A Single Class-E Inverter for Multiple Frequency Wireless Power Transfer System

In multi-MHz frequencies of wireless power transfer (WPT), the system typically operates within the ISM bands at 6.78, 13.56, and 27.12 MHz. The primary motivation for employing WPT systems in the MHz frequency range is their widespread recognition as a promising technology for midrange applications. This paper presents a multiple-frequency class-E inverter that utilizes a single transistor to reduce hardware costs. The key innovation involves modifying the traditional inverter topology to enable operation at two frequencies, achieved through the addition of an impedance transformation circuit that accurately provides a shunt capacitor for multiple-frequency operation. Additionally, the circuit model and design procedure are clearly delineated to validate the proposed algorithm. In this study, a WPT system was implemented, comprising a single class-E inverter, multiple-frequency coils, and two receivers. Measurement results demonstrate that at 6.78 MHz, the peak efficiency and output power are 71% and 17.7 W, respectively. In the 13.56 MHz band, the peak efficiency and output power reach 72% and 24.7 W, respectively. These results underscore the simultaneous achievement of high efficiency during multiple-frequency operation.