Process Control: Modeling, Design, and Simulation

Chapter 9. The IMC-Based PID Procedure

In Chapter 8 we developed a transparent framework for control-system design: the IMC structure. One nice thing about the IMC procedure is that it results in a controller with a single tuning parameter, the IMC filter (λ). For a system that is “minimum phase,” λ is equivalent to a closed-loop time constant (the “speed of response” of the closed-loop system). Although the IMC procedure is clear and IMC is easily implemented, the most common industrial controller is still the PID controller. The purpose of this chapter is to show that the IMC block diagram can be rearranged to the form of a standard feedback control diagram. We find that the IMC law, for a number of common process transfer functions, is equivalent ...