Study on Protection Method for HTS Coils With AC Current in Wireless Power Transmission System

We have been investigating a 100 kW-class WPT system for electric vehicles using a high-temperature superconducting (HTS) coil as a ground-side coil. On the other hand, there is a high risk of local burnout in the HTS coil if a local hot spot occurs inside the HTS coil with an AC current. Therefore, it is necessary to establish protection technology for the HTS coil in the WPT system. In this paper, we proposed an HTS coil structure with resonant capacitors between turns to protect the HTS coil for the WPT system. In addition, we developed a partial element equivalent circuit (PEEC) model for the WPT system using the proposed HTS coil. Additionally, we calculated the power transmission characteristics and current distribution of the WPT system using the proposed HTS coil with wire breakage points based on the PEEC model. As a results, we observed that the circumferential current in the proposed HTS coil at the resonance frequency bypassed the wire breakage points through the resonant capacitors between turns. Moreover, the WPT system using the proposed HTS coil the with wire breakage points can transmit target power by adjusting to the resonance frequency. From the above, we found that the HTS coil structure with resonant capacitors between turns is effective in protecting the HTS coil for the WPT system.