The Study Of Hight-speed Circular Tube SS-HTS Maglev System In An Circular Test Track

When the speed of a train exceeds 400 km/h in the dense atmosphere,huge aerodynamic resistance,vibration and noise will be generated.From the prospect of environmental protection and energy conservation,this is not the optimal form of ground transport.In order to overcome the aerodynamic resistance and wheel-rail adhesion in the wheel-rail train system and realize ultra high-speed ground transport,the concept of evacuated tube HTS maglev train comes into being.Compared to vacuum technology which is earlier developed and more maturely applied,the technology of HTS maglev train is still in a stage of laboratory study.Though some dynamic experiments of HTS maglev train have been carried out,they are low-speed experiments in short-distance straight track or small-radius loop track.To apply as soon as possible this high-potential technology to the society and meet people's demand on a high-speed,convenient,safe,comfortable,energy-saving and environmentally-friendly means of transportation,it is necessary to carry out deep and systematic research on dynamic characteristics of HTS maglev train at a high speed.This paper creatively introduces a SS-HTS maglev system on a small-radius loop track,i.e.fixing the PMG onto the wall surface to make the maglev train run close to the wall,thus overcoming the problem of insufficient centripetal force for maglev train when running in a large-curvature track,realizing stable high-speed operation of HTS maglev train and preventing the maglev train running off the track along the tangent direction.First,starting from the superconductivity macro-phenomenological theory and the classic electromagnetic theory,this paper establishes a critical-state model of HTS-PMG system and adopts a surface current model to solve the magnetic field distribution above single-pole PMG,analyze and compare the differences among theoretical,simulated and experimental results,deduct the analytical solutions of guidance force and levitation force of the SS-HTS maglev system,and study the characteristics of guidance force and levitaion force of superconductor when deviating from the track center and coming close to the track respectively,taking into consideration of the superconductor width upon levitation force.Next,based on the dynamic and static processes of the SS-HTS maglev circular system,this paper sets up a simulation experiment platform to make experimental research on the characteristics of guidance force and levitation force of the system under different field cooling height(FCH),horizontal position,static vertical displacement,dynamic vertical displacement and arrangement mode of YBCO bulks.The research results show that guidance force may be instable during operation of the maglev train and the stability can be improved by reducing FCH and static vertical displacement;in case of large FCH,triangular array of YBCO bulks can keep guidance force nearly unchanged during the running process of maglev train,thus realizing the maximum dynamic stability.In Chapter 4,this paper designs and builds an evacuated tube SS-HTS maglev circular track system,where a long-primary linear motor is used to drive the maglev train and a sectional and parallel power supply controller is designed for the linear motor.The research results show that the power supply controller can make quick response when the simulation speed of the maglev train is 307 km/h.The triangular array of YBCO bulks is optimized taking into consideration of difference in performance of YBCO bulks.The results show that the maximum difference in average levition force of YBCO bulks is not greater than 3.7%after optimization,which indicates an improvement in dynamic suspension stability of the maglev train.In consideration of airtightness of the evacuated tube and volatilization of liquid nitrogen,a large-power main pump and a small-power auxiliary pump are used respectively to adjust and maintain the pressure in the tube.The results show that the magnitude of pressure fluctuation is controlled within±150 Pa and the lowest pressure reaches 650 Pa.In Chapter 5,this paper studies the influence of driving mode,voltage and frequency of power,number of powered linear motor units and pressure upon the maximum speed of the maglev train in an open tube and a closed tube respectively and through differential caculation of acceleration and deceleration running curve,to study the characteristics of resultant force,motor thrust and traction resistance of maglev train.The results show that the maximal speed of maglev train can be improved within certain limits by adopting continuous drive and increasing the number of powered linear motor units,raising voltage and frequency of power and reducing the pressure.When maglev train runs at a high speed and under a normal pressure,resultant force and motor thrust may fluctuate while this fluctuation can be restrained by reducing the pressure,thus effectively improving the driving efficiency and performance of the linear motor.Besides,a 3D model for evacuated tube SS-HTS maglev train is set up to simulate the air resistance of maglev train.The experiment and simulation results show that the traction resistance of maglev train is composed of air resistance,magnetic resistance and inherent resistance.Under normal pressure,air resistance accounts for over 80%of the total traction resistance;when the pressure is lower than 2×10~4 Pa,magnetic resistance will get close to or exceed air resistance,becoming the major resistance of maglev train.Magnetic resistance is directly proportional to speed and inversely proportional to levitaion gap.