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Permanent Magnet DC Motor

 The use of permanent magnet DC motor field excitation. Motor due to no separate excitation system, and thus the small size, light weight, simple structure and high efficiency. Most of the miniature DC motors are permanent magnet. Permanent magnet DC motor starting and operating characteristics and excited, and excited DC motor is basically the same. In the structure in addition to the stator field winding, armature, brushes, commutator and other components are the same as the current excitation DC Smaller coercivity of Alnico permanent magnets require a longer effective length in order to generate enough magnetomotive force, so often used a cylindrical structure.In order to avoid armature reaction magnetic field of permanent magnet, permanent magnet motor can be added to the soft iron pole piece when the motor load, this structure can be generated by the armature current armature reaction flux through the pole shoe withoutinto the permanent magnet flux of constant work to ensure and improve the utilization of the permanent magnet, but also conducive to the commutation. Pole shoe and the permanent magnet should fit closely with higher technology.

Using ferrite excitation, the tile block structure can be used to tile with a pole piece structure and the cylindrical structure. The former applies to anisotropic materials, magnet high utilization rate of simple structure, ease of mass production, but the air gap flux density is low. Tile with a pole piece structure can improve the air gap flux density, but the structure is more complex. Cylindrical structure is simple, ease of production, material utilization is low, is not conducive to the commutation Rare earth permanent magnet excitation, the magnetic structure similar to the tile type. But its coercivity pole radial dimensions can be further reduced