DISTURBANCE REJECTION FOR A THIRD ORDER PROCESS CONTROLLED BY A PI-PD CONTROLLER

The purpose of this paper is to investigate using a PI-PD controller in the disturbance rejection associated with a third order process. The PI-PD controller having four parameters are tuned to provide efficient rejection of a step input disturbance input. Controller tuning based on using MATLAB control and optimization toolboxes with an error-based objective function: ISTSE. The control system performance during disturbance rejection is evaluated through the maximum value of the time response and its corresponding time. The ISTSE is the most suitable objective function to tune the PI-PD controller. Using the suggested tuning technique, it is possible to reduce the maximum time response of the closed loop control system to a unit step disturbance as low as 0.141 (maximum value) at 4.6 s. The PI-PD controller is superior in dealing with the disturbance rejection associated with the third order process compared with the PID controller.