Analysis and Design of Capacitive Coupling Wireless Power Transfer System Using Load-Independent Class-EF Inverter

This study proposes an analysis and design of a capacitive coupling wireless power transfer (WPT) system using a load-independent (LI) class-EF inverter. The proposed system consists of a LI class-EF inverter, two pairs of coupling capacitors, an LCCL filter, and a class-D rectifier. Conventional capacitive coupling WPT system using a LI class-E inverter increases circuit cost by introducing high-voltage switches due to the high voltage stress of the switches, which is a bottleneck for achieving higher power. Another problem is that the input-output voltage ratio is uniquely determined once the switch time ratio and coupling capacitor specifications are determined, thus limiting design freedom. The proposed system uses a class-EF inverter to reduce the voltage stress on the switches and an LCCL filter to convert the LI constant-current (CC) output characteristic of the class-EF inverter to a constant-voltage (CV) characteristic, thereby achieving zero-voltage-switching (ZVS) and constant output voltage regardless of load variations. The output voltage can also be adjusted arbitrarily depending on the design of the LCCL filter. This study analytically demonstrates the design method of the proposed circuit and shows the effectiveness of the proposed circuit through actual device verification.