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Permanent magnet motor development history
- Jan 24, 2019 -

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 made a compass using the magnetic properties of permanent magnet materials, and played a huge role in navigation and military fields. Its role has become one of the four great inventions in ancient China.

The world's first motor that emerged in the 1920s was a permanent magnet motor that generated an excitation field from a permanent magnet. However, the permanent magnet material used at that time was natural magnetite ore (Fe3O4), and the magnetic energy density was very low. The motor made of 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 conducted in-depth research on the mechanism, composition and manufacturing technology of permanent magnet materials, and successively discovered carbon steel and tungsten steel (maximum magnetic energy product is about 2.7 kJ/m3). ), a variety of permanent magnet materials such as cobalt steel (maximum magnetic energy product of about 7.2 kJ/m3). In particular, AlNiCo permanent magnets (maximum magnetic energy product up to 85 kJ/m3) appeared in the 1930s and ferrite permanent magnets (maximum magnetic energy accumulation up to 40 kJ/m3) appeared in the 1950s. Greatly improved, various miniature and small motors have used permanent magnet excitation. The power of permanent magnet motors is as small as several milliwatts and as large as several tens of kilowatts. It is widely used in military, industrial and agricultural production and daily life, and the output has increased dramatically. Correspondingly, during this period, breakthroughs have been made in the design theory, calculation methods, magnetization and manufacturing techniques of permanent magnet motors, and a set of analytical research methods represented by the permanent magnet working diagram method has been formed. However, the coercive force of AlNiCo permanent magnets is low (36-160 kA/m), and the residual magnetic 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 (collectively referred to as rare earth permanent magnets) were successively introduced, their high remanence density, high coercivity, high magnetic energy product and linear demagnetization curve. The excellent magnetic properties are particularly suitable for the manufacture of motors, thus making the development of permanent magnet motors a new historical period.

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