Implementation of a 3.3-kW DC–DC Converter for EV On-Board Charger Employing the Series-Resonant Converter With Reduced-Frequency-Range Control

A control method that improves performance of series-resonant converters that operate with a wide input voltage and/or output voltage range by substantially reducing their switching frequency range is introduced. The switching-frequency-range reduction is achieved by controlling the output voltage with a combination of variable-frequency and delay-time control. Variable-frequency control is employed to control the primary switches, while delay-time control is used to control secondary-side rectifier switches provided in place of diode rectifiers. A series-resonant converter with the proposed control method is employed as the output stage of the on-board charger module that operates with a wide battery-voltage range. By substantially reducing the switching frequency range, 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 power factor correction front end, to a battery operating with voltage range between 180 and 430 V. Two implementations of the prototype circuit, one employing gallium nitride (GaN) and the other employing silicon (Si) switches, were evaluated and compared. The prototype with Si switches that at full load over the entire output voltage range operates with a switching frequency variation from approximately 150 to 190 kHz exhibits the maximum full-load efficiency of 98.1%, whereas the corresponding frequency range and efficiency of the prototype with GaN devices are 145-190 kHz and 97.4%, respectively.