Process Control: Modeling, Design, and Simulation

9.5. Summary of IMC-Based PID Controller Design for Stable Processes

We have shown several examples where the IMC design procedure could be used to develop an equivalent PID-type control law. For stable processes with no time delay, the IMC-based PID procedure gives exactly the same feedback performance as does IMC. For stable processes with a time delay, the IMC-based PID procedure will not give exactly the same performance as IMC, because a Padé approximation for dead time is used in the controller design.

We want this following point to be clear to the reader. For process transfer functions without time delays, the IMC-based PID controller will yield exactly the same performance as does IMC. This will occur if no approximation has to be made ...