Electric vehicle (EVs), which use an electric motor, are expected to replace internal combustion engine vehicles. However, to date EVs are not highly attractive to consumers due to their unsatisfactory battery charging characteristics and high cost. In particular, the existing conductive charging method makes it more difficult to spread EVs due to the inconvenience of charging and the risk of electric shock. The wireless power transfer (WPT) system can eliminate all of the charging troubles of EVs. However, the WPT systems in existing EVs have large air gaps between the transmitter coil and the receiver coil, posing a hurdle that prevents success. The large air gap cause issues such as a loose coupling, low efficiency, and troublesome electromagnetic compatibility (EMC). An in-wheel WPT system can serve as a solution to address the issues arising due to the large air gap. In this paper, we propose a magnetic coupler structure of an in-wheel WPT system for EV applications. A design of two coils is introduced, in which the transmitter coil and receiver coil are designed based on a design method. Moreover, the pad structure according to the ferromagnetic core geometry is designed and discussed. The aim of this research is to find a suitable configuration of the magnetic coupler for an in-wheel WPT system. The values of the coupling coefficients according the magnetic coupler structure are determined. This paper is expected to provide a good reference for further research, including work on the manufacturing of a prototype.

In this paper, the overhang effect of a homopolar synchronous generator with high-temperature superconducting (HTS) field winding is analyzed. Homopolar topology can be used to implement stationary field winding, which is advantageous for superconducting electrical rotating machine applications that rotate at a relatively high speed. The homopolar machine has an axial-winding radial-flux structure, unlike general heteropolar machines that have a radial-winding radial-flux structure. Therefore, in order to analyze the characteristics of the homopolar machine more accurately, use of 3D finite element method (FEM) should be considered. The overhang of rotor poles in electrical rotating machines can be used to enhance the flux linkage in armature windings and to improve the output power. Therefore, applying the overhang structure in the development of an electrical rotating machine is a method that can further improve the performance of the machines. In this paper, we use 3D FEM to analyze the overhang effect of a homopolar HTS synchronous generator and present the overhang length required to improve the performance of the machine.

We report that the field homogeneity of a large-scale metal-clad no-insulation all-ReBa ₂ Cu ₃ O _{7− x} magnet is reproducible after occasional operating conditions, in this case the current ramp down/up and magnet warm-up/cool-down conditions. First, we shimmed the magnet by cylindrically arraying ferromagnetic shims on the wall of the room-temperature bore of the magnet to improve the spatial field homogeneity. As a result, the field homogeneity of the magnet was improved from 557.7 to 14.1 ppm in a 10 mm diameter spherical volume. The resultant acquisition of field homogeneity tremendously enhanced from an inhomogeneous state greatly degraded by screening currents qualified us to study the temporal stability of the field homogeneity. We used a magnet-energizing protocol with the field drift minimized to shrink a nuclear magnetic resonance (NMR) lineshape into a much narrower super-imposable lineshape. We demonstrate the technique by NMR experiments, showing excellent reproducibility in every case, presenting strong evidence of recovery to certain time-unvarying field gradients and to a state of homogeneity. These findings suggest a new route for high-resolution high-temperature superconducting NMR and magnetic-resonance-imaging magnet technology.

Currently, studies of flux switching machines are actively underway owing to several advantages of these machines, including their sturdy rotor structure and high output capability. This paper deals with an outer-rotor hybrid-excited flux-switching machine (FSM). The proposed machine embraces a homopolar structure and utilizes permanent magnets (PMs) for field excitation and a high-temperature superconducting (HTS) coil for flux regulation. The stator houses the HTS field coil, PMs, and armature windings. The outer rotor consists solely of an iron core. Thus, the machines are cost effective and can serve as a solution to the design and fabrication complexities of field current supplying and cooling systems. In this paper, the machine performance outcomes are analyzed using the 3D finite element method (FEM), and the validity of the proposed machine is verified.

This paper presents a dynamic characteristic analysis of an electrical rotating machine that applies no-insulation (NI) high-temperature superconductor (HTS) field coils. The HTS electrical rotating machine applying HTS field coils has high power density compared to conventional electrical rotating machines that utilize normal conductor field coils, meaning that it has great potential for next-generation mobility applications such as electric ships and aircraft. Recently, several studies have reported the possibility of solving the quench protection problem of the HTS field coil, which is one of the most pressing issues in HTS electrical rotating machines, and the key technology is the no-insulation (NI) winding technique. The NI winding technique enhances the electrical and thermal stability of the HTS field coil because the over-current can be automatically bypassed through the turn-to-turn contacts. Although there have been many studies of the electrical and thermal stability of NI HTS field coils, there are still issues related to NI HTS field coil applications to electrical rotating machines. In particular, there are few studies of the behavior of electrical rotating machines with a NI HTS field coil under dynamic conditions, such as active short-circuit and speed drop conditions. In this study, we designed an electrical rotating machine that utilizes NI HTS field coils and analyzed the dynamic characteristics of the designed machine. The results demonstrate there is a possibility of larger torque fluctuations and armature current fluctuations in the NI HTS machine than in the insulated HTS machine.

A cryogen-free portable 3 T high-temperature superconducting magnet for an electromagnetic property measurement system has been developed to serve as a user facility at the Korea Basic Science Institute. The metallic insulation method was adopted to reduce the charging delay without sacrificing the self-protecting feature. A genetic-algorithm-aided optimized design was carried out to minimize the superconducting tape consumption while satisfying several design constraints. After the design, the compact high-temperature superconducting magnet composed of eight double-pancake coil modules was wound with high-temperature superconducting tape and stainless steel tape, and integrated with a two-stage cryo-cooler. The 3 T magnet was successfully cooled to approximately 20 K with a cryo-cooler and reached the target field of 3 T without any problems. Long-term measurements and a range of other tests were also implemented to verity the performance of the magnet. Test results demonstrated the feasibility of a cryogen-free portable high-temperature superconducting magnet system for electromagnetic property measurement experiments.