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Development of permanent magnet motor
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Development of permanent magnet motor is closely related to the development of permanent magnetic material. Our country is in the world the earliest found permanent magnetic properties of magnetic materials and the application of it in the state of the practice, two thousand years ago, permanent magnetic properties of magnetic materials made of the compass by China, in the field of navigation, military play great role, and become one of the four great inventions of ancient China.

The 20 time in nineteenth Century, the first motor is the permanent magnet motor which is generated by the permanent magnet. But when the permanent magnetic material is natural magnetite (Fe3O4), the magnetic energy density is very low, and use it to make the motor bulky, was soon replaced by electrical excitation motor.

With the invention of the rapid development of all kinds of motor and magnetizing current device, people of permanent mechanism of magnetic material, composition and manufacturing technology has conducted the thorough research had been found carbon steel, tungsten steel (maximum energy product of about 2.7 kJ / m3), cobalt (maximum energy product of about 7.2 kJ / M3) and so on the many kinds of permanent magnetic materials. Especially the 30 years of the 20th century aluminum nickel cobalt permanent magnet (maximum energy product can reach 85 kJ / m3) and 50's of ferrite permanent magnet (maximum energy product is now up to 40 kJ / m3), magnetic properties have been greatly improved, a variety of micro and small motor and have to use permanent magnet excitation. Permanent magnet motor power ranging from a few milliwatts, to tens of kilowatts, in military, industry, agriculture and daily life are widely used, production increased dramatically. Accordingly, this period in permanent magnet motor design theory, calculation method, magnetization and manufacturing technology have achieved breakthrough progress, lead to the formation of a permanent magnet graphic method is represented by a set of analysis method.

But low aluminum nickel cobalt permanent magnetic coercivity (36 ~ 160 kA / M), ferrite permanent magnetic remanence density is not high (0.2 ~ 0.44 T), limiting the scope of their application in the motor. Until the 1960s and 1980s, cobalt rare earth permanent magnet and the neodymium iron boron permanent magnet (both referred to as rare earth permanent magnet) have come out in succession, the excellent magnetic properties of their high remanent flux density and high coercivity, high magnetic energy product and linear demagnetization curve is especially suitable for motor manufacturing, to enable a permanent magnet motor development entered a new historical period. The development of rare earth permanent magnetic material is divided into three stages. Found by Professor of American K.J.Strnat 1967 samarium cobalt permanent magnet for the first generation of rare earth permanent magnet, its chemical formula can be expressed as the rco5, referred to as 1:5 type rare earth permanent magnet, the maximum magnetic energy product more than 199 kJ / m3 (25mg, OE). In 1973 and the emergence of magnetic can better the second generation of rare earth permanent magnet, the chemical formula for r2co17, referred to as 2:17 type rare earth permanent magnet, the maximum magnetic energy product reached 258.6 kJ / m3 (32. 5mg, OE). 1983 Japan Sumitomo Special Metals Corporation and general motors of the United States respective development success NdFeB NdFeB permanent magnet, called the third generation rare earth permanent magnet. Because neodymium iron boron permanent magnetic energy is higher than that of the other permanent magnet materials, the price is lower than that of the permanent magnetic material of rare earth cobalt. In rare earth ore content of neodymium is ten times the SM, but not including strategic material of cobalt, which caused great concern at home and abroad the magnetic field and electric field, have invested a lot of manpower and material resources to carry out research and development. Is currently studying the new high performance permanent magnetic materials, such as samarium iron nitrogen permanent magnet, nano composite rare earth permanent magnet, hope to have new and greater breakthrough.

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