ABSTRACT
There always exists uncertainty in practice. Uncertainty means that we cannot exactly predict the output of a system even if the input is known. Hence, it is most desirable that the controller be robust; that is, the controller is insensitive to uncertainty. This chapter begins with some basic concepts of robust control, such as norm, system gain, design specification, and controller parameterization. Then robust stability and robust performance are studied based on these concepts; the necessary and sufficient conditions for robust stability and robust performance are given. The final topic is to discuss the robustness of the first-order system with time delay. This chapter sets the scene for further study in the subsequent chapters by formulating important concepts and results in robust control theory.
