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A cooperative decentralized PI control strategy: discrete-time analysis and nonlinear feedback
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
2012 (English)In: Proc. 3rd IFAC Workshop on Distributed Estimation and Control in Networked Systems, 2012, 103-108 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper discusses an extension of a PI control strategy towards the control of a large m×m-MIMO system. This strategy is fully decentralized, it requires only the tuning of m different controllers, while we only allow for neighboring controllers to exchange error signals. This makes it a strong candidate for an implementation on a decentralized, low-power and high performance Wireless Sensor Network (WSN). The main idea is to feed locally observed control errors (’feedback’) not only into the local control law, but also in a fixed proportionate way into neighboring controllers. The analysis concerns convergence to a set point. The analysis is essentially based on a conversion of the PI control law into a discrete-time gradient descent scheme. As an interesting byproduct, this analysis indicates how to deal with quantization functions and nonlinear effects in the feedback signals.

Place, publisher, year, edition, pages
2012. 103-108 p.
National Category
Control Engineering
Identifiers
URN: urn:nbn:se:uu:diva-183475OAI: oai:DiVA.org:uu-183475DiVA: diva2:562897
Conference
NecSys 2012, September 14-15, Santa Barbara, CA
Projects
ProFuN
Available from: 2012-10-31 Created: 2012-10-26 Last updated: 2014-06-12Bibliographically approved
In thesis
1. Output feedback control: Some methods and applications
Open this publication in new window or tab >>Output feedback control: Some methods and applications
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis studies some output feedback control laws. Particularly, iterative learning control (ILC) and decentralized network based algorithms are studied. Applications to control of wastewater treatment plants are outlined. For a linear, discrete time MIMO plant, it is shown that the size of the global controller gain, also referred to as the diffusion matrix, plays an important role in stabilization of a decentralized control system with possibly non-linear output feedback. Based on information from a step response experiment of the open loop system, a controller gain which is sufficient for stability can be found. For the SISO case, frequency response expressions are derived for the choice of this controller gain. The results relate nicely to notions of optimality and the Nyquist stability criterion. Various types of ILC algorithms are analysed and numerically illustrated. In particular, new expressions of the asymptotic control error variance for adjoint based iterative learning control (ILC) are derived. It is proven that the control error variance converges to its minimum if a decreasing learning gain matrix is used for ILC. In a simulation study ILC is applied to control a sequencing batch reactor. It is shown numerically that an adjoint based ILC outperforms inverse based ILC and model-free, proportional ILC. A merge of an activated sludge process simulator and a simulator for a wireless sensor network is described and used for illustrating some control performance. Finally, in a numerical optimization study it is shown that the aeration energy can be decreased if many dissolved oxygen sensors are used for aeration control in a biological reactor for nitrogen removal. This results may support future use of inexpensive wireless sensor networks for control of wastewater treatment plants.

Place, publisher, year, edition, pages
Uppsala University, 2014
Series
Information technology licentiate theses: Licentiate theses from the Department of Information Technology, ISSN 1404-5117 ; 2014-002
National Category
Control Engineering
Research subject
Electrical Engineering with specialization in Automatic Control
Identifiers
urn:nbn:se:uu:diva-226179 (URN)
Presentation
2014-03-27, Room 2245, Polacksbacken, Lägerhyddsvägen 2, Uppsala, 10:15 (English)
Supervisors
Projects
ProFuN
Available from: 2014-03-27 Created: 2014-06-12 Last updated: 2017-08-31Bibliographically approved

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