| 1. |
- Gäfvert, Magnus, et al.
(författare)
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On the Effect of Transient Data-Errors in Controller Implementations
- 2003
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Ingår i: Proceedings of the 2003 American Control Conference, vols 1-6. - 0743-1619. - 0780378962 ; 4, s. 3411-3416
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Konferensbidrag (refereegranskat)abstract
- Computer-level faults leading to data errors in computations arepredicted to occur increasingly frequent in future microprocessors.This work discusses the impact of such errors on closed-loopperformance in implementations of digital control systems. A method torender a control system more robust to data errors by introducingartificial signal limits and then combine them with an anti-windupscheme is presented and exemplified. Accepted for publication.
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| 2. |
- Robertsson, Anders, et al.
(författare)
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Analysis and design of admission control systems in web-server systems
- 2003
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Ingår i: Proceedings of the 2003 American Control Conference. Vol. 1. - 0743-1619. - 0780378962 ; , s. 254-259
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Konferensbidrag (refereegranskat)abstract
- All service control nodes, for example Web sites or Mobile Switching Centers, can be modeled as server systems with one or more servers processing the incoming requests. To avoid overload at the service control node different types of admission control mechanisms are usually implemented. In this paper we discuss, from a control point of view, the modeling of a service control-node. The queue is assumed to be an M/G/1-system and is modeled by a nonlinear flow model and a simplified discrete-time model is used in the analysis and design of the system. An admission control system based on a PI-controller combined with an anti-reset windup feature is developed. The stability of the admission control system is analyzed and the stability of the closed loop system is proved. The results from the simplified queue model are verified through discrete-event simulations of the system.
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| 3. |
- Svantesson, T, et al.
(författare)
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Taking automatic control into wood ash recycling
- 2003
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Ingår i: Proceedings of the 2003 American Control Conference. - 0743-1619. - 0780378962 ; 4, s. 3071-3076
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Konferensbidrag (refereegranskat)abstract
- In Sweden, extensive research is conducted to find alternative sources of energy that should partly replace the electric power production from nuclear power. With the ambition to create a sustainable system for producing energy, the use of renewable energy is expected to grow further and biofuels are expected to account for a significant part of this increase. However, when biofuels are burned or gasified, ash appears as a by-product. In order to overcome the problems related to deposition in land fills, the idea is to transform the ashes into a product - agglomerates - that easily could be recycled back to the forest grounds; as a fertilizer, or as a tool to reduce the acidification in the forest soil at the spreading area. This paper introduces the general ash transformation concept and presents the necessary automatic control and signal processing needed to enable an automated manufacture of these agglomerates. However, as an alternative to using the most advance control theory, the paper also stresses that implementing a novel mechanical process design can heavily reduce the complexity of a specific control problem. Furthermore, along with some previously reported topics, new results regarding the delicate issues of wood ash agglomeration and agglomerate dehydration are presented.
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| 4. |
- Velut, Stéphane, et al.
(författare)
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Analysis of a probing control strategy
- 2003
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Ingår i: Proceedings / American Control Conference 2003. - 0743-1619. - 0780378962 ; 1, s. 609-614
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Konferensbidrag (refereegranskat)abstract
- In this paper we analyse an extremum controller based on a pulsetechnique. The idea is to superimpose probing pulses to the controlsignal and use for feedback the size of the pulse response in the output. Theprobing control strategy has been used with success forthe control of the substrate feeding in E. coli cultivations. The analysis is done here for systems ofHammerstein type with a piecewise affine nonlinearity. Stability ofthe closed-loop system can be checked by solving suitable linearmatrix inequalities. Some performance analysis that can help the userfor the control design is also performed.
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| 5. |
- Abdelzaher, Tarek, et al.
(författare)
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Practical Application of Control Theory to Web Services
- 2004
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Ingår i: Proceedings of the American Control Conference. - 0743-1619. ; 3, s. 1992-1997
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Konferensbidrag (refereegranskat)abstract
- This tutorial describes experiences with applying a control theoretical approach to achieving performance guarantees in Web servers, with emphasis on delay control. A model for the server is formulated and translated into a control problem formulation. Limitations of the control theoretic approach are identified that arise due to system non-linearities and modeling inaccuracies. Solutions are proposed that augment the feedback control framework with elements of scheduling and queuing theory. The theoretical results and QoS control loops presented by the authors are implemented in a middleware package, called ControlWare, which provides the software mechanisms and interfaces that allow control of real server performance. Implementation and performance of ControlWare is described.
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| 6. |
- Bengtsson, Johan, et al.
(författare)
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Control of Homogeneous Charge Compression Ignition (HCCI) Engine Dynamics
- 2004
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Ingår i: Proceedings of the 2004 American Control Conference, ACC : June 30 - July 2, 2004, Boston Sheraton Hotel, Boston, Massachusetts. - 0743-1619. - 0780383354 ; 5, s. 4048-4053
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Konferensbidrag (refereegranskat)abstract
- The Homogeneous Charge Compression Ignition (HCCI) combustionconcept lacks direct ignition timing control, instead the autoignition depends on the operating condition. Since auto ignition of ahomogeneous mixture is very sensitive to operating conditions, a fastcombustion timing control is necessary for reliable operation. Hence,feedback is needed and the crank angle of 50% burnt (CA50) has provedto be a reliable feedback indicator of on-going combustion inpractice. CA50 or other methods for detecting on-going cylinderpressure used in the feedback control of a HCCI engine all rely onpressure sensors. This paper presents a newcandidate for control of HCCI engine by using the electronicconductive properties in the reaction zone. This phenomenon is calledion current. This paper perform combustion timing control based on ioncurrent and compare it with control based on pressure sensor. Thecombustion timing control is performed on cycle-to-cycle basis and the engine is a one-cylinder version of a heavy duty engine equipped with a port injection system using dual fuels.
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| 7. |
- Campbell, S.L., et al.
(författare)
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A numerical integrator for simulation of unstructured implicit models
- 2004
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Ingår i: Proceedings of the 2004 American Control Conference. - 0743-1619. ; 6, s. 5647-5652
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Konferensbidrag (refereegranskat)abstract
- Object oriented modeling naturally leads to implicitly defined dynamical systems or, as they are also called, differential algebraic equations (DAEs). Most existing DAE integrators require the equations defining the dynamical system to have a special structure. Progress on the development of a new integrator for general unstructured DAEs is presented. The new integrator is called UCP. Computational tests are given to show that the new method can successfully integrate problems that other methods have trouble with.
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| 8. |
- Falkman, Petter, 1972, et al.
(författare)
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Combined Process Algebra and Petri Nets for Specification of Resource Booking Problems
- 2001
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Ingår i: American Control Conference. - 0743-1619. - 0780364953 ; 6, s. 4949-4955
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Konferensbidrag (refereegranskat)abstract
- A modeling framework for general routing and resource booking problems is presented. The task is to specify desired routes for individual objects (products, data packets, vehicles), which are to be served by a number of shared resources (machines, computers, communication links). A high level language is presented in order to simplify the specification of desired routes. This modeling language combines Petri nets and process algebra. Process operators are introduced for specification of sequences, alternative choices, arbitrary ordered sequences and process synchronization. Multiple as well as alternative resources are easily specified utilizing sets of resources. These sets and operators imply a very compact and efficient representation of complex routing specifications. In fact, the representation is suitable for verification and synthesis based on symbolic tools such as BDDs.
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| 9. |
- Kao, Chien-Ya, et al.
(författare)
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A New Barrier Function for IQC Optimization Problems
- 2003
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Ingår i: Proceedings of the American Control Conference. - 0743-1619. ; 5, s. 4281-4286
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Konferensbidrag (refereegranskat)abstract
- In this paper, we propose a new barrier function for optimization problems with Integral Quadratic Constraints (IQCs). The new barrier function is used to construct an interior point algorithm which solves IQC optimization problems in a more efficient fashion. Numerical tests as well as worst-case computational complexity analysis are performed to evaluate the efficiency of the proposed algorithm.
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| 10. |
- Lincoln, Bo
(författare)
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Jitter Compensation in Digital Control Systems
- 2002
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Ingår i: Proceedings of the 2002 American Control Conference, 2002. - 0743-1619. - 0780372980 ; 4, s. 2985-2990
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Konferensbidrag (refereegranskat)abstract
- A method to compensate for time-varying, possibly random, delays (jitter) in digital control systems is presented. Using time-stampsfrom the control system, a linear compensator is designed asan add-on to an existing control system. Stability andperformance analysis is performed, and leads to frequency domainconditions. Therefore, loop-shaping can be used for thecompensator design. The design ofthe compensator can be done without a full process model.
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| 11. |
- Robertsson, Anders, et al.
(författare)
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Design and evaluation of load control in web-server systems
- 2004
-
Ingår i: Proceedings of the 2004 American Control Conference, ACC : June 30 - July 2, 2004, Boston Sheraton Hotel, Boston, Massachusetts. - 0743-1619. - 0780383354 ; , s. 1980-1985
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Konferensbidrag (refereegranskat)abstract
- Nonlinear discrete-time modeling of a Web server system is investigated. Server systems typically contain nonlinearities such as saturations and bounded queue lengths. The incoming traffic and service rates are best modeled by stochastic processes, well described and analyzed by queuing theory. Here, we develop and validate a control theoretic model of a general single server queue, a so-called G/G/1-system. Based on the nonlinear system model, design of admission controllers are presented and the closed loop stability is analyzed. The behavior of the server model is verified with respect to queue theoretic models. Finally, experimental evaluation is performed on an Apache Web server in a laboratory network. A traffic generator is used to represent client requests. The control of the Apache server has been re-written to implement our algorithms. We show that the control theoretic model aligns well with the experiments on the Web-server. Measurements in the laboratory setup show the robustness of the implemented controller, and how it corresponds to the results from the theoretical analysis and the simulations.
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| 12. |
- Sandberg, Henrik, et al.
(författare)
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Frequency-Domain Analysis of Linear Time-Periodic Systems
- 2004
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Ingår i: Proceedings of the 2004 American Control Conference.. - 0743-1619. - 0780383354 ; 4, s. 3357-3362
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Konferensbidrag (refereegranskat)abstract
- In this paper we study how a system with a time-periodic impulse response may be expanded into a sum of modulated time-invariant systems. This allows us to define a linear frequency-response operator for periodic systems, called the harmonic transfer function (HTF). Similar frequency-response operators have been derived before for sampled-data systems and periodic finite-dimensional state-space systems. The HTF is an infinite-dimensional operator that captures the frequency coupling of a time-periodic system. The paper includes analysis of convergence of truncated HTFs. For this reason the concepts of input/output roll-off are developed and related to time-varying Markov parameters.
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| 13. |
- Schinkel, Michael, et al.
(författare)
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Optimal control for systems with varying sampling rate
- 2002
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Ingår i: Proceedings of the 2002 American Control Conference, 2002.. - 0743-1619. - 0780372980 ; 4, s. 2979-2984
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Konferensbidrag (refereegranskat)abstract
- The paper addresses the aspects of control of real time systems with varying sampling rate. An example is given in which a stable continuous system is sampled at two different sampling rates. Two controllers are designed to minimize the same continuous quadratic loss function with the same weights. It is shown that although the design leads to stable controlled closed loop systems, for both discretizations, the resulting system can be unstable due to variations in sampling rate. To avoid that problem, we suggest an optimal controller design in which a bound on the cost, for all possible sampling rate variations, is computed. This results in a piecewise constant state feedback control law and guarantees stability regardless of the variations in sampling rate. The controller synthesis is cast into an LMI, which conveniently solves the synthesis problem. To illustrate the procedure, the introduction example is revised using the proposed LMI synthesis method and the stable control law is given, which is robustly stable against variations in sampling rate.
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