PatFranz (Customer) asked a question.
Why doesn't my GS4 Durapuls VFD output not match the speed reference?
For example, I am running a pump right now with the reference set at 54.00 Hz and the drive is reporting the actual speed as 55.99 - 56.00 Hz. I have checked the parameter called Gain (don't remember at the moment if that is the complete parameter name) and it is set to 1. Is there another parameter that affects the actual drive output? Thanks!
Is the reference being fed to the drive through an analog input on the drive or though a communication module?
reference fed via ethernet/ip
thanks
Is the drive simply accepting raw speed commands or is a PID in use?
Just accepting raw speed commands. It responds correctly to relative changes both up and down in speed but it always results in a higher output Hz than the speed reference entered.
thanks.
I was not able to get back to this conversation for a couple of weeks...
Any suggestions regarding this issue?
thanks,
Pat Franz
I discussed this with our engineers. We're going to have to take a phone call on this. There are a few things it could be. When you're in front of the drive give us a call at 1-800-633-0405. Ask for technical support and mention your drive model.
This is a remote location so I may not have enough cell coverage there to make the call. I will try it later today though. thanks
Is the drive in v/hz or scalar mode? If scalar, what you may be seeing is the output frequency being higher than motor frequency to account for slip. The drive will need to output faster frequency when the motor is loaded as there is slip in the motor. So output 56 hz to the motor, motor is running loaded enough that there is 2hz worth of slip, result is 54hz or actual motor rotational speed.
Drive is in "sensorless vector" mode. I will try to call tech support tomorrow morning to discuss further in person. I will post here after problem is resolved.
My guess since it is in vector mode (sensorless vector means it does not use an encoder, but still doing closed loop speed control), you are seeing that the output frequency has to be slightly faster than the requested motor frequency to account for the slip in the motor. If you are monitoring the statuses, include looking at the actual motor rpm. I bet that is running at the rpm that you want.
When in vector mode and you say 55hz, the drive interprets that to mean you want a motor rpm that matches 55hz. If it is a 4pole motor, that would mean you are asking the drive to run the motor at 1650rpm. To run the motor at 1650rpm, the drive may be outputting 56+hz.