Seminars - MAC
Seminars in Toulouse in which MAC team members are involved.
21-23 November 2018
2nd DECOD Workshop - Delays and constraints in distributed parameter systems
19 October 2018, 2:30pm, LAAS - Salle Europe
Control allocation, optimal output regulation and attack detection in cyber-physical systems
by Sergio Galeani
Abstract: For a long time, the availability of more control inputs than regulated outputs in a controlled plant has been interpreted more as an obstacle rather than as an opportunity, essentially due to the fact that the "extra inputs" make the solution of the control problem non-unique. As a result, a classic approach consists in "squaring down" the plant, by combining some of the control inputs in order to obtain a model having as many inputs as outputs, to which standard theory can be applied and unique solutions arise. In this talk, a different perspective is taken, showing that the presence of more inputs than outputs ushers in the possibility of achieving better performance or extra features by exploiting the extra degrees of freedom through optimization. Examples will be given by showing performance improvement at non-trivial (not just constant) steady-state solutions, the interest for nonlinear solutions in otherwise linear output regulation problems, and the use of input reconfiguration to unveil otherwise stealthy attacks in cyber-physical systems.
18 October 2018, 10:00am, LAAS - Salle Tourmalet
Generation of Optimal Guidance Laws Under Epistemic Uncertainty and Imprecision
by Massimiliano Vasile
Abstract: The preliminary design of interplanetary trajectories with low-thrust propulsion is subject to uncertainty that is generally epistemic. In particular the properties of the propulsion system and their variability during the operational life of the spacecraft have a degree of uncertainty that can affect the overall system design and the reliability of the design solution. This talk will present an approach to model this epistemic uncertainty with Dempster-Shafer theory of Evidence and to compute robust and reliable guidance laws that optimise a performance index and satisfy a number of constraints. The approach is applied to the case of a low-thrust transfer from the Earth to an asteroid. The talk will present also a method to compute optimal guidance laws in the case uncertainty is propagated with a generalised polynomial algebra based on Chebyshev expansions.
16 October 2018, 10:00am, LAAS - Salle Europe
Impulsive zone Model Predictive Control: a particular formulation and some applications.
by Alejandro H. Gonzalez
Abstract: Many control problems - coming from very different areas that go from diseases treatments, to spacecraft guidance, passing through electronic and Nanoelectronic control- fell into the framework of what is called impulsive control: "a control paradigm based on impulsive differential equations in which a nonimpulsive plant has at least one impulsively changeable state variable". More precisely, we are interested in nonimpulsive plants (linear, time variant or invariant, continuous-time systems) controlled by impulsive actions, i.e., by manipulated actions producing a discontinuity of the trajectory solutions at certain time instants, and leaving the system free for the rest of the time.
Such systems have some particularities: they have no formal equilibriums out of the origin, they can be characterized by two discrete time sub-models describing the system just before and after the discontinuity (the jumps), their stability has to be defined in terms of two generalized equilibria, etc. Among the control strategies able to account for the impulsive schemes, model predictive control (MPC) is one of the most promising ones, because of its well-known benefits (constraint satisfaction, optimality, stability, etc.).
More important, MPC is able to account for the stability of equilibrium or invariant sets, instead of points, which means that once the closed-loop system reaches any point or trajectory in the target set, no further control actions are implemented (i.e., there are no preferences between points or trajectories inside the target set). In this talk, the details of a particular impulsive zone MPC formulation will be discussed. As a first step, a linear impulsive system characterization is made, which includes two discrete-time sub-systems and extended equilibrium and invariant sets, even in regions far from the origin. Then, an MPC formulation that takes advantage of the aforementioned characterization is presented. The main idea is to exploit the proper uses of artificial optimization variables and output target zones, which allows us to have an enlarged domain of attraction and preserves the stability and recursive feasibility of the closed loop. To motivate the potential application of the strategy, some simulation examples are proposed.
1 October 2018, 2pm, ENSEEIHT
Salma Kuhlmann (Constance) on moments and positive polynomials,
Jean-Claude Yakoubsohn (Toulouse) on certified computations for singular value decompositions.
18 September 2018, 2:00pm, LAAS - Salle Tourmalet
On the absence of spurious optimality
by Cédric Josz
Abstract: We study the set of continuous functions that admit no spurious local optima (i.e. local minima that are not global minima) which we term global functions. They satisfy various properties for analyzing nonconvex and nonsmooth optimization problems. For instance, they satisfy a theorem akin to the uniform limit theorem in analysis regarding continuous functions. Global functions are also endowed with properties regarding the composition of functions and change of variables. Using these results, we show that a class of nonconvex and nonsmooth optimization problems arising in tensor decomposition applications are global functions. This provides a theoretical guarantee for the l1 norm to avoid outliers in nonconvex optimization.
30 August 2018, 2:00pm, LAAS - Salle Europe
Game-Theoretic Approach to Security and Resilience of Cyber-Physical Systems
by Quanyan Zhu
Abstract: Game theory is an emerging modeling tool in engineering to capture complex interactions in large-scale intelligent systems such as autonomous systems, smart cities and the Internet of Things. Also, game theory is a quantitative method to understand conflicts and contentions among players or systems. These features make the theory an appropriate tool to model and design secure and resilient cyber-physical and human systems. In this talk, we will first give a short introduction to the theory and its applications. Then, we will present a meta-game approach to the multi-layer and multi-type cyber and physical interactions to provide a holistic analytical framework for assessing cyber risks of CPS under advanced persistent threats. We will leverage the theory as a guideline for developing security-hardening strategies for the network security and designing resilient controllers to respond to failures. We use the Internet of Controlled Things and the autonomous systems as case stu! dies to illustrate the design methodologies.
31 July 2018, 3:00pm, LAAS - Salle du Conseil
Discrete-Time Linear Systems with Stochastic Dynamics and LMI-Based Control
by Yohei Hosoe
Abstract: This study is concerned with the development of a theoretical basis for controlling discrete-time linear systems with stochastic dynamics. Although the general class of such dynamics is difficult to deal with in numerical analysis and synthesis, some subclasses are relatively easy. The dynamics determined by a Markov chain is a solid example of such subclasses and has been extensively studied in the field of Markov jump systems. In this study, on the other hand, we focus on as another subclass the stochastic dynamics determined by a process that is i.i.d. (independently and identically distributed) with respect to the discrete time. We discuss equivalence of some stability notions for the systems with such dynamics, and show a Lyapunov inequality condition that is necessary and sufficient for their stability. Since our Lyapunov inequality will involve decision variables contained in the expectation operation, an idea is provided to solve it as a standard LMI (linear matrix inequality). The idea can be further exploited in stabilization state feedback synthesis for the systems.
31 July 2018, 2:00pm, LAAS - Salle du Conseil
Low-Power High-Gain Observers
by Daniele Astolfi
Abstract: High-gain observers have been extensively used in nonlinear control since the end of the 80’s for their tunability property, namely the fact that the rate of convergence of the observer can be tuned by acting with one single high-gain parameter. This important feature is motivated by the use of observers in output feedback control and it has been proved that this tunability property plays a key role in establishing a nonlinear separation principle. Despite the evident benefits of this class of observers, their use in real applications is questionable due to some drawbacks. Mainly: numerical issues due to the fact that we need to implement coefficients which increases polynomially with the system dimension; the well-known peaking phenomenon; high sensitivity to measurement noise. Motivated by these considerations, we propose a new class of nonlinear high-gain observers, denoted as “low-power high-gain observers”, that preserves the same high-gain features but which s! ubstantially overtakes (or improves) the aforementioned drawbacks. The low-power high-gain observers are characterized by having coefficients which does not grow with the system dimension, by avoiding the peaking phenomenon and by improving the sensitivity to high-frequency measurement noise. The proposed observers can be used without loss of generality with respect to standard high-gain observers in frameworks of observations, output feedback or output regulation.
2 July 2018, 11:00am, LAAS - Salle Tourmalet
Numerical Computational Techniques for Nonlinear Optimal Control - Slides
by Yasuaki Oishi
Abstract: In this talk, I present the stable-manifold method, an effective method for nonlinear optimal control introduced by Sakamoto and van der Schaft in 2008, and propose two numerical computational techniques for its improvement. The first technique is for generation of points on the stable manifold in a robust way against numerical errors. There, a special numerical method that preserves Hamiltonian is used to solve a differential equation sensitive to numerical errors. The second technique is a sort of shooting method to generate a point corresponding to the desired system state. These techniques are used for optimal swing-up of a pendulum and successfully give a swing-up trajectory with multiple swings. This is a joint work with Noboru Sakamoto and Takuto Nakamura.
27 June 2018, 2:00pm, LAAS - Salle du Conseil
Formal Verification of Convex Optimization Algorithms For Model Predictive Control
by Raphaël Cohen
Abstract: The efficiency of modern optimization methods, coupled with increasing computational resources, has led to the possibility of real-time optimization algorithms acting in safety critical roles. However, this cannot happen without addressing proper attention to the soundness of these algorithms. This work discusses the formal verification of convex optimization algorithms with a particular emphasis on receding-horizon controllers. Additionally, we demonstrate how theoretical proofs of real-time optimization algorithms can be used to describe functional properties at the code level, thereby making it accessible for the formal methods community. In seeking zero-bug software, we use the Credible Autocoding scheme. We focused our attention on the ellipsoid algorithm solving second-order cone programs (SOCP). In addition to this, we present a floating-point analysis of the algorithm and give a framework to numerically validate the method.
19 June 2018, 10:45am, LAAS - Salle Europe
Lp stability of networked control systems implemented on WirelessHART
by Dragan Nesic
Abstract: Control systems in which sensor/actuator signals are sent via a communication network are increasingly important in various areas, such as X-by-wire technologies in the aerospace and automotive industries, smart grid, vehicle platoons, swarms of UAVs and control of large irrigation networks. Such networked control systems (NCS) are much harder to design and analyse because the communication network introduces a range of undesirable effects into the closed loop system, such as the sampling jitter, quantized signals, the need for signal scheduling, data dropouts, and so on. In the past decade, a large body of research addressed various issues in NCS via “generic” network models which are sometimes hard to apply to NCS with specific networks, such as CAN, Flexray or WirelessHART. In this talk I will concentrate on control oriented modelling of NCS with WirelessHART networks and then present results on an emulation oriented approach for achieving Lp stabilisation of such systems. We show that our results are less conservative (in an appropriate sense) than prior emulation results that do not exploit the specific network structure in the analysis.
19 June 2018, 9:30am, LAAS - Salle Europe
Glocal (Global/Local) Control towards Smart Cities
by Shinji Hara
Abstract: There are many dynamical systems that can be regarded as hierarchical networked dynamical systems in a variety of fields related to smart cities. One of the ideas to treat those systems properly is "Glocal (Global/Local) Control," which means that the global purpose is achieved by only local actions of measurement and control. The background and idea of glocal control are explained by showing the control perspective of IoT (Internet of Things).
The key for realization of glocal control is hierarchical networked dynamical systems with multiple resolutions in time and space depending on the layer. After introducing a unified framework, its fundamental control theory such as stability and robust stability is provided. Then, we focus on how to design hierarchically decentralized controls with global/local objectives by aggregation. Through the talk we show the effectiveness of the theoretical results for applications to electric vehicle control and power network systems towards smart cities.
Slides GlocalControl_LAAS_June2018SH.pdf available in MAC team Intranet.
11 June 2018, 2pm, ENSEEIHT
28 May 2018, 2pm, ENSEEIHT
23 April 2018, 1:30pm, LAAS - Salle Tourmalet
Peak Effects in Stable Linear Difference Equations
by Pavel Shcherbakov
Abstract: We consider homogenous, linear, asymptotically stable scalar difference equations with constant coefficients and unit-norm initial conditions. First, it is shown that the solution may happen to deviate far away from the equilibrium point at finite time instants prior to converging to zero. Second, for a number of root distributions and initial conditions, exact values of deviations or lower bounds are provided. Several specific difference equations known from the literature are also analyzed and estimates of deviations are proposed. Possible generalizations are discussed and directions for future research are outlined.
17 April 2018, ONERA
International Workshop on Robust LPV Control Techniques and Anti-Windup Design
16 April 2018, 2pm, ENSEEIHT
5 April 2018, 2pm, LAAS - Salle du Conseil
Regulation of linear PDE's by P-I controller using a Lyapunov approach inspired by forwarding methods. Theory and application to the drilling case - Slides
by Alexandre Terrand-Jeanne
Abstract: Most of the existing results for the regulation of PDE's are based on semi-group and spectral theory. However, these results impose bounds on the control and the measurement operators. For instance, the boundary regulation of hyperbolic PDE employing control at the boundaries, can not be addressed. In order to deals with more general systems, we introduce a novel Lyapunov functionnal inspired by nonlinear forwarding technics. Our approach is then illustrated in the case of a drilling system.
8 March 2018, 11am, LAAS - Salle de Conférence
Lyapunov-based analysis of TDSs and PDEs
by Anton Selivanov
Abstract: I will briefly describe some resent results devoted to control and stability analysis of time-delay systems and PDEs. All results were obtained using Lyapunov(-Krasovskii) functionals whose properties are guaranteed by feasibility of certain linear matrix inequalities. First, I will talk about delay-induced stability – a phenomenon that occurs when a system cannot be stabilized using the output but can be stabilized using the output together with its delayed value. Then I’ll talk about the event-triggered control with a dwell time and predictor-based event-triggered control. A significant part of the talk will be devoted to control of PDEs. We will discuss event-triggered control of PDEs, relay control of PDEs, and input delay compensation using the idea of chain predictors. All the results were obtained jointly with Emilia Fridman.