volume | PIER Journals

Abstract

In the wireless power transfer (WPT) system of electric vehicles, the system leakage magnetic field and transmission efficiency depend on the coil structure, and the traditional unipolar coil has high transmission efficiency but generates high leakage magnetic field. In order to maintain the transmission efficiency while reducing the magnetic leakage and improve the safety index of the WPT system, this paper proposes a bidirectional inverse series coil of four meshes structure (FBISC), which maintains the high transmission efficiency of the WPT system only by the advantages of the coil structure without applying any metal materials and shielding coils. At the same time, the leakage field produced by the coil structure of the target area is less than the safety limit value, which makes the traditional shielding coils no longer necessary, and is light, clean, and highly efficient. First, the leakage magnetic field generated by the coil in the target region after energization is analytically calculated using a vector potential-based method for calculating the magnetic induction strength of rectangular coils. Secondly, a coil parameter assignment optimization method that weighs two structural performance indexes, namely, transmission efficiency and leakage magnetic field, is given to obtain the coil parameters that satisfy the given conditions. Furthermore, the proposed coil structure is compared with the conventional coil structure. Compared with the conventional unipolar coil, the bidirectional inverse series coil of four meshes reduces the leakage magnetic field by 56.4% and sacrifices only 2.38% of the transmission efficiency. Compared with the reverse double D coil (DD coil), the bidirectional inverse series coils of four meshes reduces the leakage magnetic field in the target region by 48.5% and sacrifices only 1.3% of the transmission efficiency. Finally, an electric vehicle WPT system with shielding is built to verify the correctness of the proposed structure. The results show that the leakage magnetic field of the FBISC coil structure in the target region is only 5.22 μT, and the transmission efficiency is more than 95% at an output power of 4 kW.

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Dr. Xueyi Zhang

Mr. Bin Li

Dr. Liquan Ren

Dr. Pengsheng Kong

Dr. Zhongqi Li