AC Loss Reduction Through Flux Diverters for Superconducting Wireless Charging Coils at High Frequencies

Wireless power transfer (WPT) for electric vehicles (EVs), also known as wireless charging, is a fast-developing technology with many advantages over conventional cable charging. Novel materials such as high temperature superconductors (HTS) can be used to increase system performance. However, HTS coils have high ac losses at wireless charging frequencies and this is crucial for WPT systems. Flux diverters have been used in the past for dc and low frequency superconducting applications but their effectiveness at high frequencies is unexplored. This article investigates the impact of flux diverters on HTS double pancake coils operating at high frequencies up to 85 kHz, commonly used for wireless charging of EVs. Various geometric characteristics of flux diverters are investigated such as air gap between diverter and coil, thickness, and width. A 2-D axisymmetric multilayer model using finite element analysis was used to examine the coil and diverter losses at such frequencies and different load factors (LFs) between 0.1 and 0.8. It is demonstrated that flux diverters are a viable option to reduce the coil losses even at high frequencies and the width of the flux diverter has the biggest impact on the loss reduction. In general, flux diverters are more suitable for applications using high LFs. Lastly, the impact of the diverter in terms of magnetic field distribution above the coil and overall loss distribution in the HTS coil was examined.