LitzImp: A Fast Impedance Extraction Algorithm for Litz Wire Coil

Litz wire coil (LWC) is an electronic component commonly used in wireless power transfer (WPT) and heating applications. However, due to its complex twisting structure with turns, existing calculation methods such as analytical methods and finite element method (FEM) cannot extract the impedance of LWC efficiently. This article proposes an efficient numerical calculation algorithm named LitzImp for fast impedance extraction of LWC. LitzImp provides different simplification schemes for different coil structures, reducing the resource consumption in the repeated calculation for the same structures and improving efficiency while maintaining high accuracy. Experiments with nine manufactured coils, including circular coils and rectangular coils, from simple to complex, are adopted to verify the performance of LitzImp. The comparative verification compared with FEM and the analytical method shows the advantages of LitzImp in terms of efficiency and accuracy. Through the analysis of the time consumption, the proposed method is 45 times faster than the similar numerical method for a given coil structure. For highly complex coils (500 strands), the impedance is obtained in less than 5.5 h with good agreement with the measurement. LitzImp will be a powerful tool for the optimal design of LWC due to its high efficiency.