Class EF2 inverters for wireless power transfer applications

Class EF inverters are hybrid inverters that combine the improved switch voltage and current waveforms of Class F and Class F-1 inverters with the efficient switching of Class E inverters. As a result, their switch voltage and current stresses are reduced, and their efficiency, output power and power-output capability can be higher than the Class E inverter. These improved features of Class EF inverters over Class E inverters can be beneficial in a wireless power transfer (WPT) via magnetic induction application. This paper demonstrates the application of a Class EF inverter operating at a 6.78MHz for a 25W WPT system. A sixth-order piecewise-linear state space model is presented to analyse the inverter and to derive values of its components to achieve optimum switching operation. Experimental results are provided to confirm validity of the state-space model and the design of the inverter and a DC-DC efficiency of 87% was achieved.