Advanced VFD controls

I am looking for some pointers on setting up a VFD (PowerFlex70 in this case) to operate beyond normal operation.
-Low speed without overheating <20Hz
-High starting torque
-High speed >100Hz
This setup will be used on a pump that will need a very wide range of operation. The motor has been oversized to help with the low speed operation.

I have been testing using the sensorless vector mode and adjusting the SV boost filter parameter[059] to help boost the voltage under load(I think). Unfortunately I am only able to test it on a small .25hp motor and the changes are hard to notice.

If anyone has any pointers to help get me it would be much appreciated.
Thank you in advance.

Probably would be a good idea to provide external cooling to the motor.

jrwb4gbm said:

Probably would be a good idea to provide external cooling to the motor.

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I have been tossing around the idea but had not decided if it would be needed or not. I will look into it a little deeper before I make a final decision.

The SVC algorithm in a PF70, sized for Heavy Duty, should be capable of making your motor deliver full Break Down Torque, you should not need to tweak it beyond that. BDT is the maximum torque the motor can deliver. If you tweak [059], it must be VERY temporary because it adds heat to the motor.

The Drive cannot "make" the motor not over heat, that is a function of the motor design. Over sizing the motor is one way to accomplish that. What type of motor are you using? If you cannot fit an external blower, then over size a TENV Inverter Duty motor, it is designed to dissipate the heat through radiation only.

Are you aware of the ramifications of over speeding a motor? If I assume this is a Positive Displacement pump, by virtue of you saying you need high torque at low speeds, then the only issue with over speeding it will be a loss of torque. If you are over sizing it, that may take care of it. But without knowing more, it's impossible to tell.

If this is a Centrifugal pump, you are in trouble on several fronts here.

Are you aware of the ramifications of over speeding a motor?

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I read the plan as running the motor for long times at less than 20 Hertz (low speed). I guess you could call that "under speeding" the motor.

I have run a variable speed wood boiler sawdust auger at low speeds and high torque for long periods. An external motor cooling fan was required. The problem with any internal motor fan is that it also reduces speed along with the motor, so provides little cooling when it is needed most.

External fans are not all that expensive compared to the motor. In a pinch, I have seen regular old household fans from Walmart bolted to the machine frame and pointed at the motor.

Lancie1 said:

I read the plan as running the motor for long times at less than 20 Hertz (low speed). I guess you could call that "under speeding" the motor....

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emroy said:

-Low speed without overheating <20Hz
-High starting torque
-High speed >100Hz

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Just trying to cover all his issues.

I find that running over base speed is something that a lot of people know is possible, but very few understand completely. The pump issue is the scariest part. I've had Pump engineers tell me to use a VFD to make their centrifugal pump move more water by running over speed. They don't understand that the affinity laws work in all directions. 100Hz on a 60Hz motor is 167% speed. At 167% speed, the pump is going to require 463% HP!

Pipe distance.
Pipe resistance.
Pipe pressure
Pipe leaking
Pipe blast
Type of Medium.
Pump spec
Motor spec
Cable spec
Bering spec
Vibration spec.

Run beyond normal then abnormal will come.
Pump already reach the consumption.
Install new pump.
Can’t.
Schedule the usage.

At 167% speed, the pump is going to require 463% HP!

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So he doesn't have enough power at 100 Hz, and not enough cooling at 10 Hz. When you try to burn a candle at both ends, usually someone gets burned fingers.

A small main pump would be more appropriate, then another pump to kick in when demand increases

request pressure? or request flow?

I am a big fan of TENV motors. I buy lots of Marathon black max motors and they are about the most trouble free piece of electrical equipment I have ever installed. I am also a fan of using closed loop flux vector control whenever possible. I don't see the advantage of using sensorless vector unless there is a really good reason you can't put an encoder on the motor shaft.

Jraef's comments about the torque is extremely important. And yes affinity laws are laws not guidelines.

I have successfully used a Pflex 700 in an application that required very precise speed control at about 5hz while also requiring high speed operation at 90HZ. It can be done but as has been mentioned you really have to wonder why you would want that kind of speed control on a pump?

Is allscott a tach, encoder, resolver salesman, by any chance? Am mystified otherwise by the comment of always using an encoder. Sure is a lot easier and cheaper to use sensorless vector with a commodity motor rather than an encoder, VFD encoder module, pipe and wire, and a motor built with a backside mounting face.

Of course, there certainly are applications that must use an encoder but, in my world that is less than 1% of the total.

Lancie1 said:

So he doesn't have enough power at 100 Hz, and not enough cooling at 10 Hz. When you try to burn a candle at both ends, usually someone gets burned fingers.

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Note that I said centrifugal pump. Not all pumps are centrifugal. If he has a Positive Displacement pump, as I suspect from the other comments, the affinity laws do not apply. PD pumps are going to have constant torque requirements.

Perhaps a variable ratio gearbox can be used to narrow the range needed for the motor to operate. Depending on the configuration, a gearbox could be added to shift gears between a high range and a low range using a solenoid. I know they do make them in two speed, but not sure who makes them. Contact your gearbox supplier and they may be able to help.

There is nothing radical about operating an inverter-duty motor like a Marathon Black Max or similar from 0 to 100hz. After all, the motor is nameplated to 120hz!

But you do have to understand the motor torque and cooling capabilities over that range and assure that the available torque exceeds the load torque demand at all speeds. In fact, as long as 2% speed error is acceptable and you don't go below 5hz, you wouldn't even need sensorless or flux vector control. Open loop scalar would be good enough if you choose a motor with less than 2% slip.

For tighter speed regulation and/or operation below 5hz, sensorless vector would be needed. That will give you around .5% speed regulation with a good sensorless vector system. If you need better speed regulation or if you need to hold the shaft perfectly still under heavy torque transients at zero speed, then you would need an encoder to close up the speed loop.