Capacitively Isolated Dual Active Bridge Converter for On-Board Charger Applications

A bidirectional isolated dc–dc converter is normally employed in on-board charger (OBC) circuits to extend the output voltage range of the power factor correction (PFC) converter because the latter alone cannot meet the electric vehicle (EV) battery charging voltage range. The isolated dc–dc converter also prevents faults propagating from one side of the circuit to the other side and prevents the flow of leakage currents during charging, which is important for safety considerations. Because the capacitor has a higher energy density than magnetic elements, this article utilized a capacitively isolated dual-active bridge (CDAB) converter to provide isolation in the OBC. Specifically, two low equivalent series resistance (ESR) film capacitors are used to replace the transformer in the traditional dual active bridge (DAB) converter. A comprehensive analysis of the operating modes of the converter, based on single phase shift control, is presented together with a discussion of converter design parameters. A 1 kW laboratory prototype is constructed to experimentally verify the proposed topology. Compared with the conventional DAB and CLLC converters, the proposed CDAB converter has a higher power density and improved efficiency, confirming the superiority of the proposed topology.