Final One

A NOVEL CONCEPT OF SINE PULSE MODULATIONUSING WAVE FORM GENERATORS A Project Report Submitted 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 Technology In

Electrical and Electronics Engineering By

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.TECH ASSOCIATE PROFESSOR

Department of Electrical and Electronics Engineering

GUDLAVLLERU ENGINEERING COLLEGE GUDLAVALLERU – 521 356 ANDHRA PRADESH 2007 1

A NOVEL CONCEPT OF SINE PULSE MODULATION USING WAVE FORM GENERATORS A Project Report Submitted 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 Technology In

Electrical and Electronics Engineering By

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.TECH ASSOCIATE PROFESSOR

Department of Electrical and Electronics Engineering

GUDLAVLLERU ENGINEERING COLLEGE GUDLAVALLERU – 521 356 ANDHRA PRADESH 2

2008

CERTIFICATE

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.

PROJECT ASSOCIATES

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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 3. STAGE-3 4. STAGE-4 5

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 3. WAVE FORM AT G2 POINT 5.3. SIMULATED CIRCUIT OF AN INVERTER

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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 2.6. FIG SHOWING GENERATION OF PULSES 2.7. FIG SHOWING PULSES WAVE FORM 7

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 5.1 FIGURE SHOWING GENERATION OF PULSES IN CASPOC 5.2 FIGURE SHOWING PULSES FOR G1 BY CASPOC

8

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 particular modulation strategy becomes more important as it affects the harmonic generated and thereby the system efficiency. In many industrial applications it is often

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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 spectra is as shown in Fig . Clearly a low pass filter can extract the modulating component fm.

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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).

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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 π / p and output voltage varies between 0 to Vs. The output voltage for single phase inverter is shown in Figure.

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1.3 Fig showing MULTIPLE PULSE WIDTH MODULATAION. If δ 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 per

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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.

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1.5.1) UNIPOLAR PULSE WIDTH MODULATION:

1.5 FIG SHOWING UNIPOLAR OPERATION.

1.6 FIG SHOWING OUT PUT PULSES OF UNIPOLAR MODULATION.

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1.5.2) BIPOLAR PULSE WIDTH MODULATION:-

1.7 FIG SHOWING BIPOLAR OPERATION

1.8 FIG SHOWING OUTPUT PULSES OF BIPOLAR OPERATION.

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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.

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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

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CHAPTER-2

CIRUIT DESCRIPTION BLOCK DIAGRAM OF SINE PWM TECHNIQUE

Sinusoidal Wave form generator

Input to Wave form generator

comparator Synchronizing circuit

Pulses obtained Pulses obtained are given to are given to inverter

inverter

Triangular Wave form generator

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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 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.

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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 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.

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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 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

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2.5) FIG TO CONVERT SINE WAVE FORM TO SQUARE WAVE FORM

3) STAGE-3

2.6) FIG SHOWING GENERATION OF PULSES

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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.

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2.8 FIG FOR GENERATION OF TRIANGULAR WAVE.

2.9 FIG FOR GENERATION OF TRIANGULAR WAVE AT PIN-3.

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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.

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2 .11 FIG SHOWING THE OUTPUT PULSES AT PIN-1 OF OA-4.

6) STAGE-6

2.12 FIG SHOWING THE PULSES OF INVERTER.

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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.

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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.

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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 gainbandwidth 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-toanalog converters, sample-and-hold circuits, and many other circuits. The LF353 is characterized for operation from 0°C to 70°C.

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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.

3.3 FIG SHOWING DIP TOP VIEW OF LF351

3) NAND GATE:-

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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:-

37

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:

38

3.7 FIG SHOWING JFET REALISATION

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,

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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 anetcurrent 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).

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This network provides decreasing shunt impedance as the potential of the triangle moves toward the two extremes.

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

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Thus a 50% duty cycle is achieved when RA = RB. 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.

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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 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

43

HARD WARE CIRCUIT RESULTS

4.1) INPUT CIRCUIT

CONTROL

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 44

AT FIRST STAGE:-

4.2 FIG SHOWING HARD WARE SINWAVE KIT.

4.3 FIG SHOWING HARDWARE OUTPUT AT POINT A

45

AT FOURTH STAGE:

4.4 FIG SHOWING TRIANGULAR HARDWARE KIT

4.5 FIG SHOWING HARD WARE OUTPUT AT POINT B

AT FIFTH STAGE: 46

4.6 FIG SHOWING HARDWARE KIT FOR GENERATION ON PULSES

4.7 FIGURE SHOWING OUTPUT PULSES GENERATED AT C

OUTPUT AT GATE G12:

47

4.8 FIGURE SHOWING OUTPUT PULSES AT GATE 12 IN KIT

4.9 FIGURE SHOWING PULSES AT GATE12

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OUTPUT FOR GATE G34:

4.10 FIGURE SHOWING OUTPUT PULSES AT G34 IN KIT .

4.11 FIGURE SHOWING OUTPUT PULSES AT G34

CHAPTER-5

49

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: 51

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:

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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 53

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:

54

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

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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

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CHAPTER-6

CONCLUSION 57

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.

APPENDIX 58

LF 353 JFET INPUT OPERATION AMPLIFIER

LF351

59

Single Operational Amplifier (JFET)

60

74LS121: MONOSTABLE WITH SCHMITT TRIGGER INPUTS

61

ICL8038

62

63

2N4392: JFET SWITCHINGN CHANNEL- DEPLETION

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