LAPORAN PROJEK SARJANA MUDA

Transcription

1 FAKULTI KEJURUTERAAN ELEKTRIK UNIVERSITI TEKNIKAL MALAYSIA MELAKA LAPORAN PROJEK SARJANA MUDA MODELING AND ANALYSIS PERFORMANCE SIMULATION PERFORMANCE OF MULTILEVEL INVERTER USING BIPOLAR AND UNIPOLAR SWITCHING SCHEMES NG SEE MAN Bachelor of Electrical Engineering (Power Electronic and Drive) June 2014

2 MODELING AND ANALYSIS PERFORMANCE SIMULATION OF MULTILEVEL INVERTER USING BIPOLAR AND UNIPOLAR SWITCHING SCHEMES NG SEE MAN A report submitted in partial fulfilment of the requirements for degree of Bachelor of Electrical Engineering (Power Electronic and Drive) Faculty of Electrical Engineering UNIVERSITI TEKNIKAL MALAYSIA MELAKA YEAR 2014

3 I declare that this report entitle Modeling and Analysis Performance Simulation of Multilevel Inverter Using Bipolar and Unipolar Switching Schemes is the result of my own research except as cited in the references. The report has not been accepted for any degree and is not concurrently submitted in candidature of any other degree. Signature :.. Name : NG SEE MAN Date :..

4 I hereby declare that I have read through this report entitle Modeling and Analysis Performance Simulation of Multilevel Inverter Using Bipolar and Unipolar Switching Schemes and found that it has comply the partial fulfilment for awarding the degree of Bachelor of Electrical Engineering (Power Electronic and Drive) Signature : Supervisor s Name : En. Musa Yusup Lada Date :

5 ACKNOWLEDGEMENT I would like to express my great appreciation to my supervisor, Mr. Musa Bin Yusup Lada for his patience guidance and enthusiastic encouragement throughout the duration of this project. The supervision and patient guidance that he gave truly help the progression and smoothness of my final year project. The support and hard work are much appreciated indeed. Next, I would like to extend my thanks to all my course mates for their supports and time during my final year project namely Joycelyn Goh, Sharul Nidzam, Hazwal, Shafiq and Izwan as well. We help each other and discuss together when we encounter some confusing problem on our projects. Last but not least, I would like to show my gratitude to my family for their encouraging and supporting in completion my final year project. Without their support, I am not able to complete my project successfully. i

6 ABSTRACT Multilevel inverter is one of the popular converter topologies used in high power medium- voltage (MV) drives due to able operate at high direct current (DC) voltage which is achieved using series connection of power semiconductor switches. Multilevel inverter can generate output voltage with very low harmonic distortion and synthesis a staircase voltage output waveform by having multiple voltage level. Various topologies of multilevel inverters are introduced; however, in this project, the cascaded seven-level multilevel inverter will be discussed due to easy control method implementation. Unipolar and bipolar switching schemes are used to analyze the performance of seven-level cascaded H-bridge inverter. Both of these SPWM voltage modulation type are selected because these method able to double the switching frequency of the inverter voltage effectively. The major problem in designing multilevel inverter is to design filtering in order to filter the low harmonic which is very hard to eliminate. Bipolar switching PWM inverter is able to filter the low frequency harmonics compared to the unipolar switching schemes inverter. From the simulation results, it can be clearly seen that by using bipolar switching scheme, the total current harmonic distortion (THD i ) and voltage harmonic distortion (THD V ) for R, RL and RC loads are low compared to unipolar switching scheme. Therefore, the bipolar switching scheme is more suitable because the common domestic loads used are RL load. MATLAB Simulink is used to model the seven levels cascaded multilevel PWM inverter. ii

7 ABSTRAK Penyongsang berperingkat adalah salah satu topologi penukar kuasa arus terus yang popular dalam voltan sederhana kuasa tinggi dengan menggunakan penyambungan siri suis suis semikonductor kuasa. Penyongsang berperingkat dapat menjanakan voltan yang berherotan harmonic yang sangat rendah dan bentuk gelombang voltan tangga yang berbilang. Pelbagai topologi penyongsang berperingkat telah diperkenalkan, walaubagaimanapun, dalam projek ini, tahap tujuh penyongsang melata berperingkat akan dibincangkan kerana pelaksanaan kaedah pengawalan lebih mudah. Pensuisan dwikutub dab ekakutub digunakan untuk menganalisi prestasi tujuh peringkat penyongsan berperingkat. Dua persuisan modulasi ini dipilih kerana kaedah ini mampu menggandakan frekuensi utama voltan penyongsang dengan berkesan. Masalah utama dalam mereka penyongsang berperingkat adalah menapis herotan harmonik yang rendah kerana herotan harmonik yang rendah sangat sukar untuk ditapis. Dwikutub persuisan lebih mudah menapis herotan harmonik ini berbanding dengan persuisan ekakutub. Keseluruhan keputusan simulasi, dengan jelasnya herotan harmonik arus dan voltan penggunaan R, RL dan RC muatan adalah rendah berbanding dengan persuisan ekakutub.lantarannya, persuisan dwikutub adalah lebih sesuai digunakan kerana muatanmuatan domestik adalah RL muatan. Simulink Matlab digunakan untuk memperagakan tujuh tahap penyongsang berperingkat. iii

8 TABLE OF CONTENT ABSTRACT... ii ABSTRAK...iii TABLE OF CONTENT... iv LIST OF FIGURES... vi LIST OF TABLES... vii LIST OF ABREVATIONS... viii CHAPTER INTRODUCTION Background Problem Statement Objective Scope Report Outline... 3 CHAPTER LITERATURE REVIEW Introduction Classification of Inverter Current-source Inverter (CSI) Voltage Source Inverter (VSI) Single-phase Half-bridge Inverter Single-phase Full- bridge Inverter Square Wave Inverter Pulse- width Modulated Inverter General Topologies of Multilevel Inverter Neutral Point Clamped Multilevel Inverter (NPC-MLI) Flying Capacitor Multilevel Inverter (FC-MLI) iv

9 2.3.3 Cascaded H-bridge Multilevel Inverter (CHB-MLI) Multilevel Inverter Modulation Control Schemes SPWM with Bipolar Switching SPWM with Unipolar Switching Comparison between Unipolar and Bipolar Switched Multilevel Inverter PWM Consideration Frequency Modulation Ratio, m f Amplitude Modulation Ratio, m a Sinusoidal PWM (SPWM) Phase- Shifted PWM (PSPWM) Level- Shifted PWM (LSPWM) Power Quality Harmonic Distortion Definition CHAPTER DESIGN METHODOLOGY Introduction Research Methodology Flowchart Control Switching Technique Used Single Phase and Three-Phase Inverter Simulink Block Unipolar Single Phase Inverter Unipolar three-phase inverter Bipolar single-phase inverter Bipolar three-phase inverter Cascaded Seven-level Multilevel Inverter Simulink Block Unipolar Three Phase Seven-Level Multilevel Inverter Bipolar Three-Phase Seven-Level Multilevel Inverter CHAPTER RESULT AND DISCUSSION v

10 4.1 Introduction Simulation Result for Unipolar and Bipolar Single Phase Inverter Unipolar Single-phase Inverter Simulation Result using R-load for Unipolar Single Phase Inverter Simulation Result using RL-load for Unipolar Single Phase Inverter Simulation Result using RC-load for Unipolar Single Phase Inverter Bipolar Single-phase Inverter Simulation Result using R-load for Bipolar Single Phase Inverter Simulation Result using RL-load for Bipolar Single Phase Inverter Simulation Result using RC-load for Bipolar Single Phase Inverter Simulation Result for Unipolar and Bipolar Three Phase Inverter Unipolar Three-phase Inverter Simulation Result using R-load for Unipolar Three Phase Inverter Simulation Result using RL-load for Unipolar Three Phase Inverter Simulation Result using RC-load for Unipolar Three Phase Inverter Bipolar Three-phase Inverter Simulation Result using R-load for Bipolar Three Phase Inverter Simulation Result using RL-load for Bipolar Three Phase Inverter Simulation Result using RC-load For Bipolar Three Phase Inverter Simulation Result for Cascaded Seven-Level Multilevel Inverter Unipolar Three Phase Seven-Level Multilevel Inverter Simulation Result using R-load for Cascaded Seven-Level Multilevel Inverter Simulation Result using RL-load for Cascaded Seven- Level Multilevel Inverter Simulation Result using RC-load for Cascaded Seven-Level Multilevel Inverter Bipolar Three Phase Seven-Level Multilevel Inverter Simulation Result using R-load for Cascaded Seven-Level Multilevel Inverter Simulation Result using RL-load for Cascaded Seven-Level Multilevel Inverter Simulation Result using RC-load for Cascaded Seven-Level Multilevel Inverter 95 CHAPTER CONCLUSION vi

11 REFERENCE PUBLICATION APPENDIX vii

12 LIST OF FIGURES Figure 2.1: Block Diagram of Inverter... 4 Figure 2.2: Circuit Configuration of CSI inverter... 5 Figure 2.3: Circuit Configuration of VSI Inverter... 5 Figure 2.4: Circuit Configuration of a Single-phase Half-bridge Inverter... 6 Figure 2.5: (a) Gating Signal for Switch S 1 (b) Gating Signal for Switch S Figure 2.6: Output Voltage of Single phase half-bridge inverter... 7 Figure 2.7: Circuit Configuration of a single-phase, full-bridge inverter... 8 Figure 2.8: (a) Gating signal for switch S 1, S 2 (b) Gating signal for switch S 3,S Figure 2.9: Output voltage for single phase, full-bridge inverter... 9 Figure 2.10: Square Wave Inverter Output for Harmonic Control... 9 Figure 2.11: Three level Neutral Point Clamped Topology Figure 2.12: Three-level Flying Capacitor Topology Figure 2.13: Five-level Cascaded H-bridge Topology Figure 2.14: Multilevel converter modulation methods Figure 2.15: (a) Switching pattern (b) Output waveform Figure 2.16: (a) Switching pattern (b) Output Waveform Figure 2.17: Multi-carrier SPWM control techniques Figure 2.18: Level-shifted multicarrier modulation: (a) PD, (b) POD, and (c) APOD Figure 3.1: Flowchart of research methodology Figure 3.2: Block Diagram of Unipolar and Bipolar Single Phase Inverter Figure 3.3: Block Diagram of Unipolar and Bipolar Three-Phase Inverter Figure 3.4: Block diagram of unipolar single phase inverter Figure 3.5: Block diagram of unipolar single-phase PWM generation Figure 3.6: Block diagram of unipolar three-phase inverter Figure 3.7: Block diagram of unipolar three-phase PWM generation Figure 3.8: Block diagram of bipolar single-phase inverter Figure 3.9: Block diagram of bipolar single-phase PWM generation Figure 3.10: Block diagram of bipolar three phase inverter Figure 3.11: Block diagram of bipolar three phase PWM generation Figure 3.12: Block Diagram of Seven-Level Cascaded Multilevel Inverter Figure 3.13: MATLAB Simulink model of unipolar seven-level multilevel inverter viii

13 Figure 3.14: PWM Generation of H-Bridge Figure 3.15: PWM Generation of H-Bridge Figure 3.16: MATLAB Simulink model of bipolar seven-level multilevel inverter Figure 3.17: PWM Generation of H-Bridge Figure 3.18: PWM Generation of H-Bridge Figure 4.1: Reference and carrier signals under condition m f = 50, m a = Figure 4.2: PWM compensator signal Figure 4.3: Current waveform (R-load) Figure 4.4:Voltage waveform (R-load) Figure 4.5: THD for load current Figure 4.6: THD for load voltage Figure 4.7: Current waveform (RL-load) Figure 4.8: Voltage waveform (RL-Load) Figure 4.9: THD for load current Figure 4.10: THD for load voltage Figure 4.11: Current Waveform (RC-load) Figure 4.12: Voltage Waveform (RC-load) Figure 4.13: THD for load current Figure 4.14: THD for load voltage Figure 4.15: Sinusoidal reference and triangular carrier m f = 50, m a = Figure 4.16: PWM Compensator Signal Figure 4.17: Current Waveform (R load) Figure 4.18: Voltage Waveform (R load) Figure 4.19: THD for load current Figure 4.20: THD for load voltage Figure 4.21: Current Waveform (RL-load) Figure 4.22: Voltage Waveform (RL-load) Figure 4.23: THD for load current Figure 4.24: THD for load voltage Figure 4.25: Current Waveform (RC-load) Figure 4.26: Voltage Waveform (RC-load) Figure 4.27: THD for load current Figure 4.28: THD for load voltage Figure 4.29: Carrier and reference waves for PWM operation for the three phase inverter under condition m f = 100, m a = Figure 4.30: PWM Compensator Signal Figure 4.31: Three phase current (R-load) ix

14 Figure 4.32: Line-to-line voltage (R-load Figure 4.33: Line-to-neutral voltage (R-load) Figure 4.34: THD for phase current Figure 4.35: THD for phase voltage Figure 4.36: THD for Line-to-line voltage Figure 4.37: Three phase current (RL-load) Figure 4.38: Line-to-neutral voltage (RL-load) Figure 4.39: Line-to-line voltage (RL-load) Figure 4.40: THD for phase current Figure 4.41: THD for phase voltage Figure 4.42: THD for Line-to-line voltage Figure 4.43: Three phase current (RC-load) Figure 4.44: Line-to-line voltage (RC-load) Figure 4.45: Line-to-neutral voltage (RC-load) Figure 4.46: THD for Phase Current Figure 4.47: THD for Line-to-line Voltage Figure 4.48: THD for Line-to-neutral voltage Figure 4.49: PWM compensator signal Figure 4.50: Three phase current (R load) Figure 4.51: Line-to-line voltage (R load) Figure 4.52: Line-to-neutral voltage (R-load) Figure 4.53: THD for phase current Figure 4.54: THD for Line-to-line voltage Figure 4.55: THD for Line-to-neutral Voltage Figure 4.56: Three phase current (RL-Load) Figure 4.57: Line-to-line voltage (RL-load) Figure 4.58: Line-to-neutral voltage (RL-load) Figure 4.59: THD for phase current Figure 4.60: THD for Line-to-neutral voltage Figure 4.61: THD for Line-to-line Voltage Figure 4.62: Three phase current (RC-load) Figure 4.63: Line-to-line voltage (RC- load) Figure 4.64: Line-to-neutral voltage (RC- load) Figure 4.65: THD for Phase Current Figure 4.66: THD for Line-to-neutral voltage Figure 4.67: THD for Line-to-line voltage x

15 Figure 4.68: Phase Dissipation (PD multicarrier modulation for Seven-level inverter under condition of m f = 100 and m a = Figure 4.69: PWM Compensator Signal (Upper) Figure 4.70: PWM Compensator Signal (Lower) Figure 4.71: Three phase current (R-load) Figure 4.72: Line-to-neutral voltage (R-load) Figure 4.73: THD for phase current (R-load) Figure 4.74: THD for phase voltage (R load) Figure 4.75: Three phase current (RL load) Figure 4.76: Line-to-neutral Voltage (RL load) Figure 4.77: THD for phase current (RL load) Figure 4.78: THD for phase voltage ( RL load) Figure 4.79: Three Phase Current (RC load) Figure 4.80: Line-to-neutral Voltage (RC load) Figure 4.81: THD for phase current (RC load) Figure 4.82: THD for phase voltage (RC load) Figure 4.83: PWM Compensator Signal (Upper) Figure 4.84: PWM compensator signal (Lower) Figure 4.85: Three phase current (R load) Figure 4.86: Line-to-neutral voltage (R-load) Figure 4.87: THD for phase current (R-load) Figure 4.88: THD for Phase Voltage (R-load) Figure 4.89: Three phase current (RL load) Figure 4.90: Line-to-neutral voltage (RL load) Figure 4.91: THD for Phase Current (RL load) Figure 4.92: THD for Phase Voltage (RL load) Figure 4.93: Three phase current (RC load) Figure 4.94: Line-to-neutral Voltage (RC load) Figure 4.95: THD for Phase Current (RC load) Figure 4.96:THD for Phase Voltage (RC load) xi

16 LIST OF TABLES Table 3.1: Simulation Parameters of Unipolar and Bipolar Single Phase Inverter 29 Table 3.2: Block Diagram of Unipolar and Bipolar Three Phase Inverter 30 Table 3.3: Simulation Parameters of Unipolar and Bipolar Cascaded Seven-level Multilevel Inveter 35 Table 4.1: Total Harmonic Distortion in Single-phase Inverter 80 Table 4.2: Total Harmonic Distortion in Three-phase Inverter 80 Table 4.3: Voltage and Current Harmonic of Unipolar Sinusoidal PWM Inverter 89 Table 4.4: Voltage and Current Harmonic of Bipolar Sinusoidal PWM Inverter 98 Table 4.5: Voltage and Current Harmonic of Sinusoidal PWM Inverter 98 Table 4.6: Voltage and Current Harmonics of Sinusoidal PWM Inverter In 3-Level and 7- Level 98 xii

17 LIST OF ABBREVATIONS AC Alternating Current APOD Alternative Phase Opposition Dissipation CSI Current Source Inverter DC Direct Current GTO Gate Turn-Off Thyristor MLI Multilevel Inverter PD Phase Dissipation POD Phase Opposition Disposition PWM Pulse Width Modulation THD Total Harmonic Distortion VSI Voltage Source Inverter xiii

18 CHAPTER 1 INTRODUCTION 1.1 Background Inverters are circuits that convert direct current (DC) to alternating current (AC). More precisely, inverters transfer power from a DC source to an AC load. Since the main objective of the inverter is to use a DC voltage source to supply a load requiring AC, it is useful to describe the quality of AC output. In the electrical power distribution system, there are many non-linear loads drawing non-sinusoidal current. The quality of a non-sinusoidal wave can be expressed in terms of total harmonic distortion (THD). If non-sinusoidal current passes through a different kind of impedance, it will produce voltage and current harmonics. The voltage and current harmonics can cause additional losses, overheating and overloading of the load. Multilevel inverter has the advantages of generating better output quality by using pulse width modulation (PWM) technique. This is because PWM inverters are able to eliminate unwanted harmonic by using suitable design of PWM scheme such as bipolar and unipolar schemes. 1

19 1.2 Problem Statement In the past, square wave inverters were widely used in independent wind or solar power systems and some industrial applications with lower requirement on power quality. In square wave inverter, the harmonics and output voltage amplitude could not be controlled by the user. In addition, in AC power distribution system, harmonics occur when the normal electric current waveform is distorted by non-linear loads such as computer equipment with switched-mode power supplies, variable speed motors and drive, fluorescent lamp ballasts and others. Harmonic decreases significantly in power quality and live cycle of electrical equipment. Basically, harmonic distortion will increase resistive losses, voltage stresses and excessive voltage distortion on power distribution system. Therefore, the multilevel inverter is used to produce multilevel-output voltages which are purely sinusoidal or synthesis a staircase voltage waveform and thus reduce harmonic content. Higher frequency harmonics are easier to filter than harmonics near the fundamental frequency. Bipolar and unipolar switching schemes are chosen because these methods able to double the switching frequency of the inverter. However, some of low frequency harmonics are formed due to non-linear loads, therefore, bipolar switched multilevel inverter is proposed due to able to filter the low frequency harmonics More number of levels of multilevel inverter will give better performance in term of total harmonic distortion. 1.3 Objective The objectives of this project are: 1. To model there phase seven-level multilevel inverter using bipolar and unipolar switching technique by using Matlab Simulink Software. 2. To analyze and evaluate the simulation of seven-level of multilevel inverter by using bipolar and unipolar switching schemes. 3. To validate the THD for bipolar and unipolar switching schemes for multilevel inverter by using varieties of load testing. 2

20 1.4 Scope This project focuses on the performance of seven-level multilevel inverter on minimizing the harmonics distortion. The Matlab Simulink is used to model the seven-level cascaded multilevel inverter. The multilevel inverter is used for various loads testing such as R, RL and RC load. The performance of seven levels cascaded inverter will be analyzed by using bipolar and unipolar switching schemes. Meanwhile, the simulation results are compared and validated that the bipolar seven-level cascaded inverter has the minimum harmonic distortion. 1.5 Report Outline This report contains five chapters and start with the introduction of project which is multilevel inverter. The following five chapters of this project are arranged as follows: Chapter 1 covers the short explanation about this research project, problem statement, objective and scope. Chapter 2 covers the theoretical background of this project including the detail about the types of inverter, the general topologies of multilevel inverter, multilevel inverter modulation control schemes, PWM consideration, power quality and total harmonic distortion definition. Chapter 3 states about the research methodology. This chapter consists of the flowchart of project and the switching methods used in this project and the simulation results which are the designing Simulink block by using bipolar and unipolar switching schemes. Chapter 4 discusses the simulation result by using different non-linear loads. Harmonic analysis for the non-linear loads will be discussed to evaluate the performance of the inverter. Chapter 5 is the summary of this project. 3

21 CHAPTER 2 LITERATURE REVIEW 2.1 Introduction Inverters are circuits that convert a DC power into an AC power at a desired output voltage and frequency. Figure 2.1 shows the block diagram of inverter. Inverters can be in single phase or multiphase and they deliver bipolar current waveform and allow for bidirectional power flow [1]. Inverters are widely used in various applications requiring variable voltage and variable frequency AC supply. Some important applications are adjustable-speed AC motor drives, DC motor drives; uninterruptible power supplies (UPS), induction heating, standby power supply and high voltage DC transmission systems [2]. Figure 2.1: Block Diagram of Inverter 2.2 Classification of Inverter There are different basis types of inverters. The two major types of inverters are current-source inverter (CSI) and voltage-source inverter (VSI). Their input sources are either a constant current or constant voltage. 4

22 2.2.1 Current-source Inverter (CSI) Current-source inverter is fed by a current source with an inductor in series with a dc source. Therefore, the supply current does not change quickly. Figure 2.2 shows the block diagram of CSI inverter. CSI inverters are in general constructed with gate-turnoff thyristor (GTO) and refer to high power levels. The load current is varied by controlling the DC input voltage to the current source inverter. CSI are used in a very high-power AC drives [3]. Figure 2.2: Circuit Configuration of CSI inverter Voltage Source Inverter (VSI) Voltage-source inverter is fed by a DC source of small internal impedance. VSI inverters are constructed with insulated-gate bipolar transistor (IGBTs) or GTO. The AC terminal output voltage remains almost constant irrespective of the load current drawn. There are two types of VSI which are square wave inverter and PWM inverter [3]. Figure 2.3: Circuit Configuration of VSI Inverter 5

23 Single-phase Half-bridge Inverter The basic topology of a single-phase is half-bridge inverter fed by a DC voltage source as shown in Figure 2.4. S1 and S2 are gate-commutated power semiconductor switches. When closed, these switches conduct current flows. The gating signal of switches, S 1 and S 2 are shown in Figure 2.5. When S 1 is closed, the load voltage is Vdc/2. When S 2 is closed, the load voltage is Vdc/2.Thus, a square wave or bipolar pulse width modulated output voltage can be produced. The output voltage of half-bridge is shown as Figure 2.6 too [3]. V/2 Io Vload load S1 V/2 S2 Figure 2.4: Circuit Configuration of a Single-phase Half-bridge Inverter S1 0 T/2 T t (a) 6

24 S2 0 T/2 T t (b) Figure 2.5: (a) Gating Signal for Switch S 1 (b) Gating Signal for Switch S 2 V Vdc/2 0 -Vdc/2 T/2 T t Figure 2.6: Output Voltage of Single phase half-bridge inverter Single-phase Full- bridge Inverter The basic topology of a single-phase is full-bridge inverter fed by a DC voltage source as shown in Figure 2.7. The inverter uses two pairs of controlled switches (S 1 S 2 and S 3 S 4 ) and two pairs of diodes (D 1 D 2 and D 3 D 4 ). The devices of one pair operate simultaneously. However, in reality, there must have switching transition time or blanking time to control the closing and opening of switches Overlapping opening of switches will result in short circuit or shoot-through fault. The gating signals of the switch-pairs S 1 S 2 and S 3 S 4 are shown in Figure