Development of permanent magnet motor and its application in various fields
Permanent magnet motor uses permanent magnet to generate the magnetic field of the motor, without excitation coil or excitation current, with high efficiency and simple structure, it is a 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.
Development history of permanent magnet motor
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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 magnet materials and apply them to practice. More than 2000 years ago, China made compass from the magnetic properties of permanent magnet materials, which played a great role in navigation, military and other fields, and became one of the four great inventions in ancient China.
In the 1920s, the world’s first motor was the permanent magnet motor which generated excitation magnetic field by permanent magnet. However, the permanent magnet material used at that time was natural magnetite (Fe3O4), and the magnetic energy density was very low. The motor made of it was huge, and it was soon replaced by electric excitation motor.
With the rapid development of all kinds of motors and the invention of current magnetizer, the mechanism, composition and manufacturing technology of permanent magnet materials have been deeply studied, and many kinds of permanent magnet materials have been found, such as carbon steel, tungsten steel (the maximum magnetic energy product is about 2.7 kJ / m3), cobalt steel (the maximum magnetic energy product is about 7.2 kJ / m3).
In particular, the alnico permanent magnet (the maximum energy product can reach 85 kJ / m3) appeared in the 1930s and the ferrite permanent magnet (the maximum energy product can reach 40 kJ / m3) appeared in the 1950s. The magnetic properties have been greatly improved, and various micro and small motors have used permanent magnet excitation. The power of permanent magnet motor is as small as several milliwatts, as large as tens of kilowatts. It has been widely used in military, industrial and agricultural production and daily life, and the output has increased dramatically. Accordingly, during this period, breakthroughs have been 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 the working diagram method of permanent magnet have been formed.
However, the coercivity of alnico permanent magnets is low (36-160 Ka / M), and the remanence density of ferrite permanent magnets is low (0.2-0.44 T), which limits their application in motor. Until the 1960s and 1980s, rare earth cobalt permanent magnet and neodymium iron boron permanent magnet (both referred to as rare earth permanent magnet) came out one after another. Their excellent magnetic properties of high remanence density, high coercivity, high magnetic energy product and linear demagnetization curve are especially suitable for manufacturing motor, which makes the development of permanent magnet motor enter a new historical period.
Characteristics and application of permanent magnet motor
Compared with the traditional electric excitation motor, the permanent magnet motor, especially the rare earth permanent magnet motor, has the advantages of simple structure and reliable operation; Small volume and light weight; Low loss and high efficiency; The shape and size of the motor can be flexible. Therefore, it is widely used in almost all fields of aerospace, national defense, industrial and agricultural production and daily life. The following introduces the main characteristics and main applications of several typical permanent magnet motors.
Compared with the traditional generator, the rare earth permanent magnet synchronous generator does not need collector ring and brush device, and has simple structure and reduces the failure rate. After using rare earth permanent magnet, the air gap flux density can be increased, the motor speed can be improved to the best value, and the power mass ratio can be improved. Rare earth permanent magnet generators are almost all used in modern aviation and aerospace. 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. The first 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 auxiliary exciter of large steam turbine generator. In the 1980s, China successfully developed the 40 KVA ~ 160 KVA rare earth permanent magnet auxiliary exciter with the largest capacity in the world. After being equipped with 200 MW ~ 600 MW steam turbine generator, the reliability of power station operation is greatly improved.
At present, the small generator driven by internal combustion engine for independent power supply, permanent magnet generator for vehicle and small permanent magnet wind generator directly driven by wind wheel are gradually promoted.
The important role of permanent magnet motor in various application fields
Energy saving rare earth permanent magnet motors take consumption as the main object, such as textile and chemical fiber industry rare earth permanent magnet synchronous motor, petroleum, mining, rare earth permanent magnet synchronous motor in coal mine transportation machinery, rare earth permanent magnet synchronous motor drives all kinds of pumps and fans.
All kinds of rare earth permanent magnet motors are used by all kinds of vehicles (cars, motorcycles, trains), and rare earth permanent magnet motors are a big market. According to statistics, about 70% of the vehicle used rare earth permanent magnet motor. Luxury cars have more than 70 sets of motors for various applications. As 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, they will continue to be ferrite in the future. SM co sintered magnet is still used in ignition coil, driving device and sensor. In addition, auto parts, as a kind of environment-friendly (EV) and hybrid electric vehicle (HEV), can not be ignored.
Rare earth permanent magnet motor AC servo system is an electronic, high-performance, speed control system of Mechatronics machinery. The system is a self-control permanent magnet synchronous motor. The system is used in the development of CNC machine tools and flexible manufacturing technology; Also used in electric vehicles, rather than traditional thermal vehicles, vehicle emissions are free. Rare earth permanent magnet motor is a high-tech industry with a bright future.
The new field is mainly for the support of new air-conditioning and refrigerator low-power rare earth permanent magnet synchronous motor variable frequency speed control system, for various kinds of rare earth permanent magnet DC micro motor wireless electric tools, rare earth permanent magnet brushless DC motor is the instrument of different power. This kind of motor is also in great demand.
The rare earth permanent magnet materials, which are superior in aerospace applications, are very suitable for Aeroengine applications. Although there are some applications of rare earth permanent magnet motor in the air (such as generator voltage and short circuit protection), experts at home and abroad agree that rare earth permanent magnet motor is an important development direction of the new generation of aero-engine.
Ferrite permanent magnet motor, especially micro permanent magnet DC motor, has been widely used because of its simple structure, low quality and low total cost. 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 saving operation cost.
In some cases, such as the voice coil motor of computer disk drive, the performance is improved, the volume and mass are significantly reduced, and the total cost is reduced. In the design, it is necessary to compare the performance and price according to the specific application situation and requirements, and to innovate the structure technology and optimize the design to reduce the cost.
Source: China Permanent Magnet Manufacturer – www.rizinia.com