The permanent magnet motor uses permanent magnets to generate the magnetic field of the motor. It does not require excitation coils or excitation current. It has high efficiency and simple structure. It is a very good energy-saving motor. With the advent of high-performance permanent magnet materials and the rapid development of control technology. The application of permanent magnet motor will become more extensive.


   The development history of permanent magnet motors. The development of permanent magnet motors 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 magnet materials and apply it to practice. More than 2,000 years ago, China used the magnetic properties of permanent magnet materials to make a compass, which played a huge role in navigation, military and other fields. It became one of the four great inventions in ancient China.

   The world's first motor that appeared in the 1920s was a permanent magnet motor that generated an excitation magnetic field from a permanent magnet. But the permanent magnet material used at that time was natural magnetite (Fe3O4), the magnetic energy density was very low, and the motor made of it was bulky, and was soon replaced by electric excitation motor.


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


   Especially the AlNiCo permanent magnets that appeared in the 1930s (the maximum energy product can reach 85 kJ/m3) and the ferrite permanent magnets that appeared in the 1950s (the maximum energy product can now reach 40 kJ/m3), the magnetic properties are excellent. It has been greatly improved, and various micro and small motors have used permanent magnet excitation. The power of permanent magnet motors is as small as a few milliwatts and as large as tens of kilowatts. It is widely used in military, industrial and agricultural production and daily life, and its output has increased sharply. Correspondingly, during this period, breakthroughs have been made in the design theory, calculation method, magnetization and manufacturing technology of permanent magnet motors, and a set of analysis and research methods represented by the diagrammatic method of permanent magnet working diagrams have been formed.


   However, the coercive force of AlNiCo permanent magnets is low (36-160 kA/m), and the remanence density of ferrite permanent magnets is not high (0.2-0.44 T), which limits their application range in motors. Until the 1960s and 1980s, rare earth cobalt permanent magnets and NdFeB permanent magnet (both collectively referred to as rare earth permanent magnets) came out one after another. Their high remanence density, high coercive force, high magnetic energy product and linear demagnetization curve. The excellent magnetic properties of the permanent magnet motor are especially suitable for the manufacture of motors, so that the development of permanent magnet motors has entered a new historical period.


   Characteristics and application of permanent magnet motor 

Compared with traditional electrically excited motors, permanent magnet motors, especially rare earth permanent magnet motors, have significant advantages such as simple structure, reliable operation, small size, light weight, low loss, high efficiency, and flexibility in the shape and size of the motor. Therefore, the application range is extremely wide, covering almost every field of aerospace, national defense, industrial and agricultural production and daily life. The main characteristics and main application occasions of several typical permanent magnet motors are introduced below.

   Compared with the traditional generator, the rare earth permanent magnet generator permanent magnet synchronous generator does not need the collector ring and the brush device, the structure is simple, and the failure rate is reduced. The use of rare earth permanent magnets can also increase the air gap flux density, increase the motor speed to the optimum value, and improve the power-to-mass ratio. Almost all generators used in contemporary aviation and aerospace use rare earth permanent magnet generators. It's 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. The first rare earth permanent magnet motor developed in China is a 3 kW 20 000 r/min permanent magnet generator.


   Permanent magnet generators are also used as auxiliary exciters for large turbogenerators. In the 1980s, my country successfully developed the 40 kVA-160 kVA rare earth permanent magnet auxiliary exciters with the largest capacity in the world at that time, equipped with 200 MW-600 MW turbogenerators. Greatly improves the reliability of power station operation.


   At present, internal combustion engine-driven small generators for independent power sources, permanent magnet generators for vehicles, and small permanent magnet wind turbines directly driven by wind wheels are being gradually promoted.


The important role of permanent magnet motors in various application fields

1. Energy-saving rare earth permanent magnet motors mainly target consumption, such as rare earth permanent magnet synchronous motors for textile and chemical fiber industries, petroleum and mining, rare earth permanent magnet synchronous motors in coal mine transportation machinery, rare earth permanent magnet synchronous motors to drive various pumps and fans.

2.  Various rare earth permanent magnet motors are used by various types of vehicles (cars, motorcycles, trains), and rare earth permanent magnet motors are the largest market. According to statistics, about 70% of vehicles use rare earth permanent magnet motors. For luxury cars, the motors for various applications have reached more than 70 sets. Since the requirements of various automotive motors are different, the selection of permanent magnet materials is different. Motor magnets are used in air conditioners, fans, and electric windows. From the perspective of price, the advantages of ferrite will continue in the future. Sm-Co sintered magnets are still used for ignition coils, drive devices, and sensors. In addition, auto parts are also not to be ignored for electric vehicles, as an environmentally friendly (EV) and hybrid electric vehicle (HEV).

3. Rare earth permanent magnet motor AC servo system A set of electronic, high-performance, speed control system mechatronics machinery. The system is a self-controlled permanent magnet synchronous motor body. The system is used in the development of CNC machine tools, flexible manufacturing technology; also, in electric vehicles instead of traditional thermodynamic vehicles, freedom of vehicle emissions. Rare earth permanent magnet motor is a promising high-tech industry.

4.  The new field is mainly for the support of frequency conversion and speed regulation system of small-power rare earth permanent magnet synchronous motors for new air conditioners and refrigerators, wireless electric gadgets for various rare earth permanent magnet DC micro motors, and rare earth permanent magnet brushless DC motors It is an instrument with different power. Such motors are also in great demand.

5. Rare earth permanent magnet materials with advantages in aerospace applications make them very suitable for aero-engine applications. Although there are some applications of rare earth permanent magnet motors in the 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 of the new generation of aircraft engines.




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