universiti teknologi malaysia
PSZ 19:16 (Pind. 1/07)
UNIVERSITI TEKNOLOGI MALAYSIA DECLARATION OF THESIS / UNDERGRADUATE PROJECT PAPER AND COPYRIGHT
Author’s full name :
MUHAMMAD NASRUL BIN AZMAN
Date of birth
:
18 JANUARY 1986
Title
:
SINGLE PHASE PWM INVERTER (DC TO AC) USING UNIPOLAR SWITCHING TECHNIQUE
Academic Session:
2008/2009 - 2
I declare that this thesis is classified as :
√
CONFIDENTIAL
(Contains confidential information under the Official Secret Act 1972)*
RESTRICTED
(Contains restricted information as specified by the organisation where research was done)*
OPEN ACCESS
I agree that my thesis to be published as online open access (full text)
I acknowledged that Universiti Teknologi Malaysia reserves the right as follows : 1. The thesis is the property of Universiti Teknologi Malaysia. 2. The Library of Universiti Teknologi Malaysia has the right to make copies for the purpose of research only. 3. The Library has the right to make copies of the thesis for academic exchange. Certified by:
SIGNATURE
860118-11-5437
DR. AWANG B. JUSOH
(NEW IC NO. /PASSPORT NO.)
NAME OF SUPERVISOR
Date : 13 MAY 2009
NOTES :
SIGNATURE OF SUPERVISOR
*
Date : 13 MAY 2009
If the thesis is CONFIDENTIAL or RESTRICTED, please attach with the letter from the organisation with period and reasons for confidentiality or restriction.
“I declared that I have read this work and in my opinion this work is adequate in term of scope and quality for the purpose of awarding a Bachelor’s Degree of Electrical Engineering (Power)”
Signature
: …………………………….
Name of supervisor
: DR. AWANG BIN JUSOH
Date
: 14 MAY 2009
SINGLE PHASE PWM INVERTER (DC TO AC) USING UNIPOLAR SWITCHING TECHNIQUE
MUHAMMAD NASRUL BIN AZMAN
Submitted to the Faculty of Electrical Engineering in partial fulfillment of the requirement for the degree of Bachelor in Electrical Engineering (Power)
Faculty of Electrical Engineering Universiti Teknologi Malaysia
MAY 2009
i
DECLARATION
I declared that this work as the product of my own effort with the exception of excerpt cited from others works of which the sources were duly noted
Signature
:
…………………………………………...
Author’s name
:
MUHAMMAD NASRUL BIN AZMAN
Date
:
MAY 2009
ii
Specially dedicated to
my beloved father, Johari Bin Abdullah my beloved mother, Zunaidah Binti Ya also my elder brothers and my sisters
iii
ACKNOWLEDGEMENTS
The author wishes to acknowledge the guidance and assistance of all those who aided in the development and implementation of this thesis. I must express my gratitude and thanks to my supervisor, Dr. Awang Bin Jusoh for his valuable guidance and encouragement throughout the year – which somehow always seemed to happen just when I needed it. I would also like to thank my fellow students for their assistance when it was required and all of those involved in my life outside my thesis for putting up with me. Most importantly, I would like to thank my family for their continuous support throughout my graduate school experience.
iv
ABSTRACT
This thesis document outlines the research, design and implementation of a single-phase inverter that produces a symmetric AC output voltage of desired magnitude and frequency. In this project the inverter output frequency of 50 Hz was used in order to meet all the objectives of this project. Unipolar PWM switching technique is employed to control the output voltage magnitude and frequency. The waveform generator integrated circuit of Intersil, ICL8038 and power switch MOSFET are two main components used for the implementation of the inverter. There are two parts of study in this project which is simulation and experimental part.
v
ABSTRAK
Tesis ini menggariskan tentang kajian, reka bentuk dan pelaksanaan penyongsang satu fasa yang menghasilkan voltan keluaran AC simentri mengikut nilai dan frekuensi yang diingini. Di dalam projek ini, frekuensi keluaran penyongsang 50 Hz telah digunakan bagi mencapai kesemua objektif projek. Kaedah permodulatan lebar denyut (PLD) menggunakan teknik pensuisan uni-kutub digunakan untuk mengawal nilai voltan keluaran dan frekuensi. Litar bersepadu penjana gelombang, ICL8038 dan peranti kuasa MOSFET adalah merupakan dua komponen utama yang digunakan di dalam projek ini. Terdapat dua bahagian kajian yang dijalankan didalam projek ini iaitu bahagian simulasi dan bahagian eksperimen.
vi
TABLE OF CONTENTS
CHAPTER
CHAPTER 1
CHAPTER 2
TITLE
PAGE
DECLARATION
i
DEDICATION
ii
ACKNOWLEDGEMENT
iii
ABSTRACT
iv
ABSTRAK
v
TABLE OF CONTENTS
vi
LIST OF TABLES
ix
LIST OF FIGURES
x
LIST OF SYMBOLS
xiii
LIST OF APPENDICES
xiv
INTRODUCTION 1.1
General introduction
1
1.2
Project objective
2
1.3
Scope
2
1.4
Project methodology
3
1.4(a) Simulation part
3
1.4(b) Experimental part
4
1.5
5
Project schedules
BASIC CONCEPT AND LITERATURE REVIEW 2.1 Introduction of PWM single phase inverter
7
2.2 PWM operation
9
vii
2.3 Low pass filter operation
CHAPTER 3
CHAPTER 4
CHAPTER 5
11
DESIGN AND IMPLEMENTATION 3.0
Introduction
12
3.1
Simulation study
12
3.2
Experimental
15
3.2.1
Power circuit
16
3.2.2 0
LC filter
18
3.2.3
Control circuit
18
3.2.3.1(a)
PWM circuit
19
3.2.3.1(a-1)
Sine wave generator circuit
19
3.2.3.1(a-2)
Triangular wave generator circuit
23
3.2.3.1(a-3)
Inverter amplifier circuit
25
3.2.3.1(a-3)
Comparator circuit
27
3.2.3.1(b)
Dead time circuit
28
3.2.3.1(c)
MOSFET drive circuit
31
SIMULATION RESULTS AND DISCUSSION 4.1
Simulation results
32
4.1.1
Inverter circuit without filter circuit
32
4.1.2
Inverter circuit with filter circuit
38
4.1.3
Changes of modulation frequency
42
4.1.4
Changes of modulation index
44
4.2
Discussion
46
4.2.a
Inverter circuit
46
4.2.b
Changes of modulation frequency
46
4.2.c
Changes of modulation index
47
EXPERIMENTAL RESULTS AND DISCUSSION 5.1 Experimental results
48
5.2 Discussion
56
viii
CHAPTER 6
CONCLUSION AND RECOMMENDATION
57
REFERENCES
59
APPENDIX
60
ix
LIST OF TABLES
TABLE
TITLE
PAGE
NO. 1
Schedule PSM1
5
2
Schedule PSM2
6
3
Specifications of simulation circuit
14
4
Logic functions of IC7408
30
x
LIST OF FIGURES
FIGURE
TITLE
PAGE
NO. 1
H-bridge inverter
1
2
Flow chart for simulation process
4
3
Flow chart for experimental process
4
4
Description of SPWM modulation
7
5
Basic of single phase inverter
9
6
Unipolar PWM scheme and output voltage
10
7(a)
Full-bridge PWM inverter circuit without filter circuit, with R-L load Full-bridge PWM inverter circuit with filter circuit, with
12
7(b)
13
R-L load 8(a)
Basic of inverter’s block diagram using unipolar switching
15
8(b)
Flow chart of control circuit design switching
16
9
The power circuit
17
10
Symbol of IRFP450 power MOSFET
17
11
LC filter & load configuration
18
12
Sine wave generator circuit
19
13
Connection to achieve minimum sine wave distortion
20
15
Two possible connections for the external timing resistors.
21
16
Rising portion, t1 and falling portion, t2
22
17
Triangular wave generator circuit
23
18
TL082 as a buffer circuit
24
19
Top view of TL082 integrated circuit
25
20
The Inverter amplifier circuit
25
21(a)
Basic inverting circuit
26
21(b)
Top view of Ua741 op-amp integrated circuit
26
22
The Comparator circuit
27
xi
23
Internal circuitry of LM339 integrated circuit
27
24
Dead time circuit
29
25(a)
Pin configuration of the IC7408
29
25(b)
Logic diagram of IC7408
29
26(a)
Pin configuration of the IC7414
30
26(b)
Logic diagram of IC7414
30
27
The MOSFET drive circuit
31
28
Full-bridge PWM inverter circuit without filter circuit,
32
with R-L load 29
Output load current waveform
33
30
Output load voltage waveform
34
31
Total harmonic distortions in Fast Fourier Transform
35
32
Total harmonic distortions wave form
36
33
Pulse waveform
37
34
Full-bridge PWM inverter circuit with filter circuit, with
38
R-L load 35
Load current waveform
39
36
Load voltage waveform
39
37
Total harmonic distortions in Fast Fourier Transform
40
38
Total harmonic distortions in Fast Fourier Transform
41
39
Pulse waveform
42
40
Total harmonic distortions in Fast Fourier Transform
43
(unfiltered circuit) 41
Total harmonic distortions in Fast Fourier Transform
43
(filtered circuit) 42
Total harmonic distortions in Fast Fourier Transform with
44
ma = 0.9 43
Total harmonic distortions in Fast Fourier Transform with
45
ma = 0.5 44
Sine wave generator circuit
48
45
Sine output waveform before buffer circuit
49
46
Sine output waveform after buffer circuit
50
47
The Inverter amplifier circuit
50
xii
48
Sine output waveform and inverted sine output waveform
51
49
Triangular output waveform
52
50
Comparator circuit.
53
51
PWM waveform
53
52
PWM waveform
54
53
logic pulse waveform
55
54
Laboratory unipolar inverter board
60
xiii
LIST OF SYMBOLS
THD
- Total Harmonic distortion
PWM
- Pulse width modulation
AC
- Alternating current
DC
- Direct current
S
- Switch
L
- Inductor
C
- Capacitor
SPWM
- Sinusoidal Pulse width modulation
fsw
- Switching frequency
mf
- Frequency modulation ratio
ma
- Amplitude modulation ratio
V1
- Fundamental voltage
Vtri
- Triangular Switching Waveform
Vref
- Sinusoidal reference signals
Eqn
- Equation
I.C
- Integrated circuit
xiv
LIST OF APPENDICES
NO.
TITLE
1
Figures of laboratory unipolar inverter board
2
Datasheet of ICL8038
3
Datasheet of IRFP450 power MOSFET
1
CHAPTER 1
INTRODUCTION
1.1
GENERAL INTRODUCTION
Nowadays, switching-mode single-phase DC-AC inverter have been widely used in many application such as ac motor, induction heating, standby power supplies, uninterruptible power supplies (UPS) and so on. Among various control technique, pulse-width modulation (PWM) is the most effective used to regulate the magnitude as well as frequency of the converter’s output voltage. This particular control technique also can reduce the total harmonic distortion easily while varying the output voltage and have been gone through in many revisions. A block diagram representation of a single-phase H-bridge inverter is given in Figure1:
+
‐ Vout
Figure 1: H-bridge inverter.
2
The H-bridge topology inverter is the most popular single-phase converter in various applications, especially in higher power rating applications.
It consists of
two arms and outputs a single-phase AC output voltage, Vout to the load. There are four switching devices that represented as ideal switches (BJTs or MOSFETs). Each switch was connected in the form of a full bridge. Then a pulse width modulation, PWM signal from control circuitry was injected to the each switching devices along with the inverted signal to produce an AC output voltage, Vout with variable frequency and amplitude. PWM techniques are used to control the switching devices on and off. PWM control is a comparison of the output waveform to a reference signal and adjusts the duty cycle of the switching mechanism. Compared to the square-wave method of control, PWM has two distinct advantages which is higher frequency harmonic content and amplitude control.
The filtering requirements for PWM generated
outputs are less stringent since the non-fundamental components are of much higher frequency than that of the fundamental sine wave.
1.2
PROJECT OBJECTIVE
The objective of this project is to design and construct a single-phase PWM inverter circuit with unipolar switching technique which can produce a symmetric AC output voltage of desired magnitude and frequency. All the outcome results between simulations and experimental results are compared to verify the effectiveness of the designed inverter.
1.3
SCOPE
After intensively reviewed on the single-phase unipolar inverter, there are many issues need to be tackled in order to achieve a preliminary objective. The scopes of this thesis are used for the guideline of the project. The project scopes are as follows:
3
•
Read all significant references and analyse the literature reviews about the operation of waveform generator, the operation of pulse-width modulation, dead time circuit, driver circuit and power circuit.
•
Design a simulation circuit by using MATLAB/SIMULINK software part by part according to the theories and methods that gain from the literature review. Then simulate and analyses the output waveforms.
•
Construct the circuit on breadboard based on collected data from simulation part and literature reviews.
1.4
PROJECT METHODOLOGY
The procedure of the analysis is the important factor to ensure that the project is completely done as expected, because it is necessary to have an efficient plan and it will help to guide into the target to achieve the objective. There are two parts of study in this project.
The first part is simulation part and the second part is
experimental part.
1.4(a) Simulation Part
The important thing in this part is modeling and simulation of single phase PWM inverter. In this part, Matlab/Simulink software with the SimPowerSystems Block Set was used to model a single phase inverter circuit. This software was chosen because of its simplicity and user-friendly environment for analysis and design.
4
The flow of project methodology is shown as Figure 2:
1 2 3 4 5
• FINDING THE REFERENCE
• BUILD SIMULATION CIRCUIT
• SIMULATE • SUCCES: TAKE A OUTPUT RESULT • NO: MODIFY THE CIRCUIT • DONE: GO TO THE NEXT PART
Figure 2: Flow chart for simulation process
1.4(b) Experimental Part
This part is implemented to verify all the simulation part in previous topics. The flow of project methodology is shown in Figure 3:
1 2 3 4 5
• DESIGN CIRCUIT • DATASHEET COMPONENT • CIRCUIT ON BREADBOARD • YES: GET A RESULT AND COMPARE • NO: TROUBLESHOOT • DONE
Figure 3: Flow chart for experimental process
5
After both are completed, the comparison results between these two parts were carried out in order to achieve the final objective of this project.
1.5
PROJECT SCHEDULES
The Gantt chart below shows overall activities that have been done during the project time. This Gantt chart consist two parts which is PSM1 and PSM2.
Table 1 summarizes the activities for PSM 1. In this table all the activities are focus on study and design a single-phase PWM inverter.
Design modification
Table 1: Schedule PSM1
6
Table 2 shows the schedule of activities for PSM 2. In this table all the activities are focus on implementation of the single-phase PWM inverter. NO
IMPLEMENTATION
1
Order the component s
2
Implementation PWM circuit
3
Implementation Comparator circuit
4
Implementation MOSFET Drive circuit
5
presentation
6
Modify
7
Submit report
1
2
3
4
5
6
Table 2: Schedule PSM2
7
8
9
10
11
12
13
7
CHAPTER 2
BASIC CONCEPT AND LITERATURE REVIEW
2.1
INTRODUCTION OF PWM SINGLE PHASE INVERTER
An inverter is an electrical or electro-mechanical device that converts direct current (dc) to alternating current (AC). In the unipolar switching scheme, the output voltage are varies between positive and zero and negative voltage levels. The rms value of the output voltage vary depend on changes of input DC voltage and/or modulation index, ma. The modulation index is a ratio between the amplitude of sinusoidal reference signals (Vref) with the triangular waveform (Vtri) as shown in Figure 4 (a):
Vref
Vtri
Figure 4: Description of SPWM modulation As show in Figure 4(b), when Vref is greater than Vtri, the PWM output is positive; otherwise the PWM output is negative. The frequency of triangular waveform, Vtri establishes the switching frequency, fsw of the inverter.
8
The modulation index, ma is defined as: Vref Vtri
… eqn. 1
And the modulation ratio is defined as: ftri fref
… eqn. 2
This is significant in the case of an unregulated DC supply voltage because the value of ma can be adjusted to compensate for variation in the DC supply, producing a constant-amplitude output. If
1, amplitude of the fundamental frequency of
the inverter output voltage,V1 is linearly proportional to
, otherwise it becoming
not linear. This not linear phenomenon is called over modulation. The quality of the inverter output waveform can be expressed by using the Fourier analysis data to calculate the total harmonic distortion (THD) of load current. The quality of output waveform that is needed from an inverter depends on the characteristics of the connected load. Some loads need a nearly perfect sine wave voltage supply in order to work properly. Other loads may work quite well with a square wave voltage. The total harmonic distortion (THD) for the inverter output current can expressed as: ∑
In rms I1 rms
… eqn. 3
Where: In = harmonic current I1 = fundamental output current. The THD for the inverter output voltage is determined by substituting current in the preceding equation. The inverter output voltage is: ∑
Vrms V1 rms
… eqn. 4
9
Where: Vn = harmonic voltage. V1 = fundamental output voltage. Pulse-width modulation (PWM) switching provides a best ways to decrease the total harmonic distortion, THD. The unfiltered PWM output will have a relatively high THD but the first harmonics will be at higher frequencies compare to the square wave switching frequency, making filter easier.
2.2
PWM OPERATION
The basic single-phase full-bridge PWM inverter is shown in Figure 5:
S1
Leg A
S2
Leg B
S3
S4
Figure 5: Basic of single phase inverter
In the unipolar switching scheme the output voltage changes between positive and zero, or between zero and negative voltage levels whereby S1 and S2 will be given PWM pulses for first (positive) output half cycle and S3 and S4 are gated for the next (negative) half cycle.
10
The (Vref) and (Vtri) for equation 1 is refer to the peak amplitude of the signals. Leg A and B of the full-bridge inverter are controlled separately by comparing (Vref) with (Vtri) and (- Vref) with (Vtri). The resulting waveforms are used to control the switches as follows: In leg A: Vref › Vtri: S1 on and Vref ‹ Vtri: S4 on and In Leg B: -Vref › Vtri: S3 on and -Vref ‹ Vtri: S2 on
The unipolar PWM pulse generation with resulting pattern is represented in Figure 6 in which a triangular carrier wave is compared with sinusoidal reference waveform to generate PWM gating pulses. Vref
Vtri
‐Vref
Pole voltage VAO Pole voltage VBO
Output voltage (VAO – VBO)
Figure 6: Unipolar PWM scheme and output voltage
11
2.3
LOW PASS FILTER OPERATION
The purpose of the low pass filter is to produce an output voltage close to purely AC of desired amplitude. Almost all frequency harmonic will be filtered in this circuit and only fundamental presented. In this part, filter circuit was designed based on the cut-off filter equation, equation 5. 1 2π√LC Where: fsw is a switching frequency. L is an inductor that uses to smooth and reduce the peak the output current. C is a capacitor that uses to hold the output voltage at a constant voltage.
… eqn. 5
12
CHAPTER 3
DESIGN AND IMPLEMENTATION
3.0
INTRODUCTION The central aim of this project was to produce a working – though non-ideal -
product to illustrate that the control principles and theory behind it are sound. With this in mind, the following sections explain the decisions made during the design and implementation, with reference to earlier literature and theory sections.
3.1
SIMULATION STUDY
Pulse PWM signal block
R‐L Load
Figure 7(a): Full-bridge PWM inverter circuit without filter circuit, with R-L load
13
Pulse PWM signal block
L‐C filter and Load
Figure 7(b): Full-bridge PWM inverter circuit with filter circuit, with R-L load
Figure 7 shows the overall simulations blocks using Matlab/Simulink software used in the simulation study.
In this part, two circuits were designed in order to get an
effect or difference implement of filter circuit. In simulation circuit, Pulse PWM signal block was used to control on/off switching state of the MOSFETs. Pulse PWM signal block in simulation circuit was referred as a discrete PWM generator 4 pulses block. This particular pulse PWM signal block will automatically produces unipolar switching technique signals for full bridge with two arms. All set point for the modulation index and frequency are set by a computer through Pulse PWM signal block.
14
The circuit specifications are shown below:
ma = 0.8
Vdc = 300 V
ftri = 7.5 kHz
fref = 50 Hz
Table 3: Specifications of simulation circuit
Based on filter equation that mentioned before, (eqn. 5) the low pass filter was designed in such way that the output voltage waveform of the inverter is sinusoidal. In doing that the value of the first fundamental frequency harmonic that occurred must be defined first. 2
1
… eqn. 6 150
7.5 kHz 50 Hz
Therefore, the switching frequency, fsw is calculated as: 150 x 2 x 50 Hz = 15 kHz
Typically all the filter was designed which will filter at least one fifth of the first frequency harmonic that occurred. Therefore only this particular range of frequency will be displayed at the measurement scope.
The cut-off frequency: fcut-off = 1/5 x 15 kHz = 3 kHz
15
If 1.5 mH of inductor was chosen, then the value of capacitor, C is: 1
3
2π√LC 1
3
2π
1.5mH C
C = 7uF
Power switch device MOSFET is used as a switching device in the Fullbridge inverter circuit. This power switch has the ability to operate at high speed switching. Besides, the MOSFET has a lower switching losses compare to the BJT. The MOSFET turn on/off is simpler than the BJT. All the output signals were displayed out through scope block that connected at desired point.
3.2
EXPERIMENTAL
The inverter consist two parts of circuit which is control circuit and power circuit. In the control circuit, three circuits was constructed. The overall system schematic can be shown in Figure 8: Figure 8(a) shows the overall process design of the Full-bridge PWM inverter.
Figure 8(a): Basic of inverter’s block diagram using unipolar switching
16
Figure 8(b) shows the process design of the control circuit. The higher block is the most important part that must completed first and followed with another part.
PWM CIRCUIT
DEAD TIME CIRCUIT
MOSFET DRIVE CIRCUIT
POWER CIRCUIT Figure 8(b): Flow chart of control circuit design
3.2.1 POWER CIRCUIT
Circuit Description
Figure 9 shows the power circuit diagram of the implemented pulse width modulated (PWM) inverter. The main converter circuit is composed of a Full-bridge inverter and power switches (MOSFETs).
The power MOSFETs are properly
switched to behave as an inverter circuit. The combination of resistor and inductor acts as a load to the PWM converter. The resistor is used to limit the maximum load current. The inductor acts to make the load current constant. The generated inverter output signals depends on the value of input DC voltage, the modulation index and the modulation frequency used in the project.
17
Figure 9: The power circuit
MOSFETS are an intrinsically fast switching device because their operation does not require the injection and removal of excess minority carriers like the BJT. MOSFET type IRFP450 was selected as a power switch in this project. This type of MOSFET is designed to be easily interfaced to 240 Volt logic devices. The IRFP450 is designed for low voltage, high speed switching applications in power supplies, and PWM converters. The ratings of this device are: Maximum Current Rating = 14 Amperes Maximum Voltage Rating = 500 Volts
Figure 10 shows a symbol of IRFP450 power MOSFET.
Figure 10: Symbol of IRFP450 power MOSFET.
18
3.2.2
LC FILTER
Circuit Description The fundamental output voltage frequency in this inverter project is selected to be 50 Hz. The filter inductance, L and capacitance, C are designed and discussed in simulation part. The configuration of the second-order LC filter and load is shown in Figure 11: 1.5 mH
7 uF
LOAD
Figure 11: LC filter & load configuration
3.2.3
CONTROL CIRCUIT
3.2.3.1:
Circuit Description
This part contains a description of the major hardware which was used to control the switches of the DC/AC PWM converter. The control circuit is the main part to control the AC output voltage. Unipolar PWM switching technique was used for this purpose. The circuit combination and operation is discussed in detail in this section.
19
3.2.3.1(a):
PWM CIRCUIT
The PWM circuit was implemented using two units ICL8038 wave generator integrated circuit and one unit LM339 comparator integrated circuit.
3.2.3.1(a-1): Sine Wave Generator Circuit
Figure 12 shows the basic diagram of a sine wave generator circuit that was constructed on the breadboards which produces frequency of 50 Hz. The sine wave output was taken and measured at the point J1 which is at pin number 6 of Ua741 I.C.
Sine wave output before buffer circuit
Sine wave output after buffer circuit
Ramp 1 14 2 13 3 12 4 11 5 10 6 9 7 8
Figure 12: Sine wave generator circuit.
1 8 2 7 3 6 4 5
20
Typically the sine wave output has relatively high output impedance. Hence, a buffer circuit was constructed which is the amplitude can be adjusted by changing the value of variable resistor, Ramp. In this project a simple op-amp follower are used. With a dual supply voltage ±10 V the external capacitor on pin 10 can be shorted to ground to halt the ICL8038 oscillation. Two potentiometers were connected as shown in Figure 13; this configuration allows a typical reduction of sine wave distortion. In this case, 100 kΩ was used therefore more reduction distortion can be made.
Potentiometers
Figure 13: Connection to achieve minimum sine wave distortion
For implementation part, ICL8038 waveform generator integrated circuit was chosen. This generator I.C is capable producing high accuracy sine and triangular waveform with a minimum of external component. Beside that, this device is stable over a wide range of temperature and supply. The frequency of this generator also can be selected externally from 0.001 Hz to more than 300 kHz. Therefore is very suitable with this project which is involving variation of frequency and input voltage,VDC.
21
Figure 14 shows the top view of ICL8038 waveform generator integrated circuit.
Figure 14: Top view of ICL8038 waveform generator integrated circuit. The symmetry of all waveforms can be adjusted with the external timing resistors. Two possible ways to accomplish this are shown in Figure 15. Best results are obtained by keeping the timing resistors RA and RB separately. RA controls the rising portion of the triangle and sine wave.
Figure 15: Two possible connections for the external timing resistors.
The magnitude of the triangle waveform is set at 1/3 of supply voltage; therefore the rising portion of the triangle is:
1
C V I
C 0.33 Vsupply R A 0.228Vsupply
RA x C 0.66
… eqn. 5
22
The falling portion of the triangle and sine wave is:
2
C V I
C 0.33 Vsupply Vsupply Vsupply 2 0.22 2 0.22 RB RA RA RB C 0.66 R B R A
… eqn. 6
The rising portion, t1 and falling portion, t2 of the triangle and sine wave is given in Figure 16: Voltage
Time t1
t2
Figure 16: Rising portion, t1 and falling portion, t2
The frequency is given by: 1
1 t1
t2
RA C 1 0.66
RB
2R A
… eqn. 7 RB
Or if RA = RB = R 0.33 RC
… eqn. 8
23
Mathematical equation of this project: Frequency 0.33 30 kΩ 220 nF
50 Amplitude 2.2 4.4
0.22x 10 V 2.2 V x 2
3.2.3.1(a-2): Triangular Wave Generator Circuit Figure 17 shows the basic diagram of a triangular wave generator circuit that was constructed on the breadboards which is produces frequency at 10 kHz. Triangular waveform signal was taken at pin number 7or 6 of TL082 integrated circuit.
Triangular wave output before buffer circuit
1 14 2 13 3 12 4 11 5 10 6 9 7 8
1 8 2 7 3 6 4 5
Figure 17: Triangular wave generator circuit
Triangular wave output after buffer circuit
24
In this case, a different integrated circuit but same type as sine wave generator was used with a few modifications. TL082 I.C was used as a buffer circuit in order to stabilize the output waveform of the triangular waveform.
Mathematical equation of this project: Frequency 0.33 20 kΩ 1.65 nF
10 Amplitude 3.3 6.6
0.33 x 10 V 3.3 V x 2
Figure 18 shows the basic diagram of a buffer circuit using TL082 I.C. Triangular wave output after buffer circuit
Figure 18: TL082 as a buffer circuit
25
TL082 is a general purpose JFET-input operational amplifier integrated circuit.
It
has function as buffer which mean it provide isolation between load and input signal by using a stage having unity voltage gain, with no phase or polarity inversion and acting as ideal circuit that have high input impedance. The Figure 19 shows the top view of TL082 integrated circuit.
Figure 19: Top view of TL082 integrated circuit
3.2.3.1(a-3): Inverter Amplifier Circuit
In PWM circuit, two sine waves are needed which have a difference’s angle at 180 degree respectively. Hence one of the sine wave’s sources must be inverted before comparison between sine wave and triangular wave can be made. Inverting amplifier circuit is given in Figure 20.
Figure 20: The Inverter amplifier circuit
The
26
Ua741 op-amp is the main component uses to construct the inverting amplifier circuit. Figure 21(a) shows a basic inverting circuit using Ua741 op-amp integrated circuit while Figure 21(b) shows the top view of Ua741 op-amp integrated circuit.
Figure 21(a): Basic inverting circuit
Figure 21(b): Top view of Ua741 opamp integrated circuit
The voltage gain for the inverting configuration is set by the ratio of the feedback resistors, Rf and the input resistor, RI and not by the internal gain of the op-amp itself. It can even be less than one, but cannot exceed the op-amp's inherent gain and should not produce such large outputs that distortion results. In this part the inverted sine wave are need with same amplitude, therefore Rf must be same with Ri. 10 kΩ for both resistors side are used. The inverted amplitude gain can be expressed as equation 9:
… eqn. 9
Mathematical equation of this project: 10 kΩ 10 kΩ
27
3.2.3.1(a-3): Comparator Circuit.
A simple comparator circuit is shown in Figure 22. This particular circuit generated two pulses which have a difference angle, difference amplitude’s voltage and condition along the signal.
1 14 2 13 3 12 4 11 5 10 6 9 7 8
Figure 22: The Comparator circuit
LM339 integrated circuit is the main component used in the comparator circuit. LM339 compares two waves which is sine wave or negative sine wave as a reference signal and triangular wave as a carrier signal. The Figure 23 shows internal circuitry of LM339 integrated circuit.
Figure 23: Internal circuitry of LM339 integrated circuit
28
The LM339 series consists of four independent precision voltage comparators with an offset voltage specification as low comparators.
as
2
mV
max
for
all
four
These were designed specifically to operate from a single power
supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage. These comparators also have unique characteristic in that the input common-mode voltage range includes ground, even though operated from a single power supply voltage.
3.2.3.1(b):
Dead Time Circuit
The switching power devices in the PWM inverter have very fast switching frequency which is above sevens of kilohertz. Hence the dead time is necessary to prevent the short circuit of the power supply in the inverter leg of Full-bridge circuit of the pulse width modulated (PWM) voltage inverters results in output voltage deviations. The dead-time circuit delays the rising pulse edge by a fixed amount of time. In other words it delays the PWM pulse to turn-on signal of the power transistor. Although individually small, when accumulated over an operating cycle, the voltage deviations are sufficient to distort the applied PWM signal.
29
The dead time circuit configuration is shown in Figure 24. The circled area shows the main part to change the rising pulse edge.
Figure 24: Dead time circuit
There are two main components was used within the dead time circuit. The first component is the IC7408. The Figure 25(a) shows pin configuration of the IC7408 while Figure 25(b) shows a logic diagram of IC7408.
Figure 25(a): Pin configuration of the
Figure 25(b): Logic diagram of
IC7408
IC7408
30
IC7408 is used in order to generate logic pulse switching signal for each MOSFET. All the PWM signals are compared with 5V in order to produce logic pulses which have same range of amplitude value and stable. The logic function table is shown in Table 4: INPUT
INPUT
OUTPUT
Dna
Dnb
Qn
L
L
L
L
H
L
H
L
L
H
H
H
Table 4: Logic function of IC7408 Where: H = high voltage level between 2 until 7 V L= low level voltage -0.5 until 0.8 V
IC7414 is the second of main component that was used in the dead time circuit. The main function of IC7414 is inverting the logic pulse signals.
This function is
similarly with get not logic. The Figure 26(a) shows pin configuration of the IC7414 while Figure 26(b) shows a logic diagram of IC7414.
Figure 26(a): Pin configuration of the Figure 26(b): Logic diagram of IC7414 IC7414
31
3.2.3.1(c):
MOSFET Drive Circuit
Figure 27 shows the MOSFET drive circuit using HCPL3150 integrated circuit. The signal from dead time circuit (S1, S2, S3, S4) injected to this particular MOSFET drive circuit and produced pulse signals, (MS1, MS2, MS3, MS4) that used to triggered the power switch MOSFETs.
1 8 2 7 3 6 4 5
Figure 27: The MOSFET drive circuit
The power transistors used as switch that on and off in power inverter circuit therefore required an appropriate gate voltage or base current signal to drive the transistor into saturation mode for low on-state voltage in order to switch it on. The control voltage (VGS) should be applied between the gate and source terminal or between the base and emitter terminals. Therefore MOSFET drive circuit is needed to use as an isolation between low-level logic gate driver and high level power circuit. This circuit will protect low level power from short circuit and overcurrent that might be happened in power circuit. In this project, MOSFET gate driver HCPL3150 is used because it can provide isolation and gate driver functions at the same time.
32
CHAPTER 4
SIMULATION RESULTS AND DISCUSSION
4.1
SIMULATION RESULTS
4.1.1: Inverter Circuit Case 1 (without filter circuit):
For the first simulation, unfiltered
circuit from Figure 28 was analyzed. A transient analysis is performed to examine the gate pulse waveforms, the output waveforms and harmonic spectrum. All the outcomes result are shown in the follows figures. In this simulation, the load is a 1 Ohm resistor connected with a 5 mH inductor in series. Modulation index, ma and modulation ratio, mf are 0.8 and 150 for this project. This circuit was supplied by 300 Vdc. Triangular wave and sine wave frequency was set to 7.5 kHz and 50 Hz by a computer through Pulse PWM signal block.
output waveforms
Pulse switching waveform Total harmonic distortions
Figure 28: Full-bridge PWM inverter circuit without filter circuit, with R-L load
33
All the output waveforms are displayed at scope 2 in this simulation circuit. The waveform of load current and load voltage are shown in Figure 29 and Figure 30. The resulted fundamental load voltage is about 300 V (rms) while the load current is about 130 A.
Figure 29: Output load current waveform Where: Axis Y =50 A/Div Axis X = 0.01s/Div
34
Figure 30: Output load voltage waveform Where: Axis Y =10 V/Div Axis X = 0.01s/Div
35
Total harmonic distortions in Fast Fourier Transform are represented in Figure 31. This result was carried out by using powergui block that already provided in this Matlab/Simulink software.
Figure 31: Total harmonic distortions in Fast Fourier Transform As shown in Figure 31, the fundamental frequency was occurred at 50 Hz while the first fundamental frequency harmonic occurred at 15 kHz and followed by second frequency at 30 kHz. Based on equation 6, mf in this project is equal to 150.
36
By using total harmonic distortion block, the total harmonic distortions for this project was measured and carried out through by scope. Figure 32 represented the total harmonic distortions waveform. The output value of total harmonic distortions is almost 0.8 for this project.
Figure 32: Total harmonic distortions waveform. Where: Axis Y =1 unit/Div Axis X = 0.002s/Div
37
Figure 33 shows the each control signal which is taken out by scope 5.
The four
traces from the top to below are switching waveforms for S1, S2, S3 and S4.
S1
S2
S3
S4
Figure 33: Pulse switching waveform Where: Axis Y =5 V/Div Axis X = 0.0005s/Div
38
4.1.2: Inverter Circuit with Filter Circuit
Case 2:
This experiment was repeated which used low pass filter circuit. The
values of parameter are fixed. The simulation circuit for this project is given in Figure 34.
output waveforms
Pulse switching waveform
Total harmonic distortions
Figure 34: Full-bridge PWM inverter circuit with filter circuit, with R-L load
All the output waveforms are displayed at scope 2 in this simulation circuit. The load current and load voltage value are shown in Figure 35 and Figure 36 which give a peak load current of 105 A and peak load voltage value of 200 V.
39
Figure 35: Load current waveform Where: Axis Y =50 A/Div Axis X = 0.01s/Div
Figure 36: Load voltage waveform Where: Axis Y =10 V/Div Axis X = 0.01s/Div
40
Total harmonic distortions in Fast Fourier Transform are represented in Figure 37. This result was carried out by using powergui block that already provided in this Matlab/Simulink software.
Figure 37: Total harmonic distortions in Fast Fourier Transform As shown in Figure 37, the fundamental frequency was occurred at 50 Hz while the first fundamental frequency harmonic occurred at 15 kHz and followed by second frequency at 30 kHz. Based on equation 6, mf in this project is equal to 150.
41
By using total harmonic distortion block, the total harmonic distortions for this project was measured and carried out through by scope. Figure 38 represented the total harmonic distortions waveform. The output value of total harmonic distortions is almost 0.2 for this project.
Figure 38: Total harmonic distortions in Fast Fourier Transform Where: Axis Y =1 unit/Div Axis X = 0.002s/Div
42
Figure 39 shows the each control signal which is taken out by scope 5.
The four
traces from the top to below are switching waveforms for s1, s2, s3 and s4.
S1
S2
S3
S4
Figure 39: Pulse waveform Where: Axis Y =5 V/Div Axis X = 0.0005s/Div
4.1.3: Changes of Modulation Frequency In this experiment, frequency carrier was varied to 20 kHz in order to change the value of modulation frequency to become 400. Other parameters are fixed. Figure 40 shows an unfiltered total harmonic distortions output in Fast Fourier transform. The first fundamental frequency harmonic was occurred at 40 kHz and followed by second frequency at 80 kHz. The value of total harmonic distortions for this project is equal to 69.76%.
43
Figure 40: (unfiltered circuit) Total harmonic distortions in Fast Fourier Transform Figure 41 shows the filtered total harmonic distortions output in Fast Fourier transform. All the fundamental frequency harmonics was erased. Only fundamental frequency was displayed. The value of total harmonic distortions is decreased to 19.51%
Figure 41: (filtered circuit) Total harmonic distortions in Fast Fourier Transform
44
4.1.4: Changes of Modulation Index In this experiment, only modulation index, ma for inverter circuit using filter was changed. Figure 42 shows the total harmonic distortion when modulation index was increased from 0.8 to 0.9.
The first harmonic frequency was occurred at 15 kHz with
amplitude value is equal to 1.95%.
Figure 42: Total harmonic distortions in Fast Fourier Transform with ma = 0.9
45
Figure 43 shows the total harmonic distortion when modulation index was decreased from 0.8 to 0.5.
The first harmonic frequency was occurred at 15 kHz with
amplitude value is increased to 2.16%
Figure 43: Total harmonic distortions in Fast Fourier Transform with ma = 0.5
46
4.2
DISCUSSION
4.2.a: Inverter Circuit Case1 and 2: In this case the slope load current waveforms for the both circuits are same in term of pattern and value but opposite for the load voltage waveform. The first harmonic cluster for both experiments was occurred at high order frequency which is 15 kHz. After the connection low pass filter circuit, AC voltage output waveform become smooth and fewer ripples produced at the voltage output waveform. This is because most of the harmonic components filter out effectively by LC filter. From the Figure 36, we can see that load output waveform is exactly at the expected output frequency 50 Hz and the peak output voltage is about 200 Vrms, which approximates the theoretical calculation. Some voltage losses may be caused by the turn-on voltage drops of the MOSFETs. Beside that, the harmonic was eliminated and the value of THD voltage is decreasing from 76.12% to 1.43%. The pulse signal waveforms are same for the both cases. Its show that, the additional filter circuit didn’t give any effect to the switching signal.
4.2.b: Changes of Modulation Frequency For this case, the first harmonic occurred at the higher frequency compared to the previous one which is 4 kHz. When filter circuit was connected, the harmonics was eliminated totally. Therefore the load voltage waveform becomes smoother and less ripple. From this observation, it can be said that the changes of modulation frequency will effect the location of first harmonic frequency.
47
4.2.C: Changes of Modulation Index In this part, the variation of modulation index, ma give the significant impact to the output voltage, where when modulation index increases the value of voltage output also increases. This condition only valid when modulation index, ma ≤ 1. Beside that, total harmonic distortions also decreases when modulation index is increase
48
CHAPTER 5
EXPERIMENTAL RESULTS AND DISCUSSION
5.1
EXPERIMENTAL RESULTS The system outlined in the previous chapter was implemented and tested on
breadboard. All the following results are shown as below. Figure 44 shows the basic diagram of a sine wave generator circuit that was constructed in this project.
1 14 2 13 3 12 4 11 5 10 6 9 7 8
Figure 44: Sine wave generator circuit.
1 8 2 7 3 6 4 5
49
Figure 45 shows the sine output waveform before buffer. This measurement was taken at pin 2 of ICL8038 waveform generator I.C.
Figure 45: Sine output waveform before buffer circuit The plot shows that the amplitude of the sine wave signal is 3.3 V at frequency almost 50 Hz. The voltage value from peak to peak for this signal is about 3.9 V
50
Figure 46 shows the output of the sign wave signal after passing through the buffer circuit. The amplitude value of the sine wave signal was increased to 5.64 V at frequency almost 50 Hz. This sine wave output was taken and measured at the point J1 which is at pin number 6 of Ua741 I.C.
Figure 46: Sine output waveform after buffer circuit
Figure 47 shows a basic inverting circuit that used in this project in order to produced inverted sine wave signal.
Figure 47: The Inverter amplifier circuit
51
Figure 48 shows the difference between the sine wave signal and inverted sine wave signal which is taken after passing trough the buffer circuit.
Figure 48: Sine output waveform and inverted sine output waveform The plot shows that both signals have a same amplitude value which is 5.68 V at same frequency which is almost at 50 Hz. These two signals only have 180 degree phase shift different.
52
Figure 49 shows the triangular output waveform that produced by circuit in Figure 18 after passing through the buffer circuit.
Figure 49: Triangular output waveform The plot shows that the amplitude value of triangular wave signal is 6.2 V at frequency almost 9 kHz. The peak to peak voltage for this signal is about 6.92 V
53
Figure 50 shows the comparator circuit that used to produce PWM waveform.
1 14 2 13 3 12 4 11 5 10 6 9 7 8
Figure 50: Comparator circuit.
Figure 51 shows the output signal when sine wave has been compared to triangular wave. This output result can be taken at pin number 1 or 14 of LM339 I.C.
Figure 51: PWM waveform The plot shows that positive 20 V was produced at positive cycle while negative 20 V was produced at negative cycle along the sine wave signal
54
Figure 52 shows PWM1 and PWM2 signals. PWM1 was produced by comparing sine wave signal with triangular wave signal while PWM2 was produced by comparing inverted sine wave signal with triangular wave signal. These pulses have phase shift different which is about 180 degree and frequency where PWM1 was produced at frequency 3.12 kHz while PWM2 at frequency 5.3 kHz.
Figure 52: PWM waveform
55
This logic pulse waveform was taken out from Figure 33 circuit which is at dead time circuit output. This pulse signals was referred as S1, S2, S3 and S4. The Figure 53 shows logic pulse signal for S1 and S2.
S1
S2
Figure 53: Logic pulse waveform The plot shows the both signals, S1 and S2 have 180 degree phase shift different. These pulses have a same amplitude value which is 5V and also frequency which is 50 Hz.
56
5.2
DISCUSSION
After sine wave output passed trough the buffer circuit the amplitude becomes higher but same frequency, 50 Hz. The inverter circuit angle was shifted at 180 degree while the amplitude and the frequency are still the same. All the pulse signals have different amplitude. For example, PWM waveform has 20 V peak amplitude compare to logic pulse waveform, 5 V. These because all this values must be follow the specifications of their circuit. Amplitude value of PWM waveform must be step down to 5 V in order to produce logic pulse waveform because the IC that used within the dead time circuit can only be operate in 5 V. Then the signal will be step-up to 15 V at the MOSFET driver circuit in order to trigger the MOSFET.
57
CHAPTER 6
CONCLUSION AND RECOMMENDATION
6.1
CONCLUSION
6.1.a
Conclusion for simulation result:
As conclusion, the objectives for this part have been achieved. A simulation model of a unipolar single phase PWM inverter was successfully designed and tested. A complete results from simulation was obtained and most of the results are verified the theoretical value.
6.1.b
Conclusion for experimental result: The final results weren’t as successful as originally planned because
there are
some areas facing design difficulties and only certain part of the
hardware project are successful.
Therefore no comparison between simulation
voltage output and hardware output can be made. However, these experiment results are quite close to the previous theoretical calculation and simulation results. If the times are permitted, there should be more interesting outcome from the project.
6.2
RECOMMENDATION
1. There are other methods of inverters which is better then PWM unipolar switches that was used in this project. This method is produce a fewer ripples at the output. For example by using: a) High-speed microcontroller of microprocessor or Digital Signal Processors (DSP) that can generate the PWM which is more flexible.
58
Beside that, source of modulation that produced is more stable and free from problem of drift. Hence more accurate results will be produces in the experimental part.
This implementation can be made by using
TMS320F2812 DSP which is generally used to satisfies the control requirement of the high switching frequency PWM schemes.
This
particular device generates the PWM signals and also provides soft start function. b) Inverted sine carrier PWM (ISCPWM) method, which uses the conventional sinusoidal reference signal and an inverted sine carrier. This method has a better spectral quality and a higher fundamental component compared to the conventional sinusoidal PWM (SPWM) without any pulse dropping. The ISCPWM strategy enhances the fundamental output voltage particularly at lower modulation index ranges while keeping the total harmonic distortion (THD) lower without involving changes in device switching losses. 2. The disadvantage of using high switching frequencies is higher losses in the switches which is used to implement the inverter. Hence, it is recommended to avoid from using a large modulation ratio for this project.
59
REFERENCES
BOOKS: 1.
“Implementation of a Single-phase Unipolar Inverter Using DSP TMS320F241”, Narong Aphiratsakun, Sanjiva Rao Bhaganagarapu and Kittiphan Techakittiroj, Faculty of Engineering, Assumption University Bangkok, Thailand, 2005
2. “Analysis, Simulation And Dsp Based Implementation Of Asymmetric Three-Level Single-Phase Inverter In Solar Power System”, Yi Tian, The Florida State University Famu-Fsu College Of Engineering, 2007 3. “Introduction to power Electronic,” published by Prentice-Hall International, INC, Daniel W. Hart, Valparaiso University, 1999
60
APPENDIX
1.
(a)
(c)
(b)
(d)
Figure 35: Laboratory unipolar inverter board (a) gate drive circuit (b) dead time circuit (c) sine wave generator circuit (d) triangular wave generator circuit
61
2. Datasheet of ICL8038
62
63
64
65
66
67
68
69
70
71
72
73
3. Datasheet of IRFP450 power MOSFET
74
75
76
77
78
79
UNIVERSITI TEKNOLOGI MALAYSIA DECLARATION OF THESIS / UNDERGRADUATE PROJECT PAPER AND COPYRIGHT
Author’s full name :
MUHAMMAD NASRUL BIN AZMAN
Date of birth
:
18 JANUARY 1986
Title
:
SINGLE PHASE PWM INVERTER (DC TO AC) USING UNIPOLAR SWITCHING TECHNIQUE
Academic Session:
2008/2009 - 2
I declare that this thesis is classified as :
√
CONFIDENTIAL
(Contains confidential information under the Official Secret Act 1972)*
RESTRICTED
(Contains restricted information as specified by the organisation where research was done)*
OPEN ACCESS
I agree that my thesis to be published as online open access (full text)
I acknowledged that Universiti Teknologi Malaysia reserves the right as follows : 1. The thesis is the property of Universiti Teknologi Malaysia. 2. The Library of Universiti Teknologi Malaysia has the right to make copies for the purpose of research only. 3. The Library has the right to make copies of the thesis for academic exchange. Certified by:
SIGNATURE
860118-11-5437
DR. AWANG B. JUSOH
(NEW IC NO. /PASSPORT NO.)
NAME OF SUPERVISOR
Date : 13 MAY 2009
NOTES :
SIGNATURE OF SUPERVISOR
*
Date : 13 MAY 2009
If the thesis is CONFIDENTIAL or RESTRICTED, please attach with the letter from the organisation with period and reasons for confidentiality or restriction.
“I declared that I have read this work and in my opinion this work is adequate in term of scope and quality for the purpose of awarding a Bachelor’s Degree of Electrical Engineering (Power)”
Signature
: …………………………….
Name of supervisor
: DR. AWANG BIN JUSOH
Date
: 14 MAY 2009
SINGLE PHASE PWM INVERTER (DC TO AC) USING UNIPOLAR SWITCHING TECHNIQUE
MUHAMMAD NASRUL BIN AZMAN
Submitted to the Faculty of Electrical Engineering in partial fulfillment of the requirement for the degree of Bachelor in Electrical Engineering (Power)
Faculty of Electrical Engineering Universiti Teknologi Malaysia
MAY 2009
i
DECLARATION
I declared that this work as the product of my own effort with the exception of excerpt cited from others works of which the sources were duly noted
Signature
:
…………………………………………...
Author’s name
:
MUHAMMAD NASRUL BIN AZMAN
Date
:
MAY 2009
ii
Specially dedicated to
my beloved father, Johari Bin Abdullah my beloved mother, Zunaidah Binti Ya also my elder brothers and my sisters
iii
ACKNOWLEDGEMENTS
The author wishes to acknowledge the guidance and assistance of all those who aided in the development and implementation of this thesis. I must express my gratitude and thanks to my supervisor, Dr. Awang Bin Jusoh for his valuable guidance and encouragement throughout the year – which somehow always seemed to happen just when I needed it. I would also like to thank my fellow students for their assistance when it was required and all of those involved in my life outside my thesis for putting up with me. Most importantly, I would like to thank my family for their continuous support throughout my graduate school experience.
iv
ABSTRACT
This thesis document outlines the research, design and implementation of a single-phase inverter that produces a symmetric AC output voltage of desired magnitude and frequency. In this project the inverter output frequency of 50 Hz was used in order to meet all the objectives of this project. Unipolar PWM switching technique is employed to control the output voltage magnitude and frequency. The waveform generator integrated circuit of Intersil, ICL8038 and power switch MOSFET are two main components used for the implementation of the inverter. There are two parts of study in this project which is simulation and experimental part.
v
ABSTRAK
Tesis ini menggariskan tentang kajian, reka bentuk dan pelaksanaan penyongsang satu fasa yang menghasilkan voltan keluaran AC simentri mengikut nilai dan frekuensi yang diingini. Di dalam projek ini, frekuensi keluaran penyongsang 50 Hz telah digunakan bagi mencapai kesemua objektif projek. Kaedah permodulatan lebar denyut (PLD) menggunakan teknik pensuisan uni-kutub digunakan untuk mengawal nilai voltan keluaran dan frekuensi. Litar bersepadu penjana gelombang, ICL8038 dan peranti kuasa MOSFET adalah merupakan dua komponen utama yang digunakan di dalam projek ini. Terdapat dua bahagian kajian yang dijalankan didalam projek ini iaitu bahagian simulasi dan bahagian eksperimen.
vi
TABLE OF CONTENTS
CHAPTER
CHAPTER 1
CHAPTER 2
TITLE
PAGE
DECLARATION
i
DEDICATION
ii
ACKNOWLEDGEMENT
iii
ABSTRACT
iv
ABSTRAK
v
TABLE OF CONTENTS
vi
LIST OF TABLES
ix
LIST OF FIGURES
x
LIST OF SYMBOLS
xiii
LIST OF APPENDICES
xiv
INTRODUCTION 1.1
General introduction
1
1.2
Project objective
2
1.3
Scope
2
1.4
Project methodology
3
1.4(a) Simulation part
3
1.4(b) Experimental part
4
1.5
5
Project schedules
BASIC CONCEPT AND LITERATURE REVIEW 2.1 Introduction of PWM single phase inverter
7
2.2 PWM operation
9
vii
2.3 Low pass filter operation
CHAPTER 3
CHAPTER 4
CHAPTER 5
11
DESIGN AND IMPLEMENTATION 3.0
Introduction
12
3.1
Simulation study
12
3.2
Experimental
15
3.2.1
Power circuit
16
3.2.2 0
LC filter
18
3.2.3
Control circuit
18
3.2.3.1(a)
PWM circuit
19
3.2.3.1(a-1)
Sine wave generator circuit
19
3.2.3.1(a-2)
Triangular wave generator circuit
23
3.2.3.1(a-3)
Inverter amplifier circuit
25
3.2.3.1(a-3)
Comparator circuit
27
3.2.3.1(b)
Dead time circuit
28
3.2.3.1(c)
MOSFET drive circuit
31
SIMULATION RESULTS AND DISCUSSION 4.1
Simulation results
32
4.1.1
Inverter circuit without filter circuit
32
4.1.2
Inverter circuit with filter circuit
38
4.1.3
Changes of modulation frequency
42
4.1.4
Changes of modulation index
44
4.2
Discussion
46
4.2.a
Inverter circuit
46
4.2.b
Changes of modulation frequency
46
4.2.c
Changes of modulation index
47
EXPERIMENTAL RESULTS AND DISCUSSION 5.1 Experimental results
48
5.2 Discussion
56
viii
CHAPTER 6
CONCLUSION AND RECOMMENDATION
57
REFERENCES
59
APPENDIX
60
ix
LIST OF TABLES
TABLE
TITLE
PAGE
NO. 1
Schedule PSM1
5
2
Schedule PSM2
6
3
Specifications of simulation circuit
14
4
Logic functions of IC7408
30
x
LIST OF FIGURES
FIGURE
TITLE
PAGE
NO. 1
H-bridge inverter
1
2
Flow chart for simulation process
4
3
Flow chart for experimental process
4
4
Description of SPWM modulation
7
5
Basic of single phase inverter
9
6
Unipolar PWM scheme and output voltage
10
7(a)
Full-bridge PWM inverter circuit without filter circuit, with R-L load Full-bridge PWM inverter circuit with filter circuit, with
12
7(b)
13
R-L load 8(a)
Basic of inverter’s block diagram using unipolar switching
15
8(b)
Flow chart of control circuit design switching
16
9
The power circuit
17
10
Symbol of IRFP450 power MOSFET
17
11
LC filter & load configuration
18
12
Sine wave generator circuit
19
13
Connection to achieve minimum sine wave distortion
20
15
Two possible connections for the external timing resistors.
21
16
Rising portion, t1 and falling portion, t2
22
17
Triangular wave generator circuit
23
18
TL082 as a buffer circuit
24
19
Top view of TL082 integrated circuit
25
20
The Inverter amplifier circuit
25
21(a)
Basic inverting circuit
26
21(b)
Top view of Ua741 op-amp integrated circuit
26
22
The Comparator circuit
27
xi
23
Internal circuitry of LM339 integrated circuit
27
24
Dead time circuit
29
25(a)
Pin configuration of the IC7408
29
25(b)
Logic diagram of IC7408
29
26(a)
Pin configuration of the IC7414
30
26(b)
Logic diagram of IC7414
30
27
The MOSFET drive circuit
31
28
Full-bridge PWM inverter circuit without filter circuit,
32
with R-L load 29
Output load current waveform
33
30
Output load voltage waveform
34
31
Total harmonic distortions in Fast Fourier Transform
35
32
Total harmonic distortions wave form
36
33
Pulse waveform
37
34
Full-bridge PWM inverter circuit with filter circuit, with
38
R-L load 35
Load current waveform
39
36
Load voltage waveform
39
37
Total harmonic distortions in Fast Fourier Transform
40
38
Total harmonic distortions in Fast Fourier Transform
41
39
Pulse waveform
42
40
Total harmonic distortions in Fast Fourier Transform
43
(unfiltered circuit) 41
Total harmonic distortions in Fast Fourier Transform
43
(filtered circuit) 42
Total harmonic distortions in Fast Fourier Transform with
44
ma = 0.9 43
Total harmonic distortions in Fast Fourier Transform with
45
ma = 0.5 44
Sine wave generator circuit
48
45
Sine output waveform before buffer circuit
49
46
Sine output waveform after buffer circuit
50
47
The Inverter amplifier circuit
50
xii
48
Sine output waveform and inverted sine output waveform
51
49
Triangular output waveform
52
50
Comparator circuit.
53
51
PWM waveform
53
52
PWM waveform
54
53
logic pulse waveform
55
54
Laboratory unipolar inverter board
60
xiii
LIST OF SYMBOLS
THD
- Total Harmonic distortion
PWM
- Pulse width modulation
AC
- Alternating current
DC
- Direct current
S
- Switch
L
- Inductor
C
- Capacitor
SPWM
- Sinusoidal Pulse width modulation
fsw
- Switching frequency
mf
- Frequency modulation ratio
ma
- Amplitude modulation ratio
V1
- Fundamental voltage
Vtri
- Triangular Switching Waveform
Vref
- Sinusoidal reference signals
Eqn
- Equation
I.C
- Integrated circuit
xiv
LIST OF APPENDICES
NO.
TITLE
1
Figures of laboratory unipolar inverter board
2
Datasheet of ICL8038
3
Datasheet of IRFP450 power MOSFET
1
CHAPTER 1
INTRODUCTION
1.1
GENERAL INTRODUCTION
Nowadays, switching-mode single-phase DC-AC inverter have been widely used in many application such as ac motor, induction heating, standby power supplies, uninterruptible power supplies (UPS) and so on. Among various control technique, pulse-width modulation (PWM) is the most effective used to regulate the magnitude as well as frequency of the converter’s output voltage. This particular control technique also can reduce the total harmonic distortion easily while varying the output voltage and have been gone through in many revisions. A block diagram representation of a single-phase H-bridge inverter is given in Figure1:
+
‐ Vout
Figure 1: H-bridge inverter.
2
The H-bridge topology inverter is the most popular single-phase converter in various applications, especially in higher power rating applications.
It consists of
two arms and outputs a single-phase AC output voltage, Vout to the load. There are four switching devices that represented as ideal switches (BJTs or MOSFETs). Each switch was connected in the form of a full bridge. Then a pulse width modulation, PWM signal from control circuitry was injected to the each switching devices along with the inverted signal to produce an AC output voltage, Vout with variable frequency and amplitude. PWM techniques are used to control the switching devices on and off. PWM control is a comparison of the output waveform to a reference signal and adjusts the duty cycle of the switching mechanism. Compared to the square-wave method of control, PWM has two distinct advantages which is higher frequency harmonic content and amplitude control.
The filtering requirements for PWM generated
outputs are less stringent since the non-fundamental components are of much higher frequency than that of the fundamental sine wave.
1.2
PROJECT OBJECTIVE
The objective of this project is to design and construct a single-phase PWM inverter circuit with unipolar switching technique which can produce a symmetric AC output voltage of desired magnitude and frequency. All the outcome results between simulations and experimental results are compared to verify the effectiveness of the designed inverter.
1.3
SCOPE
After intensively reviewed on the single-phase unipolar inverter, there are many issues need to be tackled in order to achieve a preliminary objective. The scopes of this thesis are used for the guideline of the project. The project scopes are as follows:
3
•
Read all significant references and analyse the literature reviews about the operation of waveform generator, the operation of pulse-width modulation, dead time circuit, driver circuit and power circuit.
•
Design a simulation circuit by using MATLAB/SIMULINK software part by part according to the theories and methods that gain from the literature review. Then simulate and analyses the output waveforms.
•
Construct the circuit on breadboard based on collected data from simulation part and literature reviews.
1.4
PROJECT METHODOLOGY
The procedure of the analysis is the important factor to ensure that the project is completely done as expected, because it is necessary to have an efficient plan and it will help to guide into the target to achieve the objective. There are two parts of study in this project.
The first part is simulation part and the second part is
experimental part.
1.4(a) Simulation Part
The important thing in this part is modeling and simulation of single phase PWM inverter. In this part, Matlab/Simulink software with the SimPowerSystems Block Set was used to model a single phase inverter circuit. This software was chosen because of its simplicity and user-friendly environment for analysis and design.
4
The flow of project methodology is shown as Figure 2:
1 2 3 4 5
• FINDING THE REFERENCE
• BUILD SIMULATION CIRCUIT
• SIMULATE • SUCCES: TAKE A OUTPUT RESULT • NO: MODIFY THE CIRCUIT • DONE: GO TO THE NEXT PART
Figure 2: Flow chart for simulation process
1.4(b) Experimental Part
This part is implemented to verify all the simulation part in previous topics. The flow of project methodology is shown in Figure 3:
1 2 3 4 5
• DESIGN CIRCUIT • DATASHEET COMPONENT • CIRCUIT ON BREADBOARD • YES: GET A RESULT AND COMPARE • NO: TROUBLESHOOT • DONE
Figure 3: Flow chart for experimental process
5
After both are completed, the comparison results between these two parts were carried out in order to achieve the final objective of this project.
1.5
PROJECT SCHEDULES
The Gantt chart below shows overall activities that have been done during the project time. This Gantt chart consist two parts which is PSM1 and PSM2.
Table 1 summarizes the activities for PSM 1. In this table all the activities are focus on study and design a single-phase PWM inverter.
Design modification
Table 1: Schedule PSM1
6
Table 2 shows the schedule of activities for PSM 2. In this table all the activities are focus on implementation of the single-phase PWM inverter. NO
IMPLEMENTATION
1
Order the component s
2
Implementation PWM circuit
3
Implementation Comparator circuit
4
Implementation MOSFET Drive circuit
5
presentation
6
Modify
7
Submit report
1
2
3
4
5
6
Table 2: Schedule PSM2
7
8
9
10
11
12
13
7
CHAPTER 2
BASIC CONCEPT AND LITERATURE REVIEW
2.1
INTRODUCTION OF PWM SINGLE PHASE INVERTER
An inverter is an electrical or electro-mechanical device that converts direct current (dc) to alternating current (AC). In the unipolar switching scheme, the output voltage are varies between positive and zero and negative voltage levels. The rms value of the output voltage vary depend on changes of input DC voltage and/or modulation index, ma. The modulation index is a ratio between the amplitude of sinusoidal reference signals (Vref) with the triangular waveform (Vtri) as shown in Figure 4 (a):
Vref
Vtri
Figure 4: Description of SPWM modulation As show in Figure 4(b), when Vref is greater than Vtri, the PWM output is positive; otherwise the PWM output is negative. The frequency of triangular waveform, Vtri establishes the switching frequency, fsw of the inverter.
8
The modulation index, ma is defined as: Vref Vtri
… eqn. 1
And the modulation ratio is defined as: ftri fref
… eqn. 2
This is significant in the case of an unregulated DC supply voltage because the value of ma can be adjusted to compensate for variation in the DC supply, producing a constant-amplitude output. If
1, amplitude of the fundamental frequency of
the inverter output voltage,V1 is linearly proportional to
, otherwise it becoming
not linear. This not linear phenomenon is called over modulation. The quality of the inverter output waveform can be expressed by using the Fourier analysis data to calculate the total harmonic distortion (THD) of load current. The quality of output waveform that is needed from an inverter depends on the characteristics of the connected load. Some loads need a nearly perfect sine wave voltage supply in order to work properly. Other loads may work quite well with a square wave voltage. The total harmonic distortion (THD) for the inverter output current can expressed as: ∑
In rms I1 rms
… eqn. 3
Where: In = harmonic current I1 = fundamental output current. The THD for the inverter output voltage is determined by substituting current in the preceding equation. The inverter output voltage is: ∑
Vrms V1 rms
… eqn. 4
9
Where: Vn = harmonic voltage. V1 = fundamental output voltage. Pulse-width modulation (PWM) switching provides a best ways to decrease the total harmonic distortion, THD. The unfiltered PWM output will have a relatively high THD but the first harmonics will be at higher frequencies compare to the square wave switching frequency, making filter easier.
2.2
PWM OPERATION
The basic single-phase full-bridge PWM inverter is shown in Figure 5:
S1
Leg A
S2
Leg B
S3
S4
Figure 5: Basic of single phase inverter
In the unipolar switching scheme the output voltage changes between positive and zero, or between zero and negative voltage levels whereby S1 and S2 will be given PWM pulses for first (positive) output half cycle and S3 and S4 are gated for the next (negative) half cycle.
10
The (Vref) and (Vtri) for equation 1 is refer to the peak amplitude of the signals. Leg A and B of the full-bridge inverter are controlled separately by comparing (Vref) with (Vtri) and (- Vref) with (Vtri). The resulting waveforms are used to control the switches as follows: In leg A: Vref › Vtri: S1 on and Vref ‹ Vtri: S4 on and In Leg B: -Vref › Vtri: S3 on and -Vref ‹ Vtri: S2 on
The unipolar PWM pulse generation with resulting pattern is represented in Figure 6 in which a triangular carrier wave is compared with sinusoidal reference waveform to generate PWM gating pulses. Vref
Vtri
‐Vref
Pole voltage VAO Pole voltage VBO
Output voltage (VAO – VBO)
Figure 6: Unipolar PWM scheme and output voltage
11
2.3
LOW PASS FILTER OPERATION
The purpose of the low pass filter is to produce an output voltage close to purely AC of desired amplitude. Almost all frequency harmonic will be filtered in this circuit and only fundamental presented. In this part, filter circuit was designed based on the cut-off filter equation, equation 5. 1 2π√LC Where: fsw is a switching frequency. L is an inductor that uses to smooth and reduce the peak the output current. C is a capacitor that uses to hold the output voltage at a constant voltage.
… eqn. 5
12
CHAPTER 3
DESIGN AND IMPLEMENTATION
3.0
INTRODUCTION The central aim of this project was to produce a working – though non-ideal -
product to illustrate that the control principles and theory behind it are sound. With this in mind, the following sections explain the decisions made during the design and implementation, with reference to earlier literature and theory sections.
3.1
SIMULATION STUDY
Pulse PWM signal block
R‐L Load
Figure 7(a): Full-bridge PWM inverter circuit without filter circuit, with R-L load
13
Pulse PWM signal block
L‐C filter and Load
Figure 7(b): Full-bridge PWM inverter circuit with filter circuit, with R-L load
Figure 7 shows the overall simulations blocks using Matlab/Simulink software used in the simulation study.
In this part, two circuits were designed in order to get an
effect or difference implement of filter circuit. In simulation circuit, Pulse PWM signal block was used to control on/off switching state of the MOSFETs. Pulse PWM signal block in simulation circuit was referred as a discrete PWM generator 4 pulses block. This particular pulse PWM signal block will automatically produces unipolar switching technique signals for full bridge with two arms. All set point for the modulation index and frequency are set by a computer through Pulse PWM signal block.
14
The circuit specifications are shown below:
ma = 0.8
Vdc = 300 V
ftri = 7.5 kHz
fref = 50 Hz
Table 3: Specifications of simulation circuit
Based on filter equation that mentioned before, (eqn. 5) the low pass filter was designed in such way that the output voltage waveform of the inverter is sinusoidal. In doing that the value of the first fundamental frequency harmonic that occurred must be defined first. 2
1
… eqn. 6 150
7.5 kHz 50 Hz
Therefore, the switching frequency, fsw is calculated as: 150 x 2 x 50 Hz = 15 kHz
Typically all the filter was designed which will filter at least one fifth of the first frequency harmonic that occurred. Therefore only this particular range of frequency will be displayed at the measurement scope.
The cut-off frequency: fcut-off = 1/5 x 15 kHz = 3 kHz
15
If 1.5 mH of inductor was chosen, then the value of capacitor, C is: 1
3
2π√LC 1
3
2π
1.5mH C
C = 7uF
Power switch device MOSFET is used as a switching device in the Fullbridge inverter circuit. This power switch has the ability to operate at high speed switching. Besides, the MOSFET has a lower switching losses compare to the BJT. The MOSFET turn on/off is simpler than the BJT. All the output signals were displayed out through scope block that connected at desired point.
3.2
EXPERIMENTAL
The inverter consist two parts of circuit which is control circuit and power circuit. In the control circuit, three circuits was constructed. The overall system schematic can be shown in Figure 8: Figure 8(a) shows the overall process design of the Full-bridge PWM inverter.
Figure 8(a): Basic of inverter’s block diagram using unipolar switching
16
Figure 8(b) shows the process design of the control circuit. The higher block is the most important part that must completed first and followed with another part.
PWM CIRCUIT
DEAD TIME CIRCUIT
MOSFET DRIVE CIRCUIT
POWER CIRCUIT Figure 8(b): Flow chart of control circuit design
3.2.1 POWER CIRCUIT
Circuit Description
Figure 9 shows the power circuit diagram of the implemented pulse width modulated (PWM) inverter. The main converter circuit is composed of a Full-bridge inverter and power switches (MOSFETs).
The power MOSFETs are properly
switched to behave as an inverter circuit. The combination of resistor and inductor acts as a load to the PWM converter. The resistor is used to limit the maximum load current. The inductor acts to make the load current constant. The generated inverter output signals depends on the value of input DC voltage, the modulation index and the modulation frequency used in the project.
17
Figure 9: The power circuit
MOSFETS are an intrinsically fast switching device because their operation does not require the injection and removal of excess minority carriers like the BJT. MOSFET type IRFP450 was selected as a power switch in this project. This type of MOSFET is designed to be easily interfaced to 240 Volt logic devices. The IRFP450 is designed for low voltage, high speed switching applications in power supplies, and PWM converters. The ratings of this device are: Maximum Current Rating = 14 Amperes Maximum Voltage Rating = 500 Volts
Figure 10 shows a symbol of IRFP450 power MOSFET.
Figure 10: Symbol of IRFP450 power MOSFET.
18
3.2.2
LC FILTER
Circuit Description The fundamental output voltage frequency in this inverter project is selected to be 50 Hz. The filter inductance, L and capacitance, C are designed and discussed in simulation part. The configuration of the second-order LC filter and load is shown in Figure 11: 1.5 mH
7 uF
LOAD
Figure 11: LC filter & load configuration
3.2.3
CONTROL CIRCUIT
3.2.3.1:
Circuit Description
This part contains a description of the major hardware which was used to control the switches of the DC/AC PWM converter. The control circuit is the main part to control the AC output voltage. Unipolar PWM switching technique was used for this purpose. The circuit combination and operation is discussed in detail in this section.
19
3.2.3.1(a):
PWM CIRCUIT
The PWM circuit was implemented using two units ICL8038 wave generator integrated circuit and one unit LM339 comparator integrated circuit.
3.2.3.1(a-1): Sine Wave Generator Circuit
Figure 12 shows the basic diagram of a sine wave generator circuit that was constructed on the breadboards which produces frequency of 50 Hz. The sine wave output was taken and measured at the point J1 which is at pin number 6 of Ua741 I.C.
Sine wave output before buffer circuit
Sine wave output after buffer circuit
Ramp 1 14 2 13 3 12 4 11 5 10 6 9 7 8
Figure 12: Sine wave generator circuit.
1 8 2 7 3 6 4 5
20
Typically the sine wave output has relatively high output impedance. Hence, a buffer circuit was constructed which is the amplitude can be adjusted by changing the value of variable resistor, Ramp. In this project a simple op-amp follower are used. With a dual supply voltage ±10 V the external capacitor on pin 10 can be shorted to ground to halt the ICL8038 oscillation. Two potentiometers were connected as shown in Figure 13; this configuration allows a typical reduction of sine wave distortion. In this case, 100 kΩ was used therefore more reduction distortion can be made.
Potentiometers
Figure 13: Connection to achieve minimum sine wave distortion
For implementation part, ICL8038 waveform generator integrated circuit was chosen. This generator I.C is capable producing high accuracy sine and triangular waveform with a minimum of external component. Beside that, this device is stable over a wide range of temperature and supply. The frequency of this generator also can be selected externally from 0.001 Hz to more than 300 kHz. Therefore is very suitable with this project which is involving variation of frequency and input voltage,VDC.
21
Figure 14 shows the top view of ICL8038 waveform generator integrated circuit.
Figure 14: Top view of ICL8038 waveform generator integrated circuit. The symmetry of all waveforms can be adjusted with the external timing resistors. Two possible ways to accomplish this are shown in Figure 15. Best results are obtained by keeping the timing resistors RA and RB separately. RA controls the rising portion of the triangle and sine wave.
Figure 15: Two possible connections for the external timing resistors.
The magnitude of the triangle waveform is set at 1/3 of supply voltage; therefore the rising portion of the triangle is:
1
C V I
C 0.33 Vsupply R A 0.228Vsupply
RA x C 0.66
… eqn. 5
22
The falling portion of the triangle and sine wave is:
2
C V I
C 0.33 Vsupply Vsupply Vsupply 2 0.22 2 0.22 RB RA RA RB C 0.66 R B R A
… eqn. 6
The rising portion, t1 and falling portion, t2 of the triangle and sine wave is given in Figure 16: Voltage
Time t1
t2
Figure 16: Rising portion, t1 and falling portion, t2
The frequency is given by: 1
1 t1
t2
RA C 1 0.66
RB
2R A
… eqn. 7 RB
Or if RA = RB = R 0.33 RC
… eqn. 8
23
Mathematical equation of this project: Frequency 0.33 30 kΩ 220 nF
50 Amplitude 2.2 4.4
0.22x 10 V 2.2 V x 2
3.2.3.1(a-2): Triangular Wave Generator Circuit Figure 17 shows the basic diagram of a triangular wave generator circuit that was constructed on the breadboards which is produces frequency at 10 kHz. Triangular waveform signal was taken at pin number 7or 6 of TL082 integrated circuit.
Triangular wave output before buffer circuit
1 14 2 13 3 12 4 11 5 10 6 9 7 8
1 8 2 7 3 6 4 5
Figure 17: Triangular wave generator circuit
Triangular wave output after buffer circuit
24
In this case, a different integrated circuit but same type as sine wave generator was used with a few modifications. TL082 I.C was used as a buffer circuit in order to stabilize the output waveform of the triangular waveform.
Mathematical equation of this project: Frequency 0.33 20 kΩ 1.65 nF
10 Amplitude 3.3 6.6
0.33 x 10 V 3.3 V x 2
Figure 18 shows the basic diagram of a buffer circuit using TL082 I.C. Triangular wave output after buffer circuit
Figure 18: TL082 as a buffer circuit
25
TL082 is a general purpose JFET-input operational amplifier integrated circuit.
It
has function as buffer which mean it provide isolation between load and input signal by using a stage having unity voltage gain, with no phase or polarity inversion and acting as ideal circuit that have high input impedance. The Figure 19 shows the top view of TL082 integrated circuit.
Figure 19: Top view of TL082 integrated circuit
3.2.3.1(a-3): Inverter Amplifier Circuit
In PWM circuit, two sine waves are needed which have a difference’s angle at 180 degree respectively. Hence one of the sine wave’s sources must be inverted before comparison between sine wave and triangular wave can be made. Inverting amplifier circuit is given in Figure 20.
Figure 20: The Inverter amplifier circuit
The
26
Ua741 op-amp is the main component uses to construct the inverting amplifier circuit. Figure 21(a) shows a basic inverting circuit using Ua741 op-amp integrated circuit while Figure 21(b) shows the top view of Ua741 op-amp integrated circuit.
Figure 21(a): Basic inverting circuit
Figure 21(b): Top view of Ua741 opamp integrated circuit
The voltage gain for the inverting configuration is set by the ratio of the feedback resistors, Rf and the input resistor, RI and not by the internal gain of the op-amp itself. It can even be less than one, but cannot exceed the op-amp's inherent gain and should not produce such large outputs that distortion results. In this part the inverted sine wave are need with same amplitude, therefore Rf must be same with Ri. 10 kΩ for both resistors side are used. The inverted amplitude gain can be expressed as equation 9:
… eqn. 9
Mathematical equation of this project: 10 kΩ 10 kΩ
27
3.2.3.1(a-3): Comparator Circuit.
A simple comparator circuit is shown in Figure 22. This particular circuit generated two pulses which have a difference angle, difference amplitude’s voltage and condition along the signal.
1 14 2 13 3 12 4 11 5 10 6 9 7 8
Figure 22: The Comparator circuit
LM339 integrated circuit is the main component used in the comparator circuit. LM339 compares two waves which is sine wave or negative sine wave as a reference signal and triangular wave as a carrier signal. The Figure 23 shows internal circuitry of LM339 integrated circuit.
Figure 23: Internal circuitry of LM339 integrated circuit
28
The LM339 series consists of four independent precision voltage comparators with an offset voltage specification as low comparators.
as
2
mV
max
for
all
four
These were designed specifically to operate from a single power
supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage. These comparators also have unique characteristic in that the input common-mode voltage range includes ground, even though operated from a single power supply voltage.
3.2.3.1(b):
Dead Time Circuit
The switching power devices in the PWM inverter have very fast switching frequency which is above sevens of kilohertz. Hence the dead time is necessary to prevent the short circuit of the power supply in the inverter leg of Full-bridge circuit of the pulse width modulated (PWM) voltage inverters results in output voltage deviations. The dead-time circuit delays the rising pulse edge by a fixed amount of time. In other words it delays the PWM pulse to turn-on signal of the power transistor. Although individually small, when accumulated over an operating cycle, the voltage deviations are sufficient to distort the applied PWM signal.
29
The dead time circuit configuration is shown in Figure 24. The circled area shows the main part to change the rising pulse edge.
Figure 24: Dead time circuit
There are two main components was used within the dead time circuit. The first component is the IC7408. The Figure 25(a) shows pin configuration of the IC7408 while Figure 25(b) shows a logic diagram of IC7408.
Figure 25(a): Pin configuration of the
Figure 25(b): Logic diagram of
IC7408
IC7408
30
IC7408 is used in order to generate logic pulse switching signal for each MOSFET. All the PWM signals are compared with 5V in order to produce logic pulses which have same range of amplitude value and stable. The logic function table is shown in Table 4: INPUT
INPUT
OUTPUT
Dna
Dnb
Qn
L
L
L
L
H
L
H
L
L
H
H
H
Table 4: Logic function of IC7408 Where: H = high voltage level between 2 until 7 V L= low level voltage -0.5 until 0.8 V
IC7414 is the second of main component that was used in the dead time circuit. The main function of IC7414 is inverting the logic pulse signals.
This function is
similarly with get not logic. The Figure 26(a) shows pin configuration of the IC7414 while Figure 26(b) shows a logic diagram of IC7414.
Figure 26(a): Pin configuration of the Figure 26(b): Logic diagram of IC7414 IC7414
31
3.2.3.1(c):
MOSFET Drive Circuit
Figure 27 shows the MOSFET drive circuit using HCPL3150 integrated circuit. The signal from dead time circuit (S1, S2, S3, S4) injected to this particular MOSFET drive circuit and produced pulse signals, (MS1, MS2, MS3, MS4) that used to triggered the power switch MOSFETs.
1 8 2 7 3 6 4 5
Figure 27: The MOSFET drive circuit
The power transistors used as switch that on and off in power inverter circuit therefore required an appropriate gate voltage or base current signal to drive the transistor into saturation mode for low on-state voltage in order to switch it on. The control voltage (VGS) should be applied between the gate and source terminal or between the base and emitter terminals. Therefore MOSFET drive circuit is needed to use as an isolation between low-level logic gate driver and high level power circuit. This circuit will protect low level power from short circuit and overcurrent that might be happened in power circuit. In this project, MOSFET gate driver HCPL3150 is used because it can provide isolation and gate driver functions at the same time.
32
CHAPTER 4
SIMULATION RESULTS AND DISCUSSION
4.1
SIMULATION RESULTS
4.1.1: Inverter Circuit Case 1 (without filter circuit):
For the first simulation, unfiltered
circuit from Figure 28 was analyzed. A transient analysis is performed to examine the gate pulse waveforms, the output waveforms and harmonic spectrum. All the outcomes result are shown in the follows figures. In this simulation, the load is a 1 Ohm resistor connected with a 5 mH inductor in series. Modulation index, ma and modulation ratio, mf are 0.8 and 150 for this project. This circuit was supplied by 300 Vdc. Triangular wave and sine wave frequency was set to 7.5 kHz and 50 Hz by a computer through Pulse PWM signal block.
output waveforms
Pulse switching waveform Total harmonic distortions
Figure 28: Full-bridge PWM inverter circuit without filter circuit, with R-L load
33
All the output waveforms are displayed at scope 2 in this simulation circuit. The waveform of load current and load voltage are shown in Figure 29 and Figure 30. The resulted fundamental load voltage is about 300 V (rms) while the load current is about 130 A.
Figure 29: Output load current waveform Where: Axis Y =50 A/Div Axis X = 0.01s/Div
34
Figure 30: Output load voltage waveform Where: Axis Y =10 V/Div Axis X = 0.01s/Div
35
Total harmonic distortions in Fast Fourier Transform are represented in Figure 31. This result was carried out by using powergui block that already provided in this Matlab/Simulink software.
Figure 31: Total harmonic distortions in Fast Fourier Transform As shown in Figure 31, the fundamental frequency was occurred at 50 Hz while the first fundamental frequency harmonic occurred at 15 kHz and followed by second frequency at 30 kHz. Based on equation 6, mf in this project is equal to 150.
36
By using total harmonic distortion block, the total harmonic distortions for this project was measured and carried out through by scope. Figure 32 represented the total harmonic distortions waveform. The output value of total harmonic distortions is almost 0.8 for this project.
Figure 32: Total harmonic distortions waveform. Where: Axis Y =1 unit/Div Axis X = 0.002s/Div
37
Figure 33 shows the each control signal which is taken out by scope 5.
The four
traces from the top to below are switching waveforms for S1, S2, S3 and S4.
S1
S2
S3
S4
Figure 33: Pulse switching waveform Where: Axis Y =5 V/Div Axis X = 0.0005s/Div
38
4.1.2: Inverter Circuit with Filter Circuit
Case 2:
This experiment was repeated which used low pass filter circuit. The
values of parameter are fixed. The simulation circuit for this project is given in Figure 34.
output waveforms
Pulse switching waveform
Total harmonic distortions
Figure 34: Full-bridge PWM inverter circuit with filter circuit, with R-L load
All the output waveforms are displayed at scope 2 in this simulation circuit. The load current and load voltage value are shown in Figure 35 and Figure 36 which give a peak load current of 105 A and peak load voltage value of 200 V.
39
Figure 35: Load current waveform Where: Axis Y =50 A/Div Axis X = 0.01s/Div
Figure 36: Load voltage waveform Where: Axis Y =10 V/Div Axis X = 0.01s/Div
40
Total harmonic distortions in Fast Fourier Transform are represented in Figure 37. This result was carried out by using powergui block that already provided in this Matlab/Simulink software.
Figure 37: Total harmonic distortions in Fast Fourier Transform As shown in Figure 37, the fundamental frequency was occurred at 50 Hz while the first fundamental frequency harmonic occurred at 15 kHz and followed by second frequency at 30 kHz. Based on equation 6, mf in this project is equal to 150.
41
By using total harmonic distortion block, the total harmonic distortions for this project was measured and carried out through by scope. Figure 38 represented the total harmonic distortions waveform. The output value of total harmonic distortions is almost 0.2 for this project.
Figure 38: Total harmonic distortions in Fast Fourier Transform Where: Axis Y =1 unit/Div Axis X = 0.002s/Div
42
Figure 39 shows the each control signal which is taken out by scope 5.
The four
traces from the top to below are switching waveforms for s1, s2, s3 and s4.
S1
S2
S3
S4
Figure 39: Pulse waveform Where: Axis Y =5 V/Div Axis X = 0.0005s/Div
4.1.3: Changes of Modulation Frequency In this experiment, frequency carrier was varied to 20 kHz in order to change the value of modulation frequency to become 400. Other parameters are fixed. Figure 40 shows an unfiltered total harmonic distortions output in Fast Fourier transform. The first fundamental frequency harmonic was occurred at 40 kHz and followed by second frequency at 80 kHz. The value of total harmonic distortions for this project is equal to 69.76%.
43
Figure 40: (unfiltered circuit) Total harmonic distortions in Fast Fourier Transform Figure 41 shows the filtered total harmonic distortions output in Fast Fourier transform. All the fundamental frequency harmonics was erased. Only fundamental frequency was displayed. The value of total harmonic distortions is decreased to 19.51%
Figure 41: (filtered circuit) Total harmonic distortions in Fast Fourier Transform
44
4.1.4: Changes of Modulation Index In this experiment, only modulation index, ma for inverter circuit using filter was changed. Figure 42 shows the total harmonic distortion when modulation index was increased from 0.8 to 0.9.
The first harmonic frequency was occurred at 15 kHz with
amplitude value is equal to 1.95%.
Figure 42: Total harmonic distortions in Fast Fourier Transform with ma = 0.9
45
Figure 43 shows the total harmonic distortion when modulation index was decreased from 0.8 to 0.5.
The first harmonic frequency was occurred at 15 kHz with
amplitude value is increased to 2.16%
Figure 43: Total harmonic distortions in Fast Fourier Transform with ma = 0.5
46
4.2
DISCUSSION
4.2.a: Inverter Circuit Case1 and 2: In this case the slope load current waveforms for the both circuits are same in term of pattern and value but opposite for the load voltage waveform. The first harmonic cluster for both experiments was occurred at high order frequency which is 15 kHz. After the connection low pass filter circuit, AC voltage output waveform become smooth and fewer ripples produced at the voltage output waveform. This is because most of the harmonic components filter out effectively by LC filter. From the Figure 36, we can see that load output waveform is exactly at the expected output frequency 50 Hz and the peak output voltage is about 200 Vrms, which approximates the theoretical calculation. Some voltage losses may be caused by the turn-on voltage drops of the MOSFETs. Beside that, the harmonic was eliminated and the value of THD voltage is decreasing from 76.12% to 1.43%. The pulse signal waveforms are same for the both cases. Its show that, the additional filter circuit didn’t give any effect to the switching signal.
4.2.b: Changes of Modulation Frequency For this case, the first harmonic occurred at the higher frequency compared to the previous one which is 4 kHz. When filter circuit was connected, the harmonics was eliminated totally. Therefore the load voltage waveform becomes smoother and less ripple. From this observation, it can be said that the changes of modulation frequency will effect the location of first harmonic frequency.
47
4.2.C: Changes of Modulation Index In this part, the variation of modulation index, ma give the significant impact to the output voltage, where when modulation index increases the value of voltage output also increases. This condition only valid when modulation index, ma ≤ 1. Beside that, total harmonic distortions also decreases when modulation index is increase
48
CHAPTER 5
EXPERIMENTAL RESULTS AND DISCUSSION
5.1
EXPERIMENTAL RESULTS The system outlined in the previous chapter was implemented and tested on
breadboard. All the following results are shown as below. Figure 44 shows the basic diagram of a sine wave generator circuit that was constructed in this project.
1 14 2 13 3 12 4 11 5 10 6 9 7 8
Figure 44: Sine wave generator circuit.
1 8 2 7 3 6 4 5
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Figure 45 shows the sine output waveform before buffer. This measurement was taken at pin 2 of ICL8038 waveform generator I.C.
Figure 45: Sine output waveform before buffer circuit The plot shows that the amplitude of the sine wave signal is 3.3 V at frequency almost 50 Hz. The voltage value from peak to peak for this signal is about 3.9 V
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Figure 46 shows the output of the sign wave signal after passing through the buffer circuit. The amplitude value of the sine wave signal was increased to 5.64 V at frequency almost 50 Hz. This sine wave output was taken and measured at the point J1 which is at pin number 6 of Ua741 I.C.
Figure 46: Sine output waveform after buffer circuit
Figure 47 shows a basic inverting circuit that used in this project in order to produced inverted sine wave signal.
Figure 47: The Inverter amplifier circuit
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Figure 48 shows the difference between the sine wave signal and inverted sine wave signal which is taken after passing trough the buffer circuit.
Figure 48: Sine output waveform and inverted sine output waveform The plot shows that both signals have a same amplitude value which is 5.68 V at same frequency which is almost at 50 Hz. These two signals only have 180 degree phase shift different.
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Figure 49 shows the triangular output waveform that produced by circuit in Figure 18 after passing through the buffer circuit.
Figure 49: Triangular output waveform The plot shows that the amplitude value of triangular wave signal is 6.2 V at frequency almost 9 kHz. The peak to peak voltage for this signal is about 6.92 V
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Figure 50 shows the comparator circuit that used to produce PWM waveform.
1 14 2 13 3 12 4 11 5 10 6 9 7 8
Figure 50: Comparator circuit.
Figure 51 shows the output signal when sine wave has been compared to triangular wave. This output result can be taken at pin number 1 or 14 of LM339 I.C.
Figure 51: PWM waveform The plot shows that positive 20 V was produced at positive cycle while negative 20 V was produced at negative cycle along the sine wave signal
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Figure 52 shows PWM1 and PWM2 signals. PWM1 was produced by comparing sine wave signal with triangular wave signal while PWM2 was produced by comparing inverted sine wave signal with triangular wave signal. These pulses have phase shift different which is about 180 degree and frequency where PWM1 was produced at frequency 3.12 kHz while PWM2 at frequency 5.3 kHz.
Figure 52: PWM waveform
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This logic pulse waveform was taken out from Figure 33 circuit which is at dead time circuit output. This pulse signals was referred as S1, S2, S3 and S4. The Figure 53 shows logic pulse signal for S1 and S2.
S1
S2
Figure 53: Logic pulse waveform The plot shows the both signals, S1 and S2 have 180 degree phase shift different. These pulses have a same amplitude value which is 5V and also frequency which is 50 Hz.
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5.2
DISCUSSION
After sine wave output passed trough the buffer circuit the amplitude becomes higher but same frequency, 50 Hz. The inverter circuit angle was shifted at 180 degree while the amplitude and the frequency are still the same. All the pulse signals have different amplitude. For example, PWM waveform has 20 V peak amplitude compare to logic pulse waveform, 5 V. These because all this values must be follow the specifications of their circuit. Amplitude value of PWM waveform must be step down to 5 V in order to produce logic pulse waveform because the IC that used within the dead time circuit can only be operate in 5 V. Then the signal will be step-up to 15 V at the MOSFET driver circuit in order to trigger the MOSFET.
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CHAPTER 6
CONCLUSION AND RECOMMENDATION
6.1
CONCLUSION
6.1.a
Conclusion for simulation result:
As conclusion, the objectives for this part have been achieved. A simulation model of a unipolar single phase PWM inverter was successfully designed and tested. A complete results from simulation was obtained and most of the results are verified the theoretical value.
6.1.b
Conclusion for experimental result: The final results weren’t as successful as originally planned because
there are
some areas facing design difficulties and only certain part of the
hardware project are successful.
Therefore no comparison between simulation
voltage output and hardware output can be made. However, these experiment results are quite close to the previous theoretical calculation and simulation results. If the times are permitted, there should be more interesting outcome from the project.
6.2
RECOMMENDATION
1. There are other methods of inverters which is better then PWM unipolar switches that was used in this project. This method is produce a fewer ripples at the output. For example by using: a) High-speed microcontroller of microprocessor or Digital Signal Processors (DSP) that can generate the PWM which is more flexible.
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Beside that, source of modulation that produced is more stable and free from problem of drift. Hence more accurate results will be produces in the experimental part.
This implementation can be made by using
TMS320F2812 DSP which is generally used to satisfies the control requirement of the high switching frequency PWM schemes.
This
particular device generates the PWM signals and also provides soft start function. b) Inverted sine carrier PWM (ISCPWM) method, which uses the conventional sinusoidal reference signal and an inverted sine carrier. This method has a better spectral quality and a higher fundamental component compared to the conventional sinusoidal PWM (SPWM) without any pulse dropping. The ISCPWM strategy enhances the fundamental output voltage particularly at lower modulation index ranges while keeping the total harmonic distortion (THD) lower without involving changes in device switching losses. 2. The disadvantage of using high switching frequencies is higher losses in the switches which is used to implement the inverter. Hence, it is recommended to avoid from using a large modulation ratio for this project.
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REFERENCES
BOOKS: 1.
“Implementation of a Single-phase Unipolar Inverter Using DSP TMS320F241”, Narong Aphiratsakun, Sanjiva Rao Bhaganagarapu and Kittiphan Techakittiroj, Faculty of Engineering, Assumption University Bangkok, Thailand, 2005
2. “Analysis, Simulation And Dsp Based Implementation Of Asymmetric Three-Level Single-Phase Inverter In Solar Power System”, Yi Tian, The Florida State University Famu-Fsu College Of Engineering, 2007 3. “Introduction to power Electronic,” published by Prentice-Hall International, INC, Daniel W. Hart, Valparaiso University, 1999
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APPENDIX
1.
(a)
(c)
(b)
(d)
Figure 35: Laboratory unipolar inverter board (a) gate drive circuit (b) dead time circuit (c) sine wave generator circuit (d) triangular wave generator circuit
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2. Datasheet of ICL8038
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63
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66
67
68
69
70
71
72
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3. Datasheet of IRFP450 power MOSFET
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