Hiroyasu Kobayashi

Experiments on dynamic wireless power transfer (DWPT) for electric vehicles (EVs) typically require vast testing grounds and significant costs, making them difficult to implement. As a solution, experimental systems utilizing rotational motion for DWPT have been proposed. However, few such systems have been developed and their design methods and fundamental characteristics remain unclear. This paper presents the construction of a rotation-type experimental system for DWPT and discusses its design methodology and basic characteristics. In developing the prototype, mechanical stability was verified through simulations analyzing stress and critical rotational speed of the rotating components. A sector-shaped transmitter coil, suitable for this system, was designed and analyzed using electromagnetic field simulations, confirming similar characteristics to conventional linear-rail-based systems. Furthermore, the effects of misalignment between transmitter and receiver coils and the electrical characteristics of slip rings and brushes were evaluated. Finally, power transfer characteristics were validated through experiments at a linear velocity equivalent of 40 km/h and 3.3 kW power transfer.

No-Insulation (NI) coil utilizing HTS tape conductor has become a promising option for high-field magnets, capable of delivering both excellent thermal stability and high current density. NI coil can reduce heat generation due to a current behavior that bypasses the defect when a local hot-spot is formed in HTS tape conductor. In the high-field magnet application, a coil structure with large number of bundled HTS tape conductors without insulation between layers is utilized to achieve large current capacity. In this paper, the authors examine numerically the current behavior of NI coils under sudden open-circuit conditions with varying numbers of bundled tape conductors. Additionally, a thermal analysis of the NI coil was performed to evaluate the effect of current behavior on thermal transient response. The partial element equivalent circuit (PEEC) model was employed to analyze the NI coil made of bundled HTS tape conductors. In this model, each turn of the coil and its corresponding loop section are divided and represented as an electrical circuit. This method allows for a thorough analysis of the current and temperature distribution within the NI coil. The calculation results of current behavior under the shutdown of the power supply to the coil revealed that the circumferential current concentrated in innermost and outermost layers, which results in heat generation in the NI coil. Also, temperature rise due to the current imbalance under power shutdown condition tends to become higher when the number of bundled tape conductors increases.

No-insulation (NI) coil has been developed as a means to enhance thermal stability. A notable characteristic of NI coils is the charge delay resulting from the absence of turn-to-turn insulation. In order to mitigate this charge delay in NI coils, a winding technique has been suggested, involving parallel high-temperature superconducting (HTS) tapes without insulation between layers. However, the external magnetic field fluctuation causes a large induced current in the NI coil with parallel HTS tapes. In such a situation, heat generation at the contact resistance in the path of the large induced current can be significant. In this paper, authors analyzed the current behavior of NI coils when the external magnetic field fluctuates for various number of parallel tapes. Also, a thermal analysis of the NI coil was conducted to assess the impact of induced current behavior on thermal stability. In this study, a Partial Element Equivalent Circuit (PEEC) model is utilized. Furthermore, a coupled analysis of current behavior inside the coil and thermal analysis was performed utilizing the PEEC model to analyze detailed electromagnetic phenomena. The calculation results of current behavior revealed the induced current concentrates at the particular turn to turn contact resistance. Therefore, the temperature at the point of heat generation increased to very high temperature and there is a possibility of burnout in the case of large number of parallel tapes.

Unbalanced current distribution in cable-in-conduit conductors (CICCs) is a phenomenon that shows the dependence of stability performance on the ramp rate (ramp-rate limitation) in fusion magnets. In this study, we investigated the effect of the twist pitches of the cable stages in a CICC on the current distribution among its strands. We calculated the self-inductance of each strand and the mutual inductance between strands based on a geometrical model that analytically computes the strand's trajectory. Then, we created an equivalent circuit model and calculated the current distribution in the CICC. The current distribution was analyzed for CICCs with different twist pitch configurations. The result shows that combining the cabling stage twist pitches affects the current distribution.

No-insulation coil (NIC) has been proposed for improvement of thermal stability. NIC can reduce heat generation due to a current distribution that bypass the defect when a local hot-spot is formed. However, a charge delay because of no turn-to-turn insulation is one of the important characteristics of NICs. To decrease the charge delay of NIC, a winding technique with parallel HTS tapes without insulation between layers has been proposed. However, the increase of the number of parallel layers causes the significant current imbalance between parallel tapes. In this paper, the relationship between the number of parallel tapes and the effect on charge delay reduction is investigated. In addition, the effect on the thermal stability and magnitude of central magnetic field and thermal stability due to the current imbalance is also verified. Both analyses are carried out for both NIC with and without defects. The analysis results show that charge delay of NICs is reduced according to increase of number of parallel tapes. Current imbalance between layers increases in accordance with the increase of the number of parallel tapes. However, the analysis results also show that thermal stability and central magnetic field are not degraded by this imbalance current. In terms of NIC with the defect, thermal stability and fluctuation of central magnetic field are most improved by the effect of current sharing between parallel tapes when the number of parallel tapes is largest.

Three-phase coaxial high-temperature superconducting (HTS) cables have three layers, and HTS conductors are arranged circularly in each layer. Since each arranged conductor transports current, the conductor arrangement determines the magnetic field distribution inside the cable. In addition, the AC loss varies depending on the conductor arrangement because the magnitude of the perpendicular magnetic field on each conductor determines the AC loss of the cable. Therefore, it is essential to consider the optimal conductor arrangement in cable design. In this study, we investigated the influence of the relative position of the conductors constituting each phase on the AC losses. The conductors constituting the cable were Y-based superconducting conductors, and the AC losses were calculated by one-dimension finite element analysis of the T-method. The calculation results show that shortening the gap between conductors in the radial direction reduces the AC loss. Furthermore, we have shown that simultaneously shortening the circumferential and radial gap between conductors can significantly reduce AC losses. In addition, the cost estimation shows that it is essential to consider a conductor arrangement with low AC losses in cable design.

The techniques of cell rotation benefit various fields. We have proposed a cell rotation method based on a vibration-induced flow. Vibration-induced flow is a localized flow generated when vibrations are applied to microstructures. Proposed method uses a vortex flow generated by the flow around three micropillars. This method also enables to control angular velocity by changing voltages corresponding to amplitudes of vibrations. However, there is a problem that cells stop rotating due to floating when applying high voltage for high-speed cell rotation. Therefore, we aim to design the micropillars that enables high-speed cell rotation. In this study, we analyzed a flow causing cell floating with the various heights of the micropillars. Furthermore, we evaluated rotation of mouse oocytes using the micropillars of different heights. We succeeded in high-speed rotation of mouse oocytes at approximately 802 degrees/s by using low-height structures.

Wayside Energy Storage Systems (WESSs) are studied for energy saving of railway system. To maximize the energy saving effect of WESSs, a power control strategy which realize higher charge/discharge power is necessary. Currently, Current Based Control, which regulates current of ESDs, and Voltage Based Control, which regulates DC input voltage are generally applied. However, the difference of the dynamic characteristics between Voltage Based Control and Current Based Control has not discussed before. The aim of this paper is to compare the dynamic characteristics of Voltage Based Control and Current Based Control. First of all, a theoretical analysis on dynamic characteristics of both control strategies is carried out. This analysis revealed the maximum limitation of a control gain, which has an impact on the energy saving, for each control strategy. Utilizing these maximum control gain, an analysis on the static characteristics is performed to verify the energy saving effect for each control strategy. As a result, an advantage of Voltage Based Control is verified from the viewpoint of contribution to energy saving in DC-electrified railway system.