A Two-Plate Capacitive Wireless Power Transfer System for Electric Vehicle Charging Applications

This letter proposes a two-plate capacitive wireless power transfer (CPT) system for electric vehicle charging applications. The vehicle chassis and the earth ground are used to transfer power, which can replace two plates in a conventional four-plate CPT system. Therefore, only two external plates are required in the proposed CPT system. The coupling capacitance between the plates allows the current to flow forward to the vehicle side, and the stray capacitance between the chassis and the earth ground provides the current-returning path. After analyzing the working principle of a CPT system, it shows that the voltage on the vehicle chassis can be reduced through switching frequency, the coupler structure design, and the compensation circuit design. Then, a downsized prototype is implemented to validate the proposed system, in which two inductors are used to compensate the capacitive coupler. Experimental results show that the prototype achieves 350-W power transfer with 74.1% dc-dc efficiency over an air-gap distance of 110 mm, and the RMS voltage on vehicle chassis is limited to 132 V.