Permanent magnet motor demagnetization performance of permanent magnet variable frequency air compressor

Permanent magnet motor demagnetization performance of permanent magnet variable frequency air compressor

1) Demagnetization judgment: After the permanent magnet motor loses magnetism, the most direct and accurate judgment is that the back EMF of the measured motor will drop a lot (for example, the normal back EMF is 350V, and it will drop below 300V after demagnetization. The back EMF is determined according to the magnitude of the demagnetization. size). It can also be judged according to the input voltage on the display screen, the input voltage value will decrease after demagnetization (generally about 20V lower than the standard). Because the current is large after demagnetization, if the frequency converter is equipped with self-protection, it will work at reduced frequency.

2) Reasons for loss of magnetism: First, high temperature. The permanent magnet of the motor is most afraid of high temperature. If there is a high temperature above 150°C, there may be loss of magnetism. Another reason is that if the carrier frequency of the inverter is very low, the sine wave waveform will also be bad, resulting in a larger negative value of the ID current, resulting in demagnetization. At this time, the above-mentioned demagnetization performance is manifested, and at the same time, the noise and vibration of the motor increase.

 

3）Treatment method: first prevent high temperature from appearing. When setting the carrier frequency, according to experience, a sine wave requires at least 20 points of control, so the setting of the carrier frequency = 20 × working frequency. For example, the maximum 200Hz unit, its carrier frequency should be set at least 20×200=4000Hz. The carrier frequency should not be too high, otherwise the IGBT will heat up and shut down the inverter. Different manufacturers have different standards, and the general module temperature limit is set to 85°C. When setting, you can ask the inverter manufacturer for reference settings.

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