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Automatic Control Systems - Engineering

Q1:

If Nyquist plot has a encirclement of (-1 + jo) point, the system is stable if

A there are no poles of G(s) H(s) in right-half plane

B there is one pole of G(s) H(s) in right-half plane

C there is no zeros of G(s) H(s) in right-half plane

D none of the above

ANS:A - there are no poles of G(s) H(s) in right-half plane

In Nyquis plot N=Z-P, N=no.of encirclements about origin, P=poles, Z=zeros, i.e.,if P=0 in order to get the system stable, therefore there will be no poles in the RHS plane.

N = 0 (no encirclement), so Z = P = 0 and Z = P.
If N = 0, P must be zero therefore system is stable.