DESIGN OF IMC AND ADRC CONTROLLERS FOR LINEAR AND TIME DELAYED SYSTEMS WITH FRACTIONAL ASPECTS AND THEIR APPLICATIONS

Abstract

Over the past decades, the proportional integral derivative (PID) controller has been unequivocally the most commonly used industrial control algorithm and has served as a perennial workhorse in the modern control industry. The work undertaken in this thesis deals with the incorporation of fractional order paradigm in PID control and also involves the formulation of alternative strategies that have a potential to replace the ubiquitous PID controller in industrial applications. The first part of this thesis explores the internal model control (IMC) scheme that has attained widespread popularity due to its simple structure, single tuning parameter and its ability to be seamlessly transformed into the widely used PID controller. A brief review of the internal model control technique is presented and the controller design procedure via single degree of freedom and two degree of freedom structures is expounded. Next, the fundamentals of fractional order control are introduced and the concept of model order reduction along with CRONE principle is incorporated into the IMC structure, leading to the formulation of fractional order internal model control (FO-IMC) scheme. The stability and robustness analyses are undertaken and the FO-IMC technique is compared with several existing techniques from the literature. Subsequently, a weighted internal model control scheme is proposed that attempts to subsume the merits of multiple IMC controllers having different time constants of set-point tracking filter via assignment of time varying weights to the individual IMC controllers. The weights assigned to IMC controllers are updated randomly or tuned via a fractional order optimization algorithm. The efficacy of weighted IMC approach is demonstrated via its application on hardware setup of dc servo motor as well as various illustrative examples from literature.