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
1.1 Overview………………………………………………………………………………………1
1.2 Significance of the Study…………………………………………………………………….5
1.3 Aims and Objectives of the Study…………………………………………………………..6
1.4 Limitation of the Study ………………………………………………………………………6
1.5 Thesis Outline…………………………………………………………………………………7
CHAPTER TWO: LITERATURE REIVIEW……………………………………………………………….8
2.1 Introduction…………………………………………………………………………………..8
2.2 Review of Fundamental Concepts……………………………………………………………8
2.2.1 Definition of Major Power Quality Events………………………………………………….8
2.2.2 Some Effects of Poor Power Quality………………………………………………………10
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2.2.3 Electricity Distribution Network…………………………………………………………….11
2.2.4 The Unified Power Quality Conditioner (UPQC)…………………………………………14
2.2.5 DC-DC Converters………………………………………………………………………….29
2.3 Review of Similar Works……………………………………………………………………32
2.3.1 Classification Based on Supply System……………………………………………………33
2.3.2 Classification Based on Configuration…………………………………………………….34
2.3.3 UPQC for Grid Integration of Renewable Energy Sources………………………………..35
2.4 Statement of Problem..……………………………………………………………………..38
2.5 Conclusion…………………………………………………………………………………..38
CHAPTER THREE: MATERIALS AND METHODS………………………………………39
3.1 Introduction…………………………………………………………………………………39
3.2 PHCN Data for 11kV Gaskiya Feeder Zaria……………………………………………..39
3.3 NASA Solar Insolation Data for Zaria……………………………………………………42
3.4 MATLAB/Simulink…………………………………………………………………………42
3.5 Methodology…………………………………………………………………………………45
3.5.1 Modes of Operation………………………………………………………………………..45
3.6 Conclusion…………………………………………………………………………………..49
CHAPTER FOUR: MODEL DERIVATIONS AND DESIGN CONSIDERATIONS…….51
4.1 Introduction…………………………………………………………………………………51
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4.2 Model Derivations in a-b-c: Interconnected Mode……………………………………….51
4.2.1 Model of the Distribution System………………………………………………………….51
4.2.2 Model of Rectifier………………………………………………………………………….52
4.2.3 Model of Inverter…………………………………………………………………………..54
4.2.4 Model of the DC-DC Converters………………………………………………………….55
4.2.5 Model of the DC Link………………………………………………………………………56
4.2.6 Non-Linear Model of PV…………………………………………………………………..57
4.2.7 Dynamic Model of Battery…………………………………………………………………58
4.2.8 Model of the Whole System……………………………………………………………….59
4.3 Model of the System in q-d-o: Interconnected Mode…………………………………….59
4.4 Model of the System in Complex Form: Interconnected Mode………………………….60
4.5 Model of the System in Islanding Mode……………………………………………………61
4.5.1 Possibility A………………………………………………………………………………..62
4.5.2 Possibility B………………………………………………………………………………..63
4.6 Design Consideration……………………………………………………………………….64
4.6.1 Distribution Network………………………………………………………………………64
4.6.2 Switching Devices ON Resistance…………………………………………………………65
4.6.3 Inverter LC Filter…………………………………………………………………………..65
4.6.4 DC-DC Converter Inductor Filter………………………………………………………….66
4.6.5 Active Power Balance………………………………………………………………………67
4.6.6 Simulation Equations………………………………………………………………………72
4.7 Conclusion…………………………………………………………………………………..74
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CHAPTER FIVE: RESULTS AND ANALYSIS……………………………………………..75
5.1 Introduction…………………………………………………………………………………75
5.2 Steady State Analysis……………………………………………………………………….75
5.2.1 UPQC on Distribution Network…….………………………………………………………77
5.2.2 UPQC with Limitations……………………………………………………………………90
5.2.3 UPQC with PV and Battery Energy Storage System………………………………………92
5.2.4 Loss of Supply Compensation……………………………………………………………104
5.3 Open Loop Large Signal Simulation……………………………………………………..111
5.3.1 UPQC without Limitations……………………………………………………………….112
5.4 Conclusion …………………………………………………………………………………117
CHAPTER SIX: CONCLUSION AND RECOMMENDATIONS. ……………………….118
6.1 Summary.……………………………………………………………………………………118
6.2 Conclusion.……………..…………………………………………………………………..118
6.3 Recommendations for Further Work ……………………………………………………118
CHAPTER ONE
INTRODUCTION
1.1 Overview
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 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 normal operating condition that do 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:
(i) The changing nature of loads on the distribution networks
(ii) The increased awareness of consumers of their rights to low cost electricity of high reliability and constancy in supply.
(iii) 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 which were not there in the early
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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 compliment utility supply thereby reducing 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 current total harmonic distortion of the consumers 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
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voltage interruptions and loss of supply which is necessary for systems that experience 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 as 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:
(i) Some have used PV array directly in the dc link (Marcelo et al., 2006; Khadem et al., 2010). However, such systems have the disadvantage that interruption/loss of supply compensation is only possible when there is sufficient solar insolation (Khadem et al., 2010). Also ensuring power balance in such a system involves the implementation of complex control schemes (due to the non-deterministic nature of solar resource). Moreover, the solar PV array may not be operated at Maximum Power Point (MPP) leading to wastages in several aspects.
(ii) Others have used the PV array with some form of energy storage system thereby making possible Maximum Power Point Tracking (MPPT) (Davari et al., 2009) but the power flow is unidirectional that is; the PV is used to charge the Battery Energy Storage System (BESS) and then the BESS supplies system needs with the disadvantage that excessive solar insolation is wasted.
The current effort has developed a system configuration which in addition to all the power quality compensation capabilities of the UPQC, possesses:
(i) The capability of real time collaboration between the PV cell and energy system in addressing system demands thereby ensuring efficient utilization of available renewable energy resources.
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(ii) The capability of ameliorating the effects of loss of supply at whatever period when they
occur.
This work evaluates through a thorough analysis and simulation studies, the feasibility and
performance of a combination of the UPQC and photovoltaic (PV)/Battery Energy Storage
System (BESS) when installed on a radial distribution network. The BESS is connected to the
system via a bi-directional dc-dc converter to enable bi-directional flow of power. The developed
configuration ameliorates the effect of interruptions and loss of supply without compromising
other functions of the UPQC. Also, it also made it possible to store excess solar energy when it is
available while simultaneously possessing the capability of augmenting the output power of the
PV panels at periods of low solar energy or high load demand. This has brought about the
efficient utilization of available alternative source of energy. The block diagram is shown in
Figure 1.1
Load
UPQC
L
Filter
LC
Filter
PV/BESS
3 Phase
Source
Voltage
Series
Transformer
Figure 1.1 Block Diagram of the Distribution Line Equipped with UPQC and PV/BESS.
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1.2 Significance of the Study
There is in most developing countries of the world a concerted effort at closing the gap between electrical power generation and its demand. As an immediate solution to the problem, gas turbine (GT) power plants are being set up in most places. The preference for GT stations is because of their relatively lower gestation period. As this generating stations come on stream, ailing industries are resurrected. These industries draw a lot of reactive power which makes the desired effect of the efforts of governments not to be evident to the ordinary consumer of electricity. Reactive power even though not used for any useful work, flows in the system. Moreover, because of the consumer nature of most developing economies, there is an increasing penetration of power electronics based load on the distribution network. These loads are non-linear in nature, hence generating a lot of harmonics which in a broad sense add to the reactive power demand in a network. Therefore, in order for the result of the efforts of government at increasing generation to become evident for all, there is a need not only for additional capacity in transmission but also for some sought of load conditioning. The proposed system offers such functionalities.
One effect of power quality events is economic losses as a result of equipment down time, damaged production processes and so forth. To forestall such losses it is important that sensitive load on the distribution network be protected from voltage disturbance.
The electricity supply sector in most countries of the world including Nigeria has been deregulated. It is therefore important to give consumers the flexibility in choosing their generation source and the amount of energy they need from a particular supplier and in fact offer everyone interested in generation of electricity the opportunity to participate. The proposed system can be extended such that individual consumers can install their own PV generation for their use and with the right environment hopefully to sell to the utilities.
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1.3 Aim and Objectives of the Study
The aim of this work is to carry out the feasibility and performance analysis of the combination of the UPQC and PV/BESS on a realistic distribution network.
The research objectives are stated as follows:
(i) To develop a general mathematical model of the developed system configuration.
(ii) To carry out an in-depth analytical study of the system so as to determine the behavior of the system under different operating conditions.
(iii) To realize a system which is capable of efficiently compensating for long duration interruption and load reactive power requirements.
(iv) To realize a system with the capacity to ameliorate the effects of loss of supply.
1.4 Limitation of the Study
The following limitations where encountered in this work
i. Whereas, data for the chosen feeder was obtained, experimental validation was not completely possible since the UPQC is not installed on this feeder or any other network in the entire country.
ii. NASA solar data were used rather than NIMET. It doesn’t appear as though it would introduce a significant error. However, with the absence of usable local solar data, the extent of deviation could not be determined.
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1.5 Thesis Outline
The remaining part of this thesis is organized as follows:
CHAPTER TWO presents a detailed literature review for the research. The review is divided into two viz. review of fundamental concepts and review of similar works. The necessity of the present work is highlighted within the context of reviewed works.
CHAPTER THREE presents the materials used and method adopted. Data and software tools have been used for the work. A detailed circuit configuration is given and mode switching operations (i.e. between interconnected and islanding modes) briefly discussed
CHAPTER FOUR shows the derivation of the system model in the two mode of operation. The model is derived in the physical reference frame, transformed to the q-d reference frame and then the complex form is derived. The necessity of this process is explained in the chapter. Also, certain design considerations necessary for the determination of the parameters of the system are presented.
CHAPTER FIVE shows the result of the steady state analysis. Various plots of different analysis carried out are presented and discussed. A simulation study of certain aspects of the system is also included.
CHAPTER SIX reports the important conclusions of the thesis work. Recommendations are also made for future work. At the end of the thesis, cited references and appendices are provided.
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