The AC loss in the high temperature superconducting (HTS) coil depends on the transport current and the magnetic field applied to the HTS wire. Therefore, the design guidelines for the wireless power transmission (WPT) systems using the HTS coils differ from those for the conventional WPT systems using the copper coils. This paper describes the principle of the WPT system, the analysis method using the equivalent circuit of the WPT system, the difference in Q values between the HTS coil and the copper coil, and the technological trends of the WPT systems using the HTS coils.

We have been investigating a Wireless Power Transmission (WPT) system for railway vehicles as a tool to reduce the greenhouse gas emissions in diesel vehicles. Since the WPT system for railway vehicles is required to transmit electric power of several hundred kW in a short time, it is difficult to suppress heat generation by the internal resistance of a copper coil. Therefore, we have investigated the WPT system using a high-temperature superconducting (HTS) coil for railway vehicles. This paper describes the Q values of the HTS coil and the copper coil, a low-loss HTS coil structure with a gap between layers suitable for the WPT system, and the design guidelines for the WPT system of railway vehicles using HTS coils.

This study investigated experimentally and analytically the power transmission characteristics of High Temperature Superconducting (HTS) coils at commercial power supply frequency (50 Hz) to realize highly efficient power transmission in wireless power transfer systems for railway vehicles. We proposed a solenoidal coil with a thin magnetic core as an HTS coil structure suitable for lower frequencies and investigated its effectiveness by finite element analysis. The analysis results showed that the proposed coil can significantly suppress the current increase due to the low frequency of the wireless power transfer system. We also investigated the core shape to reduce the losses of the proposed coil and found that the loss in the coil can be reduced by increasing the length and thickness of the magnetic core. Furthermore, we compared the power transmission characteristics between the proposed coil and the conventional spiral coil and showed that the proposed coil could improve the overall efficiency by about 10 %. The power transmission characteristics at 50 Hz were also measured using the scaled-down model coil. As a result, we demonstrated that highly efficient power transmission could be achieved at 50 Hz by using the proposed solenoidal coil with a magnetic core.

This paper investigates the AC loss characteristics in the resonator of the superconducting wireless power transmission system proposed by Prof. Sekiya. This superconducting resonator is characterized by the fact that the current distribution is not constant in the tape length, the REBCO tapes are double layered, and the operating frequency is 10 MHz. Since the influence of eddy current loss cannot be ignored due to the high operating frequency, we investigated the effect of the REBCO tape configuration using the finite element method.