DESIGN AND CONSTRUCTION OF DC TO AC STATIC INVERTER

CHAPTER ONE

1.0. INTRODUCTION:

A DC to AC inverter is a simple device that produces an AC output from DC supply. The technique which is used in the realization of the inverter is chosen for simplicity and efficiency basis.

The input is DC supply unit from 12V battery which is used to power the system. The triggering unit triggers the ON/OFF of the silicon control rectifier SCR thyristor component of the inverter. The output of the inverter which is a high voltage AC is in form of a square wave.

Therefore, to get sine wave, the AC output is fed to the filter unit to filter off the harmonics. The filter provides a sine wave from the square wave output of the transformer this system enables the user to obtain an unimpeded power supply from two different sources, one source from the mains.

1.1. PURPOSE OF THE STUDY:

The purpose of carrying out this research work includes the following:

1. To highlight the aim and the necessities of DC to AC inverter in modern technology.

2. It is important to our homes where there is no electricity of which equipment can be powered by inverter using 12V battery heavy duty.

3. It is used in renewable energy technology i.e. solar bio mass etc.

1.2. SCOPE OF THE STUDY:

The inverter could be used in a car or boat to power device such as laptops, videogames, television or DVD player.

DC to AC inverter has the step of effecting the flow of air into an inverter honing and exhausting at least of the air through the metal core at a power transformer. It also improves the structure of cooling itself and increase power output comprising an enclosure with cooling air inlet aperture and also inverting DC to AC electricity.

1.3. BLOCK DIAGRAM OF THE INVERTER:

Fig. 1.1 Block Diagram of the Inverter

1.3.1.THE RELAY CIRCUIT OVER DISCHARGE SECURITY:

The relay circuit performs a vital role in the system as an over discharge security whereby whenever the battery terminal voltage drops to 1.8V percent, the relay switches off and automatically switches off power supply to the main oscillator or inverter circuit.

1.3.2.THE OSCILLATOR:

The oscillator is designed with a 4047 IC particularly designed for oscillation. The 4047 IC has 14 pins, pin 1, 2, 3 are connected to the frequency determinant components which are resistors and a capacitor. Pin 10 and 11 are the output pins which go high and low at different time intervals so that AC pulse can be obtained.

1.3.3.THE BUFFER CIRCUIT:

The buffer is made up of a transistor for each output; the buffer isolates the power MOSFET arrangement from the oscillator. The MOSFET are arranged into different pairs 3 MOSFETS for each and each MOSFET rates about 30 amps.

1.3.4.TRANSFORMER:

The transformer is a stepup one and the primary is centre taped of 12012 volts turns and secondary is 240 volts. The transformed output pulse is controlled by the pulse which is controlled by the MOSFETs and by the oscillator frequency.

1.4. PRINCIPLES OF OPERATION:

Inverter is the conversion of DC power to AC power at a symmetric AC output voltage of desired magnitude and frequency. It involves the connection of the D to AC circuit through switching devices which are turned on and off for appropriate periods relative to the DC or Ac power. Opening and closing of the switching device Diodes and thyristors is affected wholly in uncontrolled rectification or partly in controlled rectification by the AC supply voltage through the process called Natural communication which is the transfer of current from one branch of circuit to another in the case of AC supply voltage change polarity. This natural communication process can be applied to inversion when feeding power from DC source into relatively large AC power system. In the second approach, a means is provided which enables the current flowing in the switching device to commutate at any instant determined these two approached load to distinct classes of static inverters namely;

I. Current fed inverter.

II. Voltage fed inverter.

CURRENT FED INVERTER: This is an inverter in which supply current cannot change quickly. It is achieved by series DC supply inductance which prevents sudden change in current. The load current magnitude is controlled by varying the input DC voltage to large inductance.

VOLTAGE FED INVERTER: The DC supply voltage is essentially constant and dependent on load currently drawn, the inverter specifies by load. It is used for uninterrupted power supply UPS.