Why does motor produce unusual noises when controlled by VFD compared to its original operation?

As we know, input current to VFD contains high-order harmonics. When a motor is controlled by a VFD, it is influenced by these high-frequency harmonics, which can affect motor noise and electromagnetic interference (EMI) generated by VFD. If you increase carrier frequency, it can improve output current waveform, reduce high-order harmonics, and minimize motor noise.

It’s important to note that default carrier frequency value is optimal in most cases. Therefore, users should avoid adjusting this value. Setting carrier frequency too high can lead to increased heat generation in VFD and greater interference. If it’s set lower than default value, it could potentially reduce motor’s output torque and increase noise.