Series cascade control: An outline survey

Series cascade control structure (SCCS) is widely used in process industries as unity feedback configuration fails to reject the load disturbances before the controlled variable deviates from the setpoint. Several variants of the conventional SCCSs have been reported in the literature to obtain improved closed-loop performance as compared to the conventional structure. For processes with large time delay, cascade control may not yield satisfactory closed-loop performance. To overcome this problem, several modified Smith predictor based SCCS have been reported in the literature. In this manuscript, various series cascade control strategies are briefly reviewed and their advantages and disadvantages are discussed. Suitable tuning strategies for a class of stable, unstable and integrating process models are recommended in order to help the user in selecting the appropriate control strategy. This review covers only model-based series cascade control strategies in which controller parameters are expressed in terms of known process model parameters.