Design of 3 MHz DC/AC inverter with resonant gate drive for a 3.3 kW EV WPT system

Air-core inductive charging systems offer significant weight, cost and reliability advantages over competing ferrite based solutions at the expense of reduced coupling factor. Acceptable magnetic link efficiencies (>95%) can nonetheless be achieved by operating at MHz frequencies where the coil Q is inherently very high (>1000). We present a design approach for transmit-side power electronics capable of efficiently handling the kilowatts of power necessary to charge an electric vehicle (EV) at MHz frequencies in a way that is also tolerant to changes in load. A new current-source resonant gate drive topology suitable for switching state-of-the-art high speed SiC Mosfets in a push-pull inverter is presented. By using the gate charge from one device to switch the opposite device in antiphase, the gate drive consumes less than half the power than would be required by two conventional gate drives for the same switching speed. A zero voltage switched (ZVS) push-pull class E inverter topology is chosen for efficient high frequency operation. The zero differential switching (ZDS) condition is relaxed to achieve the required tolerance to load variation.