In this paper, a new approach is proposed for the automatic tuning Class E power amplifier (PA) to compensate the effect of the coupling distance variation in wireless power transfer (WPT) systems. In WPT, coupling distance variations change the reflected impedance, causing Class E PA to operate under nonoptimal switching conditions. Here, a model-based approach is proposed to estimate the coil separation distance in real-time. Knowing the separation distance, the mutual inductance and reflected impedance are computed, and the Class E is retuned online by saturable reactors. A design example of Class E PA with proposed closed-loop control method is given. The results indicate that the proposed method could perfectly retune the Class E to operate under optimum conditions and compensate power delivered to the load (PDL) reduction during coupling distance variations. It can be seen that there is a closed agreement between the measured PDL when the PA is closed-loop controlled and the measured PDL when the PA is manually optimized during each coupling distance. The measurement results show that by using the proposed method, the PDL increased by 14.47%, 25.51%, 15.92%, and 12.88% at coil coupling distances of 15 mm, 20 mm, 25 mm and 30 mm, respectively.

本文针对自动调谐E类功率放大器（PA）提出了一种新方法，以补偿无线功率传输（WPT）系统中耦合距离变化的影响。在WPT中，耦合距离的变化会改变反射阻抗，从而使Class E PA在非最佳开关条件下工作。在此，提出了一种基于模型的方法来实时估计线圈间距。知道了分离距离，就可以计算出互感和反射阻抗，然后通过可饱和电抗器在线重新调整E级。给出了采用闭环控制方法的E类功率放大器的设计实例。结果表明，所提出的方法可以完美地重新调整E类，使其在最佳条件下运行，并在耦合距离变化期间补偿传递给负载的功率（PDL）的减小。可以看出，在每个耦合距离内，当对PA进行闭环控制时，测得的PDL与手动优化PA时的测得PDL之间存在一个封闭的协议。测量结果表明，通过所提出的方法，在线圈耦合距离为15 mm，20 mm，25 mm和30 mm时，PDL分别增加了14.47％，25.51％，15.92％和12.88％。