CONSTRUCTION OF A 2.5KVA PURE SINE-WAVE INVERTER WITH AN IN-BUILT CHARGE CONTROLLER
APPROVAL PAGE
This is to certify that the work in the project report entitled “CONSTRUCTION OF A 2.5KVA PURE SINEWAVE INVERTER WITH AN IN-BUILT CHARGE CONTROLLER” by AYOTUNDE EMMANUEL KEHINDE,
ND/18/MEC/FT/009. Has been carried out under my supervision in partial fulfilment of the requirement
for the award of National Diploma in " MECHANICAL ENGINEERING" during 2019-2020 academic session
in the Department of MECHANICAL ENGINEERING, Kwara State polytechnic ilorin, Kwara State and this
work has not been submitted elsewhere for any National Diploma programme.
__________________________
_____________________________
Dr. B.L ABULDQUADIR
Date
Project supervisor
___________________________
_____________________________
Head of Department.
Date
___________________________
_____________________________
External Supervisor.
Date
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DEDICATION
I dedicate this report to God Almighty for his infinite mercy and the spirit of understanding, protection
and guidance He bestowed on us during my year's of study.
I dedicate it to my Parents/guardians and also to my Loved one's for their equipollent supports which
rank as a catalyst that yielded courage, high esteem with focus and determination towards achieving the
success of the project.
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ACKNOWLEDGEMENT
I am grateful to GOD Almighty for His help and guidance with me through-out the course of the project.
My gratitude also goes to my supervisor the person of, Dr. B.L ABDULQUADIR for the supportive
corrections and words of inspiration to bring out the best in me. Also not forgetting to appreciate my
parents for their encouragement and support, spiritually, physically and financially.
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ABSTRACT
This project review the conformability of uninterrupted power supply through the use of inverter. An
inverter is a system that is primarily based on an inverter circuit across the windings of a transformer
which inverts (converts) the D.C. source voltage from a battery to AC voltage for AC powered appliances.
The purpose of this project is to design and construct a 1600Watts (2.5KVA) 220 Volts Inverter at a
frequency of 50Hz. This device is constructed with locally sourced components and materials of
regulated standards. The basic principle of its operation of this system comprises inter connections of
many sub-circuits to give optimum performances.
The sub circuit include; The oscillator circuit, PWM circuit, driver circuit, low battery/overload shutdown
circuit, charging control/soft charging circuit, surge protection circuit, change over/power supply circuit,
and the output circuit (MOSFET and transformer section). This project incorporates monitoring circuit
that employs visual display components such as light-emitting diodes and voltmeter to communicate the
state of the system to the user.
However, inverter is of different categories base on power rating such as 1KVA, 1.5KVA,2KVA, 2.5KVA,
5KVA etc. Moreover, since the invention of inverter, some problem associated with alternative power
supply had been drastically reduced. Meanwhile, the problems such as: noise, production of fumes, cost
of procurement of oil, fuel and maintenance of plant is over.
Keywords: Transformer, MOSFET, light-emitting diode (LED), battery, output supply
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TABLE OF CONTENTS
TITLE PAGE
APPROVAL PAGE.
I
DEDICATION.
II
ACKNOWLEDGEMENT.
III
ABSTRACT.
IV
TABLE OF CONTENT.
V
LIST OF TABLES.
VI
LIST OF FIGURES.
VII
NOMENCLATURE.
VIII
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
1.2 OBJECTIVE OF THE PROJECT
1.3 SIGNIFICANCE OF THE PROJECT
1.4 APPLICATION OF THE PROJECT
1.5 SCOPE OF THE PROJECT
1.6 DEFINITION OF SIGNIFICANT TERMS
1.7 LIMITATION OF THE PROJECT
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 REVIEW OF HISTORY OF AN INVERTER
2.2 TYPES OF INVERTER
2.3 REVIEW OF HOW TO CHOOSING THE RIGHT INVERTER
2.4 REVIEW OF THE DIFFERENCE BETWEEN PURE SINE WAVE AND MODIFIED SINE WAVE INVERTER.
2.5 WHY CHOOSE A PURE SINE WAVE INVERTER?
2.6 INVERTER RATING
2.7 REVIEW OF INVERTER CAPACITY
2.8 SAFETY OF INVERTER
CHAPTER THREE
3.0 CONSTRUCTION
3.1 BLOCK DIAGRAM OF THE SYSTEM
3.2 STAGES OF OPERATION
3.3 CIRCUIT DIAGRAM
3.4 CIRCUIT DESCRIPTION
3.5 HOW TO CHOOSE THE BEST INVERTER BATTERY
CHAPTER FOUR
RESULT ANALYSIS
4.0 ASSEMBLING OF SECTIONS
4.1 CASING AND PACKAGING
4.2 LOAD EVALUATION AND POWER CONSUMPTION
4.4 INSTALLATION OF THE INVETER SYSTEM
4.5 COST ANALYSIS
CHAPTER FIVE
5.0 CONCLUSION
5.1 RECOMMENDATION
5.2 REFERENCES
1.0 INTRODUCTION
In this modern society, electricity has great control over the most daily activities for instance in domestic
and industrial utilization of electric power for operations. Electricity can be generated from public supply
to consumers in different ways including the use of water, wind or steam energy to drive the turbine as
well as more recently the use of gas. Generators, solar energy and nuclear energy are also source of
electricity
In Nigeria, there is inconsistence supply of electricity by the power supplying company to the consumers.
Hence the use of additional electric power source such as electric power generators and most recently
the use of semiconductor power devices such as the Bipolar Transistor, Thyristors and particularly
MOSFET to generate electric power in conjunction with a DC battery in few kilowatts. An Inverter offers
a better additional power source to Generators as well as UPS considering its long duration, cost
effectiveness and maintainability.
An inverter is a device that changes D.C. voltage into A.C. voltage. A direct current (D.C) is a current that
flows in only one direction, while an alternating current (A.C.) is that which flows in both positive and
negative directions. At the early stage, sun was the source of energy for generating power. Due to the
inadequacy of the power generated through this source, there was a need to find other ways to improve
the power supply when the generating station could not meet the demand of the people.As the
technology advances, the hydroelectric generation was developed, gas firing generating station, and
wired tubing methods of generating power supply were developed. In spite of all these developments,
there was still failure in electrical power generation as a result of obsolete equipment at the generating
stations.
There was still need to find alternative for solving the problem. As a result of this, some options like
alternators, inverters and others were developed. The electrical inverter is a high power electronic
oscillator. It is so named because early mechanical AC to DC converters was made to work in reverse,
and thus was “inverted”, to convert DC to AC. The inverter performs the opposite function of a rectifier
formed in the late nineteenth century through the middle of the twentieth century; DC to AC power
conversion was accomplished using rotary converters or motor-generator sets (M-G set). In the early
twentieth century, vacuum tubes and gas filled tubes began to be used as switches in inverter circuits.
The most widely used type of tube was the thyratron. The origins of electromechanical inverters explain
the source of the term INVERTER.
Early A.C to D.C converters used an induction or synchronous AC motor direct – connected to a
generator (dynamo) so that the generators commutator reversed its connections at exactly the right
moments to produce DC. A later development is the synchronous converter, in which the motor and
generator windings are combined into one armature, with slip rings at one end and a commutator at the
other end only one field frame.The result is either AC – in, DC – out with an M-E 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” Given the right auxiliary and control equipment, an
M-G set or rotary converter can be run “backwards”, converting DC to AC. Hence an inverter is an
inverted converter.There have been a large number of articles written concerning power conversion in
recent years. This can be attributed in part to the rise in popularity of high voltage DC transmission
systems. And their integration with existing AC supplies grid
This project focuses on DC to AC power inverter. Whose aim is to efficiently convert a DC power source
to a 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 panels or fuel cells must be converted so that devices can run on AC power. One example of such a
situation would be converting electrical power from a car battery to run a laptop, television, lighting or
cell phone etc.
The method in which the low voltage DC power is inverted, is completed in two steps. The first being the
conversion of the low voltage DC power to a high voltage DC source, and the second step being the
conversion of the high DC source to an AC waveform using pulse width modulation. Another method to
complete the desired outcome would be to first convert the low voltage DC power to AC, and then use a
transformer to boost the voltage to 220 volts. This project focused on the second method described and
specifically the transformation of a high voltage DC source into an AC output.
Currently, whatever work we carryout in each and every field require and involve the use of electrical
devices, be it in general household use or in some specialized industrial use, the devices require
electrical power for their operation. 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 the inverter.
BACKGROUND OF THE STUDY
The quest to convert D.C. power to A.C power to run some essential appliances results due to erratic
power supply being experience. Although, between the 19th century to mid 20th century, D.C. to AC
power conversion was accomplished using rotary converters or motor generator set (M-G set). In early
20th century, vacuum tubes and gas filled tubes began to be used as switches in inverter circuit. In
contrast the early A.C. to D.C. converters used an induction or synchronous a.c motor directly connected
to a generator (dynamo) so that the generator’s commutator reverses its connections at exactly the
right moments to produce D.C.
Considering the above reasons, for the study, many electrical equipments have either developed a
problem or even stopped working entirely. As a result, many businesses have been crippled thereby
affecting the economy as a whole with respect to Nigeria.
Again, power disturbances occurrence are on increase resulting to high voltage spikes and momentary
voltage drops, this often affect the performance of sensitive electrical electronics equipment.
intermittent supply of electric power can not be over-emphasized in Nigeria presently, this has become
the order of the day and many Nigerians now presume power outages as a normal routine in the power
sector. There are factors responsible for this ugly situation such as natural disasters, vandalism,
maintainability, sustainability, inadequacy and lack of vision by the political leaders to invest adequately
in power sector, also absence of replacement policy resulting in absolute abandon of electrical
equipment or project, unsustainable human capacity and inadequate and remuneration system to
motivate human resources term to perform well on their course.
The progress made some decades ago in developing alternate source of energy has proved that
independent power system are not only possible but as well practical. A wide variety of generating
equipment is now available to allow individuals take advantage of any prefer renewable resources of
energy. Most of these systems produce only direct current (DC) for a number of reasons and at low
voltages. However, it is well known that the alternating current is the greatest and most useful form of
current being generated by the power grid due to its advantages over direct current. Thus, most of the
appliances and equipment are built using a.c. input source.
Therefore, there arises the need for converting direct current (DC) to an alternating current (A.C.) having
a constant frequency. This process is known as INVERTING.
OBJECTIVE OF THE PROJECT
The purpose of this project is to design and construct a circuit that will take a 24V dc input from a
battery and produce over 200V ac output ranging within 200V – 220V, at 50Hz with under voltage and
over voltage protection. The study intends:
i.
To design an electrical system that converts d.c. power to a.c. power to drive various appliances
used in the laboratories, theatres, rural areas etc.
ii.
iii.
iv.
v.
vi.
vii.
viii.
To have a source of generating electricity that has no negative effect on the environment (i.e. no
greenhouse effect).
To provide an exposition to the ND students to simple electrical design, analysis and building of
circuits.
To provide a noiseless and weightless source of electricity generation.
The study will also serve as a means of impacting practical knowledge and skills to students,
lecturers and other who may wish to acquaint themselves with the principles of operation of an
inverter system.
To produce a sine wave output that can be used to power appliances both in house and
industries.
To back-up the erratic power supply by PHCN.
To ensure the protection of the back-up source consumer equipment and supply.
SIGNIFICANCE OF THE PROJECT
In the recent years, inverter has become a major power source due to its environmental and economic
benefits and proven reliability. Since the inverter power system does not have moving parts, virtually it
require little or no kind of maintenance once installed.
Inverted power is produced by connecting the device to the 24V, D.C battery as the input to produce
220V, A.C as the required output. It can also be connected to a solar panel. The whole energy
production process is environmentally friendly. It produces no noise, harmful emissions or polluting
gases. The burning of natural resources for energy can create smoke, cause acid rain and pollute water
and air. Carbon dioxide, "CO2", a leading greenhouse gas, is also produced in the case of burning fuels.
Inverted power uses only the power of the battery as its fuel. It creates no harmful by-product and
contributes actively to the reduction of global warming.
The important of an inverter is that, it has the capability to convert the DC power into AC power making
it useful to operate equipment such as household items, computers, power tools and much more by
simply plugging typically equipment into the inverter. It is also important because it can deliver efficient
power to run electrical appliances with high power requirement usually as electric utility heater, air
conditioners with additional batteries connected to the inverter because of the high current they
require to run.
APPLICATION OF THE PROJECT
Below are some of the areas where an inverter can be useful;
i. DC power source utilization : Inverter designed to provide 220V A.C from the 24V D.C source An
inverter converts the DC electricity from sources such as batteries, solar panels, or fuel cells to AC
electricity. The electricity can be at any required voltage; in particular it can operate AC equipment
designed for mains operation, or rectified to produce DC at any desired voltage.
ii. Uninterrupted power supplies : An Uninterrupted power supply (UPS) uses batteries and an inverter
to supply AC power when main power is not available. When main power is restored, a rectifier supplies
DC power to recharge the batteries.
iii. Induction heating: Sine wave Inverters convert low frequency main AC power to higher frequency for
use in induction heating. To do this, AC power is first rectified to provide DC power. The inverter then
changes the DC power to high frequency AC power, due to the reduction in the number of DC sources
employed, the structure becomes more reliable and the output voltage has higher resolution due to an
increase in the number of steps so that the reference sinusoidal voltage can be better achieved.
iv. HVDC power transmission : With HVDC power transmission, AC power is rectified and high voltage DC
power is transmitted to another location. At the receiving location, an inverter in a static inverter plant
converts the power back to AC. The inverter must be synchronized with grid frequency and phase and
minimize harmonic generation.
v. Variable-frequency drives: A variable-frequency drive controls the operating speed of an AC motor by
controlling the frequency and voltage of the power supplied to the motor. An inverter provides the
controlled power. In most cases, the variable-frequency drive includes a rectifier so that DC power for
the inverter can be provided from main AC power. Since an inverter is the key component, variablefrequency drives are sometimes called inverter drives or just inverters. VFDs that operate directly from
an AC source without first converting it to DC are called cyclo-converters. They are now commonly used
on large ships to drive the propulsion motors.
vi. Electric vehicle drives: Adjustable speed motor control inverters are currently used to power the
traction motors in some electric and diesel-electric rail vehicles as well as some battery electric vehicles
and hybrid electric highway vehicles.
vi. As Power Grid: Grid-tied inverters are designed to feed into the electric power distribution system.
They transfer synchronously with the line and have as little harmonic content as possible. They also
need a means of detecting the presence of utility power for safety reasons, so as not to continue to
dangerously feed power to the grid during a power outage.
SCOPE OF THE PROJECT
This project write-up gives a step-by-step account of how the project was carried out. This includes the
design and construction with given specifications. To obtain the AC power from the inverter, the DC
power from the battery has to pass through different units that makes up the inverter.
The various stages involved in the development of this project have been properly put into five chapters
to enhance comprehensive and concise reading, of this project thesis. The project is organized
sequentially as follows:
 Chapter one contain the Introduction to an inverter, in this chapter the background, objective,
significance, application, scope, definition of significant terms and the Limitation of the project
were discussed
 Chapter two is on literature review of an inverter. In this chapter, all the literature pertaining to
this work was reviewed.
 While Chapter three is on design methodology. In this chapter all the method involved during
the design, derivation on the design circuit, calculations, and construction were discussed.
 Chapter four is on results and test analysis. All testing that result accurate functionality and
installation procedure was analyzed.
 Chapter five is on conclusion, recommendation and references.
DEFINITION OF SIGNIFICANT TERMS
Since the inverter system is an electrical/electronics system, current will flow through the various
components, voltage will be dropped at some points, and therefore, the following principles were
applied in designing the project.
Joule’s Law
Joule has two laws Viz: Joule’s first law shows the relationship between heat produced by an electric
current flowing through a conductor. That is the rate of heat generated (p) in a metallic conductor is
directly proportional to the square of the current (I) flowing through the conductor provided that
temperature is held constant
Joule’s second law: States that internal energy of a gas does not change if volume and pressure change
but does change if temperature changes.
Ampere’s Law; This relates the integrated magnetic field around a closed loop to the electric current
passing through the loop. Thus for any closed loop path, the sum of the length element times the
magnetic field in the direction of the length element is equal to the permeability times the electric
current enclosed in the loop.
Faraday’s Law of electromagnetic induction; It states that whenever there is a change in magnetic flux
linked with a circuit, an emf is always induced in it and the magnitude of the induced emf is equal to rate
of change of flux linkage.
e.m.f generated =
Ohm’s Law; This states that the ratio of potential difference (V) between any two points in a circuit is
directly proportional to the current (I) flowing through them, provided temperature and other physical
materials remain constant.
V = IR
I = V/R
R = V/I
Kirchoff’s Voltage Law
This states that the algebraic sum of voltage in each of the conductors in any closed path in a network is
equal to the algebraic sum of emf
Kirchoff’s Current Law
This states that the algebraic sum of currents in a network of conductors meeting at a point is zero. i.e.
At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the
sum of currents flowing out of that node
1.7 LIMITATION OF THE PROJECT
In spite of the construction of an inverter and its noiseless and pollution free nature unlike other
alternative sources of the generating electricity, there is a need for charging and recharging the battery
from time to time.
I.
An attempt to use it to drive more than recommended load may or will reduce the life span of
the inverter thereby causing harm to some major electronic component in it.
II. Again, limited financial resources incapacitated the project to achieve its accuracy and reliability
as well its appearance (packaging).
III. The major limitation of this project is that it cannot operate equipment or an electronic device
that is above its rated current.
2.0 LITERATURE REVIEW
Electricity is one of the greatest inventions man has ever made, due to its very important role in socioeconomic and technological development (Owen and Edward, 1996). Electricity can be transmitted in
two different ways namely: alternating currents (AC) or Direct current (DC). Alternating current is the
form obtained from power outlets in homes and offices. It consists of a sinusoidal voltage source in
which a continuous change in the direction of flow of voltage (and current) can be used to employ
magnetic components (Cooks et al., 2001). Direct current is electricity flowing in a constant direction,
and/or possessing a voltage with constant polarity and is appropriate for short-range transmission.
Direct current is the form stored up in batteries. It uses is limited and it depends on AC power (Owen
and Edward, 1996)
In the past centuries, conversion of DC to AC power was accomplished through the use of rotary
converter or motor- generator set. In the early twentieth century, vacuum tubes and gas filled tubes were
used as switches in inverter circuits. The most widely used type of tube was the thyratron (any of several
types of thermoelectric valve once used as a high-speed switch). Early AC to DC converters used an
induction or synchronous AC motor directly connected to a generator (dynamo) so that the generator’s
commutator reversed its connection at the same moment to produce DC. Latest development is the
synchronous converter in which the motor and generator windings are combined into one armature, with
slip rings at one end and a commutator at the other end with only one field frame. The result with either
AC in or DC out, with a motor generator set. The DC can be considered to be separately generated from
the AC with a synchronous converter. Given the right auxiliary and control equipment, Motor-Generator
(M-G) set or rotary converter can be “run backwards” converting DC to AC.
In applications where inverters transfer power from a DC power source to an AC power source, it is
possible to use AC to DC controlled rectifier circuits operating in the inversion mode. In the inversion
mode, a controlled rectifier circuit operates as a line commutated inverter. This type of operation can be
used in HVDC power transmission systems and in regenerative braking operation of motor control
systems. Another type of SCR inverter circuit is the current source input (CSI) inverter. A CSI inverter is
the dual type of six-step voltage source inverter. With a current source inverter, the DC power supply is
configured as a current source rather than a voltage source. The inverter SCRs is switched in a six-step
sequence to direct the current to a three-phase AC load as a stepped current waveform. CSI inverter
commutation methods include load commutation and parallel capacitor commutation. With both methods,
the input current regulation assists the commutation. With load commutation, the load is a synchronous
motor operated at a leading power phase factor. As they have become available in higher voltage and
current ratings, semiconductors such as transistor or IGBTs that can be turned off by means of control
signals have become the preferred switching components for use in inverter circuits.
In the world today, there are currently two forms of electrical transmission, Direct Current (DC) and
Alternating Current (AC), each with its advantages and disadvantages. DC power is simply the
application of a steady constant voltage across a circuit resulting in a constant current.
Alternating current, unlike DC oscillates between two voltage values at a specified frequency and its ever
changing current and voltage makes it easy to step up or down the voltage. For high voltage and long
distance transmission situations, all that is needed to step up or down the voltage is a transformer.
Developed in 1886 by William Stanley Jr.
2.1 REVIEW OF HISTORY OF AN INVERTER
The earliest inverter was the motor generator, which was developed to serve the needs of World War II.
A popular brand of that era was Redi-line, which is still around today. The motor generator was reliable
and, at the time, was the only way to convert DC power to AC. The output waveform fit a wide variety of
applications but it was inefficient. It required 30 amps to turn on, the vehicle had to be running to
support the unit, and it had no startup surge capacity.
Power electronics started with the development of mercury arc rectifier. Invented by Peter Cooper
Hewitt in 1902, the mercury arc rectifier was used to convert alternating current (AC) into direct current
(DC). A Chicago based company founded in 1922, first produced a unique automobiles headlight that
had been invented by Graham Trippe. The product line expanded to include electronic inverters. The
early units used mechanical vibrators to oscillate DC power into square wave AC. In 1933 selenium
rectifiers were invented. In 1947 the bipolar point-contact transistor was invented by Walter H. Brattain
and John Bardeen under the direction of William Shockley at the Bell Telephone Laboratory. Then in
1948 the invention of the bipolar junction transistor by Shockley all at once reduced the cost and size
while increasing the efficiency of transistors beginning a revolution in semiconductor electronics. Shortly
after, in the 1950s, semiconductor power diodes became available and started replacing vacuum tubes.
Then in 1956 the Silicon Controlled Rectifier (SCR) was introduced by General Electric marking the point
where semiconductor power electronics really began.
In the early 1960s the switching speed of BJTs allowed for DC/DC converters to be possible in high
frequency, with the MOSFET introduced in 1960. Bluebird used a motor generator in their coaches
during the late 1970's and early 1980's. In 1976 power MOSFET becomes commercially available. Vanner
Inc., was established in 1977. The company developed a warning light flasher module for emergency
vehicles and ambulances, and subsequently developed isolators and chargers. In 1979, Vanner
introduced their first inverter: a 1000-Watt modified sine wave unit used in ambulances. For this 1000W
inverter, Vanner patented true RMS regulation and a power transistor drive technique. This transistor
drive technique achieved an unheard of 87% efficiency. A few years later the product expanded into
various types of vehicles including remote television vans. The product line expanded with 2200W and
3000W inverters. Then in 1982 the Insulated Gate Bipolar Transistor (IGBT) was introduced.
In 1983, the first 24V to 12V battery equalizers were sold. In 1986, one of the inverter models included a
microprocessor control circuit. In 1988, Vanner was sold to B. Elliott, an English holding company. In
1993, Vanner and sister company, Weldon, combined. In April of 1994, Vanner-Weldon purchased the
rights to several dynamo products, including a pure sine wave inverter. In 1997, Vanner and Weldon
separated back into two divisions but both are still owned by the same parent company. Vanner
products are not common in the RV industry because the company focuses on industrial applications.
In the early 1980’s, there were two companies manufacturing inverters for the RV market, Heart
Interface and GTO Electronics. In 1986, one of the original owners of Heart split off to form a new
company, Trace Engineering, which later produced a similar product.The Heart inverter had a battery
charger/converter built in and was the first to reach over 90% efficiency. It could also surge three times
its rating. In 1985, Heart and GTO secured UL listing for inverters used in the RV industry, which opened
doors for OEM builders. Heart developed the first inverter/charger with a UL listing. First generation
inverters used Metered Darlington Technology. This special circuit metered base current to power a
transistor proportional to load. The magnetic design increased efficiency. Second-generation inverters
used FETs (Field Effect Transistors). Since FETs have almost no switching losses, efficiency was markedly
improved. In 1990, integrated circuits allowed the creation of energy management systems. In 1993, the
first microprocessor-controlled inverter/charger was introduced.
2.2 TYPES OF INVERTER
Types of Inverters and Waveforms
Inverters, besides coming in a wide variety of power capabilities, are distinguished primarily by the shape
of the alternating current wave they produced. According to the output characteristic of an inverter, the
three major waveforms are: SQUARE WAVE, MODIFIED SINE WAVE & TRUE SINE WAVE.
2.2.1 Square Wave
Square wave inverters are largely obsolete, as the waveform shape is not well suited for running most
modern appliances. Prices have come down considerably in comparison with the superior modified sine
wave and true sine wave types.
2.2.2 Modified sine wave
The least expensive type of modern inverter produces modified sine wave power. The waveform looks
like a stair step, where the power rises from zero to upper peak voltage returns to zero and straight to
lower peak voltage, resting to each point for a moment.
Modified sine wave inverters can be used to run many household appliances such as a television, radio,
and microwaves with occasional minor electrical “noise’. Sensitive equipment like battery chargers, tools
with variable speed motors, laser printers and certain heating controllers may run erratically but not with
modified sine wave power.
For a remote cabin with only the “basic” running on the electrical system, modified sine wave inverters
are also often well suited for solar powered electrical systems.
2.2.3 True Sine Wave
The power supplied by utility companies and engine generator is a pure sine waveform. This is the most
reliable waveform for household use. True sine wave power passes from the upper and lower peak
voltages in a smooth curved wave, rather than the stair step of the modified sine wave. All appliances and
electronic equipment runs as intended when using sine wave power. True sine wave inverters produces
Ac power as good as or better than utility power, ensuring that even the most sensitive equipment runs
properly. While sine wave inverters are more expensive than the modified sine wave models, the quality
of their waveform can be a definite advantage. This cost, however is made up for in its ability to provide
power to all AC electronic devices, allow inductive loads to run faster and quiet, and reduce the audible
and electric noise in audio equipment, TV’s and fluorescent lights. Image See FIG: below
Generally, the inverter to be produced must posses the following features;
1. Overload protection.
2. Miniature Circuit Breaker trip indicator (MCB).
3. Low-battery protection 4. Constant and trickle charging system.
5. Load status indicator.
SEE FIG 2.2 BELOW
2.3 REVIEW OF HOW TO CHOOSING THE RIGHT INVERTER
To choosing the right Inverter for this project the following points were be considered.
1. What's the Power Requirement?
The power requirements we intend to meet dictates the size our of inverter , This is the total load we
want to run on our inverter as backup. This is the most essential factor to take into account because an
inverter is a pure power backup solution. So any misstep in terms of calculating power can lead to a
power failure.
2. Choosing The Right VA Ratings
Based on our power requirements can we determine the right VA rating of an inverter. VA stands for
volt ampere rating of an inverter. It is the total amount of voltage supplied by the inverter for a group of
appliances.
The best way to determine the right VA rating is to divide the total power requirement in watts with the
power factor of cited place of installation, which is generally 0.8.
For example , let's consider our total load or power requirement as 1,280 watts.
So 1,280/0.8 = 1,600 VA
So building an inverter with 1,600 VA is the right choice for our needs.
3. Considering Battery Size
When considering battery size, the only factor to look for is the Ah value. The Ah value of a battery
dictates the amount of energy a battery can store. The most common Ah values of a battery are 100,
120, 150, 180, and 200 Ah. The higher the Ah value, the stronger the battery is.
Battery capacity = Power requirement (in watts) * Back up hours ( in hrs) / Battery Voltage (in volts)
Battery Capacity = (1280 × 6) / 12 = 640 Ah
Value of Battery voltage is taken 12V
4. Different Types Of Inverters
There are 3 main types of inverters available in the market. They are Sine Wave, Modified Wave, and
Square Wave inverters. And after considering their output characteristics,which is commonly used and
which has a low cost we came a conclusion that the SINE WAVE INVERTER is one we would be
constructing.
2.4 REVIEW OF THE DIFFERENCE BETWEEN PURE SINE WAVE AND MODIFIED SINE WAVE INVERTER.
Indeed inverter are of three types under classification according to Output characteristics but we would
be reviewing only the two major ones which are used in this modern time.
Modified Sine Wave (quasi-sine) ;
A modified sine wave inverter actually has a waveform more like a square wave, but with an extra step,
a modified sine wave inverter will work fine with most equipment, although the efficiency or power of
the equipment will be reduced, the modified sine wave inverter has limitations. These are some of the
appliances that may experience problems when running off Modified Sine wave inverters:
Motors, such as refrigerator motor, pumps, fans etc will use more power from the inverter due to lower
efficiency.
Some fluorescent lights will not operate quite as bright, and some may buzz or make annoying humming
noises.
Appliances with electronic timers and/or digital clocks will often not operate correctly. Because the
modified sine wave is noisier and rougher than a pure sine wave.
Items such as bread makers and light dimmers may not work at all – in many cases appliances that use
electronic temperature controls will not control. The most common is on such things as variable speed
drills will only have two speeds – on and off.
Modified sine wave inverters are usually only protected by standard fuses which, under normal
circumstances, are not always fast enough, therefore they are by far more vulnerable to failure.
Pure Sine wave Inverter;
This is the best output waveform you can get out of an inverter and all appliances are able to run off it
without interference or overheating. Some of its advantages are as follows:
Output voltage waveform is pure sine wave with very low harmonic distortion and the same as the
power grid.
Inductive loads like microwave ovens and motors run correctly, quieter and cooler
Reduces audible and electrical noise in fans, fluorescent lights, audio amplifiers, TV, Game consoles, Fax,
and answering machines
Prevents crashes in computers, unreadable print outs, glitches and noise in monitors
It can be efficiently protected in overload, over-voltage, under-voltage and over temperature conditions
2.5 WHY CHOOSE A PURE SINE WAVE INVERTER?
Pure Sine Wave A pure sine wave is what you get from your local utility company and from some pure
sine generators (most generators are not pure sine).
• A pure sine wave minimizes the risk of damage to your sensitive appliances. Compared to a modified
sine wave.
• Devices that use control circuits, which sense the phase for speed/voltage control, or devices that
sense instantaneous zero voltage crossing (for timing control) must have a sine wave supply.
• Electronic items like printers, scanners and monitors have minimal harmonic distortion. Therefore,
fewer glitches and irregular printouts are assured. This is important for sensitive commercial
applications too. Even fans.
Major advantage of a pure sine wave inverter is that all of the equipment which is sold on the market is
designed for a pure sine wave. This guarantees that the equipment will work to its full specifications.
Some appliances, such as motors and microwave ovens will only produce full output with pure sine
wave power.
A few appliances, such as bread makers, light dimmers, and some battery chargers require a pure sine
wave to work, audio equipment, satellite systems, and video equipment, will run properly using pure
sine wave inverters.
(Insert image)
As you can make out from the figure above, sine wave changes polarity instantaneously and smoothly,
when it crosses zero volts. The rise and fall of voltage is smooth as compared to the shape of the
modified sine wave. Due to this feature, inductive loads run quieter, cooler and faster.
2.8 SAFETY OF THE INVERTER
Keeping the inverter in good health condition and avoiding risk of shock or power failure the following
general safety precautions tips should be ahead to.
 Place the inverter on a reasonably flat surface, either horizontally or vertically.
 The inverter should not be installed in the engine compartment, due to possible water/oil/acid
contamination, and excessive heat under the hood, as well as potential danger from gasoline
fumes. It's best to run battery cables to a dry, cool inverter mounting location.
 Keep the inverter dry. Do not expose it to rain or moisture. DO NOT operate the inverter if your
hands are wet or any other surfaces that may come in contact with any power source are wet.
Water and many other liquids can conduct electricity which may lead to serious injury or death.
 Avoid placing the inverter on or near heating vents, radiators or other sources of heat. Do not
place the inverter in direct sunlight. Ideal air temperature is between 50F and 80F.
 In order to properly disperse heat generated while the inverter is in operation, keep it well
ventilated. While in use, maintain several inches of clearance around the top and sides of the
inverter.
 Do not use the inverter near flammable materials. Do not place the inverter in areas such as
battery compartments where fumes or gases may accumulate.
 Bad/Dead batteries should not be used with the inverter
 The battery terminals should not be removed too often. When it is removed, placement of
correct polarity must be ensured.
 The inverter must be kept in a moderate temperature environment.
 The inverter should be shut down when not in use.
 The inverter should always be partially loaded (not more than 75% of its maximum capacity).
 The input plug of the inverter should be plugged to a three-pin, properly earthed socked.
CHAPTER THREE
3.0 CONSTRUCTION
Engineering project requires a good design for it to be implemented. This project as one of such
underwent through the design process which involves mostly mathematical and engineering
calculations and derivations. The step by step approach taking in the construction of this project started
with the building of the transformer from the laminating core, followed by the rectification stage,
sensing and monitoring stage, comparator and transistor switching.
The overall method employed in the design of this inverter system is the "push-pull" method of inverter
design. This method involves the use of a *center-tapped" transformer, a pulse width modulated (PWM)
sine wave source and the two banks of MOSFETs contain ing five (5) MOSFETs in each bank as it is the
case with this design. The push-pull mechanism is the situation whereby one bank of the MOSFETS
allows the passage of current through them upon receiving a gating signal from the oscillator while the
other bank remains redundant for a period of time; this conduction state of the MOSFETs are reversed
automatically to the other redundant MOSFETs bank at the frequency of 50Hz thereby supplying the
transformer with the desired alternating input (24V AC). The transformer steps-up this 24V AC input
supplied from the output of the MOSFETs to 240V AC at the same frequency of 5OHz.
Few tools and instruments used include:
1. Lead and Soldering Iron.
4. Plier.
2. Copper stripping knife. 3. Screw driver.
5. Digital Multimeter.
6. Fero and bread board
To conform to the requirement of this project, temporary construction of the prototype was done on
bread board before finally transferring it onto the fero-board for permanent soldering. The circuit was
constructed, tested and put to use under proper load conditions. In other to achieve accuracy in the
design, some necessary adjustments were made to some of the components used.
3.1 BLOCK DIAGRAM OF THE SYSTEM
The implementation employed in this project, design and construction of a 2.5KVA inverter system, can
be segmented into blocks in order to cover all the necessary stages involved in actualizing it. See FIG 3.1
below
BLOCK DIAGRAM OF THE ENTIRE SYSTEM.
3.2 STAGES OF OPERATION