PID Control
Researchers: Karl Johan Åström, Tore Hägglund, and Per-Ola Larsson
This project has been in progress since the beginning of the eighties, and resulted in industrial products as well as several PhD theses. Three monographs on PID control that are based on experiences obtained in the project have also been published. The last is "Advanced PID Control", published in 2005. It is also translated to Spanish 2009: "Control PID avanzado". The research is currently focused on the following topics:
Filter order selection for PI and PID controllers
Measurements often have small amount of noise since sensors are not perfect. This will be reflected in the control signal behaviour in e.g. high variance or large inter-sample jumps if considering a discrete time setting. Previous work on PI and PID controllers often focus on proportional-, integral- and derivative gains at design but the filter action is added afterwords such that a resonable sensitivity to noise is given. However, the filter changes phase and gain of the controller and the initial tuning may not give satisfying results. In this project, we have developed a software optimization routine in Matlab that calculates controller settings (PI and PID) and filter settings simultaneously that minimizes the Integrated Absolute Error (IAE) with robustness and meausrement noise sensitivity constraints. The filter may be chosen to have order 1-4. For filters of orders higher than 1, all time constants are equal and the damping must be lower than 0.7, i.e., no amplification of measurements.
A simple dead-time compensator
A simple dead-time compensating controller is the Predictive PI controller, which is a simplified Smith predictor with only three parameters to tune. The motivation for the project is that this controller structure may be as easy to tune as a PI(D) controller using the developed software for PI and PID controllers (see above). The performance, measured by IAE, of the new controller has been compared to the performance of PID controllers when robustness and control signal constraints are set. The controllers are simultaneously designed together with measurement filters. Results show that the Predictive PI controller has similar performance as the PID controller for many processes representative for the process control community. However, for some processes the PID controller outperforms the Predictive PI controller.
Relation between control signal properties and robustness measures
In a realistic setting, fast response to load upsets are restricted by e.g. limitations on actuator devices, noise characteristics of measured signals, and process variations. Thus, this should be incorporated in the design of a controller. An analysis concering the optimization constraint in the PID design in this project and in the project ``Decentralized Structures for Industrial Control'' has been performed. It has shown that analytical expressions relating the M_S and M_T circles and the control signal magnitude and activity exist to a certain extent. Large robustness margins give small control signal activities and the opposite holds for small robustness margins. Thus, the proposed PID parameter optimization do take required control signal properties into consideration.
Software tools for design of PID controllers
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A new, interactive and easily modifiable software tool for robust PID design has been developed at the department. The tool has been programmed in Matlab and the goal is to find the controller that minimizes the IAE value during a load disturbance, while applying robustness constraints in terms of M-circles. The figure on this page shows a plot from the program, depicting the IAE cost as a function of the integral time and the derivative time in a PID controller. The minimum is shown by the yellow mark in the figure.
The software is free to download. The Matlab files contained in the zip-file will make it possible to design a robust, optimal PID (or PI) controller. The software has been tested on Matlab 7 and may need some changes if it is not run under that version.
Download PID Design Tool for Matlab
Interacting learning modules for PID control
We are also developing interactive learning modules for PID control. The modules are designed to speed up learning and to enhance understanding of the behaviour of loops with PID controllers. The modules are implemented in SysQuake, and the work is done in collaboration with professor Sebastián Dormido at UNED, Madrid, and José Luis Guzmán at Universidad de Almería.
The tools can be downloaded from Universidad de Almería.
Publications
Olof Garpinger, Tore Hägglund, Lars Cederqvist: "Software for PID design: benefits and pitfalls". In IFAC Conference on Advances in PID Control, Brescia, Italy, March 2012.
Tore Hägglund: "Signal Filtering in PID Control". In IFAC Conference on Advances in PID Control, Brescia, Italy, March 2012.
Olof Garpinger, Tore Hägglund, Karl Johan Åström: "Criteria and Trade-offs in PID Design". In IFAC Conference on Advances in PID Control, Brescia, Italy, March 2012.
Per-Ola Larsson, Tore Hägglund: "Comparison Between Robust PID and Predictive PI Controllers with Constrained Control Signal Noise Sensitivity". In IFAC Conference on Advances in PID Control, Brescia, Italy, March 2012.
José Luis Guzmán, Tore Hägglund, Antonio Visioli: "Feedforward compensation for PID control loops". In Ramon Vilanova, Antonio Visioli (Eds.) (Eds.): PID control in the third millenium, Springer, January 2012.
Lars Cederqvist, Olof Garpinger, Tore Hägglund, Anders Robertsson: "Cascade control of the friction stir welding process to seal canisters for spent nuclear fuel". Control Engineering Practice, 20:1, pp. 35–48, January 2012.
Per-Ola Larsson: Optimization of Low-Level Controllers and High-Level Polymer Grade Changes. PhD Thesis ISRN LUTFD2/TFRT--ISRN LUTFD2/TFRT--1088--SE--SE, Department of Automatic Control, Lund University, Sweden, November 2011.
Juan Garrido, Francisco Vázquez, Fernando Morilla, Tore Hägglund: "Practical advantages of inverted decoupling". Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control, 225:7, pp. 977–992, November 2011.
Tore Hägglund: "A shape-analysis approach for diagnosis of stiction in control valves". Control Engineering Practice, 19:8, pp. 782–789, August 2011.
José Luis Guzmán, Tore Hägglund, Karl Johan Åström, Sebastián Dormido, Manuel Berenguel, Yves Piguet: "Feedforward Control Concepts through Interactive Tools". In 18th IFAC World Congress, Milano, Italy, August 2011.
Per-Ola Larsson, Tore Hägglund: "Control Signal Constraints and Filter Order Selection for PI and PID Controllers". In 2011 American Control Conference, San Francisco, California, USA, June 2011.
José Luis Guzmán, Tore Hägglund: "Simple tuning rules for feedforward compensators". Journal of Process Control, 21:1, pp. 92-102, January 2011.
Tore Hägglund, Karl Johan Åström: "Automatic Tuning of PID Controllers". In William S. Levine (Ed.) (Eds.): The Control Handbook, Second Edition: Control System Advanced Methods, CRC Press, December 2010.
Karl Johan Åström, Tore Hägglund: "PID Control". In William S. Levine (Ed.) (Eds.): The Control Handbook, Second Edition: Control System Fundamentals, CRC Press, December 2010.
Per-Ola Larsson, Tore Hägglund: "Robustness Margins Separating Process Dynamics Uncertainties". In 2009 European Control Conference, Budapest, Hungary, August 2009.
José Luis Guzmán, Karl Johan Åström, Tore Hägglund, Sebastián Dormido, Manuel Berenguel, Yves Piguet: "Interactive Learning Module for Control Interaction Understanding". In European Control Conference, Budapest, Hungary, August 2009.
Olof Garpinger: "Design of Robust PID Controllers with Constrained Control Signal Activity". Licentiate Thesis ISRN LUTFD2/TFRT--ISRN LUTFD2/TFRT--LUTFD2/TFRT--3245--SE--SE--SE, Department of Automatic Control, Lund University, Sweden, March 2009.
Karl Johan Åström, Tore Hägglund: Control PID Avanzado. Pearson Educación, Madrid, 2009.
José Luis Guzmán, Karl Johan Åström, Sebastián Dormido, Tore Hägglund, Manuel Berenguel, Yves Piguet: "Interactive Learning Modules for PID Control". IEEE Control Systems Magazine, pp. 118-134, October 2008.
Olof Garpinger, Tore Hägglund: "A Software Tool for Robust PID Design". In Proc. 17th IFAC World Congress, Seoul, Korea, July 2008.
José Luis Guzmán, Karl Johan Åström, Sebastián Dormido, Tore Hägglund, Yves Piguet, Manuel Berenguel: "Interactive Learning Module: Basic Modelling and Identification Concepts". In Proceedings of the 17th World Congress, Seoul, Korea, July 2008.
Per-Ola Larsson, Tore Hägglund: "Relations Between Control Signal Properties and Robustness Measures". In 17th IFAC World Congress, Seoul, Korea , July 2008.
José Luis Guzmán, Pedro García, Tore Hägglund, Sebastián Dormido, Pedro Albertos, Manuel Berenguel: "Interactive tool for analysis of time-delay systems with dead-time compensators ". Control Engineering Practice, 16:7, pp. 824-835,2008.
Tore Hägglund: "Automatic On-Line Estimation of Backlash in Control Loops". Journal of Process Control, 17, pp. 489-499,2007.
José Luis Guzmán, Karl Johan Åström, Sebastián Dormido, Tore Hägglund, Yves Piguet: "Interactive Learning Modules for PID Control". In 7th IFAC Symposium on Advances in Control Education, Madrid, Spain, June 2006.
Karl Johan Åström, Tore Hägglund: Advanced PID Control. ISA - The Instrumentation, Systems, and Automation Society, Research Triangle Park, NC 27709, 2005.
2012-01-18