I. Development and Status of Magnetic Levitation Technology The development of magnetic levitation technology began in the last century. Eamshanws found that diamagnetic objects can be freely suspended in a magnetic field. This phenomenon was strictly proved in theory by Braunbeck in 1939, but its practical application research was not widely carried out until the last twenty years. In recent years, magnetic levitation technology has developed rapidly and been widely used. Due to the development of modern science and technology such as sensors, control technology (especially digital control technology), low temperature and high temperature superconducting technology, magnetic levitation technology has risen rapidly, and many countries have invested a lot of manpower and material resources in research. Because of its non-contact characteristics, magnetic levitation can avoid friction and wear between objects, prolong the service life of equipment and improve the operating conditions of equipment, so it has broad application prospects in transportation, metallurgy, machinery, electrical appliances, materials and so on. Second, the application of magnetic levitation The application of magnetic levitation technology ranges from high-speed magnetic levitation bearings to high-speed suspended trains, as well as wind tunnel magnetic levitation models with air gaps. The research of magnetic bearing is a very active research direction abroad, and the typical object is the magnetic bearing of generator (also called magnetic bearing). Active magnetic bearing (AMB) is widely used in aviation, aerospace, nuclear reactor, vacuum pump, ultra-clean environment, flywheel energy storage and other fields because of its advantages of no mechanical wear, no noise, long service life and no lubricating oil pollution. Bearingless motor is a new research direction in recent years. It integrates magnetic bearing and motor, has self-suspension and driving ability, does not need any independent bearing support, and has the characteristics of small volume, high critical speed and so on. It is more suitable for ultra-high speed operation occasions and small or even ultra-small structures. Since the mid-1990s, research has been carried out abroad, and various types of permanent magnet synchronous magnetic levitation motors, switched reluctance magnetic levitation motors and induction magnetic levitation motors have appeared one after another. Among them, the induction magnetic levitation motor has the advantages of simple structure, low cost, high reliability, uniform air gap and easy speed increase under weak magnetic field, and it is one of the most promising schemes. A traditional motor consists of a stator and a rotor, which are connected by mechanical bearings. There is mechanical friction in the process of rotor movement, which increases the friction resistance of the rotor, makes the moving parts wear, produces mechanical vibration and noise, makes the moving parts heat, makes the lubrication performance worse, and even makes the air gap of the motor uneven, the winding heats up, and the temperature rise increases, thus reducing the efficiency of the motor and ultimately shortening the service life of the motor. The magnetic suspension motor levitates the rotor by using the principle of "like repulsion and opposite attraction" between the excitation magnetic fields of the stator and the rotor, and at the same time generates propulsion to drive the rotor to move in the suspended state. The research of magnetic levitation motor has been paid more and more attention, and there are some successful reports. For example, magnetic levitation motor is used in the field of life science, and centrifugal and vibrating magnetic levitation artificial heart blood pumps have been successfully developed abroad. The magnetic suspension structure without mechanical contact not only has high efficiency, but also can prevent hemolysis, coagulation and thrombosis caused by blood cell injury. The research of magnetic suspension blood pump can not only alleviate the pain of cardiovascular patients and improve their quality of life, but also has far-reaching significance to human life. Three. Working schematic diagram of magnetic suspension ball control system 1 functional schematic diagram of magnetic suspension ball control system electromagnetic force is generated by introducing a certain current into electromagnet winding. As long as the current in the electromagnet winding is controlled to balance the generated electromagnetic force with the weight of the steel ball, the steel ball can be suspended in the air and in an unstable equilibrium state. This is because the electromagnetic force between electromagnet and steel ball is inversely proportional to the distance between them. As long as the equilibrium state is slightly disturbed, the steel ball will fall or be attracted by the electromagnet, so closed-loop control must be realized. The measuring device composed of electric light source and sensor is used to measure the change of distance y between steel ball and electromagnet. When the steel ball is disturbed and the distance between the steel ball and the electromagnet increases, the control current in the control winding of the electromagnet increases accordingly, and the steel ball is sucked back to the equilibrium state, and vice versa. What is discussed above is the control of the steel ball in the vertical direction. In order to make the steel ball stably suspended in the air, the steel ball should also have a certain stable range in the horizontal direction. In order to solve this problem, the end of the electromagnet core pointing to the steel ball is tapered, as shown in figure 1. When the steel ball deviates from the central equilibrium position in the horizontal direction, the electromagnetic force points to the hair direction of the steel ball surface again. This force can be decomposed into vertical and horizontal components, and the horizontal component returns the steel ball to its original central equilibrium position. Fourthly, the magnetic levitation ball controller is designed theoretically. Firstly, the mathematical model of steel ball is established: by selecting model parameters and analyzing the performance of magnetic suspension ball control system, the mathematical model of the system is finally established. Therefore, the transfer function of the modified magnetic levitation ball controller is as follows: 5. The performance analysis of the transfer function G(s) is shown in Figure 2. It can be seen that the bandwidth of the system is wider and the cut-off frequency is larger, so the speed of the control system is faster. The smaller the phase angle margin, the better the damping characteristics of the system and the more stable the dynamic process. High frequency slope, strong anti-interference ability of control system, and stable suspension of steel ball.

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