Electric Power Transmission Characteristics of a Wireless Power Transmission System Using High Temperature Superconducting Coils for Railway Vehicle

Abstract

In this paper, we investigated a large-capacity Wireless Power Transmission (WPT) system operating in the kHz frequency band using high-temperature superconducting (HTS) coils for a railway vehicle. We analyzed the ac losses of the HTS coils using finite element method (FEM) and obtained the transmission efficiency at the power transmission of 38.7 kW at 0.8 and 4.3 kHz. As a result, we clarified that the transmission efficiency between the primary HTS coil and the secondary HTS coil of the WPT system for the railway vehicle is more than 90%. The heat generation in the coils can be suppressed by using the HTS coils for the WPT system. The ac losses per cycle (J/cycle) increased as operating frequency decreased since the HTS tape length increased with the lower operating frequency to achieve the same power transmission. However, the total loss per unit time (W) of the HTS coils did not nearly increase with the frequency. This result suggests that the WPT system using the HTS coil can be operated at the low-frequency region around 1 kHz. The system efficiency including the cryocooler power loss was lower than the transmission efficiency using copper coils. However, the analysis result shows that, if the critical current density of a commercial HTS tape at 77 K increases by approximately four times, the WPT system with HTS coils can realize a higher-efficiency and longer-time operation in a low frequency region of kHz than the system with the copper coils.