PID controller design and tuning in networked control systems

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Doctoral thesis (article-based)
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Networked control systems (NCS) are distributed real-time computing and control systems with sensors, actuators and controllers that communicate over a shared medium. The distributed nature of NCS and issues related to the shared communication medium pose significant challenges for control design, as the control system no longer follows the rules of classical control theory. The main problems that are not well covered by the traditional control theory are varying time-delays due to communication and computation, and packet losses. During recent years, the control design of NCS and varying time-delay systems has been extensively researched. This investment has provided us with new results on stability. Often the proposed methods and solutions are far too complex for industrial use, especially if wireless automation applications are considered. The algorithms are computationally heavy, possibly requiring complete information from say, a network of hundreds or thousands of nodes. In the wireless case this is not feasible. The above justifies the use and research of simple controller structures and algorithms for NCS. Despite the growing interest towards more advanced control algorithms, the Proportional-Integral-Derivative (PID) controller still has a dominant status in the industry. Nevertheless, using PID for NCS has not been thoroughly investigated, especially with regard to controller tuning. This thesis proposes several PID tuning methods, which provide robustness against the challenges of NCS, namely varying time-delays (jitter) and packet loss. The doctoral thesis consists of a summary and eight publications that focus on the PID controller design, tuning and experimentation in NCS. The thesis includes a literature review of recent stability and control design results in NCS, a summary of publications and the original publications. The control design methods applied in the publications are also reviewed. In the thesis, several new methods for PID tuning in NCS are proposed. To make the methods usable, a PID tuning tool that implements one of the tuning methods is also developed. In order to verify the results of control design with real processes, the thesis suggests using the MoCoNet platform developed at the Helsinki University of Technology, Finland. The platform provides the tools for remote laboratory experiments in NCS settings. The results of the thesis indicate that the PID controller is well suited for NCS provided that the properties of the integrated communication and control system are taken into account in the tuning phase.
networked control systems, PID controller, tuning, varying time-delay, wireless automation
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  • [Publication 1]: Lasse Eriksson. 2005. A PID tuning tool for networked control systems. WSEAS Transactions on Systems, volume 4, number 1, pages 91-97. © 2005 World Scientific and Engineering Academy and Society (WSEAS). By permission.
  • [Publication 2]: Lasse Eriksson and Heikki N. Koivo. 2005. Tuning of discrete-time PID controllers in sensor network based control systems. In: Proceedings of the 6th IEEE International Symposium on Computational Intelligence in Robotics and Automation (CIRA 2005). Espoo, Finland. 27-30 June 2005, 6 pages. © 2005 IEEE. By permission.
  • [Publication 3]: Mikael Pohjola, Lasse Eriksson, Vesa Hölttä, and Timo Oksanen. 2005. Platform for monitoring and controlling educational laboratory processes over Internet. In: Proceedings of the 16th IFAC World Congress (IFAC 2005). Prague, Czech Republic. 3-8 July 2005, 6 pages. © 2005 International Federation of Automatic Control (IFAC). By permission.
  • [Publication 4]: Mikael Pohjola, Lasse Eriksson, and Heikki Koivo. 2006. Tuning of PID controllers for networked control systems. In: Proceedings of the 32nd Annual Conference of the IEEE Industrial Electronics Society (IECON 2006). Paris, France. 6-10 November 2006, pages 4650-4655. © 2006 IEEE. By permission.
  • [Publication 5]: Lasse Eriksson and Timo Oksanen. 2007. PID controller tuning for integrating processes: Analysis and new design approach. In: Proceedings of the 4th International Symposium on Mechatronics and its Applications (ISMA 2007). Sharjah, UAE. 26-29 March 2007, 6 pages. © 2007 ISMA07. By permission.
  • [Publication 6]: Lasse M. Eriksson and Mikael Johansson. 2007. PID controller tuning rules for varying time-delay systems. In: Proceedings of the 2007 American Control Conference (ACC 2007). New York City, USA. 11-13 July 2007, pages 619-625. © 2007 IEEE. By permission.
  • [Publication 7]: Lasse M. Eriksson and Mikael Johansson. 2007. Simple PID tuning rules for varying time-delay systems. In: Proceedings of the 46th IEEE Conference on Decision and Control (CDC 2007). New Orleans, LA, USA. 12-14 December 2007, 7 pages. © 2007 IEEE. By permission.
  • [Publication 8]: Lasse M. Eriksson and Heikki N. Koivo. 2008. Comparison of low-complexity controllers in varying time-delay systems. SICE Journal of Control, Measurement, and System Integration, volume 1, number 2, pages 111-119. © 2008 Society of Instrument and Control Engineers (SICE). By permission.
  • [Errata file]: Errata of publication 6