13. 2 The application of Cauchy's Theorem Nyquist Stability Criterion Cauchys theorem: If a closed curve T encircles P poles and Z zeros in a clockwise direction, then the image curve TF-F(T)encircles the origin N=Z-P times in the clockwise direction 13.2.1 F(s)- plane G(s) H(sI The stability is determined by the zeros of the characteristic equation: F(s)≡1+G(s)H(S)=013.2 The application of Cauchy’s Theorem: Nyquist Stability Criterion 13.2.1 F(s) — plane