Design of Internal Model Control and Internal Model Feed-Forward Control For Liquid Level System

Abstract

This project is concerned with the study of liquid level system and designing Internal Model Control (IMC) and Internal Model-Feed-Forward Control (IMC-FF) for this system. Liquid Level System has various configurations such as: Single Tank System, Two-Tank Interacting and Non-Interacting System, Three-Tank Non-Interacting System. In this project IMC and IMC-FF are designed for all these configurations and the responses of these controllers are compared with PID, PID plus Feed-Forward controllers. After comparison it is found that for first order system (single tank system) there is not much difference between IMC and IMCFF but for higher order systems (two-tank interacting, two –tank non-interacting, three-tank non-interacting system) IMC-FF performs better than IMC. PID and PID plus Feed-Forward performance are not good enough as compared to IMC and IMC-FF. PID plus Feed-Forward perform better than PID in case of negative disturbances but if the disturbances are positive the performance of PID is better than PID plus Feed-Forward.At the end of the project empirical formulae are derived for rise time, settling time,percentage overshoot and peak time. When desired values of these performance indices have to be obtained these formulae are used to evaluate the filter coefficient for IMC-FF. Once the filter coefficient is known, IMC-FF can be designed very easily.The software used for the simulation purpose is MATLAB and for mathematical modeling, a practical set up of four tank system is used.