Superconducting Materials, Power Apparatus and Systems

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(1)Theoretical and numerical analysis of electromagnetic phenomena of superconductor : In pulsed field magnetization of a melt processed bulk high Tc superconductor (HTS), there exists a peak of the trapped flux as applied pulsed field was increased. Local heat generation is considered reducing the shielding current density. Nonlinear dependence of shielding current on dynamic magnetic field is considered by using the flux flow - creep model in the analysis of the pulsed field magnetization. Flow resistivity is also evaluated in the analysis. Since heat conductivity of the HTS is small, little heat diffuses to the surrounding liquid N2 during the magnetization. We can see that local heat generation at the edge region reduces the shielding current density and the trapped field.A magnet can be levitated on a bulk HTS.On the other hand, there is a toy with a magnetically levitated spinning top. Both levitations with spinning top and with HTS are discussed from Earnshaw's theorem. Horizont … More al stability of the spinning top is evaluate from eddy current analysis, and that of HTS is evaluate from pinning of fluxoid. Both critical state model and frozen field mode are applied to the analysis of the HTS, and they are useful for the evaluation.(2)Improvement on Stability in Superconducting Wire and Control Method for Superconducting Levitation System : A hybrid conductor consisting of both low and high temperature superconductors was proposed. A simukation model on the transient stabilities in the conductor was developed and the stabilized current was analyzed and shown to be fairly increased by adding a high temperature superconductor to a low temperature one. An active control method suppressing a vibration in the magnetically levitated body due to some transient perturbation was also proposed and was shown to be effective for suppressing a vibration.(3)Superconducting Fault Current Limiter : A magnetic shield type superconducting fault current limiter(named MSFCL) with active trigger coil was proposed. The current limiting performances were analyzed and shown to be considerably improved by its method. The MSFCL's with the magnetic shielding bodies composed with Bi2223 bulk, YBCO thin film, Nb3Sn wire etc. were also developed. Their current limiting characteristics, superconducting recovery ones and so on were investigated and a data base for designing a MSFCL was developed. The concepts of "multifunction" and / or "maintenance free" for the MSFCL was also proposed and the one with such a concept was shown.(4)Energy Storage System : The energy storage systems are considered to be a dispensable technology for future power systems because of their fast response and flexibility. Several new types of energy storage systems are researched and developed in many institutes. Considering that small-scale energy storage systems will be installed dispersively in power system, this study investigates the characteristics of voltage and reactive power control using dispersed energy storage systems. Further, this study discusses several characteristics of dispersed energy storage systems considering real and reactive power control during a day.(5)System Control : A new method is developed on simultaneous design of a control system and a controlled object utilizing an asymptotic characteristics of optimal control systems. The optimal control system approaches the decoupled control system in asymptotic situation. In the design of the decoupled control system, the time constant between the reference signal and the controlled variable is independent on the selection of the parameters of the controlled object. The characteristics are helpful for simplifying the procedure and reducing trial and error in the simultaneous design because the parameters of the controlled object can be compared by only the magnitude of the control input while the response speed is fixed. Further, the method is applied to the vector control system for an induction motor drive where the preview information of the reference signal and/or disturbance can be utilized to improve the control system performance. Less