Comparative Study Between Permanent Magnet And Electromagnet Rails For HTS Maglev

Nowdays,High-Temperature Superconducting(HTS)maglev has become a new direction of rail transit research.The Meissner effect and pinning effect of HTS bulk can provide levitation and guidance force without the complex control system.The permanent magnets(PMs)were used for traditional HTS maglev rail transit system in guideway laying,which limits the large-scale industrial application of HTS maglev rail transit.In the long run,there are many advantages in constructing HTS maglev system by electromagnets(EMs).By the means of systematic comparison,this paper studies the characteristics of PMG and EMG,and compares their advantages and disadvantages respectively,and grasps the internal laws of EMG,laying a theoretical and technical foundation for the EMG development of HTS maglev transportation system in the future.For this research,a HTS maglev measurement system was designed and constructed,which has high measurement accuracy,can realize synchronous measurement of levitation force and guidance force as the HTS bulk moving,and can measure the time relaxation and magnetic field strength in high precision.The system can achieve arbitrary direction,displacement,speed in three-dimensional space and realize complex curviline motion.The possible factors causing the error are eliminated in the design,and the precision calibration and error analysis are carried out.In this study,three different PMG specimens and one EMG specimens were designed and manufactured.Based on the force-measuring system,the basic properties of the specimens were measured,including levitation force,guidance force and time relaxation characteristics at different levitation gaps and operating speeds.For the comparative study,the same magnetic field trend and similar magnetic flux distribution of PMG and EMG were designed.In the analysis,the central magnetic flux density Bz and unit magnetic potential Fu were selected as evaluation indexes respectively.The effects of different magnetic field characteristics(such as different magnetic induction intensity components and variations)on maglev performance were studied by changing the excitation mode of the EM or changing the arrangement of PMs.The experimental results show that the magnetic levitation performance is related to the change rate and component of magnetic flux density,and the magnetic field structure.Moreover,the magnetic levitation characteristics of PMs and EMs are different obviously.The function,mechanical motion and software control of the measurement system in this paper are superior to any other HTS force-measuring system that can be found in the literature at present,which can provide a new idea for the design of similar devices with wider range of applications and higher precision in the future.In this paper,the magnetic levitation properties of PMG and EMG are compared,and the key magnetic factors affecting the levitation force are analyzed,including the gradient of Bz,Bx and Bz.The experimental results will be helpful to further study the performance of HTS maglev and provide meaningful data for the subsequent design of EMG.