In recent years, permanent magnet materials have developed rapidly, and there are many kinds of permanent magnet materials.
The most common types are ferrite permanent magnets, Al-Ni-Co permanent magnets, and Nd-Fe-B rare earth permanent magnets.
The outstanding advantage of ferrite permanent magnet material is that it does not contain rare earth elements.
And cobalt, nickel, and other precious metals have low prices, a simple manufacturing process, high coercivity, strong anti-magnetic ability, low density, and lightweight. However, the ferrite permanent magnet material is hard and brittle, and it can not be processed electronically. The motor produced is of low power and low efficiency.
Aluminum-nickel-cobalt permanent magnets are characterized by a low-temperature coefficient, high residual magnetic induction, and low coercivity. They are easy to be magnetized and demagnetize but contain cobalt, which is a precious metal, so the price is very high.
Neodymium rare earth permanent magnets have become the main force of permanent magnets because of their excellent magnetic properties, and their magnetic properties far exceed those of ferrite, Al-Ni-Co, and other magnetic materials. Up to now, the residual magnetic induction strength of the new generation of NdFeB permanent magnets has reached 147 T at room temperature.
The maximum intrinsic coercivity sclera can exceed 1 000 kA/m, and the maximum magnetic energy product (BH) can reach 398 kj/m, which is 5-12 times of ferrite permanent magnets, and 3-10 times of Al-Ni-Co permanent magnets. The disadvantage of Nd-Fe-B permanent magnet material is that Curie temperature is low, the magnetic loss is large, and thermal stability, corrosion resistance, and oxidation resistance are poor when it is used at high temperatures. Therefore, the surface of the Nd-Fe-B permanent magnet should be coated according to its working environment to meet the requirements of the vehicle environment.
The magnetic and mechanical properties of Nd-Fe-B rare earth permanent magnets are obviously higher than those of ferrites and Al-Ni-Co permanent magnets.
The Performance of Permanent Magnet Synchronous Drive Motor
A permanent magnet synchronous drive motor (PMSM) can be divided into the surface type and built-in type by installing permanent magnet steel on the rotor. Surface type can be divided into the surface-mounted type and embedded type. According to the excitation direction of permanent magnet steel, the built-in type can be divided into radial type rotor structure, tangential type rotor structure and permanent magnet rotor structure with a hybrid magnetic circuit integrating radial and tangential direction.
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