TUNING OF PID CONTROLLERS FOR TIME DELAY UNSTABLE SYSTEMS WITH TWO UNSTABLE POLES

An improved continuous cycling method is proposed for PID controllers for unstable systems with two unstable poles and time delay. The method involves the determination of the controller settings by solving the magnitude and the phase angle criteria for the system with a proportional controller. Subsequently, incorporating the Proportional-Derivative-Integral (PID) controller transfer function, with unity proportional gain and pre-determined values of reset time and derivative time in the first step, with the system model and again solving the amplitude and the phase angle criteria, we get the updated gain of the controller. The method is applied by simulation on (i) a second order system with time delay and two unstable poles and (ii) a non-linear model of a CSTR with complex conjugate unstable poles and time delay. The controller settings significantly enhance the performances of both the servo and the regulatory problems and give robust performances. (C) 2016, IFAC (International Rderation or Automatic Control) Hosting by Elsevier Ltd. All rights reserved.