Minimum Backflow Power and ZVS Design for Dual-Active-Bridge DC–DC Converters

Significant improvement in the power efficiency of dual-active-bridge dc–dc converters can be achieved by implementing zero voltage switching (ZVS) which is facilitated by a negative switch current at the switching instant. Such negative current, however, causes undesirable backflow power that counteracts the efficiency gain. Thus, the conditions for achieving ZVS and maintaining minimum backflow power (MBP) are often conflicting. A design that implements ZVS and MBP simultaneously is, thus, desirable. While, existing research is short of exploring the accurate condition of MBP and ZVS. This work fully considers the influence of output capacitance of power switches on ZVS and tries to implement ZVS and MBP of a dual-active-bridge dc–dc converter by controlling the inductor current to a minimum value at the turn-off instant of a power switch. The expression of the minimum switching current for ZVS and MBP is first derived by considering the resonant transient process in dead time. The transmission power range with ZVS and MBP can be maximized by selecting appropriate voltage conversion ratio according to different values of minimum current. An optimal extended phase-shift control for enlarging the operating region for ZVS and MBP of a dual-active-bridge dc–dc converter is designed. The optimization method is experimentally verified.