ROBUST CONTROL DESIGN USING DUAL LOOP IMC AND ITS APPLICATION IN LOAD FREQUENCY CONTROL

Abstract

Over the past years, the proportional integral controller (PID) controller has been unequivocally the most commonly used industrial control algorithm and has served as a perennial workhorse in the control industry. The work undertaken in this thesis deals with the incorporation of Internal Model Control (IMC) in control and also deals with the formulation of alternative strategies to replace the ubiquitous method of determining predictive model in IMC. 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 parameters and its ability to seamlessly transformed into the widely spread PID controller. A brief review of the IMC scheme is presented and control design procedure via two degree of freedom internal model control (2DF-IMC) is expounded. Next, the fundamentals of Dual IMC are introduced and the concept of various model order reduction (MOR) is incorporated into the dual IMC structure leading to the formation of Proposed Dual IMC. The proposed scheme contains two control loops for disturbance rejection and minimization of oscillations. The inner loop contains an IMC controller and outer loop controller is derived by using a predictive model based on MOR. The step responses of various MOR and its stability is discussed w.r.t original plant model. The efficacy of Dual IMC approach is demonstrated via its application in load frequency control (LFC) issue in two area reheated thermal power system (TPS). An exhaustive comparative and robustness analysis is conducted to verify the effectiveness of controller design using various MOR. Overall, in this thesis, an attempt has been made to formulate and propose controller design technique based on the concept of Dual Loop IMC. The results obtained through simulation are a testimony to the efficacy and robustness of the proposed scheme.