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Electric Motor Drive Question

  1. Aug 16, 2013 #1
    Can a variable frequency drive with the ability to control motor torque, be programmed to run at a certain speed and torque? Or can you only control one of these variables because a change in one will affect the change in another?
    I noticed that in certain drives, there is speed control and torque control. Are these isolated from one another? Is it possible that when torque is controlled, the speed of the drive is somehow proportional?

    I understand that torque multiplied by speed is power. Is it possible to set a motor to operate at a certain torque and speed as long as it is within the motor’s rated power and torque?
    The reason I ask these questions is because I’m trying to control tension and speed of a moving web. I believe that the torque produced by the motor will determine tension, however, I don’t understand how to change how fast the web will move. It seems like if the tension remains constant, than that would mean that the motor torque would remain constant and the torque would not effect the speed. Any help?
  2. jcsd
  3. Aug 16, 2013 #2


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    Staff: Mentor

    It seems to me that speed and torque are dependent on each other based on the needs of the load, so other than establishing a torque limit, I don't see how you could control both at once.
  4. Aug 18, 2013 #3


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    Science Advisor

    The primary requirement of the VFD would be the control the RPM.
    The torque specification is probably a programmed upper limit to the permitted current. It is there to protect the motor when something goes wrong.
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