Robust internal model controller with increased closed-loop bandwidth for process control systems

• Published in: IET control theory & applications 2020-10, Vol.14 (15), p.2134-2146
• Main Authors: Arya, Pushkar Prakash, Chakrabarty, Sohom
• Format: Article
• Language: English
• Subjects: closed loop systems; closed‐loop system bandwidth; control system synthesis; delays; FOPTD systems; fractional order filter; gain margin; laboratory DC servo‐system; modified internal model control structure; m‐IMC; phase margin; PI control; process control; process control systems; Research Article; robust control; robust internal model controller; robust stability; servomotors; standard IMC structure; three‐term control; time delay process control plant
• ISSN: 1751-8644; 1751-8652
• DOI: 10.1049/iet-cta.2019.1182

This study proposes a modified internal model control (IMC) structure in which an additional controller is added to the standard IMC structure to improve the closed-loop system bandwidth. The resulting structure is evaluated to satisfy standard IMC objectives of nominal performance and robust stability. The novelty of the work is to design a fractional order (FO) filter in the IMC structure so that gain margin $(A_m)$(Am) and phase margin ($\phi _m$ϕm) specifications could be independently satisfied for a first-order plus time delay (FOPTD) process control plant. The proposed modified IMC (m-IMC) is simulated for three different FOPTD systems to validate and substantiate the theoretical analysis. The proposed m-IMC is compared with different integer order as well as FO controllers. The transient performance are compared in terms of rise time ($T_{\rm r}$Tr), settling time ($T_{\rm s}$Ts), maximum overshoot (%$M_p$Mp) and the effectiveness is measured in terms of integral square error. To validate the viability of the proposed control scheme, it is implemented on a laboratory DC servo-system.