Practical direct PID/I-PD controller tuning and its application to chemical processes

A new, practical method for direct tuning of PID controllers using operation data under feedback control is proposed. Neither open-loop nor closed-loop identification is required in the framework of direct tuning, but conventional methods have the following problems: iterative experiments are needed, changes of the manipulated variable are not evaluated, and it is difficult to properly determine a reference model without information on a process. In the present work, to solve these problems and make direct tuning practicable for process control, extended fictitious reference iterative tuning (E-FRIT) is proposed. E-FRIT can be used not only for PID control but also I-PD control, which is more suitable for process control. The usefulness of E-FRIT and its advantage over the conventional method are demonstrated through a case study of an unstable polymerization process.