Bidirectional Class e Resonant Converter in Wireless Power Transfer Systems

This paper presents a high-frequency wireless power transfer (WPT) using the bidirectional class E converter for battery-powered applications. As demand for unceasing and reliable electricity increases, battery-powered vehicles are able to serve as a distributed energy source, which requires a bidirectional operation. The capability of bidirectional operation in the vehicles is critical to managing the power flow in the electric grid system. In addition, wireless power transfer (WPT) technique is beneficial to provide galvanic isolation and reliability for the hostile environment. To increase the power density of the WPT system, high-frequency resonant converters such as a class E inverter and rectifier are advantageous to improve system efficiency. However, in the traditional class E inverter topology with an input choke, it is challenging to maintain high efficiency over the wide range of load variations. Also, the inverter and rectifier have to be symmetric for bidirectional operation and require accurate gate signals at MHZ. In this paper, we propose the high-frequency class E inverter using finite DC feed inductance and the self-synchronized class E rectifier design for the bidirectional WPT operation. The finite inductance class E topology maintains the ZVS condition in the various load variance condition. Also, the self-synchronized class E rectifier with the FET helps us obtain the identical structure to the inverter without any additional design and components. In the experiments, the two bidirectional class E modules were linked to transfer power as the forward and reverse direction operating at 13.56 MHz. At an input power of 225 W and an output resistance of 25 Omega, the total power conversion efficiency of the DC-to-DC WPT system is 82.65%.