Stacked Inverter Architecture for High-Frequency Capacitive Wireless Power Transfer Systems

This paper introduces a stacked inverter architecture for high-frequency capacitive wireless power transfer (WPT) systems suitable for electric vehicle (EV) charging. The proposed architecture combines the output voltages of two or more high-frequency inverters using parallel-in series-out air-core transformers, thereby increasing the power transfer capability of a capacitive WPT system. A comprehensive methodology to design a stacked inverter-based capacitive WPT system by leveraging magnetizing and leakage inductances of the air-core transformers is presented. Furthermore, performance of the stacked inverter-based capacitive WPT system is analyzed in the presence of mismatches between stacked inverters. A 6.78-MHz 12-cm air-gap prototype capacitive WPT system using three full bridge stacked inverters is designed, built and tested. This system achieves record performance for a capacitive EV charging system, transferring 5.48-kW at a peak efficiency of 89%, corresponding to a power transfer density of 72.08 kW/m2.