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I have a question regarding the time delay margin. I know the definition of time delay margin now I want to know that for the stability of the system is it good to have large time delay margin or small time delay margin?

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    $\begingroup$ What kind of uncertainty does the system have? $\endgroup$ – Arnfinn Aug 4 '17 at 9:12
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    $\begingroup$ What kind of system are we talking about? $\endgroup$ – Marcus Müller Aug 4 '17 at 13:51
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Time delay in frequency domain defines a frequency dependent rotation of the Nyquist curve. This means if you take the Nyquist curve and apply the pointwise rotation at each frequency that would give you a new Nyquist curve for which you can assess the stability properties.

Since delay defines a rotation there are cases where if you keep on rotating you can be stable --> unstable --> stable again. This is generally called as "stabilization via delays". There are some literature actually looking for these stability pockets so on.

Hence, there is no simple and unambiguous time delay margin with respect to Nyquist stability.

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