Implementation of a Bidirectional 400–800V Wireless EV Charging System

Abstract

A non-contact isolated bidirectional symmetrical resonant converter with dual active bridge as the main structure is proposed in this study. This scheme is combined with the symmetrical resonant network and integrated into an isolated bidirectional symmetrical resonant conversion circuit. The symmetrical resonance technique is used in this work to realize the voltage regulation of a wide range of output and the function of soft switching under the appropriate operating frequency; reduce the electromagnetic noise and power loss caused by hard switching of power switches in the circuit; and improve the overall converter efficiency, voltage regulation, and hard switching from conventional bidirectional converters. In addition, a pair of non-contact loosely coupled inductors (wireless coils) is used to replace the conventional transformer to transfer the bidirectional energy wirelessly. The digital signal processor TMS320F28335 is the control core of the system in this study. The proposed converter with DC grid input voltage is set to 400 V, and the EV battery side is set to 670–800 V. The rated power capacity of the bidirectional wireless charger is 2 kW. Besides, the proposed bidirectional wireless EV charger has CC-CV charging function to achieve the EV charging requirement. Finally, the maximum efficiency of forward charging mode (grid to vehicle [G2V; 400 V charge to 800 V]) can reach 90.2% while that of reverse discharging mode (vehicle to grid [V2G; 800V discharge to 400V]) can reach 91.4%.

Keywords

• Bidirectional resonant converter
• symmetric resonant circuit
• soft switching
• wireless power transfer
• loosely coupled inductor