Description
ABSTRACT
The speed control of separately excited ac 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
COVER PAGE
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWELDGEMENT
ABSTRACT
CHAPTER ONE
- INTRODUCTION
- BACKGROUND OF THE PROJECT
- PROBLEM STATEMENT
- PURPOSE OF THE PROJECT
- OBJECTIVE OF THE PROJECT
- SIGNIFICANCE OF THE STUDY
- MOTIVATION OF THE STUDY
- SCOPE OF THE PROJECT
- APPLICATION OF THE PROJECT
- LIMITATION OF THE PROJECT
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 INTRODUCTION
2.1 REVIEW OF RELATED STUDIES
2.2 REVIEW OF DIFFERENT SPEEED CONTROL OF INDUCTION MOTOR
2.3 CONTROL APPROACHES OF INDUCTION MOTOR
2.4 REVIEW OF VARIOUS METHODS OF CONTROLLING THE SPEED OF INDUCTION MOTOR
CHAPTER THREE
- METHODOLOGY
- SYSTEM CIRCUIT DIAGRAM
- HARDWARE MODEL
CHAPTER FOUR
- CONSTRUCTION PROCEDURE AND TESTING ANALYSIS
- CASING AND PACKAGING
- ASSEMBLING OF SECTIONS
- TESTING OF SYSTEM OPERATION
- RESULT AND DISCUSSION
CHAPTER FIVE
- CONCLUSION
- RECOMMENDATION
REFERENCES
CHAPTER ONE
1.0 INTRODUCTION
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.
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.
Now a day, by the improvement of the power electronics devices, the flow of power to the motor is controlled by the switching action of the power switches (MOSFET, IGBT, IGCT etc).
The nature of the speed control requirement for an industrial drive depends upon its type. Some drives may require continuous variation of speed throughout the operation, which ranges from zero to full speed, or a over a portion of the range. For most of the drives, however a control of speed within the range of ± 10% of rated speed may be suitable.
The existing methods for the speed control of induction motor are voltage control, frequency control, vector control, changing stator poles, rotor resistance, doubly fed motor.
Recently remarkable efforts have been made in speed control of single phase induction motor (SPIMD) drives.
There are different types of PWM strategies have been used for speed control of induction motor drive. By using PWM strategies, inverter is used to drive the speed of induction motor, AC choppers are also used for the speed control of induction motor.
Ac chopper are used to obtain variable rms voltage from fixed voltage and frequency sources.
It is used in applications such as light dimmers, industrial heating furnaces. In this paper by using AC chopper, speed control of induction motor is achieved. The input to the AC chopper is pure sinusoidal voltage and the output of the AC chopper i.e. chopped voltage is given to the Induction Motor as the input. By varying the pulses given to the
AC chopper the output voltage of AC chopper varies and by this way speed of induction motor is achieved. Generally for the speed control of induction motor drive inverters are used. For the inverter, a separate DC source or rectifier (for converting AC to DC) is required, which increases the size of the whole system. Also for both single phase and three phases Induction motor control, a three leg inverter is used, which increases the number of components and design complexity will be more.
Thus in this paper, AC chopper is implemented to control the speed of single phase induction motor by using asymmetrical pwm method
.
1.2 PROBLEM STATEMENT
Controlling the speed of a motor using traditional methods involve running the motor at full speed and then using mechanical means such as gears, hydraulic couplings or pulleys. This is not only expensive, but also consumes a lot of energy. There are many means of controlling induction motor speed, but the most popular problem discovered in them is that motor used to experience speed instability and the efficiency of the motor drops when the motor speed is varied. Voltage frequency ratio method of motor speed control came to solve this problem. By varying the voltage and frequency, but keeping their ratio constant, the torque developed can be kept constant throughout the speed range thereby maintaining the motor efficiency.
1.3 PURPOSE OF THE PROJECT
| A large number of motors are being used for general purposes in our surroundings from house-hold equipment 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. |
|
1.4 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. However the objective of this work is to control ac motor speed and direction using chopper. |
1.5 SIGNIFICANCE OF THE STUDY
This research work will throw more light on the best techniques for controlling the speed and direction of an electric motor. This study will also be designed to be of immense benefit to all the users of electric motor most especially in industries.
It will also serve as a guide to whoever that wants to purchase speed controller for induction motor.
Finally, it will also serve as a useful piece of information for both producers and users of electric motor speed controller.
1.6 MOTIVATION OF THE STUDY
Controlling the speed and direction of an induction motor is necessary for both industrial and local applications in that it gives adjustable Speed Drives include energy savings, efficient motor starting, reversing, and speed and position control. The advantages of using this method of motor speed control is because it is cheap and efficient means of controlling the speed of an induction motor. However, advantages discussed above were points that motivate the carrying out of this research work.
1.7 SCOPE OF THE PROJECT
Conventional methods for starting and speed control of single-phase induction motor need often quite expensive external electrical equipment. Moreover, they require mechanical switches, which are the most troublesome parts.
These switches suffer from mechanical wear, which affects the motor performance. Electronic methods based on using a triac in series with the stator main winding or using four triac in a bridge topology has been suggested to control the speed of the motor.
Starting is still done by a capacitor in with the auxiliary winding. In the literature many authors have suggested and analyzed the performance of single-phase induction motors fed from inverter circuits with space vector pwm. In this case, either single-phase inverter is used with permanent capacitor motors or two phase inverter is used when the capacitor is omitted. Both methods need complicated circuits with high cost. However, AC chopper seems to be an acceptable solution when a wide range of speed control is required. AC chopper is the advance method of the triac which are used to obtain variable RMS voltage from fixed AC course. It is used in the application such as light dimmers, industrial heating furnaces and induction motor speed controllers. The different type of pwm technique such as conventional pwm, asymmetrical pwm, symmetrical pwm etc, is used to drive the AC Chopper. The hysteresis pwm technique offers a reasonably clean output voltage waveform at high power factor and less harmonic distortion factor of the motor current.
1.8 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.)
1.9 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.
CHAPTER FIVE
5.1 CONCLUSION
Generally for the speed control of induction motor drives inverters are used, but in this project AC chopper is implemented to control the speed of single phase induction motor. By implementing the Asymmetrical PWM method the load with stand capacity of the motor can be improved and the Total Harmonic Distortion (THD) in motor output current will be reduced when compared to other traditional PWM techniques.
5.2 RECOMMENDATION
Having concluded this project with its obvious problems and constraints I hereby recommend that in view of the importance of this project in companies factories workshops industries in reducing the partial or total lost of electric motor as a result of mal-operation caused by indecisive operator not overemphasis. It is therefore necessary workshops etc. to give this project adequate diffusion.
