Ch-9 Nyquist Plot
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7/31/2019 Ch-9 Nyquist Plot
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Chapter 9
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Given open loop
frequency response ,
determine closedloop system stability
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.
.
.
.
P1
P2
P3
P4
s
>
3
)1+s(
1(s)H(s)G ====
K = 8
K
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Polar plot
1)s(s
K
(s)H(s)G ++++====
>
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O+
A s = 0 to
j polar plotC O - s = - j to 0
complex conjugate
of polar plot
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+
= +
90:0:90-
0where
esOO j-
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Polar plot&
its conjugate
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.A C
>
>O
-
O+
The infinite semi circle
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The infinite semi circle
maps on to origin.
For the infinitesimal
semi circle,
====j
esput
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)1s(s1(s)H(s)G
++++
====
)1e(e
1
jj ++++
====
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This is a radius
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This is a radius
vector of infinite
magnitude and angle
changes from
.90-to0to90 ++++
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ABC
O+
O-
.- 1
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P = 0
N = 0
Z = 0
Close Loop System stable
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Root locus>
>
>
>
)1+s(s
1(s)H(s)G ====
