DESIGN AND CONSTRUCTION OF A

2000W INVERTER

PRESENTED BY:

LAWAL SODIQ OLAMILEKAN

03191100
SUPERVISED BY:
MR FAYEMI
SUBMITTED TO:
DEPARTMENT OF ELECTRICAL ELECTRONICS ENGINEERING

INTELLECTUAL HARVARDE EDUCATIONAL SERVICE

ABEOKUTA STUDY CENTRE

OGUN STATE

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 CONTENTS

CHAPTER ONE: INTRODUCTION

 Background Information
 Problems Statement
 Aim And Objectives Of The Research Work
 Justification For The Research Work
 Motivation For The Work

CHAPTER TWO: LITERATURE REVIEW

 Introduction
 Brief Review Of Principles Behind This Work
 Background For Proposed Techniques
 Review Of Hardware And Software Resources ;
Capacitor, Resistor, Relay, Transistor, Diode, Transformer, Integrated Circuits (I.C), A.C
Voltage Meter, MOSFET

CHAPTER THREE: METHODOLOGY

 Overview Of Methodology;
Input Stage, Regulation, Control Logic, Oscillator, Phase Splitter, Driver Section, Step-Up
Transformer, Output Section
Input Stage, Isolating Relay, Step down Transformer, Rectifier Circuit via MOSFET

CHAPTER FOUR: RESULTS AND DISCUSSION

 Experimental Results
 User Experience
 System Evaluation

CHAPTER FIVE: SUMMARY AND FUTURE WORK

 Summary
 Future Work

REFERENCES

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 CHAPTER ONE

INTRODUCTION

 Background Information
From the late 19th century to the middle of 20th century, DC to AC power conversion was
accomplished using rotary converters or motor-generator (M-G) sets. In the early 20th
century, vacuum tube and gas filled tube began to be used as switches in inverter circuit.

The origination of electromechanical inverters explains the source of the term inverter.
Early AC to DC converters used an induction or synchronous AC motor direct-connected to a
generator (DYNAMO), so that the generator commutation reversed it connection at exactly
the right moment to produce DC. A later improvement is the synchronous converter, in
which the generator and motor winding are combined into one armature, with slip rings at
one end and the commutator at the other end and only one field frame. The result with either
AC - in, DC - out. With an M-G set, the DC can be considered to be separately generated
from the AC; with a synchronous converter, in a certain sense, it can be considered to be
“mechanically rectified AC”. Using the right auxiliary and control equipment, an M-G set or
rotary converter can “run backward”, converting DC to AC. Hence, an inverter is an inverted
converter. It should also be noted that early inverters did not use transistors for switching
purposes, because its voltage and current ratings were not high enough for most inverter
applications.

However, in 1975, the silicon control rectifier (SCR) was introduced as switches, hence
initiating a transition to solid state inverter circuits. Today, however due to an increased
knowledge in technology, modern inverters are less bulky and more efficient with the use of
various components such as ICs (Integrated Circuits).

 Problem Statement
If there is one factor that has perpetually maintained the status of Nigeria as a less
developed country, it is electricity sector. Till date, many households and businesses cannot
be guaranteed of 24 hours supply of electricity from the public grid. At this stage of Nigeria’s
social and economic development, the country cannot deliver adequate energy to the citizens
despite huge financial resources that have been expended in the sector.

Rather, Nigerians have continued to rely on electricity generators for their power supply.
Fuel marketers are taking significant portion of households’ and businesses’ incomes to

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 supply power. Noise pollution from regular humming generators has become integral part of
living for many Nigerians with imaginable consequences on their health.
The major limitation of this project is that it cannot operate equipment or an electronic
device that is above its rated current due to some form of losses during the circuit operation.

The design of this project is limited to input voltage of about 12V, capable of delivering
circuit ranging from 45A to 60A D.C. Although it can be extended further but for higher
capacity, the input voltage should be increased so as to minimize the current.

 Aim And Objective of The Research Work

The main aim of this project is to design and construct a 2KVA inverter with 12volts
supply so as to achieve the following objectives;

i. To ensure the protection of the back-up source consumer equipment and supply.

ii. To back-up the erratic power supply by PHCN.

iii To provide a noiseless source of electricity generation.

iv. To provide a source of electricity power with low maintenance cost and zero fuel cost

v. To design a circuit that will convert D.C to A.C power for various appliances used in
domestic home.

The design and construction of this project is to provide an ample chance for an
understanding of the characteristics, operations, and application of power electronic
devices.

 Justification Of The Research Work

Conventionally, there are two ways in which electrical power is transmitted. Direct
current (D.C) comes from a source of constant voltage and is suitable to short range or device
level transmission. Alternating current (A.C) consists of sinusoidal voltage source in which a
continuously changing voltage (and current) can be used. Long distance electrical
transmission favors A.C power, since the voltage can be boosted easily with the use of
transformers.
By boosting the voltage, less current is needed to deliver a given amount of power to a
load, reducing the resistive loss through conductors. The adaptation of A.C power has created
a trend where most devices adapt A.C power from an outlet into the need for mobility and
simplicity has given batteries an advantage in portable power.
Thus, for portable A.C power, inverters are needed. Inverter takes a D.C voltage from a
battery as input and converts it into an A.C voltage output. 2000 watt inverters are suitable
for heavy duty applications like washing machines, microwaves and refrigerators.

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 These inverters can be used as emergency power sources for home, at camping trips, on food
trucks or at camping sites.

 Motivation For The Work

Inverter are the best when it comes to back-up since they can come up very fast and they
generate little or no noise unlike generator. Even in an area with constant power supply,
power outage due to natural causes and faults are usually unannounced. It is therefore very
important to prevent causalities and loss of goodwill by having a reliable back-up power
installed.

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 CHAPTER TWO

LITERATURE REVIEW

 Introduction
This project is based on conversion of 12V DC to 2KVA AC power inverter whose aim is
to efficiently convert a DC power source to high voltage AC source, similar to power that
would be available at an electrical wall outlet. Inverters are used for many applications as in
a situation where low voltage DC sources such as batteries solar panel or fuel cells must be
converted so that devices can run on AC power.

Inverters are used for many applications as in a situation where low voltage DC sources
such as batteries solar panel or fuel cells must be converted so that devices can run on AC
power. One example of such a situation is converting electrical power from a car battery to
run a laptop, television, cell phones etc.

The method in which the low voltage DC power is inverted is completely in two steps. The
first step is the conversion of low voltage DC power to a high voltage DC source and
conversion of the high DC source to an AC waveform using PWM (Pulse Width
Modulation). The second step to complete the desire outcome would be to first convert the
low voltage DC power to AC and then use a transformer to step up the voltage to 220volts.
However, due to the erratic power supply of electricity in Nigeria, an alternative means of
power supply has to be incorporated to supplement the supply of electricity which one of
such form of power is inverter.

 Brief Review of Principles Behind This Work

In the early generation of inverter, vacuum tubes began to be used as switches in inverter
circuit. From the invention of inverters, a switching device is usually made use as a means to
switch the transformer to ON/ OFF state in order to generate fast rate frequency. Silicon
controlled rectifier (SCR) is an example of a switching solid electronics component adopted
to ensure the switching of the system to ON/ OFF state at a considerable faster rate compared
to a manual switching. SCR consist of three main terminals namely; Anode, Cathode and
Gate. When two SCR are connected to a center tapped transformer, current will flow in
positive half cycle (ON current) and negative half cycle (OFF current). This is the same as
the application of Silicon Controlled Rectifier as full wave rectifier.

The next generation made use of multivibrator, amplifier and transformer. The process
takes input from 12VDC source, and runs from the supply to the multivibrator, and from the
multivibrator to the amplifier, and finally to the transformer which gives AC voltage as

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 output. This is inverted to a 240V AC, the multivibrator used may be bistable or a stable
which have two stage cycles useful for generating square waves and pulses. The 12V DC
source serves as the power supply to the inverter.

With the introduction of integrated circuits (ICs), two 555 timer ICs were used for
generating oscillations of equal frequency. An astable multivibrator is used to switch ON/
OFF, to generate constant frequency of 50Hz. The frequency generated by each 555 timer
ICs is controlled by the input configuration of the RC circuit. The output from the ICs is
amplified by drivers and then fed to the gate of the MOSFET. The NE555 timer IC was used
to replace the first generation and second generation inverters due to some difficulties
experienced and the inefficiency of its components.

 Background for Proposed Techniques

A lot of research work has been carried out over the years in the quest to achieve a
noiseless, cheap, and portable converting dc power to ac power. A circuit was designed by
Lane-Fox in 1970, which consisted of two power transistors which were connected in
switching mode and controlled by an oscillator from a 9v dc source (battery) to a 120v ac
output through a transformer secondary. The problems with this circuit are:

1. Very low load current (in the order of milliamps).

2. Poor power efficiency.

In 1986, Jacob designed and constructed a dc-to-ac converter that yielded an output power
of 6KVA, 220V AC and 50Hz with efficiency of 93.5%. This solved the problem of low
output power and poor efficiency encountered by Lane-Fox’s circuit. Everon, a
manufacturing company which produces Uninterrupted Power Supplies (UPS) designed an
inverter circuit that gave a 4KVA output, 270V AC 50Hz and an efficiency of 95% in the
year 2000. This was a huge achievement in the design of inverters and uninterrupted power
supplies.

Review of Difference between Sine Wave and Modified Sine Wave

The Sine Wave Inverter

The electrical circuit of a pure sine wave inverter is far more complex than a square wave
or modified sine wave inverter. Another way to obtain a sine output is to obtain a square
wave output from a square wave inverter and then modify this output to achieve a pure sine
wave. A pure sine wave inverter has several advantages over its previous two forms.

They can be adjusted according to your personal power requirements, since several types
are available with different power outputs. The output of a pure sine wave inverter is very
reliable, but at the same time, there is a tradeoff between the price and reliability. Due to this
reason they are the best option for sensitive equipment.

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 Figure 2.1 shows a pure sine wave

The Modified Sine Wave Inverter

The construction of this type of inverter is a bit more complex than a simple square wave
inverter, but still it is a lot simpler than a pure sine wave inverter. A modified sine wave
shows some pauses before the phase shifting of the wave, i.e. unlike a square it does not shift
its phase abruptly from positive to negative, or unlike a sine wave, does not make a smooth
transition from positive to negative, but takes brief pauses and then shifts its phase.

Figure 2.2 showing the output waveform of a modified sine wave inverter.

 Review Of Hardware And Software Resources

Capacitor

The capacitor is a very important device that is essential in nearly every circuit application.
It is a device capable of storing electrical energy in the form of electrostatic energy. It is
passive circuit element. It consists of two plates separated by layer of insulating medium
called a dielectric. The strength of the dielectric determines the capacity of the energy stored
in the capacitor. The capacitance is the property of a capacitor to store electrical charges.

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 Capacitors come in various sizes and shapes, and are named according to the type of
insulation used. For instance, the ceramic capacitor used thin ceramic as its insulation, and
the oil capacitor uses oil as its insulation.

Fig. 2.3 (a) Symbol of a capacitor (b) physical appearance of capacitor

Resistors

The resistor is the most widely used circuit element. It offer opposition or introduces
resistance to the flow of charges (electrons) or current in an electric circuit. They are placed
to regulate the flow of current and voltage drop in both electrical and electronic circuits. In
power circuits, they are used to reduce voltage by dissipating power.

Resistors are also characterized by how much power they can safely dissipate as well as other
parameters such as tolerance, noise, temperature co-efficient, voltage co-efficient, stability
with time and inductance.

Figure 2.4 (a)Symbol of a resistor (b)physical

appearance of a resistor

Relay

An electromagnetic relay is basically a switch operated by a magnetic force. This

magnetic force is generated by flow of current through a coil in the relay. Current flowing
through the coil of the relay creates a magnetic field which attracts a level and changes the
switch contacts. The coil current can be on or off, so relays have two switch positions and
must have double throw (changeover) switch contacts.

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 Figure 2.5 Physical appearance of a relay

A relay basically consists of four parts:

i. An electromagnetic made of a coil and a magnetic circuit

ii. A movable armature

iii. A set of contacts

iv. A frame to mount all these components.

Transistors

The transistor is the most important example of an ‘active’ component, a device that can
amplify, producing an output signal with more power in it than the input signal. The
additional signal comes from an external source of power.

In the inverter circuit, the transistor is used to generate oscillation signal amplification of
signal and to switch on/ off various circuits. There are generally two types of Transistors
which are the;

1. Bipolar Junction Transistor and

2. Field Effect Transistor.

Fig.2.6 (a) Symbol of a transistor (b) Physical appearance of a transistor

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 There are two types of standard transistors namely: the NPN and PNP transistors. These
transistors consist of two PN junctions formed by sandwiching either P-type or N-type semi-
conductors between a pair opposite types.

Diodes

The diode is an electronic component which allows current to flow through it only in one
direction thereby opposing the flow of current in the opposite direction. Other types of diodes
used are zener diode and light emitting diode.

. Figure 2.7 Symbol and physical appearance of a diode

Transformer

A transformer is a static (or stationary) electromagnetic pieces of apparatus by which of

means electrical power in one circuit is being transformed to electric power (of the same
frequency) in another circuit. It can raise or lower the voltage in a circuit but with a
corresponding decrease or increase in current.

It works on the principle of mutual induction. Transformer needs two coils which is
wound on a laminated core. These coils are called primary coil and secondary coil. The coil
to which the AC supply is provided is called primary coil/winding while the coil in which the
elf is induced and from which the output is taken is called secondary coil/winding. There is
no direct electrical connection between the primary and secondary coil in a transformer.

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Figure 2.8 (a)transformer circuit diagram (b )transformer diagram showing coils

All transformers have the following essential elements; electrical windings insulated from
each other and from the core, a core, and insulating materials.

E.M.F. EQUATION OF A TRANSFORMER

Let

N 1 = number of turns in primary

N 2 = number of turn in secondary

Øm = maximum flux in the core,

W b = Bm x A

where;

Bm = maximum flux density in the core

A = Area of the core

f = frequency of A.C input, (in Hertz).

Therefore;

r.m.s value of e.m.f per turn = 1.11 x 4fØ max = 4.44fØ max volt

Hence, r.m.s value of induced e.m.f in the whole of the primary winding is

E1 = 4.44fØ max N1 …………………………………. (1)

r.m.s value of induced e.m.f in secondary winding is

E2 = 4.44fØmaxN2 ………………………………… (2)

Efficiency of a Transformer

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 The efficiency of a transformer at a particular level and power factor is defined as the
ratio of power output to power input. Therefore, efficiency can be calculated by determining
core losses from open circuit test and copper losses from short circuit test.

Losses in a Transformer

The major losses in a transformer are power losses. The various kinds of losses are; core
losses, copper losses, dielectric losses and stray losses.

Integrated Circuits (I.C)

An integrated circuit as the name implies is a complete electronic circuit in which both
active and passive components are fabricated on extremely single chip of silicon.

Active components are those components which have the ability to produce gain e.g.
transistors, while passive components are those components which do not have the ability to
produce gain e.g. resistors, capacitor and inductors.

Therefore, the integrated circuit is a discrete circuit which is built by connecting several
components together. The integrated circuit is preferred in electrical/electronic circuits
because it does the work of the entire components that are composed on it, and is handier and
less bulky than using the components in it.

In this project, we use SG3524IC.

Figure 2.9 Showing SG3524 IC pin diagram

Function of SG3524 IC

This integrated circuit contains all the control circuitry for a regulating power supply
inverter. Included in the 16-pin dual-in-line package is the voltage reference, error amplifier,
oscillator, pulse width modulator, pulse steering flip-flop, dual alternating output switches

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 and current limiting and shut down circuitry. This IC is a very common Integrated Circuit in
MOSFET based inverter device.

Metal Oxide Semi-Conductor Field Effect Transistor (MOSFET)

The MOSFET is a class of FET transistors. MOSFET is also called as IGFET (Insulated
Gate Field Effect Transistor). It is a voltage controlled field effect transistor that differs from
a JFET (Junction Field Effect Transistor) in that it has a “Metallic Oxide” Gate electrode
which is electrically insulated from the main semiconductor n-channel or p-channel by a very
thin layer of insulating material usually silicon dioxide, commonly known as glass.

There are no forward-biased junctions, so the gate draws no current. MOSFET are three
terminal devices with a Gate, Drain and Source.

The MOSFET is an important semi- conductor device and is widely used in many circuit
applications. In an inverter however, the MOSFETs are used as switching device at the
inverter output section.

The various terminal of MOSFET are;

i. Source: This is terminal which majority carried enter the bar. Since carrier come from it, it is
called the source.

ii. Drain: This is terminal through which majority carrier leave the bar i.e. they are drained out
from this terminal. The drain to source voltage V DS drives the drain current ID.

iii. Gate: These are two internally connected heavily doped impurity regions, which form two P-
N junctions. The gate - source voltage VGS reverse biases the gates.

The MOSFET is used in the inverter circuit as a switching device due to the following
reasons;

i. It can work on very small drive power

ii. Its efficiency is higher at the high frequency.

iii. The input impedance of MOSFET is very high, so it can work without DC current.

iv. Switching time of the ordinary transistor gets affected by temperature, whereas the
temperature has very little effect on MOSFET device.

v. The ‘safe operating area’ of the MOSFET is larger than the bipolar transistor; hence the
MOSFET device does not get easily damaged.

IRF 3205

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 The IRF3205 is N-channel MOSFET designed for high current switching applications.
Rugged EAS capability and ultra-low RDS (ON) is suitable for PWM, load switching .
Features
i. VDS =55V; ID=105A@VGS=10V; RDS (ON) <6.0mΩ @ VGS=10V
ii. Ultra-Low On-Resistance
iii. High UIS and UIS100% Test
Application
i. Hard Switched and High Frequency Circuits
ii. Uninterruptible Power Supply

Figure 2.10 Physical diagram of IRF3205

A.C Voltage Meter

A voltage regulator has only three legs and appears to be a comparatively simple device,
but it is actually a very complex integrated circuit. A regulator converts varying input voltage
and produces a constant regulated output voltage. Voltage regulators are available in a
variety of outputs, basically 5volts, 9 volts and 12 volts. The last two digits in the name
indicate the output voltage.
Voltage regulators are very robust. They can withstand over-current draw due to short
circuits. In both cases, the regulator will shut down before damage occurs. The only way to
destroy a regulator is to apply reverse voltage to its input. This reversal of polarity can
destroy the regulator almost instantly. To avoid this possibility, diode protection of the power
supply is used.

Generally, the input voltage should be limited to 2 to 3 volts above the output voltage.
The LM7812 and LM7805 regulator is used for this project.

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Figure 2.11 (a) LM7805 Physical appearance (b) LM7805 Circuit diagram

Heat Sink

This is a metallic component that is used to conduct away heat which is generated by the
MOSFET. It prevents the MOSFET from damage that may occur from overheating. The
most common heat sink materials are aluminum alloys. Aluminum alloy 1050 has one of the
higher thermal conductivity values at 229W/m.K but is mechanically soft.

Figure 2.12 Physical appearance of a heat sink.

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 CHAPTER THREE

METHODOLOGY

 Overview of Methodology
The approach used for this project is realized through the design and implementation of its
input subsystem, control unit and output subsystem. The inverter is an electronic device that
converts dc voltage form a low dc source to ac voltage of a high output voltage.

In the design we started with the overall system and begin to partition it into systems. The
handy tool used at this stage is the block diagram shown below in fig 3.1. The block diagram
depicts the hierarchy of how the inverter sub-circuits will interact and interface with each
other.

Fig. 3.1 Block diagram

DESIGN ANALYSIS

Power stage: In this stage, battery supplies the oscillator, power amplifier, and transformer
stage with the necessary voltage. A 12V battery is use in our design to power the circuit.

Oscillator Stage: An IC SG3524 is use to generate the necessary pulse needed to drive the
MOSFET (IRF260) to alternate the DC supply. The output from the oscillator stage is
amplified using power transistor MOSFET. The frequency at which circuit operate is
determined with the oscillator stage.

Power amplifier stage: In this stage power transistor MOSFET is use to increase the power
signal of the oscillator to match the power of the transformer.

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Transformer: The voltage of the amplifier is fed to the transformer to increase (step up) the
amplifier output voltage from 12Vac to 220Vac.

The electrical load: The appliances will be connected to the transformer secondary side.

The Battery and Charging Section: The figure 3.2 shows the connection and schematic of
the battery and the charging unit. A switch is used to control the flow current and voltage to
the charging unit

Fig 3.2 Circuit Diagrams of Battery and Charging Unit.

A 12V rechargeable battery is used to store dc voltage. It is connected to the low voltage
cutoff circuit. When a load is placed between a cell’s terminals, a conductive bridge is
formed that initiates chemical reactions within the cell. These reactions produce electrons in
the anode material and remove electrons from the cathode material, step down transformer is
used to step down the main 220V to 12V. It converted the high voltage from PHCN to a
voltage that can be used by the electronics component. The transformer has two terminals
both in its input and output of 0Vac – 12Vac of the secondary part. The primary side of the
transformer has a rating of 220VAc.

A bridge rectifier is an electronic components used in converting ac voltage into dc voltage.

The full-wave bridge rectifier 2W04G was used, having 50V and can pass a peak current of
2A. A bridge rectifier will be connected to the transformer as shown in fig 3.2 above.

A capacitor is used to filter off the ripples before it is then connected to the battery, for the
circuit to charge the battery.

Oscillator Section: The oscillator unit is achieved with the use of SG3524 integrated circuit
chip. The oscillator circuit is shown in figure 3.2

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Figure 3 Circuit Diagram of the Oscillator Unit.

The oscillatory circuit is the stage of the inverter that produces frequency pulse which gets
to the gate of the MOSFET drive after amplification. The signal from pin 11 and pin 14 are
connected to the second IC from where it is amplified and then taken to the MOSFET stage.
The MOSFET drive signal is amplified.

Switching Unit and Step - Up Transformer: This stage consists of FET (Field Effect
Transistor) which is arranged on the heat sink to ensure even distribution of heat on the
transistor. The drain of the MOSFET is linked together with consideration given to how they
are joined to the oscillatory circuit.

Each of this is tapped out with which will be joined to the end of the low voltage side of the
transformer. All sources of the MOSFET are connected together and taken to the negative
terminal of the battery. A center tapped transformer is required for switching of the push pull
arrangement.

The transformer consists of small AC voltage which is received from the MOSFET. It is
transformed and stepped up to an appropriate value ranging from 220V to 240V depending
on our desire which is varied from the 10k resistor to the IC SG3524. The transformer high
voltage side serves as the inverter output to the socket, it also receives from power supply
from PHCN and then used in charging the battery.

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 When large amount of power is needed, the MOSFETS is cascaded to get the amount of
power required. The power to be generated depends on the capacity of the MOSFET and the
rating of the transformer.

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