The permanent magnet motor uses permanent magnets to generate the magnetic field of the motor, does not require excitation coils or excitation current, has high efficiency and simple structure, and 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 motors will become more extensive.
The development history of permanent magnet motor
The development of permanent magnet motors is closely related to the development of permanent magnet materials. my country is the first country in the world to discover the magnetic properties of permanent magnet materials and apply them to practice. More than two thousand years ago, our country used the magnetic properties of permanent magnet materials to make a compass, which has played a huge role in navigation, military and other fields. It has become one of the four great inventions in ancient my country.
The world’s first motor that appeared in the 1820s was a permanent magnet motor with an excitation magnetic field generated by a permanent magnet. However, the permanent magnet material used at that time was natural magnetite (Fe3O4), which has a very low magnetic energy density, and the motor made from it was bulky, and was soon replaced by an electric excitation motor.
With the rapid development of various motors and the invention of current magnetizers, people have carried out 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 (the maximum magnetic energy product is about 7.2 kJ/m3) and other permanent magnet materials.
In particular, the AlNiCo permanent magnets that appeared in the 1930s (the maximum magnetic energy product can reach 85 kJ/m3) and the ferrite permanent magnets that appeared in the 1950s (the maximum magnetic energy product can now reach 40 kJ/m3) have various magnetic properties. With the great improvement, 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. They are widely used in military, industrial and agricultural production and daily life, and the 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 working diagram of permanent magnets has been formed.
However, the coercivity 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 in motors. Until the 1960s and 1980s, rare earth cobalt permanent magnets and neodymium iron boron permanent magnets (both collectively referred to as rare earth permanent magnets) came out one after another, with their high remanence density, high coercivity, high magnetic energy product and linear demagnetization curve. The excellent magnetic properties of the permanent magnet motor are especially suitable for the manufacture of electric motors, so that the development of permanent magnet motors has entered a new historical period.
Characteristics and applications of permanent magnet motors
Compared with traditional electric excitation motors, permanent magnet motors, especially rare-earth permanent magnet motors, have obvious advantages such as simple structure and reliable operation; small size and light weight; low loss and high efficiency; the shape and size of the motor can be flexible and diverse. . Therefore, the application range is extremely wide, covering almost all fields of aerospace, national defense, industrial and agricultural production and daily life. The main features of several typical permanent magnet motors and their main applications are described below.
Compared with the traditional generator, the permanent magnet synchronous generator of rare earth permanent magnet generator does not need a collector ring and a brush device, and has a simple structure and reduces the failure rate. The use of rare earth permanent magnets can also increase the air gap magnetic 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. 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.
The permanent magnet generator is also used as the auxiliary exciter of the large-scale steam turbine generator. In the 1980s, my country successfully developed the 40 kVA~160 kVA rare earth permanent magnet auxiliary exciter with the largest capacity in the world at that time. Greatly improve the reliability of power station operation.
At present, small generators driven by internal combustion engines for independent power sources, permanent magnet generators for vehicles, and small permanent magnet wind generators directly driven by wind turbines are being gradually promoted.
The important role of permanent magnet motors in various application fields
1 Energy-saving rare earth permanent magnet motors are mainly used for consumption, such as rare earth permanent magnet synchronous motors for textile and chemical fiber industries, petroleum, 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 rare earth permanent magnet motors are used in vehicles. For luxury cars, there are more than 70 sets of motors for various applications. Since the requirements of various automobile 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. Ignition coils, drives, and sensors still use Sm-Co sintered magnets. In addition, auto parts, but also electric vehicles can not be ignored, as an environmentally friendly (EV) and hybrid electric vehicles (HEV).
3 Rare earth permanent magnet motor AC servo system A set of electromechanical integration machinery with electronic, high performance and speed control system. 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; and also in electric vehicles, rather than traditional thermally powered vehicles, for the 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 the low-power rare earth permanent magnet synchronous motor variable frequency speed control system for new air conditioners and refrigerators, wireless electric gadgets for various rare earth permanent magnet DC micro motors, rare earth permanent magnet brushless DC motors are Instruments 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 for a new generation of aero-engines.
cost issue
Ferrite permanent magnet motors, especially miniature permanent magnet DC motors, have been widely used because of their simple structure and process, reduced mass, and generally lower total cost than electric excitation motors. Since rare earth permanent magnets are still relatively expensive at present, the cost of rare earth permanent magnet motors is generally higher than that of electric excitation motors, which needs to be compensated by its high performance and operating cost savings.
In some occasions, such as voice coil motors of computer disk drives, the performance of NdFeB permanent magnets 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 use occasions and requirements to decide the choice, but also to innovate the structural process and design optimization to reduce the cost.
Post time:
Jun-20-2022
