Design of Cascaded IMC-PID Controller with Improved Filter for Disturbance Rejection

IMC-PID controllers provide good set point tracking but sluggis disturbance rejection, because of introduction of slow process pole by the conventional filter. In many industrial applications disturbance rejection is important than set point tracking. In this paper PID controller with Internal model control tuning method (IMC-PID) with an improved IMC filter is presented for effective disturbance rejection and robust operation of first order process with time delay (FOPTD). The suggested filter eliminates the slow dominant pole. The present study illustrates that the suggested IMC filter provides good disturbance rejection irrespective of where the disturbance enters the process and provides good robustness to model mismatch in terms of sensitivity in comparison with other methods cited in the literature. Simulation study was performed on processes with different q t ratios to show the effectiveness of suggested method by calculating the controller parameters to have same robustness in terms of maximum sensitivity. The closed loop performance was tested using integral error criteria Viz. IAE, ISE, ITAE. The suggested IMC filter provides good disturbance rejection response for process having<1.