Generalized Nyquist Stability of Perturbed Systems

Analysis and design of control systems in the frequency domain is one of the best known methods in control engineering. The stability of single-input single-output systems is investigated via transfer function calculus and Nyquist criterion (Leithead, W.E., and O'Reilly, J., 1991). Multi-input multi-output systems require the transfer matrix operations and characteristic loci. When plants are perturbed characteristic loci can be still used if they are augmented by E-contours or structured E-contours.