Disturbance Observer-based Robust Control and Its Applications: 35th Anniversary Overview

Disturbance Observer has been one of the most widely used robust control tools since it was proposed in 1983. This paper introduces the origins of Disturbance Observer and presents a survey of the major results on Disturbance Observer-based robust control in the last thirty-five years. Furthermore, it explains the analysis and synthesis techniques of Disturbance Observer-based robust control for linear and nonlinear systems by using a unified framework. In the last section, this paper presents concluding remarks on Disturbance Observer-based robust control and its engineering applications.Comment: 12 pages, 4 figure

Peripheral control tools for a run-of-mine ore milling circuit

Run-of-mine ore milling circuits are generally difficult to control owing to the presence of strong external disturbances, poor process models and the unavailability of important process variable measurements. These shortcomings are common for processes in the mineral-processing industry. For processes that fall into this class, the peripheral control tools in the control loop are considered to be as important as the controller itself. This work addresses the implementation of peripheral control tools on a run-of-mine ore milling circuit to help overcome the deteriorated control performance resulting from the aforementioned shortcomings. The effects of strong external disturbances are suppressed through the application of a disturbance observer. A fractional order disturbance observer is also implemented and a novel Bode ideal cutoff disturbance observer is introduced. The issue of poor process models is addressed through the detection of significant mismatch between the actual plant and the available model from process data. A closed-form expression is given for the case where the controller has a transfer function. If the controller does not have a transfer function, a partial correlation analysis is used to detect the transfer function elements in the model transfer function matrix that contain significant mismatch. The mill states and important mill parameters are estimated with the use of particle filters. Simultaneous state and parameter estimation is compared with a novel dual particle filtering scheme. A sensitivity analysis shows the class of systems for which dual estimation would provide superiorestimation accuracy over simultaneous estimation. The implemented peripheral control tools show promise for current milling circuits where proportional-integral-derivative (PID) control is prevalent, and also for advanced control strategies, such as model predictive control, which are expected to become more common in the future. AFRIKAANS : Maalkringe wat onbehandelde erts maal is oor die algemeen moeilik om te beheer as gevolg van die teenwoordigheid van sterk eksterne steurings, onakkurate aanlegmodelle en metings van belangrike prosesveranderlikes wat ontbreek. Hierdie probleme is algemeen vir aanlegte in die mineraalprosesseringsbedryf. Vir aanlegte in hierdie klas word die randbeheerinstrumente as net so belangrik as die beheerder beskou. Hierdie verhandeling beskryf die implementering van randbeheerinstrumente vir ’n maalkring wat onbehandelde erts maal, om die verswakte beheerverrigting teen te werk wat veroorsaak word deur bogenoemde probleme. Die impak van sterk eksterne steurings word teengewerk deur die implementering van ’n steuringsafskatter. ’n Breuk-orde-steuringsafskatter is ook geïmplementeer en ’n nuwe Bode ideale afsnysteuringsafskatter word voorgestel. Die kwessie van onakkurate aanlegmodelle word hanteer deur van die aanlegdata af vas te stel of daar ’n verskil is tussen die aanleg en die beskikbare model van die aanleg. ’n Uitdrukking word gegee vir hierdie verskil vir die geval waar die beheerder met ’n oordragsfunksie voorgestel kan word. Indien die beheerder nie ’n oordragsfunksie het nie, word van ‘n parsiële korrelasie-analise gebruik gemaak om die element, of elemente, in die aanleg se oordragsfunksiematriks te identifiseer wat van die werklike aanleg verskil. Die toestande en belangrike parameters in die meul word beraam deur van partikel-filters gebruikte maak. Gelyktydige toestand- en parameter-beraming word vergelyk met ’n nuwe dubbel-partikelfilter skema. ’n Sensitiwiteitsanalise wys die klas van stelsels waarvoor dubbel-afskatting meer akkurate waardes sal gee as gelyktydige afskatting. Die voorgestelde randbeheerinstrumente is toepaslik vir huidige maalkringe waar PID-beheer algemeen is, asook vir gevorderde beheerstrategieë, soos model-voorspellende beheer, wat na verwagting in die toekoms meer algemeen sal word. CopyrightDissertation (MEng)--University of Pretoria, 2012.Electrical, Electronic and Computer Engineeringunrestricte

Output-based disturbance rejection control for non-linear uncertain systems with unknown frequency disturbances using an observer backstepping approach

This study is concerned with the output feedback control design for a class of non-linear uncertain systems subject to multiple sources of disturbances including model uncertainties, unknown constant disturbances, harmonic disturbances with unknown frequency and amplitude. The total disturbances and uncertainties are delicately represented by a compact exogenous model first. By incorporating the adaptive internal model principle, a set of dynamic estimators are developed for both state and disturbance observations. By means of observer backstepping technique, a composite output feedback controller is constructed based on the disturbance and state estimations. The stability of the closedloop system is rigorously established based on Lyapunov stability criterion. A missile roll stabilisation example is finally investigated to validate the effectiveness of the proposed control approach

Development and application of a model-plant mismatch expression for linear time-invariant systems

When a plant and its controller are sufficiently linear and time-invariant so that they can be representedby transfer functions, and this plant is under classical control (meaning the controller can also be repre-sented by a transfer function), the model-plant mismatch (MPM) that often plagues industrial processescan be written as a closed-form expression. This includes a variety of controllers, among which the ubiq-uitous Proportional, Integral and Derivative (PID) controller. The MPM expression can then be used toidentify a representative transfer function of the “true plant” from the currently available plant model.The MPM expression works for single-input single-output as well as multiple-input multiple-output sys-tems. The closed-loop data required for application of the expression has to be sufficiently exciting. Ifsignificant disturbances perturb the plant their values need to be available. In this article the expressionis applied to industrial data to show its applicability.http://www.elsevier.com/locate/jprocont2016-08-31hb201

Multivariable control of a rougher flotation cell

This project focussed on the investigation, development and evaluation of a closed loop control system on a rougher flotation cell that could improve PGM flotation performance. A PGM rougher flotation cell equipped with Online Stream Analysis (OSA) and machine vision system (SmartFroth) was used during the investigation. Online measurements included bubble velocity, average bubble area, bubble colour; Pt, Ni and Cu concentrate grade and concentrate flow rate and density. Air addition and pulp level was used as the manipulated variables

Hybrid non-linear model predictive control of a run-of-mine ore grinding mill circuit

A hybrid non-linear model predictive controller (HNMPC) is developed for a run-of-mine ore grinding mill circuit. A continuous-time grinding mill circuit model is presented with a hydrocyclone cluster as the primary classifier. The discrete-time component is the switching of hydrocyclones in the hydrocyclone cluster. The resulting model is a hybrid non-linear model with both continuous and discrete dynamics. A simulation of the HNMPC shows the advantages of using the hydrocyclone cluster as an additional manipulated variable. The advantages of the HNMPC is illustrated by comparing its performance to a non-linear MPC where no switching of hydrocyclones is possible. The genetic algorithm based HNMPC showed increased controller stability in its ability to incorporate discrete dynamics into the controller directly. The methods discussed in this paper can be used to incorporate different types of discrete dynamics into advanced grinding mill circuit controllers due to the modular presentation of the model and HNMPC controller design.http://www.elsevier.com/locate/mineng2019-07-01hj2018Electrical, Electronic and Computer Engineerin

Systems and control : 21th Benelux meeting, 2002, March 19-21, Veldhoven, The Netherlands

Book of abstract

Advances in Condition Monitoring, Optimization and Control for Complex Industrial Processes

The book documents 25 papers collected from the Special Issue “Advances in Condition Monitoring, Optimization and Control for Complex Industrial Processes”, highlighting recent research trends in complex industrial processes. The book aims to stimulate the research field and be of benefit to readers from both academic institutes and industrial sectors