ALTERNATIVE CURRENT PULSE WIDTH MODULATION CONTROL FOR INDUCTION MOTOR

ABSTRACT

An induction or asynchronous motor is a type of AC motor where power is supplied to the rotor by means of electromagnetic induction, rather than by slip rings and commutators as in slip-ring AC motors. Single phase induction motor is the most familiar of all electric motors & they are similar to a 3-phase squirrel cage induction motor. It has a squirrel-cage rotor identical to a 3-phase motor and a single phase winding on the stator. There are several methods for controlling the speed of DC motors. One simple method is to varying frequency and voltage of the motor. Another method is controlling SCR for DC motors convert AC power to direct current, with adjustable voltage. In PWM method, pulse width modulation is used to regulate the current sent to the motor. Unlike SCR method which switch at line frequency, PWM controls produce smoother current at higher switching frequencies, typically between 1 and 20 kHz. At 20 kHz, the switching frequency is inaudible to humans, thereby eliminating the hum which switching at lower frequency produces. However, some motor controllers for radio controlled models make use of the motor to produce audible sound, most commonly simple beeps. A PWM controller typically contains a large reservoir capacitor and an H-bridge arrangement of switching elements e.g. thyristors, MOSFET, solid state relays, or transistors. PWM is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches. The average value of voltage and current fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load is. Duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. In this paper, the basic principles and operation of PWM inverters for ACMC applications using Induction Motor controller devices has been outlined. PIC17C756 microcontroller, TRIAC and DIAC are used to control the speed of the DC motor. The performance of the proposed system in Electronic Workbench software has been evaluated in terms of duty cycle, PWM and output voltage.

TABLE OF CONTENT

PAGES 

Certification---------i

Dedication---------ii

Acknowledgements--------iii

Abstract---------iv

Table of content --------v

List of figures ---------vii

List of tables ---------viii

CHAPTER ONE

INTRODUCTION

1.1General Introduction------1

1.2 Motivation--------2

1.3  Basic concepts--------3

1.4    Problem statement-------4

1.5 Aims and objectives-------4

1.6 Scope of project-------4

CHAPTER TWO

LITERATURE REVIEW

2.1 Pulse width modulation generator-----5

2.2 Operating principle -------7

2.3 DC to AC inversion-------8

2.4 Conversion of square wave to sinusoidal wave form---15

2.5 Difference between square wave and sinusoidal wave--19

2.6 Square waveform conversion to sinusoidal waveform --23

CHAPTER THREE

ANALYSIS AND DESIGN

3.1Analysis--------25

3.2 Design Procedure-------26

3.3 Integrated circuits-------30

CHAPTER FOUR

CONSTRUCTION AND TESTING OF THE 1.5KVA SINGLE PHASE INVERTER

4.1Construction--------31

4.2 The filter section-------33

4.350 Hz frequency oscillator section -----35

4.4 Pulse Width Modulation PWM section ----40

4.5 Low Battery / overload protection circuit ----40

4.6 Charging voltage sensing section -----43

4.7 Testing and results-------47

4.8Results---------48

CHAPTER FIVE

CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion--------49

5.2 Maintenance, safety and precaution -----49

References--------50