What method is used to judge whether the permanent magnet variable frequency air compressor is demagnetized?

1. Reasons for motor demagnetization

(1) The heat dissipation fan of the motor is abnormal, resulting in high temperature of the motor

(2) The motor is not equipped with a temperature protection device

(3) The ambient temperature is too high

(4) The design of the motor is unreasonable

Solution: Correctly choose the power of the permanent magnet variable frequency air compressor. Demagnetization is related to the power selection of the permanent magnet variable frequency air compressor. Correct selection of the power of the permanent magnet variable frequency air compressor can delay demagnetization. The main reason for the demagnetization of the permanent magnet synchronous motor is that the temperature is too high, and overload is the main reason for the high temperature. Therefore, a margin should be left when selecting the power of the permanent magnet variable frequency air compressor. According to the actual situation of the load, generally about 20% is more appropriate. Avoid heavy-load starting and frequent starting. Asynchronous starting and synchronous permanent magnet variable frequency air compressors try to avoid heavy-load direct starting or frequent starting. In the process of asynchronous starting, the starting torque is oscillating, and in the trough section of the starting torque, the stator magnetic field demagnetizes the rotor magnetic poles. Therefore try to avoid heavy load and frequent starting of asynchronous permanent magnet synchronous motor.

2. Improved design

Design 1: Appropriately increase the thickness of the permanent magnet. From the perspective of permanent magnet synchronous motor design and manufacture, the relationship between armature reaction, electromagnetic torque and permanent magnet demagnetization should be considered. Under the combined action of the magnetic flux generated by the torque winding current and the magnetic flux generated by the radial force winding, the permanent magnets on the rotor surface are likely to cause demagnetization. When the air gap of the motor remains unchanged, the method to ensure that the permanent magnet does not demagnetize is to increase the thickness of the permanent magnet appropriately.

Design 2: There is a ventilation groove circuit inside the rotor to reduce the temperature rise of the rotor. An important factor affecting the reliability of the permanent magnet variable frequency air compressor is the demagnetization of the permanent magnet. If the temperature of the rotor rises too high, the permanent magnet will lose its magnetism irreversibly. When designing the structure, the internal ventilation circuit of the rotor can be designed to directly cool the magnetic steel. Not only reduces the temperature of the magnetic steel, but also improves the efficiency.

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