A Novel Active Inductive Clamping Class E Topology and Its Design Approach

Wireless power transfer (WPT) realizes nonconductor contact power transmission with the advantages of plug-free and high spatial freedom by means of electromagnetic field, mechanical wave, acoustic wave, etc. The development of WPT cannot be achieved without the advancement of high frequency power amplifiers. Class E ZVS inverters are the most efficient inverters so far, with the advantages of high-power density, simple circuit topology and low electromagnetic interference. However, WPT is an application with dramatically load variations for power amplifiers, which is really unfriendly to class E inverters. This article develops the explicit design of active inductive clamping class E inverter (AICCEI) with wide load range of zero-voltage switching (ZVS) to improve the robustness of WPT system against the variations of final load and coil-coupling. Two kinds of AICCEI design strategies are derived with the features of 50% duty cycle and non-50% duty cycle and the steady-state behavior are demonstrated. The design of bi-direction clamping source is critical to the operation of AICCEI, and the keys to design will also be presented in this paper. The steady-state behavior and transient response of AICCEI have been tested. The efficiency of the 40W AICCEI is up to 94.2% at 6.78MHz with nominal operation condition. The ZVS operation is achieved when the equivalent resistance of the capacitive load greater than the rated value in the experimental. With the active clamping source, the overshoot voltage of MOSFET is reduced from 145V to 87.6V when the load of AICCEI is cut.