Modeling of Litz-Wire DD Coil With Ferrite Core for Wireless Power Transfer System

DD planar coil with ferrite core is one popular coupling structure in wireless power transfer (WPT), especially for electric vehicle applications. The coil design is critical for improving the performance of WPT system. However, the coupler design purely relying on finite element analysis (FEA) software is time-consuming. Literature on the modeling of DD coil is lacking. Therefore, the model of DD coil with a ferrite core for calculating self-inductance, mutual inductance, and ac resistance is proposed in this article. The condition when primary and secondary coils have different sizes is also considered. The case that there is misalignment is also analyzed. Meanwhile, a genetic algorithm based on the proposed coil mathematical model is proposed to optimize the coil structure. For verifying the accuracy of the proposed model, the simulation model based on the FEA and a 1.2-kW laboratory prototype are built simultaneously. The calculation values based on the proposed model is highly consistent with the simulation results and experimental values. Error for calculating self-inductance and mutual inductance is within 5% when coils on the primary side and secondary side are in alignment. The error for calculating the ac resistance of the coil is within 10% when the frequency range is 0-200 kHz.