What should I do if there is a whistling sound when the AC motor is running?

Date:2021-07-01 15:49:16

Recently, due to insufficient factory production capacity and material shortages, the delivery time for motors has been relatively long. Our Chuangjuman Electromechanical is located closer to Jiangsu, Zhejiang, and Shanghai. In order to deliver faster, we have chosen to have drivers directly deliver the goods.

For the replacement of high energy consuming electromechanical equipment, many factories prioritize the use of more energy-efficient motor reducers due to policy subsidies.

Yesterday, a customer called and said that the variable frequency motor they used before made a whistling sound when running at high frequencies. What should be done?

Then I called their engineers and they provided a solution. Although many users also have this question when operating motion control. So I have also compiled them all for everyone to answer one by one.

The output cable contains a considerable amount of high-order harmonic voltage and current, causing distortion of the input voltage of the motor. The high-order harmonics of the stator and rotor electromotive forces further increase, resulting in severe distortion of the phase electromotive force. The maximum value increases significantly, leading to severe heating of the motor coil, insulation aging, and even breakdown.

In addition, due to the additional torque generated by the high-order harmonic magnetic field, the motor produces significant vibration and sharp noise. High order harmonics greatly shorten the mechanical and insulation life of electric motors.  

Because their electric motor is equipped with a frequency converter for use, and the harmonics output by the frequency converter are the main cause of high-frequency whistling in the motor. When the modulation pulse frequency of the power switch of the frequency converter is increased, the output current can be closer to a sine wave, and the frequency of the whistling sound can be increased to the audible range of the human ear, which will greatly reduce the whistling sound. However, when the switching frequency of the IGBT is too high, it will increase the losses on the IGBT. At this time, it is necessary to reduce the capacity of the frequency converter for use.

When the switching frequency of a general IGBT is 4KHz, if you hear a whistling sound, it is recommended to increase the switching frequency of the IGBT appropriately.  

Nowadays, the whistling sound of variable frequency motors during operation often gives people the illusion that it is caused by frequency modulation of the frequency converter, but it may not necessarily be the case. We should first confirm the source of the whistling sound before making any further adjustments.

Step one, the frequency converter adopts V/F control to run the motor to the highest speed possible;

Step two, then operate the frequency converter's OFF 2 and park the vehicle on your own;

The third step is to determine whether the motor decreases with the speed during free parking.

If the whistling or vibration still exists, there is no need for frequency converter control, it is a problem with the production of the motor, and there are resonance points in the mechanical transmission during operation. This indicates that it is a mechanical manufacturing issue, not an electrical control issue.  

If the motor runs smoothly without whistling during free parking, it is a problem with the frequency converter control. By adjusting the control parameters of the frequency converter, it can be solved.

One of the most important aspects is to use the frequency converter to calculate the dynamic and static mathematical models of the motor. If the mathematical model established by the frequency converter is accurate, the operating quality will be good. Controlling the motor, its electromagnetic noise is completely acceptable.

I hope to share more things that can be directly operated by everyone in the future, Bixin, Momo!