Help with root locus

  • Thread starter formulajoe
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  • #1
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I had to use state-variable feedback to design a control system for a motor. I first designed a deadbeat controller, which was pretty easy.
But now I have to design another controller using root locus methods.
The gain that is varied is located in the feedback loop as shown in the picture.
I am completely lost as to how to generate a root locus with the gain in the feedback loop.
Can anybody give me a general form to get into so I can draw the root locus?
 

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  • #2
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The problem I am having is that when H(s) and G(s) are multiplied together, a zero is introduced because of the feedback loop. The location of this zero changes as the gain changes. So the gain cannot be varied without moving the zero. Thus every value of gain produces a different root locus.
 

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