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http://dx.doi.org/10.6113/JPE.2018.18.4.1268

Evaluation of AC Resistance in Litz Wire Planar Spiral Coils for Wireless Power Transfer  

Wang, Xiaona (Institute of Electrical Engineering, Naval University of Engineering)
Sun, Pan (Institute of Electrical Engineering, Naval University of Engineering)
Deng, Qijun (Department of Automation, Wuhan University)
Wang, Wengbin (State Grid Jiangxi Electric Power Research Institute)
Publication Information
Journal of Power Electronics / v.18, no.4, 2018 , pp. 1268-1277 More about this Journal
Abstract
A relatively high operating frequency is required for efficient wireless power transfer (WPT). However, the alternating current (AC) resistance of coils increases sharply with operating frequency, which possibly degrades overall efficiency. Hence, the evaluation of coil AC resistance is critical in selecting operating frequency to achieve good efficiency. For a Litz wire coil, AC resistance is attributed to the magnetic field, which leads to the skin effect, the proximity effect, and the corresponding conductive resistance and inductive resistance in the coil. A numerical calculation method based on the Biot-Savart law is proposed to calculate magnetic field strength over strands in Litz wire planar spiral coils to evaluate their AC resistance. An optimized frequency can be found to achieve the maximum efficiency of a WPT system based on the predicted resistance. Sample coils are manufactured to verify the resistance analysis method. A prototype WPT system is set up to conduct the experiments. The experiments show that the proposed method can accurately predict the AC resistance of Litz wire planar spiral coils and the optimized operating frequency for maximum efficiency.
Keywords
AC resistance; Biot-Savart law; Efficiency; Litz wire; Wireless power transfer;
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