New insight into internal model control filter design for load disturbance rejection

In this study, a modified design of the internal model control (IMC) filter is proposed for improving closed-loop system performance of load disturbance rejection, especially for slow processes in industrial and chemical engineering practices. The deficiency of a conventional IMC filter design for controller tuning is revealed with regard to load disturbance rejection. By constructing one or more asymptotic canceling constraints for disturbance rejection, a modified IMC filter is proposed to reduce the influence from the time constant(s) of the process or repetitive-type load disturbance to the closed-loop disturbance rejection performance. Similar to a conventional IMC filter, there is essentially a single adjustable parameter in the proposed IMC filter, which can be monotonically tuned to meet with the compromise between the achievable disturbance rejection performance and the closed-loop system stability. Quantitative tuning formulae and guidelines for this adjustable parameter are developed in terms of the widely used first- and second-order process models with time delay. Illustrative examples are given to show the effectiveness and merits of the proposed IMC filter.