The speed of separately excited DC motor can be controlled from below and up to rated speed using chopper as a converter. The chopper firing circuit receives signal from controller and then chopper gives variable voltage to the armature of the motor for achieving desired speed. There are two control loops, one for controlling current and another for speed. The operation of a chopper was done, so also the construction of a chopper based trainer (training module). The complete layout of DC drive mechanism is obtained. The designing of current and speed controller was carried out. After carrying out the laboratory test and analysis, it was found that the measured result was in accordance with the expected result. Hence the project was confirmed okay.
TABLE OF CONTENTS
Title Page i
Table of Contents vi
List of Tables viii
List of Figures ix
List of Plates x
List of Abbreviations xi
CHAPTER 1: INTRODUCTION
1.1 Background of the Study 1
1.2 Problem Statement 5
1.3 Aims and Objectives of the Study 5
1.4 Scope of the Study 6
1.6 Significance of the Study 6
CHAPTER 2: LITERATURE REVIEW
2.1 DC Motor 9
2.2 Fuzzy Logic Controller (FLC) 11
2.2.1 Fuzzy rule base for speed control of DC motor 11
2.3 Visual Basic 11
2.4 Proportional-Integral (P-I) Controller 12
2.5 The Characteristics of P,I And O Controllers 12
2.6 Speed Control DC Motor using Microcontroller 13
2.6.1 Power rectifier (bridge) 13
2.6.2 The full-wave bridge rectifier 13
2.6.3 Filter curcuit 14
CHAPTER 3: MATERIALS AND METHODS
3.1 Design of the Pulse Width Modulator 16
3.1.1 Design of the astable multivibrator 17
3.1.2 Calculations of the astable multivibrator 19
3.1.3 Design of the mono-stable multivibrator 19
3.1.4 Calculations on the mono stable multivibrator 20
3.2 Design of the Driver Circuit 22
3.3 Design of Isolation Circuit 23
3.4 Design of the Power Circuit 25
3.4.1 Design of the power supply 26
3.5 Design and Analysis of DC Chopper 30
3.5.1 Principle of chopper operation 31
3.5.2 The ideal chopper 33
3.5.3 The classical chopper 36
3.6 Laboratory Manual for DC to DC Chopper 42
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Test on the Power Supply Circuit 48
4.2 Test of the Pulse Width Modulator Circuit 50
4.3 Test on the Control Circuit 51
4.4 Test on the Output Voltage of the Chopper Controller 52
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 61
5.2 Recommendations 61
LIST OF TABLES
3.1 Plot of the MATLAB simulated variation of chopper output voltage and mark period ratio 34
4.1 Test results obtained from digital oscilloscope connected to the chopper 56
4.2: The table of values of plot of MATLAB simulated variation of chopper duty cycle and input voltage 67
4.3 The table of values of plot of MATLAB simulated variation of chopper input voltage and speed 70
LIST OF FIGURES
2.1 (a&b) Full wave rectifier and output waveform 14
2.2 Filter circuit 15
3.1 Block diagram of chopper controller 16
3.2 (a) Circuit diagram of 555 timer astable multivibrator 18
3.2 (b) Circuit diagram of 555 timer monostable multivibrator 21
3.3 The complete circuit diagram of pulse width modulator stage 22
3.4 Circuit diagram pulse width modulator and transistor drive 23
3.5 Circuit diagram of the isolation circuit 24
3.6 Circuit diagram of pulse width modulator, driver and opto-coupler (isolator) 25
3.7 Circuit diagram of the power circuit 26
3.8 Circuit diagram of the power supply Chopper 27
3.10 Chopper circuit and voltage and current wave form 32
3.11 Diagram of an ideal chopper 34
3.12 MATLAB plot of V0 against K 35
3.13 Power circuit of a classical chopper with filter and motor circuit 35
3.14 Waveform of classical chopper 37
3.15 Path of current for conduction interval 37
3.16 Path current for the commutation interval 40
3.17 Path of current flow for the freewheel interval 42
3.18 DC chopper with RL-Load 44
4.1: The graph of duty cycle against output voltage 57
4.2: The graph of output voltage against the motor speed of the chopper 57
4.3: The graph of duty cycle against the Motor speed of the chopper 58
4.4: The graph of the output voltage against the input voltage of the chopper 58
4.5: The graph of duty cycle against the input voltage of the chopper 59
4.6: The graph of input voltage against speed of the chopper 60
LIST OF PLATES
3.1 The complete circuit diagram of chopper controller 30
4.1: The wave form of the power circuit before rectification 49
4.2: The wave form of the power supply circuit after rectification 49
4.3: The wave form of the PWM Circuit at 40% duty cycle 50
4.4 The wave form of PWM at 60% duty cycle 50
4.5: The wave form of the PWM at 80% duty cycle 51
4.6: The output wave form of the control circuit 52
4.7: The wave form of chopper system output voltage 53
4.8: The picture of astable mode output of PWM 53
4.9: The picture of chopper system output voltage waveform without load 54
4.10: Picture of current waveform 54
4.11: The test results from digital oscilloscope 55
LIST OF ABBREVIATIONS
SCR Silicon controlled rectifier
SISO Single input and single Output
DC Direct current
PWM Pulse Width Modulator
PID Proportional integral derivative
PMDC Permanent magnet DC
PCB Printed circuit board
FLC Fuxzy logic controller
GUI Graphical user interface
GTO Gate Turn On
Vcc Collector to collector Voltage
VCE Collector to Emmiter Voltage
BJT Bi-polar junction Transistor
IGBT Insulated gate bi-polar transistor
MOSFET Metallic oxide silicon field effect transistor
1.1 BACKGROUND OF THE STUDY
Development of high performance motor drives is very essential for industrial application. A high performance motor drive system must have good dynamic speed command tracking and load regulating response. DC motors provide excellent control of speed for acceleration and deceleration. The power supply of DC motor can connect directly to the field of the motor which allows for precise voltage control and is necessary for speed and torque control application (Farrer, 1973).
DC drives because of their simplicity, ease of application, reliability and favourable cost have long been important in industrial application. DC drives are less complex as compared to AC drives. DC drives are normally less expensive for low horse power ratings. DC motors have a long tradition of being used as adjustable speed machines and a wide range of options have evolved for this purpose. AC drive with this capability will be more complex and expensive (Ibekwe, 2005).
A series field DC motor is capable of proving starting and accelerating torques in excess of 400% of rated values, DC motors have long been the primary means of electric traction (Okoro,2010). They are also used for mobile equipment such as golf cart, quarry and mine winders applications. DC motor is considering SISO (Single Input and Single Output) system having torque/speed characteristics compatible with most mechanical loads. This makes a DC motor controllable over a wide range of speed by proper adjustment of the terminal voltage. Nowadays, induction motors, brushless DC motor sand synchronous motors have gained wide spread in electric traction system (Okoro, 2010). DC motors are always good option for advanced control algorithm because the theory of DC motors control is extendable to other types of motors as well (Okoro, 2010).
Before the advent of modern SCR controllers, speed control of DC machines were achieved using passive devices such as bank of resistors, mercury arc rectifiers, magnetic amplifiers or ward Leonard speed control schemes (Cyril, 2000). The Ward Leonard system is an AC motor- DC generator set that feeds a variable voltage to the armature of a stunt wound DC motor to vary the motor‟s speed. While the Ward Leonard system has good speed and torque control with a speed range of 25:1, it was phased out due to the excessive cost of purchasing thee separate rotating machines as well as the considerable maintenance necessary to keep the brushes and commutators of two DC machines in proper operating conditions.
Today SCR controlled DC drives have numerous advantages over electrical drive systems, such as the Ward Leonard drives (Ferrer, 1973). In the first method, variable resistance inserted between the fixed voltage DC source and the motor. This method is inefficient because of loses in the resistance. In the second method, the motor generator is used to supply the power to the motor whose speed is to be controlled. A variable DC output voltage of generator is obtained by controlling the field current of a DC generator which is driven by a constant speed DC motor. This system is still used in some industrial drives; therefore the system is bulky, costly, slow in response and less efficient. In 1960, high power thyristor device became available to make the solid state DC power converter practical. These converters offer greater efficiency, fast response, smooth operation, smaller size and lower weight and cost. The chopper circuit of force commutated thyristors is another effective method of controlling the armature voltage and speed of a DC machine. The chopper is a static power electronic devices that convert fixed DC input voltage to a controlled (variable) DC output voltage. It can be used to obtain a variable output voltage for varying the speed of a DC motor by changing the mark period ratio of the chopper (Erickson, 1997). The thyristor controlled (classical) chopper performs a switching action between the supply and the load. The increasing cost of fuel for operation of internal combustion engines, rapid rate of depletion of energy sources and the possibility of scarcity has necessitated the need to find alternative means of driving electric cars, trolleys and forklifts using DC choppers.
A chopper may be considered as DC equivalent to an AC transformer since they behave in an identical manner. As choppers involve stage convection, these are more efficient. Choppers are now being used all over the word as for rapid transit systems. They are also used in trolley cars, marine hoist, forklift trucks and mine haulers (Bimbhra, 2006). In this project work, to monitor and control the speed of DC motor, separately excited DC drives are used, since their simplicity, ease of applications such as reliability and favourable cost have long been a backbone of industrial applications and it will have a long tradition of use as adjustable speed machines and a wide range of options have evolved for this purpose. In these applications, the motor should be precisely controlled to give the desired performance (Bimbhra, 2006).
Many varieties of control schemes such as proportional, integral, derivative, proportional plus integral (PI), proportional plus derivative (PD), proportional plus integral plus derivative (PID), adaptive control and fuzzy logic controller have been developed for speed control of DC motors. The important aspect of the speed control of a DC motor is the armature voltage control method. By varying voltage to the armature of a v motor, the speed of the motor can be varied (Mohamed, 2003).
High performance motor drives are very much essential for industrial application. Most of the industries demand variable speed operation of motor. As synchronous motor is a constant speed motor so it is used in industries which demands constant speed operations of motors. Speed of DC motors can be varied below and above the rated, speed by terminal voltage control and field flux control respectively. So DC motors is used in many applications such as steel rolling mills, electric vehicles, electric trains, electric cranes and robotic manipulators require speed controller to perform its task smoothly. DC motors provide excellent control of speed for acceleration and deceleration. Speed controller of DC motor is carried out by means of voltage control in 1981 by Ward Leonard for the first time (Moleykutty, 2008).
Because of their simplicity, reliability and low cost, DC drives have long been used in industrial applications. Compared to AC drives systems, DC drives are less complex. For low horsepower ratings DC drives are normally less expensive. DC motors are used as adjustable speed machines since long and a wide range of option have evolved for this purpose. DC motors are capable of providing starting and accelerating torque 4 times the rated torque. DC motors have long been the primary means of electric traction. They are also being used fro mobile equipment such as quarry, golf carts and mining applications. DC motors are portable and well fitted to special applications like industrial equipment and machineries that are not easily run from remote power sources (Moleykutty, 2008).
DC motors are designed for used in industrial and commercial applications such as the pump and blowers, material handling, system and gear drives and adjustable speed drives. These motors are used to give rotary speed and position to various electromechanical systems. The developing a control system is to enable stable control since it has parameters tuning difficulties, non-linear, poor stability and imprecise control (Okoro, 2010).
The whole system is needed to be modelled, it has been found that this system results a nonlinear model, from this non-linear model, the linearization process has to be done to simplify the model. After the linearized model has been acquired, the next task to do is to control the DC motor according to the required specification (Mohamed, 2003).The main task of this work is to design and construct a chopper trainer that will control the speed of the motor. If the speed is equal to the reference signal, it can be concluded that the controller is successful in controlling the speed of the system since at that point, the speed becomes stable. The performance of the controller in controlling the speed of DC motor system can also be evaluated via computer stimulation using MATLAB/SIMULINK platform.
It is very imperative to state here that the need, importance and knowledge of DC motor control cannot be overemphasized, hence the design and construction of a DC motor training module in the laboratories becomes highly necessary so as to enable students and researchers in the study of DC motor speed control. Chopper based trainer is a self- contained set of electronic circuits that can be interlinked by students to create working circuits. Component parts cannot be removed or lost in the classroom and interlinking is performed by short coloured cables fitted with small insulated alligator clips. The trainer will be used by students and researchers to monitor and control the speed of DC motors. To accomplish this task, a teaching device known as a chopper trainer is designed, constructed and utilized.
1.2 PROBLEM STATEMENT
In every academic and research laboratories, Technical workshops or industries, DC motors plays vital roles. Hence the need to precisely learn how to control their speed becomes imperative. Prior to this research, people may have encountered difficulty in getting an efficient, reliable, durable and relatively inexpensive DC motor controller training module. This work will improve the existing types of DC motor controller modules that have been in use over the years.
1.3 AIM AND OBJECTIVES OF THE STUDY
The aim of this work is to design and construct a DC-DC Chopper trainer for laboratory applications.
The following are the objectives of the work;
i. To investigate the existing type of DC motor controller training modules.
ii. To show the need of DC motor controller training module for students and researchers.
iii. To mathematically model the DC-DC chopper drive.
iv. To construct the DC-DC chopper trainer.
v. To carryout laboratory tests to ascertain the performance of the Chopper drive.
1.3 SCOPE OF THE STUDY
The work undertaken in this project is limited to the following aspect;
i. Study of operation of the DC motor speed controller
ii. Design and implementation of the DC-DC chopper
iii. No load test of the DC-DC chopper
1.4 SIGNIFICANCE OF THE PROJECT
A chopper is an electronic device that switches voltage ON or OFF in a remarkably high speed on a motor in a process called chopping. It can therefore be called a switch. The following are the significance of a chopper based trainer;
i. Systems containing chopper have smooth control capability and are highly efficient and fast in response.
ii. A chopper can be used to step down or step up the fixed DC input voltage like a transformer. Therefore the use of transformer here is avoided thereby reducing the size and cost.
iii. Due to advantages such as simplicity, ease of application and reliability, this makes the trainer user friendly thereby making the student to understand and appreciate motor speed control.
iv. Since chopper takes a fixed DC input voltage and gives variable DC output voltage. It works on the principle pulse width modulation technique. There is no time delay in its operation. Hence, a chopper trainer is a fast and efficient means of studying speed control for students and researchers.
v. It is a relatively inexpensive, simple to use device that students and researchers could undertake DC motor speed experimentation in school or in a research laboratory.
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