Design and Modelling of Class EF Inverters for Wireless Power Transfer Applications

Class EF inverters have been widely used recently as primary coil drivers for wireless power transfer applications since they achieve constant output current across a range of link coupling factor values. As the operating frequency that the inductive link is tuned at increases the traditional circuit design techniques that are based on first order calculations fail to represent the inverter behaviour accurately. In this paper, we present a novel method of modelling Class EF inverters that is based on state space representation of the circuit and thus providing the highest accuracy possible. Our method consists of a combination of analytical and numerical calculations in such manner that any parasitic component of the circuit, such as the nonlinear output capacitance of a power switch, can be included in the tuning process.