized RMS current is achieved by applying an optimum dc voltage on the blocking capacitor at the HV side. Hybrid modulation that extended ZVS range and improved RMS current makes the proposed approach a suitable modulation for high-frequency applications and also high-voltage or high-current applications with high
$C_{\text{oss}}$
losses. The efficiency, ZVS operation, and control system performance are validated by a 5 kW converter.