Extended ZVS-On/ZCS-Off Range for CF-DAB Converter Under DCM Operation for Residential Energy Storage Systems

Current-Fed Dual-Active Bridge (CF-DAB) converters are interesting in bidirectional applications when a wide conversion voltage ratio is required, such as residential extra-low voltage energy storage systems, where conventional DAB converters have several limitations. Even though many developments have been made in the last few years to improve the CF-DAB technology for such applications, ensuring a flat efficiency curve is still challenging since it is difficult to ensure high efficiency at very low power. Current solutions include phase-shift modulations (PSM), dual phase-shift (DPSM), and hybrid approaches. This paper proposes an asymmetrical pulse width modulation (a-PWM) strategy to operate the CF-DAB in discontinuous conduction mode (DCM), improving the converter efficiency curve at low power. The DCM operation ensures soft-switching conditions over a wide operation range, providing a simple and effective solution. It is relevant to CF-DAB converter development because conventional modulations have limitations concerning the soft-switching range and usually result in overvoltage problems. A 500 W prototype was built and tested to evaluate this proposal. The experimental results show that the a-PWM ensures soft-switching from 2% to 100% of the converter rated power, and the efficiency curve is almost flat due to the improved efficiency at low power levels.