Analysis and Design of Loosely Inductive Coupled Wireless Power Transfer System Based on Class- ${\rm E}^{2}$ DC-DC Converter for Efficiency Enhancement

This paper presents a design procedure of high-frequency loosely inductive coupled wireless power transfer (LIC-WPT) system based on class- E² dc-dc converter, taking into account the power loss reduction of inverter, coupling part, and rectifier simultaneously. Analytical expressions including the dc-to-dc efficiency of the WPT system are derived and the efficiency deterioration mechanism is explained by the circuit model. Through the analytical expressions, the design procedure for satisfying both the class-E switching conditions and power loss reductions at the coupling part is proposed from the circuit-theory viewpoint. The class- E² WPT system designed by the proposed design procedure achieves high dc-to-dc efficiency at low coupling coefficient, in particular, compared with those designed by the previous design strategies. The validity and effectiveness of the proposed design procedure were confirmed by PSpice simulations and circuit experiments.