On performance of PI controllers designed for a coupled tanks system with uncertain time-varying time-delay

PI controllers are widely used in numerous process control applications in industry because of its simplicity and providing satisfactory performance. This performance may degrade if delays in the process dynamics are not taken into account. Since delays in process control applications may not be measured previously and they may vary during the process, designed PI controller should be robust in presence of uncertain time-varying time-delays. There exist numerous PI controller design approaches for systems having uncertain delays, however, in most of these approaches they are assumed to be time-invariant. In this thesis, a sufficient condition is given for the presence of a controller which stabilizes the given feedback system against the uncertain time-varying time-delays. Then, by utilizing this condition, a robust PI controller design technique for a coupled tanks, whose input is subjecting to uncertain time-varying time-delay, is presented. In addition, Smith-Predictor and delay-based PI controller design techniques are proposed for the same system. Then, in order to examine the effect of uncertain time-varying time-delays in performance of these controllers, several simulation studies are done for the considered coupled tanks system.