A Double-Pulse Energy Injection Converter With Reduced Switching Frequency for MHz WPT System

Abstract

Class-E inverter is widely used in the wireless power transmission (WPT) system due to its high efficiency. Generally, its switching frequency should be in accordance with the resonant frequency. In a weak-coupling case, the maintenance of high transmission efficiency requires a higher resonant frequency, which would restrict its application due to the corresponding high switching frequency. To solve the issue, this article proposes a Class-E-based inverter with the phase shift control strategy, which enables the operation frequency of the inverter much lower than the resonant frequency. Besides, the transmitting coil accepts power injection twice during each period, which greatly enhances emission intensity. In addition, the proposed phase shift control strategy avoids the weakness of an extremely low duty cycle. Hence, it contributes to the MHz middle power WPT system. Then, simulations and experiments are implemented to verify that the WPT system with the proposed inverter maintains a high efficiency within the middle range and realizes nearly 50% transmission efficiency even in a very weak-coupling coefficient ( $k=0.08$ ). Finally, it is proved that the proposed converter and its control strategy are available.