How can I minimise motor noise when using a frequency inverter?
Frequency inverters use pulse-width modulation (PWM) technique to generate variable voltage and frequency output to regulate fan speed. The rapid switching of the PWM signals can introduce harmonics in the electrical waveform, which may interact with the motor windings and produce noise. This noise caused by the PWM technology can be prevented by increasing the switching frequency of the built-in IGBTs in the frequency converter. At higher switching frequencies, the electric motor will run quieter.
By default, our frequency inverters switch 8.000 times per second (8 kHz). But this can be increased to 32 kHz via parameter P-17. Please note that a higher switching frequency causes faster wear of the ball bearings of your motor. It is therefore a matter of finding the right balance between motor noise and switching frequency.
The noise in an electric motor when using frequency inverters can also be attributed to other factors:
- Electromagnetic Forces: Frequency inverters control the speed of an electric motor by adjusting the frequency of the supplied electrical power. This can result in fluctuations in the electromagnetic forces within the motor. These forces can interact with the components of the motor, such as the stator and rotor, causing vibrations and generating noise.
- Mechanical Resonance: Electric motors have natural resonant frequencies at which they tend to vibrate more. When the frequency output of the inverter coincides with the resonant frequency of the motor or its connected mechanical system (such as the load or the motor mounting structure), it can lead to increased vibration and noise levels.
- Bearing Noise: The change in speed and load conditions caused by frequency inverters can affect the operating conditions of motor bearings. If the bearings are not properly lubricated or worn out, they can generate noise as the motor speed changes.
- Eddy Currents: When the frequency of the power supplied to the motor changes rapidly, eddy currents can be induced in the motor's laminated core. These currents can cause additional vibrations and contribute to the noise.
To mitigate the zooming noise in electric motors when using frequency inverters, it is important to consider factors such as motor design, proper installation, adequate insulation, vibration damping measures, and regular maintenance to ensure optimal motor performance and minimise noise generation.