FAQ: What are the conditions for stability or instability based on the number of zeroes in the RHP?

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Posted by Sean Humbert, 11 November 2002
The nyquist criterion states that Z = P - N where

Z = # of closed loop poles in the RHP (Z>0 implies instability)
P = # of open loop poles (of L=PC) in the RHP
N = # of CCW encirclements of the -1 + 0j point in the complex plane

Hence, from determining the number of unstable poles of the open loop system and the number of encirclements of -1 of the nyquist plot (polar plot of the open loop system) we can determine the closed loop stability.