High-temperature superconducting (HTS) no-insulation (NI) coil is a promising design because of high current density, high thermal stability, and self-protection mechanism. Flux pumping is a contactless charging method for a superconducting magnet, which can reduce the cryogenic losses associated with current leads. In this study, we compared the charging performance of a rotating permanent magnets-based flux pump for two different types of HTS coils: an INS coil and an NI coil. Results showed that the rotating type flux pump works well with both coils. But the charging speed of NI coil is much slower, which results from the small parallel characteristic resistance of NI coil. Results also show that the output DC voltage and inherent dynamic resistance of the flux pump increase linearly with the increase of rotating speed.

The safety of lithium-ion batteries (LIBs) in the battery energy storage station (BESS) is attracting increasing attention. To ensure the safe operation of BESS, it is necessary to detect the battery internal short circuit (ISC) fault which may lead to fire or explosion. This article proposes an early battery ISC fault diagnosis method based on the multivariate multiscale sample entropy (MMSE). The voltage, current, and temperature of the battery are utilized to extract the fault feature. The wavelet denoising method are employed to improve the MMSE performance. The adaptable threshold is proposed to diagnose the early ISC fault and prevent misdiagnosis. Finally, the ISC fault experiment and the battery overcharge experiment are used to validate the efficiency of the proposed early ISC diagnosis method. The real BESS operation data are used to validate the robustness of the proposed method. The results shows that the proposed method is effective in diagnosing the early ISC fault.

Direct current carrying Type II superconductors present a dc electric field under external perpendicular ac magnetic field. This effect can also be considered as an equivalent dynamic resistance. The minimum field magnitude required to generate the dynamic resistance is less than the fully penetration field of the superconductor, which is much less than its upper critical field. Thus, the superconductor can remain superconducting, leading to fast recovery times and meaning that it is feasible to use dynamic resistance to add a controlled impedance into the system. In this study, we built a demonstrator using a section of YBCO coated conductor controlled by an external ac field of a wide frequency range. We tested the electric field value and response time of the system. The work may be indicative for designing impedances for flux pumps or superconducting magnetic energy storage systems.

High temperature superconductor (HTS) is becoming more and more attractive for the application in high field magnets, which can be utilized in the magnetic resonance imaging (MRI) and rotating machines. To charge the HTS magnets and operate them in persistent current mode, a persistent current switch (PCS) is very necessary. This paper will focus on how to build a fast persistent current switch controlled by ac magnetic field. The PCS can present a large resistance rapidly compared with conventional PCS and recover to zero-resistance in a short recovery time. Impacting factors and strategy to control the proposed PCS are discussed. An experimental system is built and tests are carried out to verify the practicality of the proposed PCS.