Stability and Robustness of Feedback Systems

Abstract

Feedback is the main tool for control systems. Stability and robustness are two key issues associated with any feedback design, and are the topics of this chapter. Section 1 addresses internal stability of general interconnected systems and derives a powerful stability condition which is applicable to systems with any feedback and/or feedforward combinations. Section 2 focuses on the conventional unity output feedback configuration and gives the simplifying conditions and Nyquest-like criteria. The plant uncertainties and feedback system robustness to them are discussed in Section 3, both structured and unstructured perturbations are introduced. A special attention is paid to the case where the phase perturbation is limited, a realistic situation.