High-Efficiency Transmission of a Wireless Power Transmission System for Low-Frequency Using REBCO Double-Pancake Coils

Wireless power transmission has been investigated to realize more efficient and more convenient noncontact power transmission systems for electric tramways, electric vehicles, portable telephones, and so on. Since the magnetic resonance type wireless power transmission system is often used in frequency regions of megahertz, there are some problems, such as the increase of wire resistance due to skin effect and a switching loss in converter. Therefore, it is expected to realize high-power wireless power transmission in low-frequency regions of kilohertz. In a wireless power transmission system using copper coils, however, the transmission efficiency decreases with the decrease of resonance frequency because quality factor decreases with the decrease of the resonance frequency. Therefore, we fabricated a model system using high-temperature superconducting (HTS) double-pancake coils composed of REBCO tape and investigated the transmission efficiency characteristics to evaluate the possibility of application of the HTS coil to a high-efficiency wireless power transmission system operated in the low-frequency region of kilohertz. In the copper coil system, the transmission efficiency increases with the resonance frequency. In the HTS coil system, however, a high-efficiency transmission was obtained, even at a low-resonance frequency, due to a large quality factor at low frequency. Moreover, in the wireless power transmission system using HTS coils, the transmission efficiency was high not only at the resonance frequency but also around the resonance frequency. From these results, we believe that HTS coil can realize the high-efficiency wireless power transmission in a low-frequency region of kilohertz.