Automatic tuning of the Class E power amplifier applied in inductive links during coil separation variations

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. (C) 2020 Elsevier GmbH. All rights reserved.