{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,12]],"date-time":"2026-02-12T10:30:44Z","timestamp":1770892244677,"version":"3.50.1"},"reference-count":25,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2020,9,25]],"date-time":"2020-09-25T00:00:00Z","timestamp":1600992000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Agent\u00fara pre vedu a v\u00fdskum SK","award":["APVV SK-IL-RD-18-0008"],"award-info":[{"award-number":["APVV SK-IL-RD-18-0008"]}]},{"name":"Vedeck\u00e1 grantov\u00e1 agent\u00fara","award":["VEGA 1\/0745\/19"],"award-info":[{"award-number":["VEGA 1\/0745\/19"]}]},{"DOI":"10.13039\/501100004329","name":"Slovenian Research Agency","doi-asserted-by":"publisher","award":["P2-0001"],"award-info":[{"award-number":["P2-0001"]}],"id":[{"id":"10.13039\/501100004329","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>This paper analyzes the first-order and first-order time-delayed systems control approaches, focusing mainly on unstable systems. First, it discusses asymmetries between the disturbance observer-based (DOB) control with decoupled tracking and the disturbance rejection responses, stressing applications to stable and unstable plants. The paper analyzes some DOB-based control solutions for unstable systems which do not use internal closed-loop stabilization. The novelty of the paper is thorough study accompanied with a comprehensive explanation of the differences between two distinct approaches: the transfer-function- and the closed-loop-based feedforward control approach from the point of view of control constraints. It is clearly illustrated that the main cause of instability of DOB-based approaches, applied to unstable systems, is given by their effort to impose on the system the unstable dynamics of the chosen nominal process model. It is also shown that the closed-loop stability of the DOB-based control, applied to the unstable systems, can be restored by using the supervising reference model control (RMC). The main novelty of the proposed approach is that its eliminates the mentioned stability problems while maintaining the full functionality of the chosen control structures. RMC has so far only been implemented for generating a setpoint feedforward signal. However, by generalization of this approach for disturbance rejection, the methodology of DOB design, based on nominal models, can be extended to the control of unstable systems. Without the use of disturbance reference models, the interactions of the master stabilizer with disturbance compensation cannot be eliminated. Without the internal stabilization, the stable transients can only be achieved by designing controllers based on stable models, instead of unstable ones. The existing modifications of DOB-based schemes for unstable plants, proposed in some references, are shown to lead to traditional Proportional-Integrative (PI) control, thus losing all the advantages over the PI controllers. In all the considered structures, the role of integrating models is also emphasized.<\/jats:p>","DOI":"10.3390\/sym12101595","type":"journal-article","created":{"date-parts":[[2020,9,25]],"date-time":"2020-09-25T08:57:32Z","timestamp":1601024252000},"page":"1595","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Asymmetries in the Disturbance Compensation Methods for the Stable and Unstable First Order Plants"],"prefix":"10.3390","volume":"12","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-4957-1894","authenticated-orcid":false,"given":"Mikulas","family":"Huba","sequence":"first","affiliation":[{"name":"Institute of Automotive Mechatronics, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology in Bratislava, 812 19 Bratislava, Slovakia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1167-1681","authenticated-orcid":false,"given":"Pavol","family":"Bistak","sequence":"additional","affiliation":[{"name":"Institute of Automotive Mechatronics, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology in Bratislava, 812 19 Bratislava, Slovakia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8110-8985","authenticated-orcid":false,"given":"Damir","family":"Vrancic","sequence":"additional","affiliation":[{"name":"Department of Computer Automation and Control, J. Stefan Institute, SI-1000 Ljubljana, Slovenia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6347-6653","authenticated-orcid":false,"given":"Katarina","family":"Zakova","sequence":"additional","affiliation":[{"name":"Institute of Automotive Mechatronics, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology in Bratislava, 812 19 Bratislava, Slovakia"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2020,9,25]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"O\u2019Dwyer, A. (2009). Handbook of PI and PID Controller Tuning Rules, Imperial College Press. [3rd ed.].","DOI":"10.1142\/p575"},{"key":"ref_2","first-page":"217","article-title":"Closser control of loops with dead time","volume":"53","author":"Smith","year":"1957","journal-title":"Chem. Eng. Prog."},{"key":"ref_3","unstructured":"Huba, M., Kul\u2019ha, P., and \u017d\u00e1kova, K. (1995, January 4\u20137). Observer-Based Control of Unstable Process with Dead Time. Proceedings of the 10th Conference Process Control\u201995, Tatransk\u00e9 Matliare, Slovakia."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1062","DOI":"10.1016\/j.automatica.2007.08.022","article-title":"A new dead-time compensator to control stable and integrating processes with long dead-time","volume":"44","author":"Garcia","year":"2008","journal-title":"Automatica"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"197","DOI":"10.1016\/j.isatra.2017.09.020","article-title":"A generalized smith predictor for unstable time-delay SISO systems","volume":"72","author":"Sanz","year":"2018","journal-title":"ISA Trans."},{"key":"ref_6","first-page":"728","article-title":"Limits of a Simplified Controller Design Based on IPDT models","volume":"232","author":"Huba","year":"2018","journal-title":"Proc. Inst. Mech. Eng. Part I J. Syst. Control Eng."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Huba, M. (February, January 29). Improving noise attenuation in modified filtered Smith predictor. Proceedings of the 2020 Cybernetics and Informatics (KandI), Velke Karlovice, Czech Republic.","DOI":"10.1109\/KI48306.2020.9039891"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"285","DOI":"10.1049\/ip-cta:20020438","article-title":"Control of integral processes with dead-time. Part 1: Disturbance observer-based 2DOF control scheme","volume":"149","author":"Zhong","year":"2002","journal-title":"IEE Proc. Control Theory Appl."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"407","DOI":"10.1016\/j.conengprac.2007.05.006","article-title":"Dead-time compensators: A survey","volume":"16","author":"Camacho","year":"2008","journal-title":"Control. Eng. Pract."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"38","DOI":"10.1016\/j.jprocont.2008.02.003","article-title":"Unified approach for robust dead-time compensator design","volume":"19","author":"Camacho","year":"2009","journal-title":"J. Process Control"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"111","DOI":"10.1016\/S0019-0578(00)00039-2","article-title":"A new modified Smith predictor: The concept, design and tuning","volume":"40","year":"2001","journal-title":"ISA Trans."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"11646","DOI":"10.1021\/ie401395x","article-title":"Simple Tuning Rules for Dead-Time Compensation of Stable, Integrative, and Unstable First-Order Dead-Time Processes","volume":"52","author":"Torrico","year":"2013","journal-title":"Ind. Eng. Chem. Res."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"100092","DOI":"10.1016\/j.ifacsc.2020.100092","article-title":"A survey of international views on a first course in systems and control for engineering undergraduates","volume":"13","author":"Rossiter","year":"2020","journal-title":"IFAC J. Syst. Control"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"291","DOI":"10.1016\/S0959-1524(02)00062-8","article-title":"Simple analytic rules for model reduction and PID controller tuning","volume":"13","author":"Skogestad","year":"2003","journal-title":"J. Process Control"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"539","DOI":"10.1115\/1.1513570","article-title":"Disturbance Observers for Rigid Mechanical Systems: Equivalence, Stability, and Design","volume":"124","author":"Schrijver","year":"2002","journal-title":"ASME J. Dyn. Syst. Meas. Control"},{"key":"ref_16","unstructured":"Morari, M., and Zafiriou, E. (1989). Robust Process Control, Prentice Hall."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"36","DOI":"10.1016\/j.jprocont.2018.06.011","article-title":"Optimal PI and PID control of first-order plus delay processes and evaluation of the original and improved SIMC rules","volume":"70","author":"Grimholt","year":"2018","journal-title":"J. Process Control"},{"key":"ref_18","unstructured":"Abe, N., and Yamanaka, K. (2003, January 4\u20136). Smith predictor control and internal model control\u2014A tutorial. Proceedings of the SICE 2003 Annual Conference (IEEE Cat. No.03TH8734), Fukui, Japan."},{"key":"ref_19","unstructured":"Visioli, A. (2006). Practical PID Control, Springer."},{"key":"ref_20","first-page":"83","article-title":"A new servo method in mechantronics","volume":"107-D","author":"Ohishi","year":"1987","journal-title":"Trans. Jpn. Soc. Elect. Eng."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1083","DOI":"10.1109\/TIE.2015.2478397","article-title":"Disturbance-Observer-Based Control and Related Methods\u2014An Overview","volume":"63","author":"Chen","year":"2016","journal-title":"IEEE Trans. Ind. Electron."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"48","DOI":"10.1109\/37.526915","article-title":"Anti-Windup, Bumpless and Conditioned Trnasfer Techniques for PID Controllers","volume":"16","author":"Peng","year":"1996","journal-title":"IEEE Control Syst."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"283","DOI":"10.1109\/41.681227","article-title":"A load torque compensation scheme under the speed measurement delay","volume":"45","author":"Hong","year":"1998","journal-title":"IEEE Trans. Ind. Electron."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Fliess, M., and Join, C. (2014, January 24\u201327). Stability margins and model-free control: A first look. Proceedings of the 2014 European Control Conference (ECC), Strasbourg, France.","DOI":"10.1109\/ECC.2014.6862167"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"850","DOI":"10.1016\/j.isatra.2013.09.012","article-title":"On the centrality of disturbance rejection in automatic control","volume":"53","author":"Gao","year":"2014","journal-title":"ISA Trans."}],"container-title":["Symmetry"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-8994\/12\/10\/1595\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T10:13:33Z","timestamp":1760177613000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-8994\/12\/10\/1595"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,9,25]]},"references-count":25,"journal-issue":{"issue":"10","published-online":{"date-parts":[[2020,10]]}},"alternative-id":["sym12101595"],"URL":"https:\/\/doi.org\/10.3390\/sym12101595","relation":{},"ISSN":["2073-8994"],"issn-type":[{"value":"2073-8994","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,9,25]]}}}