A very-high-power-transfer-density GaN-based capacitive wireless power transfer system

Abstract

This paper introduces a very-high-power-transfer-density GaN-based capacitive wireless power transfer (WPT) system, suitable as one module of a multi-modular WPT system for charging of electric forklifts. This capacitive WPT system achieves very high power transfer density by operating at a high switching frequency (6.78 MHz) using a GaN-based inverter, and by utilizing innovatively designed L-section matching networks that provide gain and reactive compensation. A systematic design methodology is introduced to ensure zero-voltage switching of the inverter transistors with minimal circulating currents, and to minimize transistor conduction losses and matching network inductor losses. The matching networks are also designed to absorb the parasitic capacitances of the charging environment and utilize them as part of the wireless power transfer mechanism. A prototype 6.78-MHz capacitive WPT system with a coupling plate area of 50 cm2 is designed, built and tested. The prototype system transfers 257 W of power across a 1.2-cm air gap, achieving a power transfer density of 51.4 kW/m2 with an efficiency of 90.4%.