Thursday, January 24, 2013

OL vs CL plots

Whenever I plot the transfer functions of Gvg and output impedance, I get identical plots for the open loop and closed loop cases. This doesn't seem correct to me. All that I did was change the locations of the inputs and outputs. Is there something else that I need to do that I am overlooking?
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4 comments:

  1. Reid_AJanuary 24, 2013 at 2:09 PM

    Braden, From the voice of experience, beware the model mode checkbox in the mask! More importantly, check out Lecture 2 slide 28 and p 18 of the "Introduction to Modeling..." tutorial on the class website. "x marks the spot..."

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  2. BradenJanuary 24, 2013 at 2:29 PM

    I got the identical results when I did have Open Loop option set. If I uncheck that option, then I get different results. The notes make it sound like the option has to be checked. Which way should it be?

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    Replies
    1. Reid_AJanuary 24, 2013 at 3:07 PM

      ...depends on what you want to see. As a test, you can compare the open loop model syncbuck_OL with the closed loop model syncbuck_CL that has the open loop linearization option checked. Just make sure both models have the same parameters,etc. The results should match if linearized around the same quiescent operating points. Then try the closed loop model without the "open loop" option (ie with a closed loop). One expects the closed loop cases to provide improved characteristics below the loop crossover frequency.

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  3. BradenJanuary 24, 2013 at 7:19 PM

    I guess I didn't understand what that option did. I thought that it was necessary for simulink to operate correctly.

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