Search

International audience; This paper investigates the impact of embedded Voltage Source Converter-based High Voltage Direct Current (VSC-HVDC) links on AC grids transient stability. Firstly, using Transient Energy Functions (TEF), it is demonstrated that VSC-HVDC links controlled to track constant power references, do not inherently improve transient stability of the surrounding AC grid as an AC line naturally does. Then, a control law using the feedback linearization technique on a simple but representative power system is derived. The control law highlights and combines the three main actions the VSC-HVDC link can offer to enhance rotor angle stability: fast power reallocation, injection of synchronising power and injection of damping power. The control law is implemented and validated in EMT simulation. It is then shown that an HVDC link can assure the synchronisation of different AC areas even if no AC transmission lines interconnect them. Through another case study, it is shown how the HVDC link can help to share dynamic frequency reserves in order to not jeopardise the stability of the system. A last example investigates the effect of a DC fault on AC transient stability and how the control can help improving the system response.

International audience; This paper introduces a control induced time-scale separation scheme for a multiterminal high-voltage direct current system used for large scale integration of renewable energy sources. The main idea is to provide a detailed theoretical analysis to the long stand practice that consists of the empirical design of two control loops for the terminals. Experience has shown that such loops, i.e., current and voltage control loops, when heuristically tuned, often display very different dynamics. In this paper, singular perturbation theory is applied to give explanation and fundamental analysis on why and how the two control loops work and how to achieve the timescale separation between various state variables. Mathematical analysis is also carried out to illustrate a clear tradeoff between system performance (actuator constraint) and the size of the region of attraction of the controller. Numerical simulations for a system with four terminals are presented to evaluate the system performance and illustrate the theoretical analysis.

In this paper, we design a novel observer for a class of semilinear heat one dimmensional (1-D) equations under the delayed and sampled point measurements. The main novelty is that the delay is arbitrary. To handle any arbitrary delay, the observer is constituted of a chain of subobservers. Each subobserver handles a fraction of the considered delay. The resulting estimation error system is shown to be exponentially stable under a sufficient number of subobservers is used. The stability analysis is based on a specific Lyapunov–Krasovskii functional and the stability conditions are expressed in terms of linear matrix inequalities (LMIs).

International audience; In this paper it is proposed to extend the result described in Khalil and Praly (2014) and the references therein, regarding the high-gain observer-based nonlinear control to the case of systems with diffusion sensor dynamic. Based on some usual hypotheses, we provide sufficient conditions involving the high-gain parameter and the length on the PDE sensor. In fact it is brought into light an explicit trade off between them: the larger the observer gain, the smaller the length of the PDE sensor needs to be. The stability analysis of the closed loop is based on a Lyapunov functional.

The paper proposes an adaptive variable synthetic inertia strategy to provide frequency and voltage support (ancillary services) in an AC MicroGrid (weak grid) composed of diesel generators and loads. A DC MicroGrid is connected to the AC one by a Voltage Source Converter (VSC). The VSC converter is driven as a Virtual Synchronous Machine (VSM), where the control strategy follows a swing equation such the converter emulates a synchronous machine, including inertial support. A rigorous stability analysis is developed based on Lyapunov technique assuring proper stability conditions for an adaptive inertia designated, such that, frequency stability is improved and power oscillations are reduced. This strategy can be exploited in low inertia systems like MicroGrids or grids with high penetration of renewables. Simulation results illustrate the performance of the proposed control and the system’s operation, where a comparison with droop control is presented.

This paper presents the nonlinear control design with formal stability proof for a Modular Multilevel Converter (MMC), which is critical for the interaction between AC and DC grids. Lyapunov theory is used to develop the proposed controller, which is based on Backstepping and Feedback Linearization techniques and to perform the stability analysis. The proposed controller allows to asymptotically stabilize all converter’s states, i.e., AC currents, circulating currents, and internal energy. The proposed algorithm allows to manage the converter in a wide range of operation points, by means of arbitrary tuning assignment. Robustness and performances of proposed control are verified by means of Matlab Simscape Electrical simulations, including active and reactive power reference variations and grid imbalance conditions. A detailed MMC switching model, of 450 MVA is considered on Matlab validation. A phase-shift PWM is considered, with a sorting algorithm. Also, a comparison with a standard PI controller is performed. In addition, MMC’s internal energy is also controlled, which can contribute to the high-speed frequency control by using this energy for synthetic inertia.

This paper presents a distributed supplementary control for embedded Multi-Terminal VSC-HVDC (MTDC) grids to enhance the transient stability of the surrounding AC grid. Firstly, the need of supplementary controllers for embedded MTDC grids is demonstrated via the study of the Transient Energy Functions (TEF) of a simple hybrid AC/DC power system. Then, the proposed control structure is presented. This control aims to enhance the angle stability of the surrounding AC system via the modulation of the active power references of the converters. The objective of the control is to enhance AC transient stability while keeping the power balance of the DC grid even if converters reach their active power limits. The proposed control uses frequency, and angle measurements at the Point of Common Coupling (PCC) of the converters. The idea behind the proposed strategy is to match the control actions, and limits of each pair ( $i,j$ ) of converters. If converter $i$ modulates its power, converter $j$ modulates the same amount of power in the opposite direction. The concept of virtual links is used in this paper to represent this matching. Finally, the proposed controller is tested on a modified version of the IEEE 39 bus system using EMT simulations.

International audience; From the first Internet-based social networking applications designed to get people in contact and make friends to social networks made up of over 2 billion users, the combination of communication networks, portable devices, and AI has changed the way people interact and make decisions. The extent of this influence could be observed not only in marketing and social behavior but also in referendums and elections, leading to distortion of democratic manifestations and representations. Considering this, the consequences of the misuse of Internet-based social networks could have a substantial impact on society, and it is important to define ethical guidelines and policies for developers, rulers, operators, and social actors. Considering this aim, the objective of this paper is to show that an approach based on Systems & Control could be effective in evaluating the impact of such policies in order to meet ethical issues. The starting point from this analysis are the models of information spreading in dynamic social networks, and these models are adapted and updated to encompass the complex behavior from users, as well as some regulatory policies. The analyses were based on simulations of these models on small and large scale networks.

International audience; Small-gain stability analysis is developed for a class of sampled-data systems consisting of a parabolic-type PDE and a linear ODE connected in series with a sampler-ZOH block. This stability analysis is shown to be useful in designing sampled-data exponentially-convergent observers and exponentially stabilizing output-feedback controllers for some classes of ODE-PDE cascades. This work generalizes existing results in the literature in various directions. (C) 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

International audience; In this technical note, an adaptive control framework for compensation of uncertainties and perturbations that satisfy the matching condition on a class of nonlinear dynamic systems is presented. The proposed method does not need the explicit knowledge of the bound values on the uncertainties, and the resulting compensatory term is continuous. The application of this formulation for maximum power point tracking and unity power factor on grid-connected photovoltaic systems is presented.

International audience; Following in the footsteps of the renowned report “Control in an Information Rich World,” Report of the Panel on “Future Directions in Control, Dynamics, and Systems” chaired by Richard Murray (2002), this paper aims to demonstrate that Systems & Control is at the heart of the Information and Communication Technologies to most application domains. As such, Systems & Control should be acknowledged as a priority by funding agencies and supported at the levels necessary to enable technologies addressing critical societal challenges. A second intention of this paper is to present to the industrials and the young research generation, a global picture of the societal and research challenges where the discipline of Systems & Control will play a key role. Throughout, this paper demonstrates the extremely rich, current and future, cross-fertilization between five critical societal challenges and seven key research and innovation Systems & Control scientific challenges. This paper is authored by members of the IFAC Task Road Map Committee, established following the 19th IFAC World Congress in Cape Town. Other experts who authored specific parts are listed below.

In this work, a novel adaptive control scheme that allows driving a stand-alone variable-speed wind turbine system to its maximum power point is presented. The scheme is based on the regulation of the optimal rotor speed point of the wind turbine. In order to compute the rotor speed reference, a model-based extremum-seeking algorithm is derived. The wind speed signal is necessary to calculate this reference, and a novel artificial neural network is derived to approximate this signal. The neural network does not need off-line learning stage, because a nonlinear dynamics for the weight vector is proposed. A block-backstepping controller is derived to stabilize and to drive the system to the optimal power point; to avoid singularities, the gradient dynamics technique is applied to this controller. Numerical simulations are carried out to show the performance of the controller and the estimator. Copyright © 2016 John Wiley & Sons, Ltd.

International audience; In this paper we investigate the stability analysis of nonlinear sampled-data systems, which are affine in the input. We assume that a stabilizing controller is designed using the emulation technique. We intend to provide sufficient stability conditions for the resulting sampled-data system. This allows to find an estimate of the upper bound on the asynchronous sampling intervals, for which stability is ensured. The main idea of the paper is to address the stability problem in a new framework inspired by the dissipativity theory. Furthermore, the result is shown to be constructive. Numerically tractable criteria are derived using linear matrix inequality for polytopic systems and using sum of squares technique for the class of polynomial systems.

In this paper, an adaptive control scheme for maximum power point tracking of stand-alone PMSG wind turbine systems (WTS) is presented. A novel procedure to estimate the wind speed is derived. To achieve this, a neural network identifier (NNI) is designed in order to approximate the mechanical torque of the WTS. With this information, the wind speed is calculated based on the optimal mechanical torque point. The NNI approximates in real-time the mechanical torque signal and it does not need off-line training to get its optimal parameter values. In this way, it can really approximates any mechanical torque value with good accuracy. In order to regulate the rotor speed to the optimal speed value, a block-backstepping controller is derived. Uniform asymptotic stability of the tracking error origin is proved using Lyapunov arguments. Numerical simulations and comparisons with a standard passivity based controller are made in order to show the good performance of the proposed adaptive scheme.

International audience; An observer is designed for a class of nonlinear parabolic PDEs with delayed point measurements. The novelty lies is that the delay size is arbitrary. To compensate for this arbitrary delay effect, the observer consists of several chained sub-observers. Each sub-observer compensates a fraction of the global delay. The resulting estimation error system is shown to be exponentially stable provided that a sufficient number of sub-observers is used. The stability analysis is based on a specific Lyapunov-Krasovskii functional and the stability conditions are expressed in terms of LMIs.

International audience; In recent years, different protection strategies for high-voltage direct current (HVDC) grids have been developed by the industry and academia for the reliable and safe operation of direct current grids. The proposed strategies have different impacts on the AC networks where HVDC grids are connected. In the case of embedded HVDC grids embedded in a synchronous AC network, a partial loss of the HVDC grid might cause the desynchronisation of the AC grid. Therefore, it is of utmost importance to assess the impact of those protection strategies into the stability of the whole network. The objective of this study is to propose a methodology for the transient stability assessment of a simple but representative AC grid in case of DC fault. After validation of the methodology, some HVDC link protection criteria are defined in terms of the Critical Time to Return to Operation. These criteria will be helpful for the design of HVDC protection systems or for the sizing of future HVDC links in order to respect the constraints of the existing protection strategies.

The access to electricity for isolated communities is capital for improving life in thosesocieties. The use of renewable energy sources (renewables) and energy storage systems is the keyfor clean energy supply in remote areas without the main grid. The standalone operation of renewablesrepresents a challenge for operation and reliability, therefore the DC MicroGrid concept is seenas a powerful solution allowing renewables integration and reliable operation of the system is simpleway. This paper proposes a distributed nonlinear control strategy for an isolated MicroGrid composedof renewables and different time-scale storage systems to supply a DC load. The simulations resultsshow the behavior of the proposed MicroGrid and a comparison with classical linear control is doneto highlight the control performance.; L'accès à l'électricité pour les communautés isolées est un capital pour améliorer la vie dans ces sociétés. L'utilisation de sources d'énergie renouvelables et de systèmes de stockage d'énergie est la clé pour l'approvisionnement en énergie propre dans les zones reculées sans réseau principal. Le fonctionnement autonome des énergies renouvelables représente un défi pour l'exploitation et la fiabilité, par conséquent, le concept DC MicroGrid est considéré comme une solution puis-sante permettant l'intégration des énergies renouvelables et un fonctionnement fiable du système de manière simple. Cet article propose une stratégie de contrôle non linéaire distribuée pour un Micro-Grid isolé composé d'énergies renouvelables et de différents systèmes de stockage à l'échelle du temps pour fournir une charge continue. Les résultats des simulations montrent le comportement du MicroGrid proposé et une comparaison avec le contrôle linéaire classique est effectuée pour mettre en évidence les performances du contrôle. ABSTRACT. The access to electricity for isolated communities is capital for improving life in those societies. The use of renewable energy sources (renewables) and energy storage systems is the key for clean energy supply in remote areas without the main grid. The standalone operation of renew-ables represents a challenge for operation and reliability, therefore the DC MicroGrid concept is seen as a powerful solution allowing renewables integration and reliable operation of the system is simple way. This paper proposes a distributed nonlinear control strategy for an isolated MicroGrid composed of renewables and different timescale storage systems to supply a DC load. The simulations results show the behavior of the proposed MicroGrid and a comparison with classical linear control is done to highlight the control performance. MOTS-CLÉS : MicroGrids, systèmes d'alimentation isolés, contrôle non linéaire, intégration de source renouvelable, stabilité de réseau, SmartGrids

International audience; The problem of observer design is addressed for a class of triangular nonlinear systems with not-necessarily small delay and sampled output measurements. One more difficulty is that the system state matrix is dependent on the un-delayed output signal which is not accessible to measurement, making existing observers inapplicable. A new chain observer, composed of m elementary observers in series, is designed to compensate for output sampling and arbitrary large delays. The larger the time-delay the larger the number m. Each elementary observer includes an output predictor that is conceived to compensate for the effects of output sampling and a fractional delay. The predictors are defined by first-order ordinary differential equations (ODEs) much simpler than those of existing predictors which involve both output and state predictors. Using a small gain type analysis, sufficient conditions for the observer to be exponentially convergent are established in terms of the minimal number m of elementary observers and the maximum sampling interval.

International audience; The problem of state and parameter estimation is addressed for systems with cascade structure including finite-dimensional dynamics followed in series with infinite-dimensional dynamics. The formers are captured through an ODE that is state- and parameter-affine. The latter, referred to as sensor dynamics, are represented by a diffusion parabolic PDE. Both equations are subject to parameter uncertainty. Furthermore, the connection point between the ODE and the PDE blocs is not accessible to measurements. The aim is to get online estimates of all inaccessible states and unknown parameters of both the ODE and the PDE subsystems. This observation problem is dealt with by combining the backstepping design method and the extended Kalman observer approach. The obtained adaptive observer is shown to be exponentially convergent under an ad-hoc persistent excitation condition.

International audience; A small-gain approach is presented for analyzing exponential stability of a class of (dynamical) hybrid systems. The systems considered in the paper are composed of finite-dimensional dynamics, represented by a linear ordinary differential equation (ODE), and infinite-dimensional dynamics described by a parabolic partial differential equation (PDE). Exponential stability is established under conditions involving the maximum allowable sampling period (MASP). This new stability result is shown to be useful in the design of sampled-output exponentially convergent observers for linear systems that are described by an ODE-PDE cascade. The new stability result also proves to be useful in designing practical approximate observers involving no PDEs.

International audience; The problem of observer design is addressed for a class of triangular nonlinear systems in presence of output measurement sampling and time-delay. A major difficulty with the considered nonlinear systems is that the state matrix is dependent on the "undelayed output signal" which is not accessible to measurement, making existing observers inapplicable. A new observer is designed where the effects of time-delay and sampling are compensated for using an output predictor. Defined by a couple of first-order ordinary differential equations (ODEs), the present predictor turns out to be much simpler compared to previous predictors involving output and state predictors. Using the small gain technique, sufficient conditions for the observer to be exponentially convergent are established in terms of the maximum time-delay and sampling interval.

International audience; In this paper, a new hybrid method which combines radial basis function (RBF) neural network with a sliding-mode technique to take advantage of their common features is used to control a class of nonlinear systems. A real-time dynamic nonlinear learning law of the weight vector is synthesized and the closed-loop stability has been demonstrated using Lyapunov theory. The solution presented in this work does not need the knowledge of the perturbation bounds, neither the knowledge of the full state of the nonlinear system. In addition, the bounds of the nonlinear functions are assumed to be unknown and the proposed RBF structure uses reduced number of hidden units. This hybrid control strategy is applied to extract the maximum available energy from a stand-alone self-excited variable low-wind speed energy conversion system and design the dc-voltage and rotor flux controllers as well as the load-side frequency and voltage regulators assuming that the measured outputs are the rotor speed, stator currents, load-side currents and voltages despite large variation of the rotor resistance and uncertainties on the inductances. Finally, simulation results compared with those obtained using the well-known second-order sliding-mode controller are given to show the effectiveness and feasibility of the proposed approach.

International audience; We are considering the problem of state observation for a class of infinite dimensional systems modeled by parabolic type PDEs. The model is subject to parametric uncertainty entering in both the domain equation and the boundary condition. An adaptive boundary observer, providing online estimates of the system state and parameters, is designed using finite- and infinite-dimensional backstepping-like transformations. The observer is exponentially convergent under an ad hoc persistent excitation condition.

International audience; The problem of state observation is addressed for a class of systems subject to sensor delay and parameter uncertainty. The unknown parameter vector enter a finite-dimensional state equation through a possibly output-dependent regressor. The sensor delay effect is captured by a first-order hyperbolic PDE. Doing so, the system turns out to be an ODE-PDE association with a connection point not accessible to measurements. An adaptive observer is constructed by combining ideas from PDE-based and ODE-based design approaches. The observer provides estimates of the ODE subsystem states and parameters, on the one hand, and of the sensor states, on the other. Observer exponential convergence is established under an ad-hoc persistent excitation condition involving the regressor.

International audience; Motivated by neuroscience applications, and in particular by the deep brain stimulation treatment for Parkinson's disease, we have recently derived a simplified model of an interconnected neuronal population under the effect of its mean-field proportional feedback. In this paper, we rely on that model to propose conditions under which proportional mean-field feedback achieves either oscillation inhibition or desynchronization. More precisely, we show that for small natural frequencies, this scalar control signal induces an inhibition of the collective oscillation. For the closed-loop system, this situation corresponds to a fixed point which is shown to be almost globally asymptotically stable in the fictitious case of zero natural frequencies and all-to-all coupling and feedback. In the case of an odd number of oscillators, this property is shown to be robust to small natural frequencies and heterogencities in both the coupling and feedback topology. On the contrary, for large natural frequencies, we show that scalar proportional mean-field feedback is able to induce desynchronization. After having recalled a formal definition for desynchronization, we show how it can be induced in a network of originally synchronized oscillators.

International audience; A nonlinear adaptive excitation controller is proposed to enhance the transient stability and voltage regulation of synchronous generators with unknown power angle and mechanical power input. The proposed method is based on a standard third-order model of a synchronous generator which requires only information about the physical available measurements of relative angular speed, active electric power, infinite bus and generator terminal voltages. The operating conditions are computed online using the above physical available measurements, the terminal voltage reference value and the estimate of the mechanical power input. The proposed design is therefore capable of providing satisfactory voltage in the presence of unknown variations of the power system operating conditions. Using the concept of sliding mode equivalent control techniques, a robust decentralized adaptive controller which insures the exponential convergence of the outputs to the desired ones, is obtained. Real-time experimental results are reported, comparing the performance of the proposed adaptive nonlinear control scheme to one of the conventional AVR/PSS controller. The high simplicity of the overall adaptive control scheme and its robustness with respect to line impedance variation including critical unbalanced operating condition and temporary turbine fault, constitute the main positive features of the proposed approach.

International audience; The observation of a class of multi-input multi-output (MIMO) state affine systems with constant unknown parameters and discrete time output measurements is addressed. Assuming some persistent excitation conditions to hold and the sampling steps to satisfy some boundedness hypotheses, system observability is ensured and a class of global exponential observers is synthesized.

International audience; This paper studies the application of a recently proposed control scheme to globally Lipschitz nonlinear systems for which the input is delayed and applied with zero order hold, the measurements are sampled and delayed, and only an output is measured (i.e., the state vector is not available). The control scheme consists of an observer for the delayed state vector, an inter-sample predictor for the output signal, an approximate predictor for the future value of the state vector, and the nominal feedback law applied with zero order hold and computed for the predicted value of the future state vector. The resulting closed-loop system is robust with respect to modeling and measurement errors and robust to perturbations of the sampling schedule.

International audience; A new power flow for DC grids is presented in this paper. This new method gives the possibility of using more than one bus for the power balance and consequently share the responsibilities between many actors. The present paper introduces a mathematical proof for this new power flow algorithm, which guarantees the existence of unique solution when voltages are close to nominal value. This new algorithm has in addition the advantage of being easily adapted for AC systems. Besides a detailed study of the effects on power and voltages when variables change is shown.

International audience; This paper provides exponential stability results for two system classes. The first class includes a family of nonlinear ODE systems while the second consists of semi-linear parabolic PDEs. A common feature of both classes is that the systems they include involve sampled-data states and a time-varying gain. Sufficient conditions ensuring global exponential stability are established in terms of Linear Matrix Inequalities (LMIs) derived on the basis of Lyapunov–Krasovskii functionals. The established stability results prove to be useful in designing exponentially convergent observers based on sampled-data measurements. It is shown throughout simulated examples from the literature that the introduction of time-varying gains is beneficial to the enlargement of sampling intervals while preserving the stability of the system.

International audience; In this chapter we consider the stability analysis of bilinear systems controlled via a sampled-data state feedback controller. Sampling periods may be time-varying and subject to uncertainties. The goal of this study is to find a constructive manner to estimate the maximum allowable sampling period (MASP) that guarantees the local stability of the system. Stability criteria are proposed in terms of linear matrix inequalities (LMI).

International audience; The problem of state observation, based on spatially-sampled output measurements, is addressed for a class of infinite dimensional systems, modelled by a semi-linear heat equation augmented with a structured uncertain part involving a set of unknown parameters. An adaptive observer is designed that provides online estimates of the system (spatially distributed) state and unknown parameters based on sampled data (in space). Sufficient conditions for the observer to be exponentially convergent are established. These include an ad-hoc persistent excitation condition as well as a condition on how the observer gain must be selected in relation with the space sampling interval.

International audience; The problem of state-observation is addressed for nonlinear systems that can be modeled by an ODE-PDE series association. The ODE subsystem assumes a triangular structure while the PDE element is of heat diffusion type. The aim is to accurately estimate online the state vector of the ODE subsystem and the distributed state of the PDE element. One major difficulty is that the state observation must only rely on the global system output i.e. the PDE state at the terminal boundary. In particular, the connection point between the ODE and the PDE blocks is not accessible to measurements. The observation problem is dealt with by designing a high-gain type observer. Sufficient conditions involving the PDE domain length are formally established that ensure the observer exponential convergence. (C) 2015 Elsevier B.V. All rights reserved.

International audience; We are considering the problem of state observation for a class of infinite dimensional systems. The latter are modelled by a parabolic PDE and a boundary condition involving an unknown parameter. The problem is dealt with using an adaptive observer that provides online estimates of the system (spatially distributed) state and the unknown parameters. The observer is formally shown to be exponentially convergent under an ad-hoc persistent excitation condition.

SUMMARY This work presents a nonlinear adaptive output feedback excitation control, designed for a synchronous generator modelled by a standard third-order model on the basis of the physically available measurements of relative angular speed, active and reactive electric power and terminal voltage. The power angle, which is a crucial variable for the excitation control, as well as mechanical power and the impedance of the transmission line connecting the generator to an infinity bus, are not assumed to be available for feedback. The feedback control achieves transient stabilization and voltage regulation when faults occur to the turbines or the transmission lines, such that parameters (mechanical power and line impedance) may permanently take any (unknown) value. The controller recovers by adaptation the unknown values and simultaneously generates trajectories to be followed by the states, that converge to the new equilibrium point. Copyright # 2004 John Wiley & Sons, Ltd.

International audience; This paper addresses the problem of analyzing the dynamic limitations of a VSC terminal with DC voltage droop control. Thanks to its fast response, DC voltage droop control is usually used to adjust the DC voltage in case of power imbalance. To ensure the stability of the VSC terminal, the dynamics between the dq currents (il,dq) and the DC voltage (uc) must be well distinguished. Therefore, the choice of the droop control gain Ku and the dq current control gains Kdq is still a challenging problem. First, we assume that there exist Ku and Kdq such that a slow and a fast dynamics can be imposed on uc and il,dq, respectively. Then, we propose a novel methodology based on separation of dynamics to prove the existence of these control gains. Subsequently, a detailed stability analysis is carried out via Lyapunov theory, from which a necessary condition and a sufficient condition are derived for the control gains. To verify this methodology, numerical simulations are carried out in MATLAB/SIMULINK.

International audience; This note considers the problem of local stability of bilinear systems with aperiodic sampled-data linear state feedback control. The sampling intervals are time-varying and upper bounded. It is shown that the feasibility of some linear matrix inequalities (LMIs), implies the local asymptotic stability of the sampled-data system in an ellipsoidal region containing the equilibrium. The method is based on the analysis of contractive invariant sets, and it is inspired by the dissipativity theory. The results are illustrated by means of numerical examples.

International audience; This paper presents a new control scheme to regulate the DC voltage of a VSC terminal. It significantly simplifies the control design process itself and in general also results in an uncomplicated and efficient control architecture. Firstly, an equivalent state space model established in a synchronous $dq$ reference frame is presented. Next we split the overall system into two interconnected subsystems and suppose that different dynamics can be imposed on them under their own sub-controllers. During the design process, we use a reduced model obtained by singular perturbation techniques instead of the original system. The developed control law is actually based on this reduced model and an explicit division of time scales. Simulation results clearly demonstrate that the controller based on the reduced model can regulate the DC voltage with good performances and in the meantime, the real DC voltage can be well approximated by its reduced model.

International audience; Predictor-based stabilization results are provided for nonlinear systems with input delays and a compact absorbing set. The control scheme consists of an inter-sample predictor, a global observer, an approximate predictor, and a nominal controller for the delay-free case. The control scheme is applicable even to the case where the measurement is sampled and possibly delayed. The closed-loop system is shown to have the properties of global asymptotic stability and exponential convergence in the disturbance-free case, robustness with respect to perturbations of the sampling schedule, and robustness with respect to measurement errors. In contrast to existing predictor feedback laws, the proposed control scheme utilizes an approximate predictor of a dynamic type which is expressed by a system described by Integral Delay Equations. Additional results are provided for systems that can be transformed to systems with a compact absorbing set by means of a preliminary predictor feedback.

International audience; New strategies are proposed to design GAS controllers for two significant classes of nonlinear flexible systems. Inspired by a non affine control technique, we have designed some novel nonlinear control laws which use the full state in order to enhance the damping of the flexible modes: this new design is all the more interesting than the classes of considered systems belong to non triangular nonlinear systems. Finally, the effectiveness of our approach is illustrated on simplified models of a flexible launcher and spacecraft.

International audience; This paper is dedicated to the stability analysis of nonlinear sampled-data systems, which are affine in the input. Assuming that a stabilizing continuous-time controller exists and it is implemented digitally, we intend to provide sufficient asymptotic/exponential stability conditions for the sampled-data system. This allows to find an estimate of the upper bound on the asynchronous sampling periods. The stability analysis problem is formulated both globally and locally. The main idea of the paper is to address the stability problem in the framework of dissipativity theory. Furthermore, the result is particularized for the class of polynomial input-affine sampled-data systems, where stability may be tested numerically using sum of squares decomposition and semidefinite programming.

International audience; An adaptive control scheme for maximum power point tracking of a single-phase grid-connected photovoltaic system is presented. The dificulty on design a controller that may operate a photovoltaic system on its maximum power point (MPP) is that, this MPP depends on temperature and solar irradiance, ambient conditions that are time-varying and dificult to measure. A solution using an on-line sliding mode estimator is presented. It estimates three different parameters that depends on solar irradiance and temperature, eliminating the necessity of having any sensor for these environmental variables. It is capable of estimate time-varying parameters. A complete analysis was done taking into account the non-linearities showed by the closed-loop system. A variation of the Lyapunov redesign technique was used to find a controller that give globally asymptotically stable trajectories of the closed-loop system. An adaptive law was found to substitute a perturbation bound and also to eliminate possible chattering due to the discontinuous controller term. Computer simulations are presented to show the good performance of the controller.

International audience; This paper concerns the stability analysis of nonlinear sampled-data systems. Assuming the existence of a stabilizing continuous-time controller, we intend to provide sufficient asymptotic/exponential stability conditions for the digital implementation with asynchronous sampled-data. An allowable upper bound of the sampling interval is provided. The stability analysis problem is formulated both globally and locally. The main idea is to address the problem in the framework of dissipativity theory. Furthermore, the result is particularized for the class of polynomial sampled-data systems, where stability may be tested numerically using sum of squares decomposition and semidefinite programming.; Cet article est dédié à l’analyse de la stabilité de systèmes non linéaires commandés par un contrôleur échantillonné non nécessairement périodique. Nous supposons qu’il existe une commande stabilisante en temps continu. Lors de l’implantation numérique de cette commande, il s’agit de trouver des conditions préservant la stabilité asymptotique/exponentielle sous échantillonnage. Les conditions sont formulées à la fois pour la stabilité globale et la stabilité locale. Nous estimons une borne supérieure des pas d’échantillonnage dans le cas asynchrone (non périodique). L’idée principale est d’aborder le problème dans le cadre de la dissipativité. Le résultat est ensuite repris dans le cas spécifique des systèmes non linéaires polynomiaux, où les conditions de stabilité sont vérifiées numériquement en utilisant la décomposition en somme des carrés (SOS) et la programmation semi-définie.

This paper presents new results concerning the observer design for wide classes of nonlinear systems with both sampled and delayed measurements. By using a small gain approach we provide sufficient conditions, which involve both the delay and the sampling period, ensuring exponential convergence of the observer system error. The proposed observer is robust with respect to measurement errors and perturbations of the sampling schedule. Moreover, new results on the robust global exponential state predictor design problem are provided, for wide classes of nonlinear systems., 17 pages, submitted for possible publication to Systems and Control Letters

Based on developments in the theory of variational and Hamiltonian control systems by Crouch and van der Schaft (1987), this paper answers two questions: given an input-output differential equation description of a nonlinear system, what is the adjoint variational system in input-output differential form and what are the conditions for the system to be Hamiltonian, i.e., such that the variational and the adjoint variational systems coincide? This resulting set of conditions is then used to generalize classical conditions such as the well-known Helmholtz conditions for the inverse problem in classical mechanics. >

International audience; This paper presents the design of an observer for a class of nonlinear Lipschitz sampled-data systems. The proposed observer uses a predictor of the output between the sampling times. This predictor is re-initialized at each sampling time. Besides, unlike the conventional high gain observer, the observer introduced herein has a dynamic observation gain. Using a Lyapunov approach, we will derive an explicit relation between the bound on maximum allowable sampling period and the parameters of the observer in order to guarantee an asymptotic convergence of the observation error.

International audience; This note is dedicated to the stability analysis of bilinear sampled-data systems, controlled via a linear state feedback static controller. A zero order hold device is used. Our purpose is to find a constructive way to calculate the maximum allowable sampling period (MASP) that guarantees the local stability of the system. The proposed stability conditions are formulated as linear matrix inequalities (LMI).

International audience; This year the EECI-HYCON Graduate School on Control celebrates its 10th anniversary. This note aims at analyzing the evolution of this yearly event. We start by giving a historical perspective of the Graduate School since its creation and by recalling the major scientific areas covered by the lecturers. We then provide a detailed description of the organization of this event, including financial issues. As the Graduate School is part of a larger European initiative that aims at reinforcing European excellence in the wide field of the control of complex networked systems, we also present related activities.