CHAPTER ONE
1.0
Introduction
This project focuses on conversion of DC to 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. One example of such a situation is converting electrical
power from a car battery to run a laptop, television, cell phones
e.t.c.
The method in which the low voltage DC power is inverted is
completely in two steps. The first being the conversion of low
voltage DC power to a high voltage DC source, and the second step
is being the conversion of the high DC source to an AC waveform
using PWM (Pulse Width Modulation).
Another method 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.
1.1
Background Information and System Design
From the late 19th century to the middle of 20th century DC to AC
conversion was accomplished using rotary converters, or motor
generator (MG) set. In the early 20th century, vacuum tube and gas
filled tube began to be used as switches in inverter circuit. The most
widely use type of tube is thyraton.
The origination of electromechanical inverters explains the
source of the term inverter. Early AC to DC converters used on
conduction of synchronous of AC motor direct connected to a
generator (DYNAMO), so that the generator commutation reversed
it connection 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 which slip rings at one end and the commutation
at the other end and only one field frame.
The result is either with AC-on, 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, and motor generator set or rotary converter can “run
backward”, converting DC to AC. Hence, an inverter is inverter
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).
1.2
Aims and objectives
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 modify sine wave that can be used to power appliances both
in houses and industries.
iv. To safely operate any electronic devices (such as micro wave,
speed motor) that require sensitive calibration.
The design and construction of this project was to provide an
ample
chance
for
an
understanding
of
the
characteristics,
operations, and application of power electronic devices.
In addition, generally it gives an understanding of basic
design concept of inverter based on MOSFET (Metallic Oxide
Semiconductor Field Effect Transistor) switching and PWM (Pulse
Width Modulator).
1.3 Scope of the Study
The scope of this study is based on the design and
construction of 2KVA solar inverter.
1.4
Methodology
The following stages below are the following stages involve in
the construction of a 2KVA solar inverter:
The method in which the low DC voltage is inverted is
completely ion three steps. The first being the oscillator of battery
voltage at 50hz frequency step, this is been the inversion of the DC
source to an AC low voltage power.
In the second stage the oscillating low voltage will be fed to
the MOSFET BANK for amplification purpose at this stage the
oscillating low Dc voltage is amplified and switched into the
transformer.
The third stage involve the step up transformer, which would be
wound with copper wire on iron core lamination, at this stage the
switching AC voltage will be stepped up to the higher AC voltage
level of about 220V AC from the primary input of the transformer to
the secondary output.
12V DC BATTERY: A twelve volt battery has six angle cells in
series producing a fully charged output voltage of 12.6 volts. A
battery cell consist of two lead plates a positive plate covered with a
paste of lead dioxide an a negative made of sponge lead, with an
insulating material (separator) in between.
OSCILLATOR: It is an electronic network that is used to generate
clock pulse for frequency modifier. The oscillator uses DC source to
convert the unidirectional current into the bidirectional current. Due
to the usage of DC source, it does not require any moving
component to generate energy.
MOSFET BANK (Amplifier): In an inverter, pairs of MOSFETS
serve as electrical switches to deliver DC at one polarity (for the
other half-cycle), generating a square-wave AC waveform. The
inverter may use a single pair of MOSFETS (in a half-bridge circuit)
or four MOSFETS (in a full bridge circuit).
TRANSFORMER: A transformer is a device that transfers electric
energy to one alternating-current circuit to one or more other
circuits, either increasing (stepping up) or reducing (stepping up) or
reducing (stepping down) the voltage.
AC OUTPUT: The AC output voltage of a power inverter is often
regulated to be the same as the grid line voltage, typically 220 or
240 VAC at the distribution level, even when there are changes in
the load that the inverter is driving. This allows the inverter to,
power numerous devices designed for standard line power.
FEEDBACK: Is the movement of a part of faction of an output to
part of faction to the input.
CHAPTER TWO
2.0
Literature Review
In an inverter circuit, the DC power is connected to a
transformer primary through the center tap of the primary
windings. A switch is rapidly switched back and forth to allow
current to flow following two alternate paths through one end of the
primary winding and then the other end. The alternation of the
direction of flow of current in the primary winding of the
transformer produces an alternating current in the secondary
winding.
The
electromechanical
version
of
switching
devices
includes: two stationary contact and spring support moving contact.
A power inverter converts DC power or direct current to
standard AC power or alternating current, which facilitates the
running electrical equipment of the car, home or office for mobile
application, emergencies or simple convenience. The output voltage
could be fixed or variable voltage and maintaining the DC gain of
the inverter constant, on the other hand, if the DC input voltage is
fixed, a variable output voltage can be obtained by varying the gain
of the inverter, which is normally accomplished by PWM control
within the inverter.
Power inverters are great for camping at parks and picnics
where electricity is not or rarely available. The toaster, blender, and
printer can all still be used. In a utility outage, a power inverter can
be used for emergency electricity. The radio can be plugged in to
tune into important alerts, run essential medical equipment, lights
or whatever electronic garget that falls within the inverter's power
limits.
2.1
Review on early inverter
In the effort in pursuit of the conversion of DC power to AC
power has being since the late 19th century and from then to the
middle 20thcentury; DC to AC power conversion was accomplished
using rotary converter or motor generator set. In the early 20th
century, vacuum tubes began to be used as switches in inverter
circuit.
First Generation of Inverter
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.
Second Generation
This 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 output.
This is inverted to a 240V AC, the multivibrator used may be
bistable or astable which have two stage cycles useful for
generating square waves and pulses. The 12V DC source serves as
the power supply to the inverter.
Third Generation
In this generation, 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.
2.2
Basic Design Considerations
Some design considerations were fulfilled in the process of
designing this project; which was properly taken cognizance of, in
order to meet the design objectives. A close look at these
considerations would reveal that they all emphasize on obvious link
between design and we, the designers. Formulating the right
problem is one of the basic design considerations. It encompasses
ensuring that the objective and requirements of the device,
equipment, machine or facility are right to save-guard against
possible failure.
Designing an appropriate solution is one of the major factors to
be considered in the course of the project design. It entails ensuring
that the system is not only technically excellent but also appropriate
and successful. A lot of work had been done on this project before
finally arriving at the appropriate circuit to be used.
2.3 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.
More efficiency, hence consumes less power. 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
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
2.4
Safety of Inverter
The only input to the inverter subsystem is from the battery,
the battery is being charged from the power source (PHCN) through
the charging subsystem through its integrated system. Our key
concerns regarding the power inverter system were as follows:
i.
Safety - because we are dealing with high currents, many safety
concerns needed to be accounted for.
ii.
Output Waveform
iii.
Power Output needs to handle at least 2000W
iv.
Efficiency generally there are a lot of losses associated with
converting power. The inverter will receive DC power from the
battery, and convert it to usable DC and AC outputs.
All other subsystems receive information from the output of
the power inverter. As such, the inverter is critical to the integrity of
the entire system. Safety concerns must be at the forefront of the
circuit design. These concerns stem to the safety of the users, as
well as the circuitry itself.
We recognized this issue, and accounted for it with properly
placed kill-switches and fuses/circuit breakers. The circuit was
designed
so
that
if
a
power spike occurred,
or
something
malfunctioned, the key components of the system would be saved,
and the system would be shutdown.
CHAPTER THREE
3.2
Components of an Inverter
One of the purposes of this chapter is to highlight the various
components used in the construction of the circuits that makes up
the project as well as outlining whatever calculation involved where
necessary. The components making up the inverter include relays,
resistors, capacitors, transistors, voltage regulators, heat sink,
MOSFETs, switch and various ICs etc.
 Resistor
 Capacitor
 Diode
 Relay
 Transistor
 Metal Oxide Semi-Conductor Field Effect Transistor (MOSFET)
 IRF 3205
 Heat Sink
 Voltage Regulator
 Transformer
 Integrated Circuit (IC)
STAGES INVOLVED IN THE CONSTRUCTION
MOSFET Stage
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 MOSFET is connected such that its gate before they
are connected to the joint output. 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.
Showing the MOSFET stage diagram
Oscillatory Stage
The oscillatory circuit is the stage of the inverter that
produces frequency pulse which gets to the gate of the MOSFET
drive after amplification. IC SG3524 is used as the oscillator of the
inverter. 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.
showing the oscillation stage diagram
Battery Stage
The battery is used to provide the required D.C to power the
circuit, which voltage level was ensured to be 12V. SG3524N is a
fixed frequency pulse width modulation voltage regulation control
circuit.
The
regulator
operates
at
the
frequency
that
programmable by the timing resistor, and one timing capacitor.
is
Figure 3.13 showing deep cycle battery diagram
Transformer stage
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.
Showing the transformer stage diagram
3.4 How to choose the best inverter battery
Nowadays, it is almost unimaginable to survive without power
supply in our homes or workplaces. However, the moment power
supply to our appliances and other gadgets that makes our
everyday lives a lot easier and relaxed goes off, our lives becomes
boring. Such situation leaves us really bothered unless there is an
inverter with a powerful inverter battery.
Here is a list of some most important things to consider when
choosing the best inverter battery is as follows;
i.
Understand the power requirement
ii.
Be aware of the inverter battery size that you require.
iii.
Find the VA rating of the inverter you require.
i.
Consider the bigger appliances
CHAPTER FOUR
4.0 Test, Observation and Results
The design of the project, construction of a 2KVA
Inverter,
was
followed
by
its
construction.
Many
considerations were put in place in form of procedures and
instructions, which led to the successful completion of the
project. The project is constructed on a Vero board, in which
the size of the main panel board was used to choose the
dimension of the casing used.
4.1 Testing
Purpose of Testing
Testing of components is important during construction
to ensure that the works compiled together are perfect with
their specifications. Testing is also essential during operation
and after the completion of the construction made to
determine the longevity of the inverter in order to detect
common fault that may arise. There are sequences of test
needed to undergo for any successful project.
i.
Component testing
ii.
System testing
Component Testing
Every component was tested singly to ensure that each
was in good condition before assembling on the board. The
major test carried out on these components was continuity
testing done with the use of multi-meter like transistors. The
test made on transistors was used to test each terminal of a
transistor. Polarity testing was also performed on some
components like diode, capacitors, etc.
System Testing
This involves the testing of the entire circuitry and
thus, examine it for errors like short-circuits, lead flux,
joining unwanted links. Proper insertion of IC pin layout and
also checking if ICs of these pin number are slotted in their
proper base. After checking, cross check again before
powering the system.
4.2 Observation
It
was
observed
that
components
used
for
the
construction are not predominantly static, electronic data
book played a major role in identifying other available
component in the absence of one.
The first section that was carried out was the MOSFET
arrangement which was tested and was found working. The
second was the oscillating circuit while the third is the
charging circuit.
All the circuits were tested and found to be working.
The MOSFET arrangement later developed some problems
likewise the oscillating circuit, the problems were later
resolved after consulting the supervisor and our senior
colleagues.
The MOSFETS stage
The MOSFET used for this project is IRF3205 and the
drain current rating of the MOSFET is 100A (at 250C). By
considering increase in temperature (let say 1000C), the
drain current rating is taken as 105A.
This is because as the temperature increases, the drain
current also increases. Therefore, the drain current is taken
as 105A.
Inverter power rating = 2KVA
Input voltage = 12V
Therefore, in order to determining the current that will
flow in the input circuit:
P = IV ∴ I =
𝑃
𝑉
Therefore, I = 2000VA
12V
Therefore, I = 167A
Oscillator Stage
The frequency of oscillation is set to 50Hz. This is
determined by the values of the charging resistor RA and RB,
capacitor
C1
and
discharging
resistor
RB.
To
obtain
approximately 50% duty cycle, the value of RA is set to 1kΩ.
Figure 4.1 showing the circuit diagram of Astable Multivibrator Circuit using NE555IC
The Transformer stage
This is the final and output section of the inverter
circuit is always step up transformer in order to increase the
ac voltage generated. The transformer determines the power
of the inverter.
For our project (i.e. 2KVA inverter) a 12V/220V step up
center- tap transformer was used.
4.3 Results
The power rating of the inverter is 2KVA
Therefore, at the input (primary side)
V = 12V, P = 2000VA
Therefore, I =
𝑃
𝑉
=
2000𝑉𝐴
12𝑉
I = 167A
At the output (secondary side)
V = 220V
P = 2000VA
𝑃
2000𝑉𝐴
𝑉
220𝑉
I= =
I = 9.09A
Inverter Output test
After all stages had been coupled, the output of the
inverter was tested. This was done by first connecting a
voltmeter to the output terminal of the inverter to test the
output voltage. A 200W bulb was then connected to the
output terminal of the inverter to see if the bulb will bring
light at a desired brightness.
4.4
Casing and Packaging
A new casing was purchased, and also a cover board in
order to produce a neat and durable production.
We ensured that the casing purchased contains a ground
wire to give it a proper earthling.
4.5
Assembling of Section
The sections were assembled together in the casing
properly and carefully to avoid destroying the circuit
arrangements. We also ensured that the assembling does
not create avenue or chance for short circuit and so, we
connect the circuit to a ground wire.
Assembling Instruction
It is often easier while assembling the components on
the board to erect them according to their height. That is,
the lowest components first, usually the resistor and other
tiny ones while others with higher height follow. Care was
taken in getting the polarity of components like diode,
electrolytic capacitor etc., before they were being soldered
on the panel. Also, the biasing of the transistor was vividly
ascertained before permanent soldering on the board was
carried out.
The use of IC socket was employed to avoid any
damages that might result from excessive heat while
soldering the IC. The pin configuration of the IC used and its
connectivity with other components on the board were
strictly adhered to as shown on the design work before the
socket was permanently soldered. In fact, IC socket was the
first item on the board while other components were placed
around it.
4.6
Cost Analysis
Table 4.1 below shows the cost expenses of the project;
S/N
DESCRIPTION
PRICE
1.
Components
10,900
2.
Battery
45,000
3.
Transportation
4,500
4.
Transformer
5,500
purchase
5.
Casing expenses
6,300
6.
Miscellaneous
2500
expenses
TOTAL
79,200
4.7 Troubleshooting/ Fault tracing
This is a way of identifying, tracing and locating fault
for immediate rectification. Problems may result from
inadequate soldering and most likely be the reason why the
circuit may not work.
Other reasons may be due to electrical contact between
the leads of the component, excessive voltage supply to the
circuit (in case of using an adapter) etc. Soldered joints
were
carefully
checked
under
bright
light
to
ensure
adequacy. All components were also checked to make sure
they were in their correct position on the board. The
voltmeter was used to check voltage at various points on the
circuit was also embraced to follow the connection tract.
4.8 Maintenance and Repair
Maintenance and repair of an inverter is tedious to
carry out. It involves the technical know-how of an
individual to put together his garnered experiences to
properly handle the repair of an inverter. Nevertheless,
some routine maintenance checks may be carried out for
precautionary
and
safety
measures.
Some
of
this
maintenance checks are:
i.
Check for proper ventilation in the inverter which is provided
by the cooling fan.
ii.
Ensure proper charging of the battery to avoid overcharge of
battery which may cause damage to the battery.
iii.
Battery terminal should be checked regularly to ensure
proper supply to the inverter.
CHAPTER FIVE
5.0 Conclusion
This project has given us better understanding of the
practical aspect of our course of study (Electrical/Electronic
Engineering), it has also enable us to acquire more practical
skill and knowledge. The completion of this project of
construction of a 2KVA inverter with 12V DC dry cell battery
has given expected results after different tests were carried
out on each stage which gave durable and accurate results.
The proper running of this inverter is a clear indication
that the set aim and objectives have been achieved. The
construction is based on the theoretical knowledge gained so
far
during
our
lecture
times.
It
is
constructed
with
considerable cost, available and reliable components rather
than the more exorbitant unavailable ones.
The practical knowledge of the multi–purpose use of
SG3524
IC,
MOSFETs,
relay
etc.
interesting, tasking and educating.
makes
the
project
5.1 Recommendations
Logically, irrespective of how good a design might be,
there is always room for improvement. By so doing, the
following
recommendations
could
be
taken
into
consideration for more effective and useful inverter.
i.
Competent personnel should be consulted in case of any
damage to the unit and every source of power supply should
be disconnected from the inverter before removing the
cover.
ii.
Soldering of components should take a network system in
order to minimize heat to the components.
iii.
On no occasion should the inverter be loaded above 80% of
its maximum capacity. It’s an international advice.
iv.
Student should be exposed to more practical works so that
they
would
be
able
to
construct
all
practical
works
themselves.
v.
Government at various levels should encourage engineering
practice by financing and training of engineering within and
outside the country for the benefit of the students and the
nation at large.
REFERENCES
Kwaha, B. J., Iluonu, J and Danladi, C. (June 2004)
‘The design and construction of a 2kVA H-bridge inverter’
Team Not Platypus (May 12, 2010)
‘DC-AC/DC Power Inverter’
Adeyemo Sodiq (2018)