Stability margins on Nyquist plot for MIMO control systems

Question

Alexander Babin 2020-5-10

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回答： Alexander Babin 2020-5-11

Dear Friends!

I hope you are all doing fine in these strange times!

I have a question regarding the stability margins for a MIMO control system transfer function. I have a nyquist plot of a systen as a 2 by 2 window plot, as there are 2 inputs and 2 outputs. To make a long story short, this is what choice I have when I want to plot characteristics of these plots (see attached screenshot)

As you can see, I have no 'Stability margins' options, as for a SISO system I usually have 2 options to choose from- minimum and all stability margins.

If there is any option of plotting these margins, please do tell.

And take care of yourselves and one another!

Cheres, Alexander

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Answer 1

Alexander Babin 2020-5-11

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I figured it out. You could extract each input-ouput transfer function via g=tf(G.Numerator(i,j),G.Denominator(i,j)) where g is the SISO function you want and G is the original MIMO function and i,j are indeces of output and input respectively. That way when you use bode(g) you can estimate all stability margins.