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A closed-loop control system is stable if the Nyquist plot of the corresponding open-loop transfer function

1. encircles the s-plane point (-1 + j0) in the counterclockwise direction as many times as the number of right-half-s-plane poles.
2. encircles the s-plane point (0 - j1) in the clockwise direction as many times as the number of right-half-s-plane poles.
3. encircles the s-plane point (-1 + j0) in the counterclockwise direction as many times as the number of left-half-s-plane poles.
4. encircles the s-plane point (-1 + j0) in the counterclockwise direction as many times as the number of right-half-s-plane zeros.

Correct answer: encircles the s-plane point (-1 + j0) in the counterclockwise direction as many times as the number of right-half-s-plane poles.

Solution

The correct option is right because the Nyquist stability criterion states that for a closed-loop system to be stable, the Nyquist plot must encircle the critical point (-1 + j0) in a manner that corresponds to the number of unstable poles (right-half-plane poles) in the open-loop transfer function.

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