A Clamped and Harmonic Injected Class-E Converter With ZVS and Reduced Voltage Stress Over Wide Range of Distance in WPT System

The inherent frequency of magnetic coupling resonance based wireless power transfer system (MCR-WPT) is up to the level of kHz or even MHz. The class-E converter with zero-voltage switching (ZVS) could eliminate the considerable switching loss, however, the high voltage stress and sensitive ZVS condition to coils distance limit its application seriously in MCR-WPT. To solve the issues, a voltage-clamped class-E converter, consisting of an auxiliary clamped circuit to decrease the voltage stress and a harmonic circuit to realize ZVS against a wide range of coils position, is proposed for the WPT system. According to the harmonic analysis, the relationship among duty cycle, input voltage, amplitudes and phases of the harmonics is obtained. Then, the design strategy for system parameters, especially for the harmonic circuit is presented, so that, ZVS could be maintained over a wide range of coils distance. Meanwhile, the efficiency analysis is also carried out, suggesting a steady high efficiency further. Three design examples with disparate harmonic parameters and ZVS ranges are presented and one of the three examples is selected to make comparison with a typical Class-E WPT system. The experimental results agree with the theoretical analysis well.