flux control in induction motor

Discussion in 'General Electronics Chat' started by kokkie_d, May 13, 2011.

  1. kokkie_d

    Thread Starter Active Member

    Jan 12, 2009
    Hi For a project I am building a model in simulink of an the control for an induction motor. I would like to use indirect vector control strategy but am confused about where the reference flux comes from. For example, in the following picture the flux reference is defined as a look up graph. Now, my question is: does anyone know how this is defined?

    Is there anyone that can help?
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
    Wish I could, I just use commercially available 3 phase speed controllers. Every now and then one will show up used and inexpensive on eBay.
  3. steveb

    Senior Member

    Jul 3, 2008
    There are different methods for defining the flux weakening function for the flux reference. Usually, there is a defined constant rated value used at lower q-axis currents and lower speeds. Then at higher torques, which is controlled with higher q-axis currents, the commanded value of d-axis current will be reduced based on a formula or table function. The details usually depend on the motor and the application.

    As an example, when commanding high torque levels, you might exceed the maximum rated current for the motor if you use the rated flux. Lowering the flux, could allow you to get higher torque without exceeding the current limit. Similarly, you might have a voltage limit on your inverter system, and lowering the flux might get you below the limit when running at high speed.

    To get your method, you should think about your application and the details of the motor. If you have no constraints, then simply use the rated flux to find the commanded d-axis current, then implement a current limit on the q-axis current considering limits on torque, current and voltage.

    If you just want to implement something for demonstration, pick up a good book on induction motor control to get a standard technique. Tomorrow, I will be at work and can probably post a page or two from a text I have there.
    Last edited: May 15, 2011