Rafael Martínez-Guerra

Temperature control in catalytic cracking reactors via a robust PID controller

The stabilization of fluid catalytic cracking reactors is tackled in this paper. A robust PID control law is developed in order to control the outlet reactor temperature. The suggested control is based on a reduced order model of the reactor given by a system of ordinary differential equations. The controller is synthesized using an input/output linearizing control law coupled to a proportional-derivative reduced order observer to infer on-line the unknown heat of reaction. The proposed control algorithm leads to a classical PID structure. New tuning rules are given, based on the system structure, estimations and closed-loop time constants. This control strategy turns out to be robust against model uncertainties, noisy temperature measurements and set point changes. The performance of the reaction temperature in a tubular riser reactor is numerically compared when the proposed control scheme and standard PID controllers are applied. # 2002 Elsevier Science Ltd. All rights reserved.

Nonlinear estimators: A differential algebraic approach

Abstract Based on differential algebra techniques, an exponential observer is proposed for the state estimation of a class of nonlinear systems. Simulations illustrating the performance of the proposed observer are included.

Reaction heat estimation in continuous chemical reactors using high gain observers

The problem of the on-line estimation of the reaction heat in a continuous stirred tank reactor (CSTR) from temperature measurements is addressed in this paper. The proposed uncertainty observer is based on differential algebraic techniques, such that the algebraic observability condition of the uncertainty from temperature measurements is easily verified and the observer structure is very simple, which lead to feasible implementation. The observer proposed is robust against noisy measurements and sustained disturbances. The good performance of the observer is shown by means of numerical simulations.

A New Robust Sliding-Mode Observer Design for Monitoring in Chemical Reactors

The robust observer design for the online estimation of heat in continuous stirred tank reactors, containing nonstructured uncertainties within its model description as well as noisy temperature measurements, is addressed. The proposed observer contains a slidingmode term and is designed based on Differential Algebraic technique. The concept of the algebraic observability for a given class of model uncertainty is introduced. It is applied to the uncertainty estimation from noisy temperature measurements providing a simple observer structure which turns out to be robust against output (sensors) noises as well as sustained disturbances. The performance of this observer is shown to be calculated numerically. The obtained results look promising for possible industrial applications. @DOI: 10.1115/1.1789534#

CHAOTIC SYNCHRONIZATION AND SECURE COMMUNICATION VIA SLIDING-MODE OBSERVER

Information signal embedded in a chaotic transmitter can be recovered by a receiver if it is a replica of the transmitter. In this paper, a new aspect of chaotic communication is introduced. A sliding-mode observer replaces the conventional chaotic system at the receiver side, which does not need information from the transmitter. So the uncertainties in the transmitter and the transmission line do not affect the synchronization, the proposed communication scheme is robust with respect to some disturbances and uncertainties. Three chaotic systems, Duffing equation, Van der Pol oscillator and Chua’s circuit, are provided to illustrate the effectiveness of the chaotic communication.

Robust PI2 controller for continuous bioreactors

Abstract An estimation algorithm related to the kinetics terms of the main uncertainties present in a continuous stirred tank bioreactor, is developed. This algorithm is based on a proportional–integral reduced order uncertainty observer. With the estimate generated of the uncertain term, an input–output linearizing feedback control is designed which provides robust regulation model uncertainties, noisy measurements and sustained disturbances. This control strategy could be represented as PI 2 controller where new tuning rules of the controller gains are given in terms of the estimation and closed-loop time constants. The performance of the estimation algorithm and the corresponding closed-loop behaviour of the system are compared to a standard PI controller and they are illustrated by means of numerical simulations.

On nonlinear systems diagnosis using differential and algebraic methods

In this paper we tackle the diagnosis problem in nonlinear systems under failure using differential algebra. Three examples are presented in order to apply the proposed methodology. Numerical simulations of these examples are presented to illustrate the effectiveness of the suggested approach.

The fault detection problem in nonlinear systems using residual generators

In this chapter we study the fault detection problem using residual generators based upon high gain nonlinear observers in a differential algebraic framework. We analyze the stability of the residual generator when a fault occurs. We also consider two faults types: constant and time-varying faults. It is shown that under some mild conditions over the aforementioned faults the residual is different from zero.

Diagnosis for a class of non-differentially flat and Liouvillian systems

In this chapter, we tackle the diagnosis problem for non-differentially flat and Liouvillian systems by using the concept of differential transcendence degree of a differential field extension, as well as, we consider the algebraic observability concept of the variable which models the failure presence for the solvability of the diagnosis problem. The construction of a reduced-order uncertainty observer to estimate the fault variable is the main ingredient in our approach. Finally, we present a simulation example dealing with a ship in smooth landing to illustrate the effectiveness of the suggested approach.

Fault diagnosis in nonlinear systems: An application to a three-tank system

The fault diagnosis problem for nonlinear systems is treated, some results based on a differential algebraic approach are used in order to determine fault diagnosability with the minimum number of measurements from the system. Two schemes of nonlinear observers are used for reconstructing the fault signals for comparison purposes, one of them being a reduced order observer and the other a sliding mode observer. The methodology was tested in a real time implementation of the three-tank system for which a previous identification of uncertain parameters is realized in order to improve fault estimations.