Analysis and Design of a High-Efficiency 6.78-MHz Wireless Power Transfer System With Scalable Number of Receivers

For multiple-receiver wireless power transfer (WPT), a scalable solution is desired that functions with changing number of receivers. Meanwhile, challenges lie in differences in load characteristics, power level, and cross coupling between the receivers. This article employs Class E2 dc-dc converter topology for the multiple-receiver WPT systems working at megahertz (MHz). The shunt capacitor capacitances of the Class E rectifiers and magnitude of constant output current of the current-mode Class E power amplifier are chosen as design parameters aiming at decoupling the received power of each receiver. Design procedures are developed to simultaneously achieve high efficiency and desired individual load powers over a target variation range of the cross coupling. An experimental 6.78-MHz three-receiver WPT system is optimally designed. The system is shown to be capable of providing different target load powers (10, 8, and 6 W) and maintaining a high system efficiency (above 70%) with different combinations and positions of the receivers.