Inverter drive question

FriendlySteaK

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Join Date
Jul 2020
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Highland
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Hi,

I have little experience with inverter drives and was planning on using an ABB ACS310 drive to power a linear positioning system. But i had read that this ABB drive was suitable for pump and fan applications. Other than having product features specifically tailored for pump and fan applications, is there any reason why this drive won't be suitable for other applications?

In ABBs own words-

"The ACS310 drives are designed for squared torque applications"

Im not quite sure what this means

Cheers
 
Hi,



"The ACS310 drives are designed for squared torque applications"


As opposed to round torque and hexagonal torque :D




What are you looking for in a drive for your application? Constant torque? Encoder interface? Motion control options?
Start there, define your requirements and see if this drive meets them.
 
What you need to use is a Fux Vector VFD
I don't use AB but i have done this many times using the standard Yaskawa VFD
Th GA800 wil work nicely you will need to add an encoder and encoder feedback card
 
Square Torque Loads are your typical centrifugal pump/fan loads. Doubling the speed increases the torque requirement 4 times.


You want one of their higher end drives with DTC (Direct Torque Control) and an encoder on the motor.
 
Your question is quit interesting and I would like to suggest a rephrase of the question to the following:


May we use a drive designed for variable torque applications with a constant torques application?


And according to a little reading I did it mostly have to do with sizing and maybe firmware/software that is designed/has algorithm to handle torques and overloading in specific ways.


A few links:


What are the characteristics of Variable Torque and Constant Torque?


Variable torque drive for constant torque application



From here:


  • VFDs do not produce horsepower (hp)
  • VFDs do not produce torque
  • VFDs supply current that, with the correct voltage and frequency, makes the motor run at the desired speed



And from this pdf:
"The most important consideration when choosing a Variable Frequency Drive (VFD) is to know the type
of load that is being applied to the motor because it will determine the size and cost of the VFD. The VFD
must have sufficient current capability so that the motor can produce the required torque for the load"


"In order to keep a constant torque, which is
directly related to current, the voltage going
from the VFD to the motor is increased as the
speed increases. On a 460 Volt motor, 460 Volts
is only applied to the motor when the speed
reaches 60 Hz. Constant torque is achieved
because the VFD is increasing the voltage to the
motor as it increases the speed. "


And this is probably what they meant by squared torque( very poor terminology in my opinion) :


"Variable Torque Loads
Variable torque loads require much lower torque
at low speeds and the torque increases rapidly at
high speeds. As the motor spins faster, the load
on the motor increases. These types of loads are
approximately represented by assuming that the
load torque required is proportional to the
square of the speed. For example, if speed
increases by a factor of 3, torque increases by a
factor of 9.
š‘‡š‘œš‘Ÿš‘žš‘¢š‘’ āˆ š‘†š‘š‘’š‘’š‘‘ D "


Then there is a derating curves:

"The following Variable Torque (VT) and Constant Torque (CT) derating curves are for drives with 3-phase input power.
The 230VAC, CT curves also apply equally whether the drive is supplied with 3-phase or 1-phase input power."
 
Wow there is a lot of information posted here

And most of it is fairly accurate for a standard AC induction motor and a standard VFD.
But I can assure you that a standard VFD with a standard induction motor is a very poor choice for a positioning control. There are just too many things that you canā€™t control with it and you will not be happy with the results.
If you look at the torque curve you will see that you have very little torque at slow speed and the slower you go the less torque you have, but in positioning you need the high torque at the very low speeds. So you donā€™t have the control you need for accurate repeatable positioning.
For positioning you need accurate feedback and the simplest is a motor mounted encoder there are other options available but they require more hardware and complex programming to make them work.
As I have stated before your best option is a good Flux Vector VFD
With a Flux Vector Drive you can throughout all of the standard torque speed curves that everybody keeps referring to do not apply here.
A Flux Vector Drive can produce 100% motor torque at zero speed, even 150% for a limited time. That is not possible with any standard VFD. I have systems running from 0 to 200HZ they have been running for years no problems. One machine I did recently a retrofit on a large milling machine. They run the feed motor below 0.5hz to mill the final pass to get the finish they want the part weights over 2,000lb
 
Thank you for your detailed replies, this makes more sense now. The main differences are torque curves, load vs speed.

The positioning system I'm working on is quite crude and originally has a motor with mechanical brake working through a step down gearbox to drive a chain which directly moves a slide on a linear axis. This positions lumber through a mill. Because the system has lots of room for error the encoder reads the final position and relays the data to a plc which controls the vfd. Accuracy is +/-1mm .
If the position entered is far away the drive is at full speed up to the desired position and usually over shoots a few mm then the plc automatically reverses the drive using the ramp start to slowly close the gap to the desired position.
I was looking to improve this system.
 
The first obvious thing would be to decrease the speed so that it reaches the position in a controlled manner. But the current system has no serial connection between plc and vfd its all controlled through physical i/o and banks of relays. Its a mess but has been working for years. Think I'm going to re do the system and add Serial connection so that I can make use of a speed reference in the vfd for more efficient positioning.
 
If the position entered is far away the drive is at full speed up to the desired position and usually over shoots a few mm then the plc automatically reverses the drive using the ramp start to slowly close the gap to the desired position.
I was looking to improve this system.


What drive is currently there? Does it have analog inputs? There must be a way to vary the frequency either by digital or analog inputs.


If it has analog inputs that would be the way I would go.
 

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