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  • 1.
    Ahlén, Anders
    et al.
    Uppsala Univ, Signal Proc, Uppsala, Sweden.;Univ Newcastle, Dept Elect & Comp Engn, Callaghan, NSW, Australia..
    Åkerberg, Johan
    ABB Corp, Västerås, Sweden..
    Eriksson, Markus
    Scania CV, Södertalje, Sweden..
    Isaksson, Alf J.
    Linköping Univ, Linköping, Sweden.;Univ Newcastle, Callaghan, NSW, Australia.;Royal Inst Technol, Stockholm, Sweden.;ABB Corp Res, Vasteras, Sweden..
    Iwaki, Takuya
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). JGC Corp, Yokohama, Kanagawa, Japan.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Knorn, Steffi
    Univ Newcastle, Ctr Complex Dynam Syst & Control, Callaghan, NSW, Australia.;Uppsala Univ, Signals & Syst Div, Uppsala, Sweden..
    Lindh, Thomas
    Iggesund Mill, Maintenance Technol Dev, Iggesund Paperboard, Sweden..
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). CALTECH, Pasadena, CA 91125 USA.;MIT, Lab Informat & Decis Syst, 77 Massachusetts Ave, Cambridge, MA 02139 USA..
    Toward Wireless Control in Industrial Process Automation: A Case Study at a Paper Mill2019In: IEEE Control Systems Magazine, ISSN 1066-033X, Vol. 39, no 5, p. 36-57Article in journal (Refereed)
    Abstract [en]

    Wireless sensors and networks are used only occasionally in current control loops in the process industry. With rapid developments in embedded and highperformance computing, wireless communication, and cloud technology, drastic changes in the architecture and operation of industrial automation systems seem more likely than ever. These changes are driven by ever-growing demands on production quality and flexibility. However, as discussed in "Summary," there are several research obstacles to overcome. The radio communication environment in the process industry is often troublesome, as the environment is frequently cluttered with large metal objects, moving machines and vehicles, and processes emitting radio disturbances [1], [2]. The successful deployment of a wireless control system in such an environment requires careful design of communication links and network protocols as well as robust and reconfigurable control algorithms.

  • 2.
    Ahmadi, Seyed Alireza
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shames, Iman
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Scotton, Francesco
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Huang, Lirong
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wahlberg, Bo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Towards more efficient building energy management systems2012In: Proceedings - 2012 7th International Conference on Knowledge, Information and Creativity Support Systems, KICSS 2012, IEEE , 2012, p. 118-125Conference paper (Refereed)
    Abstract [en]

    As a first step towards developing efficient building energy management techniques, in this paper, we first study the energy consumption patterns of heating, ventilation and cooling (HVAC) systems across the KTH Royal Institute of Technology campus and we identify some possible areas where energy consumption can be made less wasteful. Later, we describe a test-bed where wireless sensor networks are used to collect data and eventually control the HVAC system in a distributed way. We present some of the data, temperature, humidity, and CO2 measurements, that are collected by the aforementioned network and compare them with the measurements collected by the legacy sensors already in place. In the end we present a preliminary result on modelling the dynamics of the temperature, humidity, and CO2 using the data gather by the sensor network. We check the validity of the model via comparing the out put of the system with measured data. As a future work we identify the possibility of using the models obtained here for model based control, and fault detection and isolation techniques.

  • 3.
    Alanwar, Amr
    et al.
    Jacobs Univ, Bremen, Germany..
    Berndt, Alexander
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Data-Driven Set-Based Estimation using Matrix Zonotopes with Set Containment Guarantees2022In: 2022 EUROPEAN CONTROL CONFERENCE (ECC), IEEE , 2022, p. 875-881Conference paper (Refereed)
    Abstract [en]

    We propose a method to perform set-based state estimation of an unknown dynamical linear system using a data-driven set propagation function. Our method comes with set-containment guarantees, making it applicable to safety-critical systems. The method consists of two phases: (1) an offline learning phase where we collect noisy input-output data to determine a function to propagate the state-set ahead in time; and (2) an online estimation phase consisting of a time update and a measurement update. It is assumed that known finite sets bound measurement noise and disturbances, but we assume no knowledge of their statistical properties. These sets are described using zonotopes, allowing efficient propagation and intersection operations. We propose a new approach to compute a set of models consistent with the data and noise-bound, given input-output data in the offline phase. The set of models is utilized in replacing the unknown dynamics in the data-driven set propagation function in the online phase. Then, we propose two approaches to perform the measurement update. Simulations show that the proposed estimator yields state sets comparable in volume to the 3 sigma confidence bounds obtained by a Kalman filter approach, but with the addition of state set-containment guarantees. We observe that using constrained zonotopes yields smaller sets but with higher computational costs than unconstrained ones.

  • 4.
    Alanwar, Amr
    et al.
    Constructor Univ, Sch Comp Sci & Engn, Bremen, Germany..
    Gassmann, Victor
    Tech Univ Munich, Dept Comp Engn, Munich, Germany..
    He, Xingkang
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Said, Hazem
    Ain Shams Univ, Dept Comp Engn, Cairo, Egypt..
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Althoff, Matthias
    Tech Univ Munich, Dept Comp Engn, Munich, Germany..
    Privacy-preserving set-based estimation using partially homomorphic encryption2023In: European Journal of Control, ISSN 0947-3580, E-ISSN 1435-5671, Vol. 71, p. 100786-, article id 100786Article in journal (Refereed)
    Abstract [en]

    The set-based estimation has gained a lot of attention due to its ability to guarantee state enclosures for safety-critical systems. However, collecting measurements from distributed sensors often requires out-sourcing the set-based operations to an aggregator node, raising many privacy concerns. To address this problem, we present set-based estimation protocols using partially homomorphic encryption that pre-serve the privacy of the measurements and sets bounding the estimates. We consider a linear discrete-time dynamical system with bounded modeling and measurement uncertainties. Sets are represented by zonotopes and constrained zonotopes as they can compactly represent high-dimensional sets and are closed under linear maps and Minkowski addition. By selectively encrypting parameters of the set repre-sentations, we establish the notion of encrypted sets and intersect sets in the encrypted domain, which enables guaranteed state estimation while ensuring privacy. In particular, we show that our protocols achieve computational privacy using the cryptographic notion of computational indistinguishability. We demonstrate the efficiency of our approach by localizing a real mobile quadcopter using ultra-wideband wireless devices.

  • 5.
    Alisic, Rijad
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Kim, Junsoo
    Seoul Natl Univ Sci & Technol, Dept Elect & Informat Engn, Seoul 01811, South Korea..
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Model-Free Undetectable Attacks on Linear Systems Using LWE-Based Encryption2023In: IEEE Control Systems Letters, E-ISSN 2475-1456, Vol. 7, p. 1249-1254Article in journal (Refereed)
    Abstract [en]

    We show that the homomorphic property, a desired property in encrypted control, can lead to failure in the cyber defense of a dynamical control system from undetectable attacks, even though individual signal sequences remain unknown to the attacker. We consider an encryption method based on the Learning with Errors (LWE) problem and demonstrate how model-free undetectable attacks on linear systems over integers can be computed from sampled inputs and outputs that are encrypted. Previous work has shown that computing such attacks is possible on nonencrypted systems. Applying this earlier work to our scenario, with minor modifications, typically amplifies the error in encrypted messages unless a short vector problem is solved. Given that an attacker obtains a short vector, we derive the probability that the attack is detected and show how it explicitly depends on the encryption parameters. Finally, we simulate an attack obtained by our method on an encrypted linear system over integers and conduct an analysis of the probability that the attack will be detected.

  • 6.
    Alisic, Rijad
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Molinari, Marco
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Pare, P. E.
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Maximizing Privacy in MIMO Cyber-Physical Systems Using the Chapman-Robbins Bound2020In: Proceedings of the IEEE Conference on Decision and Control, Institute of Electrical and Electronics Engineers Inc. , 2020, p. 6272-6277Conference paper (Refereed)
    Abstract [en]

    Privacy breaches of cyber-physical systems could expose vulnerabilities to an adversary. Here, privacy leaks of step inputs to linear time-invariant systems are mitigated through additive Gaussian noise. Fundamental lower bounds on the privacy are derived, which are based on the variance of any estimator that seeks to recreate the input. Fully private inputs are investigated and related to transmission zeros. Thereafter, a method to increase the privacy of optimal step inputs is presented and a privacy-utility trade-off bound is derived. Finally, these results are verified on data from the KTH Live-In Lab Testbed, showing good correspondence with theoretical results. 

  • 7.
    Alisic, Rijad
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Molinari, Marco
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Pare, Philip E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Sandberg, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Ensuring privacy of occupancy changes in smart buildings2020In: CCTA 2020 - 4th IEEE Conference on Control Technology and Applications, Institute of Electrical and Electronics Engineers Inc. , 2020, p. 871-876Conference paper (Refereed)
    Abstract [en]

    Smart building management systems rely on sensors to optimize the operation of buildings. If an unauthorized user gains access to these sensors, a privacy leak may occur. This paper considers such a potential leak of privacy in a smart residential building, and how it may be mitigated by corrupting the measurements with additive Gaussian noise. This corruption is done in order to hide when the occupancy changes in an apartment. A lower bound on the variance of any estimator that estimates the change time is derived. The bound is then used to analyze how different model parameters affect the variance. It is shown that the signal to noise ratio and the system dynamics are the main factors that affect the bound. These results are then verified on a simulator of the KTH Live-In Lab Testbed, showing good correspondence with theoretical results.

  • 8.
    Alisic, Rijad
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Pare, Philip E.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Modeling and Stability of Prosumer Heat Networks2019In: IFAC PAPERSONLINE, ELSEVIER , 2019, Vol. 52, no 20, p. 235-240Conference paper (Refereed)
    Abstract [en]

    The energy sector is going through a large transformation due to public demands of renewable energy sources. However, a major issue is that these energy sources are intermittent. If designed correctly, district heating systems can naturally contain energy storing units, for example by storing heat in the isolated pipes that make up the heat grid. Additionally, this makes it easier to reuse and transport already generated heat to other users. This paper proposes a mathematical model of such a grid, where excess energy can be retracted from one user and distributed to other users using a network of heat pumps. In some cases, one can balance residual heat production with the heat consumption, temporarily eliminating the need for a centralized heating plant. Existence conditions for stable steady states of such a network with general topology are given. Finally, energy optimal stable steady states are obtained through convex optimization. 

  • 9.
    Alisic, Rijad
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Paré, P. E.
    School of Electrical and Computer Engineering, Purdue University, WestLafayette, Indiana, USA.
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Change time estimation uncertainty in nonlinear dynamical systems with applications to COVID-192022In: International Journal of Robust and Nonlinear Control, ISSN 1049-8923, E-ISSN 1099-1239Article in journal (Refereed)
    Abstract [en]

    The impact that each individual non-pharmaceutical intervention (NPI) had on the spread rate of COVID-19 is difficult to estimate, since several NPIs were implemented in rapid succession in most countries. In this article, we analyze the detectability of sudden changes in a parameter of nonlinear dynamical systems, which could be used to represent NPIs or mutations of the virus, in the presence of measurement noise. Specifically, by taking an agnostic approach, we provide necessary conditions for when the best possible unbiased estimator is able to isolate the effect of a sudden change in a model parameter, by using the Hammersley–Chapman–Robbins (HCR) lower bound. Several simplifications to the calculation of the HCR lower bound are given, which depend on the amplitude of the sudden change and the dynamics of the system. We further define the concept of the most informative sample based on the largest (Formula presented.) distance between two output trajectories, which is a good indicator of when the HCR lower bound converges. These results are thereafter used to analyze the susceptible-infected-removed model. For instance, we show that performing analysis using the number of recovered/deceased, as opposed to the cumulative number of infected, may be an inferior signal to use since sudden changes are fundamentally more difficult to estimate and seem to require more samples. Finally, these results are verified by simulations and applied to real data from the spread of COVID-19 in France.

  • 10.
    Alisic, Rijad
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Data-injection Attacks Using Historical Inputs and Outputs2021In: Proceedings European Control Conference, ECC 2021, Institute of Electrical and Electronics Engineers (IEEE) , 2021, p. 1399-1405Conference paper (Refereed)
    Abstract [en]

    Data-driven, model-free control has become popular in recent years, due to their ease of implementation and minimal information requirement about the system. In this paper, we investigate whether the same methods could be used by an adversary to synthesize undetectable data-injection attacks on cyber-physical systems using Willems' Fundamental Lemma. We show that if the adversary is able to upper bound the order of a linear, time-invariant system and read all its inputs and outputs, then the adversary will be able to generate undetectable attack signals in the form of covert attacks. Additionally, we provide conditions on the disclosed data set that enable the adversary to generate zero dynamics attacks. These conditions give operators insights into when enough information about the system has been revealed for an adversary to conduct an undetectable attack. Finally, the different attack strategies are verified through a numerical example.

  • 11.
    Alisic, Rijad
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Privacy Enhancement of Structured Inputs in Cyber-Physical Systems2021In: 2021 60th IEEE conference on decision and control (CDC), Institute of Electrical and Electronics Engineers (IEEE) , 2021, p. 4888-4894Conference paper (Refereed)
    Abstract [en]

    Privacy is often the first line of defense against cyber-physical attacks. In this paper, we derive guarantees for the privacy of structured inputs to linear time-invariant systems, where the eavesdropper either does not know the input or only knows parts of it a priori. The input is be parametrized by a mixture of discrete and continuous parameters. Privacy guarantees for these parameters are then derived using a Barankin-style bound. Given an open-loop control objective, a modification to the cost function is proposed to enhance privacy. Privacy-utility trade-off bounds are derived for these private open-loop control signals. Finally, the theoretical results are verified both using the physical Temperature Control Lab and a numerical simulation of it.

  • 12.
    Altaf, Faisal
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Araujo, José
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hernandez, Aitor
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wireless event-triggered controller for a 3D tower crane lab process2011In: 2011 19th Mediterranean Conference on Control and Automation, MED 2011, 2011, p. 994-1001Conference paper (Refereed)
    Abstract [en]

    This paper studies the design and real-time implementation of an event-triggered controller for a nonlinear 3D tower crane where the communication between the controller and the actuators is performed over a low-power wireless network. A flexible Event-Generation Circuit (EGC) is proposed in order to implement event-driven controllers for Networked Control Systems. Furthermore, a detailed experimental analysis on the performance of the event-triggered controller and the influence of packet losses on the transmitted actuation messages are presented. The results show that the event-triggered controllers in networked control systems are able to maintain the same level of performance as compared to periodic controllers, while increasing the sensors/actuators lifetime by reducing network bandwidth utilization.

  • 13.
    Anderson, James
    et al.
    Oxford University.
    Teixeira, André
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Papachristodoulou, Antonis
    Oxford University.
    Dynamical System Decomposition Using Dissipation Inequalities2011In: Proceedings of the 50th IEEE Conference on Decision and Control and European Control Conference,  Orlando, Florida, 2011Conference paper (Refereed)
    Abstract [en]

    In this paper we investigate stability and inter-action measures for interconnected systems that have beenproduced by decomposing a large-scale linear system into aset of lower order subsystems connected in feedback. We beginby analyzing the requirements for asymptotic stability throughgeneralized dissipation inequalities and storage functions. Usingthis insight we then describe various metrics based on a system’senergy dissipation to determine how strongly the subsystemsinteract with each other. From these metrics a decompositionalgorithm is described.

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    fulltext
  • 14. Andersson, G.
    et al.
    Esfahani, P. M.
    Vrakopoulou, M.
    Margellos, K.
    Lygeros, J.
    Teixeira, André
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Cyber-security of SCADA systems2012In: 2012 IEEE PES Innovative Smart Grid Technologies, ISGT 2012, IEEE , 2012, p. 6175543-Conference paper (Refereed)
    Abstract [en]

    After a general introduction of the VIKING EU FP7 project two specific cyber-attack mechanisms, which have been analyzed in the VIKING project, will be discussed in more detail. Firstly an attack and its consequences on the Automatic Generation Control (AGC) in a power system are investigated, and secondly the cyber security of State Estimators in SCADA systems is scrutinized.

  • 15.
    Andreasson, Martin
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Amin, Saurabh
    TRUST Center, University of California, Berkeley.
    Schwartz, Galina
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sastry, Shankar
    TRUST Center, University of California, Berkeley.
    Correlated Failures of Power Systems: Analysis of the Nordic Grid2011In: Preprints of Workshop on Foundations of Dependable and Secure Cyber-Physical Systems, 2011Conference paper (Refereed)
    Abstract [en]

    In this work we have analyzed the effectsof correlated failures of power lines on the total systemload shed. The total system load shed is determined bysolving the optimal load shedding problem, which is thesystem operator’s best response to a system failure.We haveintroduced a Monte Carlo based simulation framework forestimating the statistics of the system load shed as a functionof stochastic network parameters, and provide explicitguarantees on the sampling accuracy. This framework hasbeen applied to a 470 bus model of the Nordic power systemand a correlated Bernoulli failure model. It has been foundthat increased correlations between Bernoulli failures ofpower lines can dramatically increase the expected valueas well as the variance of the system load shed.

  • 16.
    Andreasson, Martin
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed vs. centralized power systems frequency control2013In: 2013 European Control Conference, ECC 2013, 2013, p. 3524-3529Conference paper (Refereed)
    Abstract [en]

    This paper considers a distributed control algorithm for frequency control of electrical power systems. We propose a distributed controller which retains the reference frequency of the buses under unknown load changes, while asymptotically minimizing a quadratic cost of power generation. For comparison, we also propose a centralized controller which also retains the reference frequency while minimizing the same cost of power generation. We derive sufficient stability criteria for the parameters of both controllers. The controllers are evaluated by simulation on the IEEE 30 bus test network, where their performance is compared.

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    ECC_2013
  • 17.
    Andreasson, Martin
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Control of MTDC Transmission Systems under Local Information2014In: Decision and Control (CDC), 2014 IEEE 53rd Annual Conference on, IEEE conference proceedings, 2014, p. 1335-1340Conference paper (Refereed)
    Abstract [en]

    High-voltage direct current (HVDC) is a commonly used technology for long-distance electric power transmission, mainly due to its low resistive losses. In this paper a distributed controller for multi-terminal high-voltage direct current (MTDC) transmission systems is considered. Sufficient conditions for when the proposed controller renders the closed-loop system asymptotically stable are provided. Provided that the closed loop system is asymptotically stable, it is shown that in steady-state a weighted average of the deviations from the nominal voltages is zero. Furthermore, a quadratic cost of the current injections is minimized asymptotically.

    Download full text (pdf)
    fulltext
  • 18.
    Andreasson, Martin
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed controllers for multiterminal HVDC transmission systems2017In: IEEE Transactions on Control of Network Systems, E-ISSN 2325-5870, Vol. 4, no 3, p. 564-574Article in journal (Refereed)
    Abstract [en]

    High-voltage direct current (HVDC) is a commonly used technology for long-distance electric power transmission, mainly due to its low resistive losses. In this paper the voltagedroop method (VDM) is reviewed, and three novel distributed controllers for multi-terminal HVDC (MTDC) transmission systems are proposed. Sufficient conditions for when the proposed controllers render the closed-loop system asymptotically stable are provided. These conditions give insight into suitable controller architecture, e.g., that the communication graph should be identical with the graph of the MTDC system, including edge weights. Provided that the closed-loop systems are asymptotically stable, it is shown that the voltages asymptotically converge to within predefined bounds. Furthermore, a quadratic cost of the injected currents is asymptotically minimized. The proposed controllers are evaluated on a four-bus MTDC system.

    Download full text (pdf)
    fulltext
  • 19.
    Andreasson, Martin
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed PI-Control with Applications to Power Systems Frequency Control2014In: American Control Conference (ACC), 2014, IEEE conference proceedings, 2014, p. 3183-3188Conference paper (Refereed)
    Abstract [en]

    This paper considers a distributed PI-controller for networked dynamical systems. Sufficient conditions for when the controller is able to stabilize a general linear system and eliminate static control errors are presented. The proposed controller is applied to frequency control of power transmission systems. Sufficient stability criteria are derived, and it is shown that the controller parameters can always be chosen so that the frequencies in the closed loop converge to nominal operational frequency. We show that the load sharing property of the generators is maintained, i.e., the input power of the generators is proportional to a controller parameter. The controller is evaluated by simulation on the IEEE 30 bus test network, where its effectiveness is demonstrated.

  • 20.
    Andreasson, Martin
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Control of Networked Dynamical Systems: Static Feedback, Integral Action and Consensus2014In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, no 7, p. 1750-1764Article in journal (Refereed)
    Abstract [en]

    This paper analyzes distributed control protocols for first- and second-order networked dynamical systems. We propose a class of nonlinear consensus controllers where the input of each agent can be written as a product of a nonlinear gain, and a sum of nonlinear interaction functions. By using integral Lyapunov functions, we prove the stability of the proposed control protocols, and explicitly characterize the equilibrium set. We also propose a distributed proportional-integral (PI) controller for networked dynamical systems. The PI controllers successfully attenuate constant disturbances in the network. We prove that agents with single-integrator dynamics are stable for any integral gain, and give an explicit tight upper bound on the integral gain for when the system is stable for agents with double-integrator dynamics. Throughout the paper we highlight some possible applications of the proposed controllers by realistic simulations of autonomous satellites, power systems and building temperature control.

  • 21.
    Andreasson, Martin
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Nazari, Mohammad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Distributed Voltage and Current Control of Multi-Terminal High-Voltage Direct Current Transmission Systems2014In: Proceedings of the 19th IFAC World Congress, 2014, IFAC Papers Online, 2014, Vol. 19, p. 11910-11916Conference paper (Refereed)
    Abstract [en]

    High-voltage direct current (HVDC) is a commonly used technology for long-distance power transmission, due to its low resistive losses and low costs. In this paper, a novel distributed controller for multi-terminal HVDC (MTDC) systems is proposed. Under certain conditions on the controller gains, it is shown to stabilize the MTDC system. The controller is shown to always keep the voltages close to the nominal voltage, while assuring that the injected power is shared fairly among the converters. The theoretical results are validated by simulations, where the affect of communication time-delays is also studied.

    Download full text (pdf)
    fulltext
  • 22.
    Andreasson, Martin
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed integral action: stability analysis and frequency control of power systems2012In: 2012 IEEE 51st Annual Conference on Decision and Control (CDC), IEEE , 2012, p. 2077-2083Conference paper (Refereed)
    Abstract [en]

    This paper analyzes distributed proportional-integral controllers. We prove that integral action can be successfully applied to consensus algorithms, where attenuation of static disturbances is achieved. These control algorithms are applied to decentralized frequency control of electrical power systems. We show that the proposed algorithm can attenuate step disturbances of power loads. We provide simulations of the proposed control algorithm on the IEEE 30 bus test system that demonstrate its efficiency.

    Download full text (pdf)
    multiagent_andreasson_cdc12
  • 23.
    Andreasson, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM). KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sjödin, Emma
    KTH, School of Industrial Engineering and Management (ITM). KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Industrial Engineering and Management (ITM). KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Industrial Engineering and Management (ITM). KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Coherence in Synchronizing Power Networks with Distributed Integral Control2017In: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017, IEEE , 2017, p. 6683-6688Conference paper (Refereed)
    Abstract [en]

    We consider frequency control of synchronous generator networks and study transient performance under both primary and secondary frequency control. We model random step changes in power loads and evaluate performance in terms of expected deviations from a synchronous frequency over the synchronization transient; what can be thought of as lack of frequency coherence. We compare a standard droop control strategy to two secondary proportional integral (PI) controllers: centralized averaging PI control (CAPI) and distributed averaging PI control (DAPI). We show that the performance of a power system with DAPI control is always superior to that of a CAPI controlled system, which in turn has the same transient performance as standard droop control. Furthermore, for a large class of network graphs, performance scales unfavorably with network size with CAPI and droop control, which is not the case with DAPI control. We discuss optimal tuning of the DAPI controller and describe how internodal alignment of the integral states affects performance. Our results are demonstrated through simulations of the Nordic power grid.

  • 24.
    Andreasson, Martin
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tegling, Emma
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Performance and scalability of voltage controllers in multi-terminal HVDC networks2017In: Proceedings of the American Control Conference, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 3029-3034, article id 7963412Conference paper (Refereed)
    Abstract [en]

    In this paper, we compare the transient performance of a multi-terminal high-voltage DC (MTDC) grid equipped with a slack bus for voltage control to that of two distributed control schemes: A standard droop controller and a distributed averaging proportional-integral (DAPI) controller. We evaluate performance in terms of an ℋ2 metric that quantifies expected deviations from nominal voltages, and show that the transient performance of a droop or DAPI controlled MTDC grid is always superior to that of an MTDC grid with a slack bus. In particular, by studying systems built up over lattice networks, we show that the ℋ2 norm of a slack bus controlled system may scale unboundedly with network size, while the norm remains uniformly bounded with droop or DAPI control. We simulate the control strategies on radial MTDC networks to demonstrate that the transient performance for the slack bus controlled system deteriorates significantly as the network grows, which is not the case with the distributed control strategies.

  • 25.
    Araujo, Jose
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ariba, Yassine
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Park, Pangun
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Control over a Hybrid MAC Wireless Network2010In: 2010 IEEE 1ST INTERNATIONAL CONFERENCE ON SMART GRID COMMUNICATIONS, 2010, p. 197-202Conference paper (Refereed)
    Abstract [en]

    Wireless Sensor Networks and Control Systems are an essential part of the Smart Grid. We consider the problem of performing control over large complex networked systems with packet drops. More specifically, we are interested in improving the performance of the regulation of control loops when the communication is made over low-cost wireless networks. In control over wireless networks it is common to use Contention-Free (CF) schemes where no losses occur with the price of low scalability and complicated scheduling policies. In this work we propose a hybrid MAC and control architecture, where a small number of control loops with high demand of attention are scheduled in a CF scheme and well regulated loops are scheduled in a lossy, asynchronous and highly scalable, Contention-Access (CA) scheme. We model and analyze the performance of such system with Markov Jump Linear System (MJLS) tools and compare it with other architecture types. Performance is evaluated using a quadratic cost function of the state.

  • 26.
    Araujo, Jose
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Experimental Validation of a Localization System Based on a Heterogeneous Sensor Network2009In: ASCC: 2009 7TH ASIAN CONTROL CONFERENCE, NEW YORK: IEEE , 2009, p. 465-470Conference paper (Refereed)
    Abstract [en]

    The experimental implementation and validation of a localization system based on a heterogeneous sensor network is described. The sensor network consists of ultrasound ranging sensors and web cameras. They are used to localize a mobile robot under sensor communication constraints. Applying a recently proposed sensor fusion algorithm that explicitly takes communication delay and cost into account, it is shown that one can accurately trade off the estimation performance by using low-quality ultrasound sensors with low processing time and low communication cost versus the use of the high-quality cameras with longer processing time and higher communication cost. It is shown that a periodic schedule of the sensors is suitable in many cases. The experimental setup is discussed in detail and experimental results are presented.

    Download full text (pdf)
    networked_control_ascc09
  • 27. Besselink, B.
    et al.
    Feyzmahdavian, Hamid Reza
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    D-stability and delay-independent stability of monotone nonlinear systems with max-separable Lyapunov functions2016In: 2016 IEEE 55th Conference on Decision and Control, CDC 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 3172-3177, article id 2-s2.0-85010722892Conference paper (Refereed)
    Abstract [en]

    Stability properties of monotone nonlinear systems with max-separable Lyapunov functions are considered in this paper, motivated by the following observations. First, recent results have shown that such Lyapunov functions are guaranteed to exist for asymptotically stable monotone systems on compact sets. Second, it is well-known that, for monotone linear systems, asymptotic stability implies the stronger properties of D-stability and robustness with respect to time-delays. This paper shows that similar properties hold for monotone nonlinear systems that admit max-separable Lyapunov functions. In particular, a notion of D-stability for monotone nonlinear systems and delay-independent stability will be discussed. The theoretical results are illustrated by means of examples.

  • 28.
    Besselink, Bart
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Clustering-based model reduction of networked passive systems2016In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 61, no 10, p. 2958-2973, article id 7350110Article in journal (Refereed)
    Abstract [en]

    The model reduction problem for networks of interconnected dynamical systems is studied in this paper. In particular, networks of identical passive subsystems, which are coupled according to a tree topology, are considered. For such networked systems, reduction is performed by clustering subsystems that show similar behavior and subsequently aggregating their states, leading to a reduced-order networked system that allows for an insightful physical interpretation. The clusters are chosen on the basis of the analysis of controllability and observability properties of associated edge systems, representing the importance of the couplings and providing ameasure of the similarity of the behavior of neighboring subsystems. This reduction procedure is shown to preserve synchronization properties (i.e., the convergence of the subsystem trajectories to each other) and allows for the a priori computation of a bound on the reduction error with respect to external inputs and outputs. The method is illustrated by means of an example of a thermal model of a building.

  • 29.
    Besselink, Bart
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Model reduction of networked passive systems through clustering2014In: 2014 European Control Conference, ECC 2014, IEEE , 2014, p. 1069-1074Conference paper (Refereed)
    Abstract [en]

    In this paper, a model reduction procedure for a network of interconnected identical passive subsystems is presented. Here, rather than performing model reduction on the subsystems, adjacent subsystems are clustered, leading to a reduced-order networked system that allows for a convenient physical interpretation. The identification of the subsystems to be clustered is performed through controllability and observability analysis of an associated edge system and it is shown that the property of synchronization (i.e., the convergence of trajectories of the subsystems to each other) is preserved during reduction. The results are illustrated by means of an example.

  • 30.
    Besselink, Bart
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Imura, Jun-ichi
    Tokyo Institute of Technology.
    Controllability of a class of networked passive linear systems2013In: Proceedings of the 52nd IEEE Conference on Decision and Control, Florence, Italy, IEEE conference proceedings, 2013, p. 4901-4906Conference paper (Refereed)
    Abstract [en]

    In this paper, controllability properties of networks of diffusively coupled linear systems are considered through the controllability Gramian. For a class of passive linear systems, it is shown that the controllability Gramian can be decomposed into two parts. The first part is related to the dynamics of the individual systems whereas the second part is dependent only on the interconnection topology, allowing for a clear interpretation and efficient computation of controllability properties for a class of networked systems. Moreover, a relation between symmetries in the interconnection topology and controllability is given. The results are illustrated by an example.

  • 31.
    Biel, Martin
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Farokhi, Farhad
    Sandberg, Henrik
    SiMpLIfy: A toolbox for structured model reduction2015In: 2015 European Control Conference, ECC 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 1159-1164Conference paper (Refereed)
    Abstract [en]

    In this paper, we present a toolbox for structured model reduction developed for MATLAB. In addition to structured model reduction methods using balanced realizations of the subsystems, we introduce a numerical algorithm for structured model reduction using a subgradient optimization algorithm. We briefly present the syntax for the toolbox and its features. Finally, we demonstrate the applicability of various model reduction methods in the toolbox on a structured mass-spring mechanical system.

  • 32. Briat, C.
    et al.
    Yavuz, E.A
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf T.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The Conservation of Information, Towards an Axiomatized Modular Modeling Approach to Congestion Control2015In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 23, no 3, p. 851-865Article in journal (Refereed)
    Abstract [en]

    We derive a modular fluid-flow network congestion control model based on a law of fundamental nature in networks: the conservation of information. Network elements such as queues, users, and transmission channels and network performance indicators like sending/acknowledgment rates and delays are mathematically modeled by applying this law locally. Our contributions are twofold. First, we introduce a modular metamodel that is sufficiently generic to represent any network topology. The proposed model is composed of building blocks that implement mechanisms ignored by the existing ones, which can be recovered from exact reduction or approximation of this new model. Second, we provide a novel classification of previously proposed models in the literature and show that they are often not capable of capturing the transient behavior of the network precisely. Numerical results obtained from packet-level simulations demonstrate the accuracy of the proposed model.

  • 33.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nonlinear state-dependent delay modeling and stability analysis of internet congestion control2010In: 49TH IEEE CONFERENCE ON DECISION AND CONTROL (CDC), 2010, p. 1484-1491Conference paper (Refereed)
    Abstract [en]

    It is shown that the queuing delay involved in the congestion control algorithm is state-dependent and does not depend on the current time. Then, using an accurate formulation for buffers, networks with arbitrary topologies can be built. At equilibrium, our model reduces to the widely used setup by Paganini et al. Using this model, the delay-derivative is analyzed and it is proved that the delay time-derivative does not exceed one for the considered topologies. It is then shown that the considered congestion control algorithm globally stabilizes a delay-free single buffer network. Finally, using a specific linearization result for systems with state-dependent delays from Cooke and Huang, we show the local stability of the single bottleneck network.

    Download full text (pdf)
    network_cdc10
  • 34.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Yavuz, Emre Altug
    KTH, School of Electrical Engineering (EES), Communication Networks.
    An axiomatic fluid-flow model for congestion control analysis2011In: 2011 50th IEEE Conference on Decision and Control andEuropean Control Conference (CDC-ECC), 2011, p. 3122-3129Conference paper (Refereed)
    Abstract [en]

    An axiomatic model for congestion control isderived. The proposed four axioms serve as a basis for theconstruction of models for the network elements. It is shownthat, under some assumptions, some models of the literature canbe recovered. A single-buffer/multiple-users topology is finallyderived and studied for illustration.

  • 35. Cantoni, M.
    et al.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Computing the L-2 gain for linear periodic continuous-time systems2009In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 45, no 3, p. 783-789Article in journal (Refereed)
    Abstract [en]

    A method to compute the L-2 gain is developed for the class of linear periodic continuous-time systems that admit a finite-dimensional state-space realisation. A bisection search for the smallest upper bound on the gain is employed, where at each step an equivalent discrete-time problem is considered via the well known technique of time-domain lifting. The equivalent problem involves testing a bound on the gain of a linear shift-invariant discrete-time system, with the same state dimension as the periodic continuous-time system. It is shown that a state-space realisation of the discrete-time system can be constructed from point solutions to a linear differential equation and two differential Riccati equations, all subject to only single-point boundary conditions. These are well behaved over the corresponding one period intervals of integration, and as such, the required point solutions can be computed via standard methods for ordinary differential equations. A numerical example is presented and comparisons made with alternative techniques.

  • 36. Chen, J.
    et al.
    Wei, Jieqiang
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Chen, Wei
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. University of California at Berkeley, United States.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Protecting Positive and Second-Order Systems against Undetectable Attacks2017In: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 50, no 1, p. 8373-8378Article in journal (Refereed)
    Abstract [en]

    Undetectable attacks in security studies of cyber-physical systems render the measurements of the system equal to a possible physical response. In this paper, we investigate defense strategies against the undetectable single-attack for positive systems and second-order systems, which both can be reinterpreted in terms of graphs with nodes and edges, while the undetectable attack is added through one of the nodes. We show that an arbitrary placement of a sensor prevents undetectable single-attack for these classes of systems. It is worth emphasising that we do not need to measure at the corrupted node to prevent the undetectable single-attack, but can measure at any node. The defense strategy is of a low complexity and can be readily implemented.

  • 37.
    Chen, Jianqi
    et al.
    City Univ Hong Kong, Dept Elect Engn, Hong Kong, Peoples R China..
    Wei, Jieqiang
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Chen, Wei
    Peking Univ, Dept Mech & Engn Sci, Beijing, Peoples R China.;Peking Univ, Beijing Innovat Ctr Engn Sci & Adv Technol, Beijing, Peoples R China..
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Chen, Jie
    City Univ Hong Kong, Dept Elect Engn, Hong Kong, Peoples R China..
    Geometrical Characterization Of Sensor Placement For Cone-Invariant And Multi-Agent Systems Against Undetectable Zero-Dynamics Attacks\Ast2022In: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 60, no 2, p. 890-916Article in journal (Refereed)
    Abstract [en]

    Undetectable attacks are an important class of malicious attacks threatening the security of cyber-physical systems, which can modify a system's state but leave the system output measurements unaffected and hence cannot be detected from the output. This paper studies undetectable attacks on cone-invariant systems and multi-agent systems. We first provide a general characterization of zero-dynamics attacks, which characterizes fully undetectable attacks targeting the nonminimum phase zeros of a system. This geometrical characterization makes it possible to develop a defense strategy seeking to place a minimal number of sensors to detect and counter the zero-dynamics attacks on the system's actuators. The detect and defense scheme amounts to computing a set containing potentially vulnerable actuator locations and nodes and a defense union for feasible placement of sensors based on the geometrical properties of the cones under consideration.

  • 38. Chong, M. S.
    et al.
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Hespanha, J. P.
    A secure state estimation algorithm for nonlinear systems under sensor attacks2020In: Proceedings of the IEEE Conference on Decision and Control, Institute of Electrical and Electronics Engineers Inc. , 2020, p. 5743-5748Conference paper (Refereed)
    Abstract [en]

    The state estimation of continuous-time nonlinear systems in which a subset of sensor outputs can be maliciously controlled through injecting a potentially unbounded additive signal is considered in this paper. Analogous to our earlier work for continuous-time linear systems in [1], we term the convergence of the estimates to the true states in the presence of sensor attacks as 'observability under M attacks', where M refers to the number of sensors which the attacker has access to. Unlike the linear case, we only provide a sufficient condition such that a nonlinear system is observable under M attacks. The condition requires the existence of asymptotic observers which are robust with respect to the attack signals in an input-to-state stable sense. We show that an algorithm to choose a compatible state estimate from the state estimates generated by a bank of observers achieves asymptotic state reconstruction. We also provide a constructive method for a class of nonlinear systems to design state observers which have the desirable robustness property. The relevance of this study is illustrated on monitoring the safe operation of a power distribution network.

  • 39.
    Chong, Michelle S.
    et al.
    Eindhoven Univ Technol, Dept Mech Engn, Eindhoven, Netherlands..
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Adaptive voltage regulation of an inverter-based power distribution network with a class of droop controllers2020In: IFAC PAPERSONLINE, Elsevier BV , 2020, Vol. 53, no 2, p. 12416-12421Conference paper (Refereed)
    Abstract [en]

    The voltage received by each customer connected to a power distribution line with local controllers (inverters) is regulated to be within a desired margin through a class of slope-restricted controllers, known conventionally as droop controllers. We adapt the design of the droop controllers according to the known bounds of the net power consumption of each customer in each observation time window. A sufficient condition for voltage regulation is provided for each time window, which guides the design of the droop controllers, depending on the properties of the distribution line (line impedances) and the upper bound of all the customers' power consumption during each time window. The resulting adaptive scheme is verified on a benchmark model of a European low-voltage network by the CIGRE task force. 

  • 40.
    Chong, Michelle S.
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Secure patching of an output-feedback controller for a class of nonlinear systems under adversarial attack2018In: 2018 IEEE CConference on Decision and Control  (CDC), Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 7255-7260, article id 8618972Conference paper (Refereed)
    Abstract [en]

    We consider a class of nonlinear systems for which an observer-based output-feedback controller is updated at discrete time instances. However, the received update or patch can be compromised by the attacker to drive the system to instability. In this paper, we provide a checkable condition to ensure that the received patch has not been tampered with to cause instability in the control system. Moreover, we guarantee that the application of the tamper-free patch ensures global asymptotic stability of the control system by choosing the update time instances appropriately. The secure patch update protocol is illustrated on an example involving the output-feedback synchronization of two neuron population models, where the observer gains are updated at discrete time instances.

  • 41.
    Chong, Michelle
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Teixeira, Andre M. H.
    Uppsala Univ, Dept Engn Sci, Uppsala, Sweden..
    A Tutorial Introduction to Security and Privacy for Cyber-Physical Systems2019In: Proceedings 2019 18th European Control Conference (ECC), IEEE , 2019, p. 968-978Conference paper (Refereed)
    Abstract [en]

    This tutorial provides a high-level introduction to novel control-theoretic approaches for the security and privacy of cyber-physical systems (CPS). It takes a risk-based approach to the problem and develops a model framework that allows us to introduce and relate many of the recent contributions to the area. In particular, we explore the concept of risk in the context of CPS under cyber-attacks, paying special attention to the characterization of attack scenarios and to the interpretation of impact and likelihood for CPS. The risk management framework is then used to give an overview of and map different contributions in the area to three core parts of the framework: attack scenario description, quantification of impact and likelihood, and mitigation strategies. The overview is by no means complete, but it illustrates the breadth of the problems considered and the control-theoretic solutions proposed so far.

  • 42.
    Chong, Michelle
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Umsonst, David
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Local voltage control of an inverter-based power distribution network with a class of slope-restricted droop controllers2019In: IFAC PAPERSONLINE, ELSEVIER , 2019, Vol. 52, no 20, p. 163-168Conference paper (Refereed)
    Abstract [en]

    Motivated by the environmental and economical benefits of using renewable energy, we consider the problem of regulating the voltage of a power distribution network in a line configuration where each customer is equipped with an inverter. The substation at the head of the line determines the nominal voltage level which is communicated to each customer in the distribution line. The voltage level of each customer is regulated by an inverter which generates reactive power according to our class of droop controllers satisfying the sloperestriction property. This paper provides a sufficient condition for regulating the customers' voltage level within a desired band, which depends on the properties of the distribution line (line impedances) and the droop controller employed. This is achieved when only the upper bound of all the customers' net power usage is known, thereby preserving the privacy of each customer. Simulation studies are performed on a benchmark model for a distribution system with renewable sources. 

  • 43.
    Chong, Michelle
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Umsonst, David
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Voltage regulation of a power distribution network in a radial configuration with a class of sector-bounded droop controllers2019In: Proceedings of the IEEE Conference on Decision and Control, Institute of Electrical and Electronics Engineers (IEEE) , 2019, p. 3515-3520Conference paper (Refereed)
    Abstract [en]

    We consider the problem of voltage regulation for a power distribution network where each inverter-equipped customer is connected sequentially with the sub-station at the head of the line. The substation dictates the desired voltage and transmits the reference voltage to each inverter in the distribution line. The inverter generates reactive power using our modified droop control law, which regulates the voltage level by influencing the power flow in the line, described by the DistFlow model. This paper provides conditions on the distribution line (the line impedances), the droop control law employed, and the nominal voltage level at the substation such that the each customer's voltage level are within a desired margin, when only the bound on the customers' overall power consumption is known. Thereby preserving the privacy of each customer's net power usage. We have also widened the choice of droop functions by only requiring them to be sector bounded. Simulation studies are provided to illustrate our results. 

  • 44.
    de Medeiros, Marcial Guerra
    et al.
    Department of Electrical Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan.
    Sou, Kim Cheong
    Department of Electrical Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan.
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Minimum-time Secure Rollout of Software Updates for Controllable Power Loads2020In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 189, article id 106797Article in journal (Refereed)
    Abstract [en]

    Generating minimum-time and secure software update schedules for controllable power loads in low-voltage distribution grids is a problem of increasing importance because of accelerating integration of renewable energy resources. In this paper, we call such a problem the software update rollout problem and present a mathematical framework for its modeling and solution. First, it is shown that this problem can be understood as a multi-resource bin packing problem. Then several approximate and exact solution schemes are discussed, the former using greedy approximate algorithms and the later using integer linear programming (ILP). These schemes are then evaluated on benchmark networks of realistic size (CIGRE-LV, TPC 83-bus distribution system). Experimental results show that both greedy and ILP approaches perform well for real-time purposes. In particular, the greedy approach can attain high-quality approximate solutions almost instantly while the ILP approach can not only provide solutions with certifiable optimality gaps but also include extra constraints (e.g., precedence) as needed.

  • 45. Delvenne, J. -C
    et al.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Deriving thermodynamics from linear dissipativity theory2016In: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2016, p. 537-542Conference paper (Refereed)
    Abstract [en]

    Complete and rigorous foundations for basic thermodynamic laws from the statistical description of microscopic systems has been a long-standing goal for mathematicians and physicists alike since Boltzmann. In this paper, we show how Willems's dissipativity theory provides a convenient framework to study a physical system at both microscopic and macroscopic level, and suggests a natural storage function different from the usual free energy to derive the theorem of energy equipartition of energy for linear systems. In this setup, we introduce a simple and general definition for temperature defined also out of equilibrium which allows to test the limits of validity of Fourier's law describing the transfer of heat from hot systems to cold systems. In particular under time-scale separation conditions, we derive the Maxwell-Cattaneo law, allowing for instantaneous flow of energy from cold to hot systems, which should be considered instead of Fourier's law for a proper description of energy exchanges between interconnected linear systems.

  • 46. Delvenne, J. -C
    et al.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Towards a thermodynamics of control: Entropy, energy and Kalman filtering2013In: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC), IEEE conference proceedings, 2013, p. 3109-3114Conference paper (Refereed)
    Abstract [en]

    We propose a method to analyse the flows of information and energy between two systems (plant and controller) connected in feedback. Extending a work by Touchette and Lloyd (2000, 2004), we estimate the advantage, both in terms of entropy reduction and energy extraction, of a feedback controller over an open-loop control in terms of the information on the plant state that is available to the controller. By energy here we mean any objective function that we seek to minimize, for example the square of the state. We apply this methodology on the Kalman filter, and develop a physical interpretation comparable to Mitter and Newton's (2005).

  • 47. Delvenne, Jean-Charles
    et al.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dissipative open systems theory as a foundation for the thermodynamics of linear systems2017In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 375, no 2088, article id 20160218Article in journal (Refereed)
    Abstract [en]

    In this paper, we advocate the use of open dynamical systems, i.e. systems sharing input and output variables with their environment, and the dissipativity theory initiated by Jan Willems as models of thermodynamical systems, at the microscopic and macroscopic level alike. We take linear systems as a study case, where we show how to derive a global Lyapunov function to analyse networks of interconnected systems. We define a suitable notion of dynamic non-equilibrium temperature that allows us to derive a discrete Fourier law ruling the exchange of heat between lumped, discrete-space systems, enriched with the Maxwell-Cattaneo correction. We complete these results by a brief recall of the steps that allow complete derivation of the dissipation and fluctuation in macroscopic systems (i.e. at the level of probability distributions) from lossless and deterministic systems. This article is part of the themed issue 'Horizons of cybernetical physics'.

  • 48. Delvenne, Jean-Charles
    et al.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Finite-time thermodynamics of port-Hamiltonian systems2014In: Physica D: Non-linear phenomena, ISSN 0167-2789, E-ISSN 1872-8022, Vol. 267, p. 123-132Article in journal (Refereed)
    Abstract [en]

    In this paper, we identify a class of time-varying port-Hamiltonian systems that is suitable for studying problems at the intersection of statistical mechanics and control of physical systems. Those port-Hamiltonian systems are able to modify their internal structure as well as their interconnection with the environment over time. The framework allows us to prove the First and Second Laws of thermodynamics, but also lets us apply results from optimal and stochastic control theory to physical systems. In particular, we show how to use linear control theory to optimally extract work from a single heat source over a finite time interval in the manner of Maxwell's demon. Furthermore, the optimal controller is a time-varying port-Hamiltonian system, which can be physically implemented as a variable linear capacitor and transformer. We also use the theory to design a heat engine operating between two heat sources in finite-time Carnot-like cycles of maximum power, and we compare those two heat engines.

  • 49.
    Delvenne, Jean-Charles
    et al.
    Caltech, Control and Dynamical Systems.
    Sandberg, Henrik
    Caltech, Control and Dynamical Systems.
    Doyle, John C.
    Caltech, Control and Dynamical Systems.
    Thermodynamics of linear systems2007In: Proceedings of the European Control Conference, The European Union Control Association (EUCA) , 2007Conference paper (Refereed)
    Abstract [en]

    We rigorously derive the main results of thermodynamics,including Carnot’s theorem, in the framework oftime-varying linear systems.

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  • 50.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Stealth attacks and protection schemes for state estimators in power systems2010In: 2010 1st IEEE International Conference on Smart Grid Communications, SmartGridComm 2010, IEEE , 2010, p. 214-219Conference paper (Refereed)
    Abstract [en]

    State estimators in power systems are currently used to, for example, detect faulty equipment and to route power flows. It is believed that state estimators will also play an increasingly important role in future smart power grids, as a tool to optimally and more dynamically route power flows. Therefore security of the estimator becomes an important issue. The estimators are currently located in control centers, and large numbers of measurements are sent over unencrypted communication channels to the centers. We here study stealthy false-data attacks against these estimators. We define a security measure tailored to quantify how hard attacks are to perform, and describe an efficient algorithm to compute it. Since there are so many measurement devices in these systems, it is not reasonable to assume that all devices can be made encrypted overnight in the future. Therefore we propose two algorithms to place encrypted devices in the system such as to maximize their utility in terms of increased system security. We illustrate the effectiveness of our algorithms on two IEEE benchmark power networks under two attack and protection cost models.

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