Control of time-delay systems through modified Smith predictor using sliding mode controller

Abstract

Smith-Predictor (SP) is used as a dead-time compensating tool for chemical processes as they are Integrating-Plus-Dead-Time (IPDT), pure integrating-type process, and higher-order-integrating-process. The performances of these processes can be improved by modifying SP. The present work deals with the control of dead-time by integrating the first-order-plus-dead-time (IFOPDT) or first-order-plus-dead-time process (FOPDT), and a modified sliding-mode-controller (SMC) in the proposed modified-Smith-predictor (MSP) structure. Here, a modified novel SMC discontinuous tuning-parameter is derived analytically to satisfy performance criteria such as speed adjustment, reducing overshoot and chattering effects. Furthermore, the MSP-SMC structure is implemented in six different processes. This is done to counteract time-delay and constant load-disturbance for integrating processes and a nonlinear system separately. Also, the proposed work is implemented in the real-time lab setup of a neutralisation process. Furthermore, the robustness and invariance properties of the SMC have been analysed against parametric uncertainty. The optimality of the proposed controller parameters is tested by giving uncertainty in the dead time of the process parameters. The proposed design is also implemented in the non-linear and Multi-Input-Multi-Output processes. The performance metrics, IAEs, of 6 case studies have been obtained using MATLAB and the peak overshoots are compared with similar kinds of works.

Research highlights

• The discontinuous control law of SMC_MSP tuning equation KD has been modified.

• Modified novel KD equation is derived ANALYTICALLY to satisfy the performance criteria and implemented in the modified Smith predictor structure to counteract the dead time and constant load disturbance

• Set point filter implemented eliminates the peak overshoot considerably.

• Set point tracking, disturbance rejection and robustness have been analysed.

• IFOPDT, ISOPDT, IHOPDT, Nonlinear CSTR and MIMO processes were simulated.

KEYWORDS:

• Sliding mode controller
• modified Smith predictor
• dead-time
• robustness
• uncertainty

Acknowledgments

The first author is willing to acknowledge and thank CSIR-CLRI for providing the infrastructure and facilities for carrying out this research. The first author is involved in data curation, formal analysis and investigation and she is a Research Fellow at Anna University, Chennai. The 2nd author is involved in resources and validation. He is a professor at Anna University, Chennai. The third author has contributed through supervision, methodology and conceptualisation and is the corresponding author. He is working as a professor in time delay systems, process modelling, optimisation and control aspects.

Disclosure statement

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

Data availability statement

Data sharing is not applicable to this article as no new data were created or analysed in this study.

Additional information

Notes on contributors

P. Princes Sindhuja

P. Princes Sindhuja is a research scholar pursuing her PhD under Anna University. Her field of interest is PID control, Time delay systems and Sliding Mode Control. Her MTech project was on SMC and she is a full time research student.

V. Vijayan

Dr. V. Vijayan obtained his M.E degree in Instrumentation branch from Anna University, and Ph.D from Anna University, Chennai. He has 20 years of teaching experience in various Engineering colleges. His area of interest is PID control for SISO and MIMO systems. He has published many Journal papers in various International Journals and is a reviewer for many international Journals. He has presented several technical papers in National & International Conferences across the Country. He has organized many national level workshops, Conferences, Seminars and Faculty Development Programmes. At present he is guiding some Ph.D scholars from Anna University.

Rames C. Panda

Dr Rames C. Panda received the M.Tech. and Ph.D. degrees in chemical engineering in 1989 and 1994, respectively, from the Indian Institute of Technology, Madras. In 1993, he joined Chemical Engg. Dept. of CLRI, Council of Scientific & Industrial Research, as a scientist. He looks after industrial instrumentation and process control related works. He has carried out research works at University of Karlsruhe (TH), Germany in 1997-8., at PSE, Chem Engg Dept, NTU, Taiwan (2002-3) and Chem Engg Dept, Curtin Univ of Tech, Australia (2006-7). Presently, he is working as a Principal scientist & faculty at Chem Engg Dept., CLRI. His research area includes autotuning, PID controllers and analysis of control systems, process modeling, and simulation. He is involved in reviewing and in editorial board of many journals.