What is Nyquist Criteria ?

What is Nyquist Criteria ?

Nyquist Stability Criterion Definition

The Nyquist stability criterion is defined as a graphical technique used in control engineering to determine the stability of a dynamical system.

Application of Nyquist Criterion

It applies to open-loop systems and can handle transfer functions with singularities, unlike Bode plots.

Criterion Formula

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.

Examples of Nyquist Criterion

Different open-loop transfer functions demonstrate stable, unstable, and marginally stable systems using Nyquist plots.

Matlab Examples

Matlab code helps plot Nyquist diagrams to analyze the stability of various systems.