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Control Systems

Nyquist Stability Criteria-1

The open loop...

Question

The open loop part of a unity feedback control system G(s) is unstable and has two poles on the right hand side of thes-plane. However, the closed loop system is stable. The number of encirclements made by the Nyquist plot of the (-1, 0) point in the G(s) plane is

A

2

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B

0

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C

- 3

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D

- 1

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Solution

The correct option is A 2
Given that P = number of open loop poles in the right hand of s-plane = 2
Also given closed loop system is stable so Z = 0
$∵$ N = P - Z
N = 2 -0
N = 2
$∴$ Number of encirclements, N = 2

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