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PROJECT REPORT
ON
Analysis of the Square Ring Micro-Strip Antenna forCircular Polarisation with Different Height of Di-electric
Substrate
Submitted in partial fulfillment for the award of degree
Of
BACHELOR OF TECHNOLOGY
ELECTRONICS AND COMMUNICATION ENGG.
SHOBHIT UNIVERSITY
Submitted by: Project guide:
Dhananjay Kr. Dubey (MRT09UGBEC019) Mr.Manoj Sharma
Sumit Kumar Singh (MRT09UGBEC074) Assistant Professor
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DECELERATION
We hereby declare that the project entitled Stimulation Of Soft Starting Of dc
Motor Using MATLAB submitted for the award ofB.Tech Degree in Electronics
And Instrumentation Engineering to SHOBHIT UNIVERSITY, the project has not
formed the basis for the award of any degree.
Date: Nov. 30, 2012.
Submitted by:
Name signature
VINYASH CHANDRA (MRT09UGBEI010)
ANKIT (MRT09UGBEI002)
GAURAV MISHRA (MRT09UGBEI004)
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CERTIFICATE
This is to certified that the project and entitled Stimulation Of Soft
Starting Of dc Motor Using MATLAB is the work carried out by the
members name students ofB.Tech, Shobhit University, MEERUT during
the year 2012 in partial fulfillment of the requirement for the award of
degree of Bachelor Of Technology (E&I Department).
(Mr.DEEPAK KUMAR) (Dr.D.V.RAI)
Internal Examiner HOD
E&I, Department
(Mrs.Shweta Choudhary)
Project Guide External Examiner
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ACKNOWLEDGEMENT
We owe a great many thanks to a great many people who helped and supported
me during this project.
We would like to express the deepest appreciation to Mrs. Shweta
Choudhary asst. prof. department of Electronics and Instrumentation
Engineering, Shobhit University; the guide of the project for guiding and
correcting various documents of ours with attention and care; who has the
substance of a genius; he continually and convincingly conveyed a spirit of
adventure to our project, and an excitement in regard to teaching. Without his
guidance and persistent help this project would not have been possible.
We express our thanks to the Head of Department, Dr. D.B.RAI, Electronics
and Instrumentation Engineering, Shobhit University, for extending his support.
We would also thank our Institution Shobhit University and our faculty
members without whom this project would have been a distant reality. We also
extend our thanks to ours family and well wishers.
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TABLE OF CONTENTS
ChapterNo. Title Page No.
1. Objective 7
2. Introduction 7
3. DC motor starter
Matlabsimulink model 8
4. DC motor 10
5. Motor model and problem
definition 11
6. Starting means of the motor 14
7. Thyristor 16
8. Full wave rectifier 17
9. Simulation of separately
excited DC motor 21
10. Switching circuit 23
11. Circuit breaker 25
12. Controlling circuit 2613. Scope 27
14. Conclusion 28
15. Bibliography 30
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1.Abbreviations and Symbols.
Ra Armature winding resistance
La Armature winding inductance
Rf Field winding resistance
Lf Field winding inductance
Kf Constant of proportionality between motor flux ( ) and field
current (if).
J Inertia of Motor
TL Applied mechanical/ Load Torque
ia Armature current
if Field current Motor speed (radian per sec)
rpm revolution per minute
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Stimulation Of Soft Starting
Of
DC Motor Using MATLAB.
1.Objective:-Starting of dc motor with the variation of the applied voltage gradually in equal
steps from zero to the rated value limiting the starting current and giving sufficient
time for the back emf, Eb to build up. This voltage variation is achieved byvarying the firing angle delay of the power electronic device (Thyristor, GTO,
IGBT, etc), used as building blocks of the converter circuit that feeds the line,
supplying the motor.
2.Introduction:-Starting of a motor is the most important aspect in the control and operation of amachine. It becomes the utmost responsibility of a control engineer to take care of
the starting of any motor so as to reduce the starting current that would rush into
the motor. Many techniques can be adopted for achieving effective and smooth
starting of a motor. This project highlights the soft starting of a dc machine.
Soft starting of a dc machine deals with the variation of the applied voltage
gradually in equal steps from zero to the rated value limiting the starting current
and giving sufficient time for the back emf, Eb to build up. This voltage variation
is achieved by varying the firing angle delay of the power electronic device
(Thyristor, GTO, IGBT, etc), used as building blocks of the converter circuit that
feeds the line, supplying the motor.
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For certain industrial applications, it becomes essential to run an electric machine
used to drive a job, at adjustable but constant speed. Such a requirement results in
an urge to control the speed of the drive in an accurate and efficient manner. One
of the best suited methods of speed control of a DC motor is the PWM (Pulse
Width Modulation) method of control. This is an efficient method of voltage
control method of speed. As the name indicates, this method uses pulse width
modulated voltage signals to achieve a smooth speed control technique.
3.DC Motor Starter, MatLab/Simulink Models.Three possible conventional means may usually be used to control or monitor the
level of the armature current when starting a dc motor. The three possible means
are:
1. Use of a gradually decreasing tapped resistance between the supply voltage and
the motor armature circuit.
2. Use of a chopper circuit between the supply voltage and the motor armature
circuit.
3. Use of a variable DC voltage source.The third mean seems to own certainly
superiority when compared to the two first means.
It is well known that when starting a dc motor and that is by connecting its
armature circuit directly to a DC voltage source, a high value of the armature
current is expected. Such high value is primarily due to the lack of the back
electromotive force (emf) of the motor. The back electromotive force is known to
be proportional to the motor speed. The high value of the armature current may
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cause troubles to the DC motor ( like reduction of its life time, creation of false
operation of the protective devices associated with the motor, etc).
One of the classical remedies to such problem is to insert a starting resistor in
series with the motor armature circuit. The starting resistor should be gradually
removed as the motor speeds up. A careful glance at such method is that even
though there will be a control or monitor of the level of the armature current, there
will be a waste of energy at each start-up maneuver.
To overcome the last disadvantage, power electronics circuitry can be introduced.
This is possible through the insertion of achopper circuit. The chopper circuit
should be controlled by a hysterisis controller. The duty of the hysterisis controller
is to monitor or keep the motor armature current between certain two pre-set
threshold values. Unfortunately, theinsertion of chopper circuit results in a new
drawback which consists of creating ripples in the armature current.
Another alternative of starting the DC motor is to use a variable DC voltage
source. The level of source voltage should be minimum at start-up and should
increase gradually as the motor speeds up. Increasing the level of the voltage
source should be done automatically. This alternative is realized through the use of
a controlled full wave rectifier (AC-DC converter). The position of firing angle of
the rectifier should be decided by a closed loop controller. The input to the
controller should be the motor speed. The job of the controller is to have a high
value of firing angle at start-up and decreasing it gradually as the motor speeds up.
The firing angle should reach and stick to zero value as the motor reaches steady
state conditions.
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A softstarter consists of only a few main components. These are the thyristors that
can regulate the voltage to the motor and the printed circuit board assembly
(PCBA) that is used to control the thyristors. In addition to this, there are the
heatsink and fans to dissipate the heat, current transformers to measure the current
and sometimes display and keypad and then the housing itself. It is more and
morecommon to offer integrated by-pass contacts in the main circuit minimizing
the power loss in normal operation.Depending on the model of the softstarter, it
can be equipped with a built-in electronic overload relay (EOL) eliminating the
need for an external relay, PTC input, fieldbus communication possibilities etc.
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4.DC motor:-A direct-current (DC) motor is a device for converting dc electrical energy into
rotating mechanical energy. All motors have several basic characteristics in
common. They include: A stator, which is the frame and other stationary
components (provides the fixed magnetic field, could be a permanent magnet or an
electromagnet); a rotor or armature, which is the rotating shaft and its associated
parts (many coils of wire are wound on a cylindrical shaft); auxiliary equipment,
such as a brush/commutator assembly for DC motors and a starting circuit for AC
motors.Possible operation modes
Description
The DC Machine block implements a separately excited DC machine.
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An access is provided to the field terminals (F+, F-) so that the machine model can
be used as a shunt-connected or a series-connected DC machine. The torque
applied to the shaft is provided at the Simulink input TL.
The armature circuit (A+, A-) consists of an inductor La and resistor Ra in series
with a counter-electromotive force (CEMF) E.
The CEMF is proportional to the machine speed.
KEis the voltage constant and is the machine speed.
In a separately excited DC machine model, the voltage constant KE is proportional
to the field current If:
whereLafis the field-armature mutual inductance.
The electromechanical torque developed by the DC machine is proportional to the
armature current Ia.
where KT is the torque constant. The sign convention for Teand TL is
The torque constant is equal to the voltage constant.
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The armature circuit is connected between the A+ and A- ports of the DC Machine
block. It is represented by a series Ra La branch in series with a Controlled
Voltage Source and a Current Measurement block.
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5.MOTOR MODEL AND PROBLEMDEFINITION:-
Figure shows a schematic diagram of a DC shunt motor connected to a DC voltage
supply. The field winding is usually represented by an inductance (Lf) in series
with the rotor resistance (Rf). Similarly, the armature is usually represented by a
back electromotive force (Ea) in series with the rotor winding resistance (Ra) and
the winding self inductance (La). As it is known from any design textbox in
electric machines like , field winding resistance (Rf) has usually a high value while
armature winding resistance (Ra) has a small value.
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The back electromotive force (Ea) is proportional to the flux ( ) created by the
stator winding and the motor speed ( ).Assuming, that there is a linear
relationship between and the flux ( ) and the field current (if), that is the
saturation effect is neglected, the dynamic model that can be used to represent the
shunt DC motor can be easily derived. It will be of the following form:
Operation called constant torque At constant excitation, the motors speed
depends on the voltage appliedto its armature. Speed can be varied from standstill
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to the rated voltage ofthe motor chosen according to the AC voltage supply.The
motor torque is proportional to the armature current, and the ratedtorque of the
machine can be obtained continuously at all speeds.
Operation called constant power
When a machine is powered with rated voltage, it is still possible to increase its
speed by reducing the excitation current. In this case the speed controller must
have a controlled rectifier bridge powering the excitation circuit. The armature
voltage therefore remains fixed and equal to the rated voltage and the excitation
current is adjusted to obtain the requisite speed.
Power is expressed as:
P = E . I with
E as its armature voltage, and
I the armature current.
The power, for a given armature current, is therefore constant in all speed ranges,
but the maximum speed is limited by two parameters:
- the mechanical limit linked to the armature and in particular the maximum
centrifugal force a collector can support,
- the switching possibilities of the machine are generally more restrictive. The
motor manufacturer must therefore be consulted to make a good choice of motor,
particularly with regard to speed range at a constant horsepower.
By connecting the motor terminals directly to full supply voltage, the expected
waveforms of the armature current , the field current, and the motor speed are
depicted in figure
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6.STARTING MEANS OF THE MOTOR:-Using Starting Resistance
One way of limiting the armature current level is to insert a starting resistance in
series with the armature circuit as shown in figure 3. The starting resistance should
gradually be removed as the motor speeds-up. The times of moving from one tap to
another tap are usually calculated from steady state analysis.The starting resistance
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was assumed to be of five parts. The parts were gradually short-circuited and that
is by pretending the existence of a circuit breaker poles across each part terminals.
Figure shows the Matlab/Simulink block of the starting resistance.
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Using Starting Chopper Circuit
Using Chopper circuit Mean. a) Circuit Topology b) Hysteresis Controller
Function
The second possibility of controlling the armature current is to use a step-up
converter. The step-up converter is usually attributed the name chopper in the
literature.
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Results when Using Chopper Circuit.a) Armature current b) Field current. c)
Motor speed
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As it can been seen, the chopper circuit did perform its duty as intended but that
was at the expense of delaying the motor from reaching its steady state (rated
value) in a short time. The motor reaches its rated speed at time = 8 seconds. The
ratio between the maximum and rated values of the armature current is 1.23 but the
armature current has a lot of ripples which might be harmful to the armature
circuitry.
Using Starting AC/DC Converter
An indirect way of controlling the armature current is to have a variable DCvoltage source. The level of the voltage source should be of minimum level at
start-up and should increase gradually as the motor back electromotive force builds
up. This is possible through the use of a controlled full wave rectifier similar to the
one shown in figure
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Using AC/DC Converter Mean.
At standstill the Back induced Emf in a DC motor is zero. Moreover, resistance of
the armature is as low as ~0.4ohm. Hence on direct application of line voltage very
high current rushes into the armature circuit. This may lead to damage the coil by
overheating. This makes it necessary to control the inrush current.
As the rotor starts running, back emf(Eb) gets induced and gradually builds up to
oppose the line voltage. Due to the building up of the back emf (Eb) in the armature
coil, the effective voltage at no load, is considerably reduced to 2-3V which
automatically limits the armature current. This limiting of armature current to
approximately 10% of the rated current helps to achieve safer and smoother
starting of a motor.
The role of a starter is to limit the armature current till the back emf (Eb) is built
up. Traditionally this has been achieved by adding resistance in series with the
armature at the starting stage and then gradually reducing it to zero. This resistance
reduces the initial current then as Ebgradually builds up; this resistance becomes
unnecessary and hence can be cut off from the circuit. This method can be either
manual or automatic but the heat dissipation across the resistance gives the alarm
about the need for sophisticated methods of starting.
For a more reliable and automated starting of a machine, the soft starting technique
is gaining importance now-a-days. The disadvantage of the previous method can
be over come in soft starting. Thus soft starting is more efficient than the resistance
method.
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7.Thyristor:-This is a controlled semiconductor made up of four alternating layers:P-N-P-N.
Itacts like a diode by transmission of an electric pulse on an electrode control
called gate. This closing (or ignition) is only possible if the anode has a more
positive voltage than the cathode. The thyristor locks itself when the current
crossing it cancels itself out. The ignition energy to supply on the gate is not
linked to the current to switch over. And it is not necessary to maintain a current in
the gate during thyristor conduction.
The thyristor has the main following characteristics:
in a closed state:
- avotage drop composed of a threshold voltage and an internal resistance,
- a maximum admissible permanent current (up to about 5000A RMS for the most
powerful components).
in an off-state:
- an invert and direct maximum admissible voltage, (able to exceed5000 V),- in general the direct and invert voltages are identical,
- an recovery time which is the minimum time a positive anode cathode voltage
cannot be applied to the component, otherwise it will spontaneouslyrestart itself
in the close state,
- a gate current to ignite the component.
There are some thyristors which are destined to operate at mains frequency, others
called fast, able to operate with a few kilohertz, and with an auxiliary extinction
circuit. Fast thyristors sometimes have dissymmetrical direct and invert locking
voltage. In the usual arrangements, they are often linked to a connected antiparallel
diode and the manufacturers of semiconductors use this feature to increase the
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direct voltage that the component can support in an off-state. Fast thyristor are now
completely superseded by the GTO, power transistors and especially by the IBGT
(Insulated Gate Bipolar Transistor).
8.Full wave rectifier:-Electronic speed controllers are supplied from a constant voltage from an AC
network and feed the motor with DC variable voltage. A diode or thyristor bridge,
usually single-phase, powers the excitation circuit. The power circuit is a rectifier.
Since the voltage has to be variable,the rectifier must be controllable, i.e. have
power components whoseconduction can be controlled (thyristors). The variation
of the output voltage is obtained by limiting more or less the conduction time of
thecomponents.
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The more the ignition of the thyristor is delayed compared to zero of the half cycle,
the more the average value of the voltage is reduced, reducing the motor speed
(remember that extinction of the thyristor steps in automatically when the current
passes by zero). For low power controllers, or controllers supplied by a storage
battery, the power circuit, sometimes made up of power transistors (chopper),
varies the continuous output voltage by adjusting the conduction time. This
operation mode is called PWM (Pulse Width Modulation).
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Output of the fullwave rectifier
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9.Simulation of separately exited dc motorFigure sows the circuit arrangement of soft starting of separately exited dc motor.
There is a switching circuit which converts the ac input into dc output and dc goes
to the dc machine. Field is exited by external voltage. Circuit breaker is used to
change the supply from ac link to dc link after reaching the rated speed. Here
comparator is used to give the signal to circuit breaker.
Soft starting of a dc machine deals with the variation of the applied voltage
gradually in equal steps from zero to the rated value limiting the starting current
and giving sufficient time for the back emf, Eb to build up. This voltage variation
is achieved by varying the firing angle delay of the power electronic device
(Thyristor, GTO, IGBT, etc), used as building blocks of the converter circuit that
feeds the line, supplying the motor.
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Here we can change the specification of dc machine by double click ondc machine
block.
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10. Switching circuit:-A Subsystem block represents a subsystem of the system that contains it. The
Subsystem block can represent a virtual subsystem or a nonvirtual subsystem. The
primary difference is that nonvirtual subsystems provide the ability to control when
the contents of the subsystem are evaluated. Nonvirtual subsystems are executed as
a single unit (atomic execution) by the Simulink engine. A subsystem is virtual
unless the block is conditionally executed and/or you have selected the block Treat
as atomic unit check box.You can create a subsystem in these ways:
Copy the Subsystem (or Atomic Subsystem) block from the Ports &Subsystems library into your model. You can then add blocks to the
subsystem by opening the Subsystem block and copying blocks into its
window.
Select the blocks and lines that are to make up the subsystem using abounding box, then choose Create Subsystem from the Edit menu.
Simulink software replaces the blocks with a Subsystem block. When youopen the block, the window displays the blocks you selected, adding Inport
and Outport blocks to reflect signals entering and leaving the subsystem.
Now we want to change the switching circuit then we double click on the swithing
circuit and we find the dialog box shown in figure
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Now we have to change the firing angle then we double click on the pulse
generater and find dioalogboxshown in figure
We put the value of firing angle and frequency in the given expression :-
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Phase delay(sec) = (*1/f)/360
Where in degree.
For the second pulse generater we use the following expression:-
Phase delay(seec) =1/2f+(*1/f)/360
The number of input ports drawn on the Subsystem block's icon corresponds to the
number of Inport blocks in the subsystem. Similarly, the number of output ports
drawn on the block corresponds to the number of Outport blocks in the subsystem.
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We put the value of firing angle and frequency in the given expression :-
Phase delay(sec) = (*1/f)/360
Where in degree.
For the second pulse generater we use the following expression:-
Phase delay(seec) =1/2f+(*1/f)/360
We match the minimum voltage to start the moter using firing angle, we fix thefiring angle in sec at which the starting voltage is found.
11. Circuit breaker :-The Breaker block implements a circuit breaker where the opening and closing
times can be controlled either from an external Simulink signal (external controlmode), or from an internal control timer (internal control mode).A series Rs-Cs
snubber circuit is included in the model. It can be connected to the circuit breaker.
If the Breaker block happens to be in series with an inductive circuit, an open
circuit or a current source, you must use a snubber.When the Breaker block is set
in external control mode, a Simulink input appears on the block icon. The control
signal connected to the Simulink input must be either 0 or 1 (0 to open the breaker,
1 to close it).
When the Breaker block is set in internal control mode, the switching times are
specified in the dialog box of the block.When the breaker is closed, it is
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represented by a resistance Ron. The Ron value can be set as small as necessary in
order to be negligible compared with external components (a typical value is 10
mohms). When the breaker is open, it has an infinite resistance. When we double
click on the circuit breaker then we find a dialogue box as shown in figure
12. Controlling circuitAfter reaching the rated speed of the moter we change the supply from ac to dc
using logic gate and circuit breaker. We fix a rated speed in constant block there
after we compare the running speed of the motor to the rated speed using
substractor. Output of the substractor goes to the comparator and give the output in
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form of 0 and 1. Output of the comparator is given to circuit breaker as input for
the breaker as shown in the figure below.
Circuit breaker 2 is on untill the decision is 1, when our rated speed is found then
decision becomes 0 and circuit breaker 3 is on which allows the dc supply to the
machine.We have to give the vallue in constant block. We double click on constant
and find the dialoge box as shown in figure.
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13. ScopeThe Scope block displays its input with respect to simulation time. The Scope
block can have multiple axes (one per port) and all axes have a common time range
with independent y-axes. The Scope block allows you to adjust the amount of time
and the range of input values displayed. You can move and resize the Scope
window and you can modify the Scope's parameter values during the
simulation.The Scope provides toolbar buttons that enable you to zoom in on
displayed data, display all the data input to the Scope, preserve axis settings from
one simulation to the next, limit data displayed, and save data to the workspace.
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The toolbar buttons are labeled in this figure, which shows the Scope window as it
appears when you open a Scope block.You can zoom in on data in both thex andy
directions at the same time, or in either direction separately. The zoom feature is
not active while the simulation is running.
To zoom in on data in both directions at the same time, make sure you select the
leftmost Zoom toolbar button. Then, define the zoom region using a bounding box.
When you release the mouse button, the Scope displays the data in that area. You
can also click a point in the area you want to zoom in on.
If the scope has multiple y-axes, and you zoom in on one set ofx-y axes, the x-
limits on all sets ofx-y axes are changed so that they match, because all x-y axes
must share the same time base (x-axis).
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14. ConclusionThree conventional means are usually used in the control of the level of the
armature current encountered at start-upconditions. These means are attributed in
this paper thenames:
- starting resistance mean,
- chopper circuit mean, and
AC-DC converter mean.
Development of Matlab/Simulink models for the previousmeans is the main
contribution of this paper. Based on thesimulation results of the developed models,
the last mean seems to:
- control the peak of the armature current to some extent
- have less ripples in the motor armature current
- avoid the waste of energy fact encountered usually in thecase of using starting
resistance.
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15. Bibliography :-1. M. S. Sarma, Electric Machines: Steady-state Theory and
DynamicPerformance, 2nd Edition, PWS publishing Company, Boston,
1996.
2. M. H. Rashid, Power Electronics: Circuits, Devices, andApplicationsPrentice Hall, New Jersey, 1988.
3.Matlab Software, Version 6.5, The Math Works, Inc., 2002.4. J. J. Cathey, ,Electric Machine: Analysis and Design Applying
MatlabMcGraw Hill Company, New York 2001.
5. P. C. Sen, Principles of Electric Machines and Power Electronics,JohnWiley & Sons Inc., New York, 1989