DC/AC PURE SINE WAVE INVERTER WITH MINIMAL HARMONIC CONTENT

DC/AC PURE SINE WAVE INVERTER WITHMINIMAL HARMONIC

B.E (EE) PROJECT REPORT

Department of Electrical Engineering

N.E.D. University of Engineering & TechnologyKarachi -75270

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DC/AC PURE SINE WAVE INVERTER WITHMINIMAL HARMONIC CONTENT

B.E (EE) PROJECT REPORT

Prepared by:

Abdul Basit Minhas EE-174

Rana Faraz Khan EE-175

Arsalan Ahmed Usmani EE-198

Habibullah Khan EE-210

Atif Iqbal EE-214

Project Advisors:

Internal advisor: External Advisor:

Sir.Hassan Ul Haq Mr Faisal Mairaj Department of Electrical

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Engineering, Assistant Manager, NED UET. K.E.S.C.

Department of Electrical Engineering

N.E.D. University of Engineering & TechnologyKarachi -75270

ABSTRACTThis project focuses on DC to AC power inverters, which aimto efficiently transform a DC power source to a high voltageAC source, similar to power that would be available at anelectrical wall outlet. Inverters are commonly used toconvert AC from DC sources which include solar panels,batteries, etc.

There are different DC-AC inverters available in the markettoday. They principally generate two different forms of ACoutput: modified sine wave, and pure sine wave.

A modified sine wave can be seen as more of a square wavethan a sine wave; it passes the high DC voltage for specifiedamounts of time so that the average power and rms voltage arethe same as if it were a sine wave. These types of invertersare much cheaper than pure sine wave inverter.

Pure sine wave inverters, produce a sine wave output similarto the one coming out of an electrical outlet. These devices

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are able to run more sensitive devices such as: laserprinters, laptop computers, power tools, digital clocks andmedical equipment. This form of AC power also reduces audiblenoise in devices such as fluorescent lights and runsinductive loads, like motors, faster and silently due to thelow harmonic distortion.

Our basic idea is to design an economical pure sine waveinverter, which not only increases the power quality of theoutput wave generated but also protects sensitive equipmentfrom damaging.

Although the basic circuit for an inverter may seem simple,accurately switching these devices to obtain pure sine waveprovides a number of challenges for the engineers. Toovercome these problems the solution proposed is first toselect the best technique for generating PWM(switchingscheme) and the resulting output, that would be done bycomparing different switching methods and choosing the onewhich has minimal harmonic content and less complexity.

Technique chosen to achieve this target is 3-level PWMtechnique, as it is much more effective than other techniquesat low costs. Results have been taken and proved thementioned technique as producing less harmonic compared withothers, with the use of control feedback and filter, althoughthe levels can be increased for more precision but the systembecomes expensive.

To make the project more efficient it is recommended that anactive filter should be used to make it much more reliablewith improved form factor of desired output wave.

TABLE OF CONTENTS

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CHAPTER # 01 – INTRODUCTION ABOUT INVERTER

1.1 SQUARE WAVE INVERTER 01

1.2 MODIFIED SINE WAVE INVERTER 01

1.3 PURE SINE WAVE INVERTER 02

1.4 GRID TIE INVERTERS 02

1.5 BENEFICIAL FOR 03

CHAPTER # 02 – DESIGN SPECIFICATIONS

2.1 INVERTER

2.2 TYPES OF INVERTER

2.2.1 SQUARE WAVE

2.3.2 MODIFIED SINE WAVE

2.3.3 PURE SINE WAVE

2.3SINE WAVE ON THE BASIS OF SWITCHING TECHNIQUES

2.4PULSE WIDTH MODULATION

2.5TYPES OF PWM

2.5.1 SYNCHRONOUS PWM

2.5.2 ASYNCHRONOUS PWM

2.5.3 PWM (BI-POLAR SWITCHING)

2.5.4 PWM (UNI-POLAR SWITCHING)

2.6 DIFFERENT HARDWARE TOPOLOGIES

2.6.1 PWM (2-LEVEL INVERTER)


2.7 MOSFET H-BRIDGE

2.8 MOSFET GATE DRIVER CIRCUIT

2.9 SNUBBER CIRCUIT

2.10 TRANSFORMER

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2.11 LOW PASS FILTER

2.12 FEEDBACK

CHAPTER #03- TWO LEVEL INVERTER

3.1TWO-LEVEL INVERTER

3.2PWM GENERATION BLOCK

3.3 MODEL OF TWO LEVEL INVERTER

3.3.1 PULSE GENERATOR

3.3.2 CONSTANT BLOCK

3.3.3 INTEGRATOR

3.3.4 GAIN

3.3.5 CONSTANT (1) BLOCK

3.3.6 INPORT (SINEWAVE 1 & SINEWAVE 2)

3.3.7 RELATIONAL OPERATOR

3.3.8 LOGICAL OPERATOR (NOT)

3.3.9 OUTPORT

3.3.10 SCOPE

3.4 SUB SYSTEM

3.5 MODULATION AND PULSES

3.6 MAIN BLOCK DIAGRAM

3.6.1 H-BRIDGE

3.6.2 TRANSFORMER

3.6.3 DIODE

3.6.4 WAVEFORM

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3.7 HARMONIC ANALYSIS

3.7.1 HARMONIC GRAPH

3.7.2 TOTAL HARMONIC DISTORTION

CHAPTER#04 THREE LEVEL INVERTER

4.1 THREE LEVEL INVERTER

4.2 PWM GENERATION BLOCK

4.3 MOCEL OF THREE LEVEL INVERTER



4.3.3 INTERGARTOR

4.3.4 GAIN


4.3.6 INPORT (SINE WAVE 1)


4.3.8 INPUT (SINE WAVE 2)


4.3.10 OUTPORT

4.3.11 SCOPE

4.4 SUBSTSTEM



4.7 OUTPUT WAVE FORM

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4.8.1 HARMONIC DIAGRAM


4.9 PASSIVE FILTER

4.10 FEEDBACK

CHAPTER # 5

CONCLUSION

REFERENCE

CHAPTER 01

INTRODUCTION

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Electrical power system require good power quality for its

proper function, for the increased demand of power there are

many problems to be solved, one of them is to fulfill the

increasing electricity demand by using alternative

(renewable) energy resources like solar system, wind power

etc. Generations from these resources require a storage

medium(Battery). Inverters are required for converting

battery power to Ac. The use of inverter is not limited to

renewable energy source storage conversion but may also be

used in different applications such as, variable frequency

drive (VFD), uninterruptible power supply (UPS). Inverters

ensure smooth power supply and equipment safety in case of

power shortages, the fact that makes them popular among the

3rd world countries facing power deficit.

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Conversion principle of DC to AC is same, but different

techniques provide same output with different harmonic

content.

1.1 Square wave inverter:

These types of inverters are very economical but the

output is not an exact sinusoidal wave plus it contains

high harmonic content, therefore it cannot be used in

high quality power system.

1.2 Modified sine wave:

The output of this inverter is similar to a square

wave output except that the output goes to zero volts

for a time before switching positive or negative.

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Sensitive (AC) equipment will work on this power source

at reduced efficiency of approximately 20% of the

maximum efficiency. If the equipment is a motor, then

the harmonics may produce vibrations and hissing sound

while operating. The wasted energy cause abnormal heat

which reduces the reliability and longevity of

equipment, in very sensitive equipment or abnormal cases

the equipment may damage.

1.3 Pure sine wave inverter:

Pure sine wave inverters are the most expensive

inverters, which limits their production. The harmonic

content is very low with good power quality. Such type

of inverter are mostly demanded in sensitive equipment,

which cannot width stand fluctuations, in rush current

and any other problems caused by high harmonic content.

Our focus is to make an economical pure sine wave

inverter so that it may become affordably available for

home users, cottage industries, small-scale business,

and etc. For this purpose we will analyze the inverters

on the basis of switching schemes, on the basis of

levels and on the basis of transformer. After the

analysis we would design the best inverter.

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1.5BENEFICIAL FOR

1. Home consumers: Having access to reliable dc to ac

convertors at minimum cost. Safety of all household

equipment connected to the inverter. Promotion and

motivation of a pure economical sine wave inverter with

respect to local parameters.

2. Industry: The inverter design will lead to better

industrial inverters working optimally under different

loads in varying operating conditions.

3. Researchers: The project will help local researchers

and designers in gauging different options available to

them while designing inverters for specific purposes.

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CHAPTER 02

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DESIGN

SPECIFICATION

2.1 INVERTER

An inverter is an electrical device that converts direct

current (DC) to alternating current (AC)[1]; the converted AC

can be generated at any required voltage and frequency with

the use of appropriate transformers, switching and control

circuits. Inverters are commonly used to convert AC from DC

sources which include solar panels, batteries, etc. inverters

perform opposite function of rectifier.

2.2 TYPES OF INVERTER

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The power invertors that present in the market converts

DC to AC based on methods which

are as follows:

SQUARE WAVE:

MODIFIED SINE WAVE:

PURE SINE WAVE:

Two Level PWM

Three Level PWM

Five Level PWM

2.2.1 SQUARE WAVE:

A square wave is a kind of

non sinusoidal waveform, most

typically seen in electronics

and signal processing. An ideal

square wave alternates

regularly and instantaneously

between two levels.

2.2.2 MODIFIED SINE WAVE:

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The output of a modified sine wave inverter is similar

to a square wave output except that the output goes to zero

volts for a time before switching positive or negative.

It is simple and low cost but

most AC motors will run on this

power source although at

reduction in efficiency of

approximately 20%and the motors

may also produce hissing sound while operating and will

eventually reduce the life of equipment. It reduces the

energy efficiency of motors and transformers by 10 to 20

percent. The wasted energy causes abnormal heat which reduces

the reliability and longevity of motors and transformers and

other devices, including some appliances and computer, thus

the life of equipment becomes less than its actual life and

some time it also damages the equipment.

2.2.3 PURE SINE WAVE:

A pure or true sine wave inverter converts the dc supply

into a near perfect or pure sine wave, replicating the supply

attained from a domestic ac power source such as a plug

socket. The sine wave has very little harmonic distortion

resulting in a very ‘clean’ supply and makes it ideal for

running electronic systems such as computers, motors and

microwave ovens and other sensitive equipment without causing

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problems or noise. Things like mains battery chargers also

run better on pure sine wave converters [4].

There are two methods in which the low voltage DC power is

inverted .The first being the conversion of the low voltage

DC power to a high voltage DC source, and then the conversion

of the high DC source to an AC waveform, using different

switching techniques. Another method to complete the desired

outcome would be to first convert the low voltage DC power to

AC using different switching techniques, and then use a

transformer to boost the voltage to 220 volts.

2.3 SINE WAVE ON THE BASIS OF SWITCHING TECHNIQUES

a) Two level PWM

b) Three level PWM

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c) Multilevel SPWM etc.

Our first task was to study different switching techniques to

achieve AC pure sine wave. The second task was to select the

design that has minimum harmonic content in other words

inverter that has minimum power loss in converting AC to DC,

thus being more efficient. The other consideration in

selecting the best switching method would be of its being

economical. The third task was to simulate the selected

design on Simulink and select the best components to achieve

the desired design that may include use of microcontrollers,

IR’s IBGTs instead of mosfets to make the circuit more

efficient. Fourth and final task will be to design hardware

of the selected inverter.

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Inverters can be further divided in two groups on the basis

of transformer

Transformer based: Transformer Less:

• More reliable

• Less complex

• High power application

• large size and weight

• Less efficient

• More use of fuse and

contractor

• More complex

• Low power application

• Small size and weight

• More efficient

2.4 PULSE WIDTH MODULATION [4]

Pulse-width modulation (PWM) is a technique in which

pulses are generated with variable widths according to the

interest of the user to control the output voltage generated

by dc-dc or dc-ac inverter systems on constant frequency,

Generally speaking PWM compares two signals, one taken as the

repetitive signal and the other as the control signal

whenever the power of control signal increases greater than

50% of the power of repetitive signal the PWM generates an ON

pulse, elsewhere 0 is generated .For a recursive system

having feedback. The control signal may be seen as an

amplified error signal or the difference between the actual

voltage signal and desired output voltage. The ratio of ON

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time period to that of the total time period is referred to

as switch duty ratio and is expressed as:

D=tonTs

[4]

The output of inverter circuits contain harmonics for that

reason another term regarding PWM is defined as amplitude

modulation Ma, which is a decisive factor, choosing an

appropriate value for Ma reduces harmonics in the system.

Amplitude modulation is expressed as :-

Ma=¿V>con¿V>tri;

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Where<v>con= peak amplitude of control signal ,

<v>tri= amplitude of repetitive signal

The choice of selection of Ma is not independent as it relies

heavily on the frequency of modulation too of the system,

which is defined as:-

Mf=FsF1; where

Fs= carrier frequency/ frequency of repetitive waveform

signal

F1= Modulating frequency/ frequency of control signal

2.5 TYPES OF PWM

Synchronous PWM

Asynchronous PWM

2.5.1 SYNCHRONOUS PWM

Is one in which the repetitive form signal is

synchronized with control signal, i.e. the frequency of

repetitive form signal varies with the inverter frequency.

The minimum requirement for achieving this type of PWM is to

keep the modulation frequency of the system an integer value.

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2.5.2 ASYNCHRONOUS PWM

Is one in which the frequency of repetitive pattern is

kept constant and the frequency of control signal is varied

such that the ratios of their frequency result in a (non-

integer) value. Since in asynchronous PWM the value of sub

harmonics are not negligible they are preferred over high

values of Mf, at high values of Mf the sub harmonics have

very less amplitude. Still these asynchronous PWM’s cannot be

used to control delicate devices which cannot width stand

inrush starting currents due to small values of sub

harmonics.

PWM switching schemes:-

PWM with Bi-polar switching

PWM with Uni-polar switching

2.5.3 PWM (BI-POLAR SWITCHING)

PWM of such types are used in systems in which output

voltage polarity is reversible, for example a full bridge

rectifier. The operation principle is the same as discussed

but here there are two switch pairs, which are turned ON and

OFF simultaneously. Since the output voltage varies between

+Vd and –Vd, the switching scheme is referred to as bi-polar

2.5.4 PWM (UNI-POLAR SWITCHING)

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Uni-polar switching is used in systems which have uni-

polar output voltage, for example single switch inverters. In

these systems the switches in inverters legs are controlled

individually. There are two control signals shifted 180

degrees apart , compared with the repetitive pattern signal

to generate the pulses for the inverter legs. For the same

switching frequency a Uni-polar PWM generates a better output

voltage waveform than a BI-polar, since it uses effective

switching provided by doubling the output voltage reducing

the ripple.

2.6 DIFFERENT HARDWARE TOPOLOGIES


PWM for 2 level inverters employ the technique explained

in Bi-polar PWM switching. Since the output of inverter leg B

is negative of the leg A output.

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[4]

In this PWM technique bipolar voltage wave form is obtained.

The diagonally opposite switches (TA +,TB-) and (TA -,TB+) from

two legs in fig are switched as switch pair 1 and 2,

respectively.

The output of inverter leg B is negative of the leg A

output.

When TAon and VA out is equal to +1/2VD ,TB – is on at the same

time then VB out is equal to -1/2VD therefore VB out =-VA out

So,

Vout (t) =2VA(t)

The wave formis given on the next page

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[4]

The peak of fundamental component is given

Vout (t) =maVDsuch that [ma≤ 1]

The output wave switches between +VDand -VDthat’s why it is

called bipolar inverter ot two level.

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These types of inverter outputs are generated by

employing Uni-polar PWM switching scheme, since the switches

are handled independently and individually, Referring to the

above given figure of full bridge inverter, leg A and B are

controlled separately by comparing the repetitive pattern

signal with both the control signals (shifted from each other

by 180˚) as shown below in the figure.

For controlling Leg A(+veVcontrol is compared with the

repetitive signal):-

Vcontrol>Vrep: Ta+ on and Van=Vd

Vcontrol<Vrep: Ta- on and Van=0

For controlling Leg B(-veVcontrol is compared with the

repetitive signal):-

(-Vcontrol)>Vrep: Tb+ on and Vbn=Vd

(-Vcontrol)<Vrep: Tb- on and Vbn=0

Uni polar output is due to the fact that it does not take

account of the direction of travel of current in the circuit

and that is made possible by connection of feedback diodes to

switches in anti-parallel

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[4]

2.7 MOSFET H-BRIDGE

A full bridge inverter is shown in fig-2. This inverter

has two one leg inverters and is preferred over other

arrangements in higher power ratings. With the same dc input

voltage, the maximum output voltage of the full-bridge

inverter is twice that of the half-bridge inverter, and for

the same power the current is reduced by half

[4]

Figure-2

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2.8 MOSFET GATE DRIVER CIRCUIT

The difference of voltage levels between the gate and

drain terminals of a MOSFET hampers the normal operation

process of inverter, since the MOSFET do not conduct until

unless the gate terminal is approximately 10V higher than the

drain terminal, normally the drain terminal is connected to

the highest voltage in the system(Vd>Vg). To overcome this

problem IC’s known as MOSFET drivers are deployed. These IC’s

increase the gate voltage by charging the input capacitance

of MOSFET before potential difference is reached.

[4]

Figure-3

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2.9 SNUBBER CIRCUIT

SNUBBERS are circuits used for protecting semiconductor

devices and to improve performance. The two most common ones

are the resistor-capacitor (RC) damping network and the

resistor-capacitor-diode (RCD) turn-off SNUBBER. Some of the

applications are:-

Reduce or eliminate voltage or current spikes

Limit dI/dt or dV/dt

Shape the load line to keep it within the safe operating

area (SOA)

Transfer power dissipation from the switch to a resistor

or a useful load

Reduce total losses due to switching

Reduce EMI by damping voltage and current ringing

2.10 TRANSFORMER

Transformer is a simple device that can be used in the

operation of stepping up or stepping down voltages. There are

two types of transformers:

Shell type

Core type.

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Both of them have their own advantages and disadvantages. In

inverter circuits transformers are deployed for stepping up

voltage levels

2.11 LOW PASS FILTER

LPF (low pass filter) is an active filter formed by

connecting L (inductance) with C (capacitance) in such a

manner that all undesired (High frequency) components are

suppressed from the signal.

2.12 FEEDBACK

Feedback is taken to control the output voltage as per

desire. As inverter loads the output voltage wave form

becomes distorted and cannot feed the connected load

properly, to combat this problem feedback is important part.

In feedback output voltage wave is compare with the desire

signal and error signal is generate. After amplifying error

signal it is sent to the comparator which then generates the

correct gate pulses for the desired output.

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CHAPTER 03

TWO LEVEL

INVERTER

SIMULATIONS

32

3.1 TWO-LEVEL INVERTER

After the study of different topologies of sine wave

inverter, we decided to work on PWM with levels that are (2

or 3 level), for simulation purpose we have used different

blocks from SIMULINK.

Our key object is to propose an economic model for that

reason we had to work on both 2 and 3 level inverter, at the

outset we are simulating 2-level inverter.

Inverters require MOSFET driving pulses (gate pulses) in

order to turn on and turn off the MOSFETS (switches) at a

particular pattern. These driving pulses can be generated by

implementing the algorithm on SIMULINK, which is discussed

below:


In PWM model we have performed following steps:

Generation of pulses

Making square wave by providing offset to pulses

Integrating pulses to get triangular wave

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Providing sine wave from inport and triangular wave to

comparator

Comparator perform modulation

Finally gate pulses for MOSFET obtained from comparator

Invert the pulses (for H-bridge operation)

Pulses are use with the help of outports.

3.3MODEL OF TWO LEVEL INVERTER

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SYMBOL

[1]

DETAIL

We have used this block in order to get pulses, we have

selected the amplitude equal to one and frequency 39 kHz

(this is the switching frequency of MOSFETS or time interval

of switching).

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Duty cycle of pulse generator is selected to 50% because we

will integrate these pulses to get triangular wave, and no

phase delay is provided to the signals. Finally Interpret

vector parameters are selected as 1-D.


SYMBOL

[1]

DETAIL

We have used this block to provide offset (0.5) so that

pulses should lie at center and represent a square wave. This

subtraction takes place by using addition block.

3.3.3 INTEGRATOR

SYMBOL

[1]

DETAIL

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This block is used to integrate a square wave, by integrating

square wave we can get triangular wave.

3.3.4 GAIN

SYMBOL

[1]

DETAIL

This block is used to provide gain in triangular wave. After

integrating the amplitude of triangular is different from the

amplitude of square wave.

Therefore to get desired amplitude of triangular wave we have

to multiply triangular wave with some gain.


SYMBOL

[1]

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DETAIL

We have used this block to provide offset (10) so that

triangular wave should lie at center and represent a

triangular wave. This subtraction takes place by using

addition block.

3.3.6 INPORT (SINEWAVE 1 & SINEWAVE 2)

SYMBOL:

[1]

DETAIL

It is used to link the blocks or data from outside into the

system. In order to reduce the size of simulation we have

connected two Sine waves with this input block.


SYMBOL

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[1]

DETAIL

It takes two inputs and compares them according to the given

instruction, by using this comparator we comparing sine wave

and triangular wave, which is known as pulse width

modulation. The output of this wave is provided to gate

pulses for MOSFETS switching.

3.3.8LOGICAL OPERATOR (NOT)

SYMBOL

[1]

DETAIL:

It inverts the pulses, used in MOSFET switching scheme.

3.3.9OUTPORT

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SYMBOL

]

[1

DETAIL

It links the system blocks from system to outside the system.

It is also done to reduce the size of simulation.

Modulation view. It shows the modulation in main system

block diagram

Pusle1=pulse2. It represents the pulse in main system so

that we can use that pulse.

Invert pulse1=invert pulse2. It represents the invert

pulse in main system so that we can use that pulse.

3.3.10SCOPE

SYMBOL

[1]

DETAIL

It shows the graph of signals.

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Scope1 shows the Modulation

Scope2 shows the gate signals

3.4SUB SYSTEM

After the formation of above main block select all the

components and then right click then click on create

subsystem. Then make subsystem and use it on main block.

By performing these steps we got the following subsystem

These in ports and out ports in this diagram are due to use

of in port and out port blocks in PWM generation block

diagram.

3.5MODULATION AND PULSES

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Figure-1 shows the modulation in which triangular wave has

amplitude equals to 10 and sine wave has 8. Therefore the

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modulation index is 0.8(reason of this modulation index is

mentioned in the background chapter)

Figure -2 shows the pulses which are generated as a result of

modulation, these pulses are gate pulses of MOSFET. Frequency

of the wave is 50Hz.

3.6MAIN BLOCK DIAGRAM

In above diagram sine wave and sinewave1 are connected with

subsystem, the output of subsystem contain modulation view,

pulse1, invert pulse1, pulse 2, invert pulse2.

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3.6.1 H-BRIDGE

In H-bridge upper Mosfet’s drains are connected with +ve

terminal of battery and lower Mosfet sources are connected

with –ve terminal of battery. Sources of upper Mosfet and

drain of lower Mosfet are connected with each other and form

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a link, where AC voltage is obtained after switching

operation. During switching operation

Mosfet and Mosfet3 in on at the same time Mosfet2 and Mosfet1

are off , When Mosfet2 and Mosfet1 are on then Mosfetand

Mosfet3 are off. If both combination areON at same time the

high short circuit occurs.[]

3.6.2 TRANSFORMER

It is connected across the MOSFET link and step up the 12VAC

to 220 V AC.

3.6.3 DIODE:

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Diodes are connected with MOSFETS to protect them, they are

working as Snubber.

3.6.4 WAVE FORM

This wave form is at no load. It looks like a square wave but

actually it is not because it has different average values at

a particular instant. Now we have to analyze the harmonics

in this wave.

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3.7 HARMONICS ANALYSIS

3.7.1 HARMONICS GRAPH

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ORDER OF HARMONICS MAGNITUDE1 1812 1073 23.34 33.55 466 22.87 10.48 28.5


THD is the ratio of RMS value of the total harmonics of the

signal to the RMS value of the fundamental harmonics.

THD =Vh/Vf

THD = 1.36

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CHAPTER 04

THREE LEVEL INVERTER

SIMULATIONS

49

4.1 THREE -LEVEL INVERTER

The main part of an inverter is control signal block

which generates the gate signals for MOSFET. It shows a major

role in harmonic content in output wave form.

If the frequency of these gate signals vary then harmonic

content is also vary, about this effect broad detail of

switching frequency is available in power electronics by

Mohan.


The PWM generation block we are describing is for 3-

levelinverter switching purpose.

4.3 MODEL OF THREE LEVEL INVERTER

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SYMBOL

[1]

DETAIL

We have used this block in order to get pulses, we have

selected the amplitude equal to one and frequency 39 kHz

(this is the switching frequency of MOSFETS or time interval

of switching).

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Duty cycle of pulse generator is selected to 50% because we

will integrate these pulses to get triangular wave, and we

don’t have provided any phase delay. Finally Interpret vector

parameters are selected as 1-D.


SYMBOL

[1]

DETAIL

We have used this block to provide offset (0.5) so that

pulses should lie at center and represent a square wave. This

subtraction takes place by using addition block.

4.3.3 INTEGRATOR

SYMBOL

[1]

52

DETAIL

This block is used to integrate a square wave, by integrating

square wave we can get triangular wave.

4.3.4 GAIN

SYMBOL

[1]

DETAIL

This block is used to provide gain in triangular wave. After

integrating the amplitude of triangular is different from the

amplitude of square wave. Therefore to get desired amplitude

of triangular wave we have to multiply triangular wave with

some gain.


SYMBOL

53

[1]

DETAIL

We have used this block to provide offset (10) so that

triangular wave should lie at center and represent a

triangular wave. This subtraction takes place by using

addition block.

4.3.6 INPORT (sine wave1)

SYMBOL

[1]

DETAIL



connected Sine wave with this input block.

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SYMBOL:

[1]

DETAIL

It takes two inputs and compare according to the given

instruction, by using this comparator we are comparing sine

wave and triangular wave, which is pulse width modulation.

The output of this wave is gate pulses for MOSFETS switching.

4.3.8 INPORT (SINEWAVE 2)

SYMBOL

[1]

DETAIL



connected Sine wave1 with this input block. This block is

used to make subsystem, will explain later.

55

Sine wave1 is same as sine wave2. But we have multiplied sine

wave2 with -1 by using gain block. After the multiplication

sine wave2 is 180 degree out of phase with sine wave1. After

this sine wave2 and triangular wave both are connected with

relational operator1, which is also generating gate pulses

for MOSFETS switching purpose. But in these pulses are 90

degrees out of phase with the pulses generated by relational

operator.


SYMBOL

[1]

DETAIL

It inverts the pulses, used in MOSFET switching scheme.

4.3.10 OUTPORT

SYMBOL

[1]

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DETAIL

It links the system blocks from system to outside the system.

It is also done to reduce the size of simulation.

Modulation view. It shows the modulation in main system

block diagram

Pusle1. It represents the pulse in main system so that

we can use that pulse

Invert pulse1. It represents the invert pulse in main

system so that we can use that pulse.

Pulse2. It is 90 degree out of phase with pulse1

Invert pulse2. It represent inverted pulse2

4.3.11 SCOPE

SYMBOL

[1]

DETAIL

It shows the graph of signals.

Scope1 shows the Modulation

Scope2 shows the gate signals.

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4.4 SUB SYSTEM

After the formation of above main block select all the

components and then right click then click on create

subsystem. Then make subsystem and use it on main block.

By performing these steps we got the following subsystem

These in ports and out ports in this diagram are due to use

of in port and out port blocks in PWM generation block

diagram.


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Figure-1 shows the modulation process of 3-level inverter and

figure-2 shows the gate pulses, which are generated as a

result of modulation for MOSFETS switching.

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The main block diagram of 3-level inverter is given below:

4.7 OUTPUT WAVE FORM

AT NO LOAD

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AT 50W LOAD

AT 100W LOAD

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Output wave of 3-level inverter at different loads shows that

as load increases voltage of the wave form decreases. In

order to avoid this affect we have to use feedback, so that

output voltage remains constant up to the rated KVA of

inverter.

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4.8.1 HARMONIC GRAPH

4.8.2 TOTAL HARMONICS DISTORTION

THD is the ratio of RMS value of the total harmonics of

the signal to the RMS value of the fundamental harmonics.

THD =Vh/Vf THD = 0.5

ORDER OF HARMONICS MAGNITUDE1 2133 49.25 53.17 9.829 33.811 013 25.115 9.11

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4.9 PASSIVE FILTER:

L3=1m Ohm; L4=10 micro Henry; L1=4 micro Farad; L2=10 Ohm

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OUTPUT:

Without Feedback Output Voltage at no load 220Volt

Without Feedback Output Voltage At 1KVA load:

Load=1 KVA

Power factor= 0.8 lagging

Active Power= 800W

Reactive Power= 600Var

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Output Voltage= 60Volt

4.10 FEEDBACK :

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AT NO LOAD:

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AT FULL LOAD (1 KVA):

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CHAPTER 05

CONCLUSIONS

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The major problem of harmonic content in different type of

inverter limits its use. Same limitation is also proposed by

cost factor. With the increasing demand of inverter in

various field of electrical engineering this problem has to

be solved, for that reason we had analyzed the inverter on

different basis to get optimal solution of this problem.

Through the analysis of inverter on the basis of levels, we

conclude that inverter with less level, have high harmonic

content and higher THD than inverters with more levels, which

have less harmonic content and less THD. Inverters with

greater levels are very costly due to their complicated

controlling. [2]

Through the analysis of inverter on the basis of transformer,

we came to know that there is isolation and cost problem,

fault management in transformer less inverter. But location

flexibility, input wave form management of transformer less

inverter is high and size and weight is less than inverter

with transformer. [3]

Through the analysis of different switching scheme of

inverter we conclude that 3- level inverters have less

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harmonic contents and THD than 2- level inverter. The

complexity of hardware is more in 3-level inverter than 2-

level inverter, although in simulation both seem to be

identical but practically they are poles apart, for example

their gate signals generation is different therefore

controlling is different.

REFERENCES:

[1] IEEE Industry Applications Magazine January/February 1996[2] A thesis submitted to department of computer science and engineering of BRAC University bay PAUL PURIFICATION. And MODELLING and SIMULATION OF SINGLE PHASE INVERTER WITH PWM USING MATLAB/SIMULINK AZUAN BIN ALIAS Faculty of electrical &electronic Engineering University Malaysia Pahang NOVEMBER, 2007 &International Journal of Computer Applications (0975 - 8887) Volume 12-No.11, January 2011[3] Comparing Transformer less to Transformer-based UPS design by EMERSION network power

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[4] [5] [6] Power electronics by NED MOHAN, TORE M.UNDELAND, and WILLIAM P.ROBBINS[7] International rectifier data sheet No: pd60147[8] www.mathworks.comand Introduction to Simulink with Engineering Application BY Steven T. Karris[2] International Journal of Computer Applications (0975 - 8887) Volume 12-No.11, January 2011

OTHER SOURCES

PPIB, Ministry of Water and Power

DC-AC/DC Power Inverter Team Not Platypus Matthew Brown HenryGodman John Martinez Dylan Paiton Matthew Paiz May 12, 2010.

Comparative Analysis of Voltage Control Signal Techniques forSingle Phase Inverter International Journal of Computer and Electrical Engineering, Vol. 3, No. 6, December 2011 Athar Hanif, Asim Mukhtar, Umar Farooq, and Abid Javed

IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 49, NO. 4, AUGUST 2002 Multilevel Inverters: A Survey of Topologies, Controls, and Applications José Rodríguez, Senior Member, IEEE, Jih-Sheng Lai, Senior Member, IEEE, and Fang Zheng Peng, Senior Member, IEEE

DC/AC PURE SINE WAVE INVERTER WITH MINIMAL HARMONIC CONTENT

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