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CHAPTER ONE

INTRODUCTION

1.1     Background of the Study

Electrical/Electronic Engineering is a very important element that cannot be neglected in the society as it is deeply sewn into the fabric of the society. It is an important element in homes to power household devices like electric bulbs, electric cooker, refrigerator, television set, etc. It also finds applications in various work places/offices to power devices like light bulbs, air conditioners, computers, etc. In fact, electronic/electrical engineering is the foundation of careers of many people doing both white-collar and blue-collar jobs.

Despite the development, the power generation and distribution across the country is abysmally low and is very far from being enough. This is a problem that has provoked so many alternative power solutions to cater for the increasing power needs.

The popular solution is the generator set. There are sets of different sizes and ratings; they also use fuel like petrol or diesel. However, the generating set has disadvantages like noise pollution, air pollution (it has led to the death of many people in Nigeria), and an expensive alternative power solution.

That is why an alternative, the power inverter is advocated for homes since the load is small compared to industrial setups. It must be noted however that a generating set is still advisable for an industrial setup despite its disadvantages. The power inverter solves most of the disadvantages of the generating set regarding cost of fuel, noise pollution, and air pollution. The power inverter is an able alternative power supply source for homes with bad electricity supply from electricity utility companies.

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.

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 thyratron.

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     Statement of the Problem

Faced with the problem of abysmal power supply from supply authorities, noise pollution, air pollution, cost of the popular alternative: generator sets, there is a need for a less noisy, pollution free and cheap solution to power problems in the houses of individuals and families in Nigeria.

1.3    Objectives of the Study

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).

1.4     Limitation of the Study

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.

1.5     Scope of the Study

The scope of this study is based on the design and construction of a 2kVA power inverter and its process of operation.

1.6     Significance of the Study

With the obvious advantages of the inverter being a cheaper (in the long term) and cleaner source of energy, it is a device that can power essential loads in the absence of supply from power supply utilities in the country.