Use of smith predictor in the outer loop for cascaded control of unstable and integrating processes

Cascade control is an alternative to conventional single feedback control to improve the performance of a control system, particularly in the presence of disturbances. However, to date, most published papers on cascade control strategies are for control of stable processes. In this paper, further results are presented for a new cascade control structure and controller design based on standard forms for controlling unstable or integrating processes initially given by the authors. It is the outer loop, where a PI-PD Smith predictor scheme is used, that is enhanced to improve the closed-loop response of the system. Examples are given to illustrate the use of the proposed method and its superiority over the conventional cascade control (CC) and an existing cascade control scheme and design method, which has been proposed for controlling unstable and integrating processes.