A Primary Side Control Method for Wireless Energy Transmission System

This paper presents a primary side control method for a low power wireless energy transmission system (WETS), with no physical wire connection required between the primary and secondary-side circuits. The primary side control method implemented in the WETS does not require extra space in the secondary side to regulate transmission energy. A charging protection was embedded within the secondary side to monitor the charging current and battery voltage, and to protect the battery against over-charging current or voltage. LLC resonant converter and class-E amplifier structures with zero-voltage switching were utilized to minimize transmission loss due to leakage inductance. In our experiments, the secondary side battery was fed a stable charging current in constant-current mode and low current in constant-voltage mode where the battery voltage reached approximately 4.1 V. The results show that the WETS achieved primary side control in all air-gap conditions. The overall efficiency of the WETS with LLC resonant converter was between 33.5% and 54.1%, and that of the class-E amplifier was between 30% and 66.2% when operating in the constant-current mode.