Development of permanent magnet screw air compressor and its application in various fields

Permanent magnet motor uses permanent magnet to generate the magnetic field of the motor, without excitation coil nor excitation current, high efficiency and simple structure, is a good energy-saving motor, with the advent of high-performance permanent magnet materials and the rapid development of control technology. Permanent magnet motors will become more widely used.

The development history of permanent magnet motor

The development of permanent magnet motor is closely related to the development of permanent magnet materials. China is the first country in the world to discover the magnetic properties of permanent magnetic materials and apply them to practice. More than two thousand years ago, China made the compass by using the magnetic properties of permanent magnetic materials, which played a huge role in navigation, military and other fields and became one of the four great inventions in ancient China.

In the 1820s, a motor appeared in the world is a permanent magnet motor generated by a permanent magnet field. But the permanent magnet material used at that time is natural magnetite ore (Fe3O4), magnetic energy density is very low, with it made of large motor volume, soon replaced by electric excitation motor.

With the rapid development of various motors and the invention of current magnetizer, people have carried out in-depth research on the mechanism, composition and manufacturing technology of permanent magnet materials, and have discovered carbon steel, tungsten steel (magnetic energy product of about 2.7 kJ/m3), cobalt steel (magnetic energy product of about 7.2 kJ/m3) and other permanent magnet materials.

In particular, the aluminium-nickel-cobalt permanent magnet (magnetic energy product can reach 85 kJ/m3) and ferrite permanent magnet (magnetic energy product can reach 40 kJ/m3) appeared in the 1930s, and the magnetic properties have been greatly improved, and all kinds of micro and small motors have used permanent magnet excitation. The power of permanent magnet motor is small to several milliwatts and large to dozens of kilowatts. It has been widely used in military, industrial and agricultural production and daily life, and its output has increased sharply. Accordingly, during this period, breakthroughs were made in the design theory, calculation method, magnetization and manufacturing technology of permanent magnet motor, and a set of analysis and research methods represented by permanent magnet working diagram solution were formed.

However, the low coercivity of al-Ni-Co permanent magnets (36 ~ 160 kA/m) and the low remanence density of ferrite permanent magnets (0.2 ~ 0.44 T) limit their application in motors. Until the 80 s and 1960 s, cobalt rare earth permanent magnet and nd-fe-b (both a general designation of rare earth permanent magnet) thereafter, density of their high remanence, high coercive force, high magnetic energy product and excellent magnetic linear demagnetization curve can particularly suitable for manufacturing motor, so that the development of permanent magnet motor to enter a new historical period.

Characteristics and application of permanent magnet motor

Compared with traditional electric excitation motor, permanent magnet motor, especially rare earth permanent magnet motor has simple structure and reliable operation. Small size, light weight; Small loss, high efficiency; The shape and size of the motor can be flexible and varied, etc. Therefore, the application range is extremely wide, almost throughout the aerospace, national defense, industrial and agricultural production and daily life of each field. The following describes the main characteristics of several typical permanent magnet motors and their main applications.

Rare earth permanent magnet generator Permanent magnet synchronous generator does not need collector ring and brush device compared with traditional generator, has simple structure and reduces the failure rate. After using rare earth permanent magnet, the air gap density can be increased, and the motor speed can be increased to the value, and the power mass ratio can be improved. Modern aviation and space generators almost all use rare earth permanent magnet generators. Its typical products are 150 kVA 14-pole 12 000 r/min ~ 21 000 r/min and 100 kVA 60 000 r/min rare earth cobalt permanent magnet synchronous generators manufactured by GENERAL Electric Company of the United States. A rare earth permanent magnet motor developed in China is a 3 kW 20 000 r/min permanent magnet generator.

Permanent magnet generator is also used as the secondary exciter of large turbo-generator. In the 1980s, China successfully developed the world capacity of 40 kVA ~ 160 kVA rare earth permanent magnet secondary exciter, which is equipped with 200 MW ~ 600 MW turbo-generator to greatly improve the reliability of power station operation.

At present, internal combustion engine driven small generator for independent power supply, permanent magnet generator for vehicle, and small permanent magnet wind generator directly driven by wind wheel are gradually being popularized.

The important role of permanent magnet motor in various application fields

The energy-saving rare earth permanent magnet motor is mainly targeted at consumption, such as rare earth permanent magnet synchronous motor used in textile and chemical fiber industry, petroleum, mining, rare earth permanent magnet synchronous motor in coal mine transportation machinery, rare earth permanent magnet synchronous motor drives various pumps and fans.

All kinds of rare earth permanent magnet motors are used by various types of vehicles (cars, motorcycles, trains), rare earth permanent magnet motors are the largest market. According to statistics, about 70% of rare earth permanent magnet motors are used in cars. The limousine has more than 70 sets of motors for various applications. Because the requirements of various automobile motors are different, the choice of permanent magnet materials is not the same. Motor magnet used in air conditioning, fans, electric Windows, from the point of view of price, the future will continue to ferrite advantage. Sm-co sintered magnets are still used for ignition coils, drives and sensors. In addition, auto parts, also electric vehicles can not be ignored, as a kind of environmental protection (EV) and hybrid electric vehicle (HEV).

Rare earth permanent magnet motor AC servo system a set of electronic, high performance, speed control system of mechatronics machinery. The system is a self - controlled permanent magnet synchronous motor. The system is used in the development of CNC machine tools, flexible manufacturing technology; Also used in electric vehicles, rather than traditional thermal vehicles, vehicle emissions are free. Rare earth permanent magnet motor is a promising high-tech industry.

4 The new field is mainly for the new air conditioning and refrigerator low-power rare earth permanent magnet synchronous motor frequency control system support, used in all kinds of rare earth permanent magnet DC micromotor wireless electric small tools, rare earth permanent magnet brushless DC motor is an instrument with different power. This kind of motor is also in great demand.

5 in aerospace applications for the advantage of rare earth permanent magnet materials, so that it is very suitable for aero-engine applications. Although there are some applications for rare-earth permanent magnet motors in air (such as generator voltage and short circuit protection, etc.), experts at home and abroad agree that rare-earth permanent magnet motors are an important development direction for the next generation of aero engines.

Cost problem

Ferrite permanent magnet motor, especially micro permanent magnet DC motor, because of its simple structure and process, quality reduction, the total cost is generally lower than the electric excitation motor, so it has been widely used. Because the price of rare earth permanent magnet is still relatively expensive, the cost of rare earth permanent magnet motor is generally higher than that of electric excitation motor, which needs to be compensated by its high performance and operation cost savings.

In some cases, such as computer disk drive voice coil motor, using Ndfeb permanent magnet performance improved, volume and mass significantly reduced, the total cost is reduced. In the design of both according to the specific use of the occasion and requirements, performance, price after the comparison of the decision to choose, but also to carry out the innovation of the structure and design optimization to reduce the cost.

Source: network -- air compressor network

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