- Graphical Technique.
- Only considers the Nyquist plot of open-loop systems, but it can be applied without explicity computing the poles and zeros of either the closed-loop or open-loop system.
Nyquist Stability Criterion can be expressed as Z = N + P
Where:
- Z = number of roots of 1+G(s)H(s) in right-hand side (RHS) of s-plane (It is also called zeros of characteristics equation)
- N = number of encirclement of critical point 1+j0 in the clockwise direction
- P = number of poles of open loop transfer function (OLTF) [i.e. G(s)H(s)] in RHS of s-plane.
N = –P system is stable.
https://www.electrical4u.com/nyquist-stability-criterion/