| 1. |
- Axehill, Daniel, et al.
(författare)
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A Dual Gradient Projection Quadratic Programming Algorithm Tailored for Model Predictive Control
- 2008
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Ingår i: Proceedings of Reglermöte 2008. ; , s. 202-209, s. 3057-3064
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this work is to derive a QPalgorithm tailored for MPC. More specific, the primary targetapplication is MPC for discrete-time hybrid systems. A desiredproperty of the algorithm is that warm starts should be possibleto perform efficiently. This property is very important for online linear MPC, and it is crucial in branch and bound forhybrid MPC. In this paper, a dual active set-like QP methodwas chosen because of its warm start properties. A drawbackwith classical active set methods is that they often requiremany iterations in order to find the active set in optimum.Gradient projection methods are methods known to be ableto identify this active set very fast and such a method wastherefore chosen in this work. The gradient projection methodwas applied to the dual QP problem and it was tailored for theMPC application. Results from numerical experiments indicatethat the performance of the new algorithm is very good, bothfor linear MPC as well as for hybrid MPC. It is also noticed thatthe number of QP iterations is significantly reduced compared to classical active set methods.
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| 2. |
- Freidovich, Leonid, et al.
(författare)
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A passive 2DOF walker : finding gait cycles using virtual holonomic constraints
- 2008
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Ingår i: Proceedings of the 47th IEEE Conference on Decision and Control. - : IEEE. - 9781424431236 ; , s. 5214-5219
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Konferensbidrag (refereegranskat)abstract
- A planar compass-like biped on a shallow slope is the simplest model of a passive walker. It is a two-degrees-of-freedom impulsive mechanical system known to possess periodic solutions reminiscent to human walking. Finding such solutions is a challenging task. We propose a new approach to obtain stable as well as unstable hybrid limit cycles without integrating the full set of differential equations. The procedure is based on exploring the idea of parameterizing a possible periodic solution via virtual holonomic constraints. We also show that a 2-dimensional manifold, defining the hybrid zero dynamics associated with a stable hybrid cycle, in general, is not invariant for the dynamics of the model of the compass-gait walker.
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| 3. |
- Harju Johansson, Janne, et al.
(författare)
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A Tailored Inexact Interior-Point Method for Systems Analysis
- 2008
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Ingår i: Proceedings of Reglermöte 2008. - Linköping : Linköping University Electronic Press. ; , s. 176-181, s. 3071-3076
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Within the area of system analysis there are multiple problem formulations that can be rewritten as semidefiniteprograms. Increasing demand on computational efficiency andability to solve large scale problems make the available genericsolvers inadequate. In this paper structure knowledge is utilizedto derive tailored calculations and to incorporate adaptationto the different properties that appear in a proposed inexactinterior-point method.
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| 4. |
- Johansson, Björn, et al.
(författare)
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Subgradient methods and consensus algorithms for solving convex optimization problems
- 2008
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Ingår i: Decision and Control, 2008. CDC 2008. 47th IEEE Conference on. - : IEEE. - 9781424431236 ; , s. 4185-4190
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Konferensbidrag (refereegranskat)abstract
- In this paper we propose a subgradient method for solving coupled optimization problems in a distributed way given restrictions on the communication topology. The iterative procedure maintains local variables at each node and relies on local subgradient updates in combination with a consensus process. The local subgradient steps are applied simultaneously as opposed to the standard sequential or cyclic procedure. We study convergence properties of the proposed scheme using results from consensus theory and approximate subgradient methods. The framework is illustrated on an optimal distributed finite-time rendezvous problem.
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| 5. |
- Krysander, Mattias, 1977-, et al.
(författare)
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Dynamic Test Selection for Reconfigurable Diagnosis
- 2008
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Ingår i: Proceedings of the 47th IEEE Conference on Decision and Control. - : IEEE. - 9781424431243 - 9781424431236 ; , s. 1066-1072
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Konferensbidrag (refereegranskat)abstract
- Detecting and isolating multiple faults is a computationally intense task which typically consists of computing a set of tests, and then computing the diagnoses based on the test results. This paper proposes a method to reduce the computational burden by only running the tests that are currently needed, and dynamically starting new tests when the need changes. A main contribution is a method to select tests such that the computational burden is reduced while maintaining the isolation performance of the diagnostic system. Key components in the approach are the test selection algorithm, the test initialization procedures, and a knowledge processing framework that supports the functionality needed. The approach is exemplified on a relatively small dynamical system, which still illustrates the complexity and possible computational gain with the proposed approach.
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| 6. |
- Lyzell, Christian, 1980-, et al.
(författare)
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The Use of Nonnegative Garrote for Order Selection of ARX Models
- 2008
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Ingår i: Proceedings of the 47th IEEE Conferance on Decision and Control. - Linköping : Linköping University Electronic Press. - 9781424431243 - 9781424431236 ; , s. 1974-1979
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Konferensbidrag (refereegranskat)abstract
- Order selection of linear regression models has been thoroughly researched in the statistical community for some time. Different shrinkage methods have been proposed, such as the Ridge and Lasso regression methods. Especially the Lasso regression has won fame because of its ability to set less important parameters exactly to zero. However, these methods do not take dynamical systems into account, where the regressors are ordered via the time lag. To this end, a modified variant of the nonnegative garrote method will be analyzed.
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| 7. |
- Löfberg, Johan, 1974-, et al.
(författare)
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Explicit Model Predictive Control for Linear Parameter-Varying Systems
- 2008
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Ingår i: Proceedings of the 47th IEEE Conference on Decision and Control<em></em>. - 9781424431243 - 9781424431236 ; , s. 3848-3853
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Konferensbidrag (refereegranskat)abstract
- In this paper we demonstrate how one can reformulate the MPC problem for LPV systems to a series of mpLPs by a closed-loop minimax MPC algorithm based on dynamic programming. A relaxation technique is employed to reformulate constraints which are polynomial in the scheduling parameters to parameter-independent constraints. The algorithm allows the computation of explicit control laws for linear parameter-varying systems and enables the controller to exploit information about the scheduling parameter. This improves the control performance compared to a standard robust approach where no uncertainty knowledge is used, while keeping the benefits of fast online computations. The off-line computational burden is similar to what is required for computing explicit control laws for uncertain or nominal LTI systems. The proposed control strategy is applied to an example to compare the complexity of the resulting explicit control law to the robust controller.
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| 8. |
- Möller, Niels, et al.
(författare)
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Congestion control for small queues : analysis and evaluation of a new protocol
- 2008
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Ingår i: Proceedings of the 47th IEEE Conference on Decision and Control Cancun, Mexico, Dec. 9-11, 2008. - : IEEE conference proceedings. - 9781424431236 ; , s. 1416-1421
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Konferensbidrag (refereegranskat)abstract
- A new congestion control protocol is presented, analyzed and experimentally evaluated. It consists of the standard inner-loop ACK-clock and a novel outer-loop adjusting the window size based on congestion signaling from the network. The aim of the new protocol is to maintain the efficiency and fairness properties of TCP, but with significantly smaller bottleneck queues and thereby it takes the sharing with real-time traffic into account. Stability properties of the protocol is proved using a recent fluid-flow traffic model. Experimental comparisons with New Reno and Vegas illustrate the advantages of the new protocol with respect to throughput, delay, utilization, and fairness.
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| 9. |
- Ohlsson, Henrik, 1981-, et al.
(författare)
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Direct Weight Optimization Applied to Discontinuous Functions
- 2008
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Ingår i: 47th IEEE Conference on Decision and Control, 2008. CDC 2008. - Cancun, Mexico : IEEE. - 9781424431236 ; , s. 117-122
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Konferensbidrag (refereegranskat)abstract
- The Direct Weight Optimization (DWO) approach is a nonparametric estimation approach that has appeared in recent years within the field of nonlinear system identification. In previous work, all function classes for which DWO has been studied have included only continuous functions. However, in many applications it would be desirable also to be able to handle discontinuous functions. Inspired by the bilateral filter method from image processing, such an extension of the DWO framework is proposed for the smoothing problem. Examples show that the properties of the new approach regarding the handling of discontinuities are similar to the bilateral filter, while at the same time DWO offers a greater flexibility with respect to different function classes handled.
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| 10. |
- Ohlsson, Henrik, 1981-, et al.
(författare)
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Enabling Bio-Feedback using Real-Time fMRI
- 2008
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Ingår i: 47th IEEE Conference on Decision and Control, 2008, CDC 2008. - Linköping : IEEE. - 9781424431236 ; , s. 3336-3341
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Konferensbidrag (refereegranskat)abstract
- Despite the enormous complexity of the human mind, fMRI techniques are able to partially observe the state of a brain in action. In this paper we describe an experimental setup for real-time fMRI in a bio-feedback loop. One of the main challenges in the project is to reach a detection speed, accuracy and spatial resolution necessary to attain sufficient bandwidth of communication to close the bio-feedback loop. To this end we have banked on our previous work on real-time filtering for fMRI and system identification, which has been tailored for use in the experiment setup. In the experiments presented the system is trained to estimate where a person in the MRI scanner is looking from signals derived from the visual cortex only. We have been able to demonstrate that the user can induce an action and perform simple tasks with her mind sensed using real-time fMRI. The technique may have several clinical applications, for instance to allow paralyzed and "locked in" people to communicate with the outside world. In the meanwhile, the need for improved fMRI performance and brain state detection poses a challenge to the signal processing community. We also expect that the setup will serve as an invaluable tool for neuro science research in general.
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| 11. |
- Ohlsson, Henrik, 1981-, et al.
(författare)
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Manifold-Constrained Regressors in System Identification
- 2008
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Ingår i: Proceedings of the 47th IEEE Conference on Decision and Control. - Linköping : Linköping University Electronic Press. - 9781424431243 - 9781424431236 ; , s. 1364-1369
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Konferensbidrag (refereegranskat)abstract
- High-dimensional regression problems are becoming more and more common with emerging technologies. However, in many cases data are constrained to a low dimensional manifold. The information about the output is hence contained in a much lower dimensional space, which can be expressed by an intrinsic description. By first finding the intrinsic description, a low dimensional mapping can be found to give us a two step mapping from regressors to output. In this paper a methodology aimed at manifold-constrained identification problems is proposed. A supervised and a semi-supervised method are presented, where the later makes use of given regressor data lacking associated output values for learning the manifold. As it turns out, the presented methods also carry some interesting properties also when no dimensional reduction is performed.
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| 12. |
- Olofsson, K Erik J, 1982-, et al.
(författare)
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Stability analysis and model-based control in EXTRAP-T2R with time-delay compensation
- 2008
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Ingår i: Proceedings of the 47th IEEE Conference on Decision and Control, Cancun, Mexico, Dec. 9-11, 2008. - : IEEE conference proceedings. - 9781424431236 ; , s. 2044-2049
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Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the stability problems and control issues that occur in a reversed-field pinch (RFP) device, EXTRAP-T2R (T2R), used for research in fusion plasma physics and general plasma (ionized gas) dynamics. The plant exhibits, among other things, magnetohydrodynamic instabilities known as resistive-wall modes (RWMs), growing on a time-scale set by a surrounding non-perfectly conducting shell.We propose a novel model that takes into account experimental constraints, such as the actuators dynamics and control latencies, which lead to a multivariable time-delay model of the system. The open-loop field-error characteristics are estimated and a stability analysis of the resulting closed-loop delay differential equation (DDE) emphasizes the importance of the delay effects. We then design a structurally constrained optimal PID controller by direct eigenvalue optimization (DEO) of this DDE. The presented results are substantially based on and compared with experimental data.
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| 13. |
- Roll, Jacob, et al.
(författare)
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A Necessary and Sufficient Condition for Input-Output Realization of Switched Affine State Space Models
- 2008
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Ingår i: Proceedings of the 47th IEEE Conference on Decision and Control. - 9781424431243 - 9781424431236 ; , s. 935-940
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Konferensbidrag (refereegranskat)abstract
- This paper presents a necessary and sufficient condition under which a discrete-time switched affine (SWA) state space model admits equivalent representations in the class of SWA input-output models. In particular, it is shown that observability is not a necessary requirement for input-output realization of SWA models. When an equivalent input-output representation exists, a constructive procedure is presented to derive both its parameters and the switching constraints. Numerical examples illustrate and motivate the presented equivalence result.
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| 14. |
- Sjöberg, Johan, 1978-, et al.
(författare)
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Power Series Solution of the Hamilton-Jacobi-Bellman Equation for DAE Models with a Discounted Cost
- 2008
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Ingår i: Proceedings of the 47th IEEE Conference on Decision and Control. - Linköping : Linköping University Electronic Press. - 9781424431243 - 9781424431236 ; , s. 4761-4766
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Konferensbidrag (refereegranskat)abstract
- This paper considers infinite horizon optimal feedback control of nonlinear models with discounted cost. The paper includes two extensions of existing results about optimal feedback control. First, it is proven that for real analytic statespace models, a time-invariant real analytic feedback solution exists, even when the cost function includes a discount factor, provided certain regularity conditions. Second, the result is generalized to nonlinear DAE models. The feedback solution is valid in a neighborhood of the origin. In both cases, explicit formulas for the series expansions of the cost function and control law are given.
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