ZVS Operation of Class-E Inverter Based on Secondary Side Zero Compensation Switching at Variable Coupling Coefficient in WPT

The Class-E inverter is appropriate for wireless power transfer system due to its high efficiency and high inverting frequency. Meanwhile, the Class-E inverter is sensitive to the changes in load characteristics, which leads to the weak adaptability to a variable distance of the coupling coils. This article aims at providing a secondary side static zero compensation switching method. The load characteristics based on the S-S (Series-Series) compensation type coupling system were analyzed. It was found that when the compensation capacitor on the secondary side is switched off, the equivalent parameters of the load on the secondary side tend to vary with an increase in coupling strength. At the same time, the equivalent parameters satisfy the conditions where the Class-E inverter works in the ZVS state. The discussion is then extended to the output power and efficiency of the system. The result showed that a significant increase in both output power and efficiency when the coupling strength is far higher than the default standards. The correctness of the theoretical analysis and the feasibility of the method were verified by a 500 kHz experimental prototype with 10 W output while the coupling coefficient varies from 0.02 to 0.07.