generating wrong Nyquist plot of tf

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keshav agrawal
keshav agrawal 2021-5-27
评论： Paul 2021-5-28
i have been trying to plot nyquist plot of following transfer funtion but i am getting wrong.
sys =(s+3)/(s^2*(s-3))
when i tries to plot it using control technique i am getting different plot
please help
  2 个评论
Paul
Paul 2021-5-28
What is your code and why do you think the result is wrong?
keshav agrawal
keshav agrawal 2021-5-28
the code is
s = tf('s')
sys =(s+3)/(s^2*(s-3))
nyquist(sys)
the plot i got from this is
the nyquist plot i am expecting should be like this :-

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采纳的回答

Paul
Paul 2021-5-28
Keep in mind that nyquist() doesn't draw the arc at infinity due to the double pole at the origin.
If you zoom in around the origin on the Nyquist plot produced by nyquist(), you'll see that the plot crosses the imaginary axis at a value of around 0.1*j and approaches the origin from the left, as in your sketch.
  2 个评论
keshav agrawal
keshav agrawal 2021-5-28
thank you for reply ... i am statisfied with your answer. but is there any function other than nyquist() that can show infinite semi circles.

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更多回答（1 个）

Girijashankar Sahoo
编辑：Girijashankar Sahoo 2021-5-28
sys=tf([0 0 1 3],[1 -3 0 0])
nyquist(sys)

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