COMPARATIVE STUDY BETWEEN SINUSOIDAL PULSE WIDTH
MODULATION TECHNIQUE AND SIX-STEP TECHNIQUE FOR VOLTAGE
SOURCE INVERTER
&UUN BIN AKAL
This Report Is Submittkd In Partial Fulfillment of Requirements For
The Degree of Bachelor In Electrical Engineering (Industrial Power)
Faculty Of Electrical Engineering
Kolej Universiti Teknikal Kebangsaan Malaysia
4 MAY 2006
ABSTRACT
E s project discuss about inverters that transfers power from a DC source to an AC load.
Inverters are widely used in motor drives, unintermptible power supplies (ups),
5ppliances run from an automobile battery and photovoltaic utility grid interface. This
project presents a comparative study of performance between Sinusoidal Pulse Width
Modulation (SPWM) and SIX STEP technique for voltage source inverter. The circuit of
these techniques has been designed and analyzed using simulations software packages
such as MATLAB 6.5 and ORCAD 9.1. The performance comparison of both techniques
xesented in terms of the appropriate Total Harmonic Distortion (THD), Fast Fourier
rransformed (FFT) and Spectrum Analysis of the output waveforms. Basically, Total
Harmonic Distortion describes the quality of the output waveform. Fast Fourier
rransformed shows the selected signal wave and the analysis of voltage or current
.elative to fundamental or DC. While, Spectrum analysis explains a filter requirement in
Aiminating higher harmonic and unwanted noise. This project is divided into three
.mportance stages of study. Firstly, to study on how to generate the switching SPWM
iignals to drive the power switches ( i.e MOSFETs , IGBTs) and to construct the
:apologies using Sirnulink-MATLAB 6.5 for SPWM and SIX-STEP inverters. Secondly,
nvolves the discussion and performance comparison in terms of THD, FFT and
3armonic Spectrum for SIX-STEP and SPWM. Finally, this project presents the
:onstruction of schematics of the SIX-STEP and SPWM inverters using ORCAD 9.1
where the schematics can be represented as real practical experiniental set-up. Simulation
.esults using ORCAD 9.1 are in close agreement with simulation results using Simulink.
ABSTRAK
Projek ini membincangkan mengenai penyongsang yang menukarkan arus terus kepada
arus ulangalik. Penyongsang digunakan secara meluasnya dalam motor pemacu, bekalan
kuasa talc terganggu and aplikasi dalam utiliti grid antaramuka bagi voltan photo. Projek
ini menghuraikan kajian perbandingan perlaksanaan antara dua teknik dalam
penyongsang sumber voltan iaitu teknik Lebar Denyut Modulasi Sinusoidal dan teknik
Enam Langkah. Litar bagi kedua-dua teknik direkacipta dan dianalisa menggunakan
pakej perisian seperti MATLAB 6.5 and ORCAD 9..1. Perlaksanaan perbandingan
kedua-dua teknik dipersembahkan dalam bentuk Jumlah Herotan Harmonik yang
bersesuaian, Pertukaran Pantas Fourier dan analisis spektrum berdasarkan gelombang
keluaran yang diperolehi daripada keputusan simulasi. Umurnnya, Jumlah Herotan
Harmonik menjelaskan mengenai kualiti gelombang keluaran manakala Pertukaran
Fourier Pantas menjelaskan mengenai analisis bagi voltan dan arus secara relatif kepada
frekuensi asas. Sementara itu, analisis spektrum pula menerangkan keperluan
menggunakan penapis untuk menghapuskan harmonik tinggi dan bunyi yang tidak
iliperlukan. Projek ini dibahagikan kepada tiga bahagian penting dalam pengkajian.
Bahagian pertama adalah mengenai penghasilkan isyarat yang dapat memacu suis kuasa
seperti MOSFETs dan lG3Ts serta membina topologi menggunakan Simulink-MATLAB
bagi kedua dua teknik. Bahagian kedua pula merupakan perbincangan dan perbandingan
mtara kedua-dua teknik. Manakala, bahagian ketiga membincangkan tentang penggunaan
~erisianORCAD 9.1 sebagai pembinaan skematik yang lebih praktikal dan keputusan
simulasi menggunakan 9.1 adalah sama dengan keputusan simulasi menggunakan
Sirnulink-MATLAB 6.5.
CHAPTER 1
INTRODUCTION
This project will presents an overall description of Voltage Source Inverter. This
chapter includes the project overview, project objectives, project scopes, method of
analysis and report summary. Roughly, flow of work from the beginning until the
fulfillment of this project will be described in this chapter.
1.1
PROJECT OVERVIEW
Voltage Source inverters (VSI's) are utilized in ac motor drive, utility interface,
and uninterruptible power supply (UPS) applications as a means for dc ac electric energy
conversion. The classical VSI generates a low-frequency output voltage with
controllable magnitude and frequency by programming high-frequency voltage pulses.
Inverters can be broadly classified into two types, voltage source and current source
inverters. A voltage-fed inverter (VFI) or more generally a voltage-source inverter
(VSI) is one in which the dc source has small or negligible impedance. The voltage at
the input terminals is constant. A current-source inverter (CSI) is fed with adjustable
current from the dc source of high impedance that is from a constant dc source. This
project will be only focusing on Voltage Source Inverter part. A voltage source inverter
employing thyristors as switches, some type of forced commutation is required, while
the VSIs made up of using GTOs, power transistors, power MOSFETs or IGBTs, self
commutation with base or gate drive signals for their controlled turn-on and turn-off .In
this project, three-phase inverters and their operating principles are analyzed in detail.
The concept of Sinusoidal Pulse Width Modulation (SPWM) and SIX STEP technique
for inverters is described with performance analysis of waveforms. Finally the
simulation results along with all analysis for three phase inverter using the SPWM and
SIX STEP are presented. [4]
1.2
PROBLEM STATEMENT
Higher harmonics distortion appears mostly when using SIX-STEP technique.
As one of the objectives of this project is to describe the advantage of SPWM technique
in reducing power losses and heat dissipated in the output stage, it is necessary to know
on how SPWM technique method solves this problem. Basically, SPWM technique
control strategies involving either unipolar or bipolar switching. These switching are
quite common since the harmonics of significant amplitude are pushed into high
frequency range near the carrier frequency.
As the switching frequency is increased, a high quality output voltage waveform
can be more easily recovered by low-pass filtering. During a typical turn-on or turn-off
operation, however, the voltage across each power device remains near to the DC bus
voltage for a significant portion of the switching transient, while a relatively large
current is being commutated. Consequently, the devices (motor, heater or etc) undergo
high power losses which increase linearly with the switching frequency. This not only
impairs the power transfer efficiency of the inverter, but also increase the size and cost
of heat sinks required for efficiency radiating heat loss to avoid device failure.
A conventional linear output stage also applies a continuous voltage to load. This
can waste plenty of power. So, as a method of solution for this problem, it is proposed
to use SPWM technique which can applies a pulse train of fixed amplitude and
frequency where only the width is varied in proportion to an input voltage. The end
result is that, the average voltage at the load is the same as the input voltage but with less
wasted power in output stage. [2]
1.3
PROJECT OBJECTIVES
The objectives of the project are:
i.
To compare and study the performance of analysis for SIX-STEP & SPWM
inverter based on their characteristics, output waveforms and switching..
ii.
To design a circuit and obtain computer simulation results using SimulinkMATLAB 6.5 and ORCAD 9.1.
iii.
To implement the hardware of generation of the PWM signals using IC
analogue such as Operational Amplifier LM741 and Comparator LM339.
1.4
PROJECT SCOPES
The scope of work need to be done in this project will be more to analysis of
performance for both techniques using Simulink-MATLAB 6.5 and ORCAD 9.1. These
two technique will be compared based on their performance such as the existence of
higher harmonic in SPWM technique, the switching transition in SIX STEP, their
characteristic and the quality of output waveforms of both technique. Since the computer
simulation involving two kinds of software packages, my supervisor had narrowed the
using of ORCAD 9.1 simulation into SPWM simulation only. But, using SimulinkMATLAB 6.5, both SPWM and SIX-STEP simulation results will presented and
analyzed.
The development of hardware is done to get all the results that can prove the
simulation results. But, there is a problem of getting the MOSFET's part which is used
as a switches. Therefore, the implementation of the components on the project board has
limited to the available components only. Even though the hardware results is not well
obtained, the best commitment of finding and searching for the components that are
needed to build the hardware has been done.
1.5
METHOD OF ANALYSIS
This project performed in two stages. The first stage deals with the designing and
simulation process to get proved the expected result of SPWM and SIX-STEP technique
theoretically. This involves the using of Simulink-MATLAB 6.5 and ORCAD 9.1 to
design SPWM and SIX-STEP schematics which will obtained all the results in terms of
output waveform such as voltage line to line, voltage phase, load current and simple
Fourier analysis. Then, the results for both technique will be analyzed and compared
based on their performance such as the appropriate Total Harmonic Distortion (THD),
Fast Fourier Transformed (FFT) and Spectrum Analysis of the output waveforms.
For the second stage, an implementation of hardware that hoped to get the same
result obtained from the theoreticaVsimulation results is performed. Before the hardware
implemented, the simulation using ORCAD 9.1 must be done as this software provides
practical set-up where simulation can be done cycle by cycle compared to SimulinkMATLAB which only represent all components in block diagram. Some of the
information in the process of expanding the idea of analysis and comparison
performance of the results are referred fiom the research journal of related website,
power electronic reference books and from my supervisor who had contributes greatly in
guiding me for the entire project.
1.6
PROJECT REPORT SUMMARY
This project report contains of five chapters which will describe this project in
details. The first chapter is the introduction part where in this chapter, the overall
descriptions of the project are highlighted. The objectives of this project, the scopes and
the methodology are described.
Second chapter of this report will be discussing about the research and analysis
of this project. Each of the facts and the information from the analysis will be explained.
The third chapter will describe the method used in implement the project task.
The techniques and methodology of this project is split into two major parts that is the
hardware and software. In this chapter, each part will be described in depth.
The fourth chapter is the result and analysis of the project. In this chapter, all of
the final results and the analysis that had been done will be stated clearly. The analysis is
done by using computer simulation which are Simulink-MATLAB 6.5 and ORCAD
9.1.
The final chapter is the conclusion and suggestion. A conclusion about the
achievement of the project objectives and the knowledge gained while doing this project
is being stated in this chapter. The suggestion and future work is highlighted to improve
the study of the project for the next reference.
CHAPTER I1
LITERATURE REVIEW AND PROJECT BACKGROUND
This chapter will described about the background of this project and literature
review which includes the previous related project and the development made by people
in Electronic Engineering field all over the world.
2.1
PROJECT BACKGROUND
For the project background, the basic concept, characteristic and application of
SPWM and SIX-STEP technique will be explained. While for the literature review, the
people who responsible of proposing and developing the three phase Voltage Source
Inverter PWM schemes and discontinuous modulation in three phase Voltage Source
Inverter will be exposed.
2.1.1 SIX STEP TECHNIQUE
SIX-STEP three phase inverter circuit used widely in the speed of induction
motors where the output frequency is varied. The three phase load connected to this
output voltage may be connected in delta or ungrounded-neutral wye. For a wyeconnected load, which is the more common load connection, the voltage each phase of
the load is a line-neutral voltage. Figure 2.0 below shows an ungrounded-neutral wye
switching scheme for SIX -STEP Inverter. Note that, switches S1and S4close and open
opposite each other, as do pairs (S2and S5) and (Sj and S6).
N
Figure 2.0: SIX-STEP three-phase inverter
Figure 2.1 below shows the switching transition for SIX-STEP inverter. The
Switching sequence from (a) will produce the output voltage shown in voltage line to
line (b). The output frequency can be controlled by changing the switching frequency.
The magnitude of the output voltage depends on the value of the DC supply voltage. So,
to control the output voltage of SIX-STEP inverter, DC input voltage must be adjusted.
The switching scheme for voltage line to line can be summarized as follows:
For VA- B , S1and S 6 are closed - the other will opened
For VB- C, S 3 and S 2 are closed - the other will opened
For Vc - 4 S 5 and S 4 are closed - the other will opened
(a) Switching qeollence
VAN
I
I
S1
S2
I
r
s3
I
I
S4
0
ss 1
S6
1
.Oo
VBN
VAB
$BC
VCN
O o O 1 w A w
VCA
+VDC
0
-VDC
(b) line to line Voltage
(c) line to neutral Voltage
Figure 2.1: Swi$cl&gtransitions for SIX-STEP inverter
Figure 2.2 below shows waveforms of line to neutral ( phase) voltages and line
to line voltages for SIX-STEP voltage source inverter. The waveforms shows how the
switching transitions of figure 2.1 represented mathematically in terms of line to line
voltages and phase voltages..
Line to line voltages
Phase voltages
VAB=VAN-VBN
van = 2/3VAN- 1 / 3 v -~1~/ 3 V a
VBC~VBN-VCN
V b n = -1/3Vm + 2/3VBN- 1/3Vm
Vc*=Vm-VAN
V c n = -1/3Vm - 1/3VBN + 213Va
Figure 2.2 : Waveforms of line to neutral ( phase) voltages and line to line voltages
for SIX-STEP voltage source inverter
Figure 2.3 below shows the sequence of each switches, line to negative voltages
and the gating signals for SIX-STEP voltage inverter. Each switches normally has duty
ratio of 50% (not allowing for blanking time) and a switching action takes place every
116 time interval or 60' angle interval.
Figure 2.3 : Waveforms of gating signals, switching sequence, line to negative
voltages for six-step voltage source inverter.
2.1.1.1
Characteristic of SIX- STEP
I. It is called "SIX-STEP inverter" because of the presence of six "steps" in the
line to neutral (phase) voltage waveform.
11. Harmonics of order three and multiples of three are absent from both the line
to line and the line to neutral voltages and consequently absent from the
currents.
111. Output amplitude in a three-phase inverter can be controlled by only change
of DC-link voltage (Vdc).
IV. The Fourier series for the output voltage has a fundamental frequency equal
to the switching frequency. Harmonic frequencies are on order of 6k+/- 1 for
k = 1, 2... (n=5,7,11, 13...).
2.1.2 SPWM TECHNIQUE
Sinusoidal Pulse width modulation (SPWM) generated by comparing amplitude
of triangular wave (carrier) and sinusoidal reference wave (modulating) signal. SPWM
switching for three phase inverter is similar to that of a single phase inverter. Basically,
each switch is controlled by comparing a sinusoidal reference wave with a triangular
carrier wave. The fundamental frequency of the output is the same as the reference
wave, and the amplitude of the output is determined by relative amplitudes of the
reference and carrier waves. As in the case of SIX-STEP Three Phase inverter, each
switches in figure 2.0 are controlled in pairs (S1,S4), (S2,S5), and (S3, S6). When one
switch in pair is closed, the other is open. Each pair of switches requires a separate
sinusoidal reference wave. The three phase reference sinusoidal is 120' apart to produce
a balanced three phase output.
Figure 2.4 : Three-phase voltage source inverter ( SPWM )
V carrier
, V reference
Figure 2.5: Pulse-width modulation
Inverter output voltage:
When V reference > V carrier, VAO
(t) = V dc 2
When V reference < V carrier, VAO
(t)
=
-V dc 2
Control of inverter output voltage:
SPWM frequency is the same as the frequency of V carrier
Amplitude is controlled by the peak value of V
Fundamental frequency is controlled by the frequency of V
Modulation Index (m)
.
m
=
V ,ferwce
=
V carrier
V carria
Peak of VAO(t)
V dc/ 2
V reference
/
A
V reference B
V reference C
/
Figure 2.6 : Waveforms of three-phase sine PWM inverter
2.1.2.1 Characteristic of SPWM
The objective of using PWM technique is:
i.
Control of inverter output voltage
ii.
Reduction of harmonic
The disadvantage of PWM technique:
i.
Increase of switching losses due to high PWM frequency
ii.
Reduction of available voltage
iii.
EM1 problems due to high-order harmonics
Harmonic will be minimized if the carrier frequency is chosen to be an odd triple
multiple of the reference frequency that is, 3,9, 15.. ...times the reference.
2.2 LITERATURE REVIEW
2.2.1 Three Phase VSI PWM Schemes
Pulse width modulation technique using sine triangle intersection was first
proposed by Schonung and Stemmler in 1964. Due to the ease of implementation, the
SPWM is found in a wide range of applications. The drawback of this scheme is that the
output is linear between 0% and 78.5 % of the SIX-STEP voltage value. Thus there is
inefficient use of the DC bus voltage. The direct digital technique or the Space Vector
Modulation technique was proposed by Pfaff, Weschta and Wick in 1982. This scheme
was further developed by van der Broeck, Skudelny, and Stanke. The development of
micro controllers made the direct digital technique possible. This scheme became more
and more popular due to its merits of high utilization of the DC link voltage, possible
optimized output distortion and switching losses, and compatibility with a digital
controller. It has been widely used for high performance three-phase drive systems. In
1989 it was shown in that the absence of neutral current path in three wire loads
provides a degree of freedom in determining the duty cycles of the inverter switches.
This degree of freedom is achieved by partitioning of the null states. The equivalent
degree of freedom in triangle intersection method is observed by selection of appropriate
modulator. The absence of a neutral wire in star-connected three-phase loads provides
this degree of freedom in modulation methodology. Since the voltage between the
neutral of the load and the reference of the DC source, Vnocan take any value. This zero
sequence waveform is used to alter the duty cycle of the inverter switches and
alternatively the modulating signals. Appropriate zero sequence signal injection causes
increase in voltage linearity, waveform quality and reduced switching losses without
affecting the output conditions. In 1974 King employed zero sequence injection
technique using analog hardware, and showed that the output voltage linearity was
between 0% and 90.7%. This technique is also known as a Space Vector PWM. Many
other techniques were developed for harmonic elimination in order to suppress the lower
ordered harmonics. The third harmonic injection (THIPWM) techniques as mentioned in
explains that by adding a measure of third harmonic to the output of each phase of a
three-phase inverter, it is possible to obtain a line-to-line output voltage that is 15
percent greater than that obtainable when pure sinusoidal modulation is employed. The
line-to-line voltage is undistorted. The method permits the inverter to deliver an output
voltage approximately equal to the voltage of the ac supply to the inverter. This method
is still being used in dedicated applications as in which describe a technique of injecting
third harmonic zero sequence current components in the phase currents, which greatly
improves the machine torque density. Of all the PWM techniques only a few PWM
strategies have been accepted mainly due to the simplicity of implementation. [I]
2.2.2
Discontinous modulation in three phases VSI.
In 1977 Depenbrock developed a discontinuous modulation technique and
illustrated that the scheme resulted in high voltage linearity range, reduced switching
losses, and superior current quality waveform. The scheme had a limitation of poor
performance in the lower modulation region. The same modulators were studied from
the perspective of switching losses and harmonic analysis. The studied modulators
explored the dependency of the conduction and switching losses in a three phase inverter
system for various modulating signals. It is concluded that there is a significant increase
in the effective switching frequency. By using an optimal modulation for minimum
switching loss, the harmonic loss in the higher modulation region is greatly reduced. It
implies minimization of switching losses in the inverter due to low switching frequency
ratio and absence of switching in the vicinity of the load current peaks in a given phase.
The correlation between space vector PWM and Carrier based PWM was established by
Blasko. By changing the duty cycles weights of the zero state by the factor named "k;,
it was proved that the modified space vector PWM can be implemented as triangle
comparison method with added zero sequence. This helped in comprehensive analysis of
the null state vectors and their relationship with the carrier based signals. The developed
a high performance generalized discontinuous PWM algorithm employed conventional
space-vector PWM in the low modulation region and generalized discontinuous PWM
algorithms in higher modulation region. The same approach termed as adaptive space
vector modulation was considered full control range including over modulation and SIXSTEP operation. It reduced the switching loss by 50% at 33% reduction in the switching
frequency. The modulator evaluation revealed the improved performance in the higher
modulation region with reference to minimum pulse width control and voltage gain
characteristic of the inverter. [I]
CHAPTER I11
PROJECT METHODOLOGY
As this project more to case study, there will be no software to be developed but
two software tools will be applied in order to design, to simulate, to analyze, to study, to
display and to get the output waveform result of both technique. The designing and
simulation process is done to get proved the expected result of SPWM and SIX STEP.
3.1
SOFTWARE PACKAGES USED
In this project two software packages have been used to design a circuit which
will obtained all the results in form of output waveform such as line to line voltage,
Phase voltage, Load Current and Fourier analysis. The first software is SimulinkMATLAB 6.5 that enables the user to construct simulation fiom graphical (block
diagram) description of the system or process. Another software tools that been used is
called ORCAD Release 9.1. The application of this software is no different compared to
Sirnulink-MATLAB 6.5 but this software tools is more practical as it include IC's and
other popular part such as Controllers, FET drivers, opto-couplers, etc.
3.1.1 MATLAB VERSION 6.5
Simulink-MATLAB 6.5 is a high-level technical computing language and
interactive environment for algorithm development, data visualization, data analysis, and
numeric computation. Using Simulink-MATLAB 6.5, technical computing problems can
be solved faster than with traditional programming languages, such as C, C++, and
FORTRAN. Simulink-MATLAB 6.5 can be used in a wide range of applications,
including signal and image processing, communications, control design, test and
measurement, financial modeling and analysis, and computational biology. Add-on
toolboxes (collections of special-purpose Simulink-MATLAB 6.5 functions, available
separately) extend the Simulink-MATLAB 6.5 environment to solve particular classes of
problems in these application areas. Simulink-MATLAB 6.5 provides a number of
features for documenting and sharing your work. We can integrate Simulink-MATLAB
6.5 code with other languages and applications, and distribute Sirnulink-MATLAB 6.5
algorithms and applications. The key features for Simulink-MATLAB 6.5 are:I. High-level language for technical computing
11. Development environment for managing code, files, and data
111. Interactive tools for iterative exploration, design, and problem solving
IV. Mathematical functions for linear algebra, statistics, Fourier analysis,
filtering, optimization, and numerical integration
V. 2-D and 3-D graphics functions for visualizing data
VI. Tools for building custom graphical user interfaces
VII. Functions for integrating Simulink-MATLAB 6.5 based algorithms with
external
VIII. application and languages, such as C, C++. Fortran, Java, COM, and
Microsoft Excel.
3.1.2
ORCAD 9.1
Using this software, we can perform high-speed cycle-by-cycle simulation to
show true large-signal performance, simulate current-mode control using the latest
accurate modeling techniques, run CCM and DCM converter simulations, analyze
control systems including loop gain, input filter design and analysis, and measure power
stage loss and stress analysis for all major components. In summary we can simulate our
entire power system. Pulse Width Modulation (PWM) controllers, Switching Regulators,
Multi-phase controllers, PFCs, Integrated switch & boost controllers, hysteretic
controllers, IC regulators and models for other popular parts (FET drivers, optocouplers, etc.) are included. The benefits of using this software are:I. Analyze large signal effects like start-up transients, power stage
semiconductor stress, and step-load response
11. Explore different approaches to transformer, converter, filter, and control
structures
111. Compute component stresses and test for excessive power dissipation
IV. Compare circuit characteristics with linear and nonlinear magnetic
V. Analyze in both time and frequency domains
VI. Simulate and analyze your entire power supply without any limitations.
3.2
METHODOLOGY
This project divided into five sections; design the circuit, simulate the designed
schematic using Simulink-MATLAB 6.5 and ORCAD 9.1, implement hardware using
the same schematic, study the performance of analysis and then determine the
comparison. In the early phase of project, it was performed by designing and simulating
the schematics to get proved the expected result of SPWM and SIX STEP. For this
purpose, Simulink- MATLAB 6.5 had been used to design a circuit which will obtained
all the results in form of output waveform such as line to line voltage, phase voltage,
load current and Fourier analysis. For the second phase, the simulation by using
ORCAD 9.1 has proceeded. The objective of using this software is same like MATLAB
6.5 but using ORCAD 9.1 is more practical because it shows real connection and layer
of components such IC's. For ORCAD 9.1, my supervisor had narrowing the scope of
this project where only the simulation for SPWM had to be done. After succeed of
obtaining all the results, the implementation a hardware that hoped to get the same
result obtained from the theoretical/simulation results using Simulink-MATLAB 6.5 and
ORCAD 9.1 was performed. But, problem comes when the switches (MOSFET) that
needed to use in this hardware are unavailable. So, the implementation of hardware
performed based on the only available components. Some of the information in the
process of expanding the idea to produce this report are referred from the research
journal of related website, power electronic reference books and from my supervisor
who had contributes more in guiding me for this entire project.
.
/
DESIGNSPWM& SIX
)
SIMULATE USING MATLAB AND ORCAD
4
NO
SIMULATION
F
IDENTIFY
ERROR &
MAKE
CORRECTION
STUDY & MAKE ANALYSIS
OF PERFORMANCE
HARDWARE
USING
THE SUCCEED CIRCUIT
DETERMINE THE COMPARISON
OF SIX STEP & SPWM
Figure 3.0: Flowchart of Project Methodology
3.3
HARDWARE DEVELOPMENT
Hardware development is done as an experimental result after succeed of getting
the theoretical (designing and simulation) result using computer simulation. The
objective is to provide a real hardware which will have the same results as in computer
simulation which can produce SPWM and SIX-STEP output waveforms.
Figure 3.1: Hardware for SPWM
Generally, the output waveforms for hardware part was not obtained successfully
because of the unavailable MOSFET'S which is used as switches in this hardware
implementation. This hardware status will fully depends on the results from the
computer simulation part especially using ORCAD 9.1. It means that, if the designed
circuit using computer simulation could not perform as it should be, there is no point of
implementing this hardware. With a very less basic knowledge of using SimulinkMATLAB 6.5 and ORCAD 9.1, I had spent a lot of time of learning; ask for helped
from my supervisor and try to simulate the circuit by myself at home until I succeed.
But, from my own opinion, computer simulation results is quite enough to make a
comparative study between SPWM and SIX-STEP as it provides all the required
analysis of performance.
CHAPTER IV
RESULT AND DISCUSSION
This chapter will describe about simulation results of both technique used in this
project. The simulation results divided into two part which is simulation results using
Simulink-MATLAB 6.5 and ORCAD 9.1 The simulation output waveforms will be
showed graphically such as line to line voltage, phase voltage and load current. The
process of generating these two technique will be also described by detailed. Then, the
analysis of Total Harmonic Distortion using Fast Fourier Transformed (FFT) will be
stated. Lastly, the discussion related about these results will be explained clearly.
4.1
SIMULATION PARAMETER AND CIRCUIT
The parameters and the process of designing the circuit to generate SPWM and
SIX-STEP waveforms are basically similar. The only difference is that SimulinkMATLAB 6.5 provides circuit using block representation while ORCAD 9.1 provides
more practical and real connection of circuit. The Simulink model for SPWM technique