vfd displays motor output power and efficiency 2

[electricpete]

A vfd can obviously determine motor input power (vfd output power).

Is it common for vfd to also display some estimate of motor output power and motor efficiency? How is this estimated?

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[ozmosis]

Pete
for our standard range of VFD's, we have a read parameter that will display 'filtered power'[r0032], meaning motor power.
The basic formula is:

whereby r0022=rotor speed[rpm] and r0031=electrical torque[Nm](NB: this is electrical torque not mechanical torque)
The key factor is to first input the correct motor values into the VFD (power rating, voltage, current, PF, eff, slip speed etc) otherwise the whole basis of any calculation will be flawed.
The VFD in question can be used as a scalar V/F or open loop vector drive.
Motor efficiency is generally dependant on the control mode used. If standard V/F control, the motor base eff is used whereas using vector control mode there will be further optimisation of efficiency that will be dependant on load. We don't have a parameter that shows efficiency other than the initial value you input as a motor parameter.
Not sure if this answers your question.

 

[CJCPE]

AFD manufacturers attempt to display what they believe that customers want. They often have displays that attempt to indicate motor performance parameters which may indirectly indicate something about the driven machine or process performance. Motor current is a rough indication of torque and some customers request it because it is familiar to them. Some AFD manufacturers have developed better indications of torque and labeled them as percent load or percent torque. Motor power has not historically been widely used as a performance indication, but some customers have determined that it is an important indication to monitor in some processes. Since VFDs often develop a torque estimate, it is fairly easy to multiply torque X speed and provide a motor power indication.

Although some VFDs may estimate motor efficiency, I don’t recall seeing it as a display parameter. I have extensively surveyed manufacturer literature and done detailed comparisons of VFD features, but not recently. Motor efficiency can be estimated by starting with the published full-load, line-frequency efficiency. The effect of the VFD at full-load, full-speed can be estimated from “typical” test data or neglected. The effect of operation at reduced speed and load can be estimated from “typical” test data.

 

[DickDV]

electricpete, I've never seen a vfd that could display anything that would read directly against efficiency. All kinds of other stuff but not efficiency.

I believe that you were asking for motor efficiency but you might have meant system efficiency--ie, including the drive losses. Either way, I don't know of any drive product that will give you that information directly.

 

[ozmosis]

an interesting article from an old colleague:

http://www.drives.co.uk/features.asp?id=3

he was never one to stand on the fence!