This project is titled the design and construction of a DC to AC inverter system. It is designed to meet up with the power demand in the offices and in homes in the absence of power supply from the national supply authority, NEPA. In order words the device / item serves as a substitute for NEPA which almost monopolises the power supply to people.It is designed in such a way that it will take up 12v DC from battery and inverts it to an output of 230v, 50Hz AC. It makes no noise during operation and no hazardous carbon monoxide is generated in the surrounding.   This is a feature that makes it safe to use any where when compared to generator. Also, the circuit is capable of charging the battery (i.e 12v source) when the power from the supply authority is on. This greatly reduces the cost of operation of the system. This work is aimed at designing a modified sine wave inverter of power rating of 3kva that can be used to power appliances both in homes and industries.

 

TABLE OF CONTENTS
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
TABLE OF CONTENT

CHAPTER ONE
1.0      INTRODUCTION
1.1      OBJECTIVE OF THE PROJECT
1.2      SIGNIFICANCE OF THE PROJECT
1.3    APPLICATION OF THE PROJECT
1.4      SCOPE OF THE PROJECT
1.5      LIMITATION OF THE PROJECT
1.6      PURPOSE OF THE PROJECT
1.7      PROJECT ORGANISATION
1.8      INVERTER RATINGS
1.9      WHY CHOOSE A MODIFIED SINE WAVE INVERTER?
1.10    TYPES OF INVERTER
1.11    DIFFERENCE BETWEEN CONVENTIONAL GENERATOR AND INVERTER

CHAPTER TWO
2.0     LITERATURE REVIEW
2.1      REVIEW OF HISTORY OF AN INVERTER
2.2   REVIEW OF HOW TO CHOOSING THE RIGHT INVERTER
2.3      REVIEW OF THE DIFFERENCE BETWEEN SINE WAVE AND MODIFIED SINE WAVE   INVERTER.
2.4      REVIEW OF INVERTER CAPACITY
2.5      SAFETY OF INVERTER
2.6      INVERTER RATING
2.7      WHY CHOOSE A MODIFIED SINE WAVE INVERTER?
2.8      TYPES OF INVERTER

CHAPTER THREE
3.0     CONSTRUCTION
3.1      BASIC DESIGNS OF AN INVERTER
3.2      BLOCK DIAGRAM OF THE SYSTEM
3.3      SYSTEM OPERATION
3.4      CIRCUIT DIAGRAM
3.5      CIRCUIT DESCRIPTION
3.6     DESCRIPTION OF COMPONENTS USED
3.7      HOW TO CHOOSE A RIGHT INVERTER AND BATTERY
3.8      HOW TO CHOOSE THE BEST INVERTER BATTERY

CHAPTER FOUR
RESULT ANALYSIS
4.0      CONSTRUCTION PROCEDURE AND TESTING
4.1      CASING AND PACKAGING
4.2      ASSEMBLING OF SECTIONS
4.3      TESTING OF SYSTEM OPERATION
4.4      COST ANALYSIS  
  
CHAPTER FIVE     
5.0      CONCLUSION
5.1      RECOMMENDATION
5.2      REFERENCES

CHAPTER ONE
1.0                                        INTRODUCTION
A power inverter converts DC power (also known as direct current), to standard AC power (alternating current). Inverters are used to operate electrical equipment from the power produced by a car or boat battery or renewable energy sources, like solar panels or wind turbines. DC power is what batteries store, while AC power is what most electrical appliances need to run so an inverter is necessary to convert the power into a usable form. For example, when a cell phone is plugged into a car cigarette lighter to recharge, it supplies DC power; this must be converted to the required AC power by a power inverter to charge the phone.
In modified sine wave, The waveform in commercially available modified-sine-wave inverters is a square wave with a pause before the polarity transition, which only needs to cycle through a three-position switch that outputs forward, off, and reverse output at the pre-determined frequency. The peak voltage to RMS voltage does not maintain the same relationship as for a sine wave. The DC bus voltage may be actively regulated or the "on" and "off" times can be modified to maintain the same RMS value output up to the DC bus voltage to compensate for DC bus voltage variation.
The ratio of on to off time can be adjusted to vary the RMS voltage while maintaining a constant frequency with a technique called PWM. Harmonic spectrum in the output depends on the width of the pulses and the modulation frequency. When operating induction motors, voltage harmonics is not of great concern, however harmonic distortion in the current waveform introduces additional heating, and can produce pulsating torques.
Most AC motors will run on MSW inverters with an efficiency reduction of about 20% due to the harmonic content.

•                           OBJECTIVE OF THE PROJECT

The objective of this project is to design and construct a modified sine wave inverter which can be powered from the source of 12V battery to produce an output of 230vac. This inverter is capable of operating a wide variety of loads; electronic and household items including but not limited to TV, VCR, and satellite receiver, computers, and printers. This work is rated 3kva.

1.2                                           PURPOSE OF THE PROJECT
The purpose of this work is to design an electronic device or circuitry that changes direct current (DC) to alternating current (AC). The input voltage (12vdc), output voltage (230vac) and frequency (50hz), and overall power handling depend on the design of the specific device or circuitry. The inverter does not produce any power; the power is provided by the DC source.
A typical power inverter device or circuit requires a relatively stable DC power source capable of supplying enough current for the intended power demands of the system. The input voltage depends on the design and purpose of the inverter. Examples include: 12 VDC, for smaller consumer and commercial inverters that typically run from a rechargeable 12 V lead acid battery.
The waveform of this work is modified sine wave. The modified sine wave output of such an inverter is the sum of two square waves one of which is phase shifted 90 degrees relative to the other. The result is three level waveform with equal intervals of zero volts; peak positive volts; zero volts; peak negative volts and then zero volts. This sequence is repeated. The resultant wave very roughly resembles the shape of a sine wave.

1.3                                       SIGNIFICANCE OF THE PROJECT
In the recent years,  power  inverter has become a major power source due to its environmental and economic benefits and proven reliability. Since the solar power system does not have moving parts, virtually it does not require any kind of maintenance once installed.
Power inverter is produced by connecting the device on the 12VDC battery as the input to produce 230VAC as the required output. It can also be connected to solar panel.
Second, the whole energy conversion 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. Power inverter 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.

1.4                                              SCOPE OF THE PROJECT
A power inverter is a power conversion device. It converts fixed direct current (DC) voltage to frequency sinusoidal alternating current (AC) voltage output.
Power inverters are used to power and control the speed, torque, acceleration, deceleration, and direction of the motor. The use of inverter has become prevalent in wide range of industrial applications; from motion control applications to ventilation systems, waste water processing facilities to machining areas, and many others. Though power inverters offer lower operating costs and higher efficiency, they are not without their problems.

1.5                                     LIMITATION OF THE PROJECT

Input voltage:  A typical power inverter device or circuit requires a relatively stable DC power source capable of supplying enough current for the intended power demands of the system. The input voltage depends on the design and purpose of the inverter. The input voltage of this work is 12 VDC, for smaller consumer and commercial inverters that typically run from a rechargeable 12 V lead acid battery.

Waveforms: An inverter can produce a square wave, modified sine wave, pulsed sine wave, pulse width modulated wave (PWM) or sine wave depending on circuit design. The output waveform of this particular inverter is modified sine wave.

Output frequency: The AC output frequency of a power inverter device is usually the same as standard power line frequency, 50 or 60 hertz. The output frequency of the work is 50hertz.

Output voltage: The AC output voltage of a power inverter is often regulated to be the same as the grid line voltage, typically 240 VAC ( for Nigeria consumers) 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. Therefore, the output voltage of this work is 240vac.

Output power: A power inverter will often have an overall power rating expressed in watts or kilowatts. This describes the power that will be available to the device the inverter is driving and, indirectly, the power that will be needed from the DC source. The output power of this work is 3000 watts.

1.6                                           PROBLEM OF THE PROJECT

• Expensive when compared to traditional generators
• There are no large capacity inverters in the markets compared to conventional generator.
• The output supply depends wholly on the input source, which means that the inverter will stop working whenever the battery which is the input goes low.

1.7                                       APPLICATION OF THE PROJECT
The applications and uses of a power inverter which are as follows:
i. DC power source utilization: Inverter designed to provide 240 VAC from the 12 VDC source provided in an automobile. The unit shown provides more than 20 amperes of alternating current, or enough to power more than 3KW load. 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. Uninterruptible power supplies: An uninterruptible 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: Modified 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.

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, variable-frequency 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.

vii. Air conditioning: An inverter air conditioner uses a variable-frequency drive to control the speed of the motor and thus the compressor.
viii. Electroshock weapons: Electroshock weapons and tasters have a DC/AC inverter to generate several tens of thousands of V AC out of a small 12 V DC battery. First the 12VDC is converted to 400–2000V AC with a compact high frequency transformer, which is then rectified and temporarily stored in a high voltage capacitor until a pre-set threshold voltage is reached. When the threshold (set by way of an air gap or TRIAC) is reached, the capacitor dumps its entire load into a pulse transformer which then steps it up to its final output voltage of 20–60 kV. A variant of the principle is also used in electronic flash and bug zappers, though they rely on a capacitor-based voltage multiplier to achieve their high voltage.

1.8                               INVERTER RATINGS

 The ratings that you should look at when buying an inverter (depending on the type) are:

• Continuous Rating: This is the amount of power you could expect to use continuously without the inverter overheating and shutting down.
• Half Hour Rating: This is handy as the continuous rating may be too low to run a high energy consumption power tool or appliance, however if the appliance was only to be used occasionally then the half hour rating may well suffice.
• Surge Rating: A high surge is required to start some appliances and once running they may need considerably less power to keep functioning. The inverter must be able to hold its surge rating for at least 5 seconds. TVs and refrigerators are examples of items that require only relatively low power once running, but require a high surge to start.
   
• IP rating - defines the ability of the inverter seals to prevent water and dust ingress. Although some inverter manufacturers claim high IP ratings suitable for outdoor installation, the quality and location of the seals and ventilation will greatly affect the ability of the inverter to outlast the many years solar installations are expected to work. 
• Peak efficiency - represents the highest efficiency that the inverter can achieve.

1.9             WHY CHOOSE A MODIFIED SINE WAVE INVERTER?

For running typical resistive loads like lights and appliances, a modified sine wave inverter is a reliable, cost-effective choice. Though modified sine wave inverters do not produce a perfect replica of AC true sine wave power, they do provide an affordable option that for many mobile power applications is perfectly adequate. Some devices, however, may not recognize the modified sine wave and may run poorly or not at all.
Some of our most popular modified sine wave inverters are from our Heavy-Duty line up. These are excellent solutions for fleet, utility trucks and vans looking for a powerful and economical alternative to a pure sine wave product.

1.10                                 TYPES OF INVERTER
There are different types of inverters for home and industries available which can suit your various electricity needs. Following are the two basic types of inverters.

1. Modified Sine Wave Inverters

This type of home inverter obtains power from a battery of 12 volts and must be recharged using a generator or a solar panel. Appliances like microwave ovens, light bulbs, etc. can be run using these types of inverter.

• They can be rightly held as the best inverters for homes as they are efficient enough to provide power to the normal home requirement.
• They are the home inverters that are most affordable too.
• You can run the daily used home appliances using the modified sine wave home inverters.
• The electric appliances that involve motor speed controls or timers are not to be run using these types of home inverters.

The wave form of a modified sine wave inverter is as below:

2. True sine wave inverters
This is one of the better types of inverters as they provide better power as compared to the modified sine wave inverters for homes. These types of home inverter are also run using a battery of a larger capacity.

• Technically speaking, the sine waves they produce are purer, thus the efficiency.
• They are best inverters employed for the power sensitive appliances like refrigerators, televisions, air conditioners, washing machines, etc.
• These types of inverters are extremely reliable. The only drawback is that they are a bit expensive and cannot be afforded by the common man.
• There are various models available based on the electricity requirement of the house.

The wave form of a sine wave inverter is as below:

3. Square wave inverter
This is the simplest form of output wave available in the cheapest form of inverters. They can run simple appliances without problem but much else. Square wave voltage can be easily generated using a simple oscillator. With the help of a transformer, the generated square wave voltage can be transformed into a value of 240VAC or higher.
The wave form of a square wave inverter is a below:

1.11     DIFFERENCE BETWEEN CONVENTIONAL GENERATOR AND INVERTER

CONVENTIONAL GENERATOR	INVERTER GENERATOR
Conventional generators have been around for quite a while, and the basic concept behind them has remained essentially unchanged. They consist of an energy source, usually a fossil fuel such as diesel, propane or gasoline, which powers a motor attached to an alternator that produces electricity. The motor must run at a constant speed (usually 3600 rpm) to produce the standard current that most household uses require (in Nigeria, typically 220 Volts AC @ 50 Hertz). If the engine’s rpm fluctuates, so will the frequency (Hertz) of electrical output.	Inverter generators are a relatively recent development, made possible by advanced electronic circuitry. It inverter draws power from a fixed DC source (typically a comparatively fixed source like a car battery or a solar panel), and uses electronic circuitry to “invert” the DC power into the AC power. The converted AC can be at any required voltage and frequency with the use of appropriate equipment, but for consumer-level applications in Nigeria, the most common combination is probably taking the 12V DC power from car, boat or RV batteries and making it into the 220V AC power required for most everyday uses.
Conventional generators always bigger and heavier than inverter	The compact size, relatively light weight and resulting portability of inverter generators make them the clear winner in this category.
Conventional generators always noisy	Inverter generators are often designed from the ground up to be comparatively quiet
Conventional generators are often designed simply to get a certain amount of power where it is needed, and to keep the power on. Factors like the size of the unit have not been a major consideration. This has meant that conventional designs can often accommodate sizeable fuel tanks, with the obvious result being relatively long run times. This means that it uses fuel for it to operate.	Inverter generator draws power from DC source, either from battery or solar panel.
Conventional  generators emit smoke smoke which causes pollution	Inverter produces no smoke
A conventional generator is nothing more than an engine connected to an alternator and run at a speed that produces the desired AC frequency, regardless of the load on it (as the load increases the engine throttles up to keep the engine speed the same). The output of the alternator is connected directly to the load, without any processing.	With an inverter generator, a rectifier is used to convert the AC power to DC and capacitors are used to smooth it out to a certain degree. The DC power is then “inverted” back into clean AC power of the desired frequency and voltage
Many inverters can be paired with another identical unit to double your power capacity. This type of parallel capability means you can use two smaller, lighter generators to provide the same wattage and amperage of one much larger generator – without sacrificing all the benefits of the smaller, lighter, quieter, more portable inverter units.	Conventional units simply can’t offer this feature. Note that you will need a special cable to connect your generators, which is generally not

1.8                                        PROJECT WORK ORGANISATION
The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:
Chapter one of this work is on the introduction to a power inverter. In this chapter, the background, significance, objective limitation and problem of a power inverter were discussed.
Chapter two is on literature review of a power inverter. In this chapter, all the literature pertaining to this work was reviewed.
Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.
Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.
Chapter five is on conclusion, recommendation and references.

 

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