Abstract The two-stage charging mode can solve CC overcharge and CV undercharge during battery charging. There are several ways to achieve CC/CV charging for WPT systems, such as working frequency adjustment, duty cycle adjustment, and adding a DC-DC chopper at the secondary side. Such methods can achieve CC/CV charging with high accuracy, but their control schemes need to be simplified. Moreover, the output current and voltage fluctuate greatly during the charging mode switching. The spike will impact the battery on the battery life. Therefore, this paper proposes a LCC-LCC/S self-switching CC and CV composite topology, only requiring two AC switches and a compensation capacitor on the secondary side. By simultaneously opening and closing the two AC switches, the proposed WPT system can achieve the segmented CC/CV charging and improve system safety under abnormal working conditions. Moreover, ZPA in both CC and CV charging modes can be realized, and the output voltage and current fluctuate very small during switching. At last, the performance evaluation is also given by comparing the LCC-LCC/S topology with SS/PS hybrid topology. Firstly, the self-switching LCC-LCC/S-based composite topology is presented. The characteristics of CC/CV, ZPA, and the load optimal switching point are also analyzed. Secondly, several abnormal working conditions are analyzed, including the secondary side missing, load short-circuit, and load open-circuit. The corresponding solutions are presented. Thirdly, by comparing the system characteristics of the currently popular S/SP topology, the advantages of the LCC-LCC/S topology are highlighted. Finally, an experimental platform is built. The experimental results indicate that a highly efficient, reliable and safe WPT system is manufactured. The transmission efficiency is 86 %~92 % during the charging process, the maximum current is 5.03 A, and the maximum voltage is 48.92 V. The simulated and experimental results show that the LCC-LCC and the LCC-S topology can achieve load-independent CC and CV output with ZPA characteristics, respectively. The output current changes only below 0.02 A, and the output voltage changes below 0.2 V during the charging mode switching. Therefore, they will not damage the battery. In order to improve charging safety and avoid WPT system damage under abnormal operating conditions, the proposed WPT system can achieve the two charging modes freely, switching the LCC-LCC topology to the LCC-S topology in the load open-circuit and the LCC-S topology to the LCC- LCC topology in the load short circuit. Moreover, the voltage peak across the switches can be effectively reduced by controlling the switching sequence for the duration of the charging mode switching. The proposed system has higher efficiency and better anti-misalignment capability than the S/PS composite system. The experimental WPT system can produce a maximum output voltage of 48.92 V, a maximum output current of 5.03 A, a maximum output power of 242.26 W, and an efficiency of 86 % to 92 %. The following conclusions can be drawn from the simulation and the experiments: (1) The proposed LCC-LCC/S composite topology can realize a two-stage CC/CV charging output and effectively solve CC overcharge and CV undercharge problems. (2) The proposed system can effectively deal with abnormal working conditions such as secondary side missing, load short circuit, and load open circuit. In addition, the WPT system can automatically run a low-power standby state without any control after the charging completion and the load removal. (3) The voltage spike across the switches is effectively reduced through the optimal control of the switching timing. (4) The performance of the LCC-LCC/S topology on the anti-misalignment capability is better than that of the current popular S/PS composite topology.
Yang Yunhu,Jia Weina,Liang Dazhuang等. A Self-Switching Wireless Power Transfer System Based on Hybrid Topology of LCC-LCC/S with Constant Current and Constant Voltage[J]. Transactions of China Electrotechnical Society, 2023, 38(18): 4823-4837.
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