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Mechanical Engineering QUESTION #2385
Question 1
The Nyquist stability criterion states that for a closed-loop system to be stable (when open-loop system has \(P\) poles in the right-half plane):
  • The Nyquist plot must encircle the \((-1, j0)\) point clockwise \(P\) times
  • The Nyquist plot must encircle the \((-1, j0)\) point counterclockwise \(P\) times✔️
  • The Nyquist plot must not cross the negative real axis
  • The Nyquist plot must be a circle
Correct Answer Explanation
Nyquist criterion: \(N=Z-P\) where \(N\) = clockwise encirclements of \((-1,0)\), \(Z\) = closed-loop RHP poles, \(P\) = open-loop RHP poles. For stability \(Z=0\), so \(N=-P\) (i.e., \(P\) counterclockwise encirclements).