DESIGN AND CONSTRUCTION OF 0.5KVA UNINTERRUPTIBLE POWER SUPPLY (UPS)

ABSTRACT

Sequel to the incessant supply of epileptic utility power that has become the cause of great damage to most of our electrical and electronics appliances, of which damage cannot be quantified, an emergency/ Uninterruptible power supply provides electrical power for critical situation and equipment.

The Uninterruptible power supply (UPS) is designed to provide power when the utility power fails. This principle plays a great role in our growing economy and its important cannot be overemphasized.

This project deals with the design and construction of 0.5KVA (UPS) system. Special design consideration was given to the handling of inductive loads with minimum frequency drift and good voltage regulation. A small scale commercial outfit may adopt the system.

Details of the design consideration and problems encountered in the design and construction of this equipment are given in this project report.

PREFACE

The principle objective of this project is to present the detailed process necessary upon the design and construction of UPS.

To provide such a design, it is necessary to understand the basic functional aspect of each components of the system, along with their various characteristics. Hence, the following basic approach is used. The chapters are divided into six;

Chapter One:

                   It discusses the introduction and application of the device.

Chapter Two        

                   It gives the analysis of the different kinds of components used

Chapter Three

It discusses the design procedure and construction of the circuits at different stages of the UPS.

Chapter Four

                   It discusses the operation principle of UPS.          

Chapter Five       

This gives the bill of quantities used, suggestions of improvement and recommendations

Chapter Six

Give the conclusion and discuss the glossary of the whole principle involved in the design and construction of the UPS.

It is hoped that the comprehensive treatment of the material covered in this project will provide anyone with functional knowledge and understanding of the UPS.

DESIGN SPECIFICATION

INVERTER:                      INPUT – 12VOLTS D.C.

                                      OUTPUT – 220VOLTS A.C SQUARE WAVE

INPUT:                           220 VOLTS A.C. PWM SQUARE WAVE FORM

BATTERY:                       12VOLTS, 7AMP/HOUR  DRY CELL

OUTPUT POWER             500VA

TABLE OF CONTENTS

Cover Page                                                                                        

Dedication                                                                                         i

Certification                                                                                      ii

Acknowledgement                                                                              iii

Abstract                                                                                             iv

Preface                                                                                              v       

Design Specification                                                                           vi

CHAPTER ONE

          1.0     Introduction                                                                    1

          1.1     Principle of operation                                                1 - 3

          1.2     Air Traffic Control System                                               3

          1.3     Standby Power System                                               4 - 5

          1.4     Application in Micro Computer                                   5 - 6

CHAPTER TWO

          2.0     Components Description and Functions                      8 - 10

          2.1     A.C mains with distribution                                             11

          2.2     Theoretical Calculation of the Frequency                        12

          2.3     Theoretical Calculation of the Switching     

                   Action of FET                                                           13 - 15

          2.4     Charging Stage                                                                15

CHAPTER THREE

3.0     Oscillator                                                                        16

3.1     Circuit Diagram                                                               17

          3.2     Switching Effect Stage                                              18 - 19

          3.3     Change-over Comparator                                19 – 21

          3.4     Project Testing                                                               21

          3.5     Application of Uninterruptible Power Supply                   21       

          3.6     Safety of the Project                                                       22

CHAPTER FOUR

          4.0     Working principles                                                          23               4.1          Measuring the output stage with an oscilloscope             24

          4.2     Change Over Comparator                                                 24

CHAPTER FIVE

          5.0     Bill of Quantities                                                      25 - 26

          5.1     Suggestions/Recommendations                                 26 - 27

CHAPTER SIX

          6.0     Conclusion and Future Trends                                  28 - 29

          6.1     Precautions                                                                    29

          6.2     Internal Section of CD4047                                              29

          6.3     External Section of CD4047                                             30

                   Glossary                                                                          30

                   References                                                                      31

CHAPTER ONE

1.0    INTRODUCTION

Today’s complex electrical and electronics critical system often require a careful monitoring controlled by power supply to prevent shutdown in case of mains power failure. Example of such critical loads includes; Computers, TV set, DVDs, VCDs and Amplifiers. Another name for this Uninterruptible Power Supply (UPS) is known as “INVERTER” it is an external system for providing power when utility power supply fails.

This system is intended to provide Uninterruptible A.C. power of 500VA with a voltage of 220V. The Uninterruptible power supply is designed for loads which cannot tolerate a fraction of cycle of interruption from the incoming utility power supply source. The Uninterruptible power supply delivers secure and stable electrical power to the loads whatever the condition of the commercial A.C supply. This is to say that the electrical power the load (computer especially) receives is a quality supply generated by the Uninterruptible power supply (UPS).

1.1    PRINCIPLES OF OPERATION

The UPS is one of the greatest inventions and it is the best when compared with the electromechanical generator. It has no noise pollution, no smoke, no fuel and the inverter could also be referred to as Static Generator. It is connected to a 12volts D.C. battery.

When the manual switch is pressed, the oscillator would start operation and 4V A.C. would be produced at the output of the oscillator which is fed to the gate of the switching transistor i.e. FET (Field Effect Transistor) and as soon as the switching transistor is saturated, it would start modulating (Start switching positively and negatively). Anode 1 is connected to phase 1 of the switching transistor (Field Effect Transistor) and anode 2 is connected to phase 2 of the switching transistor, with respect to this connection, the circuit would start oscillating. The moment the field effect start switching, there would be a change in the current at the primary winding of the transformer i.e. at anode 1 which was 12V. 0 (zero) is the centre tapped when the current is flowing through anode 1 and anode 2, and anode 2 which is also 12V D.C. would be changed to 12V A.C. A change of current in the coil winding of the transistor brings about change in the line of flux which causes E.M.F to be induced at the secondary of the transformer.

            Fig 1a

The switch used in this arrangement can work for both manual and automatic. When the manual switch is on with the plug connected to external source, a relay which is functioning as a changeover comparator is energized, and this relay will separate the oscillator from the external supply of the power thereby connecting to charging machine to recharge the external battery back immediately there is a power failure, the UPS is switched on automatically. The relay also connects the mains voltage sent from the plug to the socket outlet so that when the transformer is charging the battery, the UPS would also supply mains voltage which could be used to power the appliances present at the socket outlet. This stage is referred to as “Automatic Change Over Comparator”

The arrangement in this circuit section is the modern way of designing an Uninterruptible Power Supply when compared with the outdated arrangement. It is observed that the old design where bipolar transistors are used, the bipolar transistor has an operating current which in turn is not good for designing because it could drain the D.C. current supply before the load is connected. In this arrangement, a Field Effect Transistor is used which has operating voltage and high input impedance which is simply the best.

1.2    AIR TRAFFIC CONTROL SYSTEMS

Radar and essential aircraft information are on constant display in air traffic control systems and mains failure could cause a break-out of radar and may lead to unprecedented disaster.

Obviously, such system will require a stand-by energy source. The source must be capable of immediate accessibility with no interruption in system output. The system is unaffected by variation in the mains supply and during  periods of power failure will continue to supply Uninterruptible power to the load for a specified period sufficient enough to allow an orderly shutdown of load equipment or activating standby generator systems.

1.3    STANDBY POWER SYSTEMS

These are the static term disturbances that are always present on the mains supply. This is shown in the diagram below:

IDEAL A.C. MAINS

Sags, surges and spites are caused by the switching on and off of nearby electrical power equipment such as photocopiers, welding gear, air conditioners, lifts and manufacturing machines. There are all deadly to computer equipment. Experience shows that they are by far the most common cause of problems such as “system hand ups” erratic entry and loss of data.   

The UPS delivers secure, stable electrical power to article loads what ever the condition of the public a.c. supply. The UPS plug into the public A.C supply and the computer equipment plug into the ups. That means that the electrical power the computer receives is a high quality supply generated by the UPS and not the mains.

When building upon the contraction of UPS system, this report covers the process of the construction of the UPS at the different stages. It also describes the various components used, such as resistors, transistors, transformers, battery among other components. The mode of design, construction, operation and test carried out were discussed fully in the following chapters. Information is also given on application and protection technique. The individual chapters are written and arranged in such a way that the report will be meaningful and digestible for readers making their acquaintance with the subject for those who are directly concerned with the construction of UPS.

1.4    APPLICATION IN MICRO COMPUTERS

In micro computer, power supply has what is called “ride through” i.e. the amount of time that the power supply can deliver energy to the logic circuit with no electricity being fed to the supply. This energy storage is directly related to the size and quality of the power supply components particularly the filter capacitors. The rise through of micro computers is from 20milliseconds to 40milliseconds, a long time in the world of digital electronics. Some designs have an even greater tolerance for every short term drop out.

This long ride through allows the standby power system to become popular for microcomputer market. The incoming utility power is fed directly into the computer under normal conditions. When the utility power fails, the transfer switch senses the happenings and sends message to the UPS which converts battery power d.c. into a.c that keeps the micro computer running. When utility power returns, it returns the micro computer to utility power and thereby starts to charge the battery back to its normal voltage (12Volts), hence there is no need to take the battery to any technician for charging.

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