| Low-speed maglev train based on normal-conducting electromagnetic suspension?EMS?technology is developing rapidly nowadays,it has the advantages of no touching,small noise as well as low abrasion,and has not only been in commercial use,but also shown wide prospect in the field of urban public transportation.However,as the normal-conducting coil has resistance and its current-carrying capacity is limited,the normal-conducting EMS system faces the disadvantages of magnetic field saturation,magnet heating and restricted carrying capacity,which are assignable causes for the restriction of the EMS system.With the improvement of the preparation technology and overall performance of high temperature superconducting?HTS?material,the appli-cation technology of the magnet based on superconducting materials is developing dramatically,and its range of application is expanding,thus making superconducting maglev transportation system to be a concerned research project.This article designed and constructed an experimental platform for EMS control system based on such research background,which used HTS-EMS scheme on account of comparing the advantages and disadvantages of four kinds of superconducting suspension system.The article introduces the related structure design,system form,electromagnetic characteristics simulation and experiment test results to the platform,and verified the feasibility of using superconducting tape to replace normal-conducting wire in the application of suspension control system.Besides,this work increased the exciting current in the superconducting coil to the level of engineering application in the temperature section of liquid nitrogen for the first time.As the superconducting suspension system is in the steady working state,its exciting current is a special alternating-direct current,i.e.,adding an alternating current component to the steady direct current component,while the research of the loss related to above-mentioned state for superconducting system is rare.In this case,the article combined theoretical estimation,simulation analysis and experiment measurement together,and carried out systematical research on the loss of alternating-direct current in superconducting suspension system in the aspects of a single tape and superconducting coil.The results of simulation analysis and experiment measurement show that the loss of superconducting suspension system is low,as the order of its magnitude is under 10-3W/m and the energy consumption is 1/10 compared to normal-conducting system in the same working condition.In the view of control system,compared with the normal-conducting system,the superconducting system has its own specialities;such as its resistance is zero,critical parameters should not be exceeded.Furthermore,as the limitation of critical current and loss characteristics,the amplitude and frequency of the control current in supercon-ducting coil is unsuitable to be so large,that is,the constrained control problem in superconducting system should be considered.So,the article built a mathematical model of the superconducting suspension system,analyzed the instability of its open-loop system and introduced the design procedures of two normal PID controllers.In addition,aiming at the constrained problem in superconducting suspension control system,the article presented a constrained internal model control algorithm based on feedback compensation and designed its inner-loop optimal subduer from the view of reducing loss.Finally,the effectiveness is verified by simulation and experiment.HTS tape has a great demand for the detection of its internal small flaw and the measurement of alternating-current magnetization loss,while superconducting quantum interference device?SQUID?has a unique advantage in such two fields.The article introduced the basic principle of SQUID and its application speciality,carried out a research on the voltage-flux characteristics of radio-frequency SQUID?rf SQUID?and simplified it using harmonic analysis method.At last,by the combination of the theoretical derivation and experimental test,it is verified that the harmonic analysis method can not only describe the output characteristic of rf SQUID in sufficient accuracy,but also bring enormous convenience in finding the optimum working point and filtrating the optimum working condition during practical application.As a whole,this article carried out comprehensive research to the superconducting electromagnetic suspension system from various angles,for instance,structure design,system form,material characteristics,loss analysis and constrained control,which has a great significance with respect to the construction of new type superconducting maglev transportation system in future and also has an effect of improving the performance of existing maglev train as well as decreasing its energy consumption. |
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