final one
TRANSCRIPT
A NOVEL CONCEPT OF SINE PULSEMODULATIONUSING WAVE FORM
GENERATORS
A Project ReportSubmitted to the Faculty of Engineering of
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY, HYDERABAD
In partial fulfillment of the requirements for award of the Degree of
Bachelor of TechnologyIn
Electrical and Electronics EngineeringBy
D.P.R.DEEPAK D.GOPI KRISHNA
(04481A0245) (04481A0210)
D.RAJYA LAKSHMI V.PUNNA RAO
(04481A0207) (04481A0249)
Under the guidance of
Smt.CH.SUJATHA, M.TECHASSOCIATE PROFESSOR
Department of Electrical and Electronics Engineering
GUDLAVLLERU ENGINEERING COLLEGEGUDLAVALLERU – 521 356
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ANDHRA PRADESH 2007A NOVEL CONCEPT OF SINE PULSEMODULATION USING WAVE FORM
GENERATORS
A Project ReportSubmitted to the Faculty of Engineering of
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY, HYDERABAD
In partial fulfillment of the requirements for award of the Degree of
Bachelor of TechnologyIn
Electrical and Electronics EngineeringBy
D.P.R.DEEPAK D.GOPI KRISHNA
(04481A0245) (04481A0210)
D.RAJYA LAKSHMI V.PUNNA RAO
(04481A0207) (04481A0249)
Under the guidance of
Smt.CH.SUJATHA, M.TECHASSOCIATE PROFESSOR
Department of Electrical and Electronics Engineering
GUDLAVLLERU ENGINEERING COLLEGE
2
GUDLAVALLERU – 521 356ANDHRA PRADESH
2008CERTIFICATE
This is to certify that the project report entitled “A NOVEL CONCEPT OF
SINE PULSE MODULATION USING WAVE FORM GENERATORS” is a
bonafide record of work carried out by D.P.R.DEEPAK, D.GOPI KRISHNA,
Y.RAJYA LAKSHMI, V.PUNNA RAO under my guidance of supervision in
partial fulfillment of the requirement for the award of the degree of BACHELOR
OF TECHNOLOGY in Electrical and Electronics Engineering of Jawaharlal
Nehru Technological University, Hyderabad.
Projectguide Head of the Department
[Smt.CH.SUJATHA] [Prof.P.V.R.L.NARASIMHAM]
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ACKNOWLEDGEMENT
We wish to express our deep sense of gratitude to our project guide
Asso.Prof.Ch.SUJATHA of Electrical and Electronics Engineering
department for her valuable guidance and constant encouragement during
our project work She has spent a lot of her valuable time on this project and
gave us the necessary modifications in bringing this work to present stage.
She has helped us in many ways and our work could not have been a success
without her contribution.
We would like to take this opportunity to thank to all our Faculty
members for providing a great support for us in completing our project.
We specially thank all our Lab technicians for their advise in solving
practical problems that we encountered during the successful completing
our project. We convey our sincere thanks to our Librarian who offered best
support at all times for providing books and internet facilities for our
reference.
We also thank our friends for their constructive criticism, which made us
to work more hard to produce better reports.
Finally, we owe our thanks to our parents whose sacrifices in all respects
made us to reach our goal.
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PROJECT ASSOCIATES
CONTENTS
LIST OF FIGURES
LIST OF SYMBOLS
LIST OF ABBREVATIONS page
No
INTRODUCTION
CHAPTER-1 PULSE WIDTH MODULATION
1.1. MODULATION
1.2. BASIC CLASSIFICATIONS OF MODULATION
LINEAR MODULATION
AMPLITUDE MODULATION
PULSE WIDTH MODULATION
1.3. SINGLE PULSE MODULATION
1.4. MULTIPLE PULSE MODULATION
1.5. SINUSOIDAL PULSE MODULATION
1.5.1 UNIPOLAR PWM
1.5.2 BIPOLAR PWM
1.6. SINGLE PHASE INVERTER
1.7. PRINCIPLE OF OPERATION OF INVERTERS.
CHAPTER-2 CIRCUIT DESCRIPTION
2.1. BLOCK DIAGRAM
2.2 OPERATION OF CIRCUIT
2.3 WAVE FORMS AT DIFFERENT STAGES
1. STAGE-1
2. STAGE-2
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3. STAGE-3
4. STAGE-4
5. STAGE-5
6. STAGE-6
CHAPTER-3 HARD WARE DESCRIPTION
3.1 LIST OF COMPONENTS
3.2 APPARATUS REQUIRED
3.3 DESCRIPTION OF COMPONENTS
1. LF 353 OP-AMP
2. LF 351 OP-AMP
3. NAND GATE
4. NOT GATE
5. 2N4392 JFET
6. ICL-8036 WAVE FORM GENERATOR
7. 74LS121 MONOSTABLE MULTI VIBRATOR
CHAPTER-4 HARD WARE CIRCUIT RESULTS
4.1. INPUT CONTROL CIRCUIT
4.2. WAVE FORM AT DIFFERENT STAGES
1. AT FIRST STAGE
2. AT FOURTH STAGE
3. AT FIFTH STAGE
4. OUT PUT PULSES TO G12
5. OUT PUT PULSES TO G34
CHAPTER-5 SOFTWARE RESULTS
5.1 INTRODUCTION TO CASPOC
5.2. SIMULATED CIRCUIT FOR GENERATION OF PULSES
1. CIRCUIT FOR GENERATION OF PULSES
2. WAVE FORM AT G1 POINT
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3. WAVE FORM AT G2 POINT
5.3. SIMULATED CIRCUIT OF AN INVERTER
1. CIRCUIT OF INVERTER
2. OUTPUT OF INVERTER CIRCUIT
5.4 ADDITIONAL WORK
INTRODUCTION TO MATLAB
PROGRAM OF SPWM
OUT PUT WAVE FORM
CHAPTER-6 CONCLUSION & FUTURE SCOPE
LIST OF REFFERENCES
APPENDIX
LIST OF FIGURES
1.1. FIG SHOWING LINEAR MODULATION
1.2. FIG SHOWING AMPLITUDE MODULATION
1.3. FIG SHOWING MULTIPLE PULSE WIDTH MODULATAION
1.4. FIG SHOWING SINUSOIDAL PULSE WIDTH MODULATION
1.5. FIG SHOWING UNIPOLAR OPERATION
1.6. FIG SHOWING OUT PUT PULSES OF UNIPOLAR MODULATION
1.7. FIG SHOWING BIPOLAR OPERATION
1.8. FIG SHOWING OUT PUT PULSES OF BIPOLAR MODULATION
1.9. FIG SHOWING INVERTER OPERATION
2.1. FIG SHOWING BLOCK DIAGRAM
2.2. FIG SHOWING SINE PWM CIRCUIT
2.3. FIG SHOWING GENERATION OF SINE WAVE
2.4. FIG SHOWING THE WAVE FORM AT PIN-2
2.5. FIG SHOWING TO CONVERT SINE WAVE FORM TO SQUARE WAVE FORM
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2.6. FIG SHOWING GENERATION OF PULSES
2.7. FIG SHOWING PULSES WAVE FORM
2.8. FIG FOR GENERATION OF TRIANGULAR WAVE
2.9. FIG FOR GENERATION OF TRIANGULAR WAVE AT PIN-3.
2.10. FIG FOR GENERATION OF PULSES
2.11. FIG SHOWING THE OUTPUT PULSES AT PIN-1 OF OA-4
2.12. FIG SHOWING THE PULSES OF INVERTER
2.13. FIG TO SHOW PULSES AT G12.
3.1 FIG SHOWING LF351 OPAMP
3.2 FIG SHOWING INTERNAL BLOCK DIAGRAM
3.3 FIG SHOWING DIP TOP VIEW OF LF351
3.4 FIG SHOWING NAND GATE
3.5 FIG SHOWING NAND DIP
3.6 FIG SHOWING DIP AND NOT GATE DIAGRAM
3.7 FIG SHOWING JFET REALISATION
3.8 FIG SHOWING PINDIAGRAM OF ICL8038
3.9 FIG SHOWING FUNCTION DIAGRAM OF ICL-8038.
3.10 FIG SHOWING PINDIAGRAM OF 74LS121.
3.11 FIG FUNCTION TABLE OF 74LS121
4.1 FIG SHOWING INPUT TO ICL-8038
4.2 FIG SHOWING HARD WARE SINWAVE KIT
4.3 FIG SHOWING HARDWARE OUTPUT AT POINT A
4.4 FIG SHOWING TRIANGULAR HARDWARE KIT
4.5 FIG SHOWING HARD WARE OUTPUT AT POINT B
4.6 FIG SHOWING HARDWARE KIT FOR GENERATION ON PULSES
4.7 FIGURE SHOWING OUTPUT PULSES GENERATED AT C
4.8 FIGURE SHOWING OUTPUT PULSES AT GATE 12 IN KIT
4.9 FIGURE SHOWING PULSES AT GATE12
4.10 FIGURE SHOWING OUTPUT PULSES AT G34 IN KIT
4.11 FIGURE SHOWING OUTPUT PULSES AT G34
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5.1 FIGURE SHOWING GENERATION OF PULSES IN CASPOC
5.2 FIGURE SHOWING PULSES FOR G1 BY CASPOC
5.3 FIGURE SHOWING OUTPUT PULSES FOR GATE G2 IN CASPOC
5.4 FIGURE SHOWING INVERTER CKT IN CASPOC
5.5 FIGURE SHOWING OUTPUT WAVE FORM OF INVETER IN CASPOC
LIST OF SYMBOLS
L: INDUCTOR
C: CAPACITOR
V: SOURCE VOLTAGE
Q1, Q2, Q3, Q4 ARE SWITCHES.
LIST OF ABBREVATIONS:
PWM: PULSE WIDTH MODULATION
OP-AMP: OPERATIONAL AMPLIFIER
J-FET: JUNCTION FIELD EFFECT TRANSISTOR
SPWM: SINUSOIDAL PULSE WIDTH MODULATION.
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ABSTRACT
In an inverter circuit, dc power is converted to ac power. The output frequency
of static inverter is determined by the rate at which semiconductor devices are switched
ON and OFF by inverter control circuitry consequently, an adjustable frequency ac
output can be readily provided. However, the basic switching action of inverter normally
results in non-sinusoidal output voltage and current waveforms that may adversely affect
motor load performance. The filtering of harmonics is not feasible when output frequency
varies over wide range; hence generation of ac waveform with low harmonic content is
important. When inverter feeds an ac motor the output voltage must be varied in
conjunction with frequency to maintain proper magnetic conditions.
Output voltage control is therefore an essential feature of adjustable
frequency system, and various techniques for achieving voltage control within inverter
are considered in this paper. The various PWM strategies which are commonly used in
inverters are multiple pulse width modulation, sinusoidal pulse width modulation, delta
modulation, trapezoidal modulation etc. The simulation results for each PWM strategy
are presented in this paper. The harmonic analysis of each PWM strategies carried out
by varying modulation index.
Keywords: Harmonic; PWM; Inverters; Modulation index
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INTRODUCTION
Pulse width modulated (PWM) inverters are widely used in industrial
motor drive and uninterrupted power supply (UPS) systems. The PWM technique offers
control of voltage, frequency and harmonics in one power stage, however, the control
circuitry is relatively complex and a large number of commutations per cycle are required
for improved performance. It is desirable that the inverter be simple to implement and
should required minimum number of commutation per cycle to improve efficiency and
output performance to be acceptable.
In PWM, the fundamental and harmonic components in the output voltage
are controlled by the proper choice of pulse pattern in each half cycle. The harmonic
components of the voltage are undesirable and are products of the inverter switching;
they produce harmonic losses in an ac load. In induction motor drive application, the
harmonic terms results in large rotor losses and heating. Therefore, it is important to
choose a modulation strategy, which would keep the harmonic loss low.
One approach in reducing harmonic losses would be to increase the number
of pulses at the inverter output, whereby the order of harmonics is increased. The higher
order harmonics are more easily filtered by the motor leakage reactance. However, the
increased number of pulses necessitates higher commutation rates, resulting in increased
commutation losses. The advantage of PWM scheme depends; therefore, on harmonic
contents generated, as well as on the commutation losses produced.
The output voltage wave shapes produced by the PWM inverters determined
by the choice of carrier and modulating signals and their frequency ratio. The choice of
11
particular modulation strategy becomes more important as it affects the harmonic
generated and thereby the system efficiency. In many industrial applications it is often
required to control the output voltage of inverters to cope with the variations in dc input
voltage, for voltage regulation of inverters, and for constant v/f control requirements.
There are various technique to vary the inverter gain. The most efficient method for
controlling the gain is to incorporate pulse width modulation control within the inverters.
The following PWM strategies for voltage control and/or selective reduction of
harmonics in inverters are considered.
The project presents a novel circuit for generating the Sine PWM control
signals for a single phase inverter. Waveform generating IC’s are used to generate the
synchronized sine and triangular waveforms with a high accuracy and wide range of
frequencies. Experimental waveforms and frequency spectra of inverter output voltage
are presented
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Chapter-1
PULSE WIDTH MOUDLATION
1.1) Modulation: Controlling or regulation a complex wave is called as Modulation. These are many
Forms of modulation used for communicating information. When a high frequency signal
has amplitude varied in response to a lower frequency signal we have AM(amplitude
modulation). When the signal frequency is varied in response to the modulating signal we
have FM(frequency modulation). These signals are used for radio modulation because the
high frequency carrier signal is needs for efficient radiation of the signal. When become
possible modulation options. In many power electronic converters where the output
voltage can be one of two values the only option is modulation of average conduction
time.
1.2) Basic Classification of Modulation:
Basically the modulation techniques can be classified as
1) Amplitude Modulation
2) Linear Modulation
3) Pulse Width Modulation
1.2.1) Linear Modulation
The simplest modulation to interpret is where the average ON time of the
pulses varies proportionally with the modulating signal. The advantage of linear
processing for this application lies in the ease of de-modulation. The modulating signal
can be recovered from the PWM by low pass filtering. For a single low frequency sine
wave as modulating signal modulating the width of a fixed frequency (fs) pulse train the
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spectra is as shown in Fig . Clearly a low pass filter can extract the modulating
component fm.
1.1 Fig showing linear modulation.
1.2.2) Amplitude modulation (AM)
This is a technique used in electronic communication, most commonly for
transmitting information via a radio carrier wave. AM works by varying the strength of
the transmitted signal in relation to the information being sent. For example, changes in
the signal strength can be used to reflect the sounds to be reproduced by a speaker, or to
specify the light intensity of television pixels. (Contrast this with frequency modulation
also commonly used for sound transmissions, in which the frequency is varied; and phase
modulation, often used in remote controls, in which the phase is varied.). A form of
amplitude modulation—initially called "adulatory currents"—was the first method to
successfully produce quality audio over telephone lines. Beginning with Reginald
Fessenden's audio demonstrations in 1906, it was also the original method used for audio
radio transmissions, and remains in use today by many forms of communication—"AM"
is often used to refer to the medium wave broadcast band (see AM radio).
14
1.2 FIG SHOWING AMPLITUDE MODULATION.
1.2.3) PULSE WIDTH MODULATION:-
In many industrial applications, to control of the output voltage of inverters
is often necessary.
1) To cope with the variations of dc input voltage
2) To regulate voltage of inverters
3) To satisfy the constant volts and frequency control requirements.
There are various techniques to vary the inverter gain. The most efficient method of
controlling the gain is to incorporate PWM control within the inverters. The commonly
used PWM techniques are
Single Pulse modulation
15
Multi Pulse modulation
Sinusoidal Pulse modulation
Phase displacement control
1.3) Single Pulse width Modulation:-
In single pulse width modulation control there is only one pulse per half
cycle and the width of the pulse is varied to control the inverter output voltage. The
figure gives how the gating signals and output voltage of single-phase full-bridge
inverters. Here the gating signals are generated by comparing a rectangular reference
signal of amplitude Ar with a triangular carrier wave of amplitude Ac. The frequency of
the reference signal determines the fundamental frequency of the output voltage. The
ratio of Ar to Ac is called the modulating index.
M=Ar/Ac.
The rms output voltage can be given by the formula VRMS= Vs√ (δ/π).
By varying Ar from 0 to Ac, the pulse width δ can be modified from 0 deg to 180 deg and
the rms output voltage VO, from 0 to Vs.
ADVANTAGES:-
a. Due to the symmetry of the output voltage along the x-axis, the even
harmonics are absent.
b. The DF increases significantly at a low output voltage.
DISADVANTAGE:-
a. The third harmonic is dominant and is high which will distort the output .
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1.4) MULTI PULSE WIDTH MODULATION:-
In multiple pulse modulation several pulses in each half cycle of output
voltage can reduce the harmonic content. The generation of gating signals for turning ON
and OFF the thyristors is shown in Figure 1 by comparing rectangular signal with a
triangular carrier wave. The frequency of the reference signal sets the output frequency fo
and the carrier frequency fc determines the number of pulse per half cycle (p). The
modulation index (MI) controls the output voltage. This type of modulation is known as
uniform pulse width modulation (UPWM), since the width of all the output pulses is
uniform. The number of pulses per half cycle is given by
p = fc / 2 f0 = mf / 2
Where mf = fc / f0, is the frequency modulation ratio
The variation of modulation index (MI) from 0 to 1 varies the pulse width from 0
to / p and output voltage varies between 0 to Vs. The output voltage for single phase
inverter is shown in Figure.
17
1.3 Fig showing MULTIPLE PULSE WIDTH MODULATAION.
If is the width of each pulse, the rms output voltage can be obtained from the following
equation.
VO= Vs√ (pδ/π).
ADVANTAGES:-
The order of harmonics is the same as that of single-pulse width modulation.
The distortion factor reduces significantly compared with that of single-pulse
modulation.
The higher order harmonics produce negligible ripple or can easily be filtered
out.
DISADVANTAGES:-
Due to larger number of switching on and off processes of power transistors, the
switching losses would increase.
With large values of P, the amplitudes of LOH would be lower, but the
amplitude of that harmonics would increases.
1.5) SINUSOIDAL PULSE WIDTH MODULATION:-
In sinusoidal PWM, Instead of maintaining the width of all the pulses same as in
case of multiple pulse modulation, the width of each pulse is varied in proportion to the
amplitude of a sine wave which is evaluated at the same pulse. The gating signals are
generated by comparing sinusoidal reference signal with a triangular carrier wave of
frequency fc. This is generally used in industrial applications. The frequency of reference
wave is fr determine the inverter output frequency fo, and its peak amplitude Ar controls
the modulation index M, and then in turn the rms output voltage Vo. The no. of pulses
18
per half-cycle depends on the carrier frequency. The output voltage can be varied by
varying the modulation index M.
1.4 FIG SHOWING SINUSOIDAL PULSE WIDTH MODULATION.
Ar controls the modulation index (MI) and the output voltage Vo. It can be observed that
the area of each pulse corresponds to the area under sine wave between the adjacent
midpoints of OFF periods on the gating signals. If δm is the width of mth pulse the rms
output voltage can be obtained as
P V0 = Vs Σ √ [δm⁄ π] m = 1 There are again two types of sinusoidal pulse modulation are observed
Unipolar sinusoidal pulse width modulation
Bipolar sinusoidal pulse width modulation.
19
1.5.1) UNIPOLAR PULSE WIDTH MODULATION:
1.5 FIG SHOWING UNIPOLAR OPERATION.
1.6 FIG SHOWING OUT PUT PULSES OF UNIPOLAR MODULATION.
20
1.5.2) BIPOLAR PULSE WIDTH MODULATION:-
1.7 FIG SHOWING BIPOLAR OPERATION
1.8 FIG SHOWING OUTPUT PULSES OF BIPOLAR OPERATION.
21
ADVANTAGES:-
The DF is significantly reduced compared with that of multiple pulse
modulations.
This type of modulation eliminates all harmonics less than or equal to 2P-1.
The output voltage of an inverter contains harmonics .The PWM pushes the
harmonics into a high-frequency range around the switching frequency fc .
Fn=(jmf±k)fc.
1.6) OPERATION OF INVERTERS USING PWM
DC-to-AC converts are known as inverters. The function of an inverter is to change a dc
input voltage to a symmetric ac output voltage of desired magnitude and frequency.
The output voltage can be obtained:-
1) By varying the input dc voltage and maintaining the gain of the inverter
constant.
2) If the dc input voltage is fixed and it is not controllable a variable output
voltage can be obtained by varying the gain of the inverter, which is generally
accomplished by pulse width modulation.
Here the gain can be identified as the ratio of AC output voltage to DC input
voltage.
Inverters can be broadly classified into two types
1) Single-Phase inverters
2) Three-Phase inverters
So, these inverters employs PWM control signal for producing an ac output voltage.
22
1.7) PRINCIPLE OF OPERATION:-
The inverter circuit consists of two choppers. When only transistor Q1 is
turned on for a time To/2 the instantaneous voltage across the load Vo is Vs/2. If the
transistor Q2 is turned on for a time To/2 ,-Vs/2 is voltage at load is observed.
The root mean square velocity can be found from
Vo= Vs/2
The logic circuit is designed in such a way that Q1 and Q2 are not turned on at the same
time. So here the PWM technique is used in such a way that the gate pulses is given to
the inverter which will decide the output of the inverter. So depending on width of pulses
the output of the inverter also varies accordingly. The below figure tells how inverter
works.
1.9 FIG SHOWING INVERTER OPERATION
23
Pulses obtained are given to inverter
CHAPTER-2
CIRUIT DESCRIPTION
BLOCK DIAGRAM OF SINE PWM TECHNIQUE
24
2.2) CIRCUIT DIAGRAM OF SINE PULSE WIDTH MODULATION
2.2) OPERATION OF THE CIRCUIT
The Waveform Generator ICL 8038 is a monolithic integrated circuit (IC)
capable of generating high-accuracy sine, triangular, and square waveforms. The
25
frequency of the waveforms can be adjusted by varying the values of the R-C elements
connected externally to the IC. It is also possible to adjust the frequency by varying the
voltage applied to its frequency modulation sweep-input pin (8). A reference sine wave
of the desired output frequency and a triangular wave of a higher frequency are used in
generating the Sine PWM signal. Each signal is generated by using a separate. IC, and
then the two are synchronized.
The diagram of the SPWM controller is shown in Fig. The output frequency of
the waveform generators WGs and WGt can be independently varied by adjusting the
potentiometers Rs (sine wave) or Rt (triangular wave). The output Vc from the non
inverting amplifier OAl is applied to the FM sweep input pins of both the IC’s to vary
their frequencies simultaneously. If fs and ft are the frequencies of the sine and triangular
waveforms, then P is given by ft/(2 fs). An integer value of P is obtained by adjusting Rs
or Rt.
In addition to maintaining an integer value of P, the sine and triangular
waveforms are to be synchronized in order to avoid the presence of sub harmonics in the
output. The two waveforms are synchronized by initializing the timing capacitor Ct of the
triangular waveform generator at the end of each sinusoidal cycle. The sine waveform is
converted into a square waveform using the comparator OA2, and is applied to a
monostable through a differentiating circuit. The monostable generates narrow pulses
with a frequency fs and coinciding with the zero crossing points of the sine wave. The
pulses are level-shifted and applied to the gate of a JFET connected across Ct. The JFET
shorts Ct at the end of each sinusoidal cycle and allows the triangular wave to restart.
Once the frequency of the triangular wave is adjusted to be an integral multiple of the
Sine wave, the triangular wave will be continuous without any break.
The sinusoidal output of the waveform generator is applied to the non
inverting amplifier that controls the amplitude of the sine wave, and hence the
modulation index of the PWM scheme. The comparator OA4 compares the sine and the
triangular waveforms, there by generating the basic SPWM output. The gate drive
Signals for the four switches (G12 and G34) of the single phase inverter are obtained by
passing the basic PWM signal through a set of inverters and NAND gates, as shown in
Fig. The gate signals are then passed through suitable gate drivers that generate signals
26
with the proper amplitude and current capability to drive the particular switching device
selected.
2.3) WAVE FORMS AT DIFFERENT STAGES
1) STAGE-1
The total circuit was divided into no. of stages to reduce the
complexity in understanding. The output waveforms at different stages will be illustrated
in the following lines.
2.3 FIG SHOWING GENERATION OF SINE WAVE
Here in the first step through op-amp OA-1 we will get 12V source by varying the
resistance 10k we can get variable voltage at the PIN-7. By varying the voltage at PIN-7
we will get FREQUENCY MODULATED WAVE FORM at ICL8038. Here the wave
form generator ICL8038 is integrated monolithic integrated chip which is used to
generate sine wave of variable frequency. Here the frequency can be varied by two ways
27
1. By varying the voltage at pin-8
2. By varying the resistance Rs which is at PIN-5 & PIN-6.
2) STAGE-2:-
Here at stage-2 we will generate triangular wave form. For generation of
the triangular wave form first the triangular wave is to be synchronized with the sine
wave form, to do this we first take the sine wave and convert it into a square wave form
by using comparator OA-2.which is not shown in figure.
2.4) FIG SHOWING THE WAVE FORM AT PIN-2
28
2.5) FIG TO CONVERT SINE WAVE FORM TO SQUARE WAVE FORM
3) STAGE-3
2.6) FIG SHOWING GENERATION OF PULSES
29
Here in the third stage we will generate pulses by using IC74LS121 which is
a monostable multivibrator here at pins B & C we will give voltage at one third and at
two third so that it will used in generating pulses at zero crossings of the sine wave. Here
by varying the 10k resistance we can change the voltage of pulses.
2.7) FIG SHOWING PULSES WAVE FORM
4) STAGE-4
Here for after generation of pulses at zero crossings of sine wave these pulses are used to
short the terminals of JFET 2N4392.so at ever zero crossing a pulse shorts the JFET
which is used to short the capacitor Ct. So at each and every time of zero crossings of
wave forms a triangular wave will be generated at PIN-3 by the wave form generator
ICL8038. Here also we can vary the frequency in two ways
1. By changing the voltage at PIN-8.
2. By changing the resistance Rt which is at PIN-5 & PIN-6.
30
2.8 FIG FOR GENERATION OF TRIANGULAR WAVE.
2.9 FIG FOR GENERATION OF TRIANGULAR WAVE AT PIN-3.
31
5) STAGE-5
2.10)FIG FOR GENERATION OF PULSES
Here at the stage-5 we first decide the modulation index at IC OA-3 so that we will have
control on the output. Then the triangular wave form and the sine wave form at
comparator OA4 so that we will get pulses.
32
2.11 FIG SHOWING THE OUTPUT PULSES AT PIN-1 OF OA-4.
6) STAGE-6
2.12 FIG SHOWING THE PULSES OF INVERTER.
33
Here the pulses obtained at one set of NAND gates 74LS00 and NOT gate 74LS04 are
carried to gate G12 another set are carried to gate G34. Here pulses obtained to gate G34
are inverted so that they can be given to another set of pulses. Which are shown in the fig
2.13) FIG TO SHOW PULSES AT G12.
34
CHAPTER-3
HARD WARE
3.1) LIST OF COMPONENTS:
1. LF353 OPAMP
2. LF351 OPAMP
3. ICL 8038 Wave form generator
4. 1N473 Zener diode.
5. 2N4392 j-fet.
6. 74LS121 Mono stable multivibrator.
7. 74LS00 Nand gate
8. 74LS04 Not gate.
9. Resistors
10. Capacitors.
3.2) APPARATUS REQUIRED:
1. Revised power supply
2. Function generator
3. Cathode Ray Oscilloscope
4. Step Down Transformer
5. Inverter.
35
3.3) DESCRIPTION OF COMPONENTS
1) LF353 OPAMP
3.1 FIG SHOWING LF351 OPAMP.
Description:
This device is a low-cost, high-speed, JFET-input operational amplifier with very
low input offset voltage. It requires low supply current yet maintains a large gain-
bandwidth product and a fast slew rate. In addition, the matched high-voltage JFET input
provides very low input bias and offset currents.
The LF353 can be used in applications such as high-speed integrators, digital-to-
analog converters, sample-and-hold circuits, and many other circuits. The LF353 is
characterized for operation from 0°C to 70°C.
36
INTERNAL BLOCK DIAGRAM:
3.2 FIG SHOWING INTERNAL BLOCK DIAGRAM.
2) LF351 OPAMP: This is also same as that of LF351, but with little modifications. These
circuits are high speed J–FET input single operational amplifiers incorporating well
matched, high voltage J–FET and bipolar transistors in a monolithic integrated circuit.
The devices feature high slew rates, low input bias and offset currents, and low offset
voltage temperature coefficient.
37
3.3 FIG SHOWING DIP TOP VIEW OF LF351
3) NAND GATE:-
3.4 FIG SHOWING NAND GATE
This NAND gate we have taken is QUAD-2 INPUT NAND gate which has 4 NAND
GATES built in it. An NAND gate has two or more than two inputs as indicated. It
recognizes only the even no. of pulses.
3.5 FIG SHOWING NAND DIP
4) NOT GATE:-
38
3.6 FIG SHOWING DIP AND NOT GATE DIAGRAM.
Here the IC designed is HEX INVERTER not gate which contains 6 NOT gates.
5)2N4392 j-fet:
3.7 FIG SHOWING JFET REALISATION
39
Here the JFET used is a N-CHANNAL which can be used for the SWITCHING purpose. The forward drain current IDss =50mA.
6) ICL8038 WAVE FORM GENERATOR:
The ICL8038 waveform generator is a monolithic integrated circuit capable of
producing high accuracy sine, square, triangular, saw tooth and pulse waveforms with a
minimum of external components. The frequency (or repetition rate) can be selected
externally from 0.001Hz to more than 300 kHz using either resistors or capacitors, and
frequency modulation and sweeping can be accomplished with an external voltage. The
ICL8038 is fabricated with advanced monolithic technology, using Schottky barrier
diodes and thin film resistors, and the output is stable over a wide range of temperature
and supply variations. These devices may be interfaced with phase locked loop circuitry
to reduce temperature drift to less than 250ppm/oC.
Application Information:
An external capacitor C is charged and discharged by two current sources. Current source
#2 is switched on and off by a flip-flop, while current source #1 is on continuously.
Assuming that the flip-flop is in a state such that current source #2 is off,
40
3.8 FIG SHOWING PINDIAGRAM OF ICL8038
and the capacitor is charged with a current I, the voltage across the capacitor rises linearly
with time. When this voltage reaches the level of comparator #1 (set at 2/3 of the supply
voltage), the flip-flop is triggered, changes states, and releases current source #2. This
current source normally carries a current 2I, thus the capacitor is discharged with anet-
current I and the voltage across it drops linearly with time. When it has reached the level
of comparator #2 (set at 1/3 of the supply voltage), the flip-flop is triggered into its
original state and the cycle starts again.
With the current sources set at I and 2I respectively, the charge and
discharge times are equal. Thus a triangle waveform is created across the capacitor and
the flip-flop produces a square wave. Both waveforms are fed to buffer stages and are
available at pins 3 and 9. The levels of the current sources can, however, be selected over
a wide range with two external resistors. Therefore, with the two currents set at values
different from I and 2I, an asymmetrical saw tooth appears at Terminal 3 and pulses with
a duty cycle from less than 1% to greater than 99% are available at Terminal 9. The sine
wave is created by feeding the triangle wave into a nonlinear network (sine converter).
This network provides decreasing shunt impedance as the potential of the triangle moves
toward the two extremes.
41
3.9 FIG SHOWING FUNCTION DIAGRAM OF ICL-8038.
WAVE FORM TIMING:
The symmetry of all waveforms can be adjusted with the external timing
resistors. Two possible ways to accomplish this are shown in Figure 3. Best results are
obtained by keeping the timing resistors RA and RB separate (A). RA controls the rising
portion of the triangle and sine wave and the 1 state of the square wave. The magnitude
of the triangle waveform is set at 1/3 VSUPPLY; therefore the rising portion of the
triangle is, neither time nor frequency are dependent on supply voltage, even though none
of the voltages are regulated inside the integrated circuit. This is due to the fact that both
currents and thresholds are direct, linear functions of the supply voltage and thus their
effects cancel. The time period of triangular wave is given in equation
T1=(Ra× C)/ 0.66
Thus a 50% duty cycle is achieved when RA = RB.
42
If the duty cycle is to be varied over a small range about 50% only, the connection shown
in Figure 3B is slightly more convenient. A 1kΩ potentiometer may not allow the duty
cycle to be adjusted through 50% on all devices. If a 50% duty cycle is required, a 2kΩ or
5kΩ potentiometer should be used. With two separate timing resistors, the frequency is
given by:
If RA = RB = R
f=0.33/RC
7)74LS121 MONOSTABLE MULTIVIBRATOR:
3.10 FIG SHOWING PINDIAGRAM OF 74LS121.
These multivibrators features dual negative-transitions-triggered inputs and
a single positive-transition triggered input which can be used as an inhibit input.
Complementary output pulses are provided.
Pulse triggering occurs at a particular voltage level and is not directly
related to the transitions time of the input pulse. Schmitt-trigger input circuitry for the B
input allow jitter free triggering from input with transition rates as slow 1 volt/sec.
providing the circuit with an excellent noise immunity of typical 1.2volts. A high
immunity to Vcc noise of typically 1.5 volts is also provided by internal latching
circuitry.
Once fired the output are independent of further transitions of the inputs
and are a function only of the timing components. Input pulses may be of any duration
relative to the output pulse. Output pulses length may be varied from 40 nanosecs to 28
43
secds by choosing appropriate timing components. With no external time in components
an output pulse of typically 30 or 35 nano secs is achieved which may be used as ad-c
triggered reset signal. Out put raise and fall times are TTL compatible and independent
for pulse length.
Pulse width stability is achieved through internal compensation and is
virtually independent of Vcc and temperature. In most applications. Pulse stability will
only be limited by the accuracy of external timing components.
Jitter free operation is maintained over the full temperature and Vcc ranges
for more than six decades of timing capacitance and more than one decade of timing
resistance.
3.11 FUNCTION TABLE OF 74LS121.
CHAPTER-4
HARD WARE CIRCUIT RESULTS
44
4.1) INPUT CONTROL CIRCUIT
4.1 FIG SHOWING INPUT TO ICL-8038
The above circuit shows the input circuit to the wave form generator of both triangular
wave form and the sinusoidal wave form generator. By varying the 10k pot we can vary
the output of the both sine wave frequency and triangular wave frequency.
4.2) WAVE FORM AT DIFFERENT STAGES
AT FIRST STAGE:-
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4.2 FIG SHOWING HARD WARE SINWAVE KIT.
4.3 FIG SHOWING HARDWARE OUTPUT AT POINT A
AT FOURTH STAGE:
46
4.4 FIG SHOWING TRIANGULAR HARDWARE KIT
4.5 FIG SHOWING HARD WARE OUTPUT AT POINT B
AT FIFTH STAGE:
47
4.6 FIG SHOWING HARDWARE KIT FOR GENERATION ON PULSES
4.7 FIGURE SHOWING OUTPUT PULSES GENERATED AT C
OUTPUT AT GATE G12:
48
4.8 FIGURE SHOWING OUTPUT PULSES AT GATE 12 IN KIT
4.9 FIGURE SHOWING PULSES AT GATE12
49
OUTPUT FOR GATE G34:
4.10 FIGURE SHOWING OUTPUT PULSES AT G34 IN KIT .
4.11 FIGURE SHOWING OUTPUT PULSES AT G34
CHAPTER-5
50
SOFTWARE RESULTS
5.1) INTRODUCTION TO CASPOC:
Simulation starts to have become an accepted tool for the design of
power electronics & electrical drives. Over the last 30 years there have been remarkable
advances in tools for the simulation of power electronics & electrical drives not only ins
the user interface of the programs but also in the methods on which there simulation tools
are based. Various methods of modeling &simulation packages are available but
integration of modeling & simulation for both motion control & power electronics into
one package is not so wide spread.
A new multi level simulation /animation tool CASPOC (compute aided
simulation of power converters) is used during simulation animate the power electronics
circuit on electrical drive. The user sees the level of node voltage, branch current &
current path is the circuit. It has many advantages like
Fast simulation of SMPS without convergence problems.
Showing simulation results immediately during simulation.
Special block diagram components for power electronics & drive simulation such
as DC motor, induction machine.
Direct link between block diagram and circuit model.
Here with the aid of CASPOC we have simulated single phase
transistorized PWM converter and the results are at the load and the load harmonics
are here under.
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5.2) SIMULATED CIRCUIT FOR GENERATION OF PULSES:
1)CIRCUIT FOR GENERATION OF PULSES
5.1 FIGURE SHOWING GENERATION OF PULSES IN CASPOC
2) WAVE FORM AT G1 POINT:
52
5.2 FIGURE SHOWING PULSES FOR G1 BY CASPOC.
Here the wave form given is generated by comparing sine wave with the triangular
wave. Here no. of pulses per half cycle are five.
3) WAVE FORM AT G2:
53
5.3 FIGURE SHOWING OUTPUT PULSES FOR GATE G2 IN CASPOC
Here the wave forms obtained are another set which are obtained by the not inverter
5.3) SIMULATION CIRCUIT OF AN INVERTER:
1) CIRCUIT OF INVERTER
54
5.4 FIGURE SHOWING INVERTER CKT IN CASPOC
Here the inverter circuit shown is simulated with an voltage of 500 VOLTS
with MOSFET.
2) OUTPUT WAVE FORM OF THE INVERTER CIRCUIT:
55
5.5 FIGURE SHOWING OUTPUT WAVE FORM OF INVETER IN CASPOC.
Here the fig shown is out put voltage of an inverter circuit here both voltage and current wave forms are giving.
ADDITIONAL WORK DONE
56
MATLAB INTRODUCTION:
Mat lab is a matrix based software package meant for power system analysis.
It gives numerical solutions to various vector matrix operations. The combination of
analysis capabilities, flexibilities, reliability and powerful graphics make MATLAB the
premier software package for electrical engineers.
MATLAB provides an interactive environment with hundreds of reliable and
accurate built in mathematical function .these functions provide solution to abroad range
of mathematical problem including matrix algebra, complex arithmetic linear systems,
differential equations, signal processing, optimization , non linear, systems and many
other types of specific computations. The most important feature of MATLAB is
programming capability, which is very easy to learn and to use and which allows user
developed functions.
In MATLAB, an elements enclosed by brackets and separated by semicolon
generate a column vector. In MATLAB a matrix is created with a rectangular array of
numbers surrounded by brackets. The elements in each row are separated by blanks or
commas. A semicolon must be used to indicate the end of row
57
CHAPTER-6
CONCLUSION
58
This project mainly describes about how the sinusoidal pulse width
modulation is realized in operation of inverters and how the output voltage is get varied
with the sinusoidal pulse width modulation eliminating the disadvantages of the single
pulse width and multiple pulse width modulations. Simulation models are developed both
in mat lab and in caspoc how we will get pulses and output voltage. From these
simulations we can observe how the pulses width is getting varied in sinusoidal pulse
width modulation.
We have developed hardware model in which the output was verified at
each stage of the circuit and the wave form resembles similar to that of practical work.
The SPWM control circuit proposed in the project is simple and gives a wide range of
output frequencies. The waveforms obtained are accurate, and the frequency and the
number of pulses per half-cycle can be easily varied. The experimental waveforms and
the frequency spectrum of the PWM signal are presented.
59
APPENDIX
LF 353 JFET INPUT OPERATION AMPLIFIER
60
LF351Single Operational Amplifier (JFET)
61
74LS121: MONOSTABLE WITH SCHMITT TRIGGER INPUTS
62
ICL8038
63
64
2N4392: JFET SWITCHINGN CHANNEL- DEPLETION
65