CHAPTER ONE

1.0      INTRODUCTION

1.0.1   What is an Inverter?

An inverter (or power inverter) is an electronic circuitry that changes direct current (DC) to alternating current (AC).

Direct current is a type of current that flows in only one direction. Using the conventional current flow, direct current is such that electrons leaves the power source from the positive terminal (usually marked red) and  flows through the circuit and then terminates at the negative terminal (usually marked blue) ofthe power source. Direct current (DC) is usually gotten from battery cells, solar panels, household generations etc.

V

Vi

t

Fig 1.1 Graph of DC voltage against time

Alternating current is one in which current direction changes with respect to time, i.e it flows in one direction for an amount of time after which it changes direction. In this case there is no fix polarity for the terminals of the power supply. This type of current is usually gotten from, public power supply distribution companies, industrial generators etc.

Alternating current graph could take the form of sine wave, square wave, triangular wave, modified square wave etc. These graphs are shown in fig. 1.2.

T

(a)

(b)

      t

T

Vi

Vmax

(c)

      t

  t

  T

Fig. 1.2 Varied forms of alternating currents (a) sine wave  (b) triangular wave  (c) square wave  (d) modified square wave

The power supplied by industrial generator and public distribution companies is usually pure sine wave. But commercial inverters could give output ranging from square wave, modified square wave to pure sine wave. Although pure sine wave is most preferable for electrical equipments, it is usually costly because of the technology involved.The modified square wave is predominate in house hold inverters. This modified sine wave is manageable for electoral equipment compared of square wave

1.0.2BASIC WORKING PRINCIPLES OF INVERTER

The basic difference between an AC and a DC source is that, while an AC alternate its current direction or polarity, a DC has fixed current direction and polarity. The major work of an inverter therefore is to alternate the polarity of the DC power supply terminals.

Consider fig 1.3 below.

Fig1.3 Basic inverter circuit

The circuit consists of a centre tapped step-up transformer, a battery and a switch. When the switch is such that the negative terminal of the battery is connected topoint A, current flows in the primary side of the transformer as shown by the curve ”a”. When this is done the secondary side of the transformer gives power with current flow in the “a” direction. When the switch is reset to connect to point B and the negative terminal of battery, the current flow in the primary side of the transformer is indicated by curve “b”. that of the secondary side is in curve “b” direction.

        This arrangement gives out a square wave output. The switching system could be mechanical or electrical. An example of an electromechanical inverter switch is a VIBRATOR. Transistors of different power ratings (depending on the power rating of the inverter) can be used as switch for the circuits.

        A pure sine wave can be realized with a better technology. This is shown in fig 1.4

Fig1.4 Setup for pure sine wave inverter

Figure 1.4 Contains A Battery, two Drivers / Motors, A Belt, Power Amplifier and a Power Transformer

The battery supplies power to the driver A. This causes its blades to rotate. The belt transmits this rotary motion to driver B. The rotational motion of driver B brings about and alternating current at the terminals of driver B. This alternating current is fed into the power amplifier. The power amplifier combines the DC  current form the battery and the AC current from driver B to give an AC with higher power.

While the battery supplies the power (voltage and current), the AC current from the driver B causes it to oscillate. The output at the power amplifier is fed into the step-up power transformer which steps up the voltage from 12 volt to 220 volts

Modern inverters are mere development of these basic inverter circuit.

1.0.3IMPORTANCE OF INVERTER

Below are some importance of inverter circuit to the engineering and the world at large;

1. 1.  DC power sources like solar power and batteries can be used for AC appliances with the aid of inverters
2. 2.  Inverter encourages storage of energy which is used in electroshock weapons and uninterruptible power supply (UPS)
3. 3.  Induction heating which requires high frequency is made possible using inverters.
4. 4.  Due to the DC/AC  conversion process of inverters, skin effect, number and size of conductors are reduced which invariably reduces cost in HVDC transmission

1.1      HISTORY AND APPLICATIONS OF INVERTER

1.1.1        History of an Inverter

Inverter dates back to late nineteen  century through the middle twentieth century. Although the term inverter is attributed to David Prince who publish an article on inverter in the GE  Review (vol. 28, No.10, P. 678 – 81) in 1925, it is not certain  if he was the one who coined the term.

DC/AC power conversion in its early days was accomplished using rotary converters. As technology improved, vacuum tubes and gas filled tubes were used as switches for inverter circuit .

The name inverter  can be related to the electromechanical forms of switching used in its early days.

1.1.2 Applications of Inverter

Inverter circuit is used in the following  areas of electrical and electronic engineering;

1. Solar power supply
2. Power grid and HVDC power transmission
3. Induction heating
4. Electric motor speed control
5. Electric shock weapons
6. Uninterruptible power supply (UPS)

1.2      AIMS AND OBJECTIVE

1.2.1 AIMS

        The aim of this project is to design and construct an inverter.

1.2.2OBJECTIVE

The objective of this project is to;

1. Design an inverter
2. Construct an inverter
3. Test the inverter.

1.2.3METHODOLOGY

1.Literature review and design of the inverter: Literatures will be reviewed to obtain the working principles and circuit diagram after which a design will be made to ascertain the rating and parameters of the different components involved in the inverter.

2. Construction of the inverter: The circuit will be constructed firstly on a breadboard before soldering.

3. Testing of the circuit: The circuit will be tested with appliances according to the calculated rating of the inverter.

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