Gain and phase margin + phase and gain crossover frequeny results

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Mahabba Almheiri
Mahabba Almheiri 2020-12-5
评论： Gollapapani 2023-8-11
I used this code to find phase and gain margin. Also to find phase and gain crossover frequeny
syms s
G = tf([7 14],[1 10 24])
[Gm,Pm,Wcg,Wcp]=margin(G)
grid on
but I got this result. can any one explain to me why Gm and Pm = Inf and Wcg and Wcp= NaN?
and what is maning of Inf and Nan?
G =
7 s + 14
---------------
s^2 + 10 s + 24
Continuous-time transfer function.
Gm =
Inf
Pm =
Inf
Wcg =
NaN
Wcp =
NaN

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回答（2 个）

Keerthana Chiruvolu
Hi,
Firstly, NaN means Not A Number and inf is infinite.
From the bode plot of the transfer function, we can observe that the Magnitude plot doesn’t cross 0. And the phase is not 180° at any frequency.
Wcp - 0-dB gain crossing frequency.
Wcg -180° phase crossing frequency
To calculate the gain and phase margins we require the crossover frequencies. Hence, the result for Wcp , Wcg is NaN and Gm, Pm are inf.
.For more information, please refer the following functions :margin(), bode()
Kingsley Osubor
Kingsley Osubor 2021-8-17
How can we explain a bode diagram with Gm with Infinity, Pm with infinity, Wcg with infinity and Wcg with not a number value.

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