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Cover
Modeling and Identification of Linear Parameter-Varying Systems
Lecture Notes in Control and Information Sciences 403
ISBN 364213811X
Preface
Contents
Acronyms
List of Symbols
Chapter 1 Introduction
New Challenges for System Identification
The Birth of LPV Systems
The Present State of LPV Identification
The Identification Cycle
General Picture of LPV Identification
LPV-IO Representation Based Methods
LPV-SS Representation Based Methods
Similarity to Other System Classes
Challenges and Open Problems
Perspectives of Orthonormal Basis Function Models
The Gain-Scheduling Perspective
The Global Identification Perspective
Approximation via OBF Structures
The Goal of the Book
Overview of Contents
Chapter 2 LTI System Identification and the Role of OBFs
The Concept of Orthonormal Basis Functions
Signal Spaces and Inner Functions
General Class of Orthonormal Basis Functions
Takenaka-Malmquist Basis
Hambo Basis
Kautz Basis
Laguerre Basis
Pulse Basis
Orthonormal Basis Functions of MIMO Systems
Basis Functions in Continuous-Time
Modeling and Identification of LTI Systems
The Identification Setting
Model Structures
Properties
Linear Regression
Identification with OBFs
Pole Uncertainty of Model Estimates
Validation in the Prediction-Error Setting
The Kolmogorov n-Width Theory
Conclusions
Chapter 3 LPV Systems and Representations
General Class of LPV Systems
Parameter Varying Dynamical Systems
Representations of Continuous-Time LPV Systems
Representations of Discrete-Time LPV Systems
Equivalence Classes and Relations
Equivalent Kernel Representations
Equivalent IO Representations
Equivalent State-space Representations
Properties of LPV Systems and Representations
State-Observability and Reachability
Stability of LPV Systems
Gramians of LPV State-Space Representations
Conclusions
Chapter 4 LPV Equivalence Transformations
State-Space Canonical Forms
The Observability Canonical Form
Reachability Canonical Form
Companion Canonical Forms
Transpose of SS Representations
LTI vs. LPV State Transformation
From State-Space to the Input-Output Domain
From the Input-Output to the State-Space Domain
The Idea of Recursive State-Construction
Cut-and-Shift in Continuous-Time
Cut-and-Shift in Discrete-Time
State-Maps and Polynomial Modules
State-Maps Based on Kernel Representations
State-Maps Based on Image-Representations
State-Construction in the MIMO Case
Conclusions
Chapter 5 LPV Series-Expansion Representations
Relevance of Series-Expansion Representations
Impulse Response Representation of LPV Systems
Filter Form of LPV-IO Representations
Series Expansion in the Pulse Basis
The Impulse Response Representation
LPV Series Expansion by OBFs
The OBF Expansion Representation
Series Expansions and Gain-Scheduling
The Role of Gain-Scheduling
Optimality of the Basis in the Frozen Sense
Optimality of the Basis in the Global Sense
Conclusions
Chapter 6 Discretization of LPV Systems
The Importance of Discretization
Discretization of LPV System Representations
Discretization of State-Space Representations
Complete Method
Approximative State-Space Discretization Methods
Discretization Errors and Performance Criteria
Local Discretization Errors
Global Convergence and Preservation of Stability
Guaranteeing a Desired Level of Discretization Error
Switching Effects
Properties of the Discretization Approaches
Discretization and Dynamic Dependence
Numerical Example
Conclusions
Chapter 7 LPV Modeling of Physical Systems
Towards Model Structure Selection
General Questions of LPV Modeling
Modeling of Nonlinear Systems in the LPV Framework
First Principle Models
Linearization Based Approximation Methods
Multiple Model Design Procedures
Substitution Based Transformation Methods
Automated Model Transformation
Summary of Existing Techniques
Translation of First Principle Models to LPV Systems
Problem Statement
The Transformation Algorithm
Handling Non-Factorizable Terms
Properties of the Transformation Procedure
Conclusions
Chapter 8 Optimal Selection of OBFs
Perspectives of OBFs Selection
Kolmogorov n-Width Optimality in the Frozen Sense
The Fuzzy-Kolmogorov c-Max Clustering Approach
The Pole Clustering Algorithm
Properties of the FKcM
Simulation Example
Robust Extension of the FKcM Approach
Questions of Robustness
Basic Concepts of Hyperbolic Geometry
Pole Uncertainty Regions as Hyperbolic Objects
The Robust Pole Clustering Algorithm
Properties of the Robust FKcM
Simulation Example
Conclusions
Chapter 9 LPV Identification via OBFs
Aim and Motivation of an Alternative Approach
OBFs Based LPV Model Structures
The LPV Prediction-Error Framework
The Wiener and the Hammerstein OBF Models
Properties of Wiener and Hammerstein OBF Models
OBF Models vs. Other Model Structures
Identification of W-LPV and H-LPV OBF Models
Identification with Static Dependence
The Identification Setting
LPV Identification with Fixed OBFs
Local Approach
Global Approach
Properties
Examples
Approximation of Dynamic Dependence
Feedback-Based OBF Model Structures
Properties of Wiener and Hammerstein Feedback Models
Identification by Dynamic Dependence Approximation
Properties
Example
Extension towards MIMO Systems
Scalar Basis Functions
Multivariable Basis Functions
Multivariable Basis Functions in the Feedback Case
General Remarks on the MIMO Extension
Conclusions
Appendix A Proofs
References
Index
Lecture Notes in Control and Information Sciences 403 Editors: M. Thoma, F. Allgöwer, M. Morari
Roland Tóth Modeling and Identification of Linear Parameter-Varying Systems ABC
Series Advisory Board P. Fleming, P. Kokotovic, A.B. Kurzhanski, H. Kwakernaak, A. Rantzer, J.N. Tsitsiklis Author Dr. Roland Tóth Delft University of Technology Faculty of Mechanical, Maritime and Materials Engineering Delft Center for Systems and Control Mekelweg 2 2628 CD, Delft The Netherlands Co-Editors Dr. Peter S.C. Heuberger Delft University of Technology Faculty of Mechanical, Maritime and Materials Engineering Delft Center for Systems and Control Mekelweg 2 2628 CD, Delft The Netherlands Prof. Dr. Paul M.J. Van den Hof Delft University of Technology Faculty of Mechanical, Maritime and Materials Engineering Delft Center for Systems and Control Mekelweg 2 2628 CD, Delft The Netherlands ISBN 978-3-642-13811-9 e-ISBN 978-3-642-13812-6 DOI 10.1007/978-3-642-13812-6 Lecture Notes in Control and Information Sciences ISSN 0170-8643 Library of Congress Control Number: 2010928272 c 2010 Springer-Verlag Berlin Heidelberg This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable for prosecution under the German Copyright Law. The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Typeset & Cover Design: Scientific Publishing Services Pvt. Ltd., Chennai, India. Printed in acid-free paper 5 4 3 2 1 0 springer.com
I dedicate this book to my beloved wife Andrea, my “great” son S´andor and my little daughter Lujza.
Preface Through the past 20 years, the framework of Linear Parameter-Varying (LPV) systems has become a promising system theoretical approach to han- dle the control of mildly nonlinear and especially position dependent systems which are common in mechatronic applications and in the process indus- try. The birth of this system class was initiated by the need of engineers to achieve better performance for nonlinear and time-varying dynamics, com- mon in many industrial applications, than what the classical framework of Linear Time-Invariant (LTI) control can provide. However, it was also a pri- mary goal to preserve simplicity and “re-use” the powerful LTI results by extending them to the LPV case. The progress continued according to this philosophy and LPV control has become a well established field with many promising applications. Unfortunately, modeling of LPV systems, especially based on measured data (which is called system identification) has seen a limited development since the birth of the framework. Currently this bottleneck of the LPV frame- work is halting the transfer of the LPV theory into industrial use. Without good models that fulfill the expectations of the users and without the under- standing how these models correspond to the dynamics of the application, it is difficult to design high performance LPV control solutions. This book aims to bridge the gap between modeling and control by investigating the fundamental questions of LPV modeling and identification. It explores the missing details of the LPV system theory that have hindered the formula- tion of a well established identification framework. By proposing an unified LPV system theory that is based on a behavioral approach, the concepts of representations, equivalence transformations, and means to compare model structures are re-established, giving a solid basis for an identification theory. It is also explored when and how first-principle nonlinear models can be effi- ciently converted to LPV descriptions and what are the pitfalls that must be avoided. Building on well founded system theoretical concepts, the classical LTI prediction-error framework is extended to the LPV case via the use of series-expansion representations.
VIII Preface Beside completing the system theoretical aspects and founding of an LPV prediction-error framework, the book proposes a novel identification approach based on orthonormal basis functions, which provides an efficient and easy to use approach of LPV identification. It has been shown in the LTI case that decomposing dynamical systems in terms of orthogonal expansions enables the accurate approximation of the system with a finite length expansion. By tuning the basis functions to the underlying system characteristics, the rate of convergence can be drastically decreased. This leads to highly accurate models (small bias) being represented by a few parameters (small variance), which in fact can be estimated efficiently via simple linear regression. This philosophy gives the basic concept of the proposed identification approach, for which the applicability in practical scenarios is investigated and powerful algorithms are provided and analyzed. The work presented here is the result of 5 years of research at the Delft University of Technology under the supervision of Prof. Paul M.J. Van den Hof and Peter S.C. Heuberger. Starting with the initial intention to apply simplicity of orthonormal basis function models to overcome the challenges of LPV system identification, a long road has led to the theory which is presented in this book. Walking on this road, many excellent people have contributed to this work. Especially Prof. Jan C. Willems, at the Catholic University of Leuven, whose advice and vision about mathematical modeling helped me to find the right track that lead to the LPV behavioral theory, that forms the basis of many concepts of this book. Prof. Carsten Scherer, at the Delft University of Technology, whose advice and extensive knowledge on LPV systems and control has always helped me to find the missing wheel. Federico Felici, whose earth-moving questions and discussions made me aware of missing key points of the LPV system theory. But the main thanks goes to Prof. Paul M.J. Van den Hof and Peter S.C. Heuberger whose excellent guid- ance led me through these years, culminating in my Ph.D. thesis [188], which served as the basis of this book. As co-editors, they also had a significant role in establishing this book in its current from. The book is written as a research monograph with a broad scope, trying to cover the key issues from system theory to modeling and identification. It is meant to be interesting for both researchers and engineers but also for graduate students in systems and control who would like to learn about the LPV framework. It also offers an easy to use guide for engineers about the off-shelf solutions in LPV modeling and identification. I hope that you as a reader will enjoy reading it as much as it was fun to write it. Delft, December 2009 Roland T´oth
Contents 1 2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 New Challenges for System Identification . . . . . . . . . . . . . . . . . 1.2 The Birth of LPV Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 The Present State of LPV Identification . . . . . . . . . . . . . . . . . . 1.3.1 The Identification Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.2 General Picture of LPV Identification . . . . . . . . . . . . . . 1.3.3 LPV-IO Representation Based Methods . . . . . . . . . . . . 1.3.4 LPV-SS Representation Based Methods . . . . . . . . . . . . 1.3.5 Similarity to Other System Classes . . . . . . . . . . . . . . . . 1.4 Challenges and Open Problems . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Perspectives of Orthonormal Basis Function Models. . . . . . . . 1.5.1 The Gain-Scheduling Perspective . . . . . . . . . . . . . . . . . . 1.5.2 The Global Identification Perspective . . . . . . . . . . . . . . 1.5.3 Approximation via OBF Structures . . . . . . . . . . . . . . . . 1.6 The Goal of the Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7 Overview of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LTI System Identification and the Role of OBFs . . . . . . . . . 2.1 The Concept of Orthonormal Basis Functions . . . . . . . . . . . . . 2.2 Signal Spaces and Inner Functions . . . . . . . . . . . . . . . . . . . . . . . 2.3 General Class of Orthonormal Basis Functions . . . . . . . . . . . . 2.3.1 Takenaka-Malmquist Basis . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Hambo Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Kautz Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.4 Laguerre Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.5 Pulse Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.6 Orthonormal Basis Functions of MIMO Systems . . . . . 2.3.7 Basis Functions in Continuous-Time . . . . . . . . . . . . . . . 1 1 3 4 4 6 9 11 14 15 17 17 18 18 19 20 21 21 22 24 24 25 26 26 26 26 27
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