Equivalent Transmission Line Circuit Model for Designing Inductive Power Transfer Systems With Constant Outputs for Charging Li‐Ion Battery

ABSTRACT Load‐independence constant current (CC) and constant voltage (CV) charging are the two stages of charging the Li‐ion battery. In this article, a method to design the inductive power transfer (IPT) system is proposed for charging the Li‐ion battery based on the equivalent transmission line circuit model with constant outputs. First, the equivalent transmission line circuit model with constant outputs is clarified, and the quarterwave transformer equivalent to the magnetic coupling unit is illuminated as well as other four usually used LC circuits. Second, the progress mapping the model to the IPT system with CV or CC output is explained in detail. By taking parasitic resistances into account, the outputs and efficiency of the system are then investigated with ABCD matrix. The method is simple, intuitive, and easy to comprehend, which can greatly simplify the design. A three‐coil IPT system for charging Li‐ion batteries is designed for example. Two switches set at the transmitter make the charging switch from CC to CV mode smoothly when the critical condition is met. An experimental platform is established and measured to verify the proposed method. The maximum efficiency is measured as 89.24% in CC stage and 91.81% in CV stage.