2SL2S  - Pre-Conference Talks

19 July 2016, 11h30 at CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40

Lyapunov-based formation-tracking control of nonholonomic systems under persistency of excitation.

Mohamed Adlene Maghenem, Antonio Loría, Elena Panteley

We present a smooth nonlinear time-varying controller for leader-follower tracking of non-holonomic mobile robots. Our design relies upon the standing assumption that either the rotational or the translational reference velocity is persistently exciting. Then, we extend our results to cover the problem of formation tracking for a swarm of vehicles interconnected under a spanning tree communication topology rooted at the virtual leader. In this case, we propose a simple distributed control law that establishes the convergence of the error coordinate of each agent, relatively to its neighbourhood, under the same condition of persistency of excitation. In addition, our proofs are based on Lyapunov's second method, that is, we provide a strict Lyapunov function.

Energy Shaping Control of an Inverted Flexible Pendulum Fixed to a Cart

Prasanna Gandhi, Luis Pablo Borja, Romeo Ortega

Control of compliant mechanical systems is increasingly being researched for several applications including flexible link robots and ultra-precision positioning systems. The control problem in these systems is challenging, especially with gravity coupling and large deformations, because of inherent underactuation and the combination of lumped and distributed parameters of a nonlinear system. In this paper we consider an ultra-flexible inverted pendulum on a cart and propose a new nonlinear energy shaping controller to keep the pendulum at the upward position with the cart stopped at a desired location. The design is based on a model, obtained via the constrained Lagrange formulation, which  previously has been validated experimentally.  The controller design consists of a partial feedback linearization step followed by a standard PID controller acting on two passive outputs. Boundedness of all signals and (local) asymptotic stability of the desired equilibrium is theoretically established. Simulations and experimental evidence assess the performance of the proposed controller.

A strict Lyapunov function for non-holonomic systems under persistently-exciting controllers.

Mohamed Adlene Maghenem, Antonio Loría, Elena Panteley

We study the stability of a non linear time-varying skew symmetric systems \dot{x} = A(t, x)x with particular structures that appear in the study problems of non holonomic systems in chained form as well as adaptive control systems. Roughly, under the condition that each non diagonal element of A(t, x) is persistently exciting or uniform  persistently exciting with respect x. Although some stability results are known in this area, our main contribution lies in the construction of Lyapunov functions that allows a computation of convergence rate estimates for the class of non linear systems under study.



2SL2S  - Pre-Conference Talks

1st July 2016, 11h30 at CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40

Particle Swarm Optimization of Matsuoka's Oscillator Parameters in Human-Like Control of Rhythmic Movements

Guillaume Avrin, Maria Makarov, Pedro Rodriguez-Ayerbe, Isabelle Anne Siegler

In the field of neuroscience, the Matsuoka's nonlinear neural oscillator is commonly used to model Central Pattern Generator (CPG) in humans/animals. How the parameters of such structure should be selected is not always clear. It was generally done in past studies thanks to a trial-and-error method that needs to be reiterated each time the task changes. Recent studies using a Describing Function Analysis (DFA) of this CPG model provide interesting analytical tuning methods. Nevertheless, as they are based on a linear approximation, they might have a limited efficiency in the particular case of timing-sensitive task, such as the ball-bouncing task considered in this study. A Particle Swarm Optimization (PSO) is thus proposed to select the parameters of a novel neural oscillator-based human-like control architecture able to face disturbances and to adapt to new reference set-points during the ball-bouncing task. The general method presented in the present paper can also be used for other Matsuoka's oscillator tunings and other tasks.



2SL2S  - Regular Talks

11 February 2016, 13h30 at CentraleSupelec (Gif-sur-Yvette) Room F3.05 (level 3)

Lyapunov Stability Analysis of Immature Cell Dynamics in Healthy and Unhealthy Hematopoiesis. 

Walid Djema, Frédéric Mazenc, Catherine Bonnet

The knowledge of Lyapunov-Krasovskii functionals offers strong advantages when investigating the local or global stability properties of equilibrium points of a system with delay. Unfortunately, in many cases the construction of these functionals is not an easy task. This is the case of the model describing hematopoiesis, which is a nonlinear system with distributed delays, which, according to some conditions,  admits one or two equilibrium points. By contrast with approaches already used to study this model, we analyze the stability properties of its equilibrium points by constructing Lyapunov-Krasovskii functionals of two types.
In a second step, we discuss the case of unhealthy hematopoiesis. The resulting model takes into account the fact that some parameters, identified as control variables (through drug delivery), are now supposed to be time-varying. Via a novel Lyapunov-Krasovskii functional, stability and instability results are derived for the zero equilibrium of the model.

Set invariance for Delay Difference Equations

Mohammed T. Laraba, Sorin Olaru, Silviu Iulian Niculescu.

This paper deals with set invariance for time delay systems. The first goal is to review the known necessary and/or sufficient conditions for the existence of invariant sets with respect to dynamical systems described by discrete-time delay difference equations (DDEs). Secondly, we address the construction of invariant sets in the original state space (also called D-invariant sets) by exploiting the forward mappings. It will be shown that bilevel optimization problems can also be used for D-invariance design problems. The difficulties related to the nonlinearity of the optimization and the complementarity constraints will be discussed as well as the objective functions which can translate additional features of the D-invariant sets. The notion of D-invariance is interesting because it provides a region of attraction, which is difficult to obtain for delay systems without taking into account the delayed states in an extended state space model.



2SL2S  - Pre-Conference Talks

7 December 2015, 9h50 at CentraleSupelec (Gif-sur-Yvette) Amphithéâtre Ampère

Global Stabilization of Multiple Integrators by a Bounded Feedback with Constraints on Its Successive Derivatives.

Jonathan Laporte, Antoine Chaillet, Yacine Chitour

In this paper, we address the global stabilization of chains of integrators by means of a bounded static feedback law whose p first time derivatives are bounded. Our construction is based on the technique of nested saturations introduced by Teel. We show that the control amplitude and the maximum value of its p first derivatives can be imposed below any prescribed values. Our results are illustrated by the stabilization of the third order integrator with prescribed bounds on the feedback and its first two derivatives.

Migration of double imaginary characteristic roots under small deviation of two delay parameters

Keqin Gu, Dina Alina Irofti, Islam Boussaada, Silviu-Iulian Niculescu

We study the migration of double imaginary roots of the characteristic equation for systems with two delays when the delay parameters are subjected to small deviations. As the double roots are not differentiable with respect to the delay parameters, Puiseux series is often used in such a situation in the literature. However, we study the ``least degenerate'' case by using a more traditional analysis, without involving Puiseux series. It was found that the local stability crossing curve has a cusp at the point in the parameter space that causes the double root, and it divides the neighborhood of this point into a G-sector and an S-sector. When the parameters move into the G-sector, one of the roots moves to the right half plane, and the other moves to the left half plane. When the parameters move into the S-sector, both roots move either to the left half plane or the right half plane depending on the sign of some value explicitly expressed in terms of derivatives of the characteristic function up to the third order.


Inverse Parametric Linear/quadratic Programming Problem for Continuous PWA Functions Defined on Polyhedral Partitions of Polyhedra

Ngoc Anh Nguyen, Sorin Olaru, Pedro Rodriguez-Ayerbe

Constructive solution to inverse parametric linear/quadratic programming problems has recently been investigated
and shown to be solvable via convex liftings. These results were stated and solved starting from polytopic
partitions of a polytope in the parameter space. Therefore, the case of polyhedral partitions of unbounded polyhedra, was not
handled by this method and deserves a complete characterization to address the general inverse optimality problem. This
paper has as main objective to overcome the unboundedness limitation of the given polyhedral partition and to extend the
constructive solution for this omitted case.