With the increasing performance of permanent magnet materials, rare earth permanent magnet materials are widely used in electrical fields. Using high-performance rare earth permanent magnet materials to make a motor, the structure does not require special electrical excitation system, which help to improve motor efficiency and power factor, and save energy, reduce the size of the motor.

Currently in the design of permanent magnet motor, the general assumption that a uniform distribution of the various parts of the magnetic field of the permanent magnet and the magnetic properties of the same batch of permanent magnets can be the same, while the need to use a permanent magnet demagnetization curve of permanent magnet at room temperature under suppliers, intrinsic connectivity magnetic parameters, residual magnetism, such as density and maximum energy product. However, since the manufacturing process and the level of the plant and other reasons, there is a temperature in each portion of a permanent magnet hereinafter actual performance differences and the performance of the same group of permanent magnets is different. The magnetic properties of the permanent magnet permanent magnet motor in normal operation can be closely related to the magnetic permanent magnet permanent magnet motor can directly determine whether reliable operation. When the permanent magnet motor is running, sometimes leaving the rotor temperature higher NdFeB irreversible demagnetization phenomenon, causing permanent magnet synchronous motor efficiency and power factor and other performance indicators deteriorated.