Enhanced IMC-based Load Disturbance Rejection Design for Integrating Processes with Slow Dynamics

By revealing the deficiency of existing internal model control (IMC) based methods for load disturbance rejection for integrating processes with slow dynamics, a modified IMC design is proposed to deal with step or ramp type load disturbance as often encountered in practice. The controller parametrization is based on a two-degree-of-freedom (2DOF) control structure which allows for independent regulation of load disturbance rejection from the setpoint tracking. Analytical controller formulae are given based on classification of the ways by which such load disturbance seeps into the process. It is an obvious merit that there is only a single adjustable parameter in the controller design, which in essence corresponds to the time constant of the closed-loop transfer function for load disturbance rejection, and can be monotonically tuned to meet a trade-off between disturbance rejection performance and closed-loop robust stability. Robust tuning constraints are given correspondingly to accommodate for process uncertainties. An illustrative example is given to show the effectiveness and merits of the proposed method.