Danfoss VFD Skip Frequencies

Hello- One of our favorite campus customers (Hi Chris!) called today and was asking about how to avoid certain “resonant” frequencies in their mechanical system.

Basically, there is a nuisance vibration from the ductwork at around 51-52Hz, is there a way in the VFD programming to fix it?

The answer is yes!

Danfoss VFDs provide up to 4 “bypass” frequency bands that you can program to avoid different speed bands that are in the operating range. The VFD will accelerate through those bands using the rampup/rampdown speeds programmed, but will not linger at those speeds. This can help avoid those nuisance vibrations and noises.

Here is an example:

Bad Mechanical Frequencies: 51-52 Hz

Start the Bypass at: 50Hz

End the Bypass at : 54 Hz

Program 4-61 [0] “Bypass Speed From” to 50Hz

Program 4-63 [0] “Bypass Speed To” to 54 Hz

• Note that this is an “array” point, there are 4 different arrays that you can program. The [0] in the example above shows that it is the first array item programmed, you can add others later if needed. There are arrays 0,1,2,3 available in this point that would make 4 different ranges for bypass speeds.

See pictures and manual sections attached! Pls call us if you have any questions.