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Energies 2018, 11(6), 1472; https://doi.org/10.3390/en11061472

Dual-Side Independent Switched Capacitor Control for Wireless Power Transfer with Coplanar Coils

School of Electric Power Engineering, South China University of Technology, Guangzhou 510641, China
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Received: 24 April 2018 / Revised: 26 May 2018 / Accepted: 29 May 2018 / Published: 6 June 2018
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Abstract

The transfer coils of traditional Magnetic Coupling Resonant Wireless Power Transfer (MCR-WPT) systems are generally arranged coaxially. Coplanar coils can be an alternative scheme that can save more space in some applications, such as mobile phone wireless charging. However, the inductances of coplanar coils are sensitive to foreign objects, which leads to a reduction in transfer efficiency and output power. A MCR-WPT system with coplanar coils and its control strategy are proposed in this paper. First, the characteristic of the mutual inductance and the magnetic field distribution between the coplanar coils are analyzed. A formula to calculate mutual inductance between the coplanar coils is proposed in this part. Secondly, the effect of inductance offset and frequency detuning on transfer efficiency and output power are analyzed. Then, the control strategy to eliminate frequency detuning is proposed. The proposed method implements switched capacitor to take place of constant compensation capacitor. The equivalent capacitance of switched capacitor is adjusted when the frequency detuning occurred. Thus, the inherent frequency of the resonant tank tracks the source frequency all the time. Since the switched capacitor of each side is controlled based on the quantity of their own, the control process is independent and does not require wireless communication. The complexity and the cost of the system are reduced. At the end of the article, the veracity of mutual inductance formula and the effectiveness of the proposed control strategy are verified by experiments. The experimental coils are placed in in an environment full of interference. The inductances of the coils are reduced from 224 μH to about 214 μH. The transfer efficiency and output power of MCR-WPT system with closed-loop control are higher than the one without control. At a distance of 5 cm from edge to edge, the transfer efficiency is 76.37% under the proposed control and 72.21% under no control. The output power is 285.66 W under the proposed control and 271.37 W under no control. View Full-Text
Keywords: wireless power transfer; dual-side independent switched capacitor control; mutual inductance; coplanar coils wireless power transfer; dual-side independent switched capacitor control; mutual inductance; coplanar coils
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Han, C.; Zhang, B.; Fang, Z.; Qiu, D.; Chen, Y.; Xiao, W. Dual-Side Independent Switched Capacitor Control for Wireless Power Transfer with Coplanar Coils. Energies 2018, 11, 1472.

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