ABSTRACT
This thesis presents the analysis of 3, 4 and 5- level diode clamped converter that is centered on the space-vector pulse width modulation technique which is considered as the most efficient and easily applied modulation technique in comparison with another controlled modulation technique which is based on the multi-carriers/sinusoidal pulse-width modulation with an injected third harmonic signal. It also focuses on the step by step development of MATLAB/SIMULINK modeling of the space vector pulse-width modulation and the multi-carriers/sinusoidal pulse-width modulation with an injected third harmonic based on the 3, 4 and 5-level inverter waveforms at 0.4, 0.6 and 0.8 modulation indices and their corresponding spectral results. The MATLAB simulation results obtained from the direct application of 3-level Voltage Source Inverter VSI on 10HP, 400 Volts, 50Hz induction machine drive are also presented in sub-chapter 3.4. In line with the above analysis is a small scale laboratory designed-experimental work that was constructed to verify the simulation results obtained from the SIMPLORER simulations for the un-modulated three-level diode clamped converter. This laboratory designed-experimental work is presented in the preceding chapter five.
TABLE OF CONTENTS
Cover page ………………………………………………………………………………I
Approval page ……………………………………………..……………………………II
Certification page ………………………………………….………………….…………IIII
Title Page ………………………………………………………………………..IV
Dedication ……………………………………………….…………………………V
Acknowledgement ………………………………………………………………………VI
Abstract ……………………………………………………………………….VII
List of Figures ………………………………………………………………………..VIII
List of Tables ………………………………………………. …………………………XI
List of Symbols …………………………………….………………………………….XII
List of Abbreviations …………………………………………………………………….XIII
Table of Contents ………………………………………………………………………..XV
Chapter One: Introduction
1.0 Background of the study ……………………………………………….……………1
1.1 Statement of problem ………………….………..………………………..……………1
1.2 Objectives / Purpose of the study ………..…………………………..………………2
1.3 Significance of the study……………….…………. ……………………….…………2
1.4 Scope of the study …………………….……………………………………………3
1.5 Limitations of the study ………………….………………………..…………………..3
1.6 Study methodology ………………………………………………………………………….4
Chapter Two: Literature Review of SVPWM for 3, 4 and 5 Level
DIODE CLAMPED CONVERTER
2.1 Principles of operations of a multilevel Diode Clamped Converter ……………….5
2.2 Principles of Multi-carrier pulse width modulation Strategy …………………………11
2.3 Space Vector representation of 3, 4 and 5 level Diode Clamped Converter …..…….17
2.4 Optimized Space Vector Switching Sequences for the 3, 4 and 5 levels DCC.……..25
2.5 Duty-Cycle and Switching Time Determination ……………………………………..32
Chapter Three: Simulink Modelling OF 3, 4 and 5 level
DIODE CLAMPED CONVERTER and Application
3.1 Model Simulation of 3-level DCC at modulation indices of 0.4, 0.6 and 0.8…….42
3.2 Model Simulation of 4-level DCC at Modulation indices of 0.4, 0.6 and 0.8 ……53
3.3 Model Simulation of 5-level DCC at Modulation indices of 0.4, 0.6 and 0.8…….56
3.4 Model Simulation of a 3-level Inverter Fed Induction Motor Drive. ..……………58
Chapter Four: Spectral Analysis of 3, 4 and 5 level
DIODE CLAMPED CONVERTER Waveforms
4.1 Specific Harmonic Elimination of Higher Harmonics ……………………………..68
4.2 Spectral Analysis of the 3-level A.C waveforms at 0.4, 0.6 and 0.8
Modulation indices …………………………………………………………………71
4.3 Spectral Analysis of the 4-level A.C waveforms at 0.4, 0.6 and 0.8
Modulation indices. ………………………………………………………………………73
4.4 Spectral Analysis of the 5-level A.C waveforms at 0.4, 0.6 and 0.8
Modulation indices. …………………………………………………………………..75
Chapter Five: Experimental VERIFICATION OF 3-level DCC
using AT89S52 MICROCONTROLLER
5.1 Architectural overview of AT89S52 Microcontroller………………………………77
5.2 Memory Organization of AT89S52 Microcontroller…………………………………..82
5.3 3-Level DCC Gate-Signal generation using AT89S52 Microcontroller..……………84
5.4 3-Level DCC Power Circuit and Isolators arrangement…..…………………………86
5.5 Experimental result of 3-level Un-modulated Diode Clamped Converter …………….89
Chapter Six: THESIS Conclusion
6.1 Thesis contribution ………………………………………………………..………….94
6.2 Future Work …………………………………………………………..………………..95
6.3 Conclusion……………………………………………………….………………………95
Cost analysis of components used in the design ….……………………………………………96
References ….………………………………………………………………………………….97
Appendix …. ………………………………………………….………………………………..100
CHAPTER ONE
Introduction
1.0 BACKGROUND OF THE STUDY
The recent development in power semi-conductor technology and the commercial availability of high power switches such as the IGBT, MOSFET and THYRISTORS have resulted in a wide spread acceptance of the two-level voltage source inverter for most electric power applications.
However, for applications that involve a higher voltage such as industrial motor drives, power lines compensator devices, high voltage direct current electrostatic generators and traction applications, the corresponding voltage rating of two-level VSI becomes very inadequate to operate the above devices. To curb this anomaly, higher voltage-levels such as the 3-level, 4level, 5-level, 7-level and above are used since they ensure the production of an efficient and better output waveforms with a reduced total harmonic distortion at a very appreciable switching frequency above the fundamental value[1,2,3]. The background of this study, therefore, centers on the development of space vector pulse width modulation of 3, 4 and 5 level voltage source inverter at different modulation indices and their direct applications to industrial motor drives.
1.1 Statement of problem
following the invention of Multi-level inverters due to the unreliability of two-level for higher power application it is pertinent to state that there are some major drawbacks associated with these multi-level space vector based modulation. They include the following:
- High cost of components involved as the voltage level increases with a corresponding increase in the switching devices.
- Complexity in phase-shifting and voltage-level-sequence of the complementary switches as the inverter level increases.
- Difficulties in dc capacitor voltage control (dvdc /dt) which may give rise to voltage surge across one or more of the inverter switches
- Large numbers of clamping diodes that require additional effort in the phase sequencing of the inverter switches to avoid short-circuit [4, 5].
The problem, which this study is meant to solve, is to see how the conventional 3-level DCC also known as Neutral Point Clamped Converter (NPC) can be used to overcome the above draw-backs associated with higher level DCC using a small scale laboratory set up as well as MATLAB / SIMULINK approach as presented in the preceding chapters
1.2 OBJECTIVES / PURPOSE OF THE study
This study is an evaluation of space vector pulse width modulation of 3, 4 and 5-levels voltage source inverter. Basically, this study will determine:
- An efficient method of pulse width modulation for higher level of voltage source inverter that ensures a reduced dvdc /dt stress and switching losses.
- The best control method of modulation among the various control schemes such as the Multicarrier SPWM, The Staircase, Injected Harmonic and Space Vector PWM of DCC.
- The best output waveforms of SVPWM for 3,4 and 5-level DCC at modulation indices of 0.4,0.6 and 0.8 with their corresponding spectral distribution as well as the weighted total harmonic distortion values for the SVPWM and third harmonic injected modulation.
- The transient and steady state output torque and speed of a 3-level fed induction motor.
- The similarity in the results obtained from the small scale laboratory design and the simplorer simulation model for the un-modulated single phase three level DCC voltage.
- Alternative recommendations for cost reduction, error amendment and efficiency of result based on the laboratory design for future work.
1.3 Significance OF THE study
The major significance of this work is to propose a space vector pulse width modulation which enhances D.C capacitor voltage balance strategy that reduces the capacitor voltage drift (dvdc /dt) of a Diode Clamped Converter supplied by a single D.C source which ensures easy digital applications to other power semi-conductor devices and also in industrial drive application. Additionally, this work proposes a space vector modulation technique that utilizes a switching frequency higher than the fundamental value thus minimizing the undue harmonic distortion encountered with a much lower frequency than the fundamental value.
The result obtained from this study will be useful to the following:
- Industrial motor drives oriented-companies in determining the steady state condition.
- Prospective Researchers on Space Vector Pulse-Width Modulation based strategy
- Power semi-conductor designers using digital signal with space vector pulse-width modulation control strategy in the reduction of excess harmonic distortion associated with Sinusoidal pulse-width modulation as presented in the spectral distributions in chapter four.
1.4 Scope OF THE study
The scope of this work is limited to the space vector pulse-width modulation of 3,4 and 5 level DCC in comparison with the multi-carrier Harmonic Injected Modulation, and the direct application of 3-level DCC to industrial drives and control as well as the experimental verification of this 3-level DCC using a small scale laboratory set up.
1.5 Limitations OF THE study
The major constraints encountered in the course of this research work include:
- Unavailability of circuit components recommended for the laboratory work in the market.
- An occasional supply of inferior power components in most of the local market which impeded progress.
- Uncertainty in the utility supply by the power holding company that disrupted the timely completion of the designed work.
- Unavailability of industrial / professional version of SIMPLORER for the simulation of higher circuit-designed model involving microcontroller chips to view the respective triggering waveforms
1.6 STUDY Methodology
The methodology of this work to a reasonable extent was realized with the aid of three basic simulation software such as the student version SIMPLORER 6.0 for the generation of four different multi-carrier waveforms which include the phase-shift, phase disposition, phase opposition disposition and alternate-phase opposition disposition carrier signals, and also in the simulation of un-modulated single phase three level DCC voltage at different load conditions.
The Matrix Laboratory (MATLAB 7.4) by the Math works company. MATLAB was extensively used in this work due to its inherent salient features which include high computation performance, efficient data analysis; high reliability, powerful graphic presentation and limitless parameter block modeling achieved with the aid of SIMULINK subsystem blocks.
The third is the MIDE and the Proteus for programming the recommended microcontroller through a Universal programmer.
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