Three-Phase Motor Control

Sounds like a job for a common servo motor and controller unit. No big engineering mystery there.

I agree with tcmtech.

Still not sure why a load cell can't be used. Hell, a fish scale of the appropriate size would work for this.

What amount of HP (lW) are we talking about here? If it's small, servo for sure but if it's big, Vector VFD with an encoder feedback would be better. There are several companies that make somewhat "universal" drives that can be used in either mode. Emerson / Control Techniques comes to mind first, they have a drive product called a "Unidrive" Siemens Sinamics S120 drives are also like that.

What you would do is set up the drive in a "torque follower" mode which will tell it to maintain torque as the most important output while running. All the while, the drive will be able to monitor the amount of torque it"thinks" the motor is putting out, check that against the performance of the motor, and determine an error, then correct for the error. You can observe any and all of those parameters on a smart system connected to the drive, i.e. a PC or SCADA HMI.

Any VFD can technically convert single phase input to 3 phase output, but you have to check with the individual manufacturer for the simple reason that they have to have designed it for that at the outset. The reason is that the VFD electronics needs to be powered up and on some VFDs the control power for that comes directly from the Line, as opposed to tapping off of the DC bus. If they tap off of the DC bus, the VFD doesn't care if the supply is 1 or 3 phase. If not, it may make a difference and so some mfrs include Phase Loss protection that cannot be disabled, rendering them unable to be used on a single phase source. So just check before buying.

But if you are not an EE with experience in this, it sounds like you need the services of a good Drives Integrator. Where are you in the world?

Thanks, JRaef, yours is the first response that tells me I did not errantly post the question on some comedy forum.

It is a 3-hp motor and the anticipated maximum torque on the output side of the 30:1 gearbox is 1225 in-lb. I have looked at Emerson (US Motors) and Baldor.

I am in New Mexico and my business is specialty fabrication. Ususally, I would have the design provided, but not in this case.

In my experience the correlation for torque is much easier to obtain from a DC machine.

The derived torque for an AC VFD (and most at 3 hp can be run from a single phase supply at this power level) is an estimated torque.

Depending on the accuracy you need you may still need to use load cells or direct toque measurement, especially if this is a certification procedure.

No longer true with modern Vector drives.

GA with the first one BUT you are going to have that encoder hanging out to be hit and/or fail and the wiring from it to the VFD to shield, shield it GOOD

It depends on the application. When there is a large "field" range as in a center unwind that was typically done with a DC motor (for argument 300HP) base speed 300rpm field weakend to 1500 rpm, the torque curve with field and armature current control is well defined. Even with 150% to 200% torque OL. Because an AC induction machine does not have a wide usable field range the frame size for this application becomes grossly oversize, and the torque regulation is now rather inaccurate due to poor resolution.

With a DC machine it is possible to run the application without "tension" feedback. With AC it has never been successful.

There are still nich applications where DC shines. I believe DC is best for wide field ranges and torque control.

AC shines in speed controled applications.

Perhaps I am still jaded by my experiences developing AC drives from the 60's. I am still pleasantly surprised when an AC drive performs as desired without a whole lot of tinkering. DC control is so simple in comparison.

Believe it or not, the electricity in your power lines IS three phase. Before it enters your house, it goes through a distributor transformer to convert it to single phase. However, power lines are EXTREMELY dangerous because they have 240V compared to our single phase houses with 120V. That is why it is occasionally used for industrial purposes, which require higher voltages. If you contact your hydro provider, they may be able to give you permission to access the three phase directly.

Although it is in the power lines, DO NOT try and hook your motor up yourself! Make sure you have contacted your hydro provider.