In the wireless power transfer (WPT) system of electric vehicles, low electromagnetic field (EMF) shielding will reduce transfer efficiency. How to reduce leakage EMF and obtain a high transfer efficiency is a difficult problem. In this paper, a double inverse series coil (DISC) structure is proposed to reduce the leakage EMF of WPT systems. First, a calculation method of EMF for rectangular coils is proposed, and the leakage EMF distribution characteristics of the coil structure on the target surface are analysed according to the proposed calculation method. Secondly, an optimization method with the optimal leakage EMF effect of the target surface is given. The parameters of each coil that meet the design requirements are obtained based on the proposed optimization method. Finally, according to the obtained coil parameters, a set of WPT system based on DISC structure is developed, and the correctness of the proposed structure and method is verified by simulated and measured results. The results show that with applying the DISC structure, the maximum leakage EMF in WPT system is only 9.56 μT on target surface without additional shielding, and the transfer efficiency is up to 95%.
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