SwePub - sökning: WFRF:(Dimarogonas Dimos V.)

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1.	Marzinotto, Alejandro, et al. (författare) Cooperative grasping through topological object representation 2015 Ingår i: IEEE-RAS International Conference on Humanoid Robots. - : IEEE Computer Society. - 9781479971749 ; , s. 685-692 Konferensbidrag (refereegranskat)abstract We present a cooperative grasping approach based on a topological representation of objects. Using point cloud data we extract loops on objects suitable for generating entanglement. We use the Gauss Linking Integral to derive controllers for multi-agent systems that generate hooking grasps on such loops while minimizing the entanglement between robots. The approach copes well with noisy point cloud data, it is computationally simple and robust. We demonstrate the method for performing object grasping and transportation, through a hooking maneuver, with two coordinated NAO robots.
2.	Teixeira, Pedro V, et al. (författare) Event-based motion coordination of multiple underwater vehicles under disturbances 2010 Konferensbidrag (refereegranskat)abstract The problem of driving a formation from an initial to a target configuration while under the effect of external disturbances is studied. Additional restrictions on agent sensing as well as inter-agent communication must be satisfied. We present a leader-follower solution that relies on a simple uncertainty model to trigger surfacing events. These events are then used to update the control signal, for which two different, provably correct, control strategies are proposed. Finally, we show how the surfacing events can be used to characterize the disturbance set. Numerical examples on relevant scenarios are also provided.
3.	Teixeira, Pedro V., et al. (författare) Multi-agent coordination with event-based communication 2010 Ingår i: Proceedings of the American Control Conference. - : IEEE. - 9781424474264 ; , s. 824-829 Konferensbidrag (refereegranskat)abstract The problem of driving a set of vehicles (agents) to a desired target configuration under event-based communication and measurement constraints is analyzed. We start by studying the single agent problem, where we propose a waypoint based solution, along with two alternative control strategies. After deriving their properties and proving some relevant results, we proceed to study the two agent case. We generalize the results obtained for this network to the multi agent network. Our strategy is able to position each agent within a given distance of its target while satisfying the constraints. We provide some numerical examples for relevant scenarios.
4.	Adaldo, Antonio, et al. (författare) Cloud-supported effective coverage of 3D structures 2018 Ingår i: 2018 European Control Conference, ECC 2018. - : Institute of Electrical and Electronics Engineers (IEEE). - 9783952426982 ; , s. 95-100 Konferensbidrag (refereegranskat)abstract In this paper, we present a distributed algorithm for cloud-supported effective coverage of 3D structures with a network of sensing agents. The structure to inspect is abstracted into a set of landmarks, where each landmark represents a point or small area of interest, and incorporates information about position and orientation. The agents navigate the environment following the proposed control algorithm until all landmarks have reached a satisfactory level of coverage. The agents do not communicate with each other directly, but exchange data through a shared cloud repository which is accessed asynchronously and intermittently. We show formally that, under the proposed control architecture, the networked agents complete the coverage mission in finite time. The results are corroborated by simulations in ROS, and experimental evaluation is in progress.
5.	Adaldo, Antonio, et al. (författare) Cloud-Supported Formation Control of Second-Order Multiagent Systems 2018 Ingår i: IEEE Transactions on Control of Network Systems. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2325-5870. ; 5:4, s. 1563-1574 Tidskriftsartikel (refereegranskat)abstract This paper addresses a formation problem for a network of autonomous agents with second-order dynamics and bounded disturbances. Coordination is achieved by having the agents asynchronously upload (download) data to (from) a shared repository, rather than directly exchanging data with other agents. Well-posedness of the closed-loop system is demonstrated by showing that there exists a lower bound for the time interval between two consecutive agent accesses to the repository. Numerical simulations corroborate the theoretical results.
6.	Adaldo, Antonio, 1989-, et al. (författare) Control of Multi-Agent Systems with Event-Triggered Cloud Access 2015 Ingår i: Proceedings of the 14th annual European Control Conference. - : IEEE. - 9783952426937 ; , s. 954-961 Konferensbidrag (refereegranskat)abstract This paper investigates a multi-agent formation control problem with event-triggered control updates and additive disturbances. The agents communicate only by exchanging information in a cloud repository. The communication with the cloud is considered a shared and limited resource, and therefore it is used intermittently and asynchronously by the agents. The proposed approach takes advantage of having a shared asynchronous cloud support while guaranteeing a reduced number of communication. More in detail, each agent schedules its own sequence of cloud accesses in order to achieve a coordinated network goal. A control law is given with a criterion for scheduling the control updates recursively. The closed loop scheme is proven to be effective in achieving the control objective and a numerical simulation corroborates the theoretical results.
7.	Adaldo, Antonio, et al. (författare) Cooperative coverage for surveillance of 3D structures 2017 Ingår i: IEEE International Conference on Intelligent Robots and Systems. - Piscataway, NJ : Institute of Electrical and Electronics Engineers (IEEE). - 9781538626825 ; , s. 1838-1845 Konferensbidrag (refereegranskat)abstract In this article, we propose a planning algorithm for coverage of complex structures with a network of robotic sensing agents, with multi-robot surveillance missions as our main motivating application. The sensors are deployed to monitor the external surface of a 3D structure. The algorithm controls the motion of each sensor so that a measure of the collective coverage attained by the network is nondecreasing, while the sensors converge to an equilibrium configuration. A modified version of the algorithm is also provided to introduce collision avoidance properties. The effectiveness of the algorithm is demonstrated in a simulation and validated experimentally by executing the planned paths on an aerial robot.
8.	Adaldo, Antonio, et al. (författare) Coordination of multi-agent systems with intermittent access to a cloud repository 2017 Ingår i: Workshop on Sensing and Control for Autonomous Vehicles. - Cham : Springer. - 9783319553719 ; , s. 453-471 Konferensbidrag (refereegranskat)abstract A cloud-supported multi-agent system is composed of autonomous agents required to achieve a common coordination objective by exchanging data over a shared cloud repository. The repository is accessed asychronously by different agents, and direct inter-agent commuication is not possible. This model is motivated by the problem of coordinating a fleet of autonomous underwater vehicles, with the aim to avoid the use of expensive and power-hungry modems for underwater communication. For the case of agents with integrator dynamics, a control law and a rule for scheduling the cloud access are formally defined and proven to achieve the desired coordination. A numerical simulation corroborate the theoretical results.
9.	Adaldo, Antonio, 1989-, et al. (författare) Event-triggered pinning control of complex networks with switching topologies 2014 Ingår i: Proceedings of the 53rd annual IEEE Conference on Decision and Control. - 9781479977468 ; , s. 2783-2788 Konferensbidrag (refereegranskat)abstract This paper investigates the problem of eventtriggered pinning control for the synchronization of networks of nonlinear dynamical agents onto a desired reference trajectory. The pinned agents are those that have access to the reference trajectory. We consider both static and switching topologies. We prove that the system is well posed and identify conditions under which the network achieves exponential convergence. A lower bound for the rate of convergence is also derived. Numerical examples demonstrating the effectiveness of the results are provided.
10.	Adaldo, Antonio, 1989-, et al. (författare) Event-Triggered Pinning Control of Switching Networks 2015 Ingår i: IEEE Transactions on Control of Network Systems. - 2325-5870. ; 2:2, s. 204-213 Tidskriftsartikel (refereegranskat)abstract This paper investigates event-triggered pinning control for the synchronization of complex networks of nonlinear dynamical systems. We consider networks described by time-varying weighted graphs and featuring generic linear interaction protocols. Sufficient conditions for the absence of Zeno behavior are derived and exponential convergence of a global normed error function is proven. Static networks are considered as a special case, wherein the existence of a lower bound for interevent times is also proven. Numerical examples demonstrate the effectiveness of the proposed control strategy.
11.	Adaldo, Antonio, et al. (författare) Hybrid coverage and inspection control for anisotropic mobile sensor teams 2017 Ingår i: IFAC-PapersOnLine. - : Elsevier. - 2405-8963. ; 50:1, s. 613-618 Tidskriftsartikel (refereegranskat)abstract In this paper, we present an algorithm for pose control of a team of mobile sensors for coverage and inspection applications. The region to cover is abstracted into a finite set of landmarks, and each sensor is responsible to cover some of the landmarks. The sensors progressively improve their coverage by adjusting their poses and by transferring the ownership of some landmarks to each other. Inter-sensor communication is pairwise and intermittent. The sensor team is formally modeled as a multi-agent hybrid system, and an invariance argument formally shows that the team reaches an equilibrium configuration, while a global coverage measure is improving monotonically. A numerical simulation corroborates the theoretical results.
12.	Adaldo, Antonio, et al. (författare) Multi-Agent Trajectory Tracking with Self-Triggered Cloud Access 2016 Ingår i: 2016 IEEE 55th Conference on Decision and Control, CDC 2016. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509018376 ; , s. 2207-2214 Konferensbidrag (refereegranskat)abstract This paper presents a cloud-supported control algorithm for coordinated trajectory tracking of networked autonomous agents. The motivating application is the coordinated control of Autonomous Underwater Vehicles. The control objective is to have the vehicles track a reference trajectory while keeping an assigned formation. Rather than relying on inter-agent communication, which is interdicted underwater, coordination is achieved by letting the agents intermittently access a shared information repository hosted on a cloud. An event-based law is proposed to schedule the accesses of each agent to the cloud. We show that, with the proposed scheduling of the cloud accesses, the agents achieve the required coordination objective. Numerical simulations corroborate the theoretical results.
13.	Ahlberg, Sofie, et al. (författare) Co-adaptive Human-Robot Cooperation : Summary and Challenges 2022 Ingår i: Unmanned Systems. - : World Scientific Pub Co Pte Ltd. - 2301-3850 .- 2301-3869. ; 10:02, s. 187-203 Tidskriftsartikel (refereegranskat)abstract The work presented here is a culmination of developments within the Swedish project COIN: Co-adaptive human-robot interactive systems, funded by the Swedish Foundation for Strategic Research (SSF), which addresses a unified framework for co-adaptive methodologies in human-robot co-existence. We investigate co-adaptation in the context of safe planning/control, trust, and multi-modal human-robot interactions, and present novel methods that allow humans and robots to adapt to one another and discuss directions for future work.
14.	Ahlberg, Sofie, et al. (författare) Human-in-the-loop control synthesis for multi-agent systems under hard and soft metric interval temporal logic specifications∗ 2019 Ingår i: Proceedings 15th IEEE International Conference on Automation Science and Engineering, CASE 2019. - : IEEE Computer Society. - 9781728103563 - 9781728103570 ; , s. 788-793 Konferensbidrag (refereegranskat)abstract In this paper we present a control synthesis framework for a multi-agent system under hard and soft constraints, which performs online re-planning to achieve collision avoidance and execution of the optimal path with respect to some human preference considering the type of the violation of the soft constraints. The human preference is indicated by a mixed initiative controller and the resulting change of trajectory is used by an inverse reinforcement learning based algorithm to improve the path which the affected agent tries to follow. A case study is presented to validate the result.
15.	Ahlberg, Sofie, et al. (författare) Human in the Loop Least Violating Robot Control Synthesis under Metric Interval Temporal Logic Specifications 2018 Ingår i: 2018 European Control Conference, ECC 2018. - : Institute of Electrical and Electronics Engineers (IEEE). - 9783952426982 ; , s. 453-458 Konferensbidrag (refereegranskat)abstract Recently, multiple frameworks for control synthesis under temporal logic have been suggested. The frameworks allow a user to give one or a set of robots high level tasks of different properties (e.g. temporal, time limited, individual and cooperative). However, the issue of how to handle tasks, which either seem to be or are infeasible, remains unsolved. In this paper we introduce a human to the loop, using the human's feedback to determine preference towards different types of violations of the tasks. We introduce a metric of violation called hybrid distance. We also suggest a novel framework for synthesizing a least violating controller with respect to the hybrid distance and the human feedback. Simulation result indicate that the suggested framework gives reasonable estimates of the metric, and that the suggested plans correspond to the expected ones.
16.	Ahlberg, Sofie, et al. (författare) Mixed-Initiative Control Synthesis: Estimating an Unknown Task Based on Human Control Input 2020 Ingår i: Proceedings of the 3rd IFAC Workshop on Cyber-Physical & Human Systems. - : Elsevier BV. Konferensbidrag (refereegranskat)abstract In this paper we consider a mobile platform controlled by two entities; an autonomousagent and a human user. The human aims for the mobile platform to complete a task, whichwe will denote as the human task, and will impose a control input accordingly, while not beingaware of any other tasks the system should or must execute. The autonomous agent will in turnplan its control input taking in consideration all safety requirements which must be met, sometask which should be completed as much as possible (denoted as the robot task), as well aswhat it believes the human task is based on previous human control input. A framework for theautonomous agent and a mixed initiative controller are designed to guarantee the satisfaction ofthe safety requirements while both the human and robot tasks are violated as little as possible.The framework includes an estimation algorithm of the human task which will improve witheach cycle, eventually converging to a task which is similar to the actual human task. Hence, theautonomous agent will eventually be able to find the optimal plan considering all tasks and thehuman will have no need to interfere again. The process is illustrated with a simulated example
17.	Aladele, Victor, et al. (författare) An Adaptive Cooperative Manipulation Control Framework for Multi-Agent Disturbance Rejection 2022 Ingår i: 2022 IEEE 61ST CONFERENCE ON DECISION AND CONTROL (CDC). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 100-106 Konferensbidrag (refereegranskat)abstract The success of a cooperative manipulation process depends on the level of disturbance rejection between the cooperating agents. However, this attribute may be jeopardized due to unexpected behaviors, such as joint saturation or internal collisions. This leads to deterioration in the performance of the manipulation task. In this paper, we present an adaptive distributed control framework that directly mitigates these internal disturbances, both in the joint (and task) spaces. With our approach, we show that including the manipulator-load coupling in the definition of the task error yields improved performance and robustness. To validate this statement, we provide stability guarantees and simulation results for two implementation cases.
18.	Alanwar, Amr, et al. (författare) Enhancing Data-Driven Reachability Analysis using Temporal Logic Side Information 2022 Ingår i: Proceedings. - : Institute of Electrical and Electronics Engineers Inc.. Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract This paper presents algorithms for performingdata-driven reachability analysis under temporal logic sideinformation. In certain scenarios, the data-driven reachablesets of a robot can be prohibitively conservative due to theinherent noise in the robot’s historical measurement data. Inthe same scenarios, we often have side information about therobot’s expected motion (e.g., limits on how much a robotcan move in a one-time step) that could be useful for furtherspecifying the reachability analysis. In this work, we showthat if we can model this side information using a signaltemporal logic (STL) fragment, we can constrain the datadriven reachability analysis and safely limit the conservatismof the computed reachable sets. Moreover, we provide formalguarantees that, even after incorporating side information, thecomputed reachable sets still properly over-approximate therobot’s future states. Lastly, we empirically validate the practicality of the over-approximation by computing constrained,data-driven reachable sets for the Small-Vehicles-for-Autonomy(SVEA) hardware platform in two driving scenarios.
19.	Alexandre, Seuret, et al. (författare) Consensus of Double Integrator Multi-agents under Communication Delay 2009 Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - : Elsevier BV. - 1474-6670. ; , s. 376-381 Konferensbidrag (refereegranskat)abstract This paper deals with the consensus problem under network induced communication delays. It is well-known that introducing a delay generally leads to a reduce of the performance or to instability. Thus, investigating the impact of time-delays in the consensus problem is an important issue. Another important issue is to obtain an estimate of the convergence rate, which is not straightforward when delays appear in the network. In this paper, the agents are modelled as double integrator systems. It is assumed that each agent receives instantaneously its own output information but receives the information from its neighbors after a constant delay. A stability criterion is provided based on Lyapunov-Krasovskii techniques and is expressed in terms of LMI. An expression of the consensus equilibrium which depends on the delay and on the initial conditions taken in an interval is derived. The results are supported through several simulations for different network symmetric communication schemes.
20.	Anderson, R. P., et al. (författare) Self-triggered sampling for second-moment stability of state-feedback controlled SDE systems 2015 Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 54, s. 8-15 Tidskriftsartikel (refereegranskat)abstract Event-triggered and self-triggered control, whereby the times for controller updates are computed from sampled data, have recently been shown to reduce the computational load or increase task periods for real-time embedded control systems. In this work, we propose a self-triggered scheme for nonlinear controlled stochastic differential equations with additive noise terms. We find that the family of trajectories generated by these processes demands a departure from the standard deterministic approach to event- and self-triggering, and, for that reason, we use the statistics of the sampled-data system to derive a self-triggering update condition that guarantees second-moment stability. We show that the length of the times between controller updates as computed from the proposed scheme is strictly positive and provide related examples.
21.	Anderson, R. P., et al. (författare) Self-triggered stabilization of continuous stochastic state-feedback controlled systems 2013 Ingår i: 2013 European Control Conference, ECC 2013. - : IEEE. - 9783033039629 ; , s. 1151-1155 Konferensbidrag (refereegranskat)abstract Event-triggered and self-triggered control, in which the time of update to the controls is based on either current or outdated sampled data, have recently been employed to reduce the computational load or resource consumption for distributed real-time control systems. In this work, we propose a self-triggered scheme for nonlinear controlled stochastic differential equations with additive noise terms. A self-triggering update condition is derived that guarantees stability in the p-th moment of the state distribution. We show that the length of the times between controller updates as computed from the proposed scheme is strictly positive and provide examples.
22.	Andersson, Sofie, et al. (författare) Control Synthesis for Multi-Agent Systems under Metric Interval Temporal Logic Specifications 2017 Ingår i: IFAC-PapersOnLine. - : Elsevier. - 2405-8963. ; , s. 2397-2402 Konferensbidrag (refereegranskat)abstract This paper presents a framework for automatic synthesis of a control sequence for multi-agent systems governed by continuous linear dynamics under timed constraints. First, the motion of the agents in the workspace is abstracted into individual Transition Systems (TS). Second, each agent is assigned with an individual formula given in Metric Interval Temporal Logic (MITL) and in parallel, the team of agents is assigned with a collaborative team formula. The proposed method is based on a correct-by-construction control synthesis method, and hence guarantees that the resulting closed-loop system will satisfy the desired specifications. The specifications considers boolean-valued properties under real-time bounds. Extended simulations has been performed in order to demonstrate the efficiency of the proposed methodology.
23.	Andreasson, Martin, 1987-, et al. (författare) Control of MTDC Transmission Systems under Local Information 2014 Ingår i: Decision and Control (CDC), 2014 IEEE 53rd Annual Conference on. - : IEEE conference proceedings. - 9781479977468 ; , s. 1335-1340 Konferensbidrag (refereegranskat)abstract High-voltage direct current (HVDC) is a commonly used technology for long-distance electric power transmission, mainly due to its low resistive losses. In this paper a distributed controller for multi-terminal high-voltage direct current (MTDC) transmission systems is considered. Sufficient conditions for when the proposed controller renders the closed-loop system asymptotically stable are provided. Provided that the closed loop system is asymptotically stable, it is shown that in steady-state a weighted average of the deviations from the nominal voltages is zero. Furthermore, a quadratic cost of the current injections is minimized asymptotically.
24.	Andreasson, Martin, et al. (författare) Distributed Control of Networked Dynamical Systems : Static Feedback, Integral Action and Consensus 2014 Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 59:7, s. 1750-1764 Tidskriftsartikel (refereegranskat)abstract This paper analyzes distributed control protocols for first- and second-order networked dynamical systems. We propose a class of nonlinear consensus controllers where the input of each agent can be written as a product of a nonlinear gain, and a sum of nonlinear interaction functions. By using integral Lyapunov functions, we prove the stability of the proposed control protocols, and explicitly characterize the equilibrium set. We also propose a distributed proportional-integral (PI) controller for networked dynamical systems. The PI controllers successfully attenuate constant disturbances in the network. We prove that agents with single-integrator dynamics are stable for any integral gain, and give an explicit tight upper bound on the integral gain for when the system is stable for agents with double-integrator dynamics. Throughout the paper we highlight some possible applications of the proposed controllers by realistic simulations of autonomous satellites, power systems and building temperature control.
25.	Andreasson, Martin, 1987-, et al. (författare) Distributed controllers for multiterminal HVDC transmission systems 2017 Ingår i: IEEE Transactions on Control of Network Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 2325-5870. ; 4:3, s. 564-574 Tidskriftsartikel (refereegranskat)abstract High-voltage direct current (HVDC) is a commonly used technology for long-distance electric power transmission, mainly due to its low resistive losses. In this paper the voltagedroop method (VDM) is reviewed, and three novel distributed controllers for multi-terminal HVDC (MTDC) transmission systems are proposed. Sufficient conditions for when the proposed controllers render the closed-loop system asymptotically stable are provided. These conditions give insight into suitable controller architecture, e.g., that the communication graph should be identical with the graph of the MTDC system, including edge weights. Provided that the closed-loop systems are asymptotically stable, it is shown that the voltages asymptotically converge to within predefined bounds. Furthermore, a quadratic cost of the injected currents is asymptotically minimized. The proposed controllers are evaluated on a four-bus MTDC system.
26.	Andreasson, Martin, et al. (författare) Distributed Frequency Control Through MTDC Transmission Systems 2017 Ingår i: IEEE Transactions on Power Systems. - : IEEE Press. - 0885-8950 .- 1558-0679. ; 32:1, s. 250-260 Tidskriftsartikel (refereegranskat)abstract In this paper, we propose distributed dynamic controllers for sharing both frequency containment and restoration reserves of asynchronous ac systems connected through a multi-terminal HVDC (MTDC) grid. The communication structure of the controller is distributed in the sense that only local and neighboring state information is needed, rather than the complete state. We derive sufficient stability conditions, which guarantee that the ac frequencies converge to the nominal frequency. Simultaneously, a global quadratic power generation cost function is minimized. The proposed controller also regulates the voltages of the MTDC grid, asymptotically minimizing a quadratic cost function of the deviations from the nominal dc voltages. The results are valid for distributed cable models of the HVDC grid (e.g., $\pi$-links), as well as ac systems of arbitrary number of synchronous machines, each modeled by the swing equation. We also propose a decentralized communication-free version of the controller. The proposed controllers are tested on a high-order dynamic model of a power system consisting of asynchronous ac grids, modeled as IEEE 14 bus networks, connected through a six-terminal HVDC grid. The performance of the controller is successfully evaluated through simulation.
27.	Andreasson, Martin, et al. (författare) Distributed integral action : stability analysis and frequency control of power systems 2012 Ingår i: 2012 IEEE 51st Annual Conference on Decision and Control (CDC). - : IEEE. - 9781467320665 ; , s. 2077-2083 Konferensbidrag (refereegranskat)abstract This paper analyzes distributed proportional-integral controllers. We prove that integral action can be successfully applied to consensus algorithms, where attenuation of static disturbances is achieved. These control algorithms are applied to decentralized frequency control of electrical power systems. We show that the proposed algorithm can attenuate step disturbances of power loads. We provide simulations of the proposed control algorithm on the IEEE 30 bus test system that demonstrate its efficiency.
28.	Andreasson, Martin, et al. (författare) Distributed PI-Control with Applications to Power Systems Frequency Control 2014 Ingår i: American Control Conference (ACC), 2014. - : IEEE conference proceedings. - 9781479932740 ; , s. 3183-3188 Konferensbidrag (refereegranskat)abstract This paper considers a distributed PI-controller for networked dynamical systems. Sufficient conditions for when the controller is able to stabilize a general linear system and eliminate static control errors are presented. The proposed controller is applied to frequency control of power transmission systems. Sufficient stability criteria are derived, and it is shown that the controller parameters can always be chosen so that the frequencies in the closed loop converge to nominal operational frequency. We show that the load sharing property of the generators is maintained, i.e., the input power of the generators is proportional to a controller parameter. The controller is evaluated by simulation on the IEEE 30 bus test network, where its effectiveness is demonstrated.
29.	Andreasson, Martin, 1987-, et al. (författare) Distributed Primary Frequency Control through Multi-Terminal HVDC Transmission Systems 2015 Ingår i: American Control Conference (ACC), 2015. - : IEEE conference proceedings. - 9781479986859 ; , s. 5029-5034 Konferensbidrag (refereegranskat)abstract This paper presents a decentralized controller for sharing primary AC frequency control reserves through a multi-terminal HVDC grid. By using passivity arguments, the proposed controller is shown to stabilize the closed-loop system consisting of the interconnected AC and HVDC grids, given any positive controller gains. The static control errors resulting from the proportional controller are quantified and bounded by analyzing the equilibrium of the closed-loop system. The proposed controller is applied to a test grid consisting of three asynchronous AC areas interconnected by an HVDC grid, and its effectiveness is validated through simulation.
30.	Andreasson, Martin, 1987-, et al. (författare) Distributed Secondary Frequency Control through MTDC Transmission Systems 2015 Ingår i: Decision and Control (CDC), 2015 IEEE 54th Annual Conference on. - : IEEE conference proceedings. - 9781479978847 ; , s. 2627-2634 Konferensbidrag (refereegranskat)abstract In this paper, we present distributed controllers for sharing primary and secondary frequency control reserves for asynchronous AC transmission systems, which are connected through a multi-terminal HVDC grid. By using passivity arguments, the equilibria of the closed-loop system are shown to be globally asymptotically stable. We quantify the static errors of the voltages and frequencies, and give upper bounds for these errors. It is also shown that the controllers have the property of power sharing, i.e., primary and secondary frequency control reserves are shared fairly amongst the AC systems. The proposed controllers are applied to a high-order dynamic model of of a power system consisting of asynchronous AC grids connected through a 6-terminal HVDC grid.
31.	Andreasson, Martin, 1987-, et al. (författare) Distributed Voltage and Current Control of Multi-Terminal High-Voltage Direct Current Transmission Systems 2014 Ingår i: Proceedings of the 19th IFAC World Congress, 2014. - : IFAC Papers Online. ; , s. 11910-11916 Konferensbidrag (refereegranskat)abstract High-voltage direct current (HVDC) is a commonly used technology for long-distance power transmission, due to its low resistive losses and low costs. In this paper, a novel distributed controller for multi-terminal HVDC (MTDC) systems is proposed. Under certain conditions on the controller gains, it is shown to stabilize the MTDC system. The controller is shown to always keep the voltages close to the nominal voltage, while assuring that the injected power is shared fairly among the converters. The theoretical results are validated by simulations, where the affect of communication time-delays is also studied.
32.	Andreasson, Martin, 1987-, et al. (författare) Distributed vs. centralized power systems frequency control 2013 Ingår i: 2013 European Control Conference, ECC 2013. - : IEEE. - 9783033039629 ; , s. 3524-3529 Konferensbidrag (refereegranskat)abstract This paper considers a distributed control algorithm for frequency control of electrical power systems. We propose a distributed controller which retains the reference frequency of the buses under unknown load changes, while asymptotically minimizing a quadratic cost of power generation. For comparison, we also propose a centralized controller which also retains the reference frequency while minimizing the same cost of power generation. We derive sufficient stability criteria for the parameters of both controllers. The controllers are evaluated by simulation on the IEEE 30 bus test network, where their performance is compared.
33.	Andreasson, Martin, 1987-, et al. (författare) Undamped Nonlinear Consensus Using Integral Lyapunov Functions 2012 Ingår i: 2012 American Control Conference (ACC). - : IEEE Computer Society. - 9781457710964 ; , s. 6644-6649 Konferensbidrag (refereegranskat)abstract This paper analyzes a class of nonlinear consensus algorithms where the input of an agent can be decoupled into a product of a gain function of the agents own state, and a sum of interaction functions of the relative states of its neighbors. We prove the stability of the protocol for both single and double integrator dynamics using novel Lyapunov functions, and provide explicit formulas for the consensus points. The results are demonstrated through simulations of a realistic example within the framework of our proposed consensus algorithm.
34.	Aragues, R., et al. (författare) Distributed algebraic connectivity estimation for adaptive event-triggered consensus 2012 Ingår i: American Control Conference (ACC), 2012. - : IEEE. - 9781457710957 ; , s. 32-37 Konferensbidrag (refereegranskat)abstract In several multi agent control problems, the convergence properties and speed of the system depend on the algebraic connectivity of the graph. We discuss a particular event-triggered consensus scenario, and show that the availability of an estimate of the algebraic connectivity could be used for adapting the behavior of the average consensus algorithm. We present a novel distributed algorithm for estimating the algebraic connectivity, that relies on the distributed computation of the powers of matrices. We provide proofs of convergence, convergence rate, and upper and lower bounds at each iteration of the estimated algebraic connectivity.
35.	Aragues, Rosario, et al. (författare) Distributed algebraic connectivity estimation for undirected graphs with upper and lower bounds 2014 Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 50:12, s. 3253-3259 Tidskriftsartikel (refereegranskat)abstract The algebraic connectivity of the graph Laplacian plays an essential role in various multi-agent control systems. In many cases a lower bound of this algebraic connectivity is necessary in order to achieve a certain performance. Lately, several methods based on distributed Power Iteration have been proposed for computing the algebraic connectivity of a symmetric Laplacian matrix. However, these methods cannot give any lower bound of the algebraic connectivity and their convergence rates are often unclear. In this paper, we present a distributed algorithm for estimating the algebraic connectivity for undirected graphs with symmetric Laplacian matrices. Our method relies on the distributed computation of the powers of the adjacency matrix and its main interest is that, at each iteration, agents obtain both upper and lower bounds for the true algebraic connectivity. Both bounds successively approach the true algebraic connectivity with the convergence speed no slower than O(1/k).
36.	Aragues, Rosario, et al. (författare) Intermittent Connectivity Maintenance With Heterogeneous Robots 2021 Ingår i: IEEE Transactions on robotics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1552-3098 .- 1941-0468. ; 37:1, s. 225-245 Tidskriftsartikel (refereegranskat)abstract In this article, we consider a scenario of cooperative task servicing, with a team of heterogeneous robots with different maximum speeds and communication radii, in charge of keeping the network intermittently connected. We abstract the task locations into a one-dimensional cycle graph that is traversed by the communicating robots, and we discuss intermittent communication strategies so that each task location is periodically visited, with a worst-case revisiting time. Robots move forward and backward along the cycle graph, exchanging data with their previous and next neighbors when they meet, and updating their region boundaries. Asymptotically, each robot is in charge of a region of the cycle graph, depending on its capabilities. The method is distributed, and robots only exchange data when they meet.
37.	Aragues, R., et al. (författare) Intermittent connectivity maintenance with heterogeneous robots using a beads-on-a-ring strategy 2019 Ingår i: Proceedings of the American Control Conference. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538679265 ; , s. 120-126 Konferensbidrag (refereegranskat)abstract We consider a scenario of cooperative task servicing, with a team of heterogeneous robots with different maximum speeds and communication radii, in charge of keeping the network intermittently connected. We abstract the task locations into a 1D cycle graph that is traversed by the communicating robots, and we discuss intermittent communication strategies so that each task location is periodically visited, with a worst-case revisiting time. Robots move forward and backward along the cycle graph, exchanging data with their previous and next neighbors when they meet, and updating their region boundaries. Asymptotically, each robot is in charge of a region of the cycle graph, depending on its capabilities. The method is distributed, and robots only exchange data when they meet.
38.	Baran, Robin, et al. (författare) A ROS Package for Human-In-the-Loop Planning and Control under Linear Temporal Logic Tasks 2021 Ingår i: IEEE International Conference on Automation Science and Engineering. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 2182-2187 Konferensbidrag (refereegranskat)abstract In this paper, we propose a ROS software package for planning and control of robotic systems with a human-in-the-Ioop focus. The software uses temporal logic specifications, specifically Linear Temporal Logic, for a language-based method to develop correct-by-design high level robot plans. The approach is structured to allow a human to adjust the high-level plan online. A human may also take control of the robot (in a low-level control fashion), but the software prevents the human from implementing dangerous behaviour that would violate the high-level task specification. Finally, the planner is able to learn human-preferred high-level tasks by tracking human low-level control inputs in an inverse learning framework. The proposed approach is demonstrated in a warehouse setting with multiple robot agents to showcase the efficacy of the proposed solution.
39.	Barbosa, Fernando S., et al. (författare) Integrated motion planning and control under metric interval temporal logic specifications 2019 Ingår i: 2019 18th European Control Conference, ECC 2019. - : Institute of Electrical and Electronics Engineers (IEEE). - 9783907144008 ; , s. 2042-2049 Konferensbidrag (refereegranskat)abstract This paper proposes an approach that combines motion planning and hybrid feedback control design in order to find and follow trajectories fulfilling a given complex mission involving time constraints. We use Metric Interval Temporal Logic (MITL) as a rich and rigorous formalism to specify such missions. The solution builds on three main steps: (i) using sampling-based motion planning methods and the untimed version of the mission specification in the form of Zone automaton, we find a sequence of waypoints in the workspace; (ii) based on the clock zones from the satisfying run on the Zone automaton, we compute time-stamps at which these waypoints should be reached; and (iii) to control the system to connect two waypoints in the desired time, we design a low-level feedback controller leveraging Time-varying Control Barrier Functions. Illustrative simulation results are included.
40.	Barbosa, Fernando S., 1992-, et al. (författare) Provably safe control of Lagrangian systems in obstacle-scattered environments 2020 Ingår i: 2020 59th IEEE Conference on Decision and Control (CDC). - : Institute of Electrical and Electronics Engineers (IEEE). Konferensbidrag (refereegranskat)abstract We propose a hybrid feedback control law that guarantees both safety and asymptotic stability for a class of Lagrangian systems in environments with obstacles. Rather than performing trajectory planning and implementing a trajectory-tracking feedback control law, our approach requires a sequence of locations in the environment (a path plan) and an abstraction of the obstacle-free space. The problem of following a path plan is then interpreted as a sequence of reach-avoid problems: the system is required to consecutively reach each location of the path plan while staying within safe regions. Obstacle-free ellipsoids are used as a way of defining such safe regions, each of which encloses two consecutive locations. Feasible Control Barrier Functions (CBFs) are created directly from geometric constraints, the ellipsoids, ensuring forward-invariance, and therefore safety. Reachability to each location is guaranteed by asymptotically stabilizing Control Lyapunov Functions (CLFs). Both CBFs and CLFs are then encoded into quadratic programs (QPs) without the need of relaxation variables. Furthermore, we also propose a switching mechanism that guarantees the control law is correct and well-defined even when transitioning between QPs. Simulations show the effectiveness of the proposed approach in two complex scenarios.
41.	Bechlioulis, C. P., et al. (författare) Robust control of large vehicular platoons with prescribed transient and steady state performance 2014 Ingår i: Proceedings of the IEEE Conference on Decision and Control. - : IEEE conference proceedings. ; , s. 3689-3694 Konferensbidrag (refereegranskat)abstract In this paper, we consider the longitudinal control problem for a platoon of vehicles with unknown nonlinear dynamics. More specifically, we design a decentralized model-free control protocol in the sense that each vehicle utilizes only local relative information regarding its front vehicle, obtained by its on-board sensors, to calculate its own control signal, without incorporating any prior knowledge of the model nonlinearities/disturbances or any approximation structures to acquire such knowledge. Additionally, the transient and steady state response is a priori determined by certain designer-specified performance functions and is fully decoupled by the agents' dynamic model, the number of vehicles composing the platoon and the control gains selection, which relaxes significantly the control design procedure. Moreover, introducing certain inter-vehicular distance constraints during the transient response shaping, collisions between successive vehicles as well as connectivity breaks owing to limited sensing capabilities are provably avoided. Finally, the proposed methodology results in a low complexity design. Actually, it is a static scheme involving very few and simple calculations to output the control signal, thus making its distributed implementation straightforward.
42.	Berkane, Soulaimane, et al. (författare) A hybrid controller for obstacle avoidance in an n-dimensional euclidean space 2019 Ingår i: 2019 18th European Control Conference, ECC 2019. - : Institute of Electrical and Electronics Engineers (IEEE). - 9783907144008 ; , s. 764-769 Konferensbidrag (refereegranskat)abstract For a vehicle moving in an n-dimensional Euclidean space, we present a construction of a hybrid feedback that guarantees both global asymptotic stabilization of a reference position and avoidance of an obstacle corresponding to a bounded spherical region. The proposed hybrid control algorithm switches between two modes of operation: stabilization (motion-to-goal) and avoidance (boundary-following). The geometric construction of the flow and jump sets of the hybrid controller, exploiting a hysteresis region, guarantees robust switching (chattering-free) between stabilization and avoidance. Simulation results illustrate the performance of the proposed hybrid control approach for a 3-dimensional scenario.
43.	Berkane, Soulaimaine, et al. (författare) Constrained stabilization on the n-sphere 2021 Ingår i: Automatica. - : Elsevier Ltd. - 0005-1098 .- 1873-2836. ; 125 Tidskriftsartikel (refereegranskat)abstract We solve the stabilization problem on the n-sphere in the presence of conic constraints. We use the stereographic projection to map this problem to the classical navigation problem on Rn in the presence of spherical obstacles. As a consequence, any obstacle avoidance algorithm for navigation in the Euclidean space can be used to solve the given problem on the n-sphere. We illustrate the effectiveness of the approach using the kinematics of the reduced attitude model on the 2-sphere.
44.	Berkane, Soulaimane, et al. (författare) Obstacle Avoidance via Hybrid Feedback 2022 Ingår i: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 67:1, s. 512-519 Tidskriftsartikel (refereegranskat)abstract In this article, we present a hybrid feedback approach to solve the navigation problem in the n-dimensional space containing an arbitrary number of ellipsoidal obstacles. The proposed algorithm guarantees both global asymptotic stabilization to a target position and avoidance of the obstacles. The controller, exploiting hysteresis regions, employs a Zeno-free switching between two modes of control: stabilization and avoidance. Simulation results illustrate the performance of the proposed approach for 2-D and 3-D scenarios.
45.	Berkane, Soulaimane, et al. (författare) Reciprocal Safety Velocity Cones for Decentralized Collision Avoidance in Multi-Agent Systems 2023 Ingår i: 22nd IFAC World CongressYokohama, Japan, July 9-14, 2023. - : Elsevier BV. ; , s. 8024-8029 Konferensbidrag (refereegranskat)abstract In this paper, we solve the inter-agent collision avoidance problem in an arbitrary n−dimensional Euclidean space using reciprocal safety velocity cones (RSVCs). We propose a decentralized feedback control strategy that guarantees simultaneously asymptotic stabilization to a reference and collision avoidance. Our algorithm is purely decentralized in the sense that each agent uses only local information about its neighbouring agents. Moreover, the proposed solution can be implemented using only inter-agent bearing measurements. Therefore, the algorithm is a sensor-based control strategy which is practically implementable using a wide range of sensors such as vision systems and range scanners. Simulation results in a two dimensional environment cluttered with agents shows that the number of possible deadlocks is marginal and decrease with the decrease in the clutteredness of the workspace.
46.	Berkane, Soulaimane, et al. (författare) State Estimation for Linear Systems With Quadratic Outputs 2023 Ingår i: IEEE Control Systems Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2475-1456. ; 7, s. 3872-3877 Tidskriftsartikel (refereegranskat)abstract This letter deals with the problem of state estimation for a class of systems involving linear dynamics with multiple quadratic output measurements. We propose a systematic approach to immerse the original system into a linear time-varying (LTV) system of a higher dimension. The methodology extends the original system by incorporating a minimum number of auxiliary states, ensuring that the resulting extended system exhibits both linear dynamics and linear output. Consequently, any Kalman-type observer can showcase global state estimation, provided the system is uniformly observable.
47.	Bhat, Sriharsha, 1991- (författare) Hydrobatics: Efficient and Agile Underwater Robots 2020 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract The term hydrobatics refers to the agile maneuvering of underwater vehicles. Hydrobatic capabilities in autonomous underwater vehicles (AUVs) can enable increased maneuverability without a sacrifice in efficiency and speed. This means innovative robot designs and new use case scenarios are possible. Benefits and technical challenges related to hydrobatic AUVs are explored in this thesis. The dissertation contributes to new knowledge in simulation, control and field applications, and provides a structured approach to realize hydrobatic capabilities in real world impact areas.Three impact areas are considered - environmental monitoring, ocean production and security. A combination of agility in maneuvering and efficiency in performance is crucial for successful AUV applications. To achieve such performance, two technical challenges must be solved. First, these AUVs have fewer control inputs than degrees of freedom, which leads to the challenge of underactuation. The challenge is described in detail and solution strategies that use optimal control and model predictive control (MPC) are highlighted. Second, the flow around an AUV during hydrobatic maneuvers transitions from laminar to turbulent flow at high angles of attack. This renders flight dynamics modelling difficult. A full 0-360 degree envelope flight dynamics model is therefore derived, which combines a multi-fidelity hydrodynamic database with a generalized component-buildup approach. Such a model enables real-time (or near real-time) simulations of hydrobatic maneuvers including loops, helices and tight turns.Next, a cyber-physical system (CPS) is presented -- it safely transforms capabilities derived in simulation to real-world use cases in the impact areas described. The simulator environment is closely integrated with the robotic system, enabling pre-validation of controllers and software before hardware deployment. The small and hydrobatic SAM AUV (developed in-house at KTH as part of the Swedish Maritime Robotics Center) is used as a test platform. The CPS concept is validated by using the SAM AUV for the search and detection of a submerged target in field operating conditions.Current research focuses on further exploring underactuated control and motion planning. This includes development of real-time nonlinear MPC implementations running on AUV hardware, as well as intelligent control through feedback motion planning, system identification and reinforcement learning. Such strategies can enable real-time robust and adaptive control of underactuated systems. These ideas will be applied to demonstrate new capabilities in the three impact areas.
48.	Bhat, Sriharsha, 1991- (författare) Hydrobatics: Real-time Control, Simulation and Learning for Underactuated AUVs in Agile Maneuvers 2023 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract The term hydrobatics refers to the agile maneuvering of underwater vehicles. Underwater robots such as autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs) are either designed as flight style, optimized for range and speed, or hover style, optimized for precise maneuverability. Hydrobatic capabilities can help balance efficiency and maneuverability in these platforms, enabling innovative robot designs for impact areas in environmental monitoring, ocean production and security. This dissertation addresses technical challenges related to hydrobatic AUVs and contributes to new knowledge in real-time control, simulation, learning and planning. Hydrobatic AUVs are underactuated systems --- new strategies using nonlinear model predictive control (MPC) and behavior trees (BTs) are presented for efficient and safe real-time control of underactuated AUVs in agile maneuvers. Further, the flow around an AUV during such maneuvers transitions from laminar to turbulent flow at high angles of attack, rendering flight dynamics modelling difficult. A full 0-360 degree envelope flight dynamics model is therefore derived, which combines a multi-fidelity hydrodynamic database with a generalized component-buildup approach. Such a model enables real-time (or near real-time) simulations of hydrobatic maneuvers including loops, helices and tight turns. To increase the intelligence and robustness of such systems, data driven methods including physics-informed learning, Gaussian processes, sparse regression and reinforcement learning are utilized to rapidly identify models of the system's dynamics and perform online adaptive control. To further enhance autonomy, informative path planning is also studied, where an adaptive sampling strategy combines AUV measurements and satellite data to track ocean fronts.These hydrobatic capabilities are safely brought to the real world through a cyber-physical system (CPS). Simulator environments are closely integrated with the robotic system, enabling pre-validation of controllers and software before hardware deployment. The small and hydrobatic SAM AUV (SAM: Small and Affordable Maritime robot) developed in-house at KTH as part of the Swedish Maritime Robotics Centre (SMaRC) is used as a test platform. The CPS concept is demonstrated with the SAM AUV in applications including detecting underwater targets, inspecting seaweed farm infrastructure and tracking algal blooms using the presented simulation, planning and control strategies.
49.	Bhat, Sriharsha, 1991-, et al. (författare) Nonlinear model predictive control for hydrobatics : Experiments with an underactuated AUV 2023 Ingår i: Journal of Field Robotics. - : Wiley. - 1556-4959 .- 1556-4967. ; 40:7, s. 1840-1859 Tidskriftsartikel (refereegranskat)abstract Hydrobatic autonomous underwater vehicles (AUVs) can be efficient in range and speed, as well as agile in maneuvering. They can be beneficial in scenarios such as obstacle avoidance, inspections, docking, and under-ice operations. However, such AUVs are underactuated systems—this means exploiting the system dynamics is key to achieving elegant hydrobatic maneuvers with minimum controls. This paper explores the use of model predictive control (MPC) techniques to control underactuated AUVs in hydrobatic maneuvers and presents new simulation and experimental results with the small and hydrobatic SAM AUV. Simulations are performed using nonlinear model predictive control (NMPC) on the full AUV system to provide optimal control policies for several hydrobatic maneuvers in Matlab/Simulink. For implementation on AUV hardware in robot operating system, a linear time varying MPC (LTV-MPC) is derived from the nonlinear model to enable real-time control. In simulations, NMPC and LTV-MPC shows promising results to offer much more efficient control strategies than what can be obtained with PID and linear quadratic regulator based controllers in terms of rise-time, overshoot, steady-state error, and robustness. The LTV-MPC shows satisfactory real-time performance in experimental validation. The paper further also demonstrates experimentally that LTV-MPC can be run real-time on the AUV in performing hydrobatic maneouvers.
50.	Bisoffi, Andrea, et al. (författare) A hybrid barrier certificate approach to satisfy linear temporal logic specifications 2018 Ingår i: 2018 Annual American Control Conference (ACC). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 634-639 Konferensbidrag (refereegranskat)abstract In this work we formulate the satisfaction of a (syntactically co-safe) linear temporal logic specification on a physical plant through a recent hybrid dynamical systems formalism. In order to solve this problem, we introduce an extension to such a hybrid system framework of the so-called eventuality property, which matches suitably the condition for the satisfaction of such a temporal logic specification. The eventuality property can be established through barrier certificates, which we derive for the considered hybrid system framework. Using a hybrid barrier certificate, we propose a solution to the original problem. Simulations illustrate the effectiveness of the proposed method. 2018 AACC.

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