Design and Experimental Evaluation of a Self-Tuning Controller Supplementing a Robust PID Controller.

PID controllers have been widely used in many chemical processes. Because they have only three control parameters and their physical meanings can be easily grasped. However, it is difficult to tune those parameters practically, since the process dynamics often change due to operating conditions or various disturbances. For this problem, a design method of robust PID controllers has been already proposed by the authors in order to guarantee the stability of the control system. However, as that control method is conservative, the desirable setpoint response can not be always obtained. In this paper, a design scheme of a self-tuning pre-filter is proposed to supplement the robust PID controller based on the two-degree-of-freedom control scheme. According to the proposed scheme, the transient property for the setpoint response can be improved keeping the robust stability. Finally, the proposed scheme is experimentally evaluated on an air pressure control system.