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What parameters of permanent magnet materials affect the performance of permanent magnet motors?
The development of permanent magnet motors is closely related to the development of permanent magnet materials. The world's first motor that appeared in the 1820s was a permanent magnet motor, which could generate an excitation magnetic field from a permanent magnet. But the permanent magnet material used at that time was natural magnetite (Fe3O4), which has a very low magnetic energy density, and the motors made of natural magnetite (Fe3O4) were bulky and were soon replaced by electric excitation motors.
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 2.7kJ/m3 ), cobalt steel (maximum energy product is about 7.2kJ/m3) and many other permanent magnet materials. In particular, the magnetic properties of AlNiCo permanent magnets (maximum energy product up to 85kJ/m3) that appeared in the 1930s and ferrite permanent magnets (maximum energy product up to 40kJ/m3) that appeared in the 1950s were greatly improved. Therefore, various micro and small motors use permanent magnets for excitation. 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 its application in motors.
Until the 1960s and 1980s, samarium cobalt permanent magnets and neodymium iron boron permanent magnets came out one after another. Their high remanence, high coercivity, high energy product and excellent linear demagnetization curve magnetism are especially suitable for manufacturing motors, making permanent The development of magneto has entered a new historical period.
1. Remanence
For DC motors, under the same winding parameters and test conditions, the higher the remanence, the lower the no-load speed, the lower the no-load current, the greater the maximum torque, and the higher the efficiency at the highest efficiency point. In practical tests, no-load speed and maximum torque are usually used to determine the remanence standard of permanent magnet materials. For the same winding parameters and electrical parameters, the higher the remanence, the lower the no-load speed, and the lower the no-load current. The reason is that the running motor generates enough reverse induced voltage at a relatively low speed, thereby reducing the The algebraic sum of the electromotive forces applied to the windings.
2. Coercivity
During the operation of the motor, it is often affected by temperature and reverse demagnetization. From the perspective of motor design, the larger the coercive force, the smaller the thickness direction of the permanent magnet material, and the smaller the coercive force, the greater the thickness direction of the permanent magnet material.
3. The flatness of the efficiency curve
Flatness only affects the flatness of the motor performance test efficiency curve. Although the flatness of the motor efficiency curve has not been listed as an important indicator standard, it is very important for the continuous driving distance of the motor under natural road conditions. Due to different road conditions, the motor cannot always work at the maximum efficiency point. This is one of the reasons why some motors have a lower maximum efficiency but run longer distances. A good motor should not only have high maximum efficiency, but the efficiency curve should be as flat as possible, with a lower slope of efficiency reduction the better. This will gradually become an important criterion as the motor market, technology and standards mature.
4. Performance consistency
Inconsistent remanence: Even some particularly high performance single remanence is not good because the magnetic flux of each unidirectional field segment is inconsistent, resulting in asymmetric torque and vibration. Inconsistent coercivity: In particular, the coercivity of individual products is too low, which is prone to reverse demagnetization, resulting in inconsistent magnet flux and motor vibration. This effect is more significant for brushless motors.
in conclusion
The motor uses permanent magnets to generate the magnetic field of the motor, it does not require excitation coil or excitation current, it has high efficiency and simple structure, and it is a good energy-saving motor. Compared with the traditional electric excitation motor, the permanent magnet motor has obvious advantages such as simple structure, reliable operation, small size, light weight, low loss and high efficiency. The application range of permanent magnet motors is extremely wide, covering almost all fields of aerospace, national defense, industrial and agricultural production and daily life. With the development of high-performance permanent magnet materials and the rapid development of control technology, the application of permanent magnet motors will be more extensive.
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