Analysis and Design of an S/S/P-Compensated Three-Coil Structure WPT System With Constant Current and Constant Voltage Output

Wireless power transfer (WPT) is a promising energy transfer method for its security, reliability, and convenience and has been applied in various scenarios. In practical applications, to prolong the battery lifecycles, the WPT system preferably has the load-independent constant current (CC) and constant voltage (CV) charging characteristics and zero phase angle (ZPA) operation for high power transfer efficiency. However, since the equivalent resistance of the battery significantly changes over the entire charging process, it is difficult to design a WPT system with the above functions. This manuscript proposes an S/S/P-compensated three-coil structure WPT system and its corresponding parameter tuning method to achieve CC and CV charging modes at two different ZPA operating frequencies. For the proposed three-coil structure WPT system, since only one compensation capacitor is required on the receiver, the compactness and portability of the receiver of the WPT system are guaranteed. First, the comprehensive theoretical analysis for the CC and CV charging modes and ZPA operation is presented, and the detailed parameter design method of the proposed system is provided. Second, the sensitivity of variations in system parameters to CC and CV characteristics is analyzed, and the implementation of ZVS operation for further improving efficiency is introduced. Third, a confirmatory experimental prototype with a charging current of 4.6 A and a charging voltage of 56 V is fabricated, and the experimental results are basically consistent with the theoretical analysis. Finally, a comprehensive comparison with previous WPT systems of the same type is carried out to highlight the superiority of the proposed three-coil structure WPT system.