A bidirectional wireless power transfer system for an electric vehicle with a relay circuit

In order to extend the transfer distance, enhance the tolerance for coil misalignment, and improve the capability of energy feedback and power transfer efficiency of conventional wireless power transfer (WPT) systems for electric vehicles, this paper presents a bidirectional WPT topology with a relay circuit. In the proposed topology, the primary and pickup circuits are implemented with virtually identical structures, which can operate in both magnetic field excitation and magnetic field receiving modes to facilitate bidirectional power flow between the primary side and the pickup side. A relay circuit is introduced to achieve high transfer efficiency under special conditions such as long distance or coil misalignment. The mathematical model of the system is established to describe its working mechanism in detail. Both the direction and amount of power flow can be regulated by controlling the shift phase voltages generated by primary and pickup switches. At the same time, the power and efficiency of system are analyzed, which provides a reference to optimize the parameters. The viability of the proposed system is verified by experiments, and the results suggest that the relay bidirectional WPT system is a reliable and efficient system for electric vehicle charging systems.