A comprehensive design analysis of a cost-effective WPT system with a class-E power amplifier and a T-matching network
Résumé
Magnetically-coupled resonant wireless power transfer systems (WPTs) operating in the megahertz range is well-suited for mid-range transmission of moderate power levels. The class-E power amplifier (PA) is attractive for the MHz WPT applications due to the high-efficiency and soft-switching properties. However, since the output power and the efficiency of the class-E PA strongly depends on the output load, any change in the mutual inductance of coupling coils, which leads to the PA load variation, results in a dramatic loss in the overall performance of WPT system. This paper provides a comprehensive design analysis to analytically and numerically mimic the PA behavior to conveniently adapt any variation of the input impedance of the coupled coils to the PA optimum load using a T-type matching network. An equivalent circuit analysis followed by the design theory for the class-E PA, coupled coils, and the T-network has been presented. For validation purposes, the class-E PA implemented by the cost-effective IRF640 MOSFET was first fabricated and its performance was measured for different load values. The PA efficiency and output power was measured as high as 96.7 and 25.8 W, respectively, for the optimum load value of 9 , which was closely predicted from the theory. A 1 MHz WPT system was then built for the operating range up to 27 cm, showcasing its behavior in presence and absence of the proposed T-type matching circuits at two arbitrary 10 cm and 25 cm distances between the coupling coils; the input impedance of the WPT system for those separation distances were 4 and 0.2 , respectively. Results demonstrate power transfer efficiencies of 88% and 15% at distances of 10 cm and 25 cm with the T-network, respectively, improved by 33% and 12% to the non-matching state, respectively. The overall DC output power achieved using a full-bridge rectifier are 21.9 W and 6.8 W at 10 cm and 25 cm, respectively.