PI-PD controllers for controlling stable processes with inverse response and dead time

Many tuning methods for controlling stable processes with dead time can be found in the literature. Usually, proportional-integral-derivative (PID) controllers are used for this purpose. In practice, stable processes with inverse response characteristics can also be encountered. Addition of inverse response characteristic makes the control of a process more troublesome. Therefore, the use of PID controllers for tuning inverse response processes may lead to unsatisfactory closed loop responses. On the other hand, PI-PD controllers have been shown to perform in very good closed loop responses where PID controllers cannot result in satisfactory closed loop responses. Therefore, this paper adopts the structure previously suggested by the author for controlling processes without inverse response. This adaptation, in conjunction with a simple but powerful factorization, eliminates the affect of the inverse response term in the closed loop transfer function, hence resulting in a simplified design procedure. Tuning parameters of the PI-PD controller used in the control structure are found using standard forms, which is a simple algebraic approach and proven to be resulting in very satisfactory closed loop responses. Simulation examples are provided to illustrate the superiority of the proposed method over some existing ones.