Realize Load-Independent Output With Soft Switching Based on Switched Capacitor for Wireless Charger System

Wireless power transfer (WPT) technology has been given more and more attentions in lithium-ion batteries charging. To ensure the charging reliability and improve the charging efficiency, the load-independent current and voltage output with inductive input impedance to realize zero voltage switching (ZVS) condition are usually necessary in WPT system. However, too many power switches and passive components in the existing methods bring the whole system inefficient, bulky and uneconomical. In this paper, the switched-controlled-capacitance (SCC) structure is investigated. Then a hybrid topology, where the SCC is employed to adjust the secondary resonant capacitor, is proposed to achieve the desired load-independent current and voltage output under two different operation frequencies. Simultaneously, the soft switching of all power devices can also be realized during the whole charging period. Besides, the transformation between two operation modes by SSC and operation frequency adjustment is very convenient and smooth, which enhances the switching safety. Finally, an experimental prototype with 60V and 3A is built to validate the proposed wireless battery charger system.