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  • 1.
    Atta, Khalid
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Gustafsson, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Accuracy Improvement of Extremum Seeking Control2017In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 62, no 4, p. 1952-1958, article id 7498657Article in journal (Refereed)
    Abstract [en]

    In this work, we present a modification for theclassic and phasor extremum seeking control algorithms in orderto improve the accuracy by removing or reducing the convergenceerror. The modulation signals were replaced by a sum of sinusoidsin order to remove the equilibrium shift in the controlled variableof the averaged system. The convergence error is calculated as afunction of the number of sinusoids used in the modulation signal.A simulation example is presented to illustrate the improvement.

  • 2.
    Bof, Nicoletta
    et al.
    Department of Information Engineering, University of Padova, Padova, Italy.
    Carli, Ruggero
    Department of Information Engineering, University of Padova, Padova, Italy.
    Notarstefano, Giuseppe
    Department of Electrical, Electronic and Information Engineering, University of Bologna, Bologna, Italy.
    Schenato, Luca
    Department of Information Engineering, University of Padova, Padova, Italy.
    Varagnolo, Damiano
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Multiagent Newton–Raphson Optimization Over Lossy Networks2019In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 64, no 7, p. 2983-2990Article in journal (Refereed)
    Abstract [en]

    In this work, we study the problem of unconstrained convex optimization in a fully distributed multiagent setting, which includes asynchronous computation and lossy communication. In particular, we extend a recently proposed algorithm named Newton-Raphson consensus by integrating it with a broadcast-based average consensus algorithm, which is robust to packet losses. We show via the separation of time-scale principle that under mild conditions (i.e., persistency of the agents activation and bounded consecutive communication failures), the proposed algorithm is provably locally exponentially stable with respect to the optimal global solution. Finally, we complement the theoretical analysis with numerical simulations and comparisons based on real datasets.

  • 3.
    Böling, Jari M.
    et al.
    Department of Engineering, Åbo Akademi.
    Mäkilä, Pertti
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    On control relevant criteria in H∞ identification1998In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 43, no 5, p. 694-700Article in journal (Refereed)
    Abstract [en]

    This paper proposes a technique for using control relevant criteria in H∞ identification. The work reported here has its background in a desire to understand the closed-loop versus open-loop issue in control relevant identification. The proposed technique has some features in common with the iterative closed-loop Schrama scheme, but is constructed so as to be able to obtain control relevant reduced complexity models also directly from open-loop data (for stable systems). It is demonstrated that the proposed technique solves, with the initial open-loop data only, the examples treated earlier in the literature using the iterative closed-loop Schrama scheme

  • 4.
    Hostettler, Roland
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Birk, Wolfgang
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Lundberg Nordenvaad, Magnus
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    Maximum Likelihood Estimation of the Non-Parametric FRF for Pulse-Like Excitations2016In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 61, no 8, p. 2276-2281Article in journal (Refereed)
    Abstract [en]

    This technical note introduces the closed form maximum likelihood estimator for estimating the coefficients of the non-parametric frequency response function from system identification experiments. It is assumed that the experiments consist of repeated pulse excitations and that both the excitation and system response are measured which leads to an error-in-variables setting. Monte Carlo simulations indicate that the estimator achieves efficiency at low signal-to-noise ratios with only few measurements. Comparison with the least-squares estimator shows that better, unbiased results are obtained.

  • 5.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    A sufficient condition for invalidation of linear state-space systems with uncertain time-varying parameters2009In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 54, no 12, p. 2915-2920Article in journal (Refereed)
    Abstract [en]

    The model validation problem for linear systems with time-varying parameter uncertainty and additive disturbances is addressed. The disturbance are modelled using the window norm, which is a generalization of the l-infinity-norm and is shown to be attractive for optimal control. An approximation of the nonlinear operator from parameters to output is found based on the Fréchet derivative. Using this approximation, a sufficient condition for invalidation of a process model is formulated as a linear feasibility problem. In this condition, an upper bound for the approximation error is included. An overhead crane is used as an illustrative example to show that the model validation test is realistic to perform even with large data sets.

  • 6.
    Medvedev, Alexander
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Continuous least-squares observers with applications1996In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 41, no 10, p. 1530-1537Article in journal (Refereed)
    Abstract [en]

    A wide class of continuous least-squares (LS) observers is treated in a common framework provided by the pseudodifferential operator paradigm. It is shown that for the operators whose symbols satisfy certain conditions, the continuous LS observer always exists, providing observability of the plant. The general result is illustrated by an LS observer stemming from a sliding-window convolution operator. Applications to state feedback control and fault detection are discussed

  • 7.
    Partington, J.R.
    et al.
    School of Mathematics, University of Leeds.
    Mäkilä, Pertti
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Modeling of linear fading memory systems1996In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 41, no 6, p. 899-903Article in journal (Refereed)
    Abstract [en]

    Motivated by questions of approximate modeling and identification, we consider various classes of linear time-varying bounded-input-bounded output (BIBO) stable fading memory systems and prove some characterizations of them. These include fading memory systems, in general, almost periodic systems, and asymptotically periodic systems. We also show that norm and strong convergence coincide for BIBO stable causal fading memory systems

  • 8.
    Partington, J.R.
    et al.
    School of Mathematics, University of Leeds.
    Mäkilä, Pertti
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Worst-case analysis of identification: BIBO robustness for closed loop data1994In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 39, no 10, p. 2171-2176Article in journal (Refereed)
    Abstract [en]

    This paper deals with the worst-case analysis of identification of linear shift-invariant (possibly) infinite-dimensional systems. A necessary and sufficient input richness condition for the existence of robustly convergent identification algorithms in l1 is given. A closed-loop identification setting is studied to cover both stable and unstable (but BIBO stabilizable) systems. Identification (or modeling) error is then measured by distance functions which lead to the weakest convergence notions for systems such that closed-loop stability, in the sense of BIBO stability, is a robust property. Worst-case modeling error bounds in several distance functions are included

  • 9.
    Varagnolo, Damiano
    et al.
    School of Electrical Engineering, KTH Royal Institute of Technology.
    Pillonetto, Gianluigi
    Department of Information Engineering, University of Padova.
    Schenato, Luca
    Department of Information Engineering, University of Padova.
    Distributed Cardinality Estimation in Anonymous Networks2014In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, no 3, p. 645-659Article in journal (Refereed)
  • 10.
    Varagnolo, Damiano
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Zanella, Filippo
    Department of Information Engineering, University of Padova.
    Cenedese, Angelo
    Department of Information Engineering, University of Padova.
    Pillonetto, Gianluigi
    Department of Information Engineering, University of Padova.
    Schenato, Luca
    Department of Information Engineering, University of Padova.
    Newton-Raphson Consensus for Distributed Convex Optimization2016In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 61, no 4, p. 994-1009Article in journal (Refereed)
    Abstract [en]

    We address the problem of distributed unconstrained convex optimization under separability assumptions, i.e., the framework where each agent of a network is endowed with a local private multidimensional convex cost, is subject to communication constraints, and wants to collaborate to compute the minimizer of the sum of the local costs. We propose a design methodology that combines average consensus algorithms and separation of time-scales ideas. This strategy is proved, under suitable hypotheses, to be globally convergent to the true minimizer. Intuitively, the procedure lets the agents distributedly compute and sequentially update an approximated Newton-Raphson direction by means of suitable average consensus ratios. We show with numerical simulations that the speed of convergence of this strategy is comparable with alternative optimization strategies such as the Alternating Direction Method of Multipliers. Finally, we propose some alternative strategies which trade-off communication and computational requirements with convergence speed

  • 11.
    Walgama, Kirthi
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Sternby, Jan
    On the convergence properties of adaptive pole-placement controllers with antiwindup compensators1993In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 38, no 1, p. 128-132Article in journal (Refereed)
    Abstract [en]

    To avoid the windup problem in adaptive pole-placement controllers in the presence of a saturating input, an antiwindup compensator based on a generalization to the conditioning technique is introduced to the controller. This modification to the controller also provides a unified approach to investigate the asymptotic properties of the adaptive controllers with a class of antiwindup compensators, at least, when applied to stable processes

1 - 11 of 11
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