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| 2. |
- Johansson, Karl Henrik, et al.
(författare)
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Limit cycles with chattering in relay feedback systems
- 2002
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Ingår i: IEEE Transactions on Automatic Control. - 0018-9286. ; 47:9, s. 1414-1423
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Tidskriftsartikel (refereegranskat)abstract
- Relay feedback has a large variety of applications in control engineering. Several interesting phenomena occur in simple relay systems. In the paper, scalar linear systems with relay feedback are analyzed. It is shown that a limit cycle where part of the limit cycle consists of fast relay switchings can occur. This chattering is analyzed in detail and conditions for approximating it by a sliding mode are derived. A result on existence of limit cycles with chattering is given, and it is shown that the limit cycles can have arbitrarily many relay switchings each period. Limit cycles with regular sliding modes are also discussed. Examples illustrate the results.
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| 4. |
- Wittenmark, Björn, et al.
(författare)
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Computer Control: An Overview
- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Computer control is entering all facets of life from home electronics to production of different products and material. Many of the computers are embedded and thus ``hidden'' for the user. In many situations it is not necessary to know anything about computer control or real-time systems to implement a simple controller. There are, however, many situations where the result will be much better when the sampled-data aspects of the system are taken into consideration when the controller is designed. Also, it is very important that the real-time aspects are regarded. The real-time system influences the timing in the computer and can thus minimize latency and delays in the feedback controller. The paper introduces different aspects of computer-controlled systems from simple approximation of continuous time controllers to design aspects of optimal sampled-data controllers. We also point out some of the pitfalls of computer control and discusses the practical aspects as well as the implementation issues of computer control. Published as a Professional Briefs by IFAC.
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| 5. |
- Åström, Karl Johan, et al.
(författare)
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Design of decoupled PI controller for two-by-two systems
- 2002
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Ingår i: IEE Proceedings: Control Theory and Applications. - : Institution of Engineering and Technology (IET). - 1350-2379 .- 1359-7035. ; 149:1, s. 74-81
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Tidskriftsartikel (refereegranskat)abstract
- The design of PI controllers for systems with interacting loops is discussed. It is advantageous to deal with the interaction at the loop level, because supervisory control seldom has sufficient bandwidth. A new scheme based on modified scalar PI design and static decoupling is developed, in which the frequency characteristic of the coupling between the lower-level loops is taken into account. This leads to a design method emphasising the trade-off between the individual loop performances and the interaction indices introduced in the paper. The controller is easily implemented, due to its simple configuration based on standard components. A useful observation is that the interaction can be reduced substantially by using set-point weighting. The method is applied to three examples, including a model of a new laboratory system called the quadruple-tank process
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| 6. |
- Aanaes, H, et al.
(författare)
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Robust factorization
- 2002
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Ingår i: IEEE Transactions on Pattern Analysis and Machine Intelligence. - 1939-3539. ; 24:9, s. 1215-1225
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Tidskriftsartikel (refereegranskat)abstract
- Factorization algorithms for recovering structure and motion from an image stream have many advantages, but they usually require a set of well-tracked features. Such a set is in generally not available in practical applications. There is thus a need for making factorization algorithms deal effectively with errors in the tracked features. We propose a new and computationally efficient algorithm for applying an arbitrary errorfunction in the factorization scheme. This algorithm enables the use of robust statistical techniques and arbitrary noise models for the individual features. These techniques and models enable the factorization scheme to deal effectively with mismatched features, missing features, and noise on the individual features. The proposed approach further includes a new method for Euclidean reconstruction that significantly improves convergence of the factorization algorithms. The proposed algorithm has been implemented as a modification of the Christy-Horaud factorization scheme, which yields a perspective reconstruction. Based on this implementation, a considerable increase in error tolerance is demonstrated on real and synthetic data. The proposed scheme can, however, be applied to most other factorization algorithms.
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| 9. |
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Control of Complex Systems
- 2001
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- The world of artificial systems is reaching hitherto undreamed-of levels of complexity. Surface traffic, electricity distribution, mobile communications, etc., demonstrate that problems are arising that are beyond classical scientific or engineering knowledge. In order that our ability to control such systems should not be hindered by lack of comprehension, there is an on-going effort to understand them. This book is an example of the types of approach that European researchers are using to tackle problems derived from systems' complexity. It has grown out of activities in the Control of Complex Systems (COSY) research program the goals of which are to promote multi-disciplinary activity leading to a deeper understanding and further development of control technologies for complex systems and if possible, to develop the theory underlying such systems. The material in this book represents a selection of the results of the COSY program and is organised as a collection of essays of varying nature: surveys of essential areas, discussion of specific problems, case studies, and benchmark problems. Topics covered include: Modelling complex physical systems; Passivity-based control of non-linear systems; Aspects of fault identification and fault tolerance; Control design; Learning control; Satellite attitude control. Complex systems appear in many different fields and for this reason this book should be of interest to scientists, researchers and industrial engineers with a broad spectrum of experience.
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| 10. |
- Eborn, Jonas, et al.
(författare)
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Modeling of a Boiler Pipe with Two-Phase Flow Instabilities
- 2000
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Ingår i: Modelica Workshop 2000 Proceedings. ; , s. 79-88
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Tubes with boiling are common elements of many processes. They appear in steam generators and refrigerators and many other systems. The behavior of such systems is complicated and many physical phenomena are involved. It has for example been observed that different types of instabilities can occur. In this paper we will discuss modeling of tubes with boiling. As an application we will discuss an instability phenomenon due to pressure oscillations that has been observed experimentally in many different situations. We will first derive a simple analytical model which is able to capture the oscillations qualitatively. The simple model also gives insight into the mechanisms that generate the oscillations. A more complicated model is then built using a recently developed model base library in Modelica. A comparison between the simple and the complicated model is also given
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