Majda Ltaief

Repetitive sliding mode control for nondecouplable multivariable systems: Periodic disturbances rejection

Disturbances rejection is an important field of control theory. In this context, our paper is proposed to deal with asymptotic rejection of periodic disturbances affecting discrete multivariable systems with an interactor matrix. A multivariable repetitive sliding mode control is proposed to cancel the disturbances when the system is nondecouplable. To synthesis this control an interactor matrix is used. A numerical example shows that the proposed strategy gives good performance in terms of rejecting periodic disturbances for nondecouplable multivariable systems.

Supervision based on partial predictors for a multimodel generalised predictive control: experimental validation on a semi-batch reactor

The multimodel approach has become a major research topic during the last few decades and unlike many other advanced techniques, it has also been successfully applied in industry. This paper describes the application of a multimodel generalised predictive control (MGPC) based on a commutation algorithm to the problem of a semi-batch reactor control. The commutation is controlled by a set of partial predictors which constitute a supervisor. The experimental results show that the multimodel generalised predictive control based on supervisor leads to good performances in terms of precision and tracking, relatively to the case where the direct adaptive generalised predictive control (DAGPC), is applied.

A new recursive algorithm for simultaneous identification of discrete time delay systems

Abstract A new algorithm for simultaneous online identification of unknown time delay and parameters of discrete-time delay systems is proposed in this paper. This algorithm consists in constructing a linear-parameters formulation and using the recursive least squares approach to solve the obtained system. Simulation example and experimental test results are presented to illustrate the performance of the proposed approach.

Hierarchical gradient based identification of discrete-time delay systems

In this paper, we apply a hierarchical identification principle to identify simultaneously the unknown time delay and dynamic parameters of discrete-time delay systems. In our approach, we separate the nonlinear cost function into two simple cost functions and present a gradient iterative algorithm for estimating directly the time delay and the parameters. The cost function used to estimate the time delay is an integer nonlinear programming problem (IP) and the solution of the integer version of a nonlinear optimization problem is obtained by rounding the solution for its continuous relaxation (CP). Furthermore, we give an appropriate choice of the convergence factor. Finally, the effectiveness of this method has been illustrated through simulation.

Multimodel reference model control: an experimental validation on a chemical reactor

The temperature control in chemical reactors has been shown to be of fundamental importance from product quality and process reproducibility points of view. This paper presents an experimental evaluation of multimodel approach involving a batch chemical reactor pilot. Two design features are worth to be mentioned. Firstly, an appropriate system identification approach is used to elaborate a family of control models describing the input-output behaviour of the reactor over its full operating range. Secondly, the control design is performed using a suitable fusion of robust model reference controllers. The underlying model reference control is particularly motivated by the required tracking performances.

Discrete sliding mode control for time-varying delay systems: a multi-delay approach

Owing to its potential for real applications, many researchers have studied the problem of modelling and control of time-varying delay systems. In this paper, we propose a new strategy called multi-delay approach for modelling and control of these systems. In this new strategy, the time-varying delay systems are modelled by a multi-delay model representation in which each elementary model is characterised by a constant delay value varying between the lower and upper bounds of the delay term supposed to be known. A systematic elementary model reproducing the real output evolution is generated. Then, a discrete sliding mode control based on the multi-delay model representation (MD-DSMC) was developed to stabilise such systems. The proposed controller guarantees a finite time convergence of systems under consideration. The controller parameters are selected by solving linear matrix inequalities (LMIs). A comparative study with the classical discrete sliding mode control was also subject of this work.

Online Identification of Multivariable Discrete Time Delay Systems Using a Recursive Least Square Algorithm

This paper addresses the problem of simultaneous identification of linear discrete time delay multivariable systems. This problem involves both the estimation of the time delays and the dynamic parameters matrices. In fact, we suggest a new formulation of this problem allowing defining the time delay and the dynamic parameters in the same estimated vector and building the corresponding observation vector. Then, we use this formulation to propose a new method to identify the time delays and the parameters of these systems using the least square approach. Convergence conditions and statistics properties of the proposed method are also developed. Simulation results are presented to illustrate the performance of the proposed method. An application of the developed approach to compact disc player arm is also suggested in order to validate simulation results.

Nonlinear approach for the identification of discrete time delay systems

A new approach for simultaneous recursive identification of an unknown time delay of discrete-time delay systems is proposed in this paper. The proposed Levenberg-Marquardts algorithm is used to deal with the identification problem. The effectiveness of this method has been illustrated through simulation.

Conditions of Disturbances Rejection for Discrete First, Second Order and Repetitive Sliding Mode Controllers

Harmonic disturbance rejection is an important field of control theory and applications. In this paper a discrete first and second order sliding mode control for multivariable systems are investigated. The necessary conditions of harmonic disturbances rejection using first and second order sliding mode control laws are elaborated. In order to improve the performances of sliding mode control in periodic disturbances rejection, a discrete repetitive sliding mode control is presented. A necessary condition for the choice of the discontinuous terms in discrete repetitive sliding mode control is then developed. The different proposed control strategies have been tested on numerical simulation example. The obtained results are very satisfactory in terms of compensation of periodic disturbances using discrete repetitive sliding mode control.

Gradient based iterative identification for discrete-time delay systems

In this paper, the problem of identification of time delay systems is addressed. This problem involves both the estimation of the dynamic parameters and the identification of the time delay. In fact, we propose a gradient based iterative algorithm for time delay discrete systems using the hierarchical identification principle. This method consists in decomposing a nonlinear cost function into two simple cost functions in order to overcome the difficulties presented in nonlinear approaches. Simulation results are presented to illustrate the performance of our method and to compare it with an existing approach.