1,722,404 research outputs found
Sufficient conditions for the synthesis of H∞ fixed-order controllers
No full textThis brief note deals with the synthesis of H∞ fixed-order controllers for linear systems. It is well known that this problem can be formulated as a bilinear matrix inequality optimization problem which is non convex and NP hard to solve. In this paper sufficient conditions are provided which allow to convert the controller design into a linear matrix inequality feasibility problem. A numerical example on a practical control problem shows the application of the proposed technique
Robust multivariable PID control for linear parameter varying systems
No full textPractical control problems often deal with uncertain systems depending on parametric and possibly time-varying uncertainties. Quadratic stability theory and recent advances in convex and nonconvex optimisation algorithms provide useful tools to cope with this kind of problems. On the other hand, PID is still the controller most commonly used for industrial problems. In this paper, we consider a certain class of Multi input-multi output linear parameter varying systems which are encountered in practical control problems and we propose a state space parameterisation which allows to convert PI and PID controller synthesis into an LMI or BMI optimisation problem. The proposed technique guarantees uniform exponential stability of the closed loop system, a desired rate of convergence, and an H∞ norm bound. © 2001 Elsevier Science Ltd. All rights reserved
An LMI approach to the design of a robust observer with application to a temperature control problem for space vehicle testing
No full textIn this paper, a new control scheme for high temperature trajectory following problems is presented. The problem of reproducing on proper test articles the thermal stress conditions occurring on parts of space vehicles during the reentry into atmosphere is considered. The model of the thermal process, in the lumped parameter domain, is described by a quasi-linear system depending on a number of parameters that are uncertain and varying with the operating conditions. An ad hoc trajectory following control system is proposed together with a robust performance analysis which makes use of the concept of quadratic stability with an H∞ norm bound. The analysis technique allows to evaluate the stability of the closed loop system in the presence of time varying parameters and uncertainties, and the rejection of disturbances acting at the system input. An LMI based observer synthesis procedure is proposed to increase the closed loop system performance. © 2001 Elsevier Science Ltd. All rights reserved
A robust multiple PI controller for the air distribution into an arc heater
No full textThis paper deals with the problem of controlling both the air total mass flow-rate and its distribution in a 70 MW electric arc heater by means of a five way air supply system. Firstly a description of the detailed dynamic model of the pneumatic process, obtained in the lumped parameter domain, is provided, then the proposed control strategy is described. In order to guarantee the desired distribution of the total air supplied along the arc heater, a multiple PI control technique is proposed to command five partitioning valves. A physical reduction of the process model allows us to reduce the control problem to the synthesis of five standard PI controllers for Linear Parameter Varying first order systems. A robust synthesis of the controller gains which makes use of the concept of quadratic stability with a fixed decay rate and with an H∞ norm bound is proposed to cope with uncertainties, nonlinearities and disturbances. Numerical simulations are carried out to show the effectiveness of the control technique
Online approximators for the actuators FDI of a small commercial aircraft
No full textin this paper the problem of detecting and isolating faults on the actuators of a small commercial aircraft using online approximators is dealt with. in particular the capabilities of radial basis neural networks to approximate faults on the engines and elevators of an AP-68 Vulcanair commercial aircraft are investigated also in the presence of model uncertainties and external disturbances. The structure of the aircraft and of the fault models appears to be well suited for this kind of application. Although some effort has to be spent in tuning a certain number of parameters, the numerical results obtained on a full nonlinear Matlab-Simulink simulator of the aircraft seem to be encouraging. Copyright © 2005 IFAC
A design oriented mathematical model for the control of wind excited structures
No full textA state space linear mathematical model oriented to the design of Passive and Active Mass Dampers for tall buildings and bridges in wind is presented. The model accounts for an arbitrary number of passive and active devices located at arbitrary points of the structure. The aerodynamic terms of the stiffness and damping matrices are considered in order to reproduce the behavior of the structure under the wind excitation. A general discussion on the application of H2/H∞ techniques to the synthesis of the active control law is carried out. For the tuning of the mechanical parameters of the devices, the problem is reformulated as a decentralized static output feedback control law design problem
Managing sensor hardware redundancy on a small commercial aircraft with H∞ FDI observers
No full textin this paper the problem of managing Hardware redundancy on the Attitude Heading System and the Air Data System of a small commercial aircraft is considered. The proposed approach is based on a bank of extended H ∞ observers guaranteeing sensor fault detection and isolation in the presence of external disturbances and model uncertainties. Each observer is composed of an open loop nonlinear part replicating the system dynamics and a linear feedback action. Sufficient conditions for the synthesis of the feedback action are provided in terms of an LMI feasibility problem. Constraints on the position of the observer poles are added to fasten the residual generation dynamics and to avoid low damped and/or high frequency modes. Numerical simulations on the model of the AP-68 Vulcanair small commercial aircraft are presented. Copyright © 2005 IFAC
An LPV approach to the robust control of a class of quasi-linear propagation processes
No full textIn this paper the trajectory tracking control problem for a certain class of propagation processes modeled as quasi-linear parameter varying systems is considered. The propagation physical models are generally described by means of partial differential equations (PDEs). However in real world control problems the PDE models are usually converted into ordinary differential equations (ODEs) models adopting numerical and/or physical approximations. In many practical problems it happens that the propagation dynamics are linear, while the boundary conditions are described by nonlinear algebraic equations. A trajectory following control scheme is proposed for this class of systems together with a robust performance analysis based on the concept of quadratic stability with an H∞ norm bound. An LMI based observer synthesis procedure is also proposed to increase the closed loop system performanc
‘Somiglianza’, ‘regole’ e ‘teorie’ nei processi di categorizzazione
No full textIn base a quale criterio certi oggetti vengono raggruppati per formare una categoria? Obiettivo della rassegna è offrire un’analisi critica delle teorie psicologiche che hanno fornito una risposta a questa domanda. Delle tre risposte: a) delle «regole» guidano la formazione delle categorie; b) sono le «teorie» sul mondo che determinano la categorizzazione; e c) la «somiglianza» tra entità sta alla base della categorizzazione, nessuna rende conto esaustivamente della variabilità riscontrata nei processi di categorizzazione che è il fenomeno più rappresentativo della dinamica sottostante la conoscenza. Nel tentativo di spiegare tale variabilità sono stati analizzati anche i modelli che tentano un’integrazione di queste alternative
A note on the solution of a class of BMIs for H-infinity problems
No full textThis note deals with the solution of a particular class of Bilinear Matrix Inequalities arising in the synthesis of H∞ fixed-order controllers. It is well known that BMI optimisation problems are non convex and NP hard to solve. In this paper sufficient conditions are provided which allow to convert the controller design problem into a Linear Matrix Inequality feasibility problem
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