Wireless power transfer (WPT) technology can transmit power through high-frequency magnetic fields, which is safer and more flexible than conventional conductive charging method. The WPT systems for charging lithium batteries need to meet the charging function of first constant current (CC) and then constant voltage (CV). In addition, to avoid reactive power loss, the input impedance of the system is preferably purely resistive, that is, to meet the zero phase angle (ZPA) condition. In view of the above problems, this paper proposes a four-coil structure WPT system based on dual-frequency switching method to realize load-independent CC and CV charging outputs at two fixed ZPA frequency points, respectively. It is worth noting that there is only one compensation capacitor on the receiving side, which ensures the compactness and portability of the receiving side of the WPT system. An experimental prototype with charging current of 2.2 A in CC mode and charging voltage of 28 V in CV mode is established to verify the correctness and practicality of the proposed four-coil structure WPT system. The experimental results are basically in good agreement with the theoretical analysis.

中文翻译：

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恒流恒压充电四线圈结构无线电力传输系统：分析、设计与实验

无线电力传输（WPT）技术可以通过高频磁场传输电力，比传统的传导充电方式更安全、更灵活。为锂电池充电的WPT系统需要满足先恒流（CC）再恒压（CV）的充电功能。此外，为避免无功功率损耗，系统的输入阻抗最好为纯阻性，即满足零相角（ZPA）条件。针对上述问题，本文提出一种基于双频切换方式的四线圈结构WPT系统，分别在两个固定ZPA频点实现负载无关的CC和CV充电输出。值得注意的是，接收端只有一个补偿电容，这确保了WPT系统接收端的紧凑性和便携性。建立了CC模式充电电流为2.2 A、CV模式充电电压为28 V的实验样机，以验证所提出的四线圈结构WPT系统的正确性和实用性。实验结果与理论分析基本吻合。