transfer function=1/2s^3+3s^2+s,draw the nyquist plot .i have not get the same plot which i have studied.

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Varun Tiwari on 13 Oct 2015

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Commented: Varun Tiwari on 24 Oct 2015

a=(1,[2,3,1,0]) nyquist(a)

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Varun Tiwari on 24 Oct 2015

sir nyquist1 command is not working in matlab 7.10 version .could it will work in above version of matlab?

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Answer 1

Arkadiy Turevskiy on 22 Oct 2015

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In your plot the half circle (from -0 to +0) has infinite magnitude, because your system has a pole at zero.

nyquist plot created with nyquist function does not show this segment that is drawn in textbooks just to help you understand concepts. All the dots of the curve you see in the nyquist plot are calculated for specific frequencies. If you zoom in around -1, you will see the correct results that will let you see if your system is stable.

If you want to get a nyquist that looks like your textbook (with "imaginary" infinite half circle), see this page , and use the function nyquist1 that is linked to from it.