ON THE DESIGN AND EVALUATION OF
HIERARCHICAL AND DECENTRALISED REGULATORS FOR AUTOMATIC GENERATION CONTROL
By
RAMINENI GOVAR DHANA RAO
Electrical Engineering Department
Thesis Submitted
In fulfilment of the requirements of the degree of DOCTOR OF PHILOSOPHY
IN
OCTOBER 1982
CERT IF ICATE.
This is to certify that the thesis entitled," On the Design and Evaluation of Hierarchical' and Decentralised Regulators for Automatic Generation Control" being submitted by R.Govardhana Rao, for the award of the degree of Doctor of Philosophy to the Indian Institute of Technology, Delhi, is a record of bonafide research work he has carried out under my guidance and supervision. The results contained in this thesis have not been submitted to any other University or Institute for the award of any degree or diploma.
S.I. Ahson Assistant Professor
Department of Electrical Engineering Indian Institute of Technology
New Delhi 110 016
ACKNOWLEDGMENTS
I am grateful to my supervisor, Dr. S.I. Ahson, Assistant Professor, Department of Electrical Engineering, from whom I received continual encouragement, advice and guidance during the course of this research work.
Thanks are due to Dr. M. Hanmandulu, Messrs Ray, Prasad, Agrawala, Mahto, Narasimham, C.V.S. Rao, Gupta and Ekbote for use- ful discussions. Thanks are also due -to Prof. V.R.K. Murthy and other colleagues at Andhra University, Waltair, for their help.
I am thankful to my wife Sobhana Devi and children Hama Chandra and Rajasekhar for their cheerful company which has made my work easier than expected. It is a pleasure to acknowledge the help received in various forms from Smt. and Sri P.R.K. Chowdary during my stay at Delhi. I am also grateful to my brother
Sri R. Prasada Rao for constant encouragement and help throughout my work.
The financial assistance received from the Ministry of Education and Culture, New Delhi, and the Andhra University, Waltair, under QIP scheme is gratefully acknowledged.
Finally, r wish to thank Sri P.M. Padmanabhan Nambiar for his patient and excellent typing of the manuscript, and Sri R. Kapoor for making neat drawings.
/*5V-c.51511P0114,a g cts,
IT Delhi R. GOVARDHANA RAO
:tober 1982
ABSTRACT
The thesis is concerned with the design and evaluation of hierarchically structured and decentralised regulators for auto-
matic generation control (AGC). AGG regulators are designed using the continuous-time (linear and non-linear) formulation and their effectiveness is evaluated through extensive computer simulation.
Some new algorithms for the design of hierarchically structured regulators are proposed and their superiority over conventional AGG regulator is demonstrated. A two-area Hydro-Thermal power system model has been considered for illustrating the results.
The design of two-level regulators using Siljak's method is also included.
Two modified versions of the linear interaction-prediction method have been developed for the design of regulators for auto- matic generation control, which take into account the practical constraints such as zero steady-state errors and generation rate constraints. The possibility of implementing the resulting
"proportional-plus-integral-feedback" type of control law is illu- strated through computer simulation on a two-area Reheat-Thermal- Hydro power system model. The responses are compared with those obtained by classical controllers. A discrete version of the con- tinuous (analog) hierarchical two-level regulator is developed.
The discrete version takes care of the practical constraints through the "proportional-state-plus-summation output-feedback"
ii
iii
type of ontrol law. The results are illustrated using a two—area Reheat—Thermal—Hydro power system model.
Since the AGC models used in this thesis contain many inacces- sible state variables, a decentralised—observer for estimating the unmeasurable state variables is proposed. The design of decentra- lised full—order observers for the AGC problem is based on the concept of unknown—input observer design. The performance of the decentralised observer is evaluated through computer simulation.
For completeness of the thesis, proper background material, reviews and suggestions for further work in this area are included.
CONTENTS
Page ACKNOWLEDGMENTS
ABSTRACT ii
LIST OF PRINCIPAL SYMBOLS viii
LIST OF FIGURES xiv
CHAPTER 1 INTRODUCTION 1
1.2 Conventional Automatic Generation 2 Control
1.3 Modern Approaches to Automatic Generation 8 Control
1.4 Hierarchical Control Strategies for 14 Large Scale Dynamic Systems
1.5 Decentralised Control Strategies 32 1.6 Hierarchical and Decentralised Regulators 36
for AGC
1.7 Scope of the Thesis 40
CHAPTER 2 THE INTERACTION—PREDICTION METHOD AND ITS 44 APPLICATION TO AGC
2.1 Introduction 44
2.2 The Interaction—Prediction Method for 46 Linear Dynamic Systems
2.3 The Interaction—Prediction Method for 59 Non—linear Systems
2.4 A Gradient Method for Co—ordination 63 2.5 Application to a Non—linear Two—Area 67
Hydro—Thermal Power System
iv
Page 2.6 Application to Linearised Power System 77
Model
2.7 Comparison of Results 100
2.8 Conclusions 102
CHAPTER 3 AUTOMATIC GENERATION CONTROL VIA SILJAK'S 104 APPROACH
3.1 Introduction 104
3.2 Siljak's Method 105
3.3 Design of a Global Controller for a 110 Two—Area Non—Reheat—Thermal—Hydro Power
System using Siljak's Approach
3.4 Regulator Design with Prespecified Degree of Stability
115
3.5 Conclusions 123
CHAPTER 4 DESIGN OF TWO—LEVEL AGC REGULATORS VIA 124 MODIFIED VERSIONS OF THE LINEAR
INTERACTION—PREDICTION METHOD
4.1 Introduction 124
4.2 The First Modified Version of the Linear 126 Interaction—Prediction Method
4.3 The Second Modified Version of the Linear 136 Interaction—Prediction Method
4.4 Application to a Two—Area Hydro—Thermal— 144 Power System Model
4.5 Conclusions 159
CHAPTER 5 DISCRETE HIERARCHICAL AGC REGULATORS 161
5.1 Introduction 161
5.2 Discrete Interaction—Prediction Method 162
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Page 5.3 Modified Discrete Interaction—Prediction 171
Method
5.4 Application to a Two—Area—Thermal—Hydro 180 Power System
5.5 Conclusions 195
CHAPTER 6 DECENTRALISED OBSERVERS FOR AUTOMATIC 196 GENERATION CONTROL
6.1 Introduction 196
6.2 Observers for Systems with Unknown and 198 Inaccessible Inputs
6.3 A New Approach for the Design of 206 Decentralised Observers
6.4 Design of Decentralised Observers for a 210 Two—Area Power System Model
225 Conclusions
SUMMARY AND SUGGESTIONS
Two—Area Non—Reheat Hydro—Thermal Power System Model
System Data
Two—Area Linear Non—Reheat Power System Model
Evaluation of the Transformation Matrices T
1 and T 2
Modelling of Two—Area Non—Reheat—Thermal- Hydro Power System with Governor and Voltage Controls
6.5
CHAPTER 7
REFERENCES APPENDICES APPENDIX 2.1
APPENDIX 2.2 APPENDIX 2.3
APPENDIX 2.4
APPENDIX 3.1
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230
240
246 247
253
255
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Page
APPENDIX 3.2 System Data 261
APPENDIX 4.1 Reheat Steam Turbine Model 262 APPENDIX 4.2 Two—Area Reheat Power System Model 265 APPENDIX 5.1 Discretisation of the Continuous Model 271
