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  • 1.
    Lucchese, Riccardo
    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.
    A study of fine and coarse actuation capabilities in air-cooled server racks: control strategies and cost analysis2019In: IEEE Transactions on Control Systems Technology, ISSN 1063-6536, E-ISSN 1558-0865Article in journal (Refereed)
  • 2.
    Lucchese, Riccardo
    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.
    ColdSpot: A thermal supervisor aimed at server rooms implementing a raised plenum cooling setup2019Conference paper (Refereed)
  • 3.
    Lucchese, Riccardo
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Controlled Direct Liquid Cooling of Data Servers2019In: IEEE Transactions on Control Systems Technology, ISSN 1063-6536, E-ISSN 1558-0865Article in journal (Refereed)
  • 4.
    Lucchese, Riccardo
    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.
    On energy efficient flow provisioning in air-cooled data servers2019In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 89, p. 103-112Article in journal (Refereed)
    Abstract [en]

    This study considers how to efficiently manage the thermal state of data servers by provisioning their cooling airflow dynamically. It introduces a thermal network framework that is tailored to capture the temperature dynamics of the on-board thermal inertiae. On top of this modeling, it devises LeakageCooling, a novel flow provisioning controller that balances the temperature dependent leakage dissipation within the electronic chips and the power consumed by the local fans to produce the cooling airflow. The prediction capabilities of the proposed modeling and the overall control performance are assessed over several relevant experimental scenarios on an Open Compute Windmill V2 server.

  • 5.
    Lucchese, Riccardo
    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.
    On server cooling policies for heat recovery: exhaust air properties of an Open Compute Windmill V2 platform2019Conference paper (Refereed)
  • 6.
    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.
    Guay, Martin
    Department of Chemical Engineering, Queens University, Kingston, ON.
    On the Generalization and Stability Analysis of Pareto Seeking Control2018In: IEEE Control Systems Letters, E-ISSN 2475-1456, Vol. 2, no 1, p. 145-150Article in journal (Refereed)
    Abstract [en]

    In this letter, we address a multi-objective on-line optimization problem for unknown dynamical systems by providing a generalization of the Pareto seeking controller (PSC). The idea of the PSC is to drive the system to the Pareto front in the absence of knowledge of the values of the objectives or the input values to achieve Pareto optimality. Two special cases are presented, for two objectives and three objectives. A stability analysis is presented for the case of two objectives and two inputs, which shows that the controller practically drives the system into the neighborhood of the Pareto front, for any initial condition. Two simulation examples for the special cases are also presented

  • 7.
    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.

  • 8.
    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.
    On the stability analysis of phasor and classic extremum seeking control2016In: Systems & control letters (Print), ISSN 0167-6911, E-ISSN 1872-7956, Vol. 91, p. 55-62Article in journal (Refereed)
    Abstract [en]

    In this work we present a semi-global practical asymptotic stability analysis for phasor extremum seeking control with a general non-linear dynamic system. With the same technique applied to the classic band pass filter algorithm, we present a more relaxed (less constrained) semi-global practical asymptotic stability condition compared to earlier work. The results are based on a non approximated averaging for both control techniques.

  • 9.
    Atta, Khalid
    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.
    Hostettler, Roland
    Department of Electrical Engineering and Automation, Aalto University.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Phasor extremum seeking control with adaptive perturbation amplitude2016In: 2016 IEEE 55th Conference on Decision and Control, CDC 2016, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 7069-7074, article id 7799358Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a perturbation amplitude adaption scheme for phasor extremum seeking control based on the plant's estimated gradient. By using phasor extremum seeking instead of classical extremum seeking, the problem of algebraic loops in the controller formulation is avoided. Furthermore, a stability analysis for the proposed method is provided, which is the first stability analysis for extremum seeking controllers using adaptive amplitudes. The proposed method is illustrated using numerical examples and it is found that changes in optimum can be tracked accurately while the steady-state perturbations can be reduced significantly.

  • 10.
    Sayyaddelshad, Saleh
    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.
    Darouach, Mohamed
    Université de Lorraine, CRAN-CNRS UMR 7039, IUT de Longwy, 186 Rue de Lorraine.
    Gustafsson, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Robust state estimation and unknown inputs reconstruction for a class of nonlinear systems: multiobjective approach2016In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 64, p. 1-7Article in journal (Refereed)
    Abstract [en]

    We consider a novel method to design H-infinity observers for a class of uncertain nonlinear systems subject to unknown inputs. First, the main system dynamics are rewritten as an augmented system with state vector including both the state vector of the main system and the unknown inputs. Then, we design a H-infinity reduced-order observer to estimate both state variables and unknown inputs simultaneously. Based on a Lyapunov functional, we derive a sufficient condition for existence of the designed observer which requires solving a nonlinear matrix inequality. To facilitate the observer design, the achieved condition is formulated in terms of a set of linear matrix inequalities (LMI). By extending the proposed method to a multiobjective optimization problem, the maximum bound of the uncertainty and the minimum value of the disturbance attenuation level are found. Finally, the proposed observer is illustrated with an example.

  • 11.
    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.
    Extremum seeking control based on phasor estimation2015In: Systems & control letters (Print), ISSN 0167-6911, E-ISSN 1872-7956, Vol. 85, p. 37-45Article in journal (Refereed)
    Abstract [en]

    We present an extremum seeking control algorithm based on the estimation of the phasor of the perturbation frequency in the output of the plant. The phasor estimator is based on a continuous time Kalman filter, which is reduced into a variable gain observer by explicitly solving the special case of the Riccati equation. Local stability of the proposed al- gorithm for general non-linear dynamic systems using averaging and singular perturbations is presented for the single input case. The advantage of the presented algorithm is that it can be used on plants with large and even variable phase lag.

  • 12.
    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.
    Cervantes, Michel J.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gustafsson, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Maximum power point tracking for micro hydro power plants using extremum seeking control2015In: 2015 IEEE International Conference on Control Applications (CCA 2015): Sydney, Australia, September 21-23 2015, Piscataway, NJ: IEEE Communications Society, 2015, p. 1874-1879, article id 7320883Conference paper (Refereed)
    Abstract [en]

    In this work, we propose using extremum seeking control (ESC) as a tool for maximum power point tracking in micro hydro power plants. The phasor ESC, which is based on estimating the phasor of the plant output at the perturbation frequency, was modified by stimating the phasors of multiple harmonics of this frequency. This modification will improve the performance of ESC by reducing the luctuations in control variables that may appear in noisy environments as a result of high-amplitude perturbation signals. A test rig was used to experimentally verify the proposed approach and to demonstrate the usability of ESC in hydro power plants.

  • 13.
    Birk, Wolfgang
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Castaño, Miguel
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    An Application Software For Visualization and Control Configuration Selection of Interconnected Processes2014In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 26, p. 188-200Article in journal (Refereed)
    Abstract [en]

    This paper presents a new application software for control conguration selection of interconnected industrial processes,called ProMoVis. Moreover, ProMoVis is able to visualize process models and process layout at the physical leveltogether with the control system dynamics. The software consists of a builder part where the visual representationof the interconnected process is created and an analyzer part where the process is analyzed using dierent controlconguration selection tools.The conceptual idea of the software is presented and the subsequent design and implementation of ProMoVis isdiscussed. The implemented analysis methods are briey described including their usage and implementation aspects.The use of ProMoVis is demonstrated by an application study on the stock preparation process at SCA Obbola AB,Sweden. The results of this study are compared with the currently used control strategy.The study indicates that ProMoVis introduces a systematic and comprehensive way to perform control congurationselection. ProMoVis has been released under the Apache Open Source license.

  • 14.
    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.
    Control oriented modeling of flow and size distribution in cone crushers2014In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 56, p. 81-90Article in journal (Refereed)
    Abstract [en]

    This work presents a dynamic model for prediction of flow and output size distribution of cone crushers. The main purpose of the model is for simulation of closed-loop control using the Closed Side Setting (CSS) and the eccentric speed (ω) as manipulated variables. The idea of modeling crushers as cascaded zones is adopted throughout this work. The capacity, the length, the stroke, and the compression ratio of each zone are taken into consideration. Simulation results are presented in the form of the Crusher Performance Map (CPM) and the dynamic response for production of different size classes to steps input in ω and CSS. The simulations also include operation with recycling of oversize output, as well as the input of mixed materials. As an example, closed-loop control of the ratio of the large-size output to the total size output was simulated.

  • 15.
    Sayyaddelshad, Saleh
    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.
    Darouach, Mohamed
    Université de Lorraine.
    Gustafsson, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    H∞ filter design for state estimation and unknown inputs reconstruction of a class of nonlinear systems2014In: 19th IFAC World Congress on International Federation of Automatic Control: IFAC 2014, Cape Town, South Africa 24 - 29 August 2014, 2014, p. 61-66Conference paper (Refereed)
    Abstract [en]

    We consider a novel method to design a H∞ filter for a class of nonlinear systems subject to unknown inputs. First, we rewrite the system dynamics as a descriptor system. Then, we design a robust H∞ reduced-order filter to estimate both state variables and unknown inputs at the same time. Based on a Lyapunov functional, we derive a sufficient condition for existence of the designed filter which requires solving a nonlinear matrix inequality. The achieved condition is further formulated in terms of a linear matrix inequality (LMI) that is straightforward to solve by popular methods. Finally, the proposed filter is illustrated with an example.

  • 16.
    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.
    Pareto Seeking Control: On-line multi-objective optimization of dynami systems2014Conference paper (Other academic)
  • 17.
    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.
    Pareto Seeking Control: On-line multi-objective optimization of dynami systems2014Conference paper (Refereed)
  • 18.
    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.
    Cervantes, Michel J.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gustafsson, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Phasor Extremum Seeking and its Application in Kaplan Turbine Control2014In: 2014 IEEE International Conference on Control Applications (CCA 2014): Juan Les Antibes, France, 8 -10 October 2014, Piscataway, NJ: IEEE Communications Society, 2014, p. 298-303Conference paper (Refereed)
    Abstract [en]

    The Combinator is an important part in Kaplan turbine control. It ensures that the turbine will operate in an optimum way, in terms of maximum efficiency of the plant. This work suggests a new sinusoidal perturbation based extremum seeking algorithm based on the phasor of the output. We propose to use this algorithm for generating the required data to build and correct the combinator. Simulations are presented showing the applicability of the proposed methods.

  • 19.
    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.
    On-Line Optimization of Cone Crushers using Extremum-Seeking Control2013In: 2013 IEEE Multi-conference on Systems and Control (Conference on Control Applications), Hyderabad, India, August 28-30, 2013, 2013, p. 1054-1060Conference paper (Refereed)
    Abstract [en]

    This article demonstrates the ability of on-lineoptimization of cone crushers, specifically maximization of thetotal throughput of the crusher by adjusting the eccentric speed(ω). The on-line optimization was based on the Extremum-Seeking Control (ESC) approach, which is advantageous whenoptimizing systems with unknown time varying characteristics.Two types of gradient based approaches are tested in simulation,the traditional Band-pass filters method and a methodutilizing the Extended Kalman Filter (EKF). Both methodsperform satisfactory, demonstrating the good potential of ESCfor online-optimization of cone crushers. To deal with unwantedbehavior of the EKF based approach for situations when thegradient is not correctly estimated, a modification is suggestedbased on detecting this condition and accommodating for it.

  • 20.
    Sayyaddelshad, Saleh
    et al.
    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.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    H∞ observer design for uncertain discrete-time nonlinear delay systems: LMI optimization approach2012In: 2012 20th Mediterranean Conference on Control & Automation (MED), Piscataway, NJ: IEEE Communications Society, 2012, p. 592-597Conference paper (Refereed)
    Abstract [en]

    In this paper, we present a robust H∞ observer for a class of nonlinear and uncertain time-delayed systems. To design the proposed observer, the time delay does not have to be exactly known. With knowledge about upper and lower bound of the delay term, we can design an H∞ observer that guarantees asymptotic stability of the estimation error dynamics and is robust against time-varying parametric uncertainties. We show that the described problem can be solved in terms of linear matrix inequalities (LMIs). In addition, the admissible Lipschitz constant of the system is maximized and the disturbance attenuation level is minimized through convex multi-objective optimization. Finally, the proposed observer is illustrated with an example.

  • 21.
    Salehpour, Soheil
    et al.
    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.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    An on-line method for estimation of piecewise constant parameters in linear regression models2011In: Proceedings of the 18th IFAC World Congress: Milano, Italy, 28 August - 2 September, 2011, IFAC, International Federation of Automatic Control , 2011, p. 3171-3176Conference paper (Refereed)
    Abstract [en]

    We present an on-line method for detecting changes and estimating parameters in AR(X) models. The method is based on the assumption of piecewise constant parameters resulting in a sparse structure of their derivative. To illustrate the algorithm and its performance, we apply it to the change in the model parameters of some ARX models. The example illustrates that the new method shows good performance for an AR(X) model with abrupt changes in the parameters.

  • 22.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Commuting operations on signal-flow graphs for visualization of interconnected systems2011In: 4th IFAC Symposium on System, Structure and Control: Ancona Italy, 15-17 September 2010, New York: Curran Associates, Inc., 2011, p. 138-145Conference paper (Refereed)
    Abstract [en]

    We explore the signal flow graph as a setup for visualizing and analyzing interconnected systems. Two operations for facilitating interpretation of signal flow graphs are defined. These are hiding of unimportant nodes and elimination of self-references and it is shown that the operations commute under some conditions and that the hiding operation preserves the physical structure of the system in a certain sense. Also, the Loop Gain Index (LGI) is introduced as a measure of the relative importance of the edges in terms of dynamic behavior of the interconnected system. The LGI isillustrated with a numerical example.

  • 23.
    Salehpour, Soheil
    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.
    Regularization with hard penalty functions for on-line estimation2011In: 2011 9th IEEE International Conference on Control and Automation (ICCA 2011): Santiago, Chile, 19 - 21 December 2011, Piscataway, NJ: IEEE Communications Society, 2011, p. 195-200Conference paper (Refereed)
    Abstract [en]

    We present two on-line methods for detecting changes and estimating parameters in AR(X) models. The methods are based on the assumption of piecewise constant parameters resulting in a sparse structure of their derivative. Smoothly Clipped Absolute Deviation (SCAD) and hard thresholding (HT) penalty functions are two alternatives to give a sparse structure of the estimate. We use local quadratic and linear approximations of the penalty function, and the optimization is carried out by using a modified Newton-Raphson algorithm.To illustrate the algorithms and their performance, we apply them to estimate changing parameters of some ARX models. We investigate the convergence, squared error, and sparsity of the methods. The examples indicate that the local linear approximation gives better performance and is more encouraging than the local quadratic approximation.

  • 24.
    Birk, Wolfgang
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Castano, Miguel
    Rönnbäck, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Nordin, Tilda
    SCA Obbola AB.
    Ekholm, Nils-Olov
    Billerud Karlsborg AB.
    Interactive modeling and visualization of complex processes in pulp and paper making2010Conference paper (Refereed)
    Abstract [en]

    This paper discusses a new approach to interactive modeling, visualization and analysis of complex industrial processes. A theoretical framework based on signal flow graphs for modeling and visualization is presented. Using this framework a software tool is designed, called ProMoVis, which can be used to model a process, to visualize the models together with process construction and control system, and to perform analysis regarding e.g. feasible control strategies for the process. Moreover, a case study is conducted, where ProMoVis is used to model, visualize and analyze a stock preparation plant. The results indicate that the proposed methods and tools improve work flows, increase process understanding and simplify decision making on control strategies for complex process.

  • 25.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    On signal-flow graphs for visualization and analysis of complex systems2010Conference paper (Other academic)
    Abstract [en]

    We explore the signal flow graph as a setup for visualizing and analyzing interconnected systems. Two operations for facilitating interpretation of signal flow graphs are defined. These are hiding of unimportant nodes and elimination of self-references and it is shown that the hiding operation preserves the physical structure of the system in a certain sense. Also, two analysis tools are introduced for determining the relative importance of the edges in terms of dynamic behavior and controllability of the complex system. The analysis tools are illustrated with numerical examples.

  • 26.
    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.

  • 27. Ding, Limei
    et al.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Gustafsson, Thomas
    Application of reduced models for robust control and state estimation of a distributed parameter system2009In: Journal of Process Control, ISSN 0959-1524, E-ISSN 1873-2771, Vol. 19, no 3, p. 539-549Article in journal (Refereed)
    Abstract [en]

    This paper studies the application of reduced models of a distributed parameter system for robust process control and state estimation. We take the approach of integrating model reduction, parameter identification, and model uncertainty analysis, in purpose to find an appropriate trade-off between complexity and robust performance. The application example is the temperature system in a continuous paper pulp digester. Physical modeling of this process results in coupled linearized partial differential equations which are then reduced into low-order nominal process models using an orthogonal collocation approximation method.Two different approaches to obtaining a model uncertainty description are adapted for use on a distributed parameter system with low-order nominal model and shown to produce similar results when tested with measurement data. It is also demonstrated how this uncertainty description, in combination with the reduced model, may be used for robust control design and verification of the control performance on the distributed parameter system.Finally, the possibility of estimating the distributed process state using a state observer for the reduced process is demonstrated. Measurements of the process state in a certain position is available and is shown to agree with the estimated state at the same position.

  • 28.
    Salehpour, Soheil
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Johansson, Andreas
    Gustafsson, Thomas
    Fault detection of a blending tank process using mixed integer linear programming2009In: The IFAC Workshop on Automation in Mining, Mineral and Metal Industry: IFACMMM 2009, 2009Conference paper (Refereed)
    Abstract [en]

    The quality of iron ore pellets depends on many factors. One important issue is the mixing of binding material and slurry. It is assumed that proper mixing is achieved by keeping the material in the blender tank at an appropriate level to achieve a suitable residence time. The level of the blender is controlled by regulating the blender's hinged outflow-valve. Then, the modelling of the hinged valve is important, and the essential idea of this article is to find a method to use the process model and the available measured data to detect two detrimental conditions of the valve and warn the operators. These two conditions are: 1) The hinged valve is coated with slurry and therefore has to be cleaned to maintain its function. 2) Slurry is improperly distributed so that it does not cover the outflow valve, which then losesits authority over outflow. The valve behaviour is nonlinear and depends on the viscosity of the materials in the tank. Therefore, we use a change detection method based on Mixed Integer Linear Programming to estimate the time-varying parameters of the valve. Simulations with measurement data from the LKAB facility at Malmberget, Sweden, shows the viability of the algorithm.

  • 29.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Modelling and simulation of cone crushers2009In: IFAC Workshop on Automation in Mining, Mineral and Metal Industry: IFACMMM 2009, 2009Conference paper (Refereed)
    Abstract [en]

    A generic structure for dynamic models of cone crushers is presented, in the form of a partial differential equation depending on both time and a spatial variable as well as the size distribution of the particles. Assumptions on the sizeclassification of the flow through the crusher and the velocity of the particles enable modelling the effect of the main manipulated variables, i.e. closed side setting and rotational velocity. It is also shown how the model may be discretized and approximated by an ordinary differential equation. Simulations show that the model exhibits the expected behavior of a cone crusher. Notable is the effect of changing the rotational speed, which suggests that this variable is potentially valuable for improving the control of the crusher.

  • 30. Salehpour, Soheil
    et al.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Gustafsson, Thomas
    Parameter estimation and change detection in linear regression models using mixed integer linear programming2009In: 15th IFAC Symposium on System Identification 2009: Saint-Malo, France, 6 - 8 July 2009 / [ed] Eric Walter, Red Hook: Curran Associates, Inc., 2009Conference paper (Refereed)
    Abstract [en]

    We present a method for detecting changes and estimating parameters in AR(X) models. The method is based on the assumption of piecewise constant parameters resulting in a sparse structure of their derivative. To illustrate the algorithm and its performance, we apply it to the change in the mean model and compare it with four other change detection algorithms. Two applications, fuel monitoring and airbag control are treated with good results. The AR(X) change model shows good performance of the method in two illustrative examples.

  • 31. Berndtsson, Magnus
    et al.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Design of a dynamic threshold generator for λ-tuned control loops2008In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 16, no 5, p. 623-631Article in journal (Refereed)
    Abstract [en]

    A dynamic threshold generator is employed for detecting faults in λ-tuned control loops. To this end, an optimizationalgorithm for dynamic threshold generators is proposed. The a priori-information from λ-tuning is used in designing astate estimator with integral action. A dynamic threshold generator for the residual of this state estimator is derived and the optimization algorithm is applied. Simulations with measurement data from an experimental water tank setup show that the method is capable of detecting a small fault without generating false alarms.

  • 32. Salehpour, Soheil
    et al.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Model quality estimation in systems with time-varying time-delay uncertainty2008In: International Conference on Computer-Aided Control Systems: [CACSD] ; San Antonio, TX, 3 - 5 September 2008, Piscataway, NJ: IEEE Communications Society, 2008, p. 371-376Conference paper (Refereed)
    Abstract [en]

    The problem of estimating bounds for timevarying parameter perturbations using measurement data is addressed. In particular, time-varying time-delay is considered. An estimate of the perturbation is produced based on a quantized approximation of the uncertainty and the sparse structure of its derivative. The Pad´e-approximation and orthogonal collocation method are used to approximate the delay. A first-order system with time-delay is used as an illustrative example. The gain, time-constant and time-delay are considered as uncertainties here.

  • 33. Salehpour, Soheil
    et al.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Model quality estimation in systems with time-varying uncertainty: application to an overhead crane2008In: Reglermöte 2008: proceedings / [ed] Thomas Gustafsson; Wolfgang Birk; Andreas Johansson, Luleå: Luleå tekniska universitet, 2008Conference paper (Other academic)
    Abstract [en]

    The problem of estimating bounds for timevarying parameter perturbations using measurement data is addressed. An estimate of the perturbation is produced based on a quantized approximation of the uncertainty and the sparse nature of its derivative. As an illustrative example, we apply the method to measurement data from an overhead crane.

  • 34. Salehpour, Soheil
    et al.
    Johansson, Andreas
    Gustafsson, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Parameter estimation and change detection in linear regression models using mixed integer linear programming2008In: Reglermöte 2008: proceedings / [ed] Thomas Gustafsson; Wolfgang Birk; Andreas Johansson, Luleå: Luleå tekniska universitet, 2008Conference paper (Other academic)
    Abstract [en]

    We present a method for change detection and parameter estimation in change in the mean models and AR(X) models. The method is based on the assumption of piecewise constant parameters resulting in a sparse structure of their derivative. To illustrate the algorithm and its performance, we apply it to the change in the mean model and compare it with four other change detection algorithms. Two applications, fuel monitoring and airbag control are treated with good results. The AR(X) change model, shows good performance of the method in two illustrative examples.

  • 35.
    Birk, Wolfgang
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Castano, Miguel
    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.
    Projekt: Metoder för strukturell optimering av styrning i massatillverkning - MeSTA2008Other (Other (popular science, discussion, etc.))
    Abstract [sv]

    Styrsystemen i bruken består av tusentals reglerloopar och det är svårt att få en helhetssyn, och förstå de komplicerade sambanden mellan de olika processtegen. Med de nya verktygen blir det möjligt att analysera strukturen och generera helhetsstrategier för optimal styrning från ved till färdig pappersprodukt.

  • 36.
    Gustafsson, Thomas (Editor)
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Birk, Wolfgang (Editor)
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Johansson, Andreas (Editor)
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Reglermöte 2008: proceedings2008Report (Other academic)
    Abstract [en]

    Proceedings for Swedish Control Meeting (Reglermöte 2008) 4-5 June 2008. The proceedings contains all the manuscripts that were presented at the conference in Luleå. Manuscripts are in Swedish and/or English.

  • 37.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Shift-invariant signal norms for fault detection and control2008In: Systems & control letters (Print), ISSN 0167-6911, E-ISSN 1872-7956, Vol. 57, no 2, p. 105-111Article in journal (Refereed)
    Abstract [en]

    Two desirable properties of a signal norm to be used for the purpose of optimal control or fault detection are highlighted. These properties are shift-invariance and the permitting of persistent signals. A class of norms, called the window norms, is analyzed. Among norms considered for control purposes, they appear to be the only ones, save the L∞-norm, that satisfy both properties. The signal spaces defined by the window norms, however, include some interesting signals that are not in the L∞-space. The window norms have been found suitable for application in fault detection and are here also considered for optimal control. It is shown that they can be taken as a support for the concept of L1-control but may also suggest a new class of optimal controllers.

  • 38.
    Salehpour, Soheil
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Johansson, Andreas
    Two algorithms for model quality estimation in state-space systems with time-varying parameter uncertainty2008In: 2008 American Control Conference: Seattle, WA, 11 - 13 June 2008 ; [annual conference of the American Automatic Control Council], Piscataway, NJ: IEEE Communications Society, 2008, p. 4809-4814Conference paper (Refereed)
    Abstract [en]

    We present two methods to estimate bounds of parameter uncertainty in state-space systems. In the first method, we minimize the l∞-norm of the perturbation and its derivative. In the second method, an estimate of the perturbation is produced based on a quantized approximation of the uncertainty and the sparse structure of its derivative. Less sensitivity to increased noise and changed model parameters is achieved by the second method. We use an overhead crane as an illustrative example.

  • 39. Ding, Limei
    et al.
    Gustafsson, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Johansson, Andreas
    Model parameter estimation of simplified linear models for a continuous paper pulp digester2007In: Journal of Process Control, ISSN 0959-1524, E-ISSN 1873-2771, Vol. 17, no 2, p. 115-127Article in journal (Refereed)
    Abstract [en]

    A physical model of a continuous paper pulp digester is simplified and two subprocesses selected from the digester are modelled by coupled linear partial differential equations. This study focuses on the parameter identification of the simplified linear models. Finite-dimensional approximation of the model is made and a software package developed for identification of distributed parameter processes is applied. This identification system is developed for flexibility to allow identification for different choices of subprocesses and process variables. Unknown parameters of the subprocess models are estimated and the results are illustrated by process simulation and model validation.

  • 40. Ding, Limei
    et al.
    Gustafsson, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Johansson, Andreas
    Physical model parameter estimation of a nonlinear process2007In: Proceedings of the 2006 IEEE International Conference on Control Applications Applications: Munich, Germany, 4 - 6 October 2006, Piscataway, NJ: IEEE Communications Society, 2007, p. 2933-2938Conference paper (Refereed)
    Abstract [en]

    A physical model of a nonlinear subprocess in a continuous paper pulp digester is discussed and simplified. Model approximation is carried out in order to produce a simple linear model to be used for unknown parameter estimation of the physical model. The Taylor series expansion and the orthogonal collocation method are applied for the model linearization and model lumping, respectively. The reduced model is expressed as a standard state space form. The model parameters are estimated in the least squares sense, and the parameters retain their own physical meanings. The results of the parameter estimation are discussed and the model is verified using validation data.

  • 41.
    Gustafsson, Thomas
    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.
    Salehpour, Soheil
    Projekt: Modellering av komplexa dynamiska system2007Other (Other (popular science, discussion, etc.))
    Abstract [sv]

    En processindustrianläggning karaktäriseras av många delprocesser som är kopplade genom t.ex. materialflöden, gemensamma resurser, regulatorer osv. Detta förhållande ger upphov till tre typer av problem. 1. Det stora antalet processvariabler gör det orimligt att lägga ner stora arbetsinsatser på varje enskild variabel för t.ex. regulatordesign och övervakning. 2. De dynamiska kopplingarna mellan processvariablerna gör anläggningen till ett enormt stort dynamiskt system som inte är realistiskt att hantera som en helhet vid design av regulatorer och övervakningsalgoritmer. 3. Den komplexa strukturen kan ge upphov till komplicerad och svårförutsägbar dynamik i anläggningen som helhet, vilket kan ge upphov till t.ex. oscillationer. Arbetet i projektet fördelas på tre arbetspaket som angriper delproblem under de tre punkterna ovan. Alla tre arbetspaket förväntas resultera i verktyg som i förlängningen kan ingå som värdefulla komponenter på den plattform som en operatörssimulator utgör.

  • 42.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Validation of state-space models with time-varying parameter uncertainty2007In: Proceedings of the 46th IEEE Conference on Decision and Control : New Orleans, LA, 12 - 14 December 2007, Piscataway, NJ: IEEE Communications Society, 2007, p. 6406-6411Conference paper (Refereed)
    Abstract [en]

    The model validation problem assuming time-varying parameter uncertainty is addressed. A particular form of this uncertainty description, here named the biaffine input/output system is shown to be quite general and yet lead to simple solutions of the model validation problem, in the form of linear feasibility problems. An overhead crane is used as an illustrative example.

  • 43.
    Johansson, Andreas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Bask, Michael
    Norlander, Torbjörn
    Dynamic threshold generators for robust fault detection in linear systems with parameter uncertainty2006In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 42, no 7, p. 1095-1106Article in journal (Refereed)
    Abstract [en]

    The problem of developing robust thresholds for fault detection is addressed. An inequality for the solution of a linear system with uncertain parameters is provided and is shown to be a valuable tool for developing dynamic threshold generators for fault detection. Such threshold generators are desirable for achieving robustness against model uncertainty in combination with sensitivity to small faults. The usefulness of the inequality is illustrated by developing an algorithm for detection of sensor faults in a turbofan engine. The proposed algorithm consists of a state observer with integral action. A dynamic threshold generator is derived under the assumption of parametric uncertainty in the process model. Successful simulations with measurement data show that the algorithm is capable of detecting faults without generating false alarms.

  • 44. Berndtsson, Magnus
    et al.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Fault detection in lambda-tuned control loops using an observer with integral action2006In: 45th IEEE Conference on Decision and Control, 2006 : 13 - 15 Dec. 2006, [San Diego, CA, USA] / [ed] Pradeep Misra, Piscataway, NJ: IEEE Communications Society, 2006, p. 538-543Conference paper (Refereed)
    Abstract [en]

    A model-based fault detection algorithm assuming uncertain process parameters is used for detecting poorly operating lambda-tuned control loops. The a priori information obtained from lambda-tuning is used to create an observer as residual generator. The observer has integral action which makes it possible to obtain a tight fault detection threshold. A linear optimization approach is used for finding the parameters in the threshold.

  • 45. Ding, Limei
    et al.
    Gustafsson, Thomas
    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.
    Model identification of a nonlinear subprocess in a continuous paper pulp digester2006In: Measurement and control - applications for the operator: Control Systems 2006, June 6-8, 2006, Tampere Finland / [ed] Risto Ritala, Finnish Society of Automation , 2006Conference paper (Refereed)
  • 46.
    Johansson, Andreas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Bask, Michael
    Dynamic threshold generators for fault detection in uncertain systems2005In: Proceedings of the 16th IFAC World Congress: Prague, Czech Republic, July 3 - 8, 2005, Oxford: Elsevier, 2005, p. 460-465Conference paper (Refereed)
    Abstract [en]

    The problem of developing robust thresholds for fault detection is addressed. An inequality for the solution of a linear system with uncertain parameters is provided and is shown to be a valuable tool for developing dynamic threshold generators for fault detection. Such threshold generators are desirable for achieving robustness against model uncertainty in combination with sensitivity to small faults.The usefulness of the inequality is illustrated by developing an algorithm for detection of clogging in the valves of a flotation process. Simulations with measurement data show that the algorithm detects faults without generating false alarms.

  • 47.
    Johansson, Andreas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Bask, Michael
    Dynamic threshold generators for fault detection in uncertain systems2005In: Proceedings of the 16th IFAC World Congress: Prague, Czech Republic, July 3 - 8, 2005, Oxford: Elsevier, 2005Conference paper (Refereed)
  • 48. Bask, Michael
    et al.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Linear optimization of parameters in dynamic threshold generators2005In: Proceedings of 16th IFAC World Congress: Prague, Czech Republic, July 3 - 8, 2005, Oxford: Elsevier, 2005Conference paper (Refereed)
    Abstract [en]

    A model-based fault detection algorithm for linear systems with uncertain parameters is treated. An error system, bilinear in the uncertainties, generates the residual. The residual is compared to a threshold, which is generated by a linear system with the unknown uncertainty upper bounds as parameters. These unknown uncertainty upper bounds can be substituted by design parameters and this article suggests an algorithm to choose design parameter values such that the threshold is larger than the residual when no fault is present. This parameter design algorithm is applied to a sensor fault detection algorithm for a jet engine.

  • 49. Bask, Michael
    et al.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Realizable upper bounds for the modulus of impulse responses2005In: SICE 2005 proceedings: SICE annual conference in Okayama : August 8-10, 2005 Okayama University, Japan, Tokyo: Society of Instrument and Control Engineers , 2005, p. 2045-2050Conference paper (Refereed)
    Abstract [en]

    This article treats the problem of finding a linear system whose impulse response is an upper bound for the modulus of the impulse response of another given system. These upper bounds are required for a newly developed fault detection algorithm1). Three different methods to calculate a realizable upper bound for an impulse response, which contains multiple real poles and distinct complex poles, are presented. The triangular inequality and linear optimization are used in the first and second method, respectively. In the third method, the original impulse response is used combined with time-delays. The upper bounds are calculated for a fictitious impulse response and compared with its modulus.

  • 50. Bask, Michael
    et al.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Robust time-varying thresholds for supervision of valves in a flotation process2004In: 2004 43rd IEEE Conference on Decision and Control: Nassau, Bahamas, 14 - 17 December 2004, Piscataway, NJ: IEEE Communications Society, 2004, p. 4305-4310Conference paper (Refereed)
    Abstract [en]

    Robust thresholds for observer-based residuals are developed for the purpose of detecting clogging in the valves of a flotation process. The observer in the residual generator is a linear model of the flotation process extended with integrators and corrected with a linear feedback term. The integral states in the observer constitute the residual. Contribution to the residual comes not only from the faults but also from uncertainties in measurements, estimates and working point To avoid false alarms generated by these uncertainties, robust time-varying thresholds depending on the uncertainties are derived. Experiments on a froth flotation process with four cascade coupled tanks are carried out successfully. The data was provided by Boliden Area Concentrator in Boliden, Sweden.

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