Robust IMC design for disturbance rejection in processes with time delay

Internal Model Control (IMC) design methods for load disturbance rejection in stable processes with a time delay and time constants are examined. The standard IMC controller which is a modified H₂-optimal controller is compared with two alternative IMC controllers. The main differences, related to the modifications for ringing-free control, the choice of the robustness filter and the location of controller poles and zeros, are discussed. The performance comparison, made for equal robust stability, is favorable to the alternative IMC controllers. The controller choice depends on the process dead time, the disturbance dynamics and the robustness demands.