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  • 151.
    Björk, Joakim
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Harnefors, Lennart
    ABB, Corp Res, Vasteras, Sweden..
    Eriksson, Robert
    Svenska kraftnat, R&D, Sundbyberg, Sweden..
    Analysis of Coordinated HVDC Control for Power Oscillation Damping2018In: Conference Record of the 3rd IEEE International Workshop on Electronic Power Grid, eGrid 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 19-24, article id 8598674Conference paper (Refereed)
    Abstract [en]

    Controlling the active power of high-voltage de (HVDC) transmission that interconnects two asynchronous ac grids can be used to improve the power oscillation damping in both of the interconnected ac systems. Using one HVDC link, achievable performance are limited since control actions may excite modes of similar frequencies in the assisting network. However, with coordinated control of two or more HVDC links, the limitations can be circumvented. With decoupling control the system interactions can be avoided all together. This paper investigates the conditions suitable for decoupling control. It is also shown that decoupling between system modes can be achieved using a proportional controller. The control method is compared to decentralized and H-2 optimal control. The best control method for different system topologies is investigated by looking on input usage and stability following dc link failure.

  • 152.
    Björk, Joakim
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Obradovic, Danilo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Harnefors, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems. ABB, Corp Res, S-72178 Västerås, Sweden..
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Influence of Sensor Feedback Limitations on Power Oscillation Damping and Transient Stability2022In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 37, no 2, p. 901-912Article in journal (Refereed)
    Abstract [en]

    Fundamental sensor feedback limitations for improving rotor angle stability using local frequency or phase angle measurement are derived. Using a two-machine power system model, it is shown that improved damping of inter-area oscillations must come at the cost of reduced transient stability margins, regardless of the control design method. The control limitations stem from that the excitation of an inter-area mode by external disturbances cannot be estimated with certainty using local frequency information. The results are validated on a modified Kundur four-machine two-area test system where the active power is modulated on an embedded high-voltage dc link. Damping control using local phase angle measurements, unavoidably leads to an increased rotor angle deviation following certain load disturbances. For a highly stressed system, it is shown that this may lead to transient instability. The limitations derived in the paper may motivate the need for wide-area measurements in power oscillation damping control.

  • 153.
    Björk, Joakim
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Pombo, Daniel
    Tech Univ Denmark DTU, Dept Elect Engn, DK-4000 Roskilde, Denmark.;Denmark Res & Dev Vattenfall AB, S-16956 Solna Stockholm, Sweden..
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Variable-Speed Wind Turbine Control Designed for Coordinated Fast Frequency Reserves2022In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 37, no 2, p. 1471-1481Article in journal (Refereed)
    Abstract [en]

    Modern power systems present low levels of inertia due to the growing shares of converter-interfaced generation. Consequently, renewable energy sources are increasingly requested to provide frequency support. In addition, due to the inertia loss, the requirements regarding frequency containment reserves (FCR) are becoming tough to meet with traditional units such as hydro, whose non-minimum phase (NMP) characteristic reduces the closed-loop stability margins. The shortcomings of traditional synchronous generation motivates new protocols for fast frequency reserves (FFR). In this work, we design a wind turbine (WT) model useful for FFR. It is shown that the dynamical shortcomings of the WT, in providing steady-power or slow FCR support, are suitably described by a first-order transfer function with a slow NMP zero. The WT model is tested in a 5-machine representation of the Nordic synchronous grid. It is shown that the NMP model is useful for designing a controller that coordinates FFR from wind with slow FCR from hydro turbines. By simulating the disconnection of a 1400 MW importing dc link in a detailed nonlinear model, it is shown that the wind-hydro combination not only satisfies the latest regulations, but also presents a smooth response avoiding overshoot and secondary frequency dips during frequency recovery.

  • 154. Boem, F.
    et al.
    Zhou, Y.
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Parisini, T.
    Distributed Pareto-optimal state estimation using sensor networks2018In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 93, p. 211-223Article in journal (Refereed)
    Abstract [en]

    A novel model-based dynamic distributed state estimator is proposed using sensor networks. The estimator consists of a filtering step – which uses a weighted combination of information provided by the sensors – and a model-based predictor of the system's state. The filtering weights and the model-based prediction parameters jointly minimize – at each time-step – the bias and the variance of the prediction error in a Pareto optimization framework. The simultaneous distributed design of the filtering weights and of the model-based prediction parameters is considered, differently from what is normally done in the literature. It is assumed that the weights of the filtering step are in general unequal for the different state components, unlike existing consensus-based approaches. The state, the measurements, and the noise components are allowed to be individually correlated, but no probability distribution knowledge is assumed for the noise variables. Each sensor can measure only a subset of the state variables. The convergence properties of the mean and of the variance of the prediction error are demonstrated, and they hold both for the global and the local estimation errors at any network node. Simulation results illustrate the performance of the proposed method, obtaining better results than state of the art distributed estimation approaches.

  • 155.
    Bombois, X.
    et al.
    Univ Lyon, Lab Ampere, Ecole Cent Lyon, Ecully, France.;CNRS, Paris, France..
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Network topology detection via uncertainty analysis of an identified static model2021In: IFAC PAPERSONLINE, Elsevier BV , 2021, Vol. 54, no 7, p. 595-600Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a methodology to detect the topology of a dynamic network that is based on the analysis of the uncertainty of the static characteristic of the matrix of transfer functions between the external excitations and the node signals.

  • 156.
    Bombois, Xavier
    et al.
    Univ Lyon, Lab Ampere, Ecole Cent Lyon, Ecully, France.;CNRS, Paris, France..
    Colin, Kevin
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Van den Hof, Paul M. J.
    Eindhoven Univ Technol, Control Syst Grp, Dept Elect Engn, Eindhoven, Netherlands..
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    On the informativity of direct identification experiments in dynamical networks2023In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 148, p. 110742-, article id 110742Article in journal (Refereed)
    Abstract [en]

    Data informativity is a crucial property to ensure the consistency of the prediction error estimate. This property has thus been extensively studied in the open-loop and in the closed-loop cases, but has only been briefly touched upon in the dynamic network case. In this paper, we consider the prediction error identification of the modules in a row of a dynamic network using the full input approach. Our main contribution is to propose a number of easily verifiable data informativity conditions for this identification problem. Among these conditions, we distinguish a sufficient data informativity condition that can be verified based on the topology of the network and a necessary and sufficient data informativity condition that can be verified via a rank condition on a matrix of coefficients that are related to a full-order model structure of the network. These data informativity conditions allow to determine different situations (i.e., different excitation patterns) leading to data informativity. In order to be able to distinguish between these different situations, we also propose an optimal experiment design problem that allows to determine the excitation pattern yielding a certain pre-specified accuracy with the least excitation power.

  • 157. Bombois, Xavier
    et al.
    Korniienko, A.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Scorletti, G.
    Optimal identification experiment design for the interconnection of locally controlled systems2018In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 89, p. 169-179Article in journal (Refereed)
    Abstract [en]

    This paper considers the identification of the modules of a network of locally controlled systems (multi-agent systems). Its main contribution is to determine the least perturbing identification experiment that will nevertheless lead to sufficiently accurate models of each module for the global performance of the network to be improved by a redesign of the decentralized controllers. Another contribution is to determine the experimental conditions under which sufficiently informative data (i.e. data leading to a consistent estimate) can be collected for the identification of any module in such a network. 

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  • 158.
    Bombois, Xavier
    et al.
    Univ Lyon, Lab Ampere, Ecole Cent Lyon, 36 Ave Guy Collongue, Ecully, France.;Ctr Natl Rech Sci CNRS, Paris, France..
    Morelli, Federico
    Univ Lyon, Lab Ampere, Ecole Cent Lyon, 36 Ave Guy Collongue, Ecully, France..
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Bako, Laurent
    Univ Lyon, Lab Ampere, Ecole Cent Lyon, 36 Ave Guy Collongue, Ecully, France..
    Colin, Kevin
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Robust optimal identification experiment design for multisine excitation2021In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 125, article id 109431Article in journal (Refereed)
    Abstract [en]

    In least costly experiment design, the optimal spectrum of an identification experiment is determined in such a way that the cost of the experiment is minimized under some accuracy constraint on the identified parameter vector. Like all optimal experiment design problems, this optimization problem depends on the unknown true system, which is generally replaced by an initial estimate. One important consequence of this is that we can underestimate the actual cost of the experiment and that the accuracy of the identified model can be lower than desired. Here, based on an a-priori uncertainty set for the true system, we propose a convex optimization approach that allows to prevent these issues from happening. We do this when the to-be-determined spectrum is the one of a multisine signal.

  • 159.
    Boskos, Dimitris
    et al.
    Univ Calif San Diego, Dept Mech & Aerosp Engn, La Jolla, CA 92093 USA..
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    ABSTRACTIONS OF VARYING DECENTRALIZATION DEGREE FOR REACHABILITY OF COUPLED MULTIAGENT SYSTEMS2019In: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 57, no 5, p. 3471-3495Article in journal (Refereed)
    Abstract [en]

    In this paper we present a decentralized abstraction framework for multiagent systems with couplings in their dynamics, which arise in their popular coordination protocols. The discrete models are basexl on a varying decentralization degree, namely, the agents' individual abstractions are obtained by using discrete information up to a tunable distance in their network graph. Deriving these models at the agent level is essential to address scalability issues which appear in the discretization of systems with a high state dimension. The approach builds on the appropriate discretization of the agents' state space and the selection of a transition time step, which enable the construction of a nonblocking transition system for each agent with quantifiable transition possibilities. The transitions are based on the design of local feedback laws for the manipulation of the coupling terms, which guarantee the execution of the transitions by the continuous systems. For a class of nonlinear agent interconnections, the derivation of such abstractions is always guaranteed, based on sufficient conditions which relate the agents' dynamics and the space/time quantization.

  • 160.
    Boskos, Dimitris
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Decentralized abstractions for multi-agent systems under coupled constraints2019In: European Journal of Control, ISSN 0947-3580, E-ISSN 1435-5671, Vol. 45, p. 1-16Article in journal (Refereed)
    Abstract [en]

    The goal of this paper is to define abstractions for multi-agent systems with feedback interconnection in their dynamics. In the proposed decentralized framework, we specify a finite or countable transition system for each agent which only takes into account the discrete positions of its neighbors. The dynamics of each agent consist of a feedback component which can guarantee certain system and network requirements and induces the coupled constraints, and additional input terms, which can be exploited for high level planning. In this work, we provide sufficient conditions for space and time discretizations which enable the abstraction of the system's behavior through a discrete transition system. Furthermore, these conditions include design parameters whose tuning provides the possibility for multiple transitions, and hence, the construction of transition systems with motion planning capabilities. Published by Elsevier Ltd. All rights reserved.

  • 161.
    Boskos, Dimitris
    et al.
    Univ Calif San Diego, Dept Mech & Aerosp Engn, San Diego, CA 92103 USA..
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Finite horizon discrete models for multi-agent control systems with coupled dynamics2020In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 115, article id 108838Article in journal (Refereed)
    Abstract [en]

    The goal of this paper is to obtain online abstractions for coupled multi-agent systems in a decentralized manner. A discrete model which captures the motion capabilities of each agent is derived over a bounded time-horizon, by discretizing a corresponding overapproximation of the agent's reachable states. The individual abstractions' composition provides a correct representation of the coupled continuous system over the horizon and renders the approach appropriate for control synthesis under high-level specifications which are assigned to the agents over this time window. Sufficient conditions are also provided for the space and time discretization to guarantee the derivation of deterministic abstractions with tunable transition capabilities.

  • 162.
    Braga, Iran M.
    et al.
    Federal University of Ceara, Wireless Telecom Research Group (GTEL), Fortaleza, Brazil.
    Antonioli, Roberto P.
    Federal University of Ceara, Wireless Telecom Research Group (GTEL), Fortaleza, Brazil, 60455-760; Instituto Atlĉntico, Fortaleza, Brazil.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Research, Stockholm, Sweden.
    Silva, Yuri C.B.
    Federal University of Ceara, Wireless Telecom Research Group (GTEL), Fortaleza, Brazil.
    Freitas, Walter C.
    Federal University of Ceara, Wireless Telecom Research Group (GTEL), Fortaleza, Brazil.
    Efficient Battery Usage in Wireless-Powered Cell-Free Systems With Self-Energy Recycling2023In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 72, no 5, p. 6856-6861Article in journal (Refereed)
    Abstract [en]

    This article investigates wireless-powered cell-free systems, in which the users send their uplink data signal while simultaneously harvesting energy from network nodes and user terminals - including the transmitting user terminal itself - by performing self-energy recycling. In this rather general setting, a closed-form lower bound of the amount of harvested energy and the achieved signal-to-interference-plus-noise ratio expressions are derived. Then, to improve the energy efficiency, we formulate the problem of minimizing the users' battery energy usage while satisfying minimum data rate requirements. Due to the non-convexity of the problem, a novel alternating optimization algorithm is proposed, and its proof of convergence is provided. Finally, numerical results show that the proposed method is more efficient than a state-of-art algorithm in terms of battery energy usage and outage rate.

  • 163.
    Braga Jr, Iran M.
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Antonioli, Roberto P.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Res, S-16480 Stockholm, Sweden..
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Freitas Jr, Walter C.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Joint Pilot and Data Power Control Optimization in the Uplink of User-Centric Cell-Free Systems2022In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 26, no 2, p. 399-403Article in journal (Refereed)
    Abstract [en]

    Joint pilot and data power control (JPDPC) is known to have a large impact on both the overall spectral/energy efficiency and fairness of cell-based systems. However, the impact of JPDPC on the inherent spectral/energy efficiency and fairness trade-off in cell-free (CF) systems is much less understood. In this letter, considering pilot contamination, user-centric clustering and multi-antenna access points, we formulate novel JPDPC problems in CF systems as distinct optimization tasks, whose objectives are maximizing the minimum spectral efficiency (SE), maximizing the total SE and maximizing the product of the individual signal-to-interference-plus-noise ratios. Since these problems are non-convex, we solve them by combining successive convex approximation and geometric programming. To the best of our knowledge, this is the first letter analyzing and optimizing JPDPC in user-centric CF systems. Our results indicate that JPDPC allows users to save more energy than the disjoint optimization of pilot and data powers when maximizing the minimum SE, while showing that JPDPC plays a crucial role in balancing between SE and fairness also in CF systems.

  • 164.
    Braga Jr, Iran M.
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Cavalcante, Eduardo de O.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil.;Fed Inst Educ Sci & Technol Ceara, BR-63660000 Taua, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Res, S-16480 Stockholm, Sweden..
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    e Silva, Carlos F. M.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Freitas Jr, Walter C.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    User Scheduling Based on Multi-Agent Deep Q-Learning for Robust Beamforming in Multicell MISO Systems2020In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 24, no 12, p. 2809-2813Article in journal (Refereed)
    Abstract [en]

    Maximizing the rate in multiple input single output (MISO) systems using distributed algorithms is an important task that typically incurs high computational cost. In this work, we propose two deep Q-learning-based user scheduling schemes to solve the beamforming problem of sum-rate maximization with per base station power constraints in multicell MISO scenarios. The two key features of the proposed algorithms are that they are executed in a distributed fashion and are robust with respect to channel state information (CSI) errors. Simulation results show that in the presence of CSI errors the proposed schemes outperform state-of-the-art algorithms both in terms of average spectral efficiency and execution time.

  • 165.
    Braga Jr, Iran Mesquita
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Antonio, Roberto Pinto
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Res, S-16480 Stockholm, Sweden.;.
    Silva, C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Silva, Carlos F. M. E.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Freitas Jr, Alter C.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Joint Resource Allocation and Transceiver Design for Sum-Rate Maximization Under Latency Constraints in Multicell MU-MIMO Systems2021In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 69, no 7, p. 1-1Article in journal (Refereed)
    Abstract [en]

    Due to the continuous advancements of orthogonal frequency division multiplexing (OFDM) and multiple antenna techniques, multiuser multiple input multiple output (MU-MIMO) OFDM is a key enabler of both fourth and fifth generation networks. In this paper, we consider the problem of weighted sum-rate maximization under latency constraints in finite buffer multicell MU-MIMO OFDM systems. Unlike previous works, the optimization variables include the transceiver beamforming vectors, the scheduled packet size and the resources in the frequency and power domains. This problem is motivated by the observation that multicell MU-MIMO OFDM systems serve multiple quality of service classes and the system performance depends critically on both the transceiver design and the scheduling algorithm. Since this problem is non-convex, we resort to the max-plus queuing method and successive convex approximation. We propose both centralized and decentralized solutions, in which practical design aspects, such as signaling overhead, are considered. Finally, we compare the proposed framework with state-of-the-art algorithms in relevant scenarios, assuming a realistic channel model with space, frequency and time correlations. Numerical results indicate that our design provides significant gains over designs based on the wide-spread saturated buffers assumption, while also outperforming algorithms that consider a finite-buffer model. Due to the continuous advancements of orthogonal frequency division multiplexing (OFDM) and multiple antenna techniques, multiuser multiple input multiple output (MU-MIMO) OFDM is a key enabler of both fourth and fifth generation networks. In this paper, we consider the problem of weighted sum-rate maximization under latency constraints in finite buffer multicell MU-MIMO OFDM systems. Unlike previous works, the optimization variables include the transceiver beamforming vectors, the scheduled packet size and the resources in the frequency and power domains. This problem is motivated by the observation that multicell MU-MIMO OFDM systems serve multiple quality of service classes and the system performance depends critically on both the transceiver design and the scheduling algorithm. Since this problem is non-convex, we resort to the max-plus queuing method and successive convex approximation. We propose both centralized and decentralized solutions, in which practical design aspects, such as signaling overhead, are considered. Finally, we compare the proposed framework with state-of-the-art algorithms in relevant scenarios, assuming a realistic channel model with space, frequency and time correlations. Numerical results indicate that our design provides significant gains over designs based on the widespread saturated buffers assumption, while also outperforming algorithms that consider a finite-buffer model.

  • 166.
    Braga Jr, Iran Mesquita
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Antonioli, Roberto Pinto
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil.;Inst Atlant, BR-60811341 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Res, SE-16480 Stockholm, Sweden.;KTH Royal Inst Technol, Div Decis & Control, S-11428 Stockholm, Sweden..
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Freitas Jr, Walter C. C.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Decentralized Joint Pilot and Data Power Control Based on Deep Reinforcement Learning for the Uplink of Cell-Free Systems2023In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 72, no 1, p. 957-972Article in journal (Refereed)
    Abstract [en]

    While the problem of jointly controlling the pilot-and-data power in cell-based systems has been extensively studied, this problem is difficult to solve in cell-free systems due to two reasons. First, both the large- and small-scale fading are markedly different between a served user and the multiple serving access points. Second, due to the user-centric architecture, there is a need for decentralized algorithms that scale well in the cell-free environment. In this work, we study the impact of joint pilot-and-data power control and receive filter design in the uplink of cell-free systems. The problem is formulated as optimization tasks considering two different objectives: 1) maximization of the minimum spectral efficiency (SE) and 2) maximization of the total SE. Since these problems are non-convex, we resort to successive convex approximation and geometric programming to obtain a local optimal centralized solution for benchmarking purposes. We also propose a decentralized solution based on actor-critic deep reinforcement learning, in which each user acts as an agent to locally obtain the best policy relying on minimum information exchange. Practical signaling aspects are provided for such a decentralized solution. Finally, numerical results indicate that the decentralized solution performs very close to the centralized one and outperforms state-of-the-art algorithms in terms of minimum SE and total system SE.

  • 167.
    Bujarbaruah, Monimoy
    et al.
    Univ Calif Berkeley, MPC Lab, Berkeley, CA 94720 USA..
    Stuerz, Yvonne R.
    Univ Calif Berkeley, MPC Lab, Berkeley, CA 94720 USA..
    Holda, Conrad
    Univ Calif Berkeley, MPC Lab, Berkeley, CA 94720 USA..
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Borrelli, Francesco
    Univ Calif Berkeley, MPC Lab, Berkeley, CA 94720 USA..
    Learning Environment Constraints in Collaborative Robotics: A Decentralized Leader-Follower Approach2021In: 2021 IEEE/RSJ IEEE International Workshop on Intelligent Robots and Systems (IROS), Institute of Electrical and Electronics Engineers (IEEE) , 2021, p. 1636-1641Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a leader-follower hierarchical strategy for two robots collaboratively transporting an object in a partially known environment with obstacles. Both robots sense the local surrounding environment and react to obstacles in their proximity. We consider no explicit communication, so the local environment information and the control actions are not shared between the robots. At any given time step, the leader solves a model predictive control (MPC) problem with its known set of obstacles and plans a feasible trajectory to complete the task. The follower estimates the inputs of the leader and uses a policy to assist the leader while reacting to obstacles in its proximity. The leader infers obstacles in the follower's vicinity by using the difference between the predicted and the real-time estimated follower control action. A method to switch the leader-follower roles is used to improve the control performance in tight environments. The efficacy of our approach is demonstrated with detailed comparisons to two alternative strategies, where it achieves the highest success rate, while completing the task fastest.

  • 168.
    Calil, Wílerson Venceslau
    et al.
    Hitachi Energy, Västerås, Sweden; Polytechnic School of the University of São Paulo, São Paulo, Brazil.
    Morozovska, Kateryna
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Laneryd, Tor
    Hitachi Energy, Västerås, Sweden.
    da Costa, Eduardo Coelho Marques
    Polytechnic School of the University of São Paulo, São Paulo, Brazil.
    Salles, Maurício Barbosa de Camargo
    Polytechnic School of the University of São Paulo, São Paulo, Brazil.
    Determining total cost of ownership and peak efficiency index of dynamically rated transformer at the PV-power plant2024In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 229, article id 110061Article in journal (Refereed)
    Abstract [en]

    Dynamic rating of the transformer is a promising technology, which is suitable for various applications. Using dynamic rating for connecting renewable energy is believed to be beneficial for the economy and flexibility of the power system. However, to safely deploy such operation strategies, it is important to have more precise estimates for the total costs of owning such units and determine how effective such operation method is for a solar power plant. This study proposes a method for calculating total ownership costs (TOC) of dynamically rated transformers used for the connection of the solar power plant to the grid as well as analyzes its efficiency. The sensitivity analysis looks into the change in TOC and peak efficiency index (PEI) after considering reactive power dispatch. Results of this study also show how TOC, PEI, and load and no-load losses change depending on the transformer size.

  • 169.
    Campos, Joao
    et al.
    Univ Lisbon, Inst Super Tecn, ISR, Lisbon, Portugal..
    Cardoso, Joao R.
    Inst Politecn Coimbra, ISEC, Coimbra, Portugal.;Univ Coimbra, Inst Syst & Robot, Coimbra, Portugal..
    Dos Santos Miraldo, Pedro
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    POSEAMM: A Unified Framework for Solving Pose Problems using an Alternating Minimization Method2019In: 2019 International Conference on Robotics and Automation (ICRA) / [ed] Howard, A Althoefer, K Arai, F Arrichiello, F Caputo, B Castellanos, J Hauser, K Isler, V Kim, J Liu, H Oh, P Santos, V Scaramuzza, D Ude, A Voyles, R Yamane, K Okamura, A, Institute of Electrical and Electronics Engineers (IEEE), 2019, p. 3493-3499Conference paper (Refereed)
    Abstract [en]

    Pose estimation is one of the most important problems in computer vision. It can be divided in two different categories - absolute and relative - and may involve two different types of camera models: central and non-central. State-of-the-art methods have been designed to solve separately these problems. This paper presents a unified framework that is able to solve any pose problem by alternating optimization techniques between two set of parameters, rotation and translation. In order to make this possible, it is necessary to define an objective function that captures the problem at hand. Since the objective function will depend on the rotation and translation it is not possible to solve it as a simple minimization problem. Hence the use of Alternating Minimization methods, in which the function will be alternatively minimized with respect to the rotation and the translation. We show how to use our framework in three distinct pose problems. Our methods are then benchmarked with both synthetic and real data, showing their better balance between computational time and accuracy.

  • 170.
    Carlemalm, Catharina
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Wahlberg, Bo
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    On the problem of blind equalization considering abrupt changes in the channel characteristics2015In: European Signal Processing Conference, European Signal Processing Conference, EUSIPCO , 2015Conference paper (Refereed)
    Abstract [en]

    The problem of blind equalization in a digital communication system is considered. Unfortunately, the circuit might suffer from abrupt changes. Thus, it is critical not to ignore this phenomenon when the problem of blind equalization is analyzed. The proposed method, which is based on an Ito stochastic differential calculus approach, describes the dynamics of the output signal with an infinite impulse response (IIR) model where the involved taps are modeled as time-varying cadlag (con-tinu a droite limites a gauche) processes. Therefore, nonlinear and time-variant changes in the channel characteristics are included.

  • 171.
    Carnevale, Guido
    et al.
    Alma Mater Studiorum Univ Bologna, Dept Elect Elect & Informat Engn, Bologna, Italy..
    Bastianello, Nicola
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Carli, Ruggero
    Univ Padua, Dept Informat Engn, Via G Gradenigo 6-B, I-35131 Padua, Italy..
    Notarstefano, Giuseppe
    Alma Mater Studiorum Univ Bologna, Dept Elect Elect & Informat Engn, Bologna, Italy..
    Distributed Consensus Optimization via ADMM-Tracking2023In: 2023 The 62nd IEEE Conference on Decision and Control (CDC 2023), CDC, Institute of Electrical and Electronics Engineers (IEEE) , 2023, p. 290-295Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a novel distributed algorithm for consensus optimization over networks. The key idea is to achieve dynamic consensus on the agents' average and on the global descent direction by iteratively solving an online auxiliary optimization problem through the Alternating Direction Method of Multipliers (ADMM). Such a mechanism is suitably interlaced with a local proportional action steering each agent estimate to the solution of the original consensus optimization problem. The analysis uses tools from system theory to prove the linear convergence of the scheme with strongly convex costs. Finally, some numerical simulations confirm our findings and show the robustness of the proposed scheme.

  • 172.
    Cavalcante, Eduardo de Olivindo
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Res, SE-16480 Stockholm, Sweden.
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Freitas Jr, Walter C.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Distributed Beamforming in Dynamic TDD MIMO Networks With BS to BS Interference Constraints2018In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 7, no 5, p. 788-791Article in journal (Refereed)
    Abstract [en]

    This letter proposes distributed beamforming as a means of reducing interference in dynamic time division duplexing multiple input multiple output networks. Specifically, we formulate an optimization task, whose objective is to minimize the base station (BS) transmit power, while satisfying a predefined signal-to-interference-plus-noise ratio threshold for each downlink user equipment and keeping the BS to BS interference power below a tolerable level. An iterative decentralized solution requiring reduced signaling load based on primal decomposition is proposed. This decentralized algorithm is shown to iterate towards the centralized solution, while feasible but suboptimal solutions can be obtained at any iteration.

  • 173.
    Cavalcante, Eduardo de Olivindo
    et al.
    Univ Fed Ceara, Ctr Technol, Dept Teleinformat Engn, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil.;Fed Inst Educ Sci & Technol Ceara, BR-63660000 Taua, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Research, Kista, 164 40, Sweden.
    Silva, Yuri C. B.
    Univ Fed Ceara, Ctr Technol, Dept Teleinformat Engn, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Freitas, Walter C., Jr.
    Univ Fed Ceara, Ctr Technol, Dept Teleinformat Engn, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Bidirectional Sum-Power Minimization Beamforming in Dynamic TDD MIMO Networks2019In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 68, no 10, p. 9988-10002Article in journal (Refereed)
    Abstract [en]

    Employing dynamic time division duplexing can increase the system-wide spectral efficiency of applications with varying and unbalanced uplink and downlink data traffic requirements. However, in order to achieve this efficiency gain, it is necessary to manage the effects of cross-link interference, which are generated among cells transmitting in opposite link directions. This paper considers bidirectional sum-power minimization beamforming as a means to deal with this cross-link interference, by forcing a minimum signal-to-interference-plus-noise ratio constraint for both uplink and downlink. We propose two iterative approaches to solve this beamforming problem. The first approach assumes centralized processing and requires the availability of global channel state information. The second approach is performed in a decentralized manner, based on the alternating direction method of multipliers and requires only local channel state information and reduced signaling load. Both approaches are shown to converge to a minimum network power expenditure, whereas close-to-optimum performance can be obtained when limiting the number of iterations.

  • 174.
    Cavaliere, Clara
    et al.
    Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy..
    Mariniello, Dario
    Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy..
    Adaldo, Antonio
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Lo Iudice, Francesco
    Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy..
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    di Bernardo, Mario
    Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy..
    Cloud-supported self-triggered control for multi-agent circumnavigation2018In: 2018 IEEE CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2018, p. 5090-5095Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a cloud-supported control framework for multi-agent circumnavigation missions. We consider a network of planar autonomous agents. Our objective is for the agents to circumnavigate a target with a desired angular speed, while forming a regular polygon around the target. We propose self-triggered rules to schedule the bearing measurements and the cloud accesses for each agent.

  • 175.
    Chaher, Mariano Perez
    et al.
    Univ Groningen, Engn & Technol Inst Groningen, Fac Sci & Engn, NL-9747 AG Groningen, Netherlands..
    Jayawardhana, Bayu
    Univ Groningen, Engn & Technol Inst Groningen, Fac Sci & Engn, NL-9747 AG Groningen, Netherlands..
    Kim, Junsoo
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Homomorphic Encryption-enabled Distance-based Distributed Formation Control with Distance Mismatch Estimators2021In: 2021 60TH IEEE CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2021, p. 4915-4922Conference paper (Refereed)
    Abstract [en]

    This paper considers the use of homomorphic encryption for the realisation of distributed formation control of multi-agent systems via edge computer. In our proposed framework, the distributed control computation in the edge computer uses only the encrypted data without the need for a reset mechanism that is commonly required to avoid error accumulation. Simulation results show that, despite the use of encrypted data on the controller and errors introduced by the quantization process prior to the encryption, the formation is able to converge to the desired shape. The proposed architecture offers insight on the mechanism for realising distributed control computation in an edge/cloud computer while preserving the privacy of local information coming from each agent.

  • 176.
    Champati, Jaya Prakash
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    Mamduhi, Mohammad H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Gross, James
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    Performance Characterization Using AoI in a Single-loop Networked Control System2019In: IEEE INFOCOM 2019 - IEEE Conference on Computer Communications Workshops, INFOCOM Workshops 2019, IEEE , 2019, p. 197-203Conference paper (Refereed)
    Abstract [en]

    The joint design of control and communication scheduling in a Networked Control System (NCS) is known to be a hard problem. Several research works have successfully designed optimal sampling and/or control strategies under simplified communication models, where transmission delays/times are negligible or fixed. However, considering sophisticated communication models, with random transmission times, result in highly coupled and difficult-to-solve optimal design problems due to the parameter inter-dependencies between estimation/control and communication layers. To tackle this problem, in this work, we investigate the applicability of Age-of-Information (AoI) for solving control/estimation problems in an NCS under i.i.d. transmission times. Our motivation for this investigation stems from the following facts: 1) recent results indicate that AoI can be tackled under relatively sophisticated communication models, and 2) a lower AoI in an NCS may result in a lower estimation/control cost. We study a joint optimization of sampling and scheduling for a single-loop stochastic LTI networked system with the objective of minimizing the time-average squared norm of the estimation error. We first show that, under mild assumptions on information structure the optimal control policy can be designed independently from the sampling and scheduling policies. We then derive a key result that minimizing the estimation error is equivalent to minimizing a non-negative and non-decreasing function of AoI. The parameters of this function include the LTI matrix and the covariance of exogenous noise in the LTI system. Noting that the formulated problem is a stochastic combinatorial optimization problem and is hard to solve, we resort to heuristic algorithms by extending existing algorithms in the AoI literature. We also identify a class of LTI system dynamics for which minimizing the estimation error is equivalent to minimizing the expected AoI.

  • 177. Chan, W. M.
    et al.
    Ghauch, H.
    Kim, T.
    De Carvalho, E.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Research, Kista, Sweden.
    Kolmogorov Model for Large Millimeter-Wave Antenna Arrays: Learning-based Beam-Alignment2019In: Conference Record - Asilomar Conference on Signals, Systems and Computers, Institute of Electrical and Electronics Engineers (IEEE) , 2019, p. 411-415Conference paper (Refereed)
    Abstract [en]

    A new approach is presented to the problem of beam alignment for large-dimensional millimeter-wave antenna systems, with a single radio-frequency chain, based on the application of the Kolmogorov Model (KM) framework to enable learning-based beam alignment. Unlike the conventional exhaustive search-based approach, the proposed KM does not require the entire beam space search, i.e., the number of beam soundings can be extremely smaller than the conventional approach, which is achieved by exploiting the predictive power of KM. We show, across several metrics, that by just sounding 25% of the beams, the proposed method approaches the performance of the exhaustive search method. Simulation results that validate the training and test performance of KM and illustrate the new method with significantly reduced overhead are presented.

  • 178.
    Charalambous, Themistoklis
    et al.
    Aalto Univ, Dept Elect Engn & Automat, Espoo, Finland..
    Kim, Su Min
    Korea Polytech Univ, Dept Elect Engn, Shihung, South Korea..
    Nomikos, Nikolaos
    Univ Aegean, Dept Informat & Commun Syst Engn, Samos, Greece..
    Bengtsson, Mats
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    Johansson, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Relay-pair selection in buffer-aided successive opportunistic relaying using a multi-antenna source2019In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 84, p. 29-41Article in journal (Refereed)
    Abstract [en]

    We study a cooperative network with a buffer-aided multi-antenna source, multiple half-duplex (HD) buffer-aided relays and a single destination. Such a setup could represent a cellular downlink scenario, in which the source can be a more powerful wireless device with a buffer and multiple antennas, while a set of intermediate less powerful devices are used as relays to reach the destination. The main target is to recover the multiplexing loss of the network by having the source and a relay to simultaneously transmit their information to another relay and the destination, respectively. Successive transmissions in such a cooperative network, however, cause inter-relay interference (IRI). First, by assuming global channel state information (CSI), we show that the detrimental effect of IRI can be alleviated by precoding at the source, mitigating or even fully cancelling the interference. A cooperative relaying policy is proposed that employs a joint precoding design and relay-pair selection. Note that both fixed rate and adaptive rate transmissions can be considered. For the case when channel state information is only available at the receiver side (CSIR), we propose a relay selection policy that employs a phase alignment technique to reduce the IRI. The performance of the two proposed relay pair selection policies are evaluated and compared with other state-of-the-art relaying schemes in terms of outage and throughput. The results show that the use of a powerful source can provide considerable performance improvements.

  • 179.
    Charitidou, Maria
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Control of Dynamical Systems subject to Spatio-Temporal Constraints2022Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Over the last decades, autonomous robots have been considered in a variety of applications such  as persistent monitoring, package delivery and cooperative transportation. These applications often require the satisfaction of a set of complex tasks that need to be possibly performed in a timely manner. For example, in search and rescue missions, UAVs are expected to cover a set of regions within predetermined time intervals in order to increase the probability of identifying the victims of an accident. Spatio-temporal tasks of this form can be easily expressed in Signal Temporal Logic (STL), a predicate language that allow us to formally introduce time-constrained tasks such as visit area A between 0 and 5 min or robot 1 should move in a formation with robot 2 until robot 1 reaches region B between 5 and 20 sec.

    Existing approaches in control under spatio-temporal tasks encode the STL constraints using mixed-integer expressions. In the majority of these works, receding horizon schemes are designed and long planning horizons are considered that depend on the temporal constraints of the STL tasks. As a result, the complexity of these problems may increase with the number of the tasks or the length of the time interval within which a STL task needs to be satisfied. Other approaches, consider a limited STL fragment and propose computationally efficient feedback controllers that ensure the satisfaction of the STL task with a minimum, desired robustness. Nevertheless, these approaches do not consider actuation limitations that are always present in real-world systems and thus, yield controllers of arbitrarily large magnitude. 

    In this thesis, we consider the control problem under spatio-temporal constraints for systems that are subject to actuation limitations. In the first part, receding horizon control schemes (RHS) are proposed that ensure the satisfaction or minimal violation of a given set of STL tasks. Contrary to existing approaches, the planning horizon of the RHS scheme can be chosen independent of the STL task and hence, arbitrarily small, given the initial feasibility of the problem. Combining the advantages of the RHS and feedback strategies, we encode the STL tasks using control barrier functions that are designed either online or offline and design controllers that aim at maximizing the robustness of the STL task. The recursive feasibility property of the framework is established and a lower bound on the violation of the STL formula is derived.

    In the next part, we consider a multi-agent system that is subject to a STL task whose satisfaction may involve a large number of agents in the team. Then, the goal is to decompose the global task into local ones the satisfaction of each one of which  depends only on a given sub-team of agents. The proposed decomposition method enables the design of decentralized controllers under local STL tasks avoiding unnecessary communication among agents.  In the last part of the thesis, the coordination problem of multiple platoons is considered and related tasks such as splitting, merging and distance maintenance are expressed as Signal Temporal Logic tasks. Then, feedback control techniques are employed ensuring the satisfaction the STL formula, or alternatively minimal violation in presence of actuation limitations. 

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  • 180.
    Charitidou, Maria
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Control Synthesis for Multi-Agent Systems under Coupled Signal Temporal Logic Tasks: A Top-Down Model Predictive Approach2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nowadays autonomous systems are expected to perform complex tasks that go beyond traditional control objectives such as setpoint tracking or consensus of multi-agent systems. More specifically, in a plethora of applications agents often need to collaborate with their peers in order to perform a variety of spatial tasks within strict deadlines. Spatio-temporal tasks of this form can be easily expressed in Signal Temporal Logic (STL), a predicate language that allow us to formally introduce time-constrained tasks defined as Boolean combinations of simpler subformulas involving temporal operators such as the always, eventually and until operator.

    In this thesis we consider the problem of control under high-level specifications for single as well as multi-agent systems. Our work is divided in three parts. In the first part we consider spatio-temporal objectives expressed in Signal Temporal Logic and propose feedback control laws guaranteeing the satisfaction of the tasks under consideration using various levels of state information. First, motivated by multi-platoon coordination scenarios we design a nonlinear feedback control law ensuring minimal violation of a STL task involving merging and splitting of given pairs of platoons when the satisfaction of the task can not be achieved due to actuation limitations. Next, we propose a novel control barrier function to encode the satisfaction of a STL fragment involving disjunctions of selected STL tasks. As a further contribution, we propose a distributed switching feedback control law for the satisfaction of a given set of relative position-based STL tasks that is based on the prescribed performance control philosophy.

    In the second part model predictive control schemes are designed for single and multi-agent systems subject to STL, input and state constraints. Contrary to state of the art, the proposed approaches encode the satisfaction of the STL tasks under consideration using continuous variables. In addition, the proposed MPC schemes are shown to be recursively feasible thanks to appropriately designed terminal ingredients while the planning horizon of the related  problems can be chosen arbitrarily small and independent of the STL task. To deal with collaborative tasks often present in multi-agent setups we present a novel approach to decompose the tasks into agent-dependent objectives allowing the design of non-cooperative control schemes that guarantee the satisfaction of the initial task with limited communication. Finally, a sequential distributed MPC scheme is proposed for coupled STL tasks offering a desired trade-off between the systems' performance and the computational complexity of previously proposed centralized approaches. The proposed scheme is solved in discrete-time yet continuous-time constraint satisfaction is ensured thanks to an appropriate tightening of the constraint sets.

    Finally, in part III we consider time-invariant objectives such as safety, formation and tracking of single and multiple agents, respectively, and propose a set of feedback control laws ensuring the satisfaction of the desired objectives at all times.

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  • 181.
    Charitidou, Maria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Barrier Function-based Model Predictive Control under Signal Temporal Logic Specifications2021In: Proceedings European Control Conference, ECC 2021, Institute of Electrical and Electronics Engineers (IEEE) , 2021, p. 734-739Conference paper (Refereed)
    Abstract [en]

    In this work a continuous-time MPC scheme is presented for linear systems under Signal Temporal Logic (STL) specifications and input constraints. The satisfaction of the STL specifications is encoded by time-varying barrier functions and a least-violating control law is designed for cases when the satisfaction of the task with a given robustness value is not achieved, e.g., due to actuation limitations. The recursive feasibility of the proposed scheme is guaranteed when a time-varying terminal constraint is introduced. This constraint ensures a desired behavior for the system that guarantees the satisfaction of the task with pre-determined robustness.

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  • 182.
    Charitidou, Maria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Control Barrier Functions for Disjunctions of Signal Temporal Logic Tasks2023In: 2023 European Control Conference, ECC 2023, Institute of Electrical and Electronics Engineers (IEEE) , 2023Conference paper (Refereed)
    Abstract [en]

    In this work we consider the control problem of systems that are subject to disjunctions of Signal Temporal Logic (STL) tasks. Motivated by existing approaches encoding the STL tasks utilizing time-varying control barrier functions (CBFs), we propose a continuously differentiable function for encoding the STL constraints that is defined as the composition of a smooth approximator of the max operator and a set of functions ensuring the satisfaction of the corresponding STL tasks with a desired robustness, and derive conditions for the choice of the class K function (when the latter is considered to be linear) to ensure that the proposed function is a CBF. Then, a control law ensuring the satisfaction of the STL task is found as a solution to a computationally efficient QP.

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  • 183.
    Charitidou, Maria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Distributed MPC With Continuous-Time STL Constraint Satisfaction Guarantees2024In: IEEE Control Systems Letters, E-ISSN 2475-1456, Vol. 8, p. 211-216Article in journal (Refereed)
    Abstract [en]

    In this letter a distributed model predictive control scheme (dMPC) is proposed for a multi-agent team that is subject to a set of time-constrained spatial tasks encoded in Signal Temporal Logic (STL). Here, the agents are subject to both individual and collaborative STL tasks. In order to ensure the satisfaction of the collaborative tasks while avoiding the computational burden of a centralized problem, we propose a sequential dMPC scheme and show the recursive feasibility property of the framework given appropriately designed terminal ingredients. The resulting MPC problems are solved in discrete-time yet continuous-time satisfaction of the STL tasks is ensured with appropriate tightening of the constraint sets.

  • 184.
    Charitidou, Maria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Edge-based funnel control for multi-agent systems using relative position measurements2024Conference paper (Refereed)
    Abstract [en]

    In this work we consider the problem of control under Signal Temporal Logic specifications (STL) that depend on relative position information among neighboring agents. In particular, we consider STL tasks for given pairs of agents whose satisfaction is translated into a set of setpoint output tracking problems with transient and steady-state constraints. Contrary to existing work the proposed framework does not require initial satisfaction of the funnel constraints but can ensure their satisfaction within a pre-specified finite time. Given a tree topology in which agents sharing a STL task form an edge, we show that the resulting control laws ensure the satisfaction of the STL task as well as boundedness of all closed loop signals using only local information.

  • 185.
    Charitidou, Maria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Predictor-based safety control for systems with multiple time-varying delays2022In: IFAC PAPERSONLINE, Elsevier BV , 2022, Vol. 55, no 36, p. 37-42Conference paper (Refereed)
    Abstract [en]

    Control barrier functions (CBFs) have been recently considered for ensuring safety of nonlinear input-affine systems by means of appropriately designed controllers rendering a desired superlevel set of the CBF function forward invariant. In this work, we consider the safety control problem for nonlinear input-affine systems with multiple time-varying input delays. In order to ensure safety, we first design a set of predictors that estimate the state of the system at different future times by utilizing the control laws designed to ensure safety of the delay-free system. Under the assumption of perfect estimation of the future states, we show that under the designed controller, the closed-loop performance of the systems with and without the input delays is the same by the time the input with the largest delay acts on the system with delays for the first time.

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  • 186.
    Charitidou, Maria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Receding Horizon Control with Online Barrier Function Design under Signal Temporal Logic Specifications2023In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 68, no 6, p. 3545-3556Article in journal (Refereed)
    Abstract [en]

    Signal Temporal Logic (STL) has been found an expressive language for describing complex, time-constrained tasks in several robotic applications. Existing methods encode such specifications by either using integer constraints or by employing set invariance techniques. While in the first case this results in MILP control problems, in the latter case designer-specific choices may induce conservatism in the robot's performance and the satisfaction of the task. In this paper a continuous-time receding horizon control scheme (RHS) is proposed that exploits the trade-off between task satisfaction and performance costs such as actuation and state costs, traditionally considered in RHS schemes. The satisfaction of the STL tasks is encoded using time-varying control barrier functions (CBFs) that are designed online, thus avoiding the integer expressions that are often used in literature. The recursive feasibility of the proposed scheme is guaranteed by the satisfaction of a time-varying terminal constraint that ensures the satisfaction of the task with pre-determined robustness. The effectiveness of the method is illustrated in a multi-robot simulation scenario.

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  • 187.
    Charitidou, Maria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Signal Temporal Logic Task Decomposition via Convex Optimization2022In: IEEE Control Systems Letters, E-ISSN 2475-1456, Vol. 6, p. 1238-1243Article in journal (Refereed)
    Abstract [en]

    In this letter we focus on the problem of decomposing a global Signal Temporal Logic formula (STL) assigned to a multi-agent system to local STL tasks when the team of agents is a-priori decomposed to disjoint subteams. The predicate functions associated to the local tasks are parameterized as hypercubes depending on the states of the agents in a given sub-team. The parameters of the functions are, then, found as part of the solution of a convex program that aims implicitly at maximizing the volume of the zero superlevel set of the corresponding predicate function. Two alternative definitions of the local STL tasks are proposed and the satisfaction of the global STL formula is proven when the conjunction of the local STL tasks is satisfied.

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  • 188.
    Charitidou, Maria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Splitting and Merging Control of Multiple Platoons with Signal Temporal Logic2022In: 2022 IEEE Conference on Control Technology and Applications (CCTA), Institute of Electrical and Electronics Engineers (IEEE), 2022, , p. 6p. 1031-1036Conference paper (Refereed)
    Abstract [en]

    Coordination of multiple platoons involves the design of vehicles' trajectories ensuring splitting and merging of different platoons in a safe and energy-optimal manner. In this work, we consider the split-merge-maintain problem between any pair of platoons in which a number of vehicles temporally split from the rest, allowing the vehicles of another platoon to merge, and move with the preceding and following vehicles as a single, large platoon. Here, the splitting, merging and distance-maintaining tasks are expressed in Signal Temporal Logic (STL) and a control barrier function (CBF) is introduced to encode the STL constraints. The control inputs of the vehicles are, then, found as a solution to a computationally efficient, convex, quadratic program. The effectiveness of the proposed method is verified in simulation.

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  • 189.
    Charitidou, Maria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Virtual leader and distance based formation control with funnel constraintsManuscript (preprint) (Other academic)
  • 190.
    Charitidou, Maria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Keviczky, Tamas
    Delft Univ Technol, Delft Ctr Syst & Control, NL-2628 CD Delft, Netherlands..
    An MILP approach for persistent coverage tasks with multiple robots and performance guarantees2022In: European Journal of Control, ISSN 0947-3580, E-ISSN 1435-5671, Vol. 64, article id 100610Article in journal (Refereed)
    Abstract [en]

    Multiple robots are increasingly being considered in a variety of tasks requiring continuous surveillance of a dynamic area, examples of which are environmental monitoring, and search and rescue missions. Motivated by these applications, in this paper we consider the multi-robot persistent coverage control problem over a grid environment. The goal is to ensure a desired lower bound on the coverage level of each cell in the grid, that is decreasing at a given rate for unoccupied cells. We consider a finite set of candidate poses for the agents and introduce a directed graph with nodes representing their admissible poses. We formulate a persistent coverage control problem as a MILP problem that aims to maximize the coverage level of the cells over a finite horizon. To solve the problem, we design a receding horizon scheme (RHS) and prove its recursive feasibility property by introducing a set of time-varying terminal constraints to the problem. These terminal constraints ensure that the agents are always able to terminate their plans in pre-determined closed trajectories. A two-step method is proposed for the construction of the closed trajectories, guaranteeing the satisfaction of the coverage level lower bound constraint, when the resulting closed trajectories are followed repeatedly. Due to the special structure of the problem, agents are able to visit every cell in the grid repeatedly within a worst-case visitation period. Finally, we provide a computational time analysis of the problem for different simulated scenarios and demonstrate the performance of the RHS problem by an illustrative example.

  • 191.
    Chen, Fei
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Cooperative Control of Leader-follower Multi-agent Systems under Transient Constraints2020Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Significant research has been devoted to the problem of distributed consensus or formation control of multi-agent systems in the last decades. These distributed control strategies are designed for all agents and sometimes it may be redundant and costly since the desired tasks may be fulfilled by steering part of the agents through the appropriately designed local control strategy while the other agents can just follow some standard distributed control protocol. Therefore, the leader-follower framework is considered in this thesis, which is meant in the sense that a group of agents with external inputs are selected as leaders in order to drive the group of followers in a way that the entire system can achieve consensus or target formation within certain transient bounds. The followers are only guided through their dynamic couplings with the steered leaders and without any additional control effort.

    The first part of the thesis deals with consensus or formation control for leader-follower multi-agent systems in a distributed manner using a prescribed performance strategy. Both the first and second-order cases are treated. Under the assumption of tree graphs, a distributed control law is proposed for the first-order case when the decay rate of the performance functions is within a sufficient bound. Then, two classes of tree graphs that can have additional followers are investigated. For the second-order case, we propose a distributed control law based on a backstepping approach for the group of leaders to steer the entire system achieving the target formation within the prescribed performance bounds. In the second part, we further discuss the results for general graphs with cycles, which are extended based on the previous results of tree graphs. The extension of general graphs with cycles has more practical applications and offers a complete theory for undirected graphs. In the last part of the thesis, we derive necessary and sufficient conditions for the leader-follower graph topology in order to achieve the desired formation while satisfying the prescribed performance transient bounds. The results developed in this thesis are further verified by several simulation examples.

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  • 192.
    Chen, Fei
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Transient Control for Leader-follower Multi-agent Systems with Application to Spatiotemporal Logic Tasks2023Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Over the past few decades, significant research has been directed towards addressing the problem of distributed control of multi-agent systems. The overall tasks include consensus, formation, flocking, and coverage control with the wide applications in multi-robot coordination, manufacturing and intelligent transportation systems. However, the distributed control strategies are usually for all agents and sometimes it may be redundant and costly since the desired tasks may be fulfilled by steering part of the agents through the appropriately designed local control strategy in a way that allows the whole group to complete the  intended tasks. Therefore, we instead consider a general leader-follower framework in this thesis, which is meant in the sense that a group of agents with external inputs are selected as leaders in order to drive the group of followers in a way that the entire system can achieve consensus or target formation within certain transient bounds. The followers are controlled according to some standard protocols and rely solely on their dynamic couplings with the steered leaders, without requiring any additional control effort and knowledge of the prescribed team bounds.   

    Beyond the traditional considerations of stabilizing and ensuring tracking for multi-agent systems, nowadays more and more applications entail more complex tasks that cannot be easily defined as classic control objectives. Instead, a more advanced level of specification definition is required to address such high-level tasks. Therefore, formal methods based approaches are considered in this thesis in order to specify more complex and high-level task specifications. Signal Temporal Logic (STL), which is based on continuous-time signals, has the added feature of formulating both time and space constraints, and thus provides potentials to deal with quantitative transient constraints for multi-agent systems. 

    In this thesis, we tackle both low-level control and high-level planning of leader-follower multi-agent systems using transient-based approaches. Firstly, in the low-level control part, we consider the classical problem of consensus or formation control for leader-follower multi-agent systems in a distributed manner using a prescribed performance strategy. Both the first and second-order cases are treated. Under the assumption of tree graphs, a distributed control law is proposed for the first-order case when the decay rate of the performance functions is within a sufficient bound. Then, two classes of tree graphs that can have additional followers are investigated. For the second-order case, we propose a distributed control law based on a backstepping approach for the group of leaders to steer the entire system achieving the target formation within the prescribed performance bounds. In the second part, we further discuss the results for general graphs with cycles, which are extended based on the previous results of tree graphs. The extension of general graphs with cycles has more practical applications and offers a complete theory for undirected graphs. In the low-level control part, we finally discuss topological conditions for leader-follower networks such that we can apply previously designed prescribed performance strategy for the leader-follower multi-agent systems to achieve target formation within the transient constraints. Specifically, we derive necessary and sufficient conditions for the leader-follower graph topology in order to achieve the desired formation while satisfying the prescribed performance transient bounds. 

    In the high-level planning part, cooperative control of leader-follower  multi-agent systems subject to certain fragments of STL specifications is considered. We first propose a funnel-based control strategy for the leader-follower multi-agent systems to enforce the satisfaction of the basic STL formulas by prescribing certain transient behavior on the funnels that constrain the closed-loop trajectories. A hybrid control strategy is then leveraged to satisfy the sequential STL formulas. Later on, we consider a large scale leader-follower network which is composed of several leader-follower subsystems with coupled dynamics. Only the leaders know the related STL specifications and are designed in a distributed fashion to drive the followers in a way such that the STL specifications are globally satisfied. Under the local feasibility assumption, we propose a funnel-based control approach for each leader-follower subsystem such that the local STL specifications are achieved, which further implies the global satisfaction of all STL specifications. In order to enforce the satisfaction of the STL formulas, the funnel parameters are appropriately designed to prescribe certain transient behavior that constrains the closed-loop trajectories. 

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    Doctoral Thesis_Fei Chen
  • 193.
    Chen, Fei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Consensus Control for Leader-follower Multi-agent Systems under Prescribed Performance Guarantees2019In: 58th IEEE Conference on Decision and Control (CDC), Institute of Electrical and Electronics Engineers (IEEE) , 2019, p. 4785-4790Conference paper (Refereed)
    Abstract [en]

    This paper addresses the problem of distributed control for leader-follower multi-agent systems under prescribed performance guarantees. Leader-follower is meant in the sense that a group of agents with external inputs are selected as leaders in order to drive the group of followers in a way that the entire system can achieve consensus within certain prescribed performance transient bounds. Under the assumption of tree graphs, a distributed control law is proposed when the decay rate of the performance functions is within a sufficient bound. Then, two classes of tree graphs that can have additional followers are investigated. Finally, several simulation examples are given to illustrate the results.

    Download full text (pdf)
    fulltext
  • 194.
    Chen, Fei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Distributed Control of Coupled Leader-follower Multi-agent Systems under Spatiotemporal Logic Tasks2023Conference paper (Refereed)
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  • 195.
    Chen, Fei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Distributed Control of Coupled Leader-follower Multi-agent Systems under Spatiotemporal Logic Tasks2023In: IFAC-PapersOnLine, Elsevier BV , 2023, Vol. 56, p. 10204-10209Conference paper (Refereed)
    Abstract [en]

    This paper addresses the problem of cooperative control of leader-follower multiagent systems under local signal temporal logic (STL) tasks in a distributed fashion, where the overall system is composed of several leader-follower subsystems with coupled dynamics. In this work, only the leaders know the related STL specifications and are designed to drive the followers in a way such that the STL specifications are globally satisfied. Under the local feasibility assumption, we propose a funnel-based control approach for each leader-follower subsystem such that the local STL specifications are achieved, which further implies the global satisfaction of all STL specifications. In order to enforce the satisfaction of the STL formulas, the funnel parameters are appropriately designed to prescribe certain transient behavior that constrains the closed-loop trajectories. The proposed approach is illustrated by a simulation example.

  • 196.
    Chen, Fei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Funnel-based Cooperative Control of Leader-follower Multi-agent Systems under Signal Temporal Logic Specifications2022In: 2022 EUROPEAN CONTROL CONFERENCE (ECC), IEEE , 2022, p. 906-911Conference paper (Refereed)
    Abstract [en]

    Control of multi-agent systems under temporal logical specifications has been popular due to its ability to tackle complex tasks that cannot be easily defined as classic control objectives. In this paper, a general class of leader-follower  multi-agent systems subject to certain fragments of signal temporal logic (STL) specifications  is considered. We first propose a funnel-based control strategy for the leader-follower multi-agent systems to enforce the satisfaction of the basic STL formulas by prescribing certain transient behavior on the funnels that constrain the closed-loop trajectories. A hybrid control strategy is then leveraged to satisfy the sequential STL formulas. Finally, a simulation example is given to illustrate the results.

    Download full text (pdf)
    fulltext
  • 197.
    Chen, Fei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Further Results on Leader-follower Multi-agent Formation Control with Prescribed Performance Guarantees2020In: IEEE Transactions on Control of Network Systems, Institute of Electrical and Electronics Engineers (IEEE), 2020, p. 4023-4030Conference paper (Refereed)
    Abstract [en]

    Distributed formation control for leader-follower multi-agent systems under prescribed performance guarantees is addressed in this paper. Leader-follower is meant in the sense that a group of agents with external inputs are selected as leaders in order to drive the group of followers in a way that the entire system can achieve the target relative position-based formation within certain prescribed performance transient bounds. In previous work, we have proposed a distributed control law for tree graphs to achieve consensus within certain prescribed transient performance when the decay rate of the performance functions is within a sufficient bound. In this paper, we further discuss the general graphs with cycles. Some necessary conditions on the graph topology are proposed in order to achieve the target formation while satisfying the prescribed performance bounds. We also discuss the roles of the cycles for the convergence benefits in this leader-follower framework. Finally,  we illustrate the results with the simulation examples. 

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  • 198.
    Chen, Fei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Leader-follower Formation Control with Prescribed Performance Guarantees2020In: IEEE Transactions on Control of Network Systems, E-ISSN 2325-5870Article in journal (Refereed)
    Abstract [en]

    This paper addresses the problem of achieving relative position-based formation control for leader-follower multi-agent systems in a distributed manner using a prescribed performance strategy. Both the first and second-order cases are treated and a leader-follower framework is introduced in the sense that a group of agents with external inputs are selected as leaders in order to drive the group of followers in a way that the entire system achieves a target formation within certain prescribed performance transient bounds. Under the assumption of tree graphs, a distributed control law is proposed for the first-order case when the decay rate of the performance functions is within a sufficient bound. Then, two classes of tree graphs that can have additional followers are investigated. For the second-order case, we propose a distributed control law based on a backstepping approach for the group ofleaders to steer the entire system achieving the target formation within the prescribed performance bounds. Finally, several simulation examples are given to illustrate the results.  

    Download full text (pdf)
    fulltext
  • 199.
    Chen, Fei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    On topological conditions for enabling transient control in leader–follower networks2024In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 166, article id 111693Article in journal (Refereed)
    Abstract [en]

    We derive necessary and sufficient conditions for leader–follower multi-agent systems such that we can further apply prescribed performance control to achieve the desired formation while satisfying certain transient constraints. A leader–follower framework is considered in the sense that a group of agents with external inputs are selected as leaders in order to drive the group of followers in a way that the entire system can achieve target formation within certain prescribed performance transient bounds. We first derive necessary conditions on the leader–follower graph topology under which the target formation together with the prescribed performance guarantees can be fulfilled. Afterwards, the derived necessary conditions are extended to necessary and sufficient conditions for leader–follower formation control under transient constraints. Finally, the proposed results are illustrated with simulation examples.

  • 200.
    Chen, Fei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Second Order Consensus for Leader-follower Multi-agent Systems with Prescribed Performance2019In: IFAC PAPERSONLINE, ELSEVIER , 2019, Vol. 52, no 20, p. 103-108Conference paper (Refereed)
    Abstract [en]

    The problem of distributed control for second order leader-follower multi-agent systems with prescribed performance guarantees is investigated in this paper. Leader-follower is meant in the sense that a group of agents with external inputs are selected as leaders in order to drive the group of followers in a way that the entire system can achieve consensus within certain prescribed performance transient bounds. Under the assumption of tree graphs, we propose a distributed control law based on a backstepping approach for the group of leaders to steer the entire system achieving consensus within the prescribed performance bounds. Finally, a simulation example is given to verify the results. 

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