Improved disturbance rejection with modified Smith predictor for integrating FOPTD processes

Abstract

Improved disturbance rejection behaviour with modified Smith predictor is reported here for controlling integrating first-order plus time delay processes. Due to location of a pole at origin, process is said to be integrating in nature. In addition, due to presence of considerable dead time, it is very difficult to obtain the desired output from such processes using conventional control technique. In practice, a good number of chemical processes (e.g. distillation, evaporation, combustion, drying etc.) are integrating as well as delay dominating in nature. To ascertain desirable close-loop response for processes with large dead time, Smith predictor is a renowned methodology due to its simplicity and efficacy. But, this technique fails to perform satisfactorily for integrating processes with time delay. A good alternative can be considered as modified Smith predictor. This technique involves more than one controller for achieving desirable servo as well as regulatory responses. To avoid the tuning complexity of controllers, our proposed scheme involves comparatively less number of controllers with relatively simple tuning guide line. Distinct feature of the proposed tuning scheme is that process overshoot can be restricted within acceptable limit as well as improved load recovery can also be achieved. Efficacy of the proposed scheme is substantiated through performance assessment as well as stability study in comparison with well-known modified Smith predictor based tuning relations is also reported.