ABSTRACT
This research presents effect of harmonic generated by variable frequency drives (VFD).In the past, electrical power system equipment and devices were designed to produce nearly sinusoidal voltage and current waveforms. However, nowadays, with much interest and wide spreads of power electronics equipment, for industrials, commercials and residential consumers, these equipment and other electronics devices are no longer operate with an ideal current and voltage waveform, because of the non-linearity of the equipment in nature, with this trend, a Recurrent Neural Network Algorithms with active power filter (SAPF) is implemented for harmonics mitigation on Variable Frequency Drive,because of its simplicity and accuracy among the artificial intelligent family controllers. Simulations were carried out using MATLAB/SIMULINK and SIMPOWER tool box environment to analyze the harmonics distortion. The total harmonics distortions (THD %) of current was calculated using relevant equations. The simulation results are in accordance with the recommended IEEE 519-2014 harmonic standard limits. However, the distortion harmonics in feeder supplying the VFD and soft starter equipment which led to frequent replacement of the drive or out of services also led the Distribution Control System Failure (DCS). 47.17% before and after the application of filter was reduced to 1.80%.
TABLE OF CONTENTS
TITLE PAGE i
DECLARATION ii
CERTIFICATION iii
DEDICATION iv
ACKNOWLEDGEMENTS v
ABSTRACT vi
TABLE OF CONTENTS xii
LIST OF TABLE viii
LIST OF FIGURES ix
LIST OF ABBREVIATIONS xi
CHAPTER ONE: INTRODUCTION
1.1 Background of the Study 1
1.2 Problem statement 5
1.3 Aim and objectives Of the study 6
1.4 Significance of the Research 6
1.5Dissertation organization 6
CHAPTER TWO: LITERATURE REVIEW
2.1Introduction 8
2.2 Review Of Fundamental Concepts 8
2.2.1 Power Quality 8
2.2.2 Frequency Variation 9
2.2.3Harmonics 13
2.2.4 Causes of Harmonics 16
2.2.5 Effects of Harmonics 16
2.2.6Load Model 17
2.2.7Non-Linear Loads 18
2.2.8Fourier Series Analysis 18
2.2.9 Harmonics Indices 19
2.2.10 Total Harmonic Distortion 19
2.2.11 Total Demand Distortion 20
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2.2.12 Imposed IEEE Harmonics Standard Limit (120V-69kV) 20
2.2.4 Power Filter 21
2.2.5 Artificial Neural Network 27
2.2.6 Neural Network Architecture 27
2.2.7 ANN Topology 27
2.3 Review of Similar Work 30
2.4 Summary of Literature Review 34
CHAPTER THREE: MATERIALS AND METHODS
3.1Introduction 35
3.2 Data Collection 35
3.3 Artificial Neural Network (ANN) operation 35
3.4 Mathematical modeling of Artificial Neural Network 47
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1Introduction 50
4.2 Simulation of the Complete Model of Shunt Active Power Filter 51
4.3 Simulation Results 51
4.4 Discussion of Results 53
CHAPTER FIVE: CONCLUSIONAND RECOMMENDATIONS
5.1Summary 59
5.2Conclusion 69
5.3 Recommendations60
REFERENCES 61
Appendix A Measurment of line parametres 65
Appendix B Single phase VFD Electronic Circuit Diagram 66
Appendix C System network Configuration 67
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CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Before the advent of power electronics most of electrical equipment were operated on nearly sinusoidal current and voltage waveforms. Nowadays, with the proliferation of modern power electronics devices such as adjustable speed drives, uninterrupted power supply, switch mode power supplies, fluorescent lamps, Television set, fax machines, photocopy machines, personal computers, printers and many more non-linear devices used in industrial, commercial and residential applications, supply current and voltage waveforms are no longer sinusoidal. The non-linearity of the devices make them draw and inject harmonics current to the supply system which affects the system performance and equipment by increasing power distribution system losses (Channi and Sohal, 2012). These harmonics injection leads to power quality degradation of the distribution system causing adverse effects such as overheating low tention (LT) conductors, power losses, interference to nearby communication facilities, electromagnetic induction (EMI) and total failure of equipment, etc. Harmonics produced by non-linear loads in power system draw current in abruptly pulses than in a smooth manner (Channi and Sohal, 2012). For the past decades and up till now, power quality issues have been a worry to utilities, consumers researchers and power quality system engineers (Channi and Sohal, 2012).
Consequently, efforts have been made in order to provide remedy to these harmonics problems in order to comply with the relevant provision of the IEEE 519-2014 standard on the minimum Total harmonics distortion (THD) of current and voltage within the Power Distribution Network. Various solutions to overcome harmonics problems as earlier maintained include use of traditional passive filters, active filters, magnetic wave shaping and
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network reconfiguration, etc (Fuchs and Masoum, 2008), (Emadi et al., 2004), (Ranjbar et al., 2009). The most popular devices among the harmonic cancellations techniques are passive and active filters. Traditionally, passive filters had been firstly introduced for the harmonic current compensation, but due to its drawbacks, such as series and parallel resonances, tuning, large in size, weight and cancellation of some selective harmonics due to the non-linear loads, that is why its operation becomes very limited nowadays. With the introduction and advancement of superior filters to the passive filters in our today‟s markets, active power filters are now the dynamic and viable solution for simultaneously compensation harmonics current and reactive power drawn by non-linear loads. In addition, shunt active filters have the advantages of power factor correction, cancellation of harmonics induced in the neutral conductor of three-phase four-wire system, and balancing of voltage levels in three-phase three-wire system. However, in Kiln unit of Dangote Cement Plant Obajana with different electromechanical equipment, such as Transformers, cyclo converter, Variable frequency drives (VFD) and soft starter which is the heart of cement production is to be use as case study. Low Voltage Distribution (LV) Line diagram for the Research work (Kiln substation of Dangote Cement Plant) is presented in figure 1.1 which feed power to various electric motor, from 11KVA substation (S/S) to 415Vol and 240Volt.
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M
In c o m in g Outgoing
11KV
11/ 0.415KV
Transformer
Bus Bar
a S b S c S
d S
D O L
C C R
S o f t s ta r t e r VFD
A d min
Feeder a
Feeder b
Feeder c
Figure 1.1 Line Diagram of the system network (Dangote kiln unit)
Parameters in the diagram are as follows
a) S/S (Substation)
b) CCR (Central control Room)
c) Sa, Sb, Sc & Sd (Molded case circuit breaker (MCCB)
d) M (Electrical motor)
e) DOL (Direct online starter)
f) VFD (Variable Frequency Drive
It was observed that among the feeders (A B C), feeder B frequently tripped and result in
constant replacement of the drive as a result of the harmonics distortion present on the feeder.
(Variable Frequency Drive & soft starter drive) which result in Distribution Control System
(DCS) failure.
However, the need to mitigate the harmonic effects with the shunt active power filter(SAPF)
based on application of RNN become important.
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Kiln is a furnace that heats up powdered material (lime stone, clay, and laterite) at 1600C0 that flow through it to produce clinker which would be mill in to cement. (Dangote kiln unit productionManual) Kiln substation is the substation that distribute power to various electrical motors that caused the kiln to rotate at a preset frequency, such as kiln main drive (900KW, 900A, 997rpm, 690V pf 0.86) kiln induced drafted fan (IDF), Electrostatic precipitator (EP) etc, all these drives are variable frequency drives (VFD) controled by central control room. (Dangote kiln unitproduction Manual) Each has a control feeder that contained VFD module that generate current harmonics due to the nonlinear load that make up the module, also the feeder is incorporated with communication link Protocol Field Bus called (profibus) that provide feedback information about the status of the motor in the field to the central control room. However, the first step of a pulse width modulation (PWM) VFD (the rectifier) generates distortion of the AC line as the rectifier charges a capacitor bank called the DC bus. Current is drawn from the AC supply line only when the rectified voltage exceeds the voltage level to which the capacitor is charged. Severe harmonic distortion can have several detrimental effects as earlier stated (A Bagini 2008). VFD controls the speed of an AC motor by varying the frequency supplied to the motor, it also regulates the output voltage in proportion to the output frequency to provide a relatively constant ratio of voltage to frequency V/F as required by the characteristic of the Ac motor to produce adequate torque. The output voltage is turned on and off at high frequency, with duration of on-time, or width of the pulse, controlled to approximate a sinusoidal waveform. In addition, the electronic circuit diagram is at appendix B. Also the network configuration at pcc is shown at appendix C The figure 1.2 shows the power circuit with the bridge inverter and ANN controller.
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Figure 1.2: Feeder Network Schematic Diagram at PCC. (Dangote kiln unit low voltage power circuit) 1.2 Problem Statement Harmonics studies in power system networks has been one of the disturbing issues militating utilities, industries, commercial and local consumers due to the wide spread of power electronic devices that drawn non-linear loads. As of now, harmonics cannot be completely eliminated but can be reduced to acceptable level, as imposed by the IEEE 519-2014 standard on minimum current and voltage THD level. A lot of researches on how to remedy effects of harmonics have been ongoing by researchers. It is observed that among the feeders (A B C), in figure 1.1 feeder B frequently tripped as a result of the harmonics distortion generated by VFD module present on the feeder and replacement of the drive, it also results in the failure of Distribution Control System (DCS). This caused total production stoppage.
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However, the need to mitigate the presence of this harmonic with the SAPF and application of Recurrent Neural Network (RANN) based become important. 1.3 Aim and Objectives The aim of this research is the modeling and simulation of single-phase shunt active power filter using recurrent neural network for harmonics reduction in Variable Frequency Drive. The objectives of this research work are summaries as follows:
1. Data collection for the power quality problems at Kiln unit of Dangote Cement Plant Obajana.
2. To model the line parameters of non-linear load of VFD module at kiln unit using MATLAB/SIMULINK software environment.
3. To model and simulate single phase shunt active power filter using Artificial Neural Network (ANN) controller by MATLAB/SIMULINK Software environment.
4. To compare the simulation results with imposed harmonic standard limit of IEEE 519-2014.
1.4 Significance of the research A lots of research works have been done on improving the power qulity both utility and consumer on mitigation of harmonics. Various control strategies were employed. However, the significance of this research study are as follows:
I. Development of Recurrent Neural Network for harmonic detection and extraction
II. Development of Analytical table for harmonic distortion using FFT
III. Selection of Alpha perfectly march for any value and optimal result was obtained.
1.5 Dissertation Organization
The organization of this research work is as follows: Chapter one presents the general background of the study. Chapter two, reviewed the fundamental concepts of this work, and detailed review of similar related works were presented. In Chapter three, the details
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explanation of methods and materials used were presented. Chapter four outlined the simulation results and discussion. Finally, Chapter five is the conclusions and recommendations with the references quoted in this work as well as appendix A, B and C used in SIMULINK simulation.
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