A Study of the Power Quality Conditioner(UPOC) for Improved Radial Distribution Network
A Study of the Power Quality Conditioner(UPOC) for Improved Radial Distribution Network.
ABSTRACT
This work assesses the feasibility and performance of an enhanced Unified Power Quality Conditioner (UPQC). A UPQC configuration has been developed which incorporates Photovoltaic (PV) cells and a Battery Energy Storage System (BESS) in the DC link of the UPQC.
The BESS is connected using a bi-directional DC-DC converter. The system operates in two modes namely: Interconnected and Islanding. This arrangement enabled the reliable and efficient compensation of interruption and the amelioration of the effects of loss of supply.
A pre-defined power management strategy has been determined in which the combination of the PV/BESS takes care of a maximum of 1.4940MW of load active power demand during interruption and loss of supply.
This value is such as to ensure active power balance in the system. A detailed model of the system has been developed in the two modes of operation.
Data for the hourly demand on the 11kV Gaskiya feeder of the Power Holding Company of Nigeria (PHCN) Zaria and that for the hourly solar insolation in Zaria (Latitude 11.067 and Longitude 7.7) have been obtained.
A thorough evaluation of the feasibility and performance of the system on the 11kV Gaskiya feeder is presented using the developed models, m-files, and the embedded function of MATLAB/Simulink.
Results show that at a solar insolation level of S = 0.07 representing the least insolation, S = 0.45 representing the most prevalent solar insolation other than the least and S = 0.85 representing the highest insolation,
there is real-time collaboration, based on the determined power management strategy, between the batteries and PV cells in meeting system demand.
In the islanding mode, a part of load active power (1.4940MW) demand is met by the combination of the PV cells and batteries. Thus, interruption and loss of supply are mitigated by the system. Also, the capabilities of the UPQC to regulate load voltage and supply power factor remain uncompromised.
TABLE OF CONTENTS
Title Page Declaration ii
Certification………………………………………………………………………………………………………………….. iii
Acknowledgement…………………………………………………………………………………………………………. iv
Abstract…………………………………………………………………………………………………………………………. v
Table of Contents…………………………………………………………………………………………………………… vi
List of Tables…………………………………………………………………………………………………………………. x
List of Figures……………………………………………………………………………………………………………….. xi
List of Appendices……………………………………………………………………………………………………….. xvi
Abbreviations and Symbols………………………………………………………………………………………….. xvii
CHAPTER ONE: INTRODUCTION……………………………………………………………………………. 1
- Overview…………………………………………………………………………………………………………………. 1
- Significance of the Study………………………………………………………………………………………….. 5
- Aims and Objectives of the Study……………………………………………………………………………… 6
- Limitation of the Study…………………………………………………………………………………………….. 6
- Thesis Outline…………………………………………………………………………………………………………… 7
CHAPTER TWO: LITERATURE REIVIEW…………………………………………………………….. 8
- Introduction…………………………………………………………………………………………………………….. 8
- Review of Fundamental Concepts…………………………………………………………………………….. 8
- Definition of Major Power Quality Events…………………………………………………………………. 8
- Some Effects of Poor Power Quality……………………………………………………………………….. 10
- Electricity Distribution Network……………………………………………………………………………… 11
- The Unified Power Quality Conditioner (UPQC)……………………………………………………… 14
- DC-DC Converters………………………………………………………………………………………………… 29
- Review of Similar Works………………………………………………………………………………………… 32
- Classification Based on Supply System…………………………………………………………………….. 33
- Classification Based on Configuration…………………………………………………………………….. 34
- UPQC for Grid Integration of Renewable Energy Sources…………………………………………. 35
- Statement of Problem…………………………………………………………………………………………….. 38
- Conclusion…………………………………………………………………………………………………………….. 38
CHAPTER THREE: MATERIALS AND METHODS………………………………………………… 39
- Introduction…………………………………………………………………………………………………………… 39
- PHCN Data for 11kV Gaskiya Feeder Zaria…………………………………………………………… 39
- NASA Solar Insolation Data for Zaria……………………………………………………………………. 42
- MATLAB/Simulink……………………………………………………………………………………………….. 42
- Methodology………………………………………………………………………………………………………….. 45
- Modes of Operation………………………………………………………………………………………………. 45
- Conclusion…………………………………………………………………………………………………………….. 49
CHAPTER FOUR: MODEL DERIVATIONS AND DESIGN CONSIDERATIONS…… 51
- Introduction…………………………………………………………………………………………………………… 51
- Model Derivations in a-b-c: Interconnected Mode……………………………………………………. 51
- Model of the Distribution System……………………………………………………………………………. 51
- Model of Rectifier…………………………………………………………………………………………………. 52
- Model of Inverter………………………………………………………………………………………………….. 54
- Model of the DC-DC Converters……………………………………………………………………………. 55
- Model of the DC Link……………………………………………………………………………………………. 56
- Non-Linear Model of PV……………………………………………………………………………………….. 57
- Dynamic Model of Battery…………………………………………………………………………………….. 58
- Model of the Whole System…………………………………………………………………………………… 59
- Model of the System in q-d-o: Interconnected Mode………………………………………………… 59
- Model of the System in Complex Form: Interconnected Mode………………………………….. 60
- Model of the System in Islanding Mode……………………………………………………………………. 61
- Possibility A…………………………………………………………………………………………………………. 62
- Possibility B………………………………………………………………………………………………………….. 63
- Design Consideration……………………………………………………………………………………………… 64
- Distribution Network…………………………………………………………………………………………….. 64
- Switching Devices ON Resistance…………………………………………………………………………… 65
- Inverter LC Filter………………………………………………………………………………………………….. 65
- DC-DC Converter Inductor Filter……………………………………………………………………………. 66
- Active Power Balance……………………………………………………………………………………………. 67
- Simulation Equations…………………………………………………………………………………………….. 72
- Conclusion…………………………………………………………………………………………………………….. 74
CHAPTER FIVE: RESULTS AND ANALYSIS…………………………………………………………. 75
- Introduction…………………………………………………………………………………………………………… 75
- Steady State Analysis………………………………………………………………………………………………. 75
- UPQC on Distribution Network……………………………………………………………………………… 77
- UPQC with Limitations…………………………………………………………………………………………. 90
- UPQC with PV and Battery Energy Storage System…………………………………………………. 92
- Loss of Supply Compensation……………………………………………………………………………….. 104
- Open Loop Large Signal Simulation………………………………………………………………………. 111
- UPQC without Limitations…………………………………………………………………………………… 112
- Conclusion…………………………………………………………………………………………………………… 117
CHAPTER SIX: CONCLUSION AND RECOMMENDATIONS……………………………… 118
- Summary……………………………………………………………………………………………………………… 118
- ………………………………………………………………………………………………………….. 118
- Recommendations for Further Work……………………………………………………………………. 118
LIST OF TABLES
Table 2.1 Some Power Switching Devices and their Characteristics…………………………………….. 17
Table 2.2 Truth Table of a Boost DC-DC Converter…………………………………………………………… 30
Table 3.1 Data of the Hourly Demand on the 11kV Gaskiya Feeder……………………………………. 41
Table 3.2 Frequency Table for Solar Insolation in Zaria……………………………………………………… 42
Table 4.1 System Parameters………………………………………………………………………………………….. 72
Table 5.1 Parameters of PV System………………………………………………………………………………… 95
LIST OF FIGURES
Figure 1.1 Block Diagram of the Distribution Line Equipped with UPQC and PV/BESS………… 4
Figure 2.1 Pictorial Views of Major Power Quality Problems on Distribution Level………………. 10
Figure 2.2 Schematic of Radial Distribution System Showing Consumers Connected to the Same Point of Common Coupling (PCC)………………………………………………………………………………….. 13
Figure 2.3 Schematic of a Radial Distribution System Showing the UPQC deployed at the premises of one Consumer………………………………………………………………………………………………. 14
Figure 2.4 General Block Diagram Representation of the UPQC System…………………………….. 15
Figure 2.5 A Three Phase Inverter……………………………………………………………………………………. 16
Figure 2.6 Single Phase Inverter Showing Switch Realization…………………………………………….. 18
Figure 2.7 Simple Switching Function……………………………………………………………………………… 19
Figure 2.8 One Phase of a Three-Phase Inverter…………………………………………………………………. 19
Figure 2.9 SPWM Illustration…………………………………………………………………………………………. 22
Figure 2.10 Switching Function in One Switching Period…………………………………………………… 23
Figure 2.11 Fundamental Component of the Average Switching Function…………………………… 24
Figure 2.12 q-d-o Transformation Shown by Trigonometric Relationship……………………………… 27
Figure 2.13 Circuit Configuration of a Boost DC-DC Converter…………………………………………. 30
Figure 2.14 Generation of Duty Ration for DC-DC Converter……………………………………………. 31
Figure 2.15 Classification of Universal Power Quality Conditioner UPQC…………………………… 32
Figure 2.16 Left Shunt Inverter Configuration of the UPQC……………………………………………… 35
Figure 2.17 Right Shunt Inverter Configuration of the UPQC……………………………………………. 35
Figure 3.1 MATLAB M-File Editor Interface…………………………………………………………………… 44
Figure 3.2 Simulink Interface for Simulation…………………………………………………………………….. 44
Figure 3.3 Detailed Configuration of the UPQC with PV/BESS Deployed on a Distribution System…………………………………………………………………………………………………………………………. 46
Figure 3.4 Line Diagram of the UPQC with Details of Switches…………………………………………. 47
Figure 3.5 Islanding Mode: A Possible Implementation……………………………………………………… 48
Figure 3.6 Islanding Mode: A Second Possible Implementation………………………………………….. 49
Figure 4.1 Distribution Network showing the Influence of the UPQC…………………………………. 52
Figure 4.2 Rectifier Connected to the Distribution Network……………………………………………….. 53
Figure 4.3 Inverter Connected to the Distribution Network……………………………………………….. 54
Figure 4.4 Boost DC-DC Converter at the Output of the PV Cells……………………………………… 55
Figure 4.5 Boost DC-DC Converter at the Output of the Battery Bank……………………………….. 56
Figure 4.6 DC-Link Circuits…………………………………………………………………………………………… 57
Figure 4.7 Battery Structure……………………………………………………………………………………………. 58
Figure 4.8 DC-DC Converter showing Details of Interconnections with other parts of the System……………………………………………………………………………………………………………………………………. 66
Figure 5.1 Flow Chart for UPQC with no Limitation…………………………………………………………. 78
Figure 5.2 Voltage Injected by Series Inverter to Regulate Load Voltage…………………………….. 79
Figure 5.3 Series Inverter Current at Different Load Power……………………………………………….. 80
Figure 5.4 Series Inverter Modulation Index with Variation in Supply Voltage at Different Load Power………………………………………………………………………………………………………………………….. 81
Figure 5.5 Supply Current at three Different Apparent Power pf = 0.8………………………………… 82
Figure 5.6 Current Drawn by Shunt Inverter at Different Load Power………………………………… 83
Figure 5.7 Shunt Inverter Modulation Index…………………………………………………………………….. 85
Figure 5.8 Flow Chart for Power Flow Studies…………………………………………………………………. 87
Figure 5.9 Average Power Flow through the System…………………………………………………………. 88
Figure 5.10 Reactive Power Flow through the System……………………………………………………….. 89
Figure 5.11 Critical Value of DC Link Capacitor Voltage…………………………………………………… 91
Figure 5.12 Optimum Voltages at Maximum Power in Different Insolation Level…………………. 94
Figure 5.13 Flow Chart for UPQC with PV and BESS……………………………………………………… 96
Figure 5.14 Voltage Injected by Series Inverter with Variation of Load at Different Supply Voltages (S = 0.85)……………………………………………………………………………………………………….. 97
Figure 5.15 Peal Supply Current with Variation of Load at Different Supply Voltages (S = 0.85)……………………………………………………………………………………………………………………………………. 98
Figure 5.16 Series Converter Modulation Index with Variation of Load at Different Supply Voltages (S = 0.85)……………………………………………………………………………………………………….. 99
Figure 5.17 Shunt Inverter Modulation Index with Variation of Load at Different Supply Voltages (S = 0.85)……………………………………………………………………………………………………………………. 100
Figure 5.18 Battery Current with Variation of Load at Different Supply Voltages (S = 0.85).. 101
Figure 5.19 Battery Current with Variation of Load at Different Supply Voltages (S = 0.45).. 103
Figure 5.20 Battery Current with Variation of Load at Different Supply Voltages (S = 0.07).. 104
Figure 5.21 Battery Current vs Load Real Power in Islanding Mode Possibility A (S = 0.85) 106
Figure 5.22 Battery Current vs Load Real Power in Islanding Mode Possibility A (S = 0.45) 107
Figure 5.23 Battery Current vs Load Real Power in Islanding Mode Possibility A (S = 0.07) 108
Figure 5.24 Battery Current vs Load Real Power in Islanding Mode Possibility B (S = 0.85)… 109
Figure 5.25 Battery Current vs Load Real Power in Islanding Mode Possibility B (S = 0.45)… 110
Figure 5.26 Battery Current vs Load Real Power in Islanding Mode Possibility B (S = 0.07).. 111
Figure 5.27 Simulation Results for Voltage Sag Condition………………………………………………. 112
Figure 5.28 Generation of SPWM Pulses for Converter Switches (Voltage Sag Condition)…… 113
Figure 5.29 Simulation Results for Normal Operation………………………………………………………. 114
Figure 5.30 Generation of SPWM (Normal Operation)…………………………………………………….. 115
Figure 5.31 Simulation Results for Voltage Swell Condition……………………………………………. 116
Figure 5.32 Generation of SPWM (Voltage Swell)…………………………………………………………… 117
LIST OF APPENDICES
APPENDIX A: SYSTEM MODEL IN ABC REFERENCE FRAME………………………………. 124
APPENDIX B: MODEL OF SYSTEM IN QDO REFERENCE FRAME………………………… 136
APPENDIX C: MODEL EQUATIONS IN COMPLEX FORM……………………………………… 144
APPENDIX D: DC-DC CONVERTER PARAMETER DETERMINATION……………………… 147
APPENDIX E: NASA HOURLY SOLAR INSOLATION IN ZARIA……………………………. 151
APPENDIX F: PROGRAM LISTING………………………………………………………………………….. 152
APPENDIX G: SIMULINK MODEL FOR SIMULATION STUDIES……………………………. 159
APPENDIX H: SCANNED COPY OF PHCN ZARIA HOURLY DEMAND ON 11kV
GASKIYA FEEDER………………………………………………………………………………………………….. 160
ABBREVIATIONS AND SYMBOLS
POWER CONVENTION USED
Real Power = +P (Power Supplied)
Real Power = -P (Real Power Absorbed) Reactive Power = +Q (Reactive Power Absorbed) Reactive Power = -Q (Reactive Power Supplied)
CHAPTER ONE INTRODUCTION
IEEE standard 1159 defines power quality as the concept of powering and grounding sensitive equipment in a manner that is suitable for the operation of the equipment (ieeexplore.ieee.org). This definition derives from the understanding that the majority of the power quality issues arise as a result of poor and/or improper grounding of equipment.
In general, the term power quality can be defined as the physical characteristics of the electrical supply provided under the normal operating conditions that does not disturb or disrupt the user processes (Khadkikar, 2008). Any deviations from these physical characteristics are termed power quality events. Power Quality has become an issue of serious concern at the electric power distribution level. According to Khadikar (2008), this is largely due to:
- The changing nature of loads on the distribution networks
- The increased awareness of consumers of their rights to low-cost electricity of high reliability and constancy in
- The growing interest in the utilization of renewable energy resources for electric power generation.
Most modern electrical appliances for example industrial drives, electronic ballast fluorescent lights, switching power supplies and so forth are becoming increasingly power electronics-based.
Whereas these loads possess certain advantages like, enhanced controllability, high power density, and so forth, they also bring with them disadvantages that were not there in the early power distribution systems.
Some of these disadvantages include increased sensitivity to supply voltage, harmonics, and reactive power requirements. These inherent characteristics of power electronic-based loads have helped to raise awareness of power quality issues.
With the deregulation of the electric power sector in most parts of the world, there is a growing interest in the utilization of renewable energy resources (mostly solar and wind) for electric power generation. Individuals and companies can now harness available renewable energy resources in their localities to complement utility supply thereby reducing the long-term cost of electricity consumption and indeed in some countries sell excess generated energy to the utility.
The integration of renewable energies and their accommodation in the existing electricity networks is often a complex issue and is making the electric power distribution networks more susceptible to power quality problems (Khadkikar, 2008).
Power quality concerns are not only on the side of the consumers alone. There are power quality issues on the side of the utilities too. The utilities are concerned for instance about the current total harmonic distortion of the consumer’s load.
Current trends in mitigating some of the major power quality problems are towards multitasking devices which are capable of simultaneously mitigating several power quality problems on the networks (Khadem et al., 2010). Of this category, the Unified Power Quality Conditioner (UPQC) is one of the most versatile.
The UPQC can be used to mitigate simultaneously a vast majority of the power quality problems both at the utility side and at the consumer end (Khadkikar, 2008; Davari et al., 2009; Khadem et al., 2010).
The UPQC, however, cannot supply large active power to customers steadily due to the limitation of energy storage (Davari et al., 2009). The UPQC cannot, therefore, compensate for voltage interruptions and loss of supply which is necessary for systems that experience a long duration of interruption and loss of supply.
The inability of the UPQC to supply large active power for a long time as noted is a result of the lack of a constant source of dc supply at the dc link. Efforts have been made by some researchers to solve this problem. Such efforts, however, perhaps due to the experiences of these researchers with their respective power utilities, have been in two major directions:
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