Conduction Loss Minimized Modulation and Design of a DAB-Based Single-Stage DC to Single-Phase AC Converter for EV Charger Application

A dual active bridge (DAB)-based single-stage single-phase ac–dc bidirectional converter is a promising candidate for many applications, including on-board and off-board chargers of electric vehicle (EV) batteries. This article presents one modulation strategy and a design of this converter to minimize the conduction loss. An existing rms current-minimized dc–dc DAB modulation strategy is extended for this converter operating at a fixed switching frequency. This strategy can synthesize sinusoidal low-frequency harmonic-free grid current at any desired power factor. This article derives the analytical closed-form expressions for two critical design parameters: the value of the series inductance and the turns ratio of the transformer that minimizes total conduction loss at a given operating condition. This assumes knowledge of the devices’ ON-state resistance and the magnetics’ ac resistances. If all these resistances are not known a priori, this article proposes a range of design parameters to start and minimize the bridge conduction loss. The analytical treatment greatly simplifies numerical search-based design techniques by reducing the coding effort and computation time. As a next step, this article finds out the worst case operating point considering the wide operating range of an EV charger (constant current (CC) or constant voltage (CV) charging and grid voltage variation). The optimal values of the design parameters are obtained at this point. The adapted modulation strategy results in zero-current-switching (ZCS) turn-on loss in a specific region over the line cycle. This article provides the analytical expressions of this ZCS turn-on loss. It further shows that this switching loss is lower for particular operating conditions than the extra conduction loss that occurs to attain full-range zero-voltage-switching (ZVS) with an additional magnetizing inductance following an existing article’s modulation strategy. The proposed design is verified on a hardware prototype at 1.2 kW with a maximum efficiency of 96.54%.