Analysis of Power Converter's Control Techniques in Grid-Tie and AC Micro/Smart Grid

142 Pages·2016·3.61 MB·English

by  Abdulgafor Mohammed Alfares

Marquette University
e-Publications@Marquette
Master's Theses (2009 -) Dissertations, Theses, and Professional Projects
Analysis of Power Converter's Control Techniques
in Grid-Tie and AC Micro/Smart Grid
Abdulgafor Mohammed Alfares
Marquette University
Recommended Citation
Alfares, Abdulgafor Mohammed, "Analysis of Power Converter's Control Techniques in Grid-Tie and AC Micro/Smart Grid" (2014).
Master's Theses (2009 -).Paper 241.
http://epublications.marquette.edu/theses_open/241
ANALYSIS OF POWER CONVERTER’S CONTROL TECHNIQUES IN GRID –TIE
AND AC MICRO/SMART GRID

by

Abdulgafor Mohammed Alfares , B.S.

A Thesis Submitted to the Faculty of the Graduate School,
Marquette University,
in Partial Fulfillment of the Requirements for
the Degree of Master of Science

Milwaukee, Wisconsin
May 2014
ii

ABSTRACT
ANALYSIS OF POWER CONVERTES’ CONTROL TECHNIQUES
IN GRID-TIE AND AC MICRO/SMART GRID

Abdulgafor Alfares , B.S.
Marquette University, 2014
Power converters have an outstanding potential in micro and smart grid applications
that require flexible and fast power control as well as rigid voltage regulation at the point
of common coupling. Power converters are required to properly operate under several
modes of operation such as grid-tie and micro-grid modes of operations. In addition, the
control system should be designed to enable proper load sharing between several units.

Several control techniques have been proposed in the literature to address most of the
control requirements of the power converters under different operating modes mentioned
above. However, references found in the literatures are usually centered on the analysis
of the system under only one mode of operation and using a single control strategy.
Comprehensive study that combines an in depth analysis of the power converters control
under several modes are very scarce in the literature.

In this thesis, a detailed survey and analysis of power converter control techniques
in Grid-Tie and AC Micro/Smart Grid applications are introduced. This analysis is based
on detailed nonlinear time domain simulations as well as average and small signal models
for system stability assessment and performance evaluation.
iii

ACKNOWLEDGMENTS
Abdulgafor Alfares , B.S.
In no particular order, I would like to thank deeply my God and Ahel Albait. Also, I
would like to thank my mother who was my role model, and to whom I dedicate this
thesis. I want to express sincere gratitude to all people who have helped and inspired me
and all my colleagues at Marquette University who made it a comfortable place to work.

I would like to thank my advisor from Rockwall Automation, Professor Ahmed Sayed
Ahmed for his guidance and support throughout the course of this work. Moreover, I am
thankful to him for creating and maintaining an excellent academic environment, a factor
which had a positive impact on this work.

Also, I would like to thank my advisor from Marquette University, Professor Michael
Johnson for his scientific contributions and support.

I would like to thank my father and my sister. I would like to thank my teachers, my
faculty, my committee, my director. I would like to thank the Graduate School and all of
the Marquette University administration.
iv

TABLE OF CONTENTS
ACKNOWLEDGMENTS ................................................................................................. iii
LIST OF TABLES ........................................................................................................... viii
LIST OF FIGURES ........................................................................................................... ix
CHAPTER 1: INTRODUCTION
1.0 INTRODUCTION .............................................................................................1
1.1 MICROGRID AND SMART GRID SYSTEMS ..............................................1
Microgrid .....................................................................................................1
Smart Grid ...................................................................................................2
The Difference Between Smart Grid and Microgrid ...................................4
Achievement of Smart Grid and Microgrid .................................................4
1.2 THE IMPORTANCE OF RENEWABLE ENERGY RESOURCES ...............5
Nuclear Power Plant ....................................................................................5
Fossil Fuel ....................................................................................................6
Fuel Cells .....................................................................................................7
Solar and Photovoltaic .................................................................................7
Wind Power Development ...........................................................................8
1.3 THE SCOPE OF THIS THESIS .....................................................................10
CHAPTER 2: CONTROL TECHNIQUES OF MICROGRID POWER
CONVERTER
2.0 INTRODUCTION ...........................................................................................11
2.1 MODES OF CONTROLLER IN SMART GRIDS .........................................12
A. Grid-Feeding Power Converters ...........................................................12
v

B. Grid-Supporting Power Converters .......................................................13
C. Stand-Alone Mode ................................................................................14
2.2 VIRTUAL DIRECT CONTROL (VDTC) .....................................................15
Virtual Torque and Flux Calculation .........................................................17
Hysteresis Control ......................................................................................18
Look-Up Table and Control .......................................................................19
2.2.1 Summary of VDTC ...........................................................................20
2.3 VOLTAGE-ORIENTED CONTROL .............................................................21
2.3.1 Summary of VOC .............................................................................25
2.4 DIRECT POWER CONTROL ........................................................................26
2.5 COMPARISON BETWEEN VDTC, VOC, AND DPC .................................27
2.6 SUMMARY OF VCTC, VOC, AND DPC .....................................................34
CHAPTER 3: GRID FILTER DESIGN
3.0 INTRODUCTION ...........................................................................................38
3.1 TYPES OF FILTER .........................................................................................38
3.2 DESIGN CONSIDERATIONS FOR LCL-FILTER ......................................39
3.3 POWER FLOW AND POWER ANGLE ANALYSIS ..................................46
3.4 SUMMARY OF CHAPTER THREE ..............................................................59
CHAPTER 4: MICROGRID SYSTEM IN STAND-ALONE APPLICATION
4.0 INTRODUCTION ..........................................................................................60
4.1 THE STRUCTURE OF A MICROGRID IN STAND-ALONE MODE
WITHOUT POWER SHARING .....................................................................61

4.1.2 First Control: Regulate the Currents and the Voltages .....................62
A. Closed Loop ..............................................................................63
vi

1. Closed Loop Voltage Control ........................................64
2. An Outer Voltage Control Loop and an Inner Current
Control Loop ................................................................64

B. Open Loop .................................................................................67
4.1.3 Control Anlysis: Average Model for the Microgrid .........................69
A. Mathematical Model ................................................................70
B. Controller Design .....................................................................75
4.2 SMALL SINGLES ANALYSIS ......................................................................77
1. Voltage Control Loop ............................................................................77
2. Cascade Control ....................................................................................82
3. Open Loop Control ................................................................................86
4.3 SUMMARY .....................................................................................................90
CHAPTER 5: MICROGRID SYSTEM IN STAND-ALONE WITH SHARING
SOURCE
5.0 INTRODUCTION .............................................................................................91
Primary Control: P/Q Droop Control ...................................................93
Secondary Control: Frequency-Voltage Restoration and
Synchronization ...................................................................................93

Tertiary Control: P/Q Import and Export.............................................93
5.1 DROOP CONTROL METHOD ......................................................................96
First, the Droop Control Method ...............................................................96
Second, Power Sharing Loop .....................................................................99
Third, Power Flow Analysis of Islanding Mode ......................................100
Forth, Simulations are conducted to verify the efficiency ......................102
vii

5.2 SUMMARY ...................................................................................................111
CHAPTER 6: CONCLUSION AND FUTURE WORK
6.0 CONCLUSION ..............................................................................................112
6.1 FUTURE WORK ...........................................................................................113
A. Hierarchical Control of AC Microgrids .............................................113
B. DC Microgrid .....................................................................................116
BIBLIOGRAPHY ..........................................................................................................118
APPENDIX A
A.0 EQUIVALENT TWO-PHASE SYSTEM ....................................................121
APPENDIX B
B.0 DESIGN CONSIDERATION FOR LCL-FILTER ......................................122
APPENDIX C
C.0 DESIGN CONSIDERATION FOR LCL-FILTER WITH A LOAD ...........127
viii

LIST OF TABLES

1.1 Time required for Production different type of energy 6
1.2 Carbon Footprint of Renewable Source for Production of Electric Energy 7
1.3 Carbon Footprint of Renewable Source for Production of Electric Energy 7
2.1 Sectors locations 19
2.2 States switching and look up Table 20
2.3 Simulations parameters 28
2.4 Comparison summary of VTPC, VOC and DPC 34
3.1 LCL-filter parameters 42
3.2 Parameters of smart grid in Fig 3.3 48
3.3 Simulations results for the case study 48
4.1 Fig4.2 Parameters Values 63
4.2 Summation results 69
4.3 Parameters of simplification circuit in Fig 4.9 71
4.4 Simulation results of signals analysis 90
5.1 Simulation parameters 103
A1 K values 121
ix

LIST OF FIGURES

1.1a Simple configuration of microgrid 2
1.1b: Simple configuration of microgrid 2
1.2: Simple smart grid structure 3
1.3 Smart Grid and Micro Grids Source 4
1.4 Solar System 8
1.5 Basic power Conversion Wind Turbine System 9
2.1 Power transfer between tow ac systems 11
2.2 Simplified parallel grid-feeding 13
2.3a Simplified Current Source based grid supporting 14
2.3b Simplified of Voltage Source based grid supporting 14
2.4 Simplified block diagram of Virtual Direct Torque Control 16
2.5 Basic virtual direct torque control scheme for smart grid (VDTC) 17
2.6 Virtual Torque and flux hysteresis control 18
2.7 Principle of space vector modulation 19
2.8 Basic Scheme of VOC 22
2.9 Stationary αβ frame and rotating dq frame 23
2.10 PQ-loop and inner Current loop 24
2.11 PQ closed loop voltage oriented control based on synchronous dq frame 25
2.12 Scheme of DPC 26
2.13 Smart grid simple configuration 27
2.14a: Fast Fourier Transform (FTT) for currents in: a) VDTC 29