A Resonant PWM DC/DC Converter with Coreless Transformer for Light Electric Vehicles On-Board Charger

This paper suggests a DC/DC converter with coreless transformer for electric vehicle chargers. Since the coreless transformer has low coupling coefficient, the converter uses resonance but its power is controlled by PWM. Appropriate design of resonant capacitor improves its switching conditions of ZVS operation of all switching devices and near ZCS of bottom switches and output rectifier. Using Wheeler approximation, coreless transformer design is suggested and converter design procedure is derived under a predetermined leakage inductance of coreless transformer. The feasibility of the proposed charger is verified with a 2kW prototype designed based on the procedure.