What are the requirements for frequency conversion of ac asynchronous motors?
I don't see any need for the asynchronous motors.I hope my answer will help you
Ordinary asynchronous motors can be used for short periods of time. In the long run, the frequency conversion motor is different from the ordinary motor. The reason is that the operating conditions have changed: 1, the frequency conversion asynchronous motor USES the frequency converter power, the waveform of the transducer output is PWM waveform, contains a large number of harmonics, the harmonics will add the added loss. The frequency of the base wave of the output waveform of the converter is varied, unlike the traditional fixed 50Hz. The operating conditions changed, and the corresponding design was different: The high peak of the output voltage of the transducer, the threat to the insulation of the motor and the need to strengthen insulation.
harmonic caused by unbalanced magnetic circuit and electrostatic induction, etc., in the shaft end or between shaft and bearing of shaft voltage than when big sine power supply, if the axis of the shaft voltage current is large, will cause great harm to bearing parts such as motor, seriously affect the safe and stable operation of the machine. An insulating design is needed for bearings. The motor of variable frequency control is no longer running at fixed frequency points. But in a more wide frequency range, electrical parameters and operation characteristics changes with the change of frequency, at the same time because the motor operating frequency range is wide, if poorly designed, the resonance frequencies of the power supply into the resonance frequency range of the motor, the motor may be strong vibration. The cooling capacity of the motor is reduced when the motor speed decreases, and the heat dissipation of the motor at low speed must be considered. 5, for constant speed operation of the motor, rating and selection of optimal working point is simpler, load characteristic of the motor is according to the rated operating conditions to consider commonly, for motor frequency control of motor speed operation, different speed running condition is different, so the rating and selection of optimal working point is a complex problem.
