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  • 201. Guo, Z.
    et al.
    Shi, D.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Shi, L.
    Consequence Analysis of Innovation-based Integrity Attacks with Side Information on Remote State Estimation2017Inngår i: IFAC-PapersOnLine, ISSN 2405-8963, Vol. 50, nr 1, s. 8399-8404Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, we study the worst-case consequence of innovation-based integrity attacks with side information in a remote state estimation scenario. A new type of linear attack strategy based on both intercepted and sensing data is proposed and a corresponding stealthiness constraint is characterized. The evolution of the remote estimation error covariance is derived in the presence of the proposed malicious attack, based on which the worst-case attack policy is obtained in closed form. Furthermore, the system estimation performance under the proposed attack is compared with that under the existing attack strategy to determine which attack is more critical in deteriorating system functionality. Simulation examples are provided to illustrate the developed results.

  • 202.
    Guo, Ziyang
    et al.
    Hong Kong Univ Sci & Technol, Dept Elect & Comp Engn, Hong Kong, Peoples R China. hi, Dawei.
    Shi, Dawei
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Shi, Ling
    Worst-Case Innovation-Based Integrity Attacks With Side Information on mote State Estimation2019Inngår i: IEEE Transactions on Big Data, ISSN 2325-5870, E-ISSN 2168-6750, Vol. 6, nr 1, s. 48-59Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we study the worst-case consequence of innovation-based tegrity attacks with side information in a remote state estimation enario where a sensor transmits its measurement to a remote estimator uipped with a false-data detector. If a malicious attacker is not only le to compromise the transmitted data packet but also able to measure e system state itself, the attack strategy can be designed based on e intercepted data, the sensing data, or alternatively the combined formation. Surprisingly, we show that launching attacks using the mbined information are not always optimal. First, we characterize the ealthiness constraints for different types of attack strategies to oid being noticed by the false-data detector. Then, we derive the olution of the remote estimation error covariance in the presence of tacks, based on which the worst-case attack policies are obtained by lving convex optimization problems. Furthermore, the closed-form pressions of the worst-case attacks are obtained for scalar systems d the attack consequences are compared with the existing work to termine which strategy is more critical in deteriorating system rformance. Simulation examples are provided to illustrate the alytical results.

  • 203. Guo, Ziyang
    et al.
    Shi, Dawei
    Johansson, Karl-Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Shi, Ling
    Optimal Linear Cyber-Attack on Remote State Estimation2017Inngår i: IEEE TRANSACTIONS ON CONTROL OF NETWORK SYSTEMS, ISSN 2325-5870, Vol. 4, nr 1, s. 4-13Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent years have witnessed the surge of interest of security issues in cyber-physical systems. In this paper, we consider malicious cyber attacks in a remote state estimation application where a smart sensor node transmits data to a remote estimator equipped with a false data detector. It is assumed that all the sensor data can be observed and modified by the malicious attacker and a residue-based detection algorithm is used at the remote side to detect data anomalies. We propose a linear deception attack strategy and present the corresponding feasibility constraint which guarantees that the attacker is able to successfully inject false data without being detected. The evolution of the estimation error covariance at the remote estimator is derived and the degradation of system performance under the proposed linear attack policy is analyzed. Furthermore, we obtain a closed-form expression of the optimal attack strategy among all linear attacks. Comparison of attack strategies through simulated examples are provided to illustrate the theoretical results.

  • 204. Heemels, W.P.M.H
    et al.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Tabuada, P.
    An introduction to event-triggered and self-triggered control2012Inngår i: IEEE 51st Annual Conference on Decision and Control (CDC), 2012, IEEE conference proceedings, 2012, s. 3270-3285Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Recent developments in computer and communication technologies have led to a new type of large-scale resource-constrained wireless embedded control systems. It is desirable in these systems to limit the sensor and control computation and/or communication to instances when the system needs attention. However, classical sampled-data control is based on performing sensing and actuation periodically rather than when the system needs attention. This paper provides an introduction to event- and self-triggered control systems where sensing and actuation is performed when needed. Eventtriggered control is reactive and generates sensor sampling and control actuation when, for instance, the plant state deviates more than a certain threshold from a desired value. Selftriggered control, on the other hand, is proactive and computes the next sampling or actuation instance ahead of time. The basics of these control strategies are introduced together with a discussion on the differences between state feedback and output feedback for event-triggered control. It is also shown how event- and self-triggered control can be implemented using existing wireless communication technology. Some applications to wireless control in process industry are discussed as well.

  • 205. Hendrickx, Julien M.
    et al.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Jungers, Raphael M.
    Sandberg, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Sou, Kin Cheong
    Efficient Computations of a Security Index for False Data Attacks in Power Networks2014Inngår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, nr 12, s. 3194-3208Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The resilience of Supervisory Control and Data Acquisition (SCADA) systems for electric power networks for certain cyber-attacks is considered. We analyze the vulnerability of the measurement system to false data attack on communicated measurements. The vulnerability analysis problem is shown to be NP-hard, meaning that unless P = NP there is no polynomial time algorithm to analyze the vulnerability of the system. Nevertheless, we identify situations, such as the full measurement case, where the analysis problem can be solved efficiently. In such cases, we show indeed that the problem can be cast as a generalization of the minimum cut problem involving nodes with possibly nonzero costs. We further show that it can be reformulated as a standard minimum cut problem (without node costs) on a modified graph of proportional size. An important consequence of this result is that our approach provides the first exact efficient algorithm for the vulnerability analysis problem under the full measurement assumption. Furthermore, our approach also provides an efficient heuristic algorithm for the general NP-hard problem. Our results are illustrated by numerical studies on benchmark systems including the IEEE 118-bus system.

  • 206. Hendrickx, Julien M.
    et al.
    Shi, Guodong
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Finite-Time Consensus Using Stochastic Matrices With Positive Diagonals2015Inngår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 60, nr 4, s. 1070-1073, artikkel-id 6887337Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We discuss the possibility of reaching consensus in finite time using only linear iterations, with the additional restrictions that the update matrices must be stochastic with positive diagonals and consistent with a given graph structure. We show that finite-time average consensus can always be achieved for connected undirected graphs. For directed graphs, we show some necessary conditions for finite-time consensus, including strong connectivity and the presence of a simple cycle of even length.

  • 207.
    Henriksson, Erik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Quevedo, Daniel
    University of Newcastle, Australia.
    Sandberg, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Self-Triggered Model Predictive Control for Network Scheduling and Control2012Inngår i: Advanced Control of Chemical Processes, Vol. 8. Part 1 2012, 2012, s. 432-438Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Herein we present an algorithm for controlling LTI processes using an adaptive sampling interval where the controller at every sampling instant not only computes the new control command but also decides the time interval to the next sample. The approach relies on MPC where the cost function depends on the control performance as well as the cost for sampling. The paper presents a method for synthesizing such a predictive controller and gives explicit conditions for when it is stabilizing. Further it is shown that the optimization problem may be solved off-line and that the controller may be implemented as a lookup table of state feedback gains. The paper is concluded with a numerical example.

  • 208. Henriksson, Erik
    et al.
    Quevedo, D.E
    Peters, E.G.W.
    Sandberg, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Multiple loop self-triggered model predictive control for network scheduling and control2015Inngår i: IEEE Transactions on Control Systems Technology, ISSN 1063-6536, E-ISSN 1558-0865, Vol. 23, nr 6, s. 2167-2181Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present an algorithm for controlling and scheduling multiple linear time-invariant processes on a shared bandwidth-limited communication network using adaptive sampling intervals. The controller is centralized and not only computes at every sampling instant the new control command for a process but also decides the time interval to wait until taking the next sample.The approach relies on model predictive control ideas, where the cost function penalizes the state and control effort as well as the time interval until the next sample is taken. The latter is introduced to generate an adaptive sampling scheme for the overall system such that the sampling time increases as the norm of the system state goes to zero. This paper presents a method for synthesizing such a predictive controller and gives explicit sufficient conditions for when it is stabilizing. Further explicit conditions are given that guarantee conflict free transmissions on the network. It is shown that the optimization problem may be solved offline and that the controller can be implemented as a lookup table of state feedback gains. The simulation studies which compare the proposed algorithm to periodic sampling illustrate potential performance gains.

  • 209.
    Henriksson, Erik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Predictive Compensation for Communication Outages in Networked Control Systems2008Inngår i: Proceedings of the 47th IEEE Conference on Decision and Control, Cancun, Mexico, 2008, s. 2063-2068Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A predictive outage compensator co-located with the actuator node in a networked control system can be used to counteract unpredictable losses of data in the feedback control loop. When a new control command is not received at the actuator node at an appropriate time instance, the predictive outage compensator suggests a replacement command based on the history of past control commands. It is shown that a simple tuning phase together with the monitoring of the control history can lead to a compensator that can improve the closed-loop control performance under communication outages considerably compared to traditional schemes. Worst case performance bounds are given that relate the quality of the tuning phase and the complexity of the compensator with the length of the communication outage period. Zero-order-hold (holding the past control command if the current is lost) and applying an a priori decided constant signal (using a redefined value on the control command if the current is lost) are special cases of the more general compensation scheme presented. The predictive outage compensator is illustrated through computer simulation with communication outages.

  • 210.
    Henriksson, Erik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Reduced-Order Predictive Outage Compensators for Networked Systems2009Inngår i: Proceedings of the combined 48th IEEE Conference on Decision and Control and 28th Chinese Control Conference, Shanghai, P.R. China, 2009, s. 3775-3780Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Control systems utilizing wireless sensor and actuator networks can be severely affected by the properties of the wireless links. Radio fading and interference may cause communication outage of several samples in situations when the radio environment is noisy and low transmission power is desirable. We propose a method to compensate for outages by introducing a predictive outage compensator (POC), which is a filter to be implemented at the receiver sides of networked control systems and that generates artificial samples during the outage. The main contribution of the paper is to show that a POC can be derived based on a Kalman filter formulation and that it is possible to achieve good performance with a low-order implementation based on Hankel norm approximation. Tradeoffs between achievable closed-loop performance, outage length, and POC order are discussed. The results are illustrated on a simulated example of a multiple-tank process.

  • 211.
    Herdeiro Teixeira, André
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Sandberg, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Strategic stealthy attacks: The output-to-output ℓ2-gain2016Inngår i: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2016, s. 2582-2587Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we characterize and analyze the set of strategic stealthy false-data injection attacks on discrete-time linear systems. In particular, the threat scenarios tackled in the paper consider adversaries that aim at deteriorating the system's performance by maximizing the corresponding quadratic cost function, while remaining stealthy with respect to anomaly detectors. As opposed to other work in the literature, the effect of the adversary's actions on the anomaly detector's output is not constrained to be zero at all times. Moreover, scenarios where the adversary has uncertain model knowledge are also addressed. The set of strategic attack policies is formulated as a non-convex constrained optimization problem, leading to a sensitivity metric denoted as the output-to-output ℓ2-gain. Using the framework of dissipative systems, the output-to-output gain is computed through an equivalent convex optimization problem. Additionally, we derive necessary and sufficient conditions for the output-to-output gain to be unbounded, with and without model uncertainties, which are tightly related to the invariant zeros of the system.

  • 212.
    Hernandez, Aitor
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Faria, Joao
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Araujo, Jose
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Park, Pangun
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Inverted Pendulum Control over an IEEE 802.15.4 Wireless Sensor and Actuator Network2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Recent research efforts are considering the problem of performing control of dynamical systems over wireless sensor and actuator networks. However, existing results lack an experimental evaluation in real platforms. In this demonstration an inverted pendulum system is controlled over an IEEE 802.15.4 wireless sensor and actuator network. This platform can evaluate several sensor networks and control algorithms and is currently used as an educational tool at KTH Royal Institute of Technology, Sweden.

  • 213. Hu, Jianghai
    et al.
    Prandini, Maria
    Johansson, Karl Henrik
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Sastry, Shankar
    Hybrid geodesics as optimal solutions to the collision-free motion planning problem2001Inngår i: Hybrid Systems: Computation and Control / [ed] M.D. Di Benedetto, A. Sangiovanni-Vincentelli, Springer Berlin/Heidelberg, 2001, s. 305-318Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    In this paper we address the problem of designing energy minimizing collision-free maneuvers for multiple agents moving on a plane. We show that the problem is equivalent to that of nding the shortest geodesic in a certain manifold with nonsmooth boundary. This allows us to prove that the optimal maneuvers are C1by introducing the concept of u-convex manifolds. Moreover, due to the nature of the optimal maneuvers, the problem can be formulated as an optimal control problem for a certain hybrid system whose discrete states consist of dierent \contact graphs". We determine the analytic expression for the optimal maneuvers in the two agents case. For the three agents case, we derive the dynamics of the optimal maneuvers within each discrete state. This together with the fact that an optimal maneuver is a C1con-catenation of segments associated with dierent discrete states gives a characterization of the optimal solutions in the three agents case.

  • 214. Ianelli, L.
    et al.
    Johansson, Karl Henrik
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Jönsson, Ulf
    KTH, Tidigare Institutioner, Matematik.
    Vasca, F.
    Analysis of dither in relay feedback systems2002Inngår i: PROCEEDINGS OF THE 41ST IEEE CONFERENCE ON DECISION AND CONTROL, VOLS 1-4, IEEE , 2002, s. 4425-4430Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Dither signals provide an effective way of compensating for nonlinearities in control systems. The seminal, works by Zames and Shneydor and more recently by Mossaheb present rigorous tools for systematic design of dithered systems. Their results rely however on a Lipschitz assumption on the nonlinearity and thus do not cover important applications with discontinuities. This paper presents initial results on how to analyze and design dither in nonsmooth systems. In particular, it is shown that a dithered relay feedback system can be approximated by a smoothed system obtained through an averaging approach. Guidelines are given for tuning the amplitude and the period time of the dither signal, in order to stabilize the nonsmooth system.

  • 215. Ianelli, Luigi
    et al.
    Johansson, Karl Henrik
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Jönsson, Ulf
    KTH, Tidigare Institutioner, Matematik.
    Vasca, F.
    Practical stability and limit cycles of dithered relay feedback systems2003Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A new constructive way for choosing dither amplitude and frequency in order to effectively stabilize relay feedback systems by triangular dither is proposed. It is argued that the proposed averaging approach is not easily extended to square dither signals. Trajectories composed by smooth and switching parts are also analyzed and their relationship with limit cycles exhibited by the smoothed system is investigated.

  • 216. Ianelli, Luigi
    et al.
    Johansson, Karl Henrik
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Jönsson, Ulf
    KTH, Tidigare Institutioner, Matematik.
    Vasca, Francesco
    Dither shape in the averaging of switched systems2004Inngår i: PROCEEDINGS OF THE 2004 AMERICAN CONTROL CONFERENCE, VOLS 1-6, IEEE , 2004, s. 5812-5817Konferansepaper (Fagfellevurdert)
    Abstract [en]

    It was shown by Zames and Shneydor that a high-frequency dither of a quite arbitrary shape can be used to smooth the effective nonlinear sector of Lipschitz continuous feedback systems. Here it is shown that also systems with discontinuous nonlinearities can be smoothed using dither signals, as long as the amplitude distribution function of the dither is Lipschitz continuous.

  • 217. Ianelli, Luigi
    et al.
    Johansson, Karl Henrik
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Jönsson, Ulf
    KTH, Tidigare Institutioner, Matematik.
    Vasca, Francesco
    Effects of dither shapes in nonsmooth feedback systems: experimental results and theoretical insight2003Inngår i: Proceedings of the 42nd IEEE Conference on Decision and Control, Vols. 1-6, IEEE , 2003, s. 4285-4290Konferansepaper (Fagfellevurdert)
    Abstract [en]

     Dither signals are commonly used to compensate for nonlinearities in feedback systems in electronics and mechanics. Recently, theoretical results were proposed for the analysis or a particularly interesting class of nonsmooth systems, namely relay feedback systems with triangular dither. In this paper the class of dither signals is enlarged by considering square and trapezoidal dither: it is shown how the dither shape affects the behavior of nonsmooth feedback systems, differently from the case of dither in Lipschitz continuous systems. Experimental results support this fact and a theoretical insight is given in order to explain the phenomena.

  • 218. Ianelli, Luigi
    et al.
    Johansson, Karl Henrik
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Jönsson, Ulf
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Vasca, Francesco
    On the averaging of a class of hybrid systems2004Inngår i: 43rd IEEE Conference on Decision and Control, 2004. CDC, IEEE , 2004, s. 1400-1405Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Modeling abstraction and time-scale separation in the design of complex systems often leads to hybrid dynamics. Discontinuities in the continuous evolution of a hybrid system may however create difficulties in the formal analysis, as well as in numerical simulation and verification. Here we study a class of hybrid systems that are excited by high-frequency external signals. These systems arise in the modeling of switched power converters, mechanical systems with friction and quantized systems. For a quite general class of excitation signals, an averaging result is shown stating that the hybrid system can be approximated by a Lipschitz-continuous system. The approximation is in the order of the maximal repetition interval of the excitation signal.

  • 219. Iannelli, L.
    et al.
    Johansson, Karl H.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Jonsson, U. T.
    Vasca, F.
    Dither for smoothing relay feedback systems2003Inngår i: IEEE Transactions on Circuits And Systems Part I: Fundamental Theory and Applications, ISSN 1057-7122, E-ISSN 1558-1268, Vol. 50, nr 8, s. 1025-1035Artikkel i tidsskrift (Fagfellevurdert)
  • 220. Iannelli, L.
    et al.
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Jönsson, U. T.
    Vasca, F.
    Averaging of nonsmooth systems using dither2006Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 42, nr 4, s. 669-676Artikkel i tidsskrift (Fagfellevurdert)
  • 221. Iannelli, Luigi
    et al.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Jönsson, Ulf T.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Vasca, Francesco
    Subtleties in the averaging of a class of hybrid systems with applications to power converters2008Inngår i: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 16, nr 8, s. 961-975Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-frequency dither signals are commonly used to implement modulation schemes in power electronics converters. These systems represent an interesting class of hybrid systems with external excitation. They have a rich dynamical behavior, which cannot be easily understood intuitively. Despite the common use of averaging techniques in power electronics, it was only recently proved that a dithered hybrid system can be approximated by an averaged system under certain conditions on the dither signal. Averaging and averaged models for various types of power converters are analyzed in the paper. It is shown that the averaged nonlinearity depends on the dither shape and that dither signals with Lipschitz-continuous averaged nonlinearities can be used to adapt the equivalent gain of power converters. Practical stability of the original dithered system can be inferred by analyzing a simpler averaged system. The main contribution of the paper is to show that the averaged and the dithered systems may have drastically different behavior if the assumptions of the recently developed averaging theory for dithered hybrid systems are violated. Several practical experiments and simulation examples of power electronics converters are discussed. They indicate that the conditions on the dither signal imposed by the averaging theory are rather tight.

  • 222. Iannelli, Luigi
    et al.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Jönsson, Ulf
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Vasca, Francesco
    Subtleties in the averaging of hybrid systems with application to power electronics2006Inngår i: 2nd IFAC Conference on Analysis and Design of Hybrid Systems, 2006 / [ed] C.G. Cassandras, A. Giua, C. Seatzu, J. Zaytoon, IFAC , 2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Dither signals are commonly used in electronics for implementing different type of modulations in power converters, which represent a very interesting class of hybrid systems. It was recently shown that a nonsmooth dithered system can be approximated by an averaged system provided that the dither frequency is sufficiently high and that the amplitude distribution function of the dither is absolutely continuous and has bounded derivative. This result is exploited in this paper for power converters. Averaged models corresponding to various shapes of dither signal are analyzed, showing that dither with Lipschitz continuous amplitude distribution function can be used to adapt the equivalent gain of the power converter.

  • 223.
    Ilic, N.
    et al.
    Faculty of Electrical Engineering, University of Belgrade.
    Stankovic, S.
    Faculty of Electrical Engineering, University of Belgrade.
    Stankovic, Milos
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Consensus based distributed change detection using generalized likelihood ratio methodology2011Inngår i: 19th Mediterranean Conference on Control and Automation, MED 2011, 2011, s. 1170-1175Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper a novel distributed recursive algorithm based on the Generalized Likelihood Ratio methodology is proposed for real time change detection using sensor networks. The algorithm is based on a combination of recursively generated local statistics and a global consensus strategy, and does not require any fusion center, so that the state of any node can be tested w.r.t. a given common threshold. Two different problems are discussed: detection of an unknown change in the mean and in the variance of an observed random process. Performance of the algorithm for change detection in the mean is analyzed in the sense of a measure of the error with respect to the corresponding centralized algorithm. The analysis encompasses constant and randomly time varying matrices describing communications in the network. Simulation results illustrate characteristic properties of the algorithms.

  • 224. Ilic, Nemanja
    et al.
    Stankovic, Srdjan S.
    Stankovic, Milos S.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Consensus based distributed change detection using Generalized Likelihood Ratio methodology2012Inngår i: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 92, nr 7, s. 1715-1728Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper a novel distributed algorithm derived from the Generalized Likelihood Ratio is proposed for real time change detection using sensor networks. The algorithm is based on a combination of recursively generated local statistics and a global consensus strategy, and does not require any fusion center. The problem of detection of an unknown change in the mean of an observed random process is discussed and the performance of the algorithm is analyzed in the sense of a measure of the error with respect to the corresponding centralized algorithm. The analysis encompasses asymmetric constant and randomly time varying matrices describing communications in the network, as well as constant and time varying forgetting factors in the underlying recursions. An analogous algorithm for detection of an unknown change in the variance is also proposed. Simulation results illustrate characteristic properties of the algorithms including detection performance in terms of detection delay and false alarm rate. They also show that the theoretical analysis connected to the problem of detecting change in the mean can be extended to the problem of detecting change in the variance.

  • 225. Ishizaki, T.
    et al.
    Sandberg, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Kashima, K.
    Imura, J. -I
    Aihara, K.
    Structured model reduction of interconnected linear systems based on singular perturbation2013Inngår i: Proceedings of the American Control Conference 2013, American Automatic Control Council , 2013, s. 5524-5529Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper proposes a singular perturbation approximation that preserves system passivity and an interconnection topology among subsystems. In the first half of this paper, we develop a singular perturbation approximation valid for stable linear systems. Using the relation between the singular perturbation and the reciprocal transformation, we derive a tractable expression of the error system in the Laplace domain, which provides a novel insight to regulate the approximating quality of reduced models. Then in the second half, we develop a structured singular perturbation approximation that focuses on a class of interconnected systems. This structured approximation provides a reduced model that not only possesses fine approximating quality, but also preserves the original interconnection topology and system passivity.

  • 226.
    Ishizaki, Takayuki
    et al.
    Tokyo Inst Technol, Meguro Ku, 2-12-1 Ookayama, Tokyo 1528552, Japan..
    Sadamoto, Tomonori
    Tokyo Inst Technol, Meguro Ku, 2-12-1 Ookayama, Tokyo 1528552, Japan..
    Imura, Jun-ichi
    Tokyo Inst Technol, Meguro Ku, 2-12-1 Ookayama, Tokyo 1528552, Japan..
    Sandberg, Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Retrofit control: Localization of controller design and implementation2018Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 95, s. 336-346Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we propose a retrofit control method for stable network systems. The proposed approach is a control method that, rather than an entire system model, requires a model of the subsystem of interest for controller design. To design the retrofit controller, we use a novel approach based on hierarchical state-space expansion that generates a higher-dimensional cascade realization of a given network system. The upstream dynamics of the cascade realization corresponds to an isolated model of the subsystem of interest, which is stabilized by a local controller. The downstream dynamics can be seen as a dynamical model representing the propagation of interference signals among subsystems, the stability of which is equivalent to that of the original system. This cascade structure enables a systematic analysis of both the stability and control performance of the resultant closed-loop system. The resultant retrofit controller is formed as a cascade interconnection of the local controller and an output rectifier that rectifies an output signal of the subsystem of interest so as to conform to an output signal of the isolated subsystem model while acquiring complementary signals neglected in the local controller design, such as interconnection signals from neighboring subsystems. Finally, the efficiency of the retrofit control method is demonstrated through numerical examples of power systems control and vehicle platoon control. 

  • 227. Ishizakiy, T.
    et al.
    Sandberg, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Kashima, K.
    Imura, J. -I
    Aihara, K.
    Singular perturbation approximation of semistable linear systems2013Inngår i: 2013 European Control Conference, ECC 2013, 2013, s. 4508-4513Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper proposes a singular perturbation approximation for semistable linear systems. In particular, we derive a novel expression of error systems in the Laplace domain. As a result, we obtain an h2-error bound in terms of the sum of eigenvalues of an index matrix, which coincides with a controllability gramian of the state-derivative. Furthermore, we show that the singular perturbation model appropriately preserves the semistability of the original system and also guarantees the stability of the error system. The efficiency of the proposed method is shown through a numerical example of a Markov chain model approximation.

  • 228. Ivarsson, Maria
    et al.
    Sahlholm, Per
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Blackenfelt, Michael
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Nielsen, Lars
    Jansson, Henrik
    Vehicle control using preview information2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The background and the aim of the project,“Vechicle control by using preview information - ’Look Ahead’ ” , are discussed. The project is raisedto explore the possibilities of reduction of fuel consumption and improvements in comfort and safety for heavy vehicles. In particular research will focus on improvements that can be made, in actual and future control systems, with knowledge of the road ahead. This paper describes the project and reports on initial findings as well as related research.

  • 229.
    Iwaki, Takuya
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    LQG Control and Scheduling Co-Design for Wireless Sensor and Actuator Networks2018Inngår i: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC, Institute of Electrical and Electronics Engineers Inc. , 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper studies a co-design problem of control, scheduling and routing over a multi-hop sensor and actuator network subject to energy-saving consideration. Sensors are observing multiple independent linear systems and transmit their data to actuators in which controllers are co-located. We formulate an optimization problem, minimizing a linear combination of the averaged linear quadratic Gaussian control performance and the averaged transmission energy consumption. Optimal solutions are derived and their performance is illustrated in a numerical example. Algorithms to reconfigure routing between sensors and actuators in case of link disconnection are also provided.

  • 230.
    Jacobsson, Krister
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Andrew, Lachlan L. H.
    Tang, Ao
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Low, Steven H.
    California Institute of Technology.
    ACK-clocking dynamics: Modelling the interaction between windows and the network2008Inngår i: 27TH IEEE CONFERENCE ON COMPUTER COMMUNICATIONS (INFOCOM): VOLS 1-5, 2008, s. 181-185Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A novel continuous time fluid flow model of the dynamics of the interaction between ACK-clocking and the link buffer is presented.. A fundamental integral equation relating the instantaneous flow rate and the window dynamics is derived. Properties of the model, such as well-posedness and stability, are investigated. Packet level experiments verily that this new model is more accurate than existing models, correctly predicting qualitatively different behaviors, for example when round trill delays are heterogeneous.

  • 231.
    Jacobsson, Krister
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Towards accurate congestion control models: validation and stability analysis2006Konferansepaper (Fagfellevurdert)
  • 232.
    Jacobsson, Krister
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Hjalmarsson, Håkan
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Unbiased bandwidth estimation in communication protocols2005Inngår i: Proceedings of the 16th IFAC World Congress, 2005, IFAC , 2005Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Heterogeneous communication networks with their variety of application demands, uncertain time-varying trafc load, and mixture of wired and wireless links pose several challenging problem in modeling and control. In this paper we focus on bandwidth estimation and elucidate why estimates based directly on bandwidth samples are biased. Previously, this phenomenon has been observed but not properly explained, it seems. Standard techniques for bandwidth estimation are based on measurements of inter-arrival times of packets as the bandwidth is proportional to the inverse of the  nterarrival time. Two main classes of bandwidth estimators are analyzed wrt how variations in the inter-arrival times affect the estimates. It is shown that linear time-invariant ltering of instantaneous bandwidth estimates does not change the bias. In contrast to this, smoothing the inter-arrival-time samples does give a bias reduction which depends on the properties of the smoothing lter. Hence, with such approach, noise attenuation can be traded against tracking ability wrt changes in the actual bandwidth.

  • 233.
    Jacobsson, Krister
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Hjalmarsson, Håkan
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Möller, Niels
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Johansson, Karl Henrik
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Estimation of RTT and bandwidth for congestion Control Applications in Communication Networks2004Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Heterogeneous communication networks with their variety of application demands, uncertain time-varying traffic load, and mixture of wired and wireless links pose several challenging problem in modeling and control. In this paper we focus on the round-trip time (RTT), which is a particularly important variable for efficient end-to-end congestion control, and on bandwidth estimation. Based on a simple aggregated model of the network, an algorithm combining a Kalman filter and a change detection algorithm is proposed for RTT estimation. It is illustrated on real data that this algorithm provides estimates of significantly better accuracy as compared to the RTT estimator currently used in TCP, especially in scenarios where new cross-trafficflows cause bottle-neck queues to rapidly build up which in turn induces rapid changes of the RTT.

    Standard techniques for bandwidth estimation is based on measurements of inter-arrival times of packets as the bandwidth is proportional to the inverse of the inter-arrival time. Two main classes of bandwidth estimators are analyzed wrt how variations in the inter-arrival times affect the estimates. It is shown that linear time-invariant filtering of instantaneous bandwidth estimates does not change the bias. In contrast to this, smoothing the inter-arrival-time samples, does give a bias reduction which depends on the smoothing filter. Hence, with such approach, noise attenuation can be traded against tracking ability wrt changes in the actual bandwidth.

  • 234.
    Jacobsson, Krister
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Hjalmarsson, Håkan
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Möller, Niels
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Johansson, Karl Henrik
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Round trip time estimation in communication networks using adaptive Kalman filtering2004Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Heterogeneous communication networks with their variety of application demands, uncertain time-varying traffic load, and mixture of wired and wireless links pose several challenging problem in modeling and control. In this paper we focus on the roundtrip time (RTT), which is a particularly important variable for efficient end-to-end congestion control. Based on a simple aggregated model of the network, an algorithm combining a Kalmanfilter and a change detection algorithm is proposed for RTT estimation. It is illustrated on real data that this algorithm provides estimates of significantly better accuracy as compared to the RTT estimator currently used in TCP, especially in scenarios where new cross-trafficflows cause a bottle-neck link to rapidly build up a queue, which in turn induces rapid changes of the RTT.

  • 235.
    Jacobsson, Krister
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Möller, Niels
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Johansson, Karl Henrik
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Hjalmarsson, Håkan
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Some modeling and estimation issues in control of heterogeneous networks2004Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Heterogeneous communication networks with their variety of application demands, uncertain time-varying trafc load, and mixture of wired and wireless links pose several challenging problem in modeling and control. In this paper we focus on the round-trip time (RTT), which is a particularly important variable for efficient end-to-end congestion control. Based on a simple aggregated model of the network, an algorithm combining a Kalman lter and a change detection algorithm is proposed for RTT estimation. It is illustrated on real data that this algorithm provides estimates of significantly better accuracy as compared to the RTT estimator currently used in TCP.We also analyze how wireless links affect the RTT distribution. Link re-transmissions induce delays which do not conform to the assumptions on which the transport protocol is based. This causes undesired TCP control actions which reduce throughput. A link layer solution based on adding carefully selected delays to certain packets is proposed to counteract this problem.

  • 236.
    Jafarian, Matin
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Yi, Xinlei
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    $$$Pirani, Mohammad
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Automat Control Dept, Stockholm, Sweden..
    Sandberg, Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Synchronization of Kuramoto oscillators in a bidirectional frequency-dependent tree network2018Inngår i: 2018 IEEE CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2018, s. 4505-4510Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper studies the synchronization of a finite number of Kuramoto oscillators in a frequency-dependent bidirectional tree network. We assume that the coupling strength of each link in each direction is equal to the product of a common coefficient and the exogenous frequency of its corresponding source oscillator. We derive a sufficient condition for the common coupling strength in order to guarantee frequency synchronization in tree networks. Moreover, we discuss the dependency of the obtained bound on both the graph structure and the way that exogenous frequencies are distributed. Further, we present an application of the obtained result by means of an event-triggered algorithm for achieving frequency synchronization in a star network assuming that the common coupling coefficient is given.

  • 237. James, Weimer
    et al.
    Varagnolo, Damiano
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Stankovic, Milos
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Parameter-invariant detection of unknown inputs in networked systems2013Inngår i: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC), IEEE conference proceedings, 2013, s. 4379-4384Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This work considers the problem of detecting unknown inputs in networked systems whose dynamics are governed by time-varying unknown parameters. We propose a strategy in opposition to the commonly employed approach of first estimating the unknown parameters and then using the estimates as the true parameter values for detection, e.g. maximum-likelihood approaches. The suggested detection scheme employs test statistics that are invariant to the unknown parameters and do not rely on parameter estimation. We specifically consider the case of severe lack of prior knowledge, i.e., the problem of detecting unknown inputs when nothing is known of the system but some primitive structural properties, namely that the system is a linear network, subject to Gaussian noise, and that a certain input signal is either present or not. The aim is thus to analyze the structure and performances of invariant tests in a limiting case, specifically where the amount of prior information is minimal. The developed test is proven to be maximally invariant to the unknown parameters and Uniformly Most Powerful Invariant (UMPI). Simulation results indicate that for arbitrary networked systems the parameterinvariant detector achieves a specified probability of false alarm while ensuring that the probability of detection is maximized.

  • 238.
    Jansson, Henrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Kozica, Eermin
    Scania CV.
    Sahlholm, Per
    Scania CV.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Improved road grade estimation using sensor fusion2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A method for estimation of the road grade basedon standard mounted sensors in a heavy duty vehicle ispresented. The method combines information from a barometerand a GPS with velocity and torque measurements of conventionaltype. The sensor information is adaptively integratedusing extended Kalman filtering. This provides a systematicmethod for dealing with varying uncertainty in the sensors.The method can handle periods of missing or unreliable datafrom one or several sensors, e.g., occasions when the satellitecoverage is low or when the brakes are applied.

  • 239. Jia, Qing-Shan
    et al.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Guest editorial: event-based control and optimization2014Inngår i: Discrete event dynamic systems, ISSN 0924-6703, E-ISSN 1573-7594, Vol. 24, nr 2, s. 99-102Artikkel i tidsskrift (Fagfellevurdert)
  • 240. Jin, L.
    et al.
    Čičić, Mladen
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Amin, S.
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Modeling the impact of vehicle platooning on highway congestion: A fluid qeuing approach2018Inngår i: HSCC 2018 - Proceedings of the 21st International Conference on Hybrid Systems: Computation and Control (part of CPS Week), Association for Computing Machinery (ACM), 2018, s. 237-246Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Vehicle platooning is a promising technology that can lead to significant fuel savings and emission reduction. However, the macroscopic impact of vehicle platoons on highway traffic is not yet well understood. In this article, we propose a new fluid queuing model to study the macroscopic interaction between randomly arriving vehicle platoons and the background traffic at highway bottlenecks. This model, viewed as a stochastic switched system, is analyzed for two practically relevant priority rules: proportional (or mixed) and segmented priority. We provide intuitive stability conditions, and obtain bounds on the long-run average length and variance of queues for both priority rules. We use these results to study how platoon-induced congestion varies with the fraction of platooned vehicles, and their characteristics such as intra-platoon spacing and arrival rate. Our analysis reveals a basic tradeoff between congestion induced by the randomness of platoon arrivals, and efficiency gain due to a tighter intra-platoon spacing. This naturally leads to conditions under which the proportional priority is preferred over segmented priority. Somewhat surprisingly, our analytical results are in agreement with the simulation results based on a more sophisticated two-class cell transmission model.

  • 241.
    Jin, Ming
    et al.
    Univ Calif Berkeley, Dept Elect Engn & Comp Sci, Berkeley, CA 94720 USA..
    Lavaei, Javad
    Univ Calif Berkeley, Dept Ind Engn & Operat Res, Berkeley, CA 94720 USA..
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    A Semidefinite Programming Relaxation under False Data Injection Attacks against Power Grid AC State Estimation2017Inngår i: 55th Annual Allerton Conference on Communication, Control, and Computing, Allerton 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 236-243Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The integration of sensing and information technology renders the power grid susceptible to cyber-attacks. To understand how vulnerable the state estimator is, we study its behavior under the worst attacks possible. A general false data injection attack (FDIA) based on the AC model is formulated, where the attacker manipulates sensor measurements to mislead the system operator to make decisions based on a falsified state. To stage such an attack, the optimization problem incorporates constraints of limited resources (allowing only a limited number of measurements to be altered), and stealth operation (ensuring the cyber hack cannot be identified by the bad data detection algorithm). Due to the nonlinear AC power flow model and combinatorial selection of compromised sensors, the problem is nonconvex and cannot be solved in polynomial time; however, it is shown that convexification of the original problem based on a semidefinite programming (SDP) relaxation and a sparsity penalty is able to recover a near-optimal solution. This represents the first study to solve the AC-based FDIA. Simulations on a 30-bus system illustrate that the proposed attack requires only sparse sensor manipulation and remains stealthy from the residual-based bad data detection mechanism. In light of the analysis, this study raises new challenges on grid defense mechanism and attack detection strategy.

  • 242.
    Jin, Ming
    et al.
    Univ Calif Berkeley, Dept Ind Engn & Operat Res, Berkeley, CA 94720 USA..
    Lavaei, Javad
    Univ Calif Berkeley, Dept Ind Engn & Operat Res, Berkeley, CA 94720 USA..
    Johansson, Karl Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Power Grid AC-Based State Estimation: Vulnerability Analysis Against Cyber Attacks2019Inngår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 64, nr 5, s. 1784-1799Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To ensure grid efficiency and reliability, power system operators continuously monitor the operational characteristics of the grid through a critical process called state estimation (SE), which performs the task by filtering and fusing various measurements collected from grid sensors. This study analyzes the vulnerability of the key operation module, namely ac-based SE, against potential cyber attacks on data integrity, also known as false data injection attack (FDIA). A general form of FDIA can be formulated as an optimization problem, whose objective is to find a stealthy and sparse data injection vector on the sensor measurements with the aim of making the state estimate spurious and misleading. Due to the nonlinear ac measurement model and the cardinality constraint, the problem includes both continuous and discrete nonlinearities. To solve the FDIA problem efficiently, we propose a novel convexification framework based on semidefinite programming (SDP). By analyzing a globally optimal SDP solution, we delineate the "attackable region" for any given set of measurement types and grid topology, where the spurious state can be falsified by FDIA. Furthermore, we prove that the attack is stealthy and sparse, and derive performance bounds. Simulation results on various IEEE test cases indicate the efficacy of the proposed convexification approach. From the grid protection point of view, the results of this study can be used to design a security metric for the current practice against cyber attacks, redesign the bad data detection scheme, and inform proposals of grid hardening. From a theoretical point of view, the proposed framework can be used for other nonconvex problems in power systems and beyond.

  • 243.
    Johansson, Alexander
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Nekouei, Ehsan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Mårtensson, Jonas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Multi-Fleet Platoon Matching: A Game-Theoretic Approach2018Inngår i: 2018 21ST INTERNATIONAL CONFERENCE ON INTELLIGENT TRANSPORTATION SYSTEMS (ITSC), IEEE , 2018, s. 2980-2985Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider the platoon matching problem for a set of trucks with the same origin, but different destinations. It is assumed that the vehicles benefit from traveling in a platoon for instance through reduced fuel consumption. The vehicles belong to different fleet owners and their strategic interaction is modeled as a non-cooperative game where the vehicle actions are their departure times. Each truck has a preferred departure time and its utility function is defined as the difference between its benefit from platooning and the cost of deviating from its preferred departure time. We show that the platoon matching game is an exact potential game. An algorithm based on best response dynamics is proposed for finding a Nash equilibrium of the game. At a Nash equilibrium, vehicles with the same departure time are matched to form a platoon. Finally, the total fuel reduction at the Nash equilibrium is studied and compared with that of a cooperative matching solution where a common utility function for all vehicles is optimized.

  • 244.
    Johansson, Alexander
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Wei, Jieqiang
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Chen, J.
    Optimization of the H∞-norm of Dynamic Flow Networks2018Inngår i: 2018 Annual American Control Conference (ACC), Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 1280-1285Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we study the H∞-norm of linear systems over graphs, which is used to model distribution networks. In particular, we aim to minimize the H∞-norm subject to allocation of the weights on the edges. The optimization problem is formulated with LMI (Linear-Matrix-Inequality) constraints. For distribution networks with one port, i.e., SISO systems, we show that the H∞-norm coincides with the effective resistance between the nodes in the port. Moreover, we derive an upper bound of the H∞-norm, which is in terms of the algebraic connectivity of the graph on which the distribution network is defined.

  • 245.
    Johansson, Björn
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Keviczky,, T.
    Johansson, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Subgradient methods and consensus algorithms for solving convex optimization problems2008Inngår i: Decision and Control, 2008. CDC 2008. 47th IEEE Conference on, IEEE , 2008, s. 4185-4190Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we propose a subgradient method for solving coupled optimization problems in a distributed way given restrictions on the communication topology. The iterative procedure maintains local variables at each node and relies on local subgradient updates in combination with a consensus process. The local subgradient steps are applied simultaneously as opposed to the standard sequential or cyclic procedure. We study convergence properties of the proposed scheme using results from consensus theory and approximate subgradient methods. The framework is illustrated on an optimal distributed finite-time rendezvous problem.

  • 246. Johansson, Björn
    et al.
    Speranzon, A.
    Johansson, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    On decentralized negotiation of optimal consensus2008Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 44, nr 4, s. 1175-1179Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A consensus problem consists of finding a distributed control strategy that brings the state or output of a group of agents to a common value, a consensus point. In this paper, we propose a negotiation algorithm that computes an optimal consensus point for agents modeled as linear control systems subject to convex input constraints and linear state constraints. By primal decomposition and incremental subgradient methods, it is shown that the algorithm can be implemented such that each agent exchanges only a small amount of information per iteration with its neighbors.

  • 247.
    Johansson, Björn
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Speranzon, Alberto
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Distributed Model Predictive Consensus2006Inngår i: Proceedings of the 17th International Symposium on Mathematical Theory of Networks and Systems, 2006, s. 2438-2444Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we consider the problem of designing a distributed control strategy such that a linear combination of the states of a number of vehicles coincide at a given time. The vehicles are described by linear difference equations and are subject to convex input constraints. It is demonstrated how primal decomposition techniques and incremental subgradient methods allow us to find a solution in which each vehicle performs individual planning of its trajectory and exchanges critical information with neighbors only. We explore various communication, computation, and control structures, and demonstrate the performance of the algorithms by numerical examples.

  • 248.
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Cyber-physical control of road freight transport2016Inngår i: 2016 IEEE INTERNATIONAL CONFERENCE ON AUTONOMIC COMPUTING (ICAC) / [ed] Kounev, S Giese, H Liu, J, IEEE, 2016, s. 4-4Konferansepaper (Fagfellevurdert)
  • 249.
    Johansson, Karl H.
    Department of Electrical Engineering & Computer Sciences, University of California, Berkeley, CA.
    Interaction bounds in multivariable control systems1999Konferansepaper (Fagfellevurdert)
  • 250.
    Johansson, Karl H.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Interaction bounds in multivariable control systems2002Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 38, nr 6, s. 1045-1051Artikkel i tidsskrift (Fagfellevurdert)
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