Magnetic bearing is a kind of support form that supports load or suspended rotor by magnetic force. In recent years, this kind of bearing has developed rapidly, especially in the application of high speed, low friction, high (low) temperature and vacuum environment. Compared with other support forms, magnetic bearing has its unique advantages and has great development prospects.
The electromagnet is arranged in the form of radial bearing and axial bearing, and provides magnetic tension to lift the rotating shaft of the ina bearing device of the rotating machine. The current in the electromagnet is regulated by an accurate digital control cabinet to provide magnetic force to cope with the change of external load at any time, so as to keep the rotating shaft well centered.
In this way, the rotating shaft is lifted without contact, and the stiffness and damping of the bearing can be adjusted by a digital control cabinet. These characteristics enhance the performance of high-speed rotating machine and make the equipment have the remarkable characteristics of high reliability and low energy consumption.
Magnetic bearings are classified according to their control mode, magnetic energy source and structural form. In addition, it can also be divided into permanent magnet type, electromagnet type and permanent magnet electromagnet hybrid type according to the type of magnetic field.
It can also be divided into suction type and repulsion type according to the type of bearing suspension force. Superconducting magnetic bearings are also divided into low-temperature superconducting and high-temperature superconducting. There are also some special restrictions between different types in the above categories, which should be paid special attention to:
① Permanent magnet bearings can only be passive (passive), while passive bearings cannot be stable in three directions, and active bearings should be used in at least one direction.
② DC excited bearings can only be active type (active type).
③ Pure electromagnet bearing can only be 5-DOF control bearing, which has large volume, mass and power consumption.
④ Repulsive magnetic bearing is rarely used because of its low magnetic utilization and complex structure compared with suction type.
(1) No contact, no wear and no lubrication: when the magnetic bearing works, it is in a suspended state, there is no contact between the relative moving surfaces, and there is no mechanical friction and contact fatigue, which solves the problems of component loss and replacement of the unit. At the same time, a series of devices such as lubrication system are omitted, which saves space and does not have the problem of environmental pollution caused by the above devices.
(2) Low vibration, low noise and low power consumption: the magnetic bearing rotor avoids the large vibration and high DB noise caused by the contact collision of the traditional bearing during operation, improves the stability, reduces the maintenance cost and prolongs its service life. At the same time, the low power consumption of the magnetic bearing is only 6% ~ 25% of that of the traditional mechanical bearing. When the speed is 10000 R / min, its power consumption is only about 15% of that of mechanical bearings.
(3) High speed, high precision and high reliability: the rotor is allowed to rotate at a high speed. Its speed is mainly limited by material strength. It can work under supercritical conditions and hundreds of thousands of revolutions per minute. Moreover, the rotation accuracy of the rotor has reached micron level or even higher, which is far from the speed and accuracy of ordinary mechanical bearings, Moreover, the reliability of electronic components is much higher than that of traditional mechanical components.
(4) Controllability, on-line condition monitoring, testing and diagnosis: we can on-line control the static and dynamic performance of magnetic bearing. In fact, the system itself realizes the integration of working condition monitoring, fault diagnosis and on-line regulation.
With the continuous progress and development of science and technology, the performance of magnetic bearing is constantly improving. At the same time, the integration of electronic components also promotes its cost to be reduced year by year. Although magnetic levitation products have been successfully applied in many fields after years of exploration at home and abroad, there are still many problems in this technical field, such as the optimal design of control system and the dynamic characteristics of material rotor shafting. In order to improve the control method and strategy more effectively, it is necessary to focus on the dynamic characteristics of the rotor system while studying the control system, so as to achieve the ideal control of the complex rotor.
At present, most air-conditioning fans use mechanical bearings, and mechanical friction will occur between the fan spindle and the bearing, and the motor must overcome this friction to drive the fan blade to rotate. At the same time, it will cause the motor to heat and produce large amplitude vibration, which will reduce the service life of the fan. In order to realize the long-term operation of the fan, it is also necessary to improve the bearing lubrication system NTN bearing and cooling system. If magnetic suspension bearing is adopted, there is no mechanical friction between stator and rotor, the operation resistance of magnetic suspension bearing is zero and will not generate heat, so it eliminates the cooling system and lubrication system, reduces volume weight, improves reliability and service life, greatly reduces mechanical noise and mechanical vibration, and the vibration amplitude is far less than that of ordinary fan, The stability of the whole air conditioner is improved.
From the current domestic technical level of magnetic bearing, although the conditions for application in normal temperature equipment have been met, there are still two problems: on the one hand, it is difficult to realize the high-precision control of magnetic bearing rotor, resulting in poor system reliability and high failure rate; On the other hand, there is a lack of standardized product technology.
The realization of various advantages of the above magnetic bearing is based on a complex electronic control system. Because the cost of sensors, which constitute an important part of the system, is relatively high, coupled with the design cost of the control system, the overall cost is more than dozens of times that of ordinary mechanical bearings, which limits its application and promotion in industry to a great extent. In the long run, the energy consumption of traditional fans and pumps is high, which accounts for a large proportion in the whole energy consumption.
The long-time operation makes the power cost expensive, especially the maintenance and loss in the middle and later stage, resulting in the increase of energy consumption and expenditure of the whole system. The use of magnetic bearing can also save the configuration cost of some devices, such as lubrication system, gear transmission device, cooling system, etc. If converted into the cost of magnetic bearing, the number is considerable. In recent years, green energy conservation is not only the main melody of low-carbon economic development, but also the future development direction of the global fag bearing Electromechanical industry. The Chinese government has set the goal of building a resource-saving and environment-friendly society and comprehensively promote the development of a green and low-carbon economy.
Since 2012, the Ministry of finance, the national development and Reform Commission and the Ministry of industry and information technology have decided to include six categories of high-efficiency and energy-saving desktop computers and high-efficiency and energy-saving unit air conditioners in the field of consumer goods and fans, water pumps, compressors and transformer lamps in the field of industrial products in the coverage of the new round of energy-saving subsidies and the scope of national financial subsidies. This will be the first to open the curtain of the promotion and popularization of energy-saving air conditioning. Foreign countries have begun to apply maglev bearing technology to air conditioning.
For example, in the United States, the market share of Maglev central air conditioning has reached 10%, but in China, the market share of similar products is less than 1%, so it has a lot of profit space. As mentioned earlier, although the economic benefits and prospects of magnetic bearing are very good, due to the high price of its control system, how to reduce its cost has become one of the research hotspots in the current technical field.