Analysis of Parasitic Capacitance of Wireless Power Transfer Coil and its Reduction Technique

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Abstract
Wireless power transfer (WPT) technology has been widely investigated and applied in recent times. Increasing operation frequency proves to be effective in enhancing power transfer distance and reducing the volume of the magnetic coupling system (MCS) in the WPT system. However, once the frequency reaches MHz, the capacitive parasitic parameters of the coil in MCS can not be ignored, as it adversely affects the output characteristics in a series/series (S/S) compensation wireless power transfer system. This paper presents a method for parasitic capacitance modelling method and introduces a technique for its reduction in MCS. The parasitic capacitance is not only determined by the coil structure, including capacitance between adjacent and nonadjacent turns, but also by the electrical potential distribution of the winding turns. Based on the mathematical model of parasitic capacitances in MCS, a distributed capacitance compensation structure is adopted, and the capacitance parameters determination method is proposed. With the method, the coil parasitic capacitance can be reduced by changing the voltage potential distribution of the coil in MCS to minimize the impact of parasitic capacitances. Experimental results verify the accuracy and effectiveness of the theoretical analysis.

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