Optimization of Magnetic Coupling for Small and Medium Power Wireless Charging System

Aiming at the problem that low coupling coefficient of small and medium power wireless charging system always leads to low charging efficiency, a method improving the coupling coefficient by optimizing magnetic coupling structure was proposed. 3-D finite-element analysis (FEA) has been carried out to compare and analyze the transmission performance of three commonly used magnetic coupling structures. In addition, the coil coupling effects at different lengths and widths were compared under the same coil area to achieve the best coupling performance. The equations about output power and efficiency were derived from the equivalent circuit,and the expressions about coupling coefficient were obtained by analyzing the equivalent magnetic circuit diagrams, which provide the basis for optimizing magnetic core structures. Then, a process of design and optimization of magnetic cores was presented and following the process a retro-shaped core structure was designed for rectangular coil. The simulation results show that compared with the original charging system, coupling coefficient of the wireless charging system using the optimized magnetic coupling structure is improved significantly, thus, verifying the effectiveness of the optimization methodology.