| The popularity of high-speed railway has a positive impact on China’s economy and society.Restricted by the wheel-rail adhesion limit and noise problems,the further increment of train’s speed is limited.Maglev train is regarded as one of the directions of rail transit technology in the future because of its non-contact characteristics which reduces the impact of friction and noise.High temperature superconducting(HTS)maglev technology is considered as a promising maglev technology because of its passive self stable levitation characteristics.The magnetic characteristics of the permanent magnet guideway(PMG)in the HTS maglev system change with the ambient temperature,which has a great impact on the levitation capacity of the HTS maglev train.Therefore,it is necessary to optimize the the PMG in order to improve the temperature stability of it and the environmental temperature adaptability of the HTS maglev system.The existing research of HTS maglev system mainly focuses on the optimization of PMG magnetic field at room temperature,the material characteristics and arrangement of HTS bulk and the working mode of the systerm.The detailed optimization of the PMG’s temperature stability has not been reported,so the magnetic characteristics of PMG at high temperature and its effect on levitation force of HTS bulk are studied in this thesis.Firstly,the magnetic characteristics of single permanent magnets(PMs)at high temperature are studied.Based on the mechanism of temperature demagnetization,the influence factors such as grade,dimension and magnetization direction of single sintered Nd Fe B PM were studied by experiment and simulation,and the optimization suggestions to improve the temperature stability of single PM are obtained.Secondly,the magnetic characteristics of the PMGs at high temperature are studied.The demagnetization mechanism of external magnetic field is introduced,the high temperature stability of three kinds of small proportion PMGs is studied by experiment and simulation.Then,the high temperature stability of two kinds of real size HTS maglev PMGs is simulated by the verified simulation method.The specific attenuation values of magnetic flux density of PMGs at different temperatures are obtained.The reasons for the difference of high temperature stability of different PMGs are summarized and analyzed.Then,the influence of the PMG’s changed magnetic field on the levitation force of the HTS bulk is studied.The small-scale HTS maglev unit is used in experiment and simulation at high temperature,and the validated simulation method is used to simulate the real size HTS maglev PMG.It is found that the the decline range of levitation force is larger than that of magnetic field of the corresponding PMG.The decline range of levitation force is the same under zero field cooling mode and field cooling mode.The specific attenuation values of levitation force under different ambient temperatures are obtained.Finally,in order to improve the high temperature magnetic stability of Halbach PMG,the optimization design is carried out.Based on the analysis of the optimization objectives and requirements,combined with the influencing factors of the temperature stability of the PMG,a new type of PMG with 60° magnetization angle is designed after controlling the variables.The absolute value and stability of the magnetic characteristics of the new PMG are better than those of the existing PMG.The peak value of the levitation force of the HTS bulk above the new PMG at room temperature is 6.37% higher than that of the existing PMG.The corresponding attenuation amplitude of the levitation force of the new PMG at each temperatures is also significantly smaller than that of the existing PMG. |
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