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  • 301.
    Liang, Kuo-Yun
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Mårtensson, Jonas
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    When is it Fuel Efficient for a Heavy Duty Vehicle to Catch Up With a Platoon?2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Vehicle platooning has in recent years become an important research eld for thevehicle industry. By establishing a platoon of heavy duty vehicles, the fuel consumption can bereduced for the follower vehicles due to the slipstream eect. However, as vehicles are scatteredon the road driving by themselves, coordination amongst the vehicles is required. In this paperwe study the problem of when it is benecial for a heavy duty vehicle to drive faster in orderto catch up and join a platoon. We derive a formula, based on at road and with no vehicleaccelerations, to calculate if it is more fuel-ecient for a vehicle to drive faster and platoonor keep driving alone. Depending on the distance between the vehicles and the distance to thedestination, the fuel savings vary. For a trip of 350 km, with a distance of 10km to the vehicleahead, the fuel saving could be up to 7% if the follower vehicle decides to increase the speed from80 km/h to 90 km/h in order to catch up and form a platoon, assuming an air drag reductionof 32% when platooning. Sensitivity analysis has shown that the speeds need to be relativelyaccurate in order to not give any false positive catch up decisions.

  • 302.
    Liang, Kuo-Yun
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    van de Hoef, Sebastian
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Terelius, Hakan
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Turri, Valerio
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Besselink, Bart
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Martensson, Jonas
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Networked control challenges in collaborative road freight transport2016Inngår i: European Journal of Control, ISSN 0947-3580, E-ISSN 1435-5671, Vol. 30, s. 2-14Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Freight transport is of major importance for the European economy and is growing thanks to increasing global trade. About three quarters of inland freight transport in the European Union is on roads. It has the potential to go through a dramatic change over the next decades thanks to the recent development of technologies such as wireless communication, cloud computing, sensor devices, and vehicle electronics. They enable a new integrated goods transport system based on optimized logistics, real-time traffic information, vehicular communications, collaborative driving, and autonomous vehicles. In this paper, we discuss challenges in creating a more efficient and sustainable goods road transportation system and how some of them can be tackled with a networked control approach. In particular, we discuss a method to improve the efficiency of the transportation system by minimizing the number of empty transports needed to fulfill the assignments on a given road network. Assignments with overlapping route segments might lead to further improvements, as the formation of vehicle platoons yields reduced fuel consumption. For realistic scenarios, it is shown that such collaboration opportunities arise already with relatively few vehicles. The fuel-efficient formation and control of platoons is also discussed. Some of the presented methods have been tested on real vehicles in traffic. The paper shows experimental results on automatic formation of vehicle platoons on a Swedish highway. The influence of traffic density on the merge maneuver is illustrated. The results indicate that platoon coordination could be improved by support from appropriate traffic monitoring technologies.

  • 303.
    Lindhé, M.
    et al.
    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.
    USING ROBOT MOBILITY TO EXPLOIT MULTIPATH FADING2009Inngår i: IEEE wireless communications, ISSN 1536-1284, E-ISSN 1558-0687, Vol. 16, nr 1, s. 30-37Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Communication-aware motion control allows mobile networked robots to increase the average communication throughput. We exploit that in a multipath fading channel, robots can measure the SNR and adapt their motion to spend slightly more time at positions where the channel is good. Two new such cross-layer strategies are analyzed and evaluated: periodic stopping, where the stop duration is a function of the SNR, and controlled stopping, where the robot stops when the communication buffer is filling up. It is shown that the expected average channel capacity can be twice as high as when no cross-layer information is utilized. Experimental evaluation of the strategies confirms the theoretical results.

  • 304.
    Lindhé, Magnus
    et al.
    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.
    A formation control algorithm using Voronoi regions2007Inngår i: Taming Heterogeneity and Complexity of Embedded Control / [ed] Françoise Lamnabhi-Lagarrigue, Antonio Loria, Elena Panteley, Salah Laghrouche, John Wiley & Sons, 2007Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    We present an algorithm for stabilizing a hexagonal lattice formation of autonomous robotic agents. The algorithm is decentralized and each agent only needs to detect the relative positions of its neighbors. By partitioning the plane into Voronoi regions we can guarantee collision safety, even when the algorithm is used to produce waypoints for a non-holonomic agent to follow. In each iteration every agent moves to the centroid of the vertices of its Voronoi region, which yields formation cohesion. We define asymptotic formation stability that is independent of rotation or translation of the whole formation and prove local asymptotic stability. Finally we present simulations that confirm the stability analysis and illustrate the use of the algorithm with car-like robots.

  • 305.
    Lindhé, Magnus
    et al.
    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.
    A formation control algorithm using Voronoi regions2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We present an algorithm for stabilizing a hexagonal lattice formation of autonomous robotic agents. The algorithm is decentralized and each agent only needs to detect the relative positions of its neighbors. By partitioning the plane into Voronoi regions we can guarantee collision safety, even when the algorithm is used to produce waypoints for a non-holonomic agent to follow. In each iteration every agent moves to the centroid of the vertices of its Voronoi region, which yields formation cohesion. We define asymptotic formation stability that is independent of rotation or translation of the whole formation and prove local asymptotic stability. Finally we present simulations that confirm the stability analysis and illustrate the use of the algorithm with car-like robots.

  • 306.
    Lindhé, Magnus
    et al.
    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.
    Adaptive Exploitation of Multipath Fading for Mobile Sensors2010Inngår i: 2010 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION (ICRA) / [ed] Rakotondrabe M; Ivan IA, IEEE , 2010, s. 1934-1939Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Mobile wireless sensors in indoor environments will experience multipath fading, causing rapid variations in the capacity of the radio link. We present a strategy that increases the throughput by modifying the trajectory of the sensor so it spends more time at positions where the capacity is high. While doing so, it still maintains some desired average velocity. Our approach includes closed-loop estimation of the parameters of the fading, which may change when moving between rooms. We prove stability of the feedback system and illustrate its behavior through simulations. Finally, we demonstrate robustness to errors in the channel model.

  • 307.
    Lindhé, Magnus
    et al.
    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), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Communication-aware trajectory tracking2008Inngår i: 2008 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION, IEEE , 2008, s. 1519-1524Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper investigates the scenario of a robot making a tradeoff between tracking a time-varying reference trajectory and stopping to communicate at points where the radio signal strength is high. Under the assumption that the signal is subject to multipath fading, we formulate this as a hybrid optimal control problem with penalties on tracking error, communication buffer length and control power. The problem is then solved using relaxed dynamic programming, resulting in control laws for the discrete switching sequence and the continuous control. We finally illustrate the results through simulations under non-ideal conditions, confirming that the system maintains a bounded buffer size and zero-mean tracking error.

  • 308.
    Lindhé, Magnus
    et al.
    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.
    Bicchi, A.
    An experimental study of exploiting multipath fading for robot communications2008Inngår i: Proceedings of Robotics: Science and Systems, 2008, s. 289-296Konferansepaper (Fagfellevurdert)
    Abstract [en]

     A simple approach for mobile robots to exploit multipath fading in order to improve received radio signal strength (RSS), is presented. The strategy is to sample the RSS at discrete points, without deviating too far from the desired  position. We first solve the problem of how many samples are needed for given communications performance and how they should be spaced. Second, we propose a circular and a grid trajectory for sampling and give lower bounds on how many samples they will yield. Third, we estimate the parameters of our strategy from measurements. Finally we demonstrate the validity of our analysis through experiments.

  • 309.
    Lindhé, Magnus
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Keviczky, Tamas
    TU Delft.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Multi-Robot Path Following with Visual Connectivity2011Inngår i: Conference Record: Asilomar Conference on Signals, Systems and Computers, IEEE , 2011, s. 1466-1471Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We consider a group of N robots moving through an obstacle field, where only robots that have a clear line of sight can communicate. When passing the obstacles, the group must coordinate its motion to remain connected. We propose using the path–velocity decomposition: Given obstacle-free paths that fulfill a higher-level goal, we propose a method to coordinate the robot motions along the paths so visual connectivity is maintained. The problem is shown to be equivalent to finding a path through an N-dimensional configuration space, avoiding unconnected configurations. We solve this problem with a rapidly exploring random tree algorithm and demonstrate by simulations how the solution time varies with the obstacle density.

  • 310.
    Lindhé, Magnus
    et al.
    Swedish Defence Research Agency.
    Ögren, Petter
    Swedish Defence Research Agency.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Flocking with obstacle avoidance: A new distributed coordination algorithm based on Voronoi partitions2005Inngår i: 2005 IEEE International Conference on Robotics and Automation (ICRA), Vols 1-4, IEEE , 2005, s. 1785-1790Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A new distributed coordination algorithm for multi-vehicle systems is presented in this paper. The algorithm combines a particular choice of navigation function with Voronoi partitions. This results not only in obstacle avoidance and motion to the goal, but also in a desirable geographical distribution of the vehicles. Our algorithm is decentralized in that each vehicle needs only to know the position of neighboring vehicles, but no other inter-vehicle communication or centralized control are required. The algorithm gives a natural priority to safety, goal convergence, and formation keeping, in that (1) collision avoidance is guaranteed under all circumstances, (2) the vehicles will move toward the goal as long as a given optimization problem is feasible, and (3) if prior criteria admit, the vehicles tend to a desirable lattice formation. These theoretical properties are discussed in the paper and the performance of the algorithm is illustrated in simulations with realistic models of twenty all-terrain vehicles. Planned experimental evaluation using customized miniature cars is also briefly described.

  • 311.
    Liu, Hanxiao
    et al.
    Nanyang Technol Univ, Sch Elect & Elect Engn, Singapore, Singapore..
    Yan, Jiaqi
    Nanyang Technol Univ, Sch Elect & Elect Engn, Singapore, Singapore..
    Mo, Yilin
    Nanyang Technol Univ, Sch Elect & Elect Engn, Singapore, Singapore..
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    An On-line Design of Physical Watermarks2018Inngår i: 2018 IEEE CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2018, s. 440-445Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper considers the problem of designing physical watermark signals to protect a control system against replay attacks. We first introduce the replay attack model, where an adversary replays the previous sensory data in order to fool the controller to believe the system is still operating normally. The physical watermarking scheme, which leverages a random control input as a watermark to detect the replay attack is introduced. The optimal watermark signal design problem is then proposed as an optimization problem, which achieves the optimal trade-off between the control performance and attack detection performance. For the system with unknown parameters, we provide a procedure to asymptotically derive the optimal watermarking signal. Numerical examples are provided to illustrate the effectiveness of the proposed strategy.

  • 312. Liu, K.
    et al.
    Fridman, E.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Xia, Y.
    Generalized Jensen inequalities with application to stability analysis of systems with distributed delays over infinite time-horizons2016Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 69, s. 222-231Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Jensen inequality has been recognized as a powerful tool to deal with the stability of time-delay systems. Recently, a new inequality that encompasses the Jensen inequality was proposed for the stability analysis of systems with finite delays. In this paper, we first present a generalized integral inequality and its double integral extension. It is shown how these inequalities can be applied to improve the stability result for linear continuous-time systems with gamma-distributed delays. Then, for the discrete-time counterpart we provide an extended Jensen summation inequality with infinite sequences, which leads to less conservative stability conditions for linear discrete-time systems with Poisson-distributed delays. The improvements obtained by the introduced generalized inequalities are demonstrated through examples.

  • 313. Liu, K.
    et al.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Fridman, E.
    Xia, Y.
    Stability analysis of discrete-time systems with poisson-distributed delays2016Inngår i: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2016, s. 7736-7741Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper is concerned with the stability analysis of linear discrete-time systems with poisson-distributed delays. Firstly, the exponential stability condition of system with poisson-distributed delays is derived when the corresponding system with the zero-delay or the system without the delayed term is asymptotically stable. Then, an augmented Lyapunov functional is suggested to handle the case that the corresponding system without the delay as well as the system without the delayed term are not necessary to be asymptotically stable. Furthermore, we show that the results can be further improved by formulating the system as a higher-order augmented one and applying the corresponding augmented Lyapunov functional. Finally, the efficiency of the proposed results is illustrated by some numerical examples.

  • 314.
    Liu, Kun
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Fridman, Emilia
    Tel Aviv University.
    Henrik Johansson, Karl
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Networked Control with a Stochastic Scheduling: a Time-Delay  Approach2014Inngår i: The 19th World Congress of IFAC, 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper is concerned with the stability analysis of networked control systems with communication constraints, variable delays and variable sampling intervals.The scheduling of sensor communication is defined by a stochastic protocol.The activation probability of each sensor node is a given constant, whereas it is assumed that collisions occur with a certain probability.The resulting closed-loop system is a stochastic impulsive system withdelays in the continuous dynamics and in the reset equations. The system matrices have stochastic parameters with Bernoulli distributions.Sufficient conditions for the exponential mean-square stabilityare derived via a Lyapunov-Krasovskii-based method. The efficiency of the method is illustrated on the examples of a cart-pendulum system and a batch reactor.It is demonstrated how our time-delay approach allows treating network-induced delays larger thanthe sampling intervals.

  • 315. Liu, Kun
    et al.
    Fridman, Emilia
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Xia, Yuanqing
    Quantized Control Under Round-Robin Communication Protocol2016Inngår i: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 63, nr 7, s. 4461-4471Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper analyzes the exponential stability of a discrete-time linear plant in feedback control over a communication network with N sensor nodes, dynamic quantization, large communication delays, variable sampling intervals, and round-robin scheduling. The closedloop system is modeled as a switched system with multiple-ordered time-varying delays and bounded disturbances. We propose a time-triggered zooming algorithm implemented at the sensors that preserves exponential stability of the closed-loop system. A direct Lyapunov approach is presented for initialization of the zoom variable. The proposed framework can be applied to the plants with polytopic type uncertainties. The effectiveness of the method is illustrated on cart-pendulum and quadruple-tank processes.

  • 316.
    Liu, Kun
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. Beijing Institute of Technology, China.
    Fridman, Emilia
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Dynamic quantization of uncertain linear networked control systems2015Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 59, s. 248-255Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper is concerned with the stability analysis of networked control systems with dynamic quantization, variable sampling intervals and communication delays. A time-triggered zooming algorithm for the dynamic quantization at the sensor side is proposed that leads to an exponentially stable closed-loop system. The algorithm includes proper initialization of the zoom parameter. More precisely, given a bound on the state initial conditions and the values of the quantizer range and error, we derive conditions for finding the initial value of the zoom parameter, starting from which the exponential stability is guaranteed by using "zooming-in" only. Polytopic type uncertainties in the system model can be easily included in the analysis. The efficiency of the method is illustrated on an example of an uncertain cart-pendulum system.

  • 317.
    Liu, Kun
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Fridman, Emilia
    Tel Aviv University.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Networked control with stochastic scheduling2015Inngår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, nr 99Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper develops the time-delay approach to networked control systems with scheduling protocols, variable delays and variable sampling intervals. The scheduling of sensor communication is defined by a stochastic protocol. Two classes of protocols are considered. The first one is defined by an independent and identically-distributed stochastic process. The activation probability of each sensor node for this protocol is a given constant, whereas it is assumed that collisions occur with a certain probability. The resulting closed-loop system is a stochastic impulsive system with delays both in the continuous dynamics and in the reset equations, where the system matrices have stochastic parameters with Bernoulli distributions. The second scheduling protocol is defined by a discrete-time Markov chain with a known transition probability matrix taking into account collisions. The resulting closed-loop system is a Markovian jump impulsive system with delays both in the continuous dynamics and in the reset equations. Sufficient conditions for exponential mean-square stability of the resulting closed-loop system are derived via a Lyapunov-Krasovskii-based method. The efficiency of the method is illustrated on an example of a batch reactor. It is demonstrated how the time-delay approach allows treating network-induced delays larger than the sampling intervals in the presence of collisions.

  • 318. Liuzza, D.
    et al.
    Dimarogonas, Dimos. V.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Di Bernardo, M.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Distributed model based event-triggered control for synchronization of multi-agent systems2013Inngår i: IFAC Proceedings Volumes (IFAC-PapersOnline), 2013, nr PART 1, s. 329-334Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper investigates the problem of event-based control for the synchronization of networks of nonlinear dynamical agents. A distributed model based approach able to guarantee that all the agents converge to an adjustable synchronization region is derived. In such control scheme all the agents use a model of their neighborhood in order to generate triggering instants in which the local controller is updated and, if needed, local information is broadcasted to neighboring agents. The existence of a minimum lower bound between inter-event times is proven both for broadcasted information as well as for control signal updating, thus allowing implementation of the proposed strategy in applications where both the communication bandwidth and the maximum updating frequency of actuators are critical.

  • 319.
    Liuzza, Davide
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Dimarogonas, Dimos V.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    di Bernardo, Mario
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Distributed model based event-triggered control for synchronization of multi-agent systems2016Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 73, s. 1-7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the problem of event-triggered control for the synchronization of networks of nonlinear dynamical agents; distributed model-based approaches able to guarantee the synchronization of the overall system are derived. In these control schemes all the agents use a model of their neighbourhood in order to generate triggering instants in which the local controller is updated and, if needed, local information based on the adopted control input is broadcasted to neighbouring agents, Synchronization of the network is proved and the existence of Zeno behaviour is excluded; an event triggered strategy able to guarantee the existence of a minimum lower bound between inter-event times for broadcasted information and for control signal updating is proposed, thus allowing applications where both the communication bandwidth and the maximum updating frequency of actuators are critical. This idea is further extended in an asynchronous periodic event-triggered schemes where the agents check a trigger condition via a periodic distributed communication without requiring a model based computation.

  • 320.
    Liuzza, Davide
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Generalized PID Synchronization of Higher Order Nonlinear Systems With a Recursive Lyapunov Approach2018Inngår i: IEEE Transactions on Big Data, ISSN 2325-5870, E-ISSN 2168-6750, Vol. 5, nr 4, s. 1608-1621Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the problem of synchronization for nonlinear systems. Following a Lyapunov approach, we first study the global synchronization of nonlinear systems in the canonical control form with both distributed proportional-derivative and proportional-integral-derivative control actions of any order. To do so, we develop a constructive methodology and generate in an iterative way inequality constraints on the coupling matrices that guarantee the solvability of the problem or, in a dual form, provide the nonlinear weights on the coupling links between the agents such that the network synchronizes. The same methodology allows us to include a possible distributed integral action of any order to enhance the rejection of heterogeneous disturbances. The considered approach does not require any dynamic cancellation, thus preserving the original nonlinear dynamics of the agents. The results are then extended to linear and nonlinear systems admitting a canonical control transformation. Numerical simulations validate the theoretical results.

  • 321. Long, Y.
    et al.
    Liu, S.
    Xie, L.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    A scenario-based distributed stochastic MPC for building temperature regulation2014Inngår i: IEEE International Conference on Automation Science and Engineering, 2014, s. 1091-1096Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we focus on the temperature regulation of rooms in buildings. By using the dynamic model of the thermal process, weather condition, occupancy and so on, a Stochastic Model Predictive Control (SMPC) problem is formulated to keep the temperature of rooms within a comfortable range with a predefined probability while consuming less energy. The temperature regulation problem in this paper is an optimal control problem of a linear system with additive uncertainty. To overcome the computational burden caused by the large number of rooms, a subgradient-based dual decomposition method is used to solve the SMPC problem in a distributed manner. Simulation results show the effectiveness of our results.

  • 322. Long, Y.
    et al.
    Liu, S.
    Xie, L.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Distributed non-cooperative robust MPC based on reduced-order models2016Inngår i: Control Theory and Technology, ISSN 2095-6983, Vol. 14, nr 1, s. 11-20Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, a non-cooperative distributed MPC algorithm based on reduced order model is proposed to stabilize large-scale systems. The large-scale system consists of a group of interconnected subsystems. Each subsystem can be partitioned into two parts: measurable part, whose states can be directly measured by sensors, and the unmeasurable part. In the online computation phase, only the measurable dynamics of the corresponding subsystem and neighbour-to-neighbour communication are necessary for the local controller design. Satisfaction of the state constraints and the practical stability are guaranteed while the complexity of the optimization problem is reduced. Numerical examples are given to show the effectiveness of this algorithm.

  • 323. Long, Yushen
    et al.
    Liu, Shuai
    Xie, Lihua
    Johansson, K. H.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    A Hierarchical Distributed MPC for HVAC Systems2016Inngår i: 2016 AMERICAN CONTROL CONFERENCE (ACC), IEEE conference proceedings, 2016, s. 2385-2390Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper a hierarchical distributed model predictive control scheme is proposed for heating, ventilation and air-conditioning (HVAC) systems in buildings. The building consists in multiple connected rooms and zones. The control objective is to keep the temperature of each room and zone at a given comfortable level with minimal energy consumption. This control scheme is divided into two levels. The upper level controller collects temperature and predictive information of all rooms and zones to generate reference trajectories while a lower level controller only uses local information to track the reference and optimize energy efficiency and thermal comfort. By using a contraction property of building's dynamics, recursive feasibility of the proposed algorithm is guaranteed. Simulation results are given to show the performance of our proposed control strategy.

  • 324. Lou, Y.
    et al.
    Hong, Y.
    Xie, L.
    Shi, G.
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Nash equilibrium computation in subnetwork zero-sum games with switching communications2016Inngår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 61, nr 10, s. 2920-2935, artikkel-id 7345550Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we investigate a distributed Nash equilibrium computation problem for a time-varying multi-agent network consisting of two subnetworks, where the two subnetworks share the same objective function. We first propose a subgradientbased distributed algorithm with heterogeneous stepsizes to compute a Nash equilibrium of a zero-sum game. We then prove that the proposed algorithm can achieve a Nash equilibrium under uniformly jointly strongly connected (UJSC) weight-balanced digraphs with homogenous stepsizes. Moreover, we demonstrate that for weighted-unbalanced graphs a Nash equilibrium may not be achieved with homogenous stepsizes unless certain conditions on the objective function hold. We show that there always exist heterogeneous stepsizes for the proposed algorithm to guarantee that a Nash equilibrium can be achieved for UJSC digraphs. Finally, in two standard weight-unbalanced cases, we verify the convergence to a Nash equilibrium by adaptively updating the stepsizes along with the arc weights in the proposed algorithm. © 2015 IEEE.

  • 325.
    Lou, Youcheng
    et al.
    Chinese Academy of Sciences, Beijing, China .
    Shi, Guodong
    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.
    Hong, Y.
    Convergence of random sleep algorithms for optimal consensus2013Inngår i: Systems & control letters (Print), ISSN 0167-6911, E-ISSN 1872-7956, Vol. 62, nr 12, s. 1196-1202Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we propose a random sleep algorithm for a network to cooperatively find a point within the intersection of some convex sets, each of which is known only to a particular node. At each step, each node first chooses to project its own set or not at random by a Bernoulli decision independently. When a node has chosen to project its set, we assume that it can detect only the projection direction rather than the exact projection point, based on which the node obtains an estimate for the projection point. Then the agents update their states by averaging the estimates with their neighbors. Under directed and time-varying communication graph, sufficient and/or necessary stepsize conditions are presented for the considered algorithm converging to a consensus within the intersection set.

  • 326. Lou, Youcheng
    et al.
    Shi, Guodong
    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.
    Hong, Yiguang
    Approximate Projected Consensus for Convex Intersection Computation: Convergence Analysis and Critical Error Angle2014Inngår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, nr 7, s. 1722-1736Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we study an approximate projected consensus algorithm for a network to cooperatively compute the intersection of convex sets, where each set corresponds to one network node. Instead of assuming exact convex projection that each node can compute, we allow each node to compute an approximate projection with respect to its own set. After receiving the approximate projection information, nodes update their states by weighted averaging with the neighbors over a directed and time-varying communication graph. The approximate projections are related to projection angle errors, which introduces state-dependent disturbance in the iterative algorithm. Projection accuracy conditions are presented for the considered algorithm to converge. The results indicate how much projection accuracy is required to ensure global consensus to a point in the intersection set when the communication graph is uniformly jointly strongly connected. In addition, we show that pi/4 is a critical angle for the error of the projection approximation to ensure the boundedness. Finally, the results are illustrated by simulations.

  • 327. Lou, Youcheng
    et al.
    Shi, Guodong
    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.
    Hong, Yiguang
    Reaching optimal consensus for multi-agent systems based on approximate projection2012Inngår i: 10th World Congress on Intelligent Control and Automation (WCICA), 2012, IEEE conference proceedings, 2012, s. 2794-2800Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we propose an approximately projected consensus algorithm (APCA) for a network to cooperatively compute the intersection of several convex sets, each of which is known only to a particular node. Instead of assuming the exact convex projection, we allow each node to just compute an approximate projection. The communication graph is directed and time-varying, and nodes can only exchange information via averaging among local view. We present sufficient and/or necessary conditions for the APCA, which shows on how much projection accuracy is required to ensure a global consensus within the intersection set when the communication graphs is uniformly jointly strongly connected. We show that π/4 is a critical angle error in the projection approximation to ensure a bounded solution for iterative projections. A numerical example indicates that the APCA may achieve better performance than the exact projected consensus algorithm. The results add the understanding of the fundamentals of distributed convex intersection computation.

  • 328. Lucchese, R.
    et al.
    Varagnolo, D.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Distributed detection of topological changes in communication networks2014Inngår i: IFAC Proceedings Volumes (IFAC-PapersOnline), IFAC Papers Online, 2014, s. 1928-1934Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Changes in the topology of communication networks, such as sudden appearance or disappearance of links or nodes, may signal malicious attacks or malfunctions. A topology change detector may thus be useful to trigger alarms or self-reconfiguration procedures. Here we present a novel approach that enjoys several desirable qualities such as fast convergence, intrinsically distributed computations, and scalability w.r.t. communication and computational requirements. We characterize the performance of this technique from analytical and practical points of view, providing theoretical results on its performance. We thus show how it is possible to tune and trade-off the accuracy of the change detection results with the communication requirements of the procedure.

  • 329. Ludovici, Alessandro
    et al.
    Di Marco, Piergiuseppe
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Calveras, Anna
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Analytical Model of Large Data Transactions in CoAP Networks2014Inngår i: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 14, nr 8, s. 15610-15638Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a novel analytical model to study fragmentation methods in wireless sensor networks adopting the Constrained Application Protocol (CoAP) and the IEEE 802.15.4 standard for medium access control (MAC). The blockwise transfer technique proposed in CoAP and the 6LoWPAN fragmentation are included in the analysis. The two techniques are compared in terms of reliability and delay, depending on the traffic, the number of nodes and the parameters of the IEEE 802.15.4 MAC. The results are validated trough Monte Carlo simulations. To the best of our knowledge this is the first study that evaluates and compares analytically the performance of CoAP blockwise transfer and 6LoWPAN fragmentation. A major contribution is the possibility to understand the behavior of both techniques with different network conditions. Our results show that 6LoWPAN fragmentation is preferable for delay-constrained applications. For highly congested networks, the blockwise transfer slightly outperforms 6LoWPAN fragmentation in terms of reliability.

  • 330. Lygeros, J.
    et al.
    Johansson, Karl H.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Simic, S. N.
    Zhang, J.
    Sastry, S. S.
    Dynamical properties of hybrid automata2003Inngår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 48, nr 1, s. 2-17Artikkel i tidsskrift (Fagfellevurdert)
  • 331. Lygeros, John
    et al.
    Johansson, Karl H.
    Sastry, Shankar
    Egerstedt, Magnus
    On the existence of executions of hybrid automata1999Inngår i: Proceedings of the 38th IEEE Conference on Decision and Control, 1999, IEEE , 1999, s. 2249-2254Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Necessary and sufficient conditions for hybrid automata to be non-blocking and deterministic (local existence and uniqueness of executions, respectively) are, developed. The problem of global existence of executions is discussed in the context of Zeno hybrid automata, that is, hybrid automata that exhibit infinitely many discrete transitions in finite time

  • 332. Lygeros, John
    et al.
    Johansson, Karl H.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Simic, Slobodan
    Zhang, Jun
    Sastry, Shankar
    Continuity and invariance in hybrid automata2001Inngår i: Proceedings of the 40th IEEE Conference on Decision and Control, 2001, IEEE , 2001, s. 340-345Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Hybrid automata have been proposed as a language for modelling and analysing the interaction of digital and analogue dynamics in embedded computer systems. In the paper, hybrid automata are studied from a dynamical systems perspective. Extending earlier work on conditions for existence and uniqueness of executions of hybrid automata, we characterise a class of hybrid automata whose executions depend continuously on the initial state. The continuity conditions are subsequently used to derive an extension of LaSalle's principle for studying the stability of invariant sets of states of hybrid automata

  • 333. Mazo Jr, M.
    et al.
    Johansson, Karl Henrik
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Robust area coverage using hybrid control2004Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Efficient coverage of an area by a mobile vehicle is a common challenge in many applications. Examples include automatic lawn mowers and vacuum cleaning robots. In this paper a vehicle with uncertain heading is studied. Five control strategies based on position measurements available only when the vehicle intersects the boundary of the area are compared. It is shown that the performance depends heavily on the heading error. The results are evaluated through extensive Monte Carlo simulations. An experimental implementation on a mobile robot is also presented.

  • 334.
    Mazo, Manuel
    et al.
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Speranzon, Alberto
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Johansson, Karl Henrik
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Hu, Xiaoming
    KTH, Tidigare Institutioner, Matematik.
    Multi-robot tracking of a moving object using directional sensors2004Inngår i: 2004 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION, VOLS 1- 5, PROCEEDINGS, 2004, s. 1103-1108Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The problem of estimating and tracking the motion of a moving target by a team of mobile robots is studied in this paper. Each robot is assumed to have a directional sensor with limited range, thus more than one robot (sensor) is needed for solving the problem. A sensor fusion scheme based on inter-robot communication is proposed in order to obtain accurate real-time information of the target's position and motion. Accordingly a hierarchical control scheme is applied, in which a consecutive set of desired formations is planned through a discrete model and low-level continuous-time controls are executed to track the resulting references. The algorithm is illustrated through simulations and on an experimental platform.

  • 335. Meng, Z.
    et al.
    Shi, G.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Multiagent systems with compaßes2015Inngår i: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 53, nr 5, s. 3057-3080Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates agreement protocols over cooperative and cooperativeantagonistic multiagent networks with coupled continuous-time nonlinear dynamics. To guarantee convergence for such systems, it is common in the literature to assume that the vector field of each agent is pointing inside the convex hull formed by the states of the agent and its neighbors, given that the relative states between each agent and its neighbors are available. This convexity condition is relaxed in this paper, as we show that it is enough that the vector field belongs to a strict tangent cone based on a local supporting hyperrectangle. The new condition has the natural physical interpretation of requiring shared reference directions in addition to the available local relative states. Such shared reference directions can be further interpreted as if each agent holds a magnetic compass indicating the orientations of a global frame. It is proved that the cooperative multiagent system achieves exponential state agreement if and only if the time-varying interaction graph is uniformly jointly quasi-strongly connected. Cooperative-antagonistic multiagent systems are also considered. For these systems, the relation has a negative sign for arcs corresponding to antagonistic interactions. State agreement may not be achieved, but instead it is shown that all the agents' states asymptotically converge, and their limits agree componentwise in absolute values if and in general only if the time-varying interaction graph is uniformly jointly strongly connected.

  • 336. Meng, Z.
    et al.
    Xia, W.
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Hirche, S.
    Stability of Positive Switched Linear Systems: Weak Excitation and Robustness to Time-Varying Delay2017Inngår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 62, nr 1, s. 399-405, artikkel-id 7409998Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This article investigates the stability of positive switched linear systems. We start from motivating examples and focus on the case when each switched subsystem is marginally stable (in the sense that all the eigenvalues of the subsystem matrix are in the closed left-half plane with those on the imaginary axis simple) instead of asymptotically stable. A weak excitation condition is first proposed such that the considered positive switched linear system is exponentially stable. An extension to the case without dwell time assumption is also presented. Then, we study the influence of time-varying delay on the stability of the considered positive switched linear system. We show that the proposed weak excitation condition for the delay-free case is also sufficient for the asymptotic stability of the positive switched linear system under unbounded time-varying delay. In addition, it is shown that the convergence rate is exponential if there exists an upper bound for the delay, irrespective of the magnitude of this bound. The motivating examples are revisited to illustrate the theoretical results.

  • 337. Meng, Ziyang
    et al.
    Dimarogonas, Dimos V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Attitude Coordinated Control of Multiple Underactuated Axisymmetric Spacecraft2017Inngår i: IEEE Transactions on Big Data, ISSN 2325-5870, E-ISSN 2168-6750, Vol. 4, nr 4, s. 816-825Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Attitude coordinated control of multiple underactuated spacecraft is studied in this paper. We adopt the parametrization proposed by Tsiotras et al. (1995) to describe attitude kinematics, which has been shown to be very convenient for control of underactuated axisymmetric spacecraft with two control torques. We first propose a partial attitude coordinated controller with angular velocity commands. The controller is based on the exchange of each spacecraft's information with local neighbors and a self-damping term. Under a necessary and general connectivity assumption and by use of a novel Lyapunov function, we show that the symmetry axes of all spacecraft are eventually aligned. Full attitude control of multiple underactuated spacecraft is also considered and a discontinuous distributed control algorithm is proposed. It is shown that the proposed algorithm succeeds in achieving stabilization given that control parameters are chosen properly. Discussions on the cases without self damping are also provided for both partial and full attitude controls. Simulations are given to validate the theoretical results and different steadystate behaviors are observed.

  • 338.
    Meng, Ziyang
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    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.
    Partial and full attitude synchronization of multiple underactuated spacecraft2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We study leaderless attitude synchronization problem of multiple underactuated spacecraft in this paper. We adopt the special parameterizations of attitude proposed by Tsiotras et al. (1995) to describe attitude kinematics, which has been shown to be very convenient for control of underactuated axisymmetric spacecraft with two control torques. It is assumed that angular velocity commands are possible and this paper is confined to the kinematic level. We first propose a partial attitude synchronization controller that is based on the exchange of each spacecraft's information with local neighbors. Under a necessary and general connectivity assumption and by use of an appropriate Lyapunov function, we show that the attitudes of spacecraft converge to a fixed or time-varying synchronization trajectory. Then, full attitude synchronization of multiple underactuated spacecraft is considered, where the discontinuous distributed algorithm is proposed. Simulations are given to validate the theoretical results and indicate several interesting observations.

  • 339.
    Meng, Ziyang
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    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.
    Leader-Follower Coordinated Tracking of Multiple Heterogeneous Lagrange Systems Using Continuous Control2014Inngår i: IEEE Transactions on robotics, ISSN 1552-3098, E-ISSN 1941-0468, Vol. 30, nr 3, s. 739-745Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we study the coordinated tracking problem of multiple heterogeneous Lagrange systems with a dynamic leader. Only nominal parameters of Lagrange dynamics are assumed to be available. Under the local interaction constraints, i.e., the followers only have access to their neighbors' information and the leader being a neighbor of only a subset of the followers, continuous coordinated tracking algorithms with adaptive coupling gains are proposed. Except for the benefit of the chattering-free control achieved, the proposed algorithm also has the attribute that it does not require the neighbors' generalized coordinate derivatives. Global asymptotic coordinated tracking is guaranteed, and the tracking errors between the followers and the leader are shown to converge to zero. Examples are given to validate the effectiveness of the proposed algorithms.

  • 340.
    Meng, Ziyang
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    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.
    Zero-error coordinated tracking of multiple lagrange systems using continuous control2013Inngår i: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC), IEEE conference proceedings, 2013, s. 6712-6717Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we study the coordinated tracking problem of multiple Lagrange systems with a time-varying leader's generalized coordinate derivative. Under a purely local interaction constraint, i.e., the followers only have access to their local neighbors' information and the leader is a neighbor of only a subset of the followers, a continuous coordinated tracking algorithm with adaptive coupling gains is proposed. Tracking errors between the followers and the leader are shown to converge to zero. Then, we extend this result to the case when the leader's generalized coordinate derivative is constant. Examples are given to validate the effectiveness of the proposed continuous coordinated tracking algorithms.

  • 341.
    Meng, Ziyang
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Shi, Guodong
    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.
    Multi-agent systems with compasses: Cooperative and cooperative-antagonistic networks2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we first study agreement protocols for coupled continuous-time nonlinear dynamics over cooperative multi-agent networks. To guarantee convergence for such systems, it is common in the literature to assume that the vector field of each agent is pointing inside the convex hull formed by the states of the agent and its neighbors given the relative states between each agent and its neighbors are available. This convexity condition is relaxed in this paper, as we show that it is enough that the vector field belongs to a strict tangent cone based on a local supporting hyperrectangle. The new condition has the natural physical interpretation of adding a compass for each agent in addition to the available local relative states, as each agent needs only to know in which orthant each of its neighbor is. It is proven that the multi-agent system achieves exponential state agreement if and only if the time-varying interaction graph is uniformly jointly quasi-strongly connected. Cooperative-antagonistic multi-agent networks are also considered. For these systems, the (cooperative-antagonistic) relation has a negative sign for arcs corresponding to antagonistic interactions. State agreement may not be achieved for cooperative-antagonistic multi-agent systems. Instead it is shown that asymptotic modulus agreement is achieved if the time-varying interaction graph is uniformly jointly strongly connected.

  • 342. Meng, Ziyang
    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.
    Cao, Ming
    Hong, Yiguang
    Behaviors of networks with antagonistic interactions and switching topologies2016Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 73, s. 110-116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we study the discrete-time consensus problem over networks with antagonistic and cooperative interactions. A cooperative interaction between two nodes takes place when one node receives the true state of the other while an antagonistic interaction happens when the former receives the opposite of the true state of the latter. We adopt a quite general model where the node communications can be either unidirectional or bidirectional, the network topology graph may vary over time, and the cooperative or antagonistic relations can be time-varying. It is proven that, the limits of all the node states exist, and the absolute values of the node states reach consensus if the switching interaction graph is uniformly jointly strongly connected for unidirectional topologies, or infinitely jointly connected for bidirectional topologies. These results are independent of the switching of the interaction relations. We construct a counterexample to indicate a rather surprising fact that quasi-strong connectivity of the interaction graph, i.e., the graph contains a directed spanning tree, is not sufficient to guarantee the consensus in absolute values even under fixed topologies. Based on these results, we also propose sufficient conditions for bipartite consensus to be achieved over the network with joint connectivity. Finally, simulation results using a discrete-time Kuramoto model are given to illustrate the convergence results showing that the proposed framework is applicable to a class of networks with general nonlinear dynamics.

  • 343.
    Meng, Ziyang
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. Technische Universität München, Germany .
    Yang, Tao
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. Pacific Northwest National Laboratory (PNNL), United States .
    Dimarogonas, Dimos V.
    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.
    Coordinated output regulation of heterogeneous linear systems under switching topologies2015Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 53, s. 362-368Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we construct a framework to describe and study the coordinated output regulation problem for multiple heterogeneous linear systems. Each agent is modeled as a general linear multiple-input multiple-output system with an autonomous exosystem which represents the individual offset from the group reference for the agent. The multi-agent system as a whole has a group exogenous state which represents the tracking reference for the whole group. Under the constraints that the group exogenous output is only locally available to each agent and that the agents have only access to their neighbors' information, we propose observer-based feedback controllers to solve the coordinated output regulation problem using output feedback information. A high-gain approach is used and the information interactions are allowed to be switching over a finite set of networks containing both graphs that have a directed spanning tree and graphs that do not. Simulations are shown to validate the theoretical results.

  • 344.
    Meng, Ziyang
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Yang, Tao
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    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.
    Coordinated output regulation of multiple heterogeneous linear systems2013Inngår i: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC), IEEE conference proceedings, 2013, s. 2175-2180Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The coordinated output regulation problem for multiple heterogeneous linear systems is studied in this paper. Each agent is modeled as a linear multiple-input multiple-output (MIMO) system with an exogenous input which represents the individual tracking objective for the agent. The multi-agent system as a whole has a group exogenous input which represents the tracking objective for the whole group. Under the constraints that the group exogenous input is only locally available to each agent and that the agents have only access to their neighbors' information, we propose an observer-based feedback controller to solve the coordinated output regulation problem. A high-gain approach is introduced and the information interactions are allowed to be switching over a finite set of fixed networks containing both graphs having a spanning tree and graphs that do not. A lower bound of the high gain parameters is explicitly given. It describes a fundamental relationship between the information interactions, the dwell time, the non-identical dynamics of different agents, and the high gain parameters.

  • 345. Meng, Ziyang
    et al.
    Yang, Tao
    Shi, Guodong
    Dimarogonas, Dimos V.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Hong, Yiguang
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Targeted agreement of multiple Lagrangian systems*2017Inngår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 84, s. 109-116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we study the targeted agreement problem for a group of Lagrangian systems. Each system observes a convex set as its local target and the objective of the group is to reach a generalized coordinate agreement towards these target sets. Typically, the generalized coordinate represents position or angle. We first consider the case when the communication graphs are fixed. A control law is proposed based on each system's own target sensing and information exchange with neighbors. With necessary connectivity, the generalized coordinates of multiple Lagrangian systems are shown to achieve agreement in the intersection of all the local target sets while generalized coordinate derivatives are driven to zero. We also discuss the case when the intersection of the local target sets is empty. Exact targeted agreement cannot be achieved in this case. Instead, we show that approximate targeted agreement can be guaranteed if the control gains are properly chosen. In addition, when communication graphs are allowed to be switching, we propose a model-dependent control algorithm and show that global targeted agreement is achieved when joint connectivity is guaranteed and the intersection of local target sets is nonempty. Simulations are given to validate the theoretical results. 

  • 346.
    Meng, Ziyang
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Yang, Tao
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Shi, Guodong
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Hong, Yiguang
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Set target aggregation of multiple mechanical systems2014Inngår i: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2014, nr February, s. 6830-6835Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we study the set target aggregation problem of multiple mechanical systems. Each system is modeled by a Lagrangian dynamical equation and observes a convex set as its local target. The objective of the group is to reach an aggregation towards these target sets.We propose a set target aggregation algorithm that is constructed based on each mechanical system's own target sensing and the exchange of its information with local neighbors. With necessary connectivity for both fixed and switching communication topologies, multiple mechanical systems are shown to converge to the intersection of all the local target sets while the vectors of generalized coordinate derivatives are driven to zero. Simulations are given to validate the theoretical results.

  • 347. Millán, P.
    et al.
    Orihuela, L.
    Vivas, C.
    Rubio, F. R.
    Dimarogonas, Dimos V.
    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.
    Sensor-network-based robust distributed control and estimation2013Inngår i: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 21, nr 9, s. 1238-1249Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper proposes a novel distributed estimation and control method for uncertain plants. It is of application in the case of large-scale systems, where each control unit is assumed to have access only to a subset of the plant outputs, and possibly controls a restricted subset of input channels. A constrained communication topology between nodes is considered so the units can benefit from estimates of neighboring nodes to build their own estimates. The paper proposes a methodology to design a distributed control structure so that the system is asymptotically driven to equilibrium with L2-gain disturbance rejection capabilities. A difficulty that arises is that the separation principle does not hold, as every single unit ignores the control action that other units might be applying. To overcome this, a two-stage design is proposed: firstly, the distributed controllers are obtained to robustly stabilize the plant despite the observation errors in the controlled output. At the second stage, the distributed observers are designed aiming to minimize the effects of the communication noise in the observation error. Both stages are formulated in terms of linear matrix inequalities. The performance is shown on a level-control real plant.

  • 348.
    Milosevic, Jezdimir
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Sandberg, Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    A Security Index for Actuators Based on Perfect Undetectability: Properties and Approximation2019Inngår i: 2018 56th Annual Allerton Conference on Communication, Control, and Computing, Allerton 2018, Institute of Electrical and Electronics Engineers Inc. , 2019, s. 235-241Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A novel security index based on the definition of perfect undetectability is proposed. The index is a tool that can help a control system operator to localize the most vulnerable actuators in the network. In particular, the security index of actuator i represents the minimal number of sensors and actuators that needs to be compromised in addition to i, such that a perfectly undetectable attack is possible. A method for computing this index for small scale systems is derived, and difficulties with the index once the system is of large scale are outlined. An upper bound for the index that overcomes these difficulties is then proposed. The theoretical developments are illustrated on a numerical example. 

  • 349.
    Milošević, Jezdimir
    et al.
    KTH.
    Tanaka, Takashi
    KTH.
    Sandberg, Henrik
    KTH.
    Johansson, Karl H.
    KTH.
    Exploiting Submodularity in Security Measure Allocation for Industrial Control Systems2017Inngår i: Proceedings of the 1st ACM Workshop on the Internet of Safe Things, ACM , 2017, s. 64-69Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Industrial control systems are cyber-physical systems that are used to operate critical infrastructures such as smart grids, traffic systems, industrial facilities, and water distribution networks. The digitalization of these systems increases their efficiency and decreases their cost of operation, but also makes them more vulnerable to cyber-attacks. In order to protect industrial control systems from cyber-attacks, the installation of multiple layers of security measures is necessary. In this paper, we study how to allocate a large number of security measures under a limited budget, such as to minimize the total risk of cyber-attacks. The security measure allocation problem formulated in this way is a combinatorial optimization problem subject to a knapsack (budget) constraint. The formulated problem is NP-hard, therefore we propose a method to exploit submodularity of the objective function so that polynomial time algorithms can be applied to obtain solutions with guaranteed approximation bounds. The problem formulation requires a preprocessing step in which attack scenarios are selected, and impacts and likelihoods of these scenarios are estimated. We discuss how the proposed method can be applied in practice.

  • 350.
    Minnema Lindhé, Magnus
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Exploiting multipath fading with a mobile robot2013Inngår i: The international journal of robotics research, ISSN 0278-3649, E-ISSN 1741-3176, Vol. 32, nr 12, s. 1363-1380Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In indoor or urban applications, a moving robot with wireless communications will experience multipath fading. This causes rapid signal strength variations due to interfering reflections of the radio signal. By making short stops at positions with high signal-to-noise ratio (SNR), the robot can trade trajectory tracking accuracy for increased link quality. This represents a type of opportunistic communication-aware motion planning. We propose two novel strategies for improving the link capacity or throughput when either the robot has full knowledge of how the SNR varies along the trajectory, or when only the SNR distribution is known or can be estimated. In the latter case, this leads to an optimal stopping problem over a finite horizon. Both cases are analyzed for independent as well as correlated SNR samples, and a bounded maximum trajectory tracking error. We derive the resulting SNR distributions for the proposed strategies and use them to show how the expected capacity and throughput vary with the allowed tracking error. The results are confirmed by simulations and experiments. Experiments in six different locations validate the communication model and show that the proposed motion planning is robust to non-static fading and can yield throughput improvements of more than 100%.

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