AC loss mitigation for high temperature superconducting coils in wireless power transfer

With the rapid development of high temperature superconducting (HTS) technology, second generation (2G) HTS materials have become a promising alternative to traditional conductive materials in the power transmission industry. Recently, the topic of using HTS materials in wireless power transfer (WPT) systems for electric vehicles (EVs) has attracted widespread attention in the background of net zero transport. With virtually zero DC resistance and superior current-carrying capacity, HTS materials can achieve high quality factor and power density in the WPT resonant circuits compared to conventional metals, e.g., copper. However, the optimal working frequency for the conventional WPT system is relatively high in the order of kilohertz level. Superconducting coils working at high frequencies could generate high AC losses, reducing the overall power transfer efficiency (PTE) and increasing the cooling burden. In order to improve the PTE of HTS-WPT systems, the AC loss mitigation methods for different HTS coil topologies have been investigated in this paper by varying the inter-turn gap and tape width. Three HTS coil structures, namely the spiral coil, the solenoid coil and the double pancake (DP) coil, have been studied with a 2D axisymmetric multi-layer numerical model based on the H - formulation, and the simulation results have been validated by the published experimental data. The general loss characteristics, loss distributions in each turn, as well as magnetic flux densities have been analysed in detail for three types of HTS coils. Moreover, the impact of these two loss reduction methods on the WPT performance has also been evaluated. Findings have shown that increasing the inter-turn gap and tape width can effectively reduce the AC power losses and increase the PTE of the HTS-WPT system. The spiral coil demonstrates the highest AC power loss reduction effect and PTE while maintaining a stable level of magnetic fields. This paper is believed to deepen the understanding of superconducting WPT and provide a useful reference for more efficient wireless energisation applications.