Research On The Forces And Thermo-Electromagnetic Properties Of High-Temperature Superconducting Magnets In 3-Phase Travelling Magnetic Field

High Temperature Superconducting(HTS)Linear Synchronous Motor(LSM)with high thrust density,low power loss,greatly turning radii,strongly climbing ability,and light quality as well as compact structure,than the conventional one becomes the promising propulsion system for future high-speed rail traffic and even ultra-high-speed vacuum maglev train,because which is able to overcome the more high-speed challenge and also keep the high efficiency and stability for the propulsive system.At present,although the static electromagnetic force of HTS LSM has been researched richly and greatly,the electromagnetic properties as well as the temperature distribution of HTS magnet in LSM still are short of research.To take full advantage of the properties of HTS magnet in LSM and promote the application of HTS LSM into wheel-rail train and Maglev,this thesis,served as a fundamental research on a linearly driven system for rail transit or Maglev,studied the electromagnetic properties and temperature rise of a HTS LSM by means of simulation,experiment and analytic method.In the d-q coordinate system,the expressions of both the thrust and normal forces of LSM were obtained on the basis of power balance.Based on the Maxwell equations,the electromagnetic governing equation of LSM was derived and both the 2-D(two-dimensional)and 3-D finite element models of HTS LSM were established to investigate the static electromagnetic forces of HTS LSM,the magnetic field distribution as well as the AC loss in HTS magnet.By means of the experiment,the magnetic field distribution of flat stator and the electromagnetic forces of HTS LSM were measured under the mover-locked condition of LSM.Meanwhile,the induced transport current in HTS magnets under different electromagnetic gaps and varied frequencies of stator current was also measured.Based on the Biot-Savart law and Lorentz’s equation,a set of analytic expressions to describe the magnetic field distribution and electromagnetic forces of coreless-typed LSM were derived,and then the magnetic field distribution,magnetic force,back electromotive force and synchronous force of LSM were calculated using the analytic model.Combining the finite element model with the analytic expression,the critical current as well as AC loss of HTS magnet when subjected to a travelling magnetic field were achieved under varied amplitudes and frequencies of stator current.Besides,the air-gap magnetic field and electromagnetic forces also were calculated via the analytic method when considering the back iron in the primary stator or secondary HTS magnet.Thanks to the image theory of iron material for response to magnetic field,it has been verified that the magnetic field distribution of an iron-core HTS LSM is able to be communicated analytically as long as the iron core is not saturated.Allowing for the complex geometry structure and the high width/thickness aspect ratio of YBCO layer as well as the thermal conductivity of each layer in tape,a unidirectional coupling model from the electromagnetic field to temperature field of HTS magnet subject to a three-phase travelling magnetic field was built and tailored to study the AC loss and temperature field distribution in HTS magnet.Adopting a series-parallel circuit principle and generally well-accepted homogeneous technique,the equivalent thermal conductivity of HTS coils was obtained,and thus a bidirectional electrical-thermal coupling model for the electromagnetic field and temperature field of HTS magnet was built and then tailored to calculate the AC loss and temperature field distribution inside HTS magnet in the condition of start-up or synchronous operation of linear motor.