The efficiency analysis and optimization methods for achieving optimal efficiency in two-coil wireless power transfer (WPT) systems have been considerably discussed. Recently, that the efficiency of three-coil WPT can be higher than its two-coil WPT counterpart with an extended transmission distance has been verified. Nevertheless, the research on the efficiency analysis and optimization of the three-coil WPT system still needs to be examined. Therefore, this paper systematically investigates the efficiency characteristics of the three-coil WPT system. Especially, an optimal current ratio control strategy is developed with an active rectifier to achieve efficiency optimization and keep the output voltage constant. Consequently, overall efficiency can be improved using the optimal current ratio compared with traditional three-coil WPT systems. A scaled-down experimental prototype is established to validate the effectiveness of the proposed coupling structure and the feasibility of the proposed control approach. Overall, a three-coil WPT system with an active rectifier is proposed, which utilizes the optimal current ratio control strategy. Experimental results successfully validate that the proposed methods can substantially improve the efficiency of three-coil WPT.

在两线圈无线功率传输（WPT）系统中实现最佳效率的效率分析和优化方法已经进行了相当多的讨论。最近，已经证实了三线圈WPT的效率可以比其二线圈WPT的效率更高，并且传输距离更长。尽管如此，关于三线圈WPT系统效率分析和优化的研究仍需进行研究。因此，本文系统地研究了三线圈WPT系统的效率特性。尤其是，开发了具有有源整流器的最佳电流比控制策略，以实现效率优化并保持输出电压恒定。因此，与传统的三线圈WPT系统相比，使用最佳电流比可以提高整体效率。建立了按比例缩小的实验原型，以验证所提出的耦合结构的有效性和所提出的控制方法的可行性。总体而言，提出了一种具有有源整流器的三线圈WPT系统，该系统利用了最佳的电流比率控制策略。实验结果成功验证了所提出的方法可以大大提高三线圈WPT的效率。