Electronic tuning of a high frequency DC/AC inverter for inductive power transfer

The misalignment and displacement of the coupled coils in an inductive power transfer system reduce the power efficiency and limit the amount of power that can be transferred. Coil misalignment results in the primary coil driver to operate in an un-tuned state which causes non-optimum switching operation and results in an increase in switching losses. This paper presents a novel method to electronically tune a Class E inverter used as a primary coil driver in an inductive power transfer system to minimize the detrimental effects of misalignment between the inductively coupled coils which may occur during operation. The tuning method uses current controlled inductors (saturable reactors) and a variable switching frequency to achieve optimum switching conditions regardless of the misalignment. Mathematical analysis is performed on a Class E inverter based on a piecewise linear state-space model. Experimental results are presented to confirm the analysis approach and the suitability of the proposed tuning method.