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Analytical tuning method for cascade control system via multi-scale control scheme

Cascade control strategy has been widely used in process industry owing to its superior disturbance rejection performance over that of the standard single-loop control. Designing the cascade control system is a challenging task, especially for an unstable time-delay process. In this paper, based on the multi-scale control scheme, a new analytical tuning method is presented. The method is applicable to stable and unstable processes where it can be implemented through a fixed or variable tuning approach. In the variable tuning approach, one adjustable tuning parameter is sufficient to obtain desired cascade control performance with the aid of a set of analytical tuning formulae providing direct relationship between the controller parameters and model parameters. Meanwhile, the fixed tuning approach uses a set of empirically developed rules to determine the controller parameters. Numerical studies demonstrate the effectiveness of the proposed method compared with several established cascade control designs reported in the literature.