Basic Experimental Study on a 1 kW-Class WPT System Using HTS and Copper Coils for EVs

We have been investigated a large-capacity wireless power transmission (WPT) system for electric vehicles (EVs) in which a high-temperature superconducting (HTS) coil is installed only on the ground side. However, the WPT systems using HTS and copper coils (HTS-Cu system) have generally been discussed for low-capacity and high-frequency operation, specifically below 1 kW and above 10 kHz, respectively. Therefore, the design guidelines based on experimental results for the large-capacity and low-frequency HTS-Cu system have not been sufficiently discussed. In this paper, we fabricated a 1 kW-class HTS-Cu system at the operating frequency of 4.8 kHz, and investigated the differences in power transmission characteristics between the HTS-Cu system and a conventional WPT system using only copper coils (Cu-Cu system). As a results, we found that the system efficiency of the HTS-Cu system could obtain more than 98% at the receiving power of 1 kW, although it decreased slightly with increasing the receiving power. Moreover, the loss of the copper coil of the HTS-Cu system was lower than that of the Cu-Cu system. Furthermore, in the HTS-Cu system, the primary capacitor loss exceeded the secondary capacitor loss, and the losses of the primary and secondary wire resistances were almost as significant as the ac loss of the HTS coil. From the above, it is necessary to focus on suppression of the losses primary capacitor and the wiring resistances for the design of the several 100 kW-class WPT system using the HTS and copper coils for EVs.