ABSTRACT
This work aimed at designing and implementation of Shunt Active Power Filter (SAPF) for power quality improvement through harmonic reduction. The current harmonics are being caused by nonlinear characteristic of power electronics based equipments which increase power losses and in turn reduce power quality. This work employed a three phase three wire shunt active power filter implemented by simulation in MATLAB/Simulink for harmonic reduction. Synchronous Reference Frame (SRF) was used as a control strategy and for reference harmonic current generation and Space Vector Pulse Width Modulation (SVPWM) was adopted as current controller for switching signal generation of Voltage Source Inverter (VSI). With RL load under balanced voltage condition, the developed SAPF-SVPWM achieved a reduction of Total Harmonic Distortion (THD) of 0.91% as compared to 0.92% with Fuzzy Logic Pulse Width Modulation. In addition, the developed SAPF- SVPWM model was compared with SAPF without compensation using RL load under unbalanced voltage and the result shows that the developed SVPWM achieved reduction in THD from 26.68% to 1.74 % after and before compensation. All the results obtained are within IEEE 519 harmonics standard (i.e. THD less than 5%) with nonlinear load under balanced and unbalanced voltage. The result also shows an improvement of 1.087% with RL load under balanced voltage. This confirmed the effectiveness of the SAPF in harmonics reduction.
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TABLE OF CONTENTS
TITLE PAGE DECLARATION i CERTIFICATION ii DEDICATION iii ACKNOWLEDGEMENT iv ABBREVIATIONS v ABSTRACT vi TABLE OF CONTENTS vii LIST OF FIGURES ix LIST OF TABLES xiv LIST OF APPENDICES xiv LIST OF SYMBOLS xv CHAPTER ONE: INTRODUCTION 1.1 Background 1 1.2 Significance of Research 3 1.3 Statement of Problem 3 1.4 Aim and Objectives 4 CHAPTER TWO: LITERATURE REVIEW 2.1 Introduction 6 2.2 Review of Fundamental Concepts 6
2.2.1 Power Quality 6
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2.2.2 Waveform Distortion 11
2.2.3 Filters 15
2.2.4 Shunt Active Power Filter Parameters Design Approach 21
2.2.5 Harmonics Current Extraction Strategies 24
2.2.6 Control Strategies in SAPF 25
2.3 Review of Similar Works 34
CHAPTER THREE: METHODOLOGY
3.1 Introduction 41
3.2 Methodology 41
3.3 Selection of Shunt Active Power Filter Design Parameters 42
3.3.1 Selection of DC Reference Voltage 43
3.3.2 Selection of Coupling Inductor
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3.3.3 Selection of DC Side Capacitor 43
3.4 Modeling of Shunt Active Power Filter in d-q 44
3.4.1 Control in Synchronous Frame Reference (d-q) 47
3.4.2 DC Bus Control Using PI 48
3.5 Design of Space Vector Pulse Width Modulation (SVPWM) 50
3.5.1 Determination of d V , q V , ref V and Angle 50
3.5.2 Determination of Time Duration 0 T , 1 T and 2 T
52
3.5.3 Determination of Switching Time of Each Transistor 55
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CHAPTER FOUR: RESULTS AND DISCUSSION 4.1 Introduction 59 4.2 Output Waveform of SVPWM with SAPF 59 4.3 SAPF with Balanced Voltage 60 4.3.1 Waveform of RL Load before Compensation 60 4.3.2 Waveform of RL Load after Compensation with SVPWM 61 4.3.3 Result of FFT Analysis of RL Load before Compensation 62 4.3.4 Result of FFT Analysis of RL Load after Compensation with SVPWM 62 4.3.5 Waveform of RC Load before Compensation 64 4.3.6 Waveform of RC Load after Compensation with SVPWM 64 4.3.7 Result of FFT Analysis of RC Load before Compensation 66 4.3.8 Result of FFT Analysis of RC Load after Compensation with SVPWM 66 4.4 SAPF with Unbalanced Voltage 68 4.4.1 Waveform of RL load before compensation 68 4.4.2 Waveform of RL Load after Compensation with SVPWM 69 4.4.3 Result of FFT Analysis of RL Load before Compensation 70 4.4.4 Result of FFT Analysis of RL Load after Compensation with SVPWM 70 4.4.5 Waveform of RC Load before Compensation 72 4.4.6 Waveform of RC Load after Compensation with SVPWM 72 4.4.7 Result of FFT Analysis of RC Load before Compensation 74 4.4.8 Result of FFT Analysis of RC Load after Compensation with SVPWM 74
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CHAPTER FIVE: CONCLUSION AND RECOMMENDATION 5.1 Conclusion 76 5.2 Limitation 76 5.3 Significant Contributions 76 5.4 Recommendations 77 REFERENCES 78
CHAPTER ONE
INTRODUCTION 1.1 Background Power quality is greatly influenced by nonlinear loads such as power electronics equipment, electrical drives, compact fluorescent lamp, oven among others which inject harmonics into distribution system (Abhijit & Kompelli, 2016; Chennia & Benchouia, 2011; Soomro et al., 2015: Umar, 2017). Therefore, as electric power is generated, distributed and utilized, voltage and current waveforms distortions are produced. These distortions are known as harmonics, and thereby cause changes in the electrical nature of the current and voltage of the power supply. Harmonics degrade power quality by increasing Total Harmonic Distortion (THD) and reactive power consumption lead to poor power factor, voltage flicker, bad voltage regulation, voltage sags and swells (Suresh & Anup, 2011; Suleiman et al., 2017; Akash et al., 2016). It also leads to significant economic losses due to fact that some electrical equipments are sensitive to power quality problem (Suleiman et al., 2017).
Passive power filter is a traditional restraint harmonic mitigation method; because it is limited in its ability to reduce harmonic current in the distribution system. Passive power filter also suffers many drawbacks such as heavy weight and bulky sizes, series and parallel resonance with system impedance (Abhijit & Kompelli, 2016; Chennia & Benchouia, 2011; Sindhu et al., 2015; Suleiman et al., 2017; Varaprasad & Siva, 2014; Naresh & Prabhat, 2012). Passive filter (combination of capacitor and inductor) were used to mitigate the Power Quality (PQ) problems. This approach was extensively used in High Voltage Direct Current transmission (HVDC) for
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filtering the harmonics on AC and DC sides. However, this approach is not suitable at the distribution level as passive filter can only correct specific load condition (Soomro et al., 2015) In recent times Active Power Filters (APF) were introduced and accepted as one of the most common compensation method. APF are switch mode power electronics converters that injects harmonics current in equal and opposite phase at point of common coupling (PCC) so that utility need to supply only the distortion free currents (Saravanan & Balachrishnan, 2014; Sindhu et al., 2015; Akash et al., 2016; Niklesh & Sandeep, 2017). There are three types of active power filter (APF) which are shunt, series and hybrid which is the combination of active and passive filter (Soomro et al., 2015). The effectiveness of shunt active power filter (SAPF) depends on the methods used to obtain the reference current, current controller, power inverter topology and DC-link voltage (Venkata et al., 2014; Chennia & Benchouia, 2014; Akash & Mukund, 2015; Ali et al., 2015; Suleiman et al., 2017).
There are many control scheme for reference current generation and harmonics extraction techniques that have been used for improving the steady state and dynamic performance of APF, such as synchronous reference frame (d-q-o) theory, instantaneous real-reactive power (p-q) theory, modified instantaneous (p-q) theory, flux-based controller, notch filter and Artificial Neural Network (ANN) techniques (Zahira & Peer, 2011; Narsesh & Prabhat, 2012; Chelli et al., 2015). Instantaneous power theory is widely used in different research work; this technique provide good results under different voltage source conditions but present some drawbacks such as much calculation which necessitates complex mathematical transformation and difficult implementation in practice (Chennia & Benchouia, 2011; Chelli et al., 2015). Synchronous Reference Frame (SRF) theory is commonly used in three phase system for reference current
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generation from the load current and this due because of its simplicity, easy implementation, accuracy and dynamics response (Abhijit & Kompelli, 2016). Similarly, various current control methods such as hysteresis, triangular wave control, dead beat control, Space vector pulse width modulation among others have been presented in the literature (Naresh & Prabhat, 2012). Space Vector Pulse Width Modulation (SVPWM) is a more sophisticated, advanced, computation intensive technique for generating sine wave that provides a higher voltage with lower total harmonic distortion and is one of the best among all the pulse width modulation techniques because of advantages of low switching loss, wide range of modulation index and less harmonics distortion. SVPWM technique also utilizes the DC bus voltage more efficiently when compared with the other techniques (Phuong 2012). 1.2 Significance of Research The significance of this research is the development of a shunt active power filter based SVPWM techniques for switching pulse generation to mitigate the load current harmonic cause by non linear loads under balanced and unbalanced input voltage condition. 1.3 Problem Statement Harmonic generation is undesirable outcome of industrial electronic devices and non-linear loads. The harmonics in the system induce several undesirable issues; such as increased heating in transformers, low power factor, and voltage drop across the network impedance (Akash et al., 2016).
Shunt active power filter has proven to be the best for both harmonics current and reactive-power compensation. Shunt active power line conditioner is most commonly used among the topologies of active power filter. The effectiveness of shunt active power filter depends on the methods used
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to obtain the reference current. Several methods of harmonics current identification and extraction techniques such as synchronous reference frame (d-q), instantaneous real-reactive power (p-q) and synchronous detection method have been used (Chelli, et al., 2015). SRF technique is chosen because of simplicity and easy implementation. Generation of compensation current by SAPF depends also on switching strategy used. The hysteresis, SPWM and artificial intelligent current control techniques are generally used by many researchers (Naresh & Prabhat, 2012). The drawback of fuzzy logic is the over dependent on expert rules and large number of membership function for it effective performance and this drawbacks make fuzzy logic difficult or almost impossible to achieve. In this work, SVPWM is used to improve the performance of SAPF because of the advantages of low switching loss, wide range of modulation index and less harmonics distortion. 1.4 Aim and Objectives The aim of the research is to design shunt active power filter for harmonic reduction using synchronous reference frame with space vector pulse width modulation. The objectives of the research are as follows:
1. Development of Shunt Active Filter (SAPF) parameters. Adopted from the work of Suleiman et al., (2017).
2. Development of a control strategy model for Shunt Active Power Filter (SAPF) for the extraction of reference harmonic current.
3. Implementation of a current controller technique for switching pulse generation for voltage source inverter using MATLAB/SIMULINK.
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