A large air-gap capacitive power transfer system with a 4-plate capacitive coupler structure for electric vehicle charging applications

Abstract

This paper proposes a compact 4-plate capacitive coupler structure for large-air-gap capacitive power transfer (CPT). An LCL-compensated circuit topology is applied at both the primary and secondary sides to resonate with the power transmitting plates. The resonance boosts the voltage on the plates to kV levels to increase the power capacity of the CPT system. On each side, the two plates are aligned vertically with a small distance between them to provide a large coupling capacitance, which can eliminate the need for an external capacitor. An equivalent circuit model of the 4-plate coupler is presented to simplify the design process of the system parameters. Finite Element Analysis (FEA) is used to determine the coupler capacitance. The leakage electric field is also simulated at high power to demonstrate the potential safety issues. A 2.2kW input power CPT system is designed and implemented, which can achieve a dc-dc efficiency of 85.87% at a 150 mm air-gap distance. This study demonstrates that the CPT system is also a solution to electric vehicle charging applications.