References of "Automatica"
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See detailEvent-triggered transmission for linear control over communication channels
Forni, Fulvio ULg; Galeani, Sergio; Nesic, Dragan et al

in Automatica (2014), 50(2), 490498

We consider an exponentially stable closed loop interconnection of a continuous linear plant and a continuous linear controller, and we study the problem of interconnecting the plant output to the ... [more ▼]

We consider an exponentially stable closed loop interconnection of a continuous linear plant and a continuous linear controller, and we study the problem of interconnecting the plant output to the controller input through a digital channel. We propose a family of "transmission-lazy" sensors whose goal is to transmit the measured plant output information as little as possible while preserving closed-loop stability. In particular, we propose two transmission policies, providing conditions on the transmission parameters. These guarantee global asymptotic stability when the plant state is available or when an estimate of the state is available (provided by a classical continuous linear observer). Moreover, under a specific condition, they guarantee global exponential stability [less ▲]

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See detailCooperative frequency control with a multi-terminal high-voltage DC network
Sarlette, Alain; Dai, Jing; Phulpin, Yannick et al

in Automatica (2012), 48(12), 31283134

We consider frequency control in power systems made of several non-synchronous AC areas connected by a multi-terminal high-voltage direct current (HVDC) grid. We propose two HVDC control schemes to make ... [more ▼]

We consider frequency control in power systems made of several non-synchronous AC areas connected by a multi-terminal high-voltage direct current (HVDC) grid. We propose two HVDC control schemes to make the areas collectively react to power imbalances, so that individual areas can schedule smaller power reserves. The first scheme modifies the power injected by each area into the DC grid as a function of frequency deviations of neighboring AC areas. The second scheme changes the DC voltage of each converter as a function of its own area's frequency only, relying on the physical network to obtain a collective reaction. For both schemes, we prove convergence of the closed-loop system with heterogeneous AC areas. [less ▲]

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See detailModel recovery anti-windup for continuous-time rate and magnitude saturated linear plants
Forni, Fulvio ULg; Galeani, Sergio; Zaccarian, Luca

in Automatica (2012), 48(8), 15021513

In this paper two approaches are given for anti-windup design for nonlinear control systems with linear plants subject to limitations both in the magnitude and the rate of variation of the control input ... [more ▼]

In this paper two approaches are given for anti-windup design for nonlinear control systems with linear plants subject to limitations both in the magnitude and the rate of variation of the control input. Both approaches are based on the so-called Model Recovery Anti-windup (MRAW) framework. The first approach is built by treating the rate+magnitude saturation as a single dynamic nonlinearity, while in the second one, the dynamic compensator dynamics is extended with extra states to treat the two saturations separately. Both approaches lead to global stability with exponentially stable plants and local stability in all other cases. For both approaches, stability and performance guarantees are proven, numerical recipes are given and the relative merits are comparatively highlighted on a simulation example. [less ▲]

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See detailReset passivation of nonlinear controllers via a suitable time-regular reset map
Forni, Fulvio ULg; Nešić, Dragan; Zaccarian, Luca

in Automatica (2011), 47(9), 2099-2106

For a class of square continuous-time nonlinear controllers we design a suitable resetting rule inspired by the resetting rule for Clegg integrators and First Order Reset Elements (FORE). With this rule ... [more ▼]

For a class of square continuous-time nonlinear controllers we design a suitable resetting rule inspired by the resetting rule for Clegg integrators and First Order Reset Elements (FORE). With this rule, we prove that the arising hybrid system with temporal regularization is passive in the conventional continuous-time sense with a small shortage of input passivity decreasing with the temporal regularization constant. Based on the passivity property, we then investigate the finite gain stability of the interconnection between this passive controller and a passive nonlinear plant. [less ▲]

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See detailApproximate dynamic programming with a fuzzy parameterization
Busoniu, Lucian; Ernst, Damien ULg; De Schutter, Bart et al

in Automatica (2010), 46(5), 804-814

Dynamic programming (DP) is a powerful paradigm for general, nonlinear optimal control. Computing exact DP solutions is in general only possible when the process states and the control actions take values ... [more ▼]

Dynamic programming (DP) is a powerful paradigm for general, nonlinear optimal control. Computing exact DP solutions is in general only possible when the process states and the control actions take values in a small discrete set. In practice, it is necessary to approximate the solutions. Therefore, we propose an algorithm for approximate DP that relies on a fuzzy partition of the state space, and on a discretization of the action space. This fuzzy Q-iteration algorithm works for deterministic processes, under the discounted return criterion. We prove that fuzzy Q-iteration asymptotically converges to a solution that lies within a bound of the optimal solution. A bound on the suboptimality of the solution obtained in a finite number of iterations is also derived. Under continuity assumptions on the dynamics and on the reward function, we show that fuzzy Q-iteration is consistent, i.e., that it asymptotically obtains the optimal solution as the approximation accuracy increases. These properties hold both when the parameters of the approximator are updated in a synchronous fashion, and when they are updated asynchronously. The asynchronous algorithm is proven to converge at least as fast as the synchronous one. The performance of fuzzy Q-iteration is illustrated in a two-link manipulator control problem. [less ▲]

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See detailGain-scheduled, model-based anti-windup for LPV systems
Forni, Fulvio ULg; Galeani, Sergio

in Automatica (2010), 46(1), 222-225

The aim of this paper is to show that a recently proposed technique for anti-windup control of exponentially unstable plants can be easily extended to solve the corresponding robust anti-windup problem ... [more ▼]

The aim of this paper is to show that a recently proposed technique for anti-windup control of exponentially unstable plants can be easily extended to solve the corresponding robust anti-windup problem for linear parameter varying systems, for which the time varying parameters are measured online. The proposed technique is minimally conservative with respect to the size of the resulting operating region (which coincides, up to an arbitrarily small quantity, with the largest set on which asymptotic stability can be guaranteed for the considered plant with the given saturation level and uncertainty characteristics), and is not limited to plants having only small uncertainties or being open-loop stable. [less ▲]

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See detailAutonomous rigid body attitude synchronization
Sarlette, Alain ULg; Sepulchre, Rodolphe ULg; Leonard, Naomi

in Automatica (2009), 45(2), 572-577

Control laws to synchronize attitudes in a swarm of fully actuated rigid bodies, in the absence of a common reference attitude or hierarchy in the swarm, are proposed in [Smith, T. R., Hanssmann, H ... [more ▼]

Control laws to synchronize attitudes in a swarm of fully actuated rigid bodies, in the absence of a common reference attitude or hierarchy in the swarm, are proposed in [Smith, T. R., Hanssmann, H., & Leonard, N.E. (2001). "Orientation control of multiple underwater vehicles with symmetry-breaking potentials". In Proc. 40th IEEE conf. decision and control (pp. 4598–4603); Nair, S., Leonard, N. E. (2007). "Stable synchronization of rigid body networks". In Networks and Heterogeneous Media, 2(4), 595–624]. The present paper studies two separate extensions with the same energy shaping approach: (i) locally synchronizing the rigid bodies’ attitudes, but without restricting their final motion and (ii) relaxing the communication topology from undirected, fixed and connected to directed, varying and uniformly connected. The specific strategies that must be developed for these extensions illustrate the limitations of attitude control with reduced information. [less ▲]

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See detailSynchronization in Networks of Identical Linear Systems
Scardovi, Luca; Sepulchre, Rodolphe ULg

in Automatica (2009), 45(11), 2557-2562

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See detailAdaptive lambda-tracking for nonlinear higher relative degree systems
Bullinger, Eric ULg; Allgöwer, Frank

in Automatica (2005), 41(7), 1191-1200

This paper proposes a relatively simple adaptive controller for nonlinear systems with higher relative degree. The controller achieves lambda-tracking for a large class of nonlinear systems, i.e. it ... [more ▼]

This paper proposes a relatively simple adaptive controller for nonlinear systems with higher relative degree. The controller achieves lambda-tracking for a large class of nonlinear systems, i.e. it asymptotically stabilizes the system up to an error of at most lambda which is chosen by the user. Only little information on the system is needed in the sense that no model needs to be known for the controller design, but only structural information like the relative degree and a lower bound on the positive high-frequency gain. The zero-dynamics does not need to be asymptotically stable, boundedness is sufficient. The controller consists of a high-gain observer, a high-gain observer-state feedback and a common adaptation of both high-gain parameters. The adaptation increases the gains of the observer and the state-feedback whenever the control objective, namely that the tracking error is of magnitude not larger than lambda, is not attained. It is proved that the controller's adaptation converges and the control objective is achieved at least asymptotically. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailImproving the performance of low-gain designs for bounded control of linear systems
Grognard, F.; Sepulchre, Rodolphe ULg; Bastin, G.

in Automatica (2002), 38(11), 1777-1782

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See detailA control strategy for controllable series capacitor in electric power systems
Ghandhari, Mehrdad; Andersson, Goran; Pavella, Mania ULg et al

in Automatica (2001), 37

It has been veri"ed that a controllable series capacitor with a suitable control scheme can improve transient stability and help to damp electromechanical oscillations. A question of great importance is ... [more ▼]

It has been veri"ed that a controllable series capacitor with a suitable control scheme can improve transient stability and help to damp electromechanical oscillations. A question of great importance is the selection of the input signals and a control strategy for this device in order to damp power oscillations in an e!ective and robust manner. Based on Lyapunov theory a control strategy for damping of electromechanical power oscillations in a multi-machine power system is derived. Lyapunov theory deals with dynamical systems without inputs. For this reason, it has traditionally been applied only to closed-loop control systems, that is, systems for which the input has been eliminated through the substitution of a predetermined feedback control. However, in this paper, we use Lyapunov function candidates in feedback design itself by making the Lyapunov derivative negative when choosing the control. This control strategy is called control Lyapunov function for systems with control inputs. Also, two input signals for this control strategy are used. The "rst one is based on local information and the second one on remote information derived by the single machine equivalent method. [less ▲]

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See detailGlobal adaptive stabilization of cascade nonlinear systems
Jankovic, M.; Sepulchre, Rodolphe ULg; Kokotovic, Petar V.

in Automatica (1997), 33(2), 263-368

An adaptive controller is developed for a class of nonlinear systems for which other approaches (e.g. backstepping) may fail to be applicable. The new design employs feedback passivation and an explicit ... [more ▼]

An adaptive controller is developed for a class of nonlinear systems for which other approaches (e.g. backstepping) may fail to be applicable. The new design employs feedback passivation and an explicit construction of a Lyapunov function for the zero dynamics with respect to a relative degree 1 output. As an illustration a longstanding "nonlinear benchmark problem" is solved. [less ▲]

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See detailIntegrator forwarding : a new recursive nonlinear robust design
Sepulchre, Rodolphe ULg; Jankovic, M.; Kokotovic, Petar V.

in Automatica (1997), 33(5), 979-984

We consider the global stabilization of nonlinear systems in strict feedforward form. We show that these systems, while not feedback linearizable, can be (globally) transformed by feedback and ... [more ▼]

We consider the global stabilization of nonlinear systems in strict feedforward form. We show that these systems, while not feedback linearizable, can be (globally) transformed by feedback and diffeomorphism into a lower-triangular form. The transformation is explicit and recursive. We employ this transformation to design a globally stabilizing controller with optimality properties and an input-to-state stability property with respect to matched uncertainties. [less ▲]

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See detailDecision Trees and Transient Stability of Electric Power Systems
Wehenkel, Louis ULg; Pavella, Mania ULg

in Automatica (1991), 27(1), 115-134

An inductive inference method for the automatic building of decision trees is investigated. Among its various tasks, the splitting and the stop splitting criteria successively applied to the nodes of a ... [more ▼]

An inductive inference method for the automatic building of decision trees is investigated. Among its various tasks, the splitting and the stop splitting criteria successively applied to the nodes of a grown tree, are found to play a crucial role on its overall shape and performances. The application of this general method to transient stability is systematically explored. Parameters related to the stop splitting criterion, to the learning set and to the tree classes are thus considered, and their influence on the tree features is scrutinized. Evaluation criteria appropriate to assess accuracy are also compared. Various tradeoffs are further examined, such as complexity vs number of classes, or misclassification rate vs type of misclassification errors. Possible uses of the trees are also envisaged. Computational issues relating to the building and the use of trees are finally discussed. [less ▲]

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See detailDynamic state prediction and hierarchical filtering for power system estimation
Rousseaux, Patricia ULg; Van Cutsem, Thierry ULg; Mallieu, Didier et al

in Automatica (1988), 25(5), 595-618

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See detailDecision theory for fault diagnosis in electric power systems
Mili, Lamine; Van Cutsem, Thierry ULg; Pavella, Mania

in Automatica (1987), 23

Detailed reference viewed: 5 (1 ULg)