Analysis and Design of a High Frequency Wireless Battery Charging System With Smooth Mode Transition Characteristics

With the improvement of wireless power transfer technology has been widely used. The scheme of realizing wireless battery charging based on Class-E converter has gradually attracted attention. In this article, a detailed analysis is carried out for high-frequency system impedance compression technology, input voltage adaptability, compensation network structure, circuit stress, and sensitivity. The difficulties in realizing constant current/constant voltage adaptive charging with traditional design methods are summarized. To this end, a dual-channel system design method based on power synthesis technology is proposed, with a highly sensitive 6.78 MHz system assisted by a robust 500 kilohertz (kHz) subsystem. Combined with the traditional high-frequency passive constant-voltage impedance compression technology, the kHz subsystem provides active state locking, active load compression, and power adaptive compensation to achieve smooth impedance connection during mode switching, thereby completing safe and efficient battery charging. In order to verify the feasibility of the proposed method, a 170 W experimental prototype was built to simulate the charging process of the battery at 45–72 V/2.4 A and 72 V/2.4–0.3 A. The system maximum efficiency reaches 92%. The soft switching characteristics of the power amplifier and system efficiency are still guaranteed under a wide range of load variation, and an approximately ideal battery charging curve is output.