Basic Coil Structure for Rapid Charge in a Low-Frequency and High-Efficiency Wireless Power Transmission System Using High-Temperature Superconducting Coil for Railway Vehicle

We have been investigating the possibility of a low-frequency and high-efficiency wireless power transmission (WPT) system for the railway vehicle using a high-temperature superconducting (HTS) coil. We investigated a basic HTS coil structure having a low ac loss and a high coupling coefficient between the primary and secondary coils by adjusting a radial gap between turns. The devised HTS coil was configured to have a radial gap approximately equal to the HTS tape width and increase the number of turns while reducing the inner diameter of the coil. Also, we analyzed the power transmission characteristics in the 40 kW class WPT system using the devised HTS coils operated at a low frequency around 1 kHz for the railway vehicle. Furthermore, we fabricated the 1 kW class WPT model system at an operating frequency of 0.92 kHz using the devised HTS coil and demonstrated the effectiveness of the low-frequency and high-efficiency WPT system using the devised HTS coil structure. As a result, we clarified that the low-frequency WPT system using the devised HTS coil for the railway vehicle can perform more rapid charging and the high-efficiency transmission than that using the copper coils.