VFD control motor at 0 rpm

Does anyone know if any of the readily available vfds that will control torque at 0 speed?

The need for this is on a 60hp motor.

This is for a potential test rig. The rig is going to have a motor driving a test piece. There is going to be an inline torque flange in the shaft. For calibration, we have thought about using a torque arm connected to a load cell in such a way as to lock out the rotor. If we could control the torque on the motor at 0 speed, we would be able to load the load cell and the torque flange.

I know this is possible with certain large drives (I know this is done on UNICO motoring dyno drives). Does anyone know if this is available on any off the shelf drives?


Thanks

ABB ACS800.
http://www.abb.us/product/us/9AAC133421.aspx

dmargineau said:

ABB ACS800.
http://www.abb.us/product/us/9AAC133421.aspx

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Yep, that's it.
Use their DTC function (Dynamic Torque Control) which comes with the 800.

bkottaras said:

Yep, that's it.
Use their DTC function (Dynamic Torque Control) which comes with the 800.

Click to expand...

http://en.wikipedia.org/wiki/Direct_torque_control

While the ACS800 and its predecessor the ACS600 are remarkable drives and can definitely manage motor torque at zero speed, you have to be careful when the application is a test cell, as the poster describes. If, at zero speed, the shaft has to remain motionless, then DTC alone will not get the job done. You will need to add an encoder to the motor shaft. Without the encoder, the shaft speed will be zero but there is a little "jitter" in the shaft position which, in some applications, can not be tolerated.

I have encountered just that situation when testing hydraulic actuators for leakage at zero speed. The shaft has to be held motionless for the test to be valid. Thus, encoders required in those types of test cells.

...or implement a good ol' DC system...
As DickDV has already stated, even a DTC VFD will need at least 0.5rpm speed reference in order to generate "slip" and consequently produce torque...
If an absolute 0 RPM is a must, then your only option will be a DC Drive/Motor system.

Pretty sure the Powerflex 755 drives does this as well.

Helliana said:

Pretty sure the Powerflex 755 drives does this as well.

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Not really...Quite far from it...
Allen-Bradley hasn't come up with a DTC VFD yet...One of these days...

dmargineau, the DTC does a true zero rpm. I've done it many times. The problem with test cells is that there is a little quiver or oscillation in the shaft around the zero position point which can be unacceptable in certain types of tests.

A DTC drive does not need a .5rpm speed reference for zero speed. You would get .5rpm shaft rotation if you gave it that reference. Give it zero rpm speed reference and you will get zero rpm but with a little twitching as it holds the position.

All of the above assumes the drive is tuned up to near optimum condition as any zero speed application would require.

dmargineau said:

Not really...Quite far from it...
Allen-Bradley hasn't come up with a DTC VFD yet...One of these days...

Click to expand...

wondering why is no one talking about encoder feedback on the pf 755 or a servo?

Thanks for all of the suggestions. I had planned to put on an encoder on whatever drive I use. The potential need for this is for calibrating/checking the torque flange. We would mount an arm to the end of the shaft that would be pinned with a load cell as to keep the motor from spinning. We could then load the motor and check torque flange torque against load cell & torque arm torque. This is not by any means a necessity. Pinning the shaft and hanging weights on a torque are works just as well, is cheaper, easier, etc.

As of right now, this whole test rig is in the concept stage. If we decide we must have this ability, I will be going with the ABB 800. If we don't need this ability, I will probably be going with a AD DuraPulse drive. The ABB is super nice, but the +$5k premium may not be needed.


Thanks again.

DickDV said:

dmargineau, the DTC does a true zero rpm. I've done it many times. The problem with test cells is that there is a little quiver or oscillation in the shaft around the zero position point which can be unacceptable in certain types of tests.

A DTC drive does not need a .5rpm speed reference for zero speed. You would get .5rpm shaft rotation if you gave it that reference. Give it zero rpm speed reference and you will get zero rpm but with a little twitching as it holds the position.

All of the above assumes the drive is tuned up to near optimum condition as any zero speed application would require.

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DickDV, I believe that that "quiver" you are mentioning of experiencing is the +/- 0.5 rpm I was talking about.
"Electrically speaking", any AC motor, in order to generate torque, needs "electromagnetic slip" between the stator and rotor windings ; the stator field needs to be phased off the rotor one, this angle being the "work" producer.
When any VFD is commanded to produce torque, it will "rotate" the stator's electromagnetic field out of phase of the rotor's one directly prooportional to the speed reference thus the rotor will "chase" the stator and producing torque.
The DTC method of controlling an AC motor vastly decreases the "reaction" time of the motor to a command change or maintaining of a command when the load conditions vary; this is realized by eliminating of most of the time consuming algorithms of the Field Oriented Control VFDs(FOC) such as the A-B PowerFlex family or most of the commercially available ones.
Again, practically, with a properly designed control system, including encoder feedback, you could achieve Maximum Rated Torque at Zero Speed when using a DTC VFD and I have been doing it for quite a few years with the ABB ACS600s and more recently the ACS800s.
However, theoretically, this cannot be achieved within an AC environment; this is the only reason DC applications are still around and will be for quite some time; a higly critical Max Torque at Absolute Zero Speed cannot be achieved but by using of two constant magnitude electromagnetic fields at opposing polarities(Direct Current).
Or at least this is the way I am approaching this matter...

Any Closed Loop Vector Drive along with an Encoder & Encoder card will do the trick

Just keep in mind that many motor are self cooled by a shaft mounted fan and at 0 speed for long time at full torque, the motor will overheat if no external fan is used.

2rlp said:

Any Closed Loop Vector Drive along with an Encoder & Encoder card will do the trick

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I called Automation Direct tech support. They say that the DuraPulse cannot do this. So if I end up needing this ability, ABB is the choice.

Jeff23spl said:

Just keep in mind that many motor are self cooled by a shaft mounted fan and at 0 speed for long time at full torque, the motor will overheat if no external fan is used.

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Agreed. I would be needing either a TEBC motor, or atleast TEFC with thermostats.