Multiple-load inductive power transfer system with automatic conversion from constant current to constant voltage charging for batteries

Due to the battery-life and practicality considerations, realizing only constant current (CC) or constant voltage (CV) output for a single load in a wireless charging system is not attractive. This paper proposes a compact inductive power transfer (IPT) system for multiple-load applications with automatic switching from CC to CV charging, based on transmitter-repeater-receivers coupler. The simplified equivalent circuit of the proposed coupler is established through circuit analysis. Based on this, the constant output characteristics and transmission efficiency are theoretically clarified. The safety and reliability of the system are assessed. The proposed system can achieve CC and CV switching for multiple loads, zero phase angle operation, and fixed operating frequency, which can improve the efficiency. Additionally, the communication between the transmitter side and the receiver side is not needed in the proposed system as well as complex control strategies. An experimental prototype with two loads is established and tested. Experimental results show that the output characteristics of each receiver remain almost unchanged when other receiver is removed or added. The maximum measured efficiency is 89.56% with a single load and 93.66% with two loads.