Analysis and Synthesis in the Frequency Domain

Abstract

This chapter begins with a brief discussion of the Nyquist stability criterion and recalling the important concepts of gain and phase margins. Next, the feedback specification for single-input single-output system is discussed, together with various representations of the unstructured uncertainty, robust performance, and robust stability. It is followed by a discussion of Bode’s gain–phase relationships (Bode integrals) and how they can be used in design (Bode Ideal Cutoff). Next, the penalty associated with a non-minimum phase system is examined, followed by a brief discussion of usual compensators (Lead, PI, PID). Finally, the discussion is extended to multi-input multi-output system; the small gain theorem allows to derive sufficient conditions for stability. These robustness tests are useful to evaluate a lower bound to the stability margin with respect to spillover (when the high order dynamics is neglected). The chapter concludes with a short list of references and a set of problems.