Analysis and Design of Three-Coil Coupler for Inductive Power Transfer System With Automatic Seamless CC-to-CV Charging Capability

The three-coil loosely coupled inductive power transfer (IPT) charging system can achieve constant current (CC) to constant voltage (CV) output automatically and smoothly during battery charging process. However, due to cross-coupling that existed between the assistive and receiver coils, a voltage deviation will generate in CV output compared with the ideal CV charging voltage threshold of battery. In this paper, the practical effect of the cross-coupling between the assistive and receiver coils and the impedance matching at full load for efficiency optimization are further taken into consideration based on three-coil coupler design. Four design schemes of the assistive coil are compared by finite-element analysis (FEA) and an effective design approach is provided. Then, the proposed approach is theoretically analyzed to relieve the cross-coupling issue on the CV output even with efficiency optimization. Also, it decreases the space occupancy of the three-coil coupler. Finally, an experimental prototype is built to verify the proposed design method and the theoretical analysis.