Relocated internal model control based cascade control strategy for stable and unstable systems with delay

Abstract

To control unstable and stable plants a new series cascade control structure (SCCS) is proposed. The proposed SCCS incorporates two or three controllers (setpoint tracking controller, secondary disturbance rejection controller and stabilising controller for only unstable plants). Internal model control scheme (IMCS) augmented with integration of square error (ISE) minimisation along with robustness considerations are applied to design the secondary loop disturbance rejection controller. In contrast, relocated IMCS augmented with ISE minimisation is applied for the outer loop or setpoint tracking controller. Routh Hurwitz stability criteria and maximum sensitivity considerations are used to design the proportional-derivative (PD) controller, which stabilises the unstable plant. It is important to note that the suggested SCCS only needs four controller parameters to be tuned, which is less than the recently reported techniques. Robust stability analysis of the proposed SCCS is performed in the presence of uncertainty. The simulation results depict that the suggested approach imparts pre-eminent improvement in closed-loop performance such as faster setpoint tracking and better disturbance rejection for nominal and perturbed plants.

KEYWORDS:

• Series cascade control structure
• time delay
• disturbance rejection
• unstable
• robustness
• integration of square error

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors confirm that data and materials that support the results or analyses presented in this paper are freely available upon request.

Additional information

Notes on contributors

Sridhar

Sridhar received the Bachelor's degree in Electrical & Electronics Engineering from the Birla Institute of Technology, Mesra, Ranchi, India, in 2019 and the M.Tech degree in Control System Engineering from the National Institute of Technology Patna, India, in 2023. His research interest is process control. He is currently working as a Senior Design Engineer in L&T Construction.

Deepak Kumar

Deepak Kumar received his B.Tech degree in Electrical Engineering from Muzaffarpur Institute of Technology, Muzaffarpur, Bihar, India in 2018 and M.Tech degree in Electrical engineering (Control System Engineering) from National Institute of Technology, Patna, India in 2021. He is currently working towards the Ph.D. degree in Electrical engineering (Process Control) from National Institute of Technology, Patna, India. His current research focuses on control strategies for industrial processes.

G. Lloyds Raja

G. Lloyds Raja (Member, IEEE and IFAC-ACDOS) received his Bachelors (in Electronics and Communication Engineering) and Master's (in Embedded System Technologies) degrees from Anna University in 2009 and 2011, respectively. He was awarded Ph.D. from the Electrical Engineering Department of Indian Institute of Technology Patna in 2018. While serving as an Assistant Professor at Kalinga Institute of Industrial Technology (between 2017 and 2020), he visited the department of Automation at Shanghai Jiao Tong University (China) for a short duration as a postdoctoral researcher. Since 2020, he is with the Electrical Engineering Department of National Institute of Technology Patna where he serves as an Assistant Professor. In 2023, he received the IEEE-Industry Electronics society, Student and Young Professional Prize. His current research interests include chemical process control, advanced load frequency control strategies, adaptive control and applications of meta-heuristic optimization techniques for controller tuning. He has edited two books on control engineering, authored several book chapters and has more than 45 publications in peer-reviewed international conference proceedings and reputed journals.

Sudipta Chakraborty

Sudipta Chakraborty obtained his B.Tech degree in Electronics and Instrumentation Engineering from WBUT, India in 2012. After which, he received his M.Tech degree from National Institute of Technology Rourkela, India in 2014. In 2018, he was awarded Ph.D. degree in Electrical Engineering from the same institute. He is currently working as an Assistant Professor in Department of Electronics and Instrumentation Engineering, National Institute of Technology Silchar, India. His research area includes Process control, PID control, Robust control, Time-delay systems, Fractional Order Control.