This paper presents a study of the isolated DC/DC stage of Bi-directional on-board battery charger module (OBCM) for electric vehicle (EV) and plug-in hybrid electric vehicle (PHEV) application. The conventional series resonant converter and secondary-side-switch delay-time control is employed. The delay-time control is used to assist the conventional variable-switching-frequency control of primary switches to reduce the switching-frequency range. By utilizing gallium nitride (GaN) switches, the operating frequency is increased to over 300kHz and the sizes of the passive components are reduced. The new integrated magnetic transformer including two primary windings, one secondary winding, bobbin, and a magnetic core, are designed and implemented. With the magnetic integration, the converter with high power density is achieved while the number of its components and cost are reduced. A standard 3.3kW prototype DC/DC converter designed for a high-frequency galvanic isolation of 400Vdc bus is developed with 250V~430V output range. The prototype circuit exhibits the maximum full-load efficiency of over 97% with a switching frequency variation from 300 kHz to 600 kHz over the entire output-voltage range.
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