【作者】 张龙财；

【导师】 王家素；

【作者基本信息】 西南交通大学 ， 电工理论与新技术， 2008， 博士

【摘要】 自从1986年高温超导材料被首次发现以来,世界上许多科学家纷纷对其表示了极大的兴趣并投入大量的精力进行研究,使得高温超导体的性能不断提高,为其在工程方面的应用开辟了广阔的前景。由于高温超导块材YBCO可以工作在液氮温区,具有较强的磁通钉扎能力,可以构成自稳定的悬浮系统,因此在实际应用中具有巨大的开发潜力,其应用主要包括:高温超导磁悬浮旋转轴承、飞轮储能、无源振动自由平台、陀螺仪和磁悬浮列车等。本研究小组对高温超导磁悬浮列车系统进行了大量的研究工作,并于2000年12月31日研制成功世界首辆载人高温超导磁悬浮实验车。为了使高温超导磁悬浮车系统早日走向工程应用,本论文对在时变外磁场作用情况下稳定悬浮于永磁导轨上方的高温超导体块材的导向力性能进行研究,目的在于揭露时变外磁场对块材导向力性能影响的作用机理,从而为高温超导磁悬浮车系统的动态悬浮性能研究提供一定的实验依据与理论指导。本文对高温超导磁悬浮车用永磁导轨表面磁场的不均匀性进行研究。借助高温超导磁悬浮测试系统SCML-01对导轨表面磁场进行扫描测试,并辅以计算机仿真计算,通过实验测试结果和计算结果的对比,得出导轨表面磁场确实存在不均匀性的结论。此外,在准静态测试条件下,实验研究了导轨表面磁场不均匀性对高温超导块材的悬浮力性能的影响情况。导向力是反映高温超导体悬浮特性的特征量,同时也是磁悬浮系统设计中的关键参数之一。本文通过实验的方法研究了时变外磁场对稳定悬浮于永磁导轨上方的高温超导体块材的导向力性能的衰减影响。首先研究了时变外磁场扰动对导向力磁滞回线以及导向力弛豫性能的影响情况,借助于Bean模型分析了在时变外磁场作用情况下,块材的各种性能参数(包括交流损耗、俘获磁通、温度以及临界电流密度等)的变化情况;阐述了时变外磁场对块材导向力衰减影响的作用原理。接着研究在不同场冷高度或者工作高度情况下,时变外磁场对导向力性能的衰减影响情况,最后研究了块材在结冰冷却不充分的情况,其导向力受时变外磁场扰动影响的变化情况。基于Bean临界态模型,针对目前的高温超导磁悬浮车系统,提出了一种模拟计算方法,该方法可计算在时变外磁场中块材导向力的衰减变化情况。通过实验结果和模拟计算结果的对比,验证了该方法的可行性。另外,在此基础上对实验中难以进行或者不能进行的一些研究进行拓展。讨论了超导体相关各参数(临界电流密度、热导率、热容以及块材尺寸大小)对时变外磁场中高温超导块材导向力的影响情况;最后研究了时变外磁场对超导体各性能参数(俘获磁通、平均温度、交流损耗以及导向力)的影响情况。所有这些模拟计算结果为高温超导磁悬浮车的研究和工程实践提供了较为重要的科学依据。更多还原

【Abstract】 Since the first discovery of high-temperature superconductors(HTSs) in 1986, Many scientists on the world have expressed a great interesting in it and done a lot of research.So the performance of the HTS is improved constantly,and it makes its application in engineering became easier.Because the high-temperature materials can operate at temperatures within the cooling capabilities of liquid nitrogen and have strong flux pinning effect,the stable levitation can be achieved without any complex control system out of superconducting materials.Bulk superconductors have great potential for various engineering applications,such as non-contact bearings,flywheels,momentum wheels,passive vibration free platforms and Maglev vehicles.Our group did a lot of research on HTS maglev vehicle system and successfully developed the first man-loading HTS maglev test vehicle on Dec.31,2000.In order to promote the application of the HTS maglev vehicle system in engineering,guidance force characteristics of a HTS exposed to time-vary magnetic field over a permanent magnetic guideway(PMG)were investigated in this dissertation,whose aim was to understand the interaction between the time-vary magnetic field and the guidance force decay of the HTS bulk and to provide corresponding experiment bases and theoretical direction so as to investigate the dynamical characteristics of the HTS maglev vehicle system.The magnetic inhomogeneity over the permanent magnet guideway used in the high-temperature superconducting maglev vehicle system was investigated.The surface magnetic field of the PMG was measured by a HTS maglev measuring system and simulated by a computer.From the experimental and the simulation results,it was found that the surface magnetic field was did non-uniform. Moreover,we investigated the influence of the magnetic inhomogeneity of the PMG on levitation force of the bulk superconductor in a quasi-static state.The guidance force is a characteristic parameter reflecting guidance characteristics of a HTS,also one of the key parameters for the design of HTS maglev vehicle.The influence of the time-vary external magnetic field perturbation on the guidance force of HTS bulk over the PMG was investigated by experimental methods in this dissertation.Firstly,the hysteresis curve and the ralaxation of the guidance force in the time-vary external magnetic field were studied.Based on the Bean critical model,we discussed the influence of the time-vary external magnetic field perturbation on the performance parameters, such as ac losses,trapped magnetic field,temperature,critical current density and so on,and explained the interaction between the time-vary external magnetic field and the decay of the guidance force.Secondly,we compared the guidance fore decay of the bulk exposed to the time-vary external magnetic field under the conditions of different field-cooled height or different work height.Finally,the effect of the time-vary external magnetic field on the guidance force of HTS bulk, which was covered with ice and was not cooled totally,was investigated.Based on the Bean critical model,a simulation method was adopted to calculate the guidance force decay of the bulk exposed to the time-vary magnetic field for the current HTS maglev system.Compared the experimental results with the simulation ones,it was found that the simulation method was feasibility and could qualitatively reveal the characteristics of guidance force of HTS bulk in this situation.Furthermore,some researches that were difficult or unable to be done systemically by experiments were carried out by this simulation method. The influence of relevant parameters,such as critical current density,thermal conductivity,thermal capacity,the dimension of a superconductor and so on,on the guidance force of the bulk exposed to time-vary magnetic field.With the help of the simulation method,we discussed the effect of the time-vary external magnetic field perturbation on the performance parameters,such as ac losses, trapped magnetic field,temperature,critical current density and so on.All the simulation results provide important scientific bases for the research and engineering practice of HTS Maglev vehicle.更多还原