The speed control of separately excited dc motor is carried out by varying the armature voltage for below rated speed and by varying field flux to achieve speed above the rated speed. This thesis presents the speed control methodology by varying armature voltage using chopper by providing control signal to the switches. Speed can be controlled from below and up to rated speed .The firing circuit of chopper receives signal from controller and variable voltage is given to the armature of dc motor according to the desired speed .There are two controllers we are using here one is speed controller and other is current controller. Both controllers are of proportional - integral type. The reason behind using PI type controller is it removes the delay and provides fast control.
ABBREVIATIONS AND ACRONYMS
AC - Alternating Current
MOSFET-Metal Oxide Semiconductor Field Effect Transistor
DC-Direct Current
PWM-Pulse Width Modulation
MATLAB -MatrixLaboratory
BJT -Bipolar junction transistor
IGBT -Insulated gate bipolar junction transistor
EMF -Electromagnetic field
GTO -Gate turn off thyristor
PI -Proportional -integral
PID -Proportional –integral-derivative
TABLE OF CONTENTS
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWELDGEMENT
ABSTRCT
TABLE OF CONTENT
CHAPTER ONE
- INTRODUCTION
- AIM/OBJECTIVE OF THE PROJECT
- SIGNIFICANCE OF THE PROJECT
- PURPOSE OF THE PROJECT
- SCOPE OF THE PROJECT
- LIMITATION OF THE PROJECT
- APPLICATION OF THE PROJECT
- ADVANTAGES OF THE PROJECT
- PROJECT ORGANISATION
CHAPTER TWO
LITERATURE REVIEW
2.0 LITERATURE REVIEW
2.1 DESCRIPTION OF CHOPPER
2.2 PRINCIPLE OF CHOPPER OPERATION
2.3 DESCRIPTION OF AN AC INDUCTION MOTOR
2.4 REVIEW OF OPERATING PRINCIPLES OF AN AC INDUCTION MOTOR
2.5 HISTORICAL BACKGROUND OF AN AC INDUCTION MOTOR
CHAPTER THREE
3.0 CONSTRUCTION METHODOLOGY
3.1 BLOCK DIAGRAM OF THE SYSTEM
3.2 CIRCUIT DIAGRAM
3.3 CIRCUIT DESCRIPTION
3.4 SYSTEM OPERATION
3.5 COMPONENTS LIST
3.6 DESCRIPTION OF MAJOR COMPONENTS USED
CHAPTER FOUR
4.0 RESULT ANALYSIS
4.1 CONSTRUCTION PROCEDURE AND TESTING
4.2 ASSEMBLING OF SECTIONS
4.3 CONSRUCTION OF THE CASING
4.4 TESTING OF SYSTEM OPERATION
4.5 RESULT AND DISCUSSION
CHAPTER FIVE
- CONCLUSIONS
- RECOMMENDATION
5.3 REFERENCES
CHAPTER ONE
1.0 INTRODUCTION
An electrical drive consists of electric motors, power controller and energy transmitting shaft. In modern electric drive system power electronic converters are used as power controller. Electric drives are mainly of two types: DC drives and AC drives. They differ from each other in this way that the power supply in DC drives is provided by DC motor and power supply in AC drives is provided by AC motor. DC drives are widely used in applications requiring adjustable speed control, frequent starting, good speed regulation, braking and reversing. Some important applications are paper mills, rolling mills, mine winders, hoists, printing presses, machine tools, traction, textile mills, excavators and cranes.. For industrial applications development of high performance motor drives are very essential. DC drives are less costly and less complex than AC drives. DC motors are used extensively in adjustable speed drives and position control system. The speed of DC motors can be adjusted above or below rated speed. Their speed above rated speed is controlled by field flux control and speed below rated speed is controlled by armature voltage. DC motors are widely used in industry because of its low cost, less complex control structure and wide range of speed and torque. There are various methods of speed control of DC drives – armature voltage control, field flux control and armature resistance control. For controlling the speed and current of DC motor, speed and current controllers are used. The main work of controller is to minimize the error and the error is calculated by comparing output value with the set point. This paper mainly deals with controlling DC motor speed using Chopper as power converter and PI as speed and current controller.
1.2 PURPOSE OF THE PROJECT
A large number of motors are being used for general purposes in our surroundings from house-hold equipments to machine tools in industrial applications. The electric motor is now a necessary and indispensable source of power in many industries. The function and the applications of these motors are wide-ranging. For the many applications, the speed control of the motor plays a major role, which can be done using a wide range of control strategies.
The purpose of a motor speed controller is to take a signal representing the demanded speed, and to drive a motor at that speed. The controller may or may not actually measure the speed of the motor. If it does, it is called a Feedback Speed Controller or Closed Loop Speed Controller, if not it is called an Open Loop Speed Controller. Feedback speed control is better, but more complicated, and may not be required for a simple design.
1.3 OBJECTIVE OF THE PROJECT
Generally speed control of the motor can be achieved by varying the input parameters of the motor such as current, voltage etc. This can be achieved by various methods such as field control method, armature control method, Ward- Leonard method etc for DC motors and AC motors. However the objective of this work is to control ac motor speed and direction using chopper.
1.4 SIGNIFICANCE OF THE PROJECT
Can be used to drive small conveyor belts in 2 directions and with dimmer would be able to handle both directional control and speed control.
• It is also possible to use this circuit for any robotic application where directional control is needed with speed control such as RC helicopters’ or aircrafts’ propellers. "Single Phase Induction Motor Speed Control Using PWM AC Chopper Fan Applicaitons”
1.5 SCOPE OF THE PROJECT
This circuit can easily be used for fan applications and anywhere we need dc motor to rotate permanently. A switch can be used to switch between “turbo” mode in which we want more power and torque (overspeeding) from the motor where we need performance. (Which is directly connecting to 12V by a switch.)
For overspeeding there must be calculation done how much time it will be overspeeded and how much the motor can handle. For fan applications temperature sensors would be beneficial. (Closed loop control system).This circuit can also be used for lighting. Since there is a net voltage drop of about 6 volts a group of LED can be directly controlled. Small light bulbs can be directly handled by this circuit but for higher ranges need to increase voltage.
1.6 APPLICATION OF THE PROJECT
This work is used in the following devices:
- Electronic bikes
- Swing machines
- Robotic controls
- Mobile air condition fans
- Ac operated drill machines
- Winding machines
- Electronic door controllers
- Toys
- Electronic chairs (beauty parlor. Etc.)
1.7 LIMITATION OF THE PROJECT
Drawback of this method of dc motor speed control is that they are not able to control the motor speed smoothly at lower levels, and as the desired speed is decreased, the torque of the motor also decreases proportionately. Due to this, at any unpredictable point the motor may just halt very abruptly. Also, during power ON, the motor may just not start up at lower speed settings and may require an initial boost by increasing the setting. Such situations are pretty undesirable and do not constitute an ideal speed control.
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