Robust Controller Design for Uncertain Dynamic Systems Using Approximate Models

Controller design for continuous and discrete systems whose models are unknown or highly complex are frequently based upon the use of a simple, approximate and, very often, rough and ready model. In such circumstances it is vital to be able to quantify the degree of uncertainty to be expected from the use of such a model for prediction of close-loop characteristics. It is shown how classical frequency -domain design techniques can be extended to incorporate information deduced from the observed differences between open-loop plant and approximate model step response to quantify this uncertainty and in particular, to guarantee closed-loop stability and tracking of step demands.