Analysis and Design of A Robust Class $E^2$ DC–DC Converter for Megahertz Wireless Power Transfer

Wireless power transfer (WPT) working at megahertz (MHz) is widely considered a promising technology for midrange and low-power applications. A Class E
²
dc-dc converter is composed of a Class E power amplifier (PA) and a Class E rectifier. It is attractive for applications in MHz WPT due to the soft-switching properties of both the PA and the rectifier. Using the existing design, the Class E
²
dc-dc converter can only achieve optimal performance such as a high efficiency under a fixed operating condition. Meanwhile, in real applications variations in the coil relative position and the final load are common. The purpose of this paper is to analyze and develop a general design methodology for a robust Class E
²
dc-dc converter in MHz WPT applications. Component and system efficiencies are analytically derived, which serve as the basis for the determination of the design parameters. The classical matching network of the Class E PA is also improved that provides the required impedance compression capability. Then, a robust parameter design procedure is developed. Both the experimental and calculated results show that proposed design approach can significantly improve the robustness of the efficiency of the Class E
²
dc-dc converter against variations in coil relative position and final load. Finally, the experiments show that the range of variation of the system efficiency is narrowed from 47.5%-85.0% to 73.3%-83.7% using the proposed robust design.