Wide-Air-Gap Transformer Model for the Design-Oriented Analysis of Contactless Power Converters

Abstract

Wireless power converter topology with small size and high conversion efficiency has an increasing demand on small power applications. Some design techniques to transmit power by customized cores are already developed. However, when transferring energy by wide-gap transformers employing small size commercialized cores, the power losses on the winding greatly increase as the frequency increases. Then, the efficiency of the contactless power system decreases significantly due to the conduction loss and reactive components in the resonant circuit. Even though series parallel resonant converters (SPRC) are largely employed which can provide infinite shunt impedance regardless of the coupling coefficient, when a commercialized core is employed for loosely coupled contactless power transfer applications, the large leakage inductance of the transformer significantly influences on additional power dissipation on transformer windings. In this paper, an operating principle how the contactless transformer with commercialized core contributes to the low efficiency is discussed. Also, a new frequencydependent R-L ladder circuit model is introduced for the designoriented analysis of wide air-gap contactless power converters including the frequency dependent losses of the transformer. New design procedure with the proposed model is suitable for the contactless transformers employing commercialized cores. The proposed design approach is validated by 98.8W hardware experiments. Finally the simulation waveforms and the hardware results are compared to verify the accuracy of the frequency dependant-transformer model. 0278-0046 (c)

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