Frequency Adaptive Topology to Realize Constant Output and Soft Switching for the WPT System

The main emphasis of research for battery wireless charger should be on four parts, including load-independent output to satisfy the charging requirement, zero voltage switching of power devices to increase transmission efficiency, minimum component counts to reduce cost and simple control strategy. However, the existing studies have not taken these all into account, which greatly limits the application of battery wireless charger. This paper proposes a WPT system based on the simplest S/S compensation network. By replacing the secondary compensation capacitor with an $L$ - $C$ branch, the same circuit structure can realize the load-independent constant current (CC) and voltage (CV) output with zero voltage switching at two different switching frequency. A current amplitude detection circuit is added in the primary side to determine the switching point of CC mode and CV mode. Compared with existing research, the component numbers in proposed circuit are less, the control strategy is easier to implement and avoids the communication between the primary and secondary sides. Finally, a wireless battery charger for 60V/3.6A is built to verify the feasibility of proposed system. And the experimental results perform well on realizing a load-independent output with ZVS operation.