Research and design of automatic alternation between constant‐current and constant‐voltage modes on the secondary side in wireless charging systems

Abstract

During wireless charging, the constant-current (CC) mode must be quickly and stably changed to constant-voltage (CV) mode to ensure battery safety. This switch often requires communication between the primary side and the secondary side along with complex control methods on the primary side. The authors propose a method for automatically and rapidly switching from CC mode to CV mode by changing the resonant compensation network on the secondary side without requiring communication or any complex control processes. Additionally, a method for designing the parameters of the secondary side is presented to ensure battery voltage stability at the transition point. By examining two examples of revised circuitry for the different power levels needed in industry applications, the proposed design methods are analysed and verified, two sets of experiments with a 20 cm coil spacing are conducted, and two systems with output powers of 1 and 2.7 kW and average efficiencies of 90.8 and 93% are implemented. Experimental results show that as the load varies, the output current and voltage obtained using the proposed methods essentially remain constant. In addition, the process of changing from CC mode to CV mode is stable, which satisfies battery-charging requirements.