Péricles R. Barros

Brief Relay-based closed loop transfer function frequency points estimation

In this paper, the following frequency response estimation problem is addressed: Given a closed loop transfer function, such as the loop transfer function or the sensitivity function, find a frequency for which it achieves a user-defined magnitude. The procedure presented here is based on a relay feedback, which makes it suitable to apply to actual systems. In addition to the frequency, the system phase at that frequency is computed simultaneously. The procedure can be used to evaluate and redesign controllers.

Design of Observers With Error Limitation in Discrete-Time Descriptor Systems: A Case Study of a Hydraulic Tank System

A novel descriptor observer structure is proposed in the context of discrete-time descriptor linear systems. On the basis of this new structure, the characterization of conditioned-invariant polyhedral sets with the purpose of limiting the estimation error is carried out. Limitation of the estimation error can be achieved by the computation of an as small as possible conditioned-invariant polyhedron, that contains the set of possible initial errors, and by a suitable output injection law. The approach is applied to an experimental tanks platform, for which a descriptor model is identified and validated. The obtained results confirm the merits of the proposed observer for applications in this kind of systems.

Estimating the parameters of an induction motor in open-loop and closed-loop operation

The purpose of this paper is to present two methods for estimating all the parameters of induction motors operating in open-loop or in closed-loop. The parameters are obtained by solving a recursive least squares minimization problem. The estimation procedure is performed in two parts. First, the stator leakage inductance and the stator resistance are determined by using the homopolar machine model. Then, given the previously estimated homopolar parameters and by using the dynamic dq model, all the other parameters are determined. The first method is derived for open-loop operation. In the second method, the model is derived for the case where the stator currents of the motor are regulated via a linear feedback controller. Selected experimental results are used to demonstrate the feasibility and performance of the proposed methods.

Continuous-time identification of first-order plus dead-time models from step response in closed loop

Abstract In this work the identification of first-order plus dead-time models from closed loop step response experiments is considered. Existing approaches for closed loop identification are examined and simple algorithm are proposed for dealling with the dead-time. Simulation examples are used to illustrate the techniques.

Automation of an anaerobic-aerobic wastewater treatment process

In this paper, the treatment capacity and effluent quality of an anaerobic-aerobic sewage treatment system composed of a upflow anaerobic sludge blanket unit in series with a sequencing batch reactor (SBR) is evaluated. The aerobic part of the system (the SBR) is automated and the concentration of dissolved oxygen is used as a control parameter for the aeration period.

A Flexible Laboratory-Scale Quadruple-Tank Coupled System for Control Education and Research Purposes

Abstract In this paper it is described a flexible laboratory-scale quadruple-tank coupled system designed for Control Education and Research purposes. The quadruple-tank process presented is a flexible structure for experimental implementation and evaluation of different control strategies in a multivariable non-linear process. The structure allows the implementation of different experiments, such as SISO (single-input single-output), TITO (two-input two-output) and MIMO (multiple-input multiple-output), with the option of coupling or cascade effect between tanks. A general description for the system is presented. A linear dynamic model of the tank system is presented for a SISO configuration and simple experiments are shown which illustrate the use of the laboratory-scale system in undergraduate control course.

Estimation of dissolved oxygen dynamics for sequencing batch aerobic reactors

In this paper a wastewater treatment pilot plant, which consists of an upflow anaerobic sludge blanket reactor (UASB) in series with a batch reactor operated in aerobic conditions is under study. Both reactors are based in the activated sludge process. The work is focused on the estimation of the dissolved oxygen dynamics of the aerobic reactor: the oxygen transfer function and the respiration rate are estimated first in nonrecursive mode in the beginning of the batch and then, the respiration rate is estimated in recursive mode. Simulation and experimental estimates are performed.

Dynamic output feedback control of constrained descriptor systems

This paper aims to present an approach for design of dynamic output feedback compensators for linear discrete-time descriptor systems subject to state and control constraints. To this end, output-feedback controlled-invariant polyhedra are constructed by taking a pair of polyhedral sets: a controlled-invariant set and a conditioned-invariant set. By defining an augmented system composed of the original system plus the dynamic compensator, a control action can be computed online, which optimizes the contraction rate of the augmented state trajectory and enforces the constraints. The results are illustrated through numerical examples, which show that the proposed dynamic compensators outperform static feedback controllers under the same conditions.

Output feedback control of constrained descriptor systems: a case study of a hydraulic tank system:

A novel technique is proposed for output feedback control of constrained linear discrete-time causal descriptor systems. In particular, it is shown how linear state and control constraints can be satisfied by using only output measurements corrupted by unknown but bounded noise. To this end, conditions are established under which a polyhedron contained in the set defined by the state constraints can be made invariant through output feedback. The control input which enforces the constraints can be computed online through the solution of linear programming problems. The proposed technique is then applied to the control of a hydraulic three-tank system. Simulated as well as experimental results illustrate the proposed technique and indicate that it can be potentially used in practical situations.

Evaluation and redesign of decouplers for TITO processes using relay experiment

In this paper the decoupling control of two-inputs two-outputs (TITO) processes using a simplified dynamic decoupler is considered. A frequency-domain identification technique that uses a relay experiment to estimate a first-order plus dead-time (FOPDT) TITO model is presented. The resulting FOPDT TITO model is accurate around at the frequency of interest and is used to design a simplified decoupler. A new decoupler evaluation and redesign method to reach effective decoupling at the frequency of interest is proposed. Simulation examples are used to illustrate the method.