Papers by Gianmaria De Tommasi
2015 European Control Conference (ECC), 2015
ABSTRACT In this paper we investigate the stochastic finite-time stability (SFTS) problem for lin... more ABSTRACT In this paper we investigate the stochastic finite-time stability (SFTS) problem for linear time-varying systems. The system under consideration is described by an Itô type differential equation and the Itô differentiation rule is exploited to derive conditions for SFTS. The main contribution of the paper is that we use an approach based on time-varying quadratic Lyapunov functions, which allow us to obtain less conservative conditions than the time-invariant Lyapunov functions commonly used in the literature. More specifically, we obtain a sufficient condition based on the solution of a generalized Lyapunov differential equation (GLDE) and a sufficient condition requiring the solution of a feasibility problem involving a differential LMIs (DLMI) constraint. We shall show that the DLMI based condition is less conservative and is useful to develop a sufficient condition for stochastic finite-time stabilizability via state feedback; on the other hand the GLDE condition is more efficient from the computational point of view. Numerical examples illustrate that the proposed approach attains less conservative results than those obtainable with the existing literature.
International Journal of Robust and Nonlinear Control, 2014
ABSTRACT In recent years, a number of papers have treated the problem of the finite-time stabilit... more ABSTRACT In recent years, a number of papers have treated the problem of the finite-time stability and stabilization of impulsive (or, more in general, switching) dynamical linear systems. Generally, these works assume that the sequence of switching (in the following resetting) times is a priori known. In this paper, we remove such (strong) assumption, so making the technique more appealing from the practical control engineering point of view. A first result provided in this work is a sufficient condition for finite-time stability when the resetting times are known with a certain degree of uncertainty. Such condition requires the solution of a suitable feasibility problem based on coupled difference/differential LMIs. We show that as the uncertainty intervals reduce in size, our condition becomes less conservative, becoming necessary and sufficient in the certain case (i.e., the resetting instants are perfectly known). Eventually, we consider the conceptually different situation in which the resetting times are totally unknown, namely, the arbitrary switching case. The analysis results are then used to derive sufficient conditions for the existence of state-feedback controllers that finite time stabilizes the closed-loop system in the three cases mentioned earlier. A nontrivial example, considering the finite-time control of the liquid levels into three interconnected reservoirs, shows the effectiveness of the proposed approach. Copyright © 2014 John Wiley & Sons, Ltd.
2011 IEEE International Conference on Control Applications (CCA), 2011
In this paper we propose a solution to the input saturation avoidance problem in the JET tokamak ... more In this paper we propose a solution to the input saturation avoidance problem in the JET tokamak shape control by illustrating its capabilities to enforce coil currents selections that tend to move away from the saturation limits within the allowable degrees of freedom. The proposed solution revisits the dynamic allocation scheme first proposed in (10) for input redundant plants and
IET Control Theory & Applications, 2014
ABSTRACT In this study, the problem of input??output finite-time stabilisation of linear time-var... more ABSTRACT In this study, the problem of input??output finite-time stabilisation of linear time-varying systems is dealt with. The classical definition of input-output finite-time stability (IO-FTS) is extended to that one of structured IO-FTS, which allows to incorporate, in the definition of the stabilisation problem, some amplitude constraints on the control input variables. A sufficient condition and a necessary and sufficient condition for structured IO finite-time stabilisation are provided in the case of L∞ and L2 inputs, respectively. Such conditions require the existence of a solution to a certain differential linear matrix inequality. The theory is applied to design the active suspension control system for a two-degree-of-freedom quarter-car model.
Lecture Notes in Control and Information Sciences, 2014
Abstract The concept of Bounded-Input Bounded-Output (BIBO) stability arises when one wants to fo... more Abstract The concept of Bounded-Input Bounded-Output (BIBO) stability arises when one wants to focus on the study of the the input-output behavior of a dynamical system, as opposed to the classical Lyapunov stability. The present paper investigates the analogous concept in the framework of Finite Time Stability (FTS), namely the Input-Output FTS. A system is said to be IO finite time stable if, assigned a bounded input class and some boundaries in the output signal space, the output never exceeds such boundaries over a ...
IFAC Proceedings Volumes (IFAC-PapersOnline), 2011
Abstract Bounded-Input Bounded-Output (BIBO) stability is usually studied when only the input-out... more Abstract Bounded-Input Bounded-Output (BIBO) stability is usually studied when only the input-output behavior of a dynamical system is of interest. The present paper investigates the analogous concept in the framework of Finite Time Stability (FTS), namely the Input-Output FTS (IO-FTS). FTS has been already investigated in several papers in terms of state boundedness, whereas in this work we deal with the characterization of the input-output behavior. A system is said to be input-output finite time stable if, assigned a class of input ...
ABSTRACT The eXtreme Shape Controller (XSC) has been originally designed to control the plasma sh... more ABSTRACT The eXtreme Shape Controller (XSC) has been originally designed to control the plasma shape at JET during the flat-top phase, when the plasma current has a constant value. During the JET 2012 experimental campaigns, the XSC has been used to improve the shape control during the transient phases of plasma current ramp-up and ramp-down. In order to avoid the saturation of the actuators with these transient phases, a current limit avoidance system has been designed and implemented. This paper presents the experimental results achieved at JET during the 2012 campaigns using the XSC.
Lecture Notes in Control and Information Sciences, 2014
Lecture Notes in Control and Information Sciences, 2014
Nuclear Fusion, 2013
ABSTRACT The scientific goal of the Ignitor experiment is to approach, for the first time, the ig... more ABSTRACT The scientific goal of the Ignitor experiment is to approach, for the first time, the ignition conditions of a magnetically confined D-T plasma. The IGNIR collaboration between Italy and Russia is centred on the construction of the core of the Ignitor machine in Italy and its installation and operation within the Triniti site (Troitsk). A parallel initiative has developed that integrates this programme, involving the study of plasmas in which high-energy populations are present, with ongoing research in high-energy astrophysics, with a theory effort involving the National Institute for High Mathematics, and with INFN and the University of Pisa for the development of relevant nuclear and optical diagnostics. The construction of the main components of the machine core has been fully funded by the Italian Government. Therefore, considerable attention has been devoted towards identifying the industrial groups having the facilities necessary to build these components. An important step for the Ignitor programme is the adoption of the superconducting MgB2 material for the largest poloidal field coils (P14) that is compatible with the He-gas cooling system designed for the entire machine. The progress made in the construction of these coils is described. An important advance has been made in the reconfiguration of the cooling channels of the toroidal magnet that can double the machine duty cycle. A facility has been constructed to test the most important components of the ICRH system at full scale, and the main results of the tests carried out are presented. The main physics issues that the Ignitor experiment is expected to face are analysed considering the most recent developments in both experimental observations and theory for weakly collisional plasma regimes. Of special interest is the I-regime that has been investigated in depth only recently and combines advanced confinement properties with a high degree of plasma purity. This is a promising alternative to the high-density L-regime that had been observed by the Alcator experiment and whose features motivated the Ignitor project. The provisions that are incorporated in the machine design, in that of the plasma chamber in particular, and the relevant analyses in order to withstand or prevent the development of macroscopic instabilities with deleterious amplitudes are presented.
Uploads
Papers by Gianmaria De Tommasi