Implementation of 3.3-kW GaN-based DC-DC converter for EV on-board charger with series-resonant converter that employs combination of variable-frequency and delay-time control

An isolated dc-dc series-resonant converter that is controlled by a combination of variable-frequency and secondary-side-switch delay-time control is employed as the output stage of the on-board charger module (OBCM) that operates with a wide battery-voltage range. The delay-time control which is implemented by the modulation of secondary-side switches is used to assist the conventional variable-switching-frequency control of primary switches to reduce the switching-frequency range. By substantially reducing the switching-frequency range and utilizing gallium nitride (GaN) switches, the overall operating frequency is increased to reduce the sizes of the passive components, and hence, increase power density. The performance evaluation of the proposed series-resonant converter with delay-time control was done on a 3.3-kW prototype delivering energy from 400-V bus, which is the output of the PFC front end, to a battery operating with voltage range between 180 V and 430 V. The prototype circuit exhibits the maximum full-load efficiency of 97.3% with a switching frequency variation from 144 kHz to 175 kHz over the entire output-voltage range.