Keywords
Computer Science and Digital Science
 A6.1.1. Continuous Modeling (PDE, ODE)
 A6.1.3. Discrete Modeling (multiagent, people centered)
 A6.4.1. Deterministic control
 A6.4.3. Observability and Controlability
 A6.4.4. Stability and Stabilization
Other Research Topics and Application Domains
 B2.5. Handicap and personal assistances
 B3.6. Ecology
 B4.3.1. Biofuels
 B5.2.3. Aviation
 B7.2.1. Smart vehicles
1 Team members, visitors, external collaborators
Research Scientists
 Catherine Bonnet [Team leader, Inria, Senior Researcher, HDR]
 Islam Boussaada [CNRS, Researcher, HDR]
 Guilherme Mazanti [Inria, from Oct 2020, Starting Faculty Position]
 Frédéric Mazenc [Inria, Senior Researcher, HDR]
Faculty Members
 SilviuIulian Niculescu [CNRS, Professor, HDR]
 Giorgio Valmorbida [CentraleSupélec, Associate Professor]
PostDoctoral Fellow
 Guilherme Mazanti [IPSA, CentraleSupélec, Inria, until Sep 2020]
PhD Students
 Amina Benarab [Univ ParisSud]
 Jose De Jesus Castillo Zamora [Univ ParisSud]
 Ali Diab [Univ ParisSaclay]
 Ricardo Falcon Prado [Univ ParisSud]
 Jose Hernandez Diez [Université autonome de San Luis Potosí  Mexique]
 Alejandro Martinez Gonzalez [CentraleSupélec]
 Javier Pereyra Zamudio [Institut Polytechnique National de Mexico  Mexique]
 Jeanne Redaud [CentraleSupélec, from Nov 2020]
 Saeed Sadeghi Arjmand [École polytechnique]
Administrative Assistant
 Irina Lahaye [Inria]
External Collaborator
 Ali Zemouche [Univ de Lorraine, HDR]
2 Overall objectives
2.1 Objectives
The goal of the project is to better understand and well formalize the effects of complex environments on the dynamics of the interconnections, as well as to develop new methods and techniques for the analysis and control of such systems.
It is wellknown that the interconnection of dynamic systems has as consequence an increased complexity of the behavior of the total system.
In a simplified way, as the concept of dynamics is wellunderstood, the interconnections can be seen as associations (by connections of materials or information flows) of distinct systems to ensure a pooling of the resources with the aim of obtaining a better operation with the constraint of continuity of the service in the event of a fault. In this context, the environment can be seen as a collection of elements, structures or systems, natural or artificial constituting the neighborhood of a given system. The development of interactive games through communication networks, control from distance (e.g. remote surgical operations) or in hostile environment (e.g. robots, drones), as well as the current trend of large scale integration of distribution (and/or transport and/or decision) and open information systems with systems of production, lead to new modeling schemes in problems where the dynamics of the environment have to be taken into account.
In order to tackle the control problems arising in the above examples, the team investigates new theoretical methods, develops new algorithms and implementations dedicated to these techniques.
3 Research program
3.1 Analysis of interconnected systems
The major questions considered are those of the characterization of the stability (also including the problems of sensitivity compared to the variations of the parameters) and the determination of stabilizing controllers of interconnected dynamic systems. In many situations, the dynamics of the interconnections can be naturally modelled by systems with delays (constant, distributed or timevarying delays) possibly of fractional order. In other cases, partial differential equations (PDE) models can be better represented or approximated by using systems with delays. Our expertise on this subject, on both time and frequency domain methods, allows us to challenge difficult problems (e.g. systems with an infinite number of unstable poles).

Robust stability of linear systems
Within an interconnection context, lots of phenomena are modelled directly or after an approximation by delay systems. These systems may have constant delays, timevarying delays, distributed delays $...$
For various infinitedimensional systems, particularly delay and fractional systems, inputoutput and timedomain methods are jointly developed in the team to characterize stability. This research is developed at four levels: analytic approaches (${H}_{\infty}$stability, BIBOstablity, robust stability, robustness metrics) 1, 2, 6, 7, symbolic computation approaches (SOS methods are used for determining easytocheck conditions which guarantee that the poles of a given linear system are not in the closed right halfplane, certified CAD techniques), numerical approaches (rootloci, continuation methods) and by means of softwares developed in the team 6, 7.

Robustness/fragility of biological systems
Deterministic biological models describing, for instance, species interactions, are frequently composed of equations with important disturbances and poorly known parameters. To evaluate the impact of the uncertainties, we use the techniques of designing of global strict Lyapunov functions or functional developed in the team.
However, for other biological systems, the notion of robustness may be different and this question is still in its infancy (see, e.g. 64). Unlike engineering problems where a major issue is to maintain stability in the presence of disturbances, a main issue here is to maintain the system response in the presence of disturbances. For instance, a biological network is required to keep its functioning in case of a failure of one of the nodes in the network. The team, which has a strong expertise in robustness for engineering problems, aims at contributing at the develpment of new robustness metrics in this biological context.
3.2 Stabilization of interconnected systems

Linear systems: Analytic and algebraic approaches are considered for infinitedimensional linear systems studied within the inputoutput framework.
In the recent years, the YoulaKu$\stackrel{\u02c7}{\mathrm{c}}$era parametrization (which gives the set of all stabilizing controllers of a system in terms of its coprime factorizations) has been the cornerstone of the success of the ${H}_{\infty}$control since this parametrization allows one to rewrite the problem of finding the optimal stabilizing controllers for a certain norm such as ${H}_{\infty}$ or ${H}_{2}$ as affine, and thus, convex problem.
A central issue studied in the team is the computation of such factorizations for a given infinitedimensional linear system as well as establishing the links between stabilizability of a system for a certain norm and the existence of coprime factorizations for this system. These questions are fundamental for robust stabilization problems 1, 2.
We also consider simultaneous stabilization since it plays an important role in the study of reliable stabilization, i.e. in the design of controllers which stabilize a finite family of plants describing a system during normal operating conditions and various failed modes (e.g. loss of sensors or actuators, changes in operating points). Moreover, we investigate strongly stabilizable systems, namely systems which can be stabilized by stable controllers, since they have a good ability to track reference inputs and, in practice, engineers are reluctant to use unstable controllers especially when the system is stable.

Nonlinear systems
In any physical systems a feedback control law has to account for limitation stemming from safety, physical or technological constraints. Therefore, any realistic control system analysis and design has to account for these limitations appearing mainly from sensors and actuators nonlinearities and from the regions of safe operation in the state space. This motivates the study of linear systems with more realistic, thus complex, models of actuators. These constraints appear as nonlinearities as saturation and quantization in the inputs of the system 10.
The project aims at developing robust stabilization theory and methods for important classes of nonlinear systems that ensure good controller performance under uncertainty and time delays. The main techniques include techniques called backstepping and forwarding, contructions of strict Lyapunov functions through socalled "strictification" approaches 4 and construction of LyapunovKrasovskii functionals 5, 6, 7 or or Lyapunov functionals for PDE systems 9.
3.3 Synthesis of reduced complexity controllers

PID controllers
Even though the synthesis of control laws of a given complexity is not a new problem, it is still open, even for finitedimensional linear systems. Our purpose is to search for good families of “simple” (e.g. low order) controllers for infinitedimensional dynamical systems. Within our approach, PID candidates are first considered in the team 2, 68.
For interconnected systems appearing in teleoperation applications, such as the steerbywire, ProportionalDerivative laws are simple control strategies allowing to reproduce the efforts in both ends of the teleoperation system. However, due to delays introduced in the communication channels these strategies may result in loss of closed loop stability or in performance degradation when compared to the system with a mechanical link (no communication channel). In this context we search for nonlinear proportional and derivative gains to improve performance. This is assessed in terms of reduction of overshoot and guaranteed convergence rates.

Delayed feedback
Control systems often operate in the presence of delays, primarily due to the time it takes to acquire the information needed for decisionmaking, to create control decisions and to execute these decisions. Commonly, such a time delay induces desynchronizing and/or destabilizing effects on the dynamics. However, some recent studies have emphasized that the delay may have a stabilizing effect in the control design. In particular, the closedloop stability may be guaranteed precisely by the existence of the delay. The interest of considering such control laws lies in the simplicity of the controller as well as in its easy practical implementation. It is intended by the team members to provide a unified approach for the design of such stabilizing control laws for finite and infinite dimensional plants 3, 8.

Finite Time and Interval Observers for nonlinear systems
We aim to develop techniques of construction of output feedbacks relying on the design of observers. The objectives pertain to the design of robust control laws which converge in finite time, the construction of intervals observers which ensure that the solutions belong to guaranteed intervals, continuous/discrete observers for systems with discrete measurements and observers for systems with switches.
Finally, the development of algorithms based on both symbolic computation and numerical methods, and their implementations in dedicated Scilab/Matlab/Maple toolboxes are important issues in the project.
4 Application domains
4.1 Analysis and Control of life sciences systems
The team is involved in life sciences applications. The two main lines are the analysis of bioreactors models (microorganisms; bacteria, microalgae, yeast, etc..) and the modeling of cell dynamics in Acute Myeloblastic Leukemias (AML) in collaboration with St Antoine Hospital in Paris.
4.2 Energy Management
The team is interested in Energy management and considers control problems in energy networks.
5 Highlights of the year
5.1 Invited Professorship
Giorgio Valmorbida was awarded the “Chaires FrancoBrésiliennes” de l'état de São Paulo de l'année 2020.
6 New software and platforms
6.1 New software
6.1.1 P3δ
 Name: Partial pole placement via delay action
 Keywords: Delay systems, Control design, Automatic control
 Functional Description: A Python implementation of recent methods for the stability analysis and stabilization of linear timedelay systems exploiting the delay action. Its control design strategy is based on properties of the spectral distribution of the timedelay system.
 Release Contributions: Generic and controloriented MID

URL:
https://
iboussaa. gitlabpages. inria. fr/ partialpoleplacementviadelayaction/ P3dHome. html  Contacts: Islam Boussaada, Guilherme Mazanti, SilviuIulian Niculescu
 Partners: Cyb'AirIPSA, ICODE, CentraleSupélec
7 New results
7.1 Multiplicityinduceddominancy
Participants: Jean Auriol, Tamas Balogh, Amina Benarab, Catherine Bonnet, Islam Boussaada, Ali El Ati, Tamas Insperger, Guilherme Mazanti, Csenge Molnar, Hugues Mounier, SilviuIulian Niculescu, Karim Trabelsi.
The effects of the multiplicity of spectral values on the exponential stability of reducedorder retarded differential equation were studied in recent works by the team, in which a property called multiplicityinduceddominancy (MID) was introduced for reducedorder systems. The MID is explored in the general class of $n$th order retarded differential equations with a single delay in 38 where the existence of a real root with maximal multiplicity is characterized in terms of the equation parameters. This root is shown to be always strictly dominant, determining thus the asymptotic behavior of the system. The dominancy proof is based on improved a priori bounds on the imaginary part of roots on the complex right halfplane and a suitable factorization of the characteristic function, which is an alternative technique to the argument principle.
A controloriented version of the MID property is proposed in 50. As a matter of fact, it is shown that the dominancy of a multiple spectral value holds even if the corresponding multiplicity is not maximal. A sufficient condition is given for the dominancy of a real root with multiplicity $n+1$ for $n$th order retarded equations. In particular, the stabilizing effect of such a multiplicity holds for realrooted openloop plants. The delay intervals are derived as well as the set of parameters satisfying stabilizability and dominancy conditions. The efficiency of the proposed controller design is shown in the case of a multilink inverted pendulum.
In 39, the MID property is extended to a given pair of complex conjugate roots for a generic secondorder retarded differential equation. Necessary and sufficient conditions for the existence of such a pair are provided, and it is also shown that such a pair is always necessarily dominant. It appears also that when the frequency corresponding to this pair of roots tends to 0, then the pair of roots collapse into a real root of maximal multiplicity. The latter property is exploited in the dominancy proof together with a study of crossing imaginary roots.
Further extension of the MID is shown for a wider class of delay differentialalgebraic system. It is shown in 36 that the MID property holds for scalar firstorder neutral delay equations as well as for a firstorder lossless propagation model. In 51, for second order neutral timedelay differential equations, necessary and sufficient conditions for the existence of a root of maximal multiplicity are given in terms of this root and the parameters of the given equation. Links with dominancy of this root and with the exponential stability property of the solution of the considered equations are emphasized.
In 25 single and double inverted pendulum systems subjected to delayed state feedback are analyzed in terms of stabilizability. The maximum (critical) delay that allows a stable closedloop system is determined via the MID property of the characteristic roots. It is shown that, using the MIDbased approach, the critical delay and the associated control gains can be easily carried out from the expression of the characteristic equation and its derivatives. Such a combination of inverted pendulums is usually used to describe biomechanics structures such as the human balance. The delayed nature of the central nervous system (CNS) action on the interaction muscletendon is essentially due to the propagation of the neural signals. In 48, the CNS is modeled as a delayed proportionalderivative (PD) controller exploiting the MID property. The birth of oscillation in the muscletendon junction is characterized through a critical delay and PD gains.
In 49 a controloriented model of torsional vibrations occurring in rotary oilwell drilling process is proposed. Such vibrations are known to constitute an important source of economic losses; drill bit wear, pipe disconnection, borehole disruption and prolonged drilling time, among other consequences. More precisely, torsional vibrations are assumed to be governed by a wave equation with weak damping term. An appropriate stabilizing controller with a reduced number of parameters is proposed for damping such torsional vibrations. Such a controller allows further exploration of the effect of multiple roots with maximal admissible multiplicity for linear neutral systems with a single delay. The MIDbased design is further exploited to quench the torsional vibrations along the rotary drilling system. The proposed control law guarantees the existence of robustness margins with respect to delays and parameters uncertainties.
7.2 Pole placement techniques for timedelay systems
Participants: Amrane Souad, Fazia Bedouhene, Islam Boussaada, SilviuIulian Niculescu, Sami Tliba.
The interest in investigating multiple spectral values does not rely on the multiplicity itself, but rather on its connection with the dominance of the corresponding root, and the ensuing applications in stability analysis and control design. The effect of the coexistence of such distinct real spectral values on the asymptotic stability of the trivial solution were recently emphasized by the team and shown for reducedorder systems. It was stressed that the coexistence of an appropriate number of real spectral values makes them rightmost roots of the corresponding quasipolynomial. Furthermore, if they are negative, this guarantees the asymptotic stability of the trivial solution. This property was called coexistent real roots inducing dominancy (CRRID).
For instance, 47 provides an appropriate stability criterion for secondorder systems based on the manifold defined by the coexistence of the maximal number of negative spectral values. Next, such ideas are exploited in the context of delayed output feedback by an appropriate partial pole placement guaranteeing simultaneously the stability in closedloop and an appropriate exponential decay rate. To perform such an analysis, the argument principle is employed.
The CRRID is further explored in 11 where the structural properties of a class of functional Vandermonde matrices is exploited to emphasize some qualitative properties of a class of linear autonomous $n$th order differential equation with forcing term consisting in the delayed dependentvariable. More precisely, it deals with the stabilizing effect of delay parameters coupled with the coexistence of the maximal number of real spectral values. The derived conditions are necessary and sufficient and represent a novelty in the litterature. Under appropriate conditions, such a configuration characterizes the spectral abscissa corresponding to the studied equation. A new stability criterion is proposed. This criterion extends recent results in factorizing quasipolynomial functions. The applicative potential of the proposed method is illustrated through the stabilization of coupled oscillators.
As an application of the proposed partial pole placement, the problem of active vibration damping for a thin axisymmetric membrane is considered in 44. The considered mechanical system is equipped with two piezoelectric circular patches: one of them works as a sensor and the other is used as an actuator. Both are fixed on the membrane, one on each side, and centered according to its axis of symmetry. The model of this system is obtained from a finite element analysis, leading to a linear statespace model. The design of the proposed control scheme is based on delayed proportional actions. The CRRID is exploited to an assignment of spectral values in an appropriate sector corresponding to a desired damping. The purpose of this work is to investigate the properties of the proposed output feedback controller in terms of vibration damping of the main observable and controllable vibrating modes as well as its robustness with respect to the neglected modes.
7.3 PID tuning for controlling delayed dynamics
Participants: Catherine Bonnet, Islam Boussaada, Jie Chen, Jianqi Chen, Andong Liu, Dan Ma, Silviu Niculescu.
Nowadays, the PID controller is the most used in controlling industrial processes. In 55, the MID property which is merely a delayedoutputfeedback where the candidates' delays and gains result from the manifold defining the maximal multiplicity of a real spectral value, is employed in the PID tuning for delayed plants. More precisely, the controller gains $({k}_{i},\phantom{\rule{0.277778em}{0ex}}{k}_{p},\phantom{\rule{0.277778em}{0ex}}{k}_{d})$ are tuned using the intentional multiplicity algebraic constraints allowing the stabilization of unstable delayed plants. The specificity of such a design is related to the analytical assignment of the closedloop solution decay rate.
7.4 Characterizing PID Controllers for Linear TimeDelay Systems: A ParameterSpace Approach
Participants: SilviuIulian Niculescu, XuGuang Li, JunXiu Chen, Tianyou Chai.
The paper 18 addresses the proportionalintegralderivative (PID) controller design problem for linear timedelay systems. All the controller gains and the delay are treated as free parameters and no particular constraints are imposed on he controlled plants. First, we will develop an algebraic algorithm to solve the stability problem w.r.t. to the delay parameter. Consequently, for any given PID controller, the distribution of the characteristic roots in the complex plane can be accurately obtained and the exhaustive stability range of the delay be automatically calculated. Next, a global understanding of the distribution of the characteristic roots in the righthalf plane over the whole 3dimensional controller gainparameter space may be achieved and all structural changes regarding the distribution on the unstable characteristic roots can be analytically determined. To achieve such a goal, a complete positive real root classification (for some appropriate auxiliary characteristic equation) will be explicitly proposed. Finally, a new parameterbased methodology is proposed for determining the stability set in the whole set of parameters defined by the controller gains (proportional, integral, derivative) and the delay.
7.5 Frequencysweeping techniques in delayed dynamics analysis
Participants: Arben Cela, XuGuang Li, Xu Li, JiangChian Li, ZhiZhong Mao, Silviu Niculescu, Lu Zhang.
The stability of linear systems with multiple (incommensurate) delays is investigated in 66, by extending a recently proposed frequencysweeping approach. First, we consider the case where only one delay parameter is free while the others are fixed. The complete stability w.r.t. the free delay parameter can be systematically investigated by proving an appropriate invariance property. Next, we propose an iterative frequencysweeping approach to study the stability under any given multiple delays. Moreover, we may effectively analyze the asymptotic behavior of the critical imaginary roots (if any) w.r.t. each delay parameter, which provides a possibility for stabilizing the system through adjusting the delay parameters. The approach is simple (graphical test) and can be applied systematically to the stability analysis of linear systems including multiple delays. A deeper discussion on its implementation is also proposed. Finally, various numerical examples complete the presentation.In most of the numerical examples of timedelay systems proposed in the literature, the number of unstable characteristic roots remains positive before and after a multiple critical imaginary root (CIR) appears (as the delay, seen as a parameter, increases). This fact may lead to some misunderstandings: (i) A multiple CIR may at most affect the instability degree; (ii) It cannot cause any stability reversals (stability transitions from instability to stability). As far as we know, whether the appearance of a multiple CIR can induce stability is still unclear (in fact, when a CIR generates a stability reversal has not been specifically investigated). In 65, we provide a finer analysis of stability reversals and some new insights into the classification: the link between the multiplicity of a CIR and the asymptotic behavior with the stabilizing effect. Based on these results, we present an example illustrating that a multiple CIR’s asymptotic behavior is able to cause a stability reversal. To the best of the authors’ knowledge, such an example is a novelty in the literature on timedelay systems.
The work 69 focuses on the stability property of a class of distributed delay systems with constant coefficients. More precisely, we will discuss deeper the stability analysis with respect to the delay parameter. Our approach will allow to give new insights in solving the socalled complete stability problem. There are three technical issues need to be studied: First, the detection of the critical zero roots; second, the analysis of the asymptotic behavior of such critical zero roots; third, the asymptotic behavior analysis of the critical imaginary roots with respect to the infinitely many critical delays. We extended our recentlyestablished frequencysweeping approach, with which these technical issues can be effectively solved. More precisely, the main contributions of this paper are as follows: (i) Proposing a method for the detection of the critical zero roots. (ii) Proposing an approach for the asymptotic behavior analysis of such critical zero roots. (iii) The invariance property for the critical imaginary roots can be proved. Based on these results, a procedure was proposed, with which the complete stability analysis of such systems was accomplished systematically. Moreover, the procedure represents a unified approach: Most of the steps required by the complete stability problem may be fulfilled through observing the frequencysweeping curves. Finally, some examples illustrate the effectiveness and advantages of the approach.
7.6 Weierstrass approach to asymptotic behavior of retarded differential equations
Participants: Jie Chen, Liliana Felix, Alejandro MartinezGonzalez, Cesar F. MendezBarrios, Silviu Niculescu.
The work 67 focuses on the analysis of the behavior of characteristic roots of timedelay systems, when the delay is subject to small parameter variations. The analysis is performed by means of the Weierstrass polynomial. More specifically, such a polynomial is employed to study the stability behavior of the characteristic roots with respect to small variations on the delay parameter. Analytic and splitting properties of the Puiseux series expansions of critical roots are characterized by allowing a full description of the cases that can be encountered. Several numerical examples encountered in the control literature are considered to illustrate the effectiveness of the proposed approach.7.7 Some remarks on the regular splitting of quasipolynomials with two delays. Characterization of double roots in degenerate cases
Participants: SilviuIulian Niculescu, Alejandro MartinezGonzalez, Fernando MendezBarrios.
The paper 34 addresses the classification of multiple critical roots of dynamical continuous linear timeinvariant systems including two constant delays in their mathematical representation. By considering the associated Weierstrass polynomial and its algebraic properties, the paper presents the splitting behavior of such critical roots when the delays are subject to small variations. Some degenerate cases are also considered. Furthermore, the proposed methodology allows to relax some of the existing assumptions in the literature and can be generalized to systems including more than two delays. The effectiveness of the proposed approach is illustrated through several numerical examples.
7.8 Controllability of linear delay systems and of its samples version
Participants: SilviuIulian Niculescu, Hugues Mounier.
The paper 56 focuses on the controllability preservation through sampling of linear timedelay systems. We make use of a module theoretic framework acting as a unifying one for most of the existing delay system controllability notions. The controllability properties are envisioned through ring theoretic properties. Some illustrative examples complete the presentation.
7.9 Some Insights on the Asymptotic Stabilization of a Class of SISO Marginally Stable Systems Using One Delay Block
Participants: SilviuIulian Niculescu, JoséEnrique HernándezDíez, Fernando MendezBarrios.
The stability of a class of marginally stable SISO systems is studied by applying one delay block as a feedback controller. More precisely, we consider an openloop system with no zeros and whose poles are located exactly on the imaginary axis. Furthermore, a control law formed uniquely by a proportional gain and a delayed behavior is proposed for its closedloop stabilization. The main ideas are based on a detailed analysis of the characteristic quasipolynomial of the closedloop system as the controller parameters (gain, delay) are varied. More precisely, by using the Mikhailov stability criterion, for a fixed delay value, some gains margin guaranteeing the closedloop stability are explicitly computed. The particular case when the characteristic roots of the openloop system are equidistantly distributed on the imaginary axis is also addressed. Finally, an illustrative example shows the effectiveness of the approach.
7.10 Bézout Identity in Pseudoratoinal Transfer Functions
Participants: Catherine Bonnet, Yutaka Yamamoto.
Coprime factorizations of transfer functions play various important roles, e.g., minimality of realizations, stabilizability of systems, etc. We have studied the Bézout condition over the ring ${\u03f5}^{\text{'}}\left({\mathbb{R}}_{}\right)$ of distributions of compact support and the ring $\mathcal{M}\left({\mathbb{R}}_{}\right)$ of measures with compact support. These spaces are known to play crucial roles in minimality of state space representations and controllability of behaviors. We have given a new attempt of deriving general results from that for measures. It is clarified that there is a technical gap in generalizing the result for $\mathcal{M}\left({\mathbb{R}}_{}\right)$ to that for ${\u03f5}^{\text{'}}\left({\mathbb{R}}_{}\right)$. A detailed study of a concrete example is given in 46.7.11 Stability analysis of PieceWise Affine Systems
Participants: Giorgio Valmorbida, Leonardo Broering Groff, Joao Manoel Gomes da Silva Jr, Francesco Ferrante.
Piecewise affine systems appear when linear dynamics are defined in different partitions of the state space. This type of system naturally appears whenever actuators have different stages or saturate or whenever nonlinear control laws are obtained as the solution to a parameterised optimization problem as, for instance for systems with feedback laws based on the socalled explicit Model Predictive Control. Even though the dynamics is simple to describe, the stability analysis, performance assessment and robustness analysis are difficult to perform since, due to the often used explicit representation, the Lyapunov stability and dissipation tests are often described in terms of a number of inequalities that increase exponentially on the number of sets in the partition since they are based on the enumeration of the partition transitions. Moreover regional stability and uncertainties corresponding to modification on the partition are difficult to study in this scenario.To overcome these difficulties we have proposed an implicit representation for this class of systems in terms of ramp functions. The main advantage of such a representation lies on the fact that the ramp function can be exactly characterized in terms of linear inequalities and a quadratic equation, namely a linear complementarity condition. Thanks to the characterization of the ramp function and the implicit description of the PWA system the verification of Lyapunov inequalities related to piecewise quadratic functions can be cast as a pair of linear matrix inequalities.
We are now applying the results to the local analysis and synthesis of PWA control laws. These results generalise the local analysis of saturating systems and avoid the complexity of PWA system analysis which is currently based on enumeration of the transition in a PWA partition. We have also developed an eventtriggered strategy that also avoids the enumeration and relies on an piecewise quadratic triggering function. This strategies allow to reduce the number of evaluation of control actions.
We have also shown that the step function can be written as an illposed algebraic loop with two ramp functions. We were thus able to unify the analysis of continuous and discontinuous PWA functions and thus to perform the analysis with partitionbased Lyapunov functions. As a first case to apply the developed methodology, we have studied the class of systems with ternary inputs.
A strategy for the solution of quadratic programs, based on the representation of PWA function in terms of ramp function, is currently under development.
7.12 Stability analysis of Slope Restricted Lurie Systems
Participants: Giorgio Valmorbida, Ross Drummond, Pedro Luis Dias Peres, Ricardo C. L. Fontoura Oliveira .
For nonlinear Lurie Systems in discretetime, the stability or stabilisation can be studied with two main approaches: the Lyapunov analysis and the multiplier analysis. For the Lyapunov analysis, a model given by a difference equation is considered and, if the nonlinearity is sector and slope restricted, no necessary and sufficient condition for stability is known to date. We have proposed new classes of Lyapunov functions to study the local and global properties for the nonlinear distcretetime systems.
For the design of control laws, we have recently proposed an iterative method for the approaches of Lyapunov functions computation. This method is now being extended to consider the frequencydomain strategy of obtaining ZamesFalb multipliers.
7.13 New advances on backstepping
Participants: Frédéric Mazenc, Michael Malisoff, Sabine Mondie, Javier Zamudio, Laurent Burlion.
In the paper 42, we develop an alternative approach of the fundamental design of nonlinear control laws called 'backstepping'. It relies on the introduction of artificial delays combined with LyapunovKrasovskii functionals of complete type, thus allowing a constructive approach for the design of asymptotically stabilizing controls of linear systems with delay in the input and state that are too long for being neglected.
In the work 13, we provide a new output feedback control design for a chain of saturating integrators with imprecise measurements where the outputs can also contain delays and sampling. Using a backstepping approach with a dynamic extension that leads to pointwise delays in the control and a dynamic extension, we obtain a stability result whose robustness is of inputtostate type. We use this theoretical result to solve a problem in the visual landing of aircraft in the glide phase in the presence of delayed and sampled image processing.
7.14 Bounded control for discretetime systems
Participants: Xuefei Yang, Bin Zhou, James Lam, Frédéric Mazenc.
In the work 27, we address the problem of globally stabilizing discretetime multiple integrators with bounded controls by utilizing the energy function based approach. In a first part, we stabilize a discretetime double integrators system subject to input additive disturbances by a bounded feedback whose formula involves a linear function of the state and a saturation function only. Next, we use this result to stabilize a discretetime chain of multiple integrators of arbitrary length by bounded control with the aid of a special canonical form. Compared with the existing results, the proposed controllers require fewer saturation functions, which allow a better use of the control energy. Moreover, some free parameters that are introduced into these controllers can help improve the transient performance of the closedloop systems significantly. A numerical example to assess the effectiveness of the proposed method is given. The contribution 26, is devoted to the global asymptotic stabilization of discretetime chains of integrators with bounded controls by utilizing the energy function based approach. First, a discretetime double integrators system affected by input additive disturbances is stabilized by a bounded feedback whose formula involves a linear function of the state and only one saturation function. Next, this result is used to globally asymptotically stabilize by bounded feedback a chain of multiple integrators of arbitrary length. Compared with the existing results, the proposed controllers require fewer saturation functions, which allow a better use of the control energy. Moreover, some tuning parameters in these controllers can help improve the transient performance of the closedloop systems significantly.
7.15 Observers
Participants: Frédéric Mazenc, Thach Dinh, Tarek Raissi, Saeed Ahmed, Michael Malisoff, Silviu Niculescu.
The aim of the contribution 32 is to cope with estimation issues for discretetime nonlinear timevarying systems with input and output. We propose a new design technique which yields fixedtime observers, i.e. observers whose solution converges to the solution of the studied system before an instant chosen by the user. The construction relies on the use of past values of the output and the theory of the monotone systems to construct dead bit observer or fixedtime interval estimator depending on the absence or the presence of uncertainties. Finally, simulations are conducted to assess the effectiveness of the proposed schemes.
The work 20 is devoted to observers which converge in finite time too. We propose a reduced order observers for a class of nonlinear timevarying continuoustime systems. In a second step, we take advantage of the observers to design globally asymptotically stabilizing output feedback controls. We illustrate these observer and control designs in a tracking dynamics for a nonholonomic system in chained form.
Due to the fact that, usually in practice, the measured variables of a system are available at discrete times only, the paper 40 studies the problem of stabilizing continuoustime nonlinear systems with discrete measurements with a fast rate of convergence. We propose an estimate of the state variable that converges with a rate of convergence that can be made arbitrarily large by reducing the size of the largest sampling interval. The proof of the convergence result is based on a the stability analysis technique called " trajectory based approach " and developed by F. Mazenc and coauthors in recent contributions.
7.16 Sequential predictors
Participants: Frédéric Mazenc, Michael Malisoff, Indra Bhogaraju.
The contributions 41 and 21are dedicated to the study of timevarying linear discrete time systems with uncertainties and timevarying measurement delays, whose outputs are perturbed by uncertainty. We design sequential predictors, that is interconnected predictors whose number is proportional to the size of the delay. They ensure a robustness property of inputtostate stability type with respect to the considered uncertainties. The number of required sequential predictors is any upper bound for the delay in our feedback stabilized closed loop systems. Using this technique, arbitrarily large delays can be handled. We illustrate the work in a digital control problem for a continuous time system that is discretized through sampling.
7.17 Stability Analysis of Linear Partial Differential Equations
Participants: Giorgio Valmorbida, Aditya Gahlawat.
We proposed a method to perform stability analysis of onedimensional Partial IntegroDifferential Equations. The relevance of the proposed results lies on the fact that we cast the Lyapunov inequalities as a differential inequality in two dimensions. The proposed structure for the inequalities is motivated by the same structure as the one used in the study of backstepping feedback laws, a successful strategy applied for several onedimensional PDE systems. The advantage of the proposed Lyapunov analysis can be studied in a simpler manner as well as the fact that the backstepping law can be approximated by simpler laws and the stability can still be studied trhough the solution to the set of proposed inequalities.
We rely on Lyapunov analysis to establish the exponential stability of the systems. Then we present a test for the verification of the underlying Lyapunov inequalities, which relies on the existence of solutions of a system of coupled differential equations.
We illustrate the application of this method in several examples of PDEs defined by polynomial data, we formulate a numerical methodology in the form of a convex optimization problem which can be solved algorithmically. We show the effectiveness of the proposed numerical methodology using examples of different types of PDEs.
We are currently studying the extensions of coupled PDEODE systems.
7.18 Stability analysis of wave equations in one space dimension with nonlinear boundary conditions
Participants: Yacine Chitour, Swann Marx, Guilherme Mazanti.
Wave equations in one space dimension are useful models for propagation phenomena and the analysis of the asymptotic behavior of their solution is an important question both from theoretical and applied points of view. In many practical applications, the action of a controller on a wave propagation phenomenon can only occur through the boundary of the propagation domain, and, even though such a controller can often be designed to be linear, nonlinearities are usually present in its practical implementation, due to nonlinearities in the components used for implementation or saturation phenomena.
The work 62 considers a wave equation in one space dimension with a setvalued boundary condition, which contains nonlinear boundary conditions as particular cases but can also be used to describe switching phenomena or uncertainties. The study is performed within an ${L}^{p}$ functional framework, for $p\in [1,+\infty ]$. Necessary and sufficient conditions for existence and uniqueness of solutions are derived, showing in particular that setvalued boundary dampings are a quite natural framework for the analysis of wave equations: solutions may exist and be unique even when the boundary condition is not described by a functional relation, which allows one to easily address problems involving dry damping or sliding mode.
The work also provides several results characterizing the asymptotic behavior of such wave equations, retrieving some already known optimal estimates of decay rates but also providing new ones and solving some open problems in the literature, in particular involving saturationtype dampings. In case the boundary damping is subject to perturbations, the paper also derives sharp results regarding asymptotic perturbation rejection and inputtostate stability. The techniques used in the paper might be applied to more general hyperbolic systems, a line of research currently in investigation.
7.19 Existence and characterization of equilibria of some game models for crowd motion
Participants: Romain Ducasse, Guilherme Mazanti, Saeed Sadeghi Arjmand, Filippo Santambrogio.
Mean field games have been introduced around 2006 as an approximation, as the number of players tends to infinity, of games with rational, indistinguishable players interacting with other only through their “average” behavior. Originally motivated by problems in economics and engineering, mean field games have been also used as models in many other applications.
This line of research aims at proposing mean field game models for crowd motion, in which players are the agents of the crowd and their goal is typically to reach a certain target set minimizing some criterion involving their travel time. The recent work 63 has adressed the case of stochastic minimaltime mean field games in which agents wish to reach the boundary of a given set in minimal time, but the movement of each agent is submitted to a Brownian motion. The main results of the paper concern the existence of equilibria, characterized as a solution to a system of PDEs, as well as the description of some of its properties, in particular its longtime asymptotic behavior.
Despite recent advances on mean field games, their practical applications are still quite limited due to the difficulties in the theoretical analysis of mean field games with more realistic assumptions. An ongoing research effort by G. Mazanti and S. Sadeghi Arjmand deals with studying mean field games for crowd motion with more realistic assumption, involving in particular the study of manypopulation games and games submitted to state constraints. Interesting preliminary results have been obtained and are the topic of a work in preparation.
7.20 A Current Sensorless Delay–Based Control Scheme for MPPT–Boost Converters in Photovoltaic Systems
Participants: SilviuIulian Niculescu, JoséEnrique HernándezDíez, Fernando MendezBarrios, Ernesto BárcenasBárcenas.
We have dealt with the design of a current sensorless delay–based controller for the closed–loop stabilization of a photovoltaic system under an MPPT scheme using a boost dc/dc converter. Some applications of such topology are dc microgrids, solar vehicles, or standalone systems, to mention a few. The basis of this control scheme relies on the feedback linearization control technique coupled with a delay–based loworder controller. In order to study the stability, the proposed approach uses a geometric point of view which allows the partitioning of the controller parameters space into regions with similar stability characteristics (same number of unstable characteristic roots). Our most important contribution relies on providing practical guidelines to tune the gains of the proposed delay–based controller, ensuring asymptotic stability of the closed–loop system and fulfilling the requirements for photovoltaic applications. In addition, the proposed approach allows the design a nonfragile controller with respect to the controller gains. Furthermore, in order to test the effectiveness of the control scheme presented, experimental results evaluating the closed–loop system performance under setpoint changes and abrupt irradiance disturbances are addressed using a solar array simulator and a battery bank as load.
8 Partnerships and cooperations
8.1 International initiatives
Informal international partners
 Kyoto University
 Leeds University
 Louisiana State University
 City University of Hong Kong
 CTU in Prague
 KU Leuven
 Harbin Institute
 University of Kaiserslautern
 Rutgers University
 Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional
 University Mouloud Mammeri
8.2 International research visitors
8.2.1 Visits of international scientists
Jaqueline Godoy Mesquita, from University of Brasília (Brazil) and at the time in a sabbatical year at Justus Liebig Universität (Giessen, Germany), visited DISCO Team in February 10–14, 2020. In addition to scientific work, discussions were held to improve collaborations between DISCO Team and researchers from University of Brasília.
Fazia Bedouhene, from University Mouloud Mammeri (Algeria), visited the Disco Team in January 1525, 2020.
8.3 National initiatives
Islam Boussaada is a member of the administration council of the Association SAGIP (https://
8.3.1 ANR
 Giorgio Valmorbida is a member of the ANR HANDY  Hybrid And Networked Dynamical sYstems (http://
9 Dissemination
9.1 Promoting scientific activities
9.1.1 Scientific events: selection
Catherine Bonnet was Associate Editor for the 2020 American Control Conference, Denver, USA and the 2021 American Control Conference, New Orleans, USA.
Frederic Mazenc was Associate Editor for European Control Conference, Rotterdam, The Netherlands (2021).
Giorgio Valmorbida is a member of the Editorial Board of the Control Systems Society, serving as an editor for the ACC and the CDC (2018, 2019, 2020, 2021).
SilviuIulian Niculescu was Editor of the 2020 IFAC World Congress (Berlin, Germany).
Member of the conference program committees
Catherine Bonnet and Islam Boussaada are members of the International Program Committee of the 16th IFAC Workshop on Time Delay Systems (TDS 2021), Guangzhou, China.
Frederic Mazenc is member of the IFAC Technical Committee on Linear Control Systems, 4th IFAC Workshop on Linear Parametervarying systems, 1920 July 2021.
Catherine Bonnet and Giorgio Valmorbida are members of the scientific committee of the GDRI (International Research Group funded by CNRS) SpaDisco since 2017.
Giorgio Valmorbida is a member of the steering committee of the GDRI (International Research Group funded by CNRS) SpaDisco since 2017.
Reviewer
The team reviewed papers for several international conferences including IEEE Conference on Decision and Control, IEEE American Control Conference, European Control Conference, Mathematical Theory of Networks and Systems $...$
9.1.2 Journal
Member of the editorial boards
Frederic Mazenc is Editor of the Asian Journal of Control.
Frederic Mazenc is Associate Editor of IEEE Control Systems Letters.
Giorgio Valmorbida is Associate Editor of IMA Journal of Mathematical Control and Information.
Giorgio Valmorbida is Associate Editor of Journal of Control, Automation and Electrical Systems.
SilviuIulian Niculescu is FoundigEditor and EditorinChief of the Springer Nature series “Advances in Delays and Dynamics” (since its creation in 2012): https://
SilviuIulian Niculescu is Editor of IFAC PapersOnLine (20202023).
SilviuIulian Niculescu is Editor of the IMA Journal of Mathematical Control and Information (since 2010).
SilviuIulian Niculescu is Editor of the European Journal of Control (since 2010).
SilviuIulian Niculescu is Editor of Frontiers in Control Engineering (since its creation in 2020).
SilviuIulian Niculescu is Guest Editor for the special issue devoted to “PID Control in the Information Age: Theoretical Advances and Applications” at the International Journal of Robust and Nonlinear Control (20202021): https://
Reviewer  reviewing activities
The team reviewed papers for several journals including SIAM Journal on Control and Optimization, Automatica, IEEE Transactions on Automatic Control, Systems and Control Letters, IEEE Control Systems Letters $...$
9.1.3 Invited talks
 Guilherme Mazanti gave an invited talk at the conference Mean Field Games: Recent Progress, which took place in Chicago–IL, United States, in February 2020.
 Guilherme Mazanti gave an invited talk at the conference Mean Field Games and Applications, which was part of the program High Dimensional Hamilton–Jacobi PDEs organized by the Institute for Pure and Applied Mathematics (IPAM), UCLA, United States, and which took place in May 2020.
 Guilherme Mazanti gave an invited talk at the Virtual Thematic Workshop in Math Sciences: Nonlinear Dynamical Systems and Delay Equations, organized by the Young Affiliates Network of The World Academy of Sciences (TYAN / TWAS), which took place on October 26th, 2020.
9.1.4 Leadership within the scientific community
Catherine Bonnet is a member of the IFAC Technical Committees on Distributed Parameter Systems, on Biological and Medical Systems and on Robust Control. She is a member of the management committee of the COST Action FRACTAL (20162020).
Silviu Niculescu is the chair of the IFAC TC 2.2 "Linear Control Systems" since 2017 (including 300350 researchers throught the world). The TC is coordinating 4 "Working Groups" (WG) including the WG on "TimeDelay Systems".
9.1.5 Scientific expertise
Since September 2015, Catherine Bonnet is a member of the Evaluation Committee of Inria and since 2019 of the Bureau of the Evaluation Committee of Inria. In 2020, she has been an expert for Ville de Paris, France.
Since September 2016, Islam Boussaada is a member of the Scientific Council of IPSA (Engineering School in Aeronautic and Aerospace approved by CTI).
Since September 2018, Islam Boussaada is a member of the Development Council of Sup'Biotech (Engineering School in Biotechnologies approved by CTI).
Since 2019 Frederic Mazenc is Membre of the "Commission de Développement Technologique" (Inria Saclay).
9.1.6 Research administration
Catherine Bonnet is a member of the :
 Parity Committee of Inria created sice its creation in 2015.
 Bureau du Comité des Projets du CRI SaclayIledeFrance since 2018.
 Coordination committee of the Mentoring Program of Inria SaclayÎledeFrance.
 PhD referent committee at L2S, CentraleSupelec.
She is the Parity Referent at L2S for CNRS since November 2020.
Since 2019 Frederic Mazenc is Membre of the "Commission de Développement Technologique" (Inria Saclay).
9.2 Teaching  Supervision  Juries
9.2.1 Teaching
 Licence: Islam Boussaada, Control of bioprocesses, 27h, 1st year, CentraleSupélec Université ParisSaclay, France.
 Licence: Silviu Niculescu, Mathematics, 15h, 1st year, ENSMP Paris, France.
 Licence: Silviu Niculescu, Introduction to optimization, 30h, 1st year, ESIEE Paris, France.
 Licence: Giorgio Valmorbida, Signal Processing, 1st year, 43h CentraleSupélec Université ParisSaclay.
 Master: Giorgio Valmorbida, Optimization, 2nd year, 43h CentraleSupélec Université ParisSaclay.
 Master: Giorgio Valmorbida, Hybrid Systems, 3rd year, 18h CentraleSupélec Université ParisSaclay.
 Master: Giorgio Valmorbida, Control, , 2nd years, 55.5h, CentraleSupélec Université ParisSaclay.
 Master: Giorgio Valmorbida, Projects and Internship supervision, 2nd and 3rd years, 81h, CentraleSupélec Université ParisSaclay.
 Master: Giorgio Valmorbida, Nonlinear Systems, 3h, CentraleSupélec Executive Education, Université ParisSaclay.
 Master : Catherine Bonnet, Stability properties and stabilization of interconnected dynamical systems involving delays, 20h, IPSA, France.
 Master : Silviu Niculescu, Signals and Systems, 12h, ESIEE Paris, France.
 Master : Giorgio Valmorbida, Control, 40.5, Master MAE (M1), Université ParisSaclay.
 Master : Giorgio Valmorbida, Stability of Dynamical Systems, Master ATSI (M2), Université ParisSaclay.
 Master: Guilherme Mazanti, Tutorials — Optimization, 21h, 2nd year, CentraleSupélec, Université ParisSaclay.
 Master: Guilherme Mazanti, Introductory course to research and innovation: MID, a novel approach in control design, 10h, 4th year, IPSA.
 Doctorat : Silviu Niculescu, Controlling Delayed Dynamics: Advances in Theory, Methods and Applications, 7h, CISM Udine, Italy.
9.2.2 Supervision
 PhD in progress: Souad Amrane, on real poleplacement for retarded functional differential equations, University Mouloud Mammeri. Since 09/2017. Supervisors: Fazia Bedouhene and Islam Boussaada.
 PhD in progress: Amina Benarab, Characterization of the exponential decay of linear delay systems solutions, University Paris Saclay. Since 10/2019. Supervisors: Catherine Bonnet, Islam Boussaada and Karim Trabelsi.
 PhD in progress: Jose Castillo, Design, Modeling and control of multi drones for aerial handling, University Paris Saclay, 10/2018, Islam Boussaada and Juan Escareno.
 PhD in progress: Naouel Debiane, Bond Graph modeling for robust control and diagnosis of macatronic systems, University of Lille. Since 03/2017. Supervisors: Belkacem OuldBouamama and Islam Boussaada.
 PhD in progress: Ali Diab, Commande par filtrage non linéaire des systèmes d’assistance direction, Université ParisSaclay. Since 10/2019. Supervisors: Giorgio Valmorbida and William PasillasLepine.
 PhD in progress: Ricardo Falcon Prado, Active vibration control of flexible structures under input saturation through delaybased controllers and anti windup compensators, University Paris Saclay. Since 10/2019. Supervisors: Islam Boussaada and Sami Tliba.
 PhD: Javier Eduardo Pereyra Zamundio, New backstepping design for systems with delay: finite time stabilization, robust stabilization, CINVESTAV, Instituto Politecnico Nacional. Since 10/2019. Supervisors: Sabine Mondié and Frédéric Mazenc. This Phd student resigned for personal reasons in October 2020.
 PhD in progress : Amira Remadna, On poleplacement approach for retarded functional differential equations, University Badji MokhtarAnnaba. Since 09/2019. Supervisors: Islam Boussaada and Azzedine Benchettah.
 PhD in progress: Saeed Sadeghi Arjmand, Mean field games with free final time, École Polytechnique. Since 10/2019. Supervisors: AnneSophie de Suzzoni and Guilherme Mazanti.
9.2.3 Juries
 Catherine Bonnet was member of the Grenoble and Nancy Junior Researcher Inria recruiting committees. She was also a member of a Lecturer recruiting committee of the Claude Bernard University, Lyon 1.
 Catherine Bonnet was a member of the PhD thesis of Deesh Dileep Design tools for the robustdecentralised control oflargescale systems withtimedelays', 6 March 2020, KU Leuven and an external examiner of the PhD thesis of Asmahan Alajyan, Delay systems with variable delays, 4 December 2020, Leeds University.
 Frederic Mazenc was member of the committe of mid term supervision of the Phd of Mattia Giaccagli, who is supervised by Vincent Andrieu and Daniele Astolfi.
10 Scientific production
10.1 Major publications
 1 articleStability of Neutral Systems with Commensurate Delays and Poles Asymptotic to the Imaginary AxisSIAM Journal on Control and Optimization492March 2011, 498516
 2 articleStabilization of some fractional delay systems of neutral typeAutomatica432007, 20472053
 3 articleInverted pendulum stabilization: characterization of codimensionthree triple zero bifurcation via multiple delayed proportional gainsSystems Control Lett.822015, 19
 4 book Constructions of Strict Lyapunov Functions Communications and Control Engineering Series SpringerVerlag London Ltd. 2009
 5 articleReduction Model Approach for Linear TimeVarying Systems with DelaysIEEE Transactions on Automatic Control5982014, 20682014
 6 book S.I. Niculescu W. Michiels Stability, Control, and Computation for TimeDelay Systems Philadelphia, PA Society for Industrial and Applied Mathematics 2014
 7 book Delay Effects on Stability: a Robust Control Approach 269 Lecture Notes in Control and Information Sciences Springer 2001
 8 book Analysis and Control of Oilwell Drilling Vibrations Springer International Publishing May 2015
 9 articleStability Analysis for a Class of Partial Differential Equations via Semidefinite ProgrammingIEEE Transactions on Automatic Control616June 2016, 16491654
 10 articleDesign of Polynomial Control Laws for Polynomial Systems Subject to Actuator SaturationIEEE Transactions on Automatic Control587July 2013, 17581770
10.2 Publications of the year
International journals
 11 articleReal spectral values coexistence and their effect on the stability of timedelay systems: Vandermonde matrices and exponential decayComptes Rendus Mathématique358910September 2020, 10111032

12
article
${L}_{2}$ and BIBO stability of systems with variable delays' Systems and Control Letters May 2020  13 articleStabilization for a Chain of Saturating Integrators Arising in the Visual Landing of Aircraft with SamplingSystems and Control Letters135January 2020, 104574
 14 articleOn the gap between deterministic and probabilistic joint spectral radii for discretetime linear systemsLinear Algebra and its Applications613March 2021, 2445
 15 articleA Current Sensorless Delay–Based Control Scheme for MPPT–Boost Converters in Photovoltaic SystemsIEEE Access8September 2020, 174449174462
 16 articleFrom ObstacleBased Space Partitioning to Corridors and Path Planning. A Convex Lifting ApproachIEEE Control Systems Letters412020, 7984
 17 articleAlgorithms for cablesuspended payload sway damping by vertical motion of the pivot baseMechanical Systems and Signal Processing149February 2021, 107131
 18 article Characterizing PID Controllers for Linear TimeDelay Systems: A ParameterSpace Approach IEEE Transactions on Automatic Control October 2020
 19 articleMultiplicityinduceddominancy for delaydifferential equations of retarded typeJournal of Differential Equations28615March 2021, 84118
 20 articleReduced Order Finite Time Observers and Output Feedback for TimeVarying Nonlinear SystemsAutomatica119September 2020, 109083
 21 article Sequential Predictors for Delay Compensation for Discrete Time Systems with TimeVarying Delays Automatica 122 December 2020
 22 article ReducedOrder Fast Converging Observers for Systems with Discrete Measurements and Measurement Error Systems and Control Letters 2021
 23 articleStability Analysis for TimeVarying Systems with Asynchronous Sampling using Contractivity ApproachIEEE Control Systems Letters51January 2021, 4954
 24 article Stability and Observer Designs Using New Variants of Halanay's Inequality * Automatica 123 January 2021
 25 articleCalculation of the critical delay for the double inverted pendulumJournal of Vibration and Control27342020, 356364
 26 article Global Stabilization of DiscreteTime Integrators System By Bounded Controls IEEE Transactions on Circuits and Systems  Part I December 2020
 27 article Global Stabilization of DiscreteTime Linear Systems Subject to Input Saturation and Time Delay IEEE Transactions on Automatic Control 2021
International peerreviewed conferences
 28 inproceedings Estabilização quadrática por realimentação de saída de sistemas Lur'e a tempo contínuo via LMIs Congresso Brasileiro de Automática  2020 Porto Alegre, Brazil November 2020
 29 inproceedingsAn LMIbased iterative algorithm for state and output feedback stabilization of discretetime Lur’e systemsCDC 2020  59th IEEE Conference on Decision and ControlJeju Island, South KoreaDecember 2020, 25612566
 30 inproceedings Poleplacement by PID Control with guaranteed delay robustness 24th International Symposium on Mathematical Theory of Networks and Systems (MTNS 2021) IFACPapersOnLine Cambridge, United Kingdom https://mtns2020.eng.cam.ac.uk/ August 2021
 31 inproceedingsPartial Pole Placement via Delay Action: A Python Software for Delayed Feedback Stabilizing DesignICSTCC 2020  24th International Conference on System Theory, Control and Computing2020 24th International Conference on System Theory, Control and Computing (ICSTCC)Sinaia, Romaniahttp://ace.ucv.ro/icstcc2020/October 2020, 196201
 32 inproceedings On FixedTime Interval Estimation of DiscreteTime Nonlinear TimeVarying Systems With Disturbances ACC 2020  American Control Conference Denver, CO, United States July 2020
 33 inproceedings Stability of SampledData Control for Lurie Systems with SlopeRestricted Nonlinearities Congresso Brasileiro de Automática  2020 Porto Alegre, Brazil November 2020
 34 inproceedings Some remarks on the regular splitting of quasipolynomials with two delays. Characterization of double roots in degenerate cases IFAC 2020  21st IFAC World Congress IFACPapersOnLine Berlin / Virtual, Germany https://www.ifac2020.org/ July 2020
 35 inproceedings Navigation in cluttered environments with feasibility guarantees IFAC 2020  21st IFAC World Congress IFACPapersOnLine Berlin / Virtual, Germany https://www.ifac2020.org/ July 2020
 36 inproceedings Effects of Roots of Maximal Multiplicity on the Stability of Some Classes of Delay DifferentialAlgebraic Systems: The Lossless Propagation Case 24th International Symposium on Mathematical Theory of Networks and Systems (MTNS 2021) IFACPapersOnLine Cambridge, United Kingdom https://mtns2020.eng.cam.ac.uk/ August 2021
 37 inproceedings On pole placement and spectral abscissa characterization for timedelay systems 10th European Nonlinear Dynamics Conference Proceedings of the 10th European Nonlinear Dynamics Conference Lyon, France July 2021
 38 inproceedings On qualitative properties of singledelay linear retarded differential equations: Characteristic roots of maximal multiplicity are necessarily dominant IFAC 2020  21st IFAC World Congress IFACPapersOnLine Berlin / Virtual, Germany https://www.ifac2020.org/ July 2020
 39 inproceedings Spectral dominance of complex roots for singledelay linear equations IFAC 2020  21st IFAC World Congress IFACPapersOnLine Berlin / Virtual, Germany https://www.ifac2020.org/ July 2020
 40 inproceedingsSampledData Estimator for Nonlinear Systems with Arbitrarily Fast Rate of ConvergenceACC 2020  American Control ConferenceDenver, FranceJuly 2020, 16851689
 41 inproceedings Sequential Predictors for Delay Compensation for Perturbed Discrete Time Systems ACC 2020  American Control Conference Denver, United States July 2020
 42 inproceedings Constructive backstepping for a class of delay systems based on functionals of complete type IFAC 2020  21st IFAC World Congress Berlin / Virtual, Germany July 2020
 43 inproceedings An MIDbased control of a vibrating axisymmetric membrane using piezoelectric transducers 10th European Nonlinear Dynamics Conference Proceedings of the 10th European Nonlinear Dynamics Conference Lyon, France July 2021
 44 inproceedingsDelayed control design of a vibrating thin membrane via a partial pole placementICSTCC 2020  24th International Conference on System Theory, Control and Computing2020 24th International Conference on System Theory, Control and Computing (ICSTCC)Sinaia, Romaniahttp://ace.ucv.ro/icstcc2020/October 2020, 196201
 45 inproceedings On Quantization in DiscreteTime Control Systems: Stability Analysis of Ternary Controllers CDC 2020  59th IEEE Conference on Decision and Control Jeju Island (virtual), South Korea https://cdc2020.ieeecss.org/ December 2020
 46 inproceedings Bézout Identity in Pseudoratoinal Transfer Functions MTNS 2020  24th International Symposium on Mathematical Theory of Networks and Systems Cambridge, France August 2021
Conferences without proceedings
 47 inproceedings Some insights on rightmost spectral values assignment for time delay systems IFAC 2020  21st IFAC World Congress Berlin / Virtual, Germany July 2020
 48 inproceedings Analysis of the Delayed Central Nervous System Action in the Regulation of a Thirdorder MuscleTendon Model ICSTCC 2020  24th International Conference on System Theory, Control and Computing Sinaia, Romania October 2020
 49 inproceedings Torsionalvibrations Damping in Drilling Systems: MultiplicityInducedDominancybased design 24th International Symposium on Mathematical Theory of Networks and Systems Cambridge, United Kingdom August 2021
 50 inproceedings Towards an MIDbased Delayed Design for Arbitraryorder Dynamical Systems with a Mechanical Application IFAC 2020  21st IFAC World Congress Berlin / Virtual, Germany July 2020
 51 inproceedingsThe MID property for a secondorder neutral timedelay differential equationICSTCC 2020  24th International Conference on System Theory, Control and ComputingSinaia, RomaniaOctober 2020, 202207
 53 inproceedingsPIDDesignDelay: A MATLAB Toolbox for Stability ParameterSpace Characterization2020 24th International Conference on System Theory, Control and Computing (ICSTCC)Sinaia, RomaniaOctober 2020, 1318
 54 inproceedings Some Insights on the Asymptotic Stabilization of a Class of SISO Marginally Stable Systems Using One Delay Block IFAC World Congress Berlin, Germany July 2020
 55 inproceedings MultiplicityInducedDominancy extended to neutral delay equations: Towards a systematic PID tuning based on Rightmost root assignment ACC 2020  American Control Conference Denver, United States July 2020
 56 inproceedings Controllabilies of linear delay systems and of its samples version IFAC 2020  21st IFAC World Congress Berlin / Virtual, Germany July 2020
 57 inproceedings Control Systems Engineering made Easy: Motivating Students through Experimentation on UAVs IFAC 2020  21st IFAC World Congress Berlin / Virtual, Germany July 2020
 58 inproceedings Insights from a qualitative analysis of a gene expression model with delays 24th International Symposium on Mathematical Theory of Networks and Systems Cambridge, United Kingdom August 2021
Scientific books
 59 book Analytic eigenvalue perturbation theory for dynamical systems analysis Advances in design and control 2021
Scientific book chapters
 60 inbook Low complexity controller for active vibration damping of thin mechanical structures Vibration Control and Actuation of LargeScale Systems Emerging Methodologies and Applications in Modelling, Identification and Control 2020
Edition (books, proceedings, special issue of a journal)
 61 proceedings J. CastilloZamora J. AguileraAlvarez J.A. Escareno I. Boussaada J. MartinezNolasco A. JimenezGaribay A pedagogical approach to data fusion and kalman filter Congreso Internacional en Sistemas Mecatronicos 42 Número Especial  Difusión del Conocimiento 2020 Celaya, Mexico November 2020
Reports & preprints
 62 misc Onedimensional wave equation with setvalued boundary damping: wellposedness, asymptotic stability, and decay rates November 2020
 63 misc Second order local minimaltime Mean Field Games January 2021
10.3 Cited publications
 64 articleBiological robustnessNature52004, 826837
 65 articleReversals in stability of linear timedelay systems A finer characterizationAutomatica1082019, 108479
 66 articleAn iterative frequencysweeping approach for stability analysis of linear systems with multiple delaysIMA Journal of Mathematical Control and Information3602June 2019, 379398
 67 articleWeierstrass approach to asymptotic behavior characterization of critical imaginary roots for retarded differential equationsSIAM Journal on Control and Optimization571January 2019, 122
 68 articlePID Controller Design for FractionalOrder Systems with Time DelaysSystems and Control Letters611January 2012, 1823
 69 articleStability analysis for a class of distributed delay systems with constant coefficients by using a frequencysweeping approachIET Control Theory and Applications1312019, 8795