Internal Model Control Schemes

Abstract

In this chapter, we introduce the class of internal model control (IMC) schemes. These schemes derive their name from the fact that the controller implementation includes an explicit model of the plant as a part of the controller. Such schemes enjoy immense popularity in process control applications where, in most cases, the plant to be controlled is open-loop stable. As will be seen in this chapter, the IMC configuration for a stable plant is really a particular case of the Youla-Jabr-Bongiorno-Kucera (YJBK) parametrization of all controllers that preserve closed loop stability [46]. The IMC parameter here plays the same role as the Youla parameter in the YJBK parametrization, and consequently can be chosen to meet one of several design objectives. Choices of the IMC parameter that lead to some familiar control schemes are discussed. Finally, the chapter concludes with an appraisal of the inherent robustness of the IMC structure to plant perturbations. Throughout this chapter, as indeed in the rest of this monograph, we focus on plants whose modelled parts are linear, time-invariant and finite dimensional. The controllers considered are also assumed to belong to the same class so that the modelled part of the plant and the controller can both be described in the Laplace domain using rational, proper transfer functions.