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CHAPTER - 1
INTRODUCTION
The issue of calculating the energy saving amount due to regenerative
braking implementation in modern AC and DC drives is of great importance,
since it will decide whether this feature is cost effective. However, as the
increase of the electric energy cost at the industrial sector, the need for
advanced energy saving techniques emerged in order to cut down operational
costs. To this direction, this project presents a theoretical, simulation and
experimental investigation on the quantization of energy recovery due to
regenerative braking application in industrial rotating loads. Finally, a power
conversion scheme is proposed for the storage/exploitation of the recovered
energy amount.
Fossil fuels become each time less abundant and expensive, and with
the problems of worldwide pollution, they also become inadequate to be used
in such a large scale.
The automotive industry is one of the biggest spenders of this limited
resource. This fact may be changed with the use of electronic propelling
systems, such as the appliance of a three-phase induction motor driven by a
controlled inverter, replacing the internal combustion engine. The objective of
this project is to research, design and implement the most effective
regenerative system . The extra energy obtained from braking is used for light
the bulb.
1.1 BRAKING SYSTEM
All electric machines have two mechanical operations, motoring and
braking. The nature of braking can be regenerative, where the kinetic energy of
the rotor is converted into electricity and sent back to the power source or non-
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regenerative, where the source supplies electric power to provide braking. This
project investigates several critical issues related to regenerative braking in
both DC and AC electric machines, including the re generative braking
capability region and the evaluation of operating points within that capability
region that result in maximum regenerative braking recharge current. Electric
machines are used in the power trains of electric and hybrid-electric vehicles to
provide motoring or braking torque in response to the driver’s request and
power management logic. Since such vehicles carry a limited amount of
electrical energy on-board their energy storage systems (such as a battery
pack), it is important to conserve as much electrical energy as possible in order
to increase the range of travel.
Therefore, the concept of regenerative braking is of importance for such
vehicles since operating in this mode during a braking event sends power back
to the energy storage system thereby replenishing its energy level. Since the
electric machine assists the mechanical friction braking system of the vehicle,
it results in reduced wear on components within the mechanical friction brake
system. As both mechanical friction braking and electric machine braking are
used to provide the requested vehicle braking torque, braking strategies which
relate to splitting of the braking command between the two braking
mechanisms are discussed.
1.2 GENERALDISCRIPTION
The most common form of regenerative brake involves using an electric
motor as an electric generator. In electric railways the generated electricity is
fed back into the supply system. In battery electric and hybrid electric vehicles,
the energy is stored chemically in a battery, electrically in a bank of capacitors,
or mechanically in a rotating flywheel. Hydraulic hybrid vehicles use hydraulic
motors to store energy in form of compressed air Vehicles driven by electric
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motors use the motor as a generator when using regenerative braking: it is
operated as a generator during braking and its output is supplied to an electrical
load; the transfer of energy to the load provides the braking effect.
Regenerative braking is used on hybrid gas or electric automobiles to recoup
some of the energy lost during stopping. This energy is saved in a storage
battery and used later to supply AC power.
1.3 PROJECTMETHODS
This project has various different design paths to complete our product
while meeting the majority objectives. This means we will have to implement
and compare our different designs to insure the best product based on our set
of objectives. These paths have changed as we progressed through our project,
and there were a few foreseen methods that we expand upon in the design
section.
The basic design for the regenerative braking is to have an induction
motor, alternator, rectifier, battery, relay, step up transformer and load.While
an alternator is easier to find and purchase with many functioning units
available in scrap yards, they also tend to be less efficient in the output of DC
power compared to a dynamo. One option is to use two contacting wheels to
connect the two components. There are bound to be various other obstacles and
design methods to be implemented as the project progresses, and will be
observed and recorded as they occur.
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CHAPTER -2
DESIGN AND METHODOLOGY
2.1 BLOCK DIAGRAM
A simple block diagram of the overall project design is shown in Fig 2.1
Fig 2.1 Block diagram of overall project design
In our project, we consider single phase induction motor as prime
mover. Prime mover is directly coupled with an alternator by using belt and
pulley arrangement. Output of the alternator is connected to a step-up
transformer. The transformer step up into 230 V AC supply and this is fed into
an incandescent lamp.
While we applying the brake, giving DC supply to rotor. The rotor will
produce flux. Due to the kinetic energy, the rotor will slowly rotate and come
to rest. During this time an emf will produce in the stator winding and fed to
the step-up transformer and then fed to the load
The DC supply is provided with 12 V battery and this battery is charging
by using rectified output of alternator. Three phase diode bridge rectifier is
used as rectifier.
PRIME MOVER ALTERNATOR STEP-UP
TRANSFORMER
LOAD
RECTIFIER
BATTERY
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The relay circuit is used to control the braking system properly. Here we
used a 12 V single pole double throw relay.
In an ordinary system, during braking energy will lost in the form of
heat and noise. If we use this system, we can conserve the energy loss due to
braking.
2.2 PRIME MOVER
All generators, large and small, ac and dc, require a source of
mechanical power to turn their rotors. This source of mechanical energy is
called a prime mover. The type of prime mover plays an important part in the
design of alternators since the speed at which the rotor is turned determines
certain characteristics of alternator construction and operation. Here we use an
induction motor as prime mover for alternator and braking is applied to this
motor itself.
2.2.1 BELT AND PULLEY ARRANGMENT
Fig 2.2 Belt and pulley arrangement
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A pulley is a wheel on an axle or shaft that is designed to support
movement and change of direction of a cable or belt along its
circumference. Pulleys are used in a variety of ways to lift loads, apply forces,
and to transmit power. In nautical contexts, the assembly of wheel, axle, and
supporting shell is referred to as a "block."A pulley may also be called
a sheave or drum and may have a groove between two flanges around
its circumference. The drive element of a pulley system can be
a rope, cable, belt, or chain that runs over the pulley inside the groove. Hero of
Alexandria identified the pulley as one of six simple machines used to lift
weights. Pulleys are assembled to form a block and tackle in order to
provide mechanical advantage to apply large forces. Pulleys are also assembled
as part of belt and chain drives in order to transmit power from one rotating
shaft to another.
Here we use motor shaft as driver pulley and alternator shaft as driven
pulley
2.3 SINGLE PHASE INDUCTION MOTOR
An induction or asynchronous motor is an AC electric motor in which
the electric current in the rotor needed to produce torque is obtained
by electromagnetic induction from the magnetic field of the stator winding. An
induction motor therefore does not require mechanical commutation, separate-
excitation or self-excitation for all or part of the energy transferred from stator
to rotor, as in universal, DC and large synchronous motors.
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Fig 2.3 Single phase Induction Motor
Like any other electrical motor asynchronous motor also have two main
parts namely rotor and stator.
Stator: As its name indicates stator is a stationary part of induction
motor. A single phase ac supply is given to the stator of single phase induction
motor.
Rotor: The rotor is a rotating part of induction motor. The rotor is
connected to the mechanical load through the shaft. The rotor in single
phase induction motor is of squirrel cage rotor type.
The construction of single phase induction motor is almost similar to the
squirrel cage three phase motor except that in case of asynchronous motor the
stator have two windings instead of one as compare to the single stator winding
in three phase induction motor.
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2.3.1 STATOR OF SINGLE PHASE INDUCTION MOTOR
The stator of the single phase induction motor has laminated stamping to
reduce eddy current losses on its periphery. The slots are provided on its
stamping to carry stator or main winding. In order to reduce the hysteresis
losses, stamping are made up of silicon steel. When the stator winding is given
a single phase ac supply, the magnetic field is produced and the motor rotates
at a speed slightly less than the synchronous speed Ns which is given by
The construction of the stator of asynchronous motor is similar to that
of three phase induction motor except there are two dissimilarity in the
winding part of the single phase induction motor.
Firstly the single phase induction motors are mostly provided with
concentric coils. As the number of turns per coil can be easily adjusted with the
help of concentric coils, the mmf distribution is almost sinusoidal. Except for
shaded pole motor, the asynchronous motor has two stator windings namely
the main winding and the auxiliary winding. These two windings are placed in
spacequadrature with respectto each other.
2.3.2 ROTOR OF SINGLE PHASE INDUCTION MOTOR
The construction of the rotor of the single phase induction motor is
similar to the squirrel cage three phase induction motor. The rotor is cylindrical
in shape and has slots all over its periphery. The slots are not made parallel to
each other but are bit skewed as the skewing prevents magnetic locking of
stator and rotor teeth and makes the working of induction motor more smooth
and quieter.
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The squirrel cage rotor consists of aluminium, brass or copper bars.
These aluminium or copper bars are called rotor conductors and are placed in
the slots on the periphery of the rotor. The rotor conductors are permanently
shorted by the copper or aluminium rings called the end rings. In order to
provide mechanical strength these rotor conductor are braced to the end ring
and hence form a complete closed circuit resembling like a cage and hence got
its name as “squirrel cage induction motor”.
As the bars are permanently shorted by end rings, the rotor electrical
resistance is very small and it is not possible to add external resistance as the
bars are permanently shorted. The absence of slip ring and brushes make the
construction of single phase induction motor very simple and robust.
2.3.3 WORKING PRINCIPLE
When single phase ac supply is given to the stator winding of single
phase induction motor, the alternating current starts flowing through the stator
or main winding. This alternating current produces an alternating flux called
main flux. This main flux also links with the rotor conductors and hence cut
the rotor conductors. According to the Faraday’s law of electromagnetic
induction, emf gets induced in the rotor. As the rotor circuit is closed one so,
the current starts flowing in the rotor. This current is called the rotor current.
This rotor current produces its own flux called rotor flux. Since this flux is
produced due to induction principle so, the motor working on this principle got
its name as induction motor. Now there are two fluxes one is main flux and
another is called rotor flux. These two fluxes produce the desired torque which
is required by the motor to rotate.
According to double field revolving theory, any alternating quantity can
be resolved into two components, each component have magnitude equal to the
half of the maximum magnitude of the alternating quantity and both these
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component rotates in opposite direction to each other. For example – a flux, φ
can be resolved into two components
Each of these components rotates in opposite direction i. e if one φm / 2
is rotating in clockwise direction then the other φm / 2 rotates in anticlockwise
direction.
When a single phase ac supply is given to the stator winding of single
phase induction motor, it produces its flux of magnitude, φm. According to the
double field revolving theory, this alternating flux, φm is divided into two
components of magnitude φm /2. Each of these components will rotate in
opposite direction, with the synchronous speed, Ns. Let us call these two
components of flux as forward component of flux, φf and backward component
of flux, φb. The resultant of these two component of flux at any instant of time,
gives the value of instantaneous stator flux at that particular instant.
Now at starting, both the forward and backward components of flux are
exactly opposite to each other. Also both of these components of flux are equal
in magnitude. So, they cancel each other and hence the net torque experienced
by the rotor at starting is zero. So, the single phase induction motors are not
self starting motors.
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2.3.4 SINGLE PHASE INDUCTION MOTOR AS SELF STARTING
MOTOR
From the above topic we can easily conclude that the single phase
induction motors are not self starting because the produced stator flux is
alternating in nature and at the starting the two components of this flux cancel
each other and hence there is no net torque. The solution to this problem is that
if the stator flux is made rotating type, rather than alternating type, which
rotates in one particular direction only. Then the induction motor will become
self starting. Now for producing this rotating magnetic field we require two
alternating flux, having some phase difference angle between them. When
these two fluxes interact with each other they will produce a resultant flux.
This resultant flux is rotating in nature and rotates in space in one particular
direction only. Once the motor starts running, the additional flux can be
removed. The motor will continue to run under the influence of the main flux
only. Depending upon the methods for making asynchronous motor as Self
Starting Motor, there are mainly four types of single phase induction
motor namely,
 Split phase induction motor,
 Capacitor start inductor motor,
 Capacitor start capacitor run induction motor,
 Shaded pole induction motor.
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2.3.5 CAPACITOR START INDUCTION MOTOR
This motor is similar to the three-phase motor except that it has only two
windings (a-a′ and b-b′) on its stator displaced 90° from each other. The a-a′
winding is connected directly to the single-phase supply. For starting, the b-b′
winding (commonly called the auxiliary winding) is connected through a
capacitor (a device that stores electric charge) to the same supply. The effect of
the capacitor is to make the current entering the winding b-b′ lead the current
in a-a′ by approximately 90°, or one-quarter of a cycle, with the rotor at
standstill. Thus, the rotating field and the starting torque are provided.
Fig 2.4 Internal Diagram of Capacitor Start Induction Motor
As the motor speed approaches its rated value, it is no longer necessary
to excite the auxiliary winding to maintain the rotating field. The currents
produced in the rotor squirrel-cage bars as they pass the winding a-a′ are
retained with negligible change as they rotate past the winding b-b′. The rotor
can continue to generate the rotating field with only winding a-a′connected.
The winding b-b′ is usually disconnected by a centrifugal switch that opens
when the speed is about 80 percent of rated value.
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Power ratings for these capacitor-start induction motors are usually
restricted to about two kilowatts for a 120-volt supply and 10 kilowatts for a
230-volt supply because of the limitations on voltage drop in the supply lines,
which would otherwise occur on starting. Typical values of synchronous speed
on a 60-hertz supply are 1,800 or 1,200 revolutions per minute for four- and
six-pole motors, respectively. Lower-speed motors can be constructed with
more poles but are less common.
The efficiency of the motor can be somewhat increased and the line
current decreased by the use of two capacitors, only one of which is taken out
of the circuit (by means of a centrifugal switch) as the rated speed is
approached. The remaining capacitor continues to provide a leading current to
phase b-b′, approximating a two-phase supply. This arrangement is known as a
capacitor-start, capacitor-run motor.
Capacitor induction motors are widely used for heavy-duty applications
requiring high starting torque. Examples are refrigerator compressors, pumps,
and conveyor.
2.4 ALTERNATOR
An alternator is an electrical generator that converts mechanical energy
to electrical energy in the form of alternating current. For reasons of cost and
simplicity, most alternators use a rotating magnetic field with a
stationary armature.
Occasionally, a linear alternator or a rotating armature with a stationary
magnetic field is used. In principle, any AC electrical generator can be called
an alternator, but usually the term refers to small rotating machines driven by
automotive and other internal combustion engines. An alternator that uses
a permanent magnet for its magnetic field is called a magneto.
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Alternators in power stations driven by steam turbines are called turbo-
alternators. A conductor moving relative to a magnetic field develops
an electromotive force (EMF) in it, (Faraday's Law). This emf reverses its
polarity when it moves under magnetic poles of opposite polarity. Typically, a
rotating magnet, called the rotor turns within a stationary set of conductors
wound in coils on an iron core, called the stator. The field cuts across the
conductors, generating an induced EMF (electromotive force), as the
mechanical input causes the rotor to turn. The rotating magnetic field induces
an AC voltage in the stator windings. Since the currents in the stator windings
vary in step with the position of the rotor, an alternator is a synchronous
generator. The rotor's magnetic field may be produced by permanent magnets,
or by a field coil electromagnet. Automotive alternators use a rotor winding
which allows control of the alternator's generated voltage by varying the
current in the rotor field winding.
Permanent magnet machines avoid the loss due to magnetizing current
in the rotor, but are restricted in size, due to the cost of the magnet material.
Since the permanent magnet field is constant, the terminal voltage varies
directly with the speed of the generator. Brushless AC generators are usually
larger machines than those used in automotive applications.
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2.4.1 ALTERNATOR COMPONENTS
A typical rotating-field ac generator consists of an alternator and a
smaller dc generator built into a single unit. The output of the alternator section
supplies alternating voltage to the load. The only purpose for the dc exciter
generator is to supply the direct current required to maintain the alternator
field. This dc generator is referred to as the exciter. A typical alternator is
shown in fig
Fig 2.5 AC generator schematic drawings.
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Main parts of the alternator obviously consist of stator and rotor. But,
the unlike other machines, in most of the alternators, field exciters are rotating
and the armature coil is stationary.
Stator: Unlike in DC machine stator of an alternator is not meant to
serve path for magnetic flux. Instead, the stator is used for holding armature
winding. The stator core is made up of lamination of steel alloys or magnetic
iron, to minimize the losses. Armature winding is stationary in an alternator
because;
 At high voltages, it easier to insulate stationary armature winding, which
may be as high as 30 kV or more.
 The high voltage output can be directly taken out from the stationary
armature. Whereas, for a rotary armature, there will be large brush contact
drop at higher voltages, also the sparking at the brush surface will occur.
 Field exciter winding is placed in rotor, and the low dc voltage can be
transferred safely.
 The armature winding can be braced well, so as to prevent deformation
caused by the high centrifugal force.
Rotor: There are two types of rotor used in an AC generator / alternator:
(i) Salient and (ii) Cylindrical type
 Salient pole type: Salient pole type rotor is used in low and medium
speed alternators. Construction of AC generator of salient pole type
rotor is shown in the figure above. This type of rotor consists of large
number of projected poles (called salient poles), bolted on a magnetic
wheel. These poles are also laminated to minimize the eddy current
losses. Alternators featuring this type of rotor are large in diameters and
short in axial length.
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 Cylindrical type: Cylindrical type rotors are used in high speed
alternators, especially in turbo alternators. This type of rotor consists of
a smooth and solid steel cylinder havingg slots along its outer periphery.
Field windings are placed in these slots.
The armature is wound for a three-phase output. Remember, a voltage is
induced in a conductor if it is stationary and a magnetic field is passed across
the conductor, the same as if the field is stationary and the conductor is moved.
The alternating voltage in the ac generator armature windings is connected
through fixed terminals to the ac load.
2.5 VOLTAGE REGULATOR
Fig 2.6 Alternator with voltage regulator
A voltage regulator circuit for an alternator includes voltage responsive
circuitry having a zener diode. The regulator will maintain a pre-determined
charging system voltage level. When the system voltage decreases the
regulator strengthens the magnetic field and thereby increases the alternator
output voltage. When the system voltage increases the regulator weakens the
magnetic field and thereby decreases the alternator output voltage.
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Zener diodes are especially used on applications with sensitive
electronic components. These can prevent major damage caused by voltage
peaks due to sudden discharges. In 12V systems, Zener diodes with a voltage
range 24V - 32V are used and in 28V systems the range is 36V - 44V.
When ac generators are operated in parallel, frequency and voltage must
both be equal. Where a synchronizing force is required to equalize only the
voltage between dc generators, synchronizing forces are required to equalize
both voltage and speed (frequency) between ac generators. On a comparative
basis, the synchronizing forces for ac generators are much greater than for dc
generators. When ac generators are of sufficient size and are operating at
unequal frequencies and terminal voltages, serious damage may result if they
are suddenly connected to each other through a common bus. To avoid this, the
generators must be synchronized as closely as possible before connecting them
together.
The output voltage of an alternator is best controlled by regulating the
voltage output of the dc exciter, which supplies current to the alternator rotor
field. This is accomplished as shown in Fig 2.5, by a zener diode regulator of a
28 volt system connected in the field circuit of the exciter. The zener diode
regulator controls the exciter field current and thus regulates the exciter output
voltage applied to the alternator field.
The only difference between the dc system and the ac system is that the
voltage coil receives its voltage from the alternator line instead of the dc
generator. In this arrangement, a three phase, step down transformer connected
to the alternator voltage supplies power to a three phase, full wave rectifier.
The 28 volt, dc output of the rectifier is then applied to the zener diode voltage
regulator. Changes in alternator voltage are transferred through the transformer
rectifier unit to the zener diode. This controls the exciter field current and the
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exciter output voltage. The exciter voltage antihunting or damping transformer
is similar to those in dc systems and performs the same function.
The DC output voltage from the half or full-wave rectifiers contains
ripple superimposed onto the DC voltage and that as the load value changes so
to does the average output voltage. By connecting a simple zener stabilizer
circuit as shown below across the output of the rectifier, a more stable output
voltage can be produced.
2.5.1 ZENER DIODE REGULATOR
Fig 2.7 Zener Diode Regulator
Zener Diodes can be used to produce a stabilized voltage output with
low ripple under varying load current conditions. By passing a small current
through the diode from a voltage source, via a suitable current limiting resistor,
the zener diode will conduct sufficient current to maintain a voltage drop of
output voltage.
The resistor, RS is connected in series with the zener diode to limit the
current flow through the diode with the voltage source, VS being connected
across the combination. The stabilized output voltage Vout is taken from across
the zener diode. The zener diode is connected with its cathode terminal
connected to the positive rail of the DC supply so it is reverse biased and will
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be operating in its breakdown condition. Resistor RS is selected so to limit the
maximum current flowing in the circuit.
With no load connected to the circuit, the load current will be zero,
( IL = 0 ), and all the circuit current passes through the zener diode which in turn
dissipates its maximum power. Also a small value of the series resistor RS will
result in a greater diode current when the load resistance RL is connected and
large as this will increase the power dissipation requirement of the diode so
care must be taken when selecting the appropriate value of series resistance so
that the zener’s maximum power rating is not exceeded under this no-load or
high-impedance condition.
The load is connected in parallel with the zener diode, so the voltage
across RL is always the same as the zener voltage, ( VR = VZ ). There is a minimum
zener current for which the stabilization of the voltage is effective and the
zener current must stay above this value operating under load within its
breakdown region at all times. The upper limit of current is of course
dependent upon the power rating of the device. The supply voltage VS must be
greater than VZ.
One small problem with zener diode stabilizer circuits is that the diode
can sometimes generate electrical noise on top of the DC supply as it tries to
stabilize the voltage. Normally this is not a problem for most applications but
the addition of a large value decoupling capacitor across the zener’s output
may be required to give additional smoothing.
Then to summarize a little. A zener diode is always operated in its
reverse biased condition. A voltage regulator circuit can be designed using a
zener diode to maintain a constant DC output voltage across the load in spite of
variations in the input voltage or changes in the load current. The zener voltage
regulator consists of a current limiting resistor RS connected in series with the
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input voltage VS with the zener diode connected in parallel with the load RL in
this reverse biased condition. The stabilized output voltage is always selected
to be the same as the breakdown voltage VZ of the diode.
2.6 RECTIFIER
Rectifier is an electrical device that converts alternating current (AC),
which periodically reverses direction, to direct current (DC), which flows in
only one direction. The process is known as rectification. Physically, rectifiers
take a number of forms, including vacuum tube diodes, mercury-arc valves,
copper and selenium oxide rectifiers, semiconductor diodes, silicon-controlled
rectifiers and other silicon-based semiconductor switches. Historically, even
synchronous electromechanical switches and motors have been used. Early
radio receivers, called crystal radios, used a "cat's whisker" of fine wire
pressing on a crystal of galena (lead sulfide) to serve as a point-contact rectifier
or "crystal detector".
Rectifiers have many uses, but are often found serving as components of
DC power supplies and high-voltage direct current power transmission
systems. Rectification may serve in roles other than to generate direct current
for use as a source of power.
Because of the alternating nature of the input AC sine wave, the process
of rectification alone produces a DC current that, though unidirectional,
consists of pulses of current. Many applications of rectifiers, such as power
supplies for radio, television and computer equipment, require
a steady constant DC current (as would be produced by a battery). In these
applications the output of the rectifier is smoothed by an electronic
filter (usually a capacitor) to producea steady current.
Rectifier circuits may be single-phase or multi-phase (three being the
most common number of phases). Most low power rectifiers for domestic
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equipment are single-phase, but three-phase rectification is very important for
industrial applications and for the transmission of energy as DC (HVDC).
2.6.1 THREE PHASE DIODE RECTIFIER
Single-phase rectifiers are commonly used for power supplies for
domestic equipment. However, for most industrial and high-power
applications, three-phase rectifier circuits are the norm. As with single-phase
rectifiers, three-phase rectifiers can take the form of a half-wave circuit, a full-
wave circuit using a center-tapped transformer, or a full-wave bridge circuit.
Fig 2.8 –Three phase AC full-wave rectifier
A rectifier is an electrical device that converts alternating current (AC),
which periodically reverses direction, to direct current (DC), which flows in
only one direction. The process is known as rectification. Physically, rectifiers
take a number of forms, including vacuum tube diodes, mercury-arc valves,
copper and selenium oxide rectifiers, semiconductor diodes, silicon-controlled
rectifiers and other silicon-based semiconductor switches. Historically, even
synchronous electromechanical switches and motors have been used. Early
radio receivers, called crystal radios, used a "cat's whisker" of fine wire
pressing on a crystal of galena (lead sulfide) to serve as a point-contact rectifier
or "crystal detector". Rectifiers have many uses, but are often found serving as
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components of DC power supplies and high-voltage direct current power
transmission systems. Rectification may serve in roles other than to generate
direct current for use as a source of power. As noted, detectors of radio signals
serve as rectifiers. In gas heating systems flame rectification is used to detect
presence of a flame. Because of the alternating nature of the input AC sine
wave, the process of rectification alone produces a DC current that, though
unidirectional, consists of pulses of current. Many applications of rectifiers,
such as power supplies for radio, television and computer equipment, require
a steady constant DC current (as would be produced by a battery). In these
applications the output of the rectifier is smoothed by an electronic
filter (usually a capacitor) to produce a steady current. A more complex
circuitry device that performs the opposite function, converting DC to AC, is
called an inverter
For a three-phase full-wave diode rectifier, the ideal, no-load average
output voltage is
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2.6.2 RECTIFIER OPERATION
Fig 2.9 rectification circuit
• Two diodes are connected to each stator lead. One positive the other
negative.
• Because a single diode will only block half the the AC voltage.
• Six or eight diodes are used to rectify the AC stator voltage to DC
voltage.
• Diodes used in this configuration will redirect both the positive and
negative polarity signals of the AC voltage to produce DC voltage. This
process is called ‘Full - Wave Rectification’.
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At first you can see current pass through to the rectifier as it goes to the
battery. In the second, you can see the return path. Now, current passes through
to the rectifier however, this time current has the opposite polarity. In second
circuit you can see the new return path. Even though it enters the rectifier at a
different location, current goes to the battery in the same direction.
2.7 BATTERY
Battery is essential to supply DC power for the alternator rotor and for
the storage of generated power. An electric battery is a device consisting of
one or more electrochemical cells that convert stored chemical energy into
electrical energy. Each cell contains a positive terminal, or cathode, and a
negative terminal, or anode. Electrolytes allow ions to move between the
electrodes and terminals, which allows current to flow out of the battery to
perform work. Battery we used is 12V, 10 Ah rating.
Fig 2.10 Internal diagram of lead acid battery
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The battery is a two-terminal device that provides DC supply to the
inverter section when the AC mains are not available. This DC is then
converted into 220V AC supply and output at the inverter output socket. It is
pertinent to state that lead-acid batteries used in automobiles are very good for
this purpose as they provide good quality power for a long duration and can be
recharged once the power stored in them are consumed. The backup time
provided by the inverter depends on the battery type and its current capacity
Primary (single-use or "disposable") batteries are used once and
discarded; the electrode materials are irreversibly changed during discharge.
Common examples are the alkaline battery used for flashlights and a multitude
of portable devices. Secondary (rechargeable batteries) can be discharged
and recharged multiple times; the original composition of the electrodes can be
restored by reverse current. Examples include the lead-acid batteries used in
vehicles and lithium ion batteries used for portable electronics.
The battery was selected based on the amount of time we wanted to
operate the system at full load. As mentioned in the specifications, we wanted
to be able to power the lights. Fulfilling the 12 V DC battery requirements, we
found a unit from Universal Battery with 18 Ah. If the battery is discharged to
50% at most, this battery leaves us with 9 Ah.
Our load of lighting, music, and an iPod charger uses about 20 watts, but
with an alternative appliance connected (e.g. phone), the total power consumed
could be estimated at 25 watts. With a 12 VDC battery and a 25 W load, we
have about 2 A of current, which gives us about 4.5 hours of use at full load –
this is consistent with our design specifications. The exact battery we selected
is UB12180 (12V 10Ah). An electric battery is a device consisting of one or
more electrochemical cells that convert stored chemical energy into electrical
energy. Each cell contains a positive terminal, or cathode, and a negative
27
terminal, or anode. Electrolytes allow ions to move between the electrodes and
terminals, which allows current to flow out of the battery to perform work.
A lead-acid battery charger is most popular though it will very large size
than others battery type. But them have advantage are : cheap, easy to buy and
long life if correctly uses.
2.7.1 CHARGING AND DISCHARGING
Over charging with high charging voltages generates
oxygen and hydrogen gas by electrolysis of water, which is lost to the cell.
Periodic maintenance of lead-acid batteries requires inspection of the
electrolyte level and replacement of any water that has been lost. Due to
the freezing-point depression of the electrolyte, as the battery discharges and
the concentration of sulfuric acid decreases, the electrolyte is more likely to
freeze during winter weather when discharged.
Fig 2.11 Fully discharged: two identical lead sulfate plates
In the discharged state both the positive and negative plates
become lead (II) sulfate (PbSO4), and the electrolyte loses much of its
dissolved sulfuric acid and becomes primarily water. The discharge process is
driven by the conduction of electrons from the negative plate back into the cell
at the positive plate in the external circuit.
28
2.7.2 ION MOTION
During discharge, H+ produced at the negative plates moves into
the electrolyte solution and then is consumed into the positive plates,
while HSO−4 is consumed at both plates. The reverse occurs during charge.
This motion can be by electrically driven proton flow or Grotthuss mechanism,
or by diffusion through the medium, or by flow of a liquid electrolyte medium.
Since the density is greater when the sulfuric acid concentration is higher, the
liquid will tend to circulate by convection. Therefore a liquid-medium cell
tends to rapidly discharge and rapidly charge more efficiently than an
otherwise similar gel cell.
2.7.3 BATTERYCHARGER
A battery charger is a device used to put energy into a cell or
(rechargeable) battery by forcing an electric current through it. Lead-acid
battery chargers typically have two tasks to accomplish. The first is to restore
capacity, often as quickly as practical. The second is to maintain capacity by
compensating for self discharge.
In both instances optimum operation requires accurate sensing of battery
voltage. When a typical lead-acid cell is charged, lead sulphate is converted to
lead on the battery’s negative plate and lead dioxide on the positive plate.
Over-charge reactions begin when the majority of lead sulphate has been
converted, typically resulting in the generation of hydrogen and oxygen gas. At
moderate charge rates, most of the hydrogen and oxygen will recombine in
sealed batteries. In unsealed batteries however, dehydration will occur. The
onset of over-charge can be detected by monitoring battery voltage.
29
Over charge reactions are indicated by the sharp rise in cell voltage. The
point at which over-charge reactions begin is dependent on charge rate, and as
charge rate is increased, the percentage of returned capacity at the onset of
over-charge diminishes. For overcharge to coincide with 100% return of
capacity, the charge rate must typically be less than 1/100 amps of its amp-
hour capacity. At high charge rates, controlled over-charging is typically as
quickly as possible. To maintain capacity on a fully charged battery, a constant
voltage is applied. The voltage must be high enough to compensate for self
discharge, yet not too high as to cause excessive over-charging.
2.8 RELAY
A relay is an electrically operated switch. Many relays Automotive-style
miniature relay, dust cover is taken off use an electromagnet to mechanically
operate a switch, but other operating principles are also used, such as solid
state relays. Relays are used where it is necessary to control a circuit by a low-
power signal (with complete electrical isolation between control and controlled
circuits), or where several circuits must be controlled by one signal. The first
relays were used in long distance telegraph circuits as amplifiers: they repeated
the signal coming in from one circuit and re-transmitted it on another circuit.
Relays were used extensively in telephone exchanges and early computers to
perform logical operations. A type of relay that can handle the high power
required to directly control an electric motor or other loads is called a
contactor. Solid-state relays control power circuits with no moving parts,
instead using a semiconductor device to perform switching. Relays with
calibrated operating characteristics and sometimes multiple operating coils are
used to protect electrical circuits from overload or faults.
30
Fig2.12 Relay
2.9 CAPACITOR-INPUT FILTER
The capacitor-input filter, also called the pi filter due to its shape that
looks like the Greek letter π, is a type of electronic filter. Filter circuits are
used to remove unwanted or undesired frequencies from a signal .A simple pi
filter, containing a pair of capacitors, an inductor, and a load .A typical
capacitor input filter consists of a filter or reservoir capacitor C1, connected
across the rectifier output, an inductor L, in series and another filter or
smoothing capacitor, C2, connected across the load, RL. A filter of this sort is
designed for use at a particular frequency, generally fixed by the AC line
frequency and rectifier configuration. When used in this service, filter
performance is often characterized by its regulation and ripple.
1. The capacitor C1 offers low reactance to the AC component of the rectifier
output while it offers infinite resistance to the DC component. As a result the
capacitor shunts an appreciable amount of the AC component while the DC
component continues its journey to the inductor L.
2. The inductor L offers high reactance to the AC component but it offers
almost zero resistance to the DC component. As a result the DC component
31
flows through the inductor while the AC componentis blocked.
3. The capacitor C2 bypasses the AC component which the inductor had
failed to block. As a result only the DC componentappears across the load RL.
The component value for the inductor can be estimated as an inductance that
resonates the smoothing capacitor(s) at or below one tenth of the minimum AC
frequency in the power supplied to the filter (100 Hz from a full-wave rectifier
in a region where the power supply is 50Hz). Thus if reservoir and smoothing
capacitors of 2200 microfarads are used, a suitable minimum value for the
inductor would be that which resonates 2200 microfarads (μF) to 10 Hz, i.e.
115 mH. A larger value is preferable provided the inductor can carry the
required supply current. In general, the relationship between the resonant
frequency (in hertz), which should be less than or equal to one tenth of the
minimum AC frequency, in this case 100 Hz, the capacitance (in farads), and
the inductance (in henries) can be characterized by the following resonance
equation: f_0 = {1 over {2 pi sqrt{LC}}}.Comparison with other filters
Capacitor input filters can provide extremely pure DC supplies, but have fallen
out of favour because inductors tend to be unavoidably heavy, which has led to
the often-preferred choice of voltage regulators instead.
32
Fig 2.13 Capacitor-Input Filter
Fig 2.14 Capacitor-Input Filter -Charging and Discharging
33
Advantages of pi filters:
 More output voltage
 Ripple-free output
Disadvantages of pi filters:
 Large size
 Heavy
 High cost
2.10 STEP-UP TRANSFORMER
The output of the alternator is 12V ac supply with a frequency of 50 Hz
. This Ac supply is step up to 230 V by using step-up transformer. The Voltage
Transformer can be thought of as an electrical component rather than an
electronic component. A transformer basically is very simple static (or
stationary) electro-magnetic passive electrical device that works on the
principle of Faraday’s law of induction by converting electrical energy from
one value to another.
On a step-up transformer there are more turns on the secondary coil than
the primary coil. The induced voltage across the secondary coil is greater than
the applied voltage across the primary coil or in other words the voltage has
been “stepped-up”.
34
Fig 2.15 Step up transformer
The transformer does this by linking together two or more electrical
circuits using a common oscillating magnetic circuit which is produced by the
transformer itself. A transformer operates on the principals of “electromagnetic
induction”, in the form of Mutual Induction. Mutual induction is the process
by which a coil of wire magnetically induces a voltage into another coil located
in close proximity to it. Then we can say that transformers work in the
“magnetic domain”, and transformers get their name from the fact that they
“transform” one voltage or current level into another.
Transformers are capable of either increasing or decreasing the voltage
and current levels of their supply, without modifying its frequency, or the
amount of electrical power being transferred from one winding to another via
the magnetic circuit.
A single phase voltage transformer basically consists of two electrical
coils of wire, one called the “Primary Winding” and another called the
“Secondary Winding”. We will define the “primary” side of the transformer as
the side that usually takes power and the “secondary” as the side that usually
35
delivers power. In a single-phase voltage transformer the primary is usually the
side with the higher voltage.
These two coils are not in electrical contact with each other but are
instead wrapped together around a common closed magnetic iron circuit called
the “core”. This soft iron core is not solid but made up of individual
laminations connected together to help reduce the core’s losses.
The two coil windings are electrically isolated from each other but are
magnetically linked through the common core allowing electrical power to be
transferred from one coil to the other. When an electric current passed through
the primary winding, a magnetic field is developed which induces a voltage
into the secondary winding .The output of the transformer is 230 V, 50 Hz
,single phase AC, which is fed to the load.
36
CHAPTER- 3
LITERATURE REVIEW
3.1 A BRIEF HISTORY REGENERATIVE BRAKING
Regenerative Braking for an Electric Vehicle Using Ultra capacitors and
a Buck-Boost Converter:An ultra capacitor bank control system for an Electric
Vehicle has been simulated. The purpose of this device is to allow higher
accelerations and decelerations of the vehicle with minimal loss of energy, and
minimal degradation of the main battery pack. The system uses an IGBT Buck-
Boost converter, which is connected to the ultra capacitor bank at the Boost
side, and to the main battery at the Buck side. The control of the system
measures the battery voltage, the battery state-of-charge, the car speed, the
instantaneous currents in both the terminals (load and ultra capacitor), and the
actual voltage of the ultra capacitor. This last indication allows to know the
amount of energy stored in the ultra capacitor. A microcomputer control
manipulates all the variables and generates the PWM switching pattern of the
IGBTs. When the car runs at high speeds, the control keeps the capacitor
discharged. If the car is not running, the capacitor bank remains charged at full
voltage. Medium speeds keep the ultra capacitors at medium voltages, to allow
future accelerations or decelerations. The battery voltage is an indication of the
car instantaneous situation. When the vehicle is accelerating, the battery
voltage goes down, which is an indication for the control to take energy from
the ultra capacitor. In the opposite situation(regenerative braking), the battery
voltage goes up, and then the control needs to activate the Buck converter to
store the kinetic energy of the vehicle inside the ultra capacitor. The
measurement of the currents in both sides allows to keep the current levels
inside maximum ratings. The battery state-of charge is used to change the
37
voltage level of the ultra capacitor at particular values. If the battery is fully
charged, the voltage level of the capacitors is kept at lower levels than when
the battery is partially discharged. The converter also has an IGBT controlled
power resistor, which allows to drop energy when in some extreme situations
cannot be accepted neither for the ultra capacitors nor for the battery pack. The
car that will be used for future implementation of this experiment is a
Chevrolet LUV truck, similar in shape and size to a Chevrolet S-10. This
vehicle was already converted to an electric car at the Catholic University of
Chile.
Fully Regenerative braking and Improved Acceleration for Electrical
Vehicles:Generally, car brake systems use hydraulic brake technology, which
converts the excess of kinetic energy into heat, effectively resulting in an
energy loss. Regenerative braking technology focuses on converting this
kinetic energy of the decelerating vehicle back into electrical energy that can
then be reused for example during acceleration. Current hybrid vehicles are
equipped with such regenerative braking technology, which makes them
particularly interesting for situations with frequent deceleration, like city
traffic. However, the technology used in these vehicles has its limitations and
therefore does not stand on its own, but is always assisted with conventional
hydraulic brakes. This paper looks at removing this limitation and allowing a
vehicle to fully rely on regenerative braking technology to deal with any
braking situation ranging from simple slow down to emergency stops. To
enable this, multiple generators with different gear ratios are used. The
additional benefit of this construction is that, by introducing the appropriate
control circuit, the generators can be used as electrical engines. Since these
motors are connected with different gear ratios there is a more consistent
acceleration at any speed. The paper shows that the overall efficiency of the
38
system is very close to the efficiency of the generators used while achieving
braking performance similar to conventional braking mechanisms.
Study on Regenerative Braking of Electric Vehicle: In this paper, a
control scheme for a constant regenerative current is given based on the
analysis of several regenerative braking schemes. The three main control
strategies discussed are maximum regenerative efficiency control, maximum
regenerative power control and the constant regenerative current control.
Analysis is performed for two modes, the continuous current mode and the
discrete current mode. Using the above analysis, a formula for regenerative
efficiency of a control scheme is derived. The analysis of the braking system is
done to find out two aspects, the electric loop efficiency and the regenerative
energy efficiency. Using the results of the analysis, the paper concludes that
the constant regenerative current control scheme is better than the maximum
regenerative power control scheme and the maximum regenerative efficiency
control scheme. Also, the paper concludes that the used method gives a higher
regenerative braking efficiency and better controlperformance.
Regenerative Braking for Electric Vehicle based on Fuzzy Logic
Control Strategy: In this paper to recycle more energy during regenerative
braking, a regenerative braking force calculation controller is designed based
on fuzzy logic. Here, Sugeno's fuzzy logic controller is used which has 3
inputs and the output is the braking force. The three inputs are vehicle speed;
driver’s braking requirements and the battery’s state of charge. Fuzzy
membership functions are defined for the above inputs and outputs and the
output is found out in the range of 0 to 1. Each input has a membership value
of high, medium and low based on which the fuzzy rules are developed. The
simulations which are carried out show a substantial improvement in energy
efficiency of an electric vehicle.
Benchmarking of Regenerative Braking for a Fully Electric Car:
39
Short range of electric vehicles is one of the stumbling blocks in the way of
electric cars to gaining wide user acceptance and becoming a major market
player. The possibility to recover vehicle energy otherwise lost as heat during
braking is an inherent advantage of a hybrid electric or a fully electric vehicle.
Regeneration has the potential to answer this problem by aiding in range
extension with recuperation of vehicle energy during braking. The control and
dynamics of braking undergoes a major change as compared to a conventional
vehicle with friction braking, due to the addition of motor-generator. In this
research two regenerative braking concepts namely serial and parallel have
been studied and implemented on an electric vehicle. Also a point of interest is
to find if any additional states are required from the TNO Vehicle state
estimator (VSE) which would aid in regeneration. From the results obtained
we try to draw a conclusion on the difference in energy recuperation level in
the two strategies with consistent pedal feel in mind. The proposed brake
torque distribution strategy has been tested through the simulation on the New
European Driving Cycle (NEDC) drive cycle and straight line braking
scenario. Care has been taken to observe and adjust brake torque such that
wheel lock up is prevented and hence regeneration is un-interrupted. The
research couldn’t come with any additional parameters to be added to VSE.
However, it would be worthwhile to employ VSE to achieve a more accurate
estimation of the braking force, which may aid in prolonging regeneration time
and hence more energy recuperation. The results provide a good case to invest
more time and money into developing serial regenerative braking as it clearly
out-performs parallel regenerative braking strategy. The simulation tests
conducted in this research are for a longitudinal braking scenario. Further
investigation is required to study effects with lateral motion and cornering
manoeuvres
40
A Flywheel Regenerative Braking System : This thesis presents a flywheel
based mechanical regenerative braking system (RBS) concept for a Formula
SAE type race car application, to improve the performance and/or efficiency of
the race car. A mechanical system is chosen to eliminate losses related to
energy conversion while capturing the rotational braking energy. The
Flywheel-Regenerative Braking System (f-RBS) concept consists of a metal
flywheel design of truncated cone geometry for the energy storage system
(ESS) component and a V-belt CVT with a fixed gear for the transmission
component of the RBS system. Race car lap data and race car specifications
are used for designing/sizing the components. Mathematical models are
developed for design, integration and operation of the f-RBS system. It was
observed that a maximum of 27 % of energy requirements of the race car can
be supplied by the f-RBS. Also, a Virtual test rig model is created using MSC
ADAMS, an advanced dynamics/virtual prototyping software, in order to test
the whole f-RBS system for performance, as a preliminary alternative to
experimental testing. Initial testing is performed to validate the regenerative
braking principle employed, to establish the actual operating limits of the
virtual test rig and for an initial analysis of performance improvement by
utilization of the f-RBS system. From the results, it was inferred that using the
f-RBS concept can have a significant impact in recycling wasteful the braking
energy and provide additional energy to the racecar.
3.2 REGENERATIVE BREAKING IN TRAINS
In 1886, the Sprague Electric Railway & Motor Company, founded
by Frank J. Sprague, introduced two important inventions: a constant-speed,
non-sparking motor with fixed brushes, and regenerative braking, the method
braking that uses the drive motor to return power to the main supply system.
During braking, the traction motor connections are altered to turn them into
electrical generators. The motor fields are connected across the main traction
41
generator (MG) and the motor armatures are connected across the load. The
MG now excites the motor fields. The rolling locomotive or multiple unit
wheels turn the motor armatures, and the motors act as generators, either
sending the generated current through onboard resistors (dynamic braking) or
back into the supply (regenerative braking). Compared to electro-pneumatic
friction brakes, braking with the traction motors can be regulated faster
improving the performance of protection. For a given direction of travel,
current flow through the motor armatures during braking will be opposite to
that during motoring. Therefore, the motor exerts torque in a direction that is
opposite from the rolling direction Braking effort is proportional to the product
of the magnetic strength of the field windings, multiplied by that of the
armature windings. Savings of 17% are claimed for Virgin
Trains Pendolinos. There is also less wear on friction braking components.
It is expected that the Delhi Metro will save over
100,000tonsof CO2 from being emitted per year once its phase II is complete
through the use of regenerative braking. The train is slowed by the climb, and
then leaves down a slope, so kinetic energy is converted to gravitational
potential energy in the station. This is normally found on the deep tunnel
sections of the network and not generally above ground or on the cut and
cover sections of the Metropolitan and District Lines. Electricity generated by
regenerative braking may be fed back into the traction power supply; either
offset against other electrical demand on the network at that instant, used
for head end power loads, or stored in line side storage systems for later use.
42
3.3 EXISTING SYSTEM
In the existing system it uses mechanical breaking and it also
needs break shoes. In the existing system the wear and tear is more. The
existing system consist of brake shoes, which is very costly. The noise
produced is more in this system. In this system break shoes needs to be
frequently changed due to the mechanical friction. In the existing system the
energy during breaking is lost in the form of heat
3.4 PROPOSED SYSTEM
In the proposed system it uses electrical energy. In this system during
the breaking time the electrical energy is produced. In this system the noise is
less. Frequent replacement of brake shoes is not required in this system It is
more advantageous than the existing system, it produces electrical energy
during the breaking time. It is a cost effective system and it is a flexible system
The energy during breaking is converted to electrical energy
43
CHAPTER-4
ANALYSIS AND RESULT
4.1 ELECTRICALSCHEMATIC DIAGRAM
Fig.4.1.ELECTRICALSCHEMATIC DIAGRAM
44
4.2 CIRCUIT DISCRIPTION
In our design we use 230V, ¼ HP Capacitor start- run single phase
induction motor as prime mover. Prime mover is directly coupled with an
alternator by using belt and pulley arrangement. 120VA, 12V, 10A, 300 rpm
alternator is used. Output of the alternator is connected to a step-up
transformer. The transformer step up 12V AC into 230 V AC supply and this is
fed into an incandescent lamp.
While we applying the brake, giving DC supply to rotor. The rotor will
produce flux. Due to the kinetic energy, the rotor will slowly rotate and come
to rest. During this time an emf will produce in the stator winding and fed to
the step-up transformer and then fed to the load
The DC supply is provided with 12 V 10Ah deep cycle lead acid battery
and this battery is charging by using rectified output of alternator. Three phase
diode bridge rectifier is used as rectifier.
The relay circuit is used to control the braking system properly. Here we
used a 12 V single pole double throw relay.
In an ordinary system, during braking energy will lost in the form of
heat and noise. If we use this system, we can conserve the energy loss due to
braking.
During braking, the traction motor connections are altered turn the
electrical generators. The motor fields are connected across the main traction
generator(MG) and the motor armatures are connected across the load. The
MG now excites the motor fields. The rolling locomotive or multiple unit
wheels turn the motor armatures, and the motors act as generators, either
sending the generated current through onboard resistors (dynamic braking) or
45
back into the supply (regenerative braking).Compared to electro-pneumatic
friction brakes, braking with the traction motors can be regulated faster
improving the performance of wheel slide protection. For a given direction of
travel, current flow through the motor armatures during braking will be
opposite to that during motoring. Therefore, the motor exerts torque in a
direction that is opposite from the rolling direction.
Braking effort is proportional to the product of the magnetic strength of
the field windings, multiplied by that of the armature windings. Savings of
17% are claimed for Virgin Trains. There is also less wear on friction braking
components. The Delhi Metro saved around 90,000 tons of carbon dioxide
(CO2) from being released into the atmosphere by regenerating112,500
megawatt hours of electricity through the use of regenerative braking systems
between 2004 and2007. It is expected that the Delhi Metro will save
over100,000 tons of CO2 from being emitted per year once its phase II is
complete through the use of regenerative braking. Another form of
regenerative braking is used on some parts of the London Underground, which
is achieved by having small slopes leading up and down from stations.
The train is slowed by the climb, and then leaves down a slope, so
kinetic energy is converted to gravitational potential energy in the station. This
is normally found on the deep tunnel sections of the network and not generally
above ground or on the cut and cover sections of the Metropolitan and District
Lines.
46
4.3 COMPARISON OF DYNAMIC BRAKING AND
REGENERATIVE BRAKING
Dynamic brakes unlike regenerative brakes, dissipate the electric energy
as heat by passing the current through large banks of variable resistors.
Vehicles that use Dynamic brakes ("rheostatic brakes" in the UK), unlike
regenerative brakes, dissipate the electric dynamic brakes
include forklifts, diesel-electricl ocomotives, and streetcars. This heat can be
used to warm the vehicle interior, or dissipated externally by large radiator-like
cowls to house the resistor banks. The main disadvantage of regenerative
brakes when compared with dynamic brakes is the need to closely match the
generated current with the supply characteristics and increased maintenance
cost of the lines. With DC supplies, this requires that the voltage be closely
controlled. The AC power supply and frequency converter pioneer Miro Zoric
and his first AC power electronics have also enabled this to be possible with
AC supplies.
The supply frequency must also be matched (this mainly applies to
locomotives where an AC supply is rectified for DC motors).In areas where
there exists a constant need for power unrelated to moving the vehicle such as
electric train heat or air conditioning, this load requirement can be utilized as a
sink for the recovered energy via modern AC traction systems. This method
has become popular with North American passenger railroads where Head End
Power loads are typically in the area of 500 kW year round. Using HEP loads
in this way has prompted recent electric locomotive designs such as the ALP-
46 andACS-64 to eliminate the use of dynamic brake resistor grids and also
eliminates any need for any external power infrastructure to accommodate
power recovery allowing self-powered vehicles to employ regenerative braking
as well. A small number of steep grade railways have used 3-phase power
supplies and 3-phase induction motors. This results in a near constant speed for
47
all trains as the motors rotate with the supply frequency both when motoring
and braking.
4.4 FEASIBILITY OF TECHNOLOGY AND OPERATIONAL
NECESSITIES
Various types of trains can be equipped with regenerative braking:
electric trains, hybrid diesel locomotives and subway trains The more
frequently a train stops, the more it can benefit from regenerative breaking.
Therefore the technique is especially valuable for commuter trains and
subways, which both stop frequently. Electric railway systems can be either
DC or AC powered. It is much easier to implement regenerative breaking for
AC powered systems. For DC powered systems, there are two main barriers.
Most DC powered systems use relatively low voltages and often the generated
electricity cannot be fed back into the public electricity grid. In very dense
suburban DC powered networks, however, regenerative breaking can be an
effective way to reduce the electricity demand. In all other cases, the
effectiveness of regenerative braking is rather low but may be enhanced by
technological upgrades of vehicles and/or substations. These upgrades are
associated with relatively high investment costs. Railway systems working
with AC power can implement regenerative braking with almost no additional
costs. Also the implementation of regenerative braking in diesel powered
locomotives poses no obstacle. Virtually all locomotives are diesel-electric, so
the capacity to do regenerative braking is available
48
4.5 STATUS OF THE TECHNOLOGY AND ITS FUTURE MARKET
POTENTIALTOP
Regenerative braking is a mature technology. Within Europe,
there is still a considerable difference between countries in the share of rolling
stock that is equipped with regenerative braking, but the share is relatively high
already. Regenerative breaking is relatively standard in new trains. It is also
used in major new high-speed trains. However, friction brakes are still needed
as backup in the case that the regenerative brakes fail. It is possible to use
regenerative braking on these high speed trains because most cars have their
own electric motors, this is in contrast to trains in which only the locomotive
has electric motors. The fourth generation TGVs in France, which are expected
to be commissioned in 2010, will also be equipped with regenerative brakes, as
will the German ICE 3 trains which are to be commissioned in 2012.
4.6 CONTRIBUTION OF THE TECHNOLOGY TO SOCIAL
DEVOLEPMENTTOP
Contribution by the use of regenerative breaking to socio-
economic development is expected to be low. The Delhi Metro CDM project
(DMRC, 2007) argues for marginally improved local employment in the
operation and maintenance of the trains, but does not go into details on this.
The effects of regenerative braking on air quality depend mainly on the way
the electricity is produced. In general, the introduction of regenerative braking
on electric trains and subway trains will have no direct effect on the local air
quality. However, lowering the electricity demand will lower the emission of
air pollutants, like NOx, SO2 and particulate matter in power generation, if
power generation is based on fossil fuels. For diesel powered locomotives,
hybridization can have a positive direct effect on air quality, depending on the
usage pattern. Locomotives used solely on a marshalling yard can achieve very
49
high reductions in emissions, due to frequent need for braking. However, the
reduction in local air pollution will be limited when the locomotive is used in
long-haul freight trains.
4.7 ELEMENT SPECIFICATIONS
Our design will provide all of the following:
 Single Phase Induction Motor: 230V, ¼ HP Capacitor start- run single
phase induction motor
 Belt and pulley arrangement
 Alternator: 120VA, 12V, 10A, 300 rpm alternator
 Voltage Regulator: Zener diode is used to regulate the output voltage
 Rectifier: Three phase bridge rectifier. Diode used IN4007
 Battery: 10Ah 12VDC deep cycle lead acid battery for compatibility,
convenience, and cost.
 Relay: 12V single pole double throw.
 Step-up transformer: 12V to 230V AC single phase transformer
 Load: 40W 230V incandescent bulb is connected as load.
4.8 RESULT
We construct the regenerative braking system by using the
induction motor, alternator, rectifier, battery, step-up transformer, relay and
incandescent lamp. We successfully take the energy lost due to braking and
convert to 230 V single phase 50 Hz output supply and it is fed to the load.
50
CHAPTER 5
CONCLUSION
In ordinary braking system there is a huge amount of energy wasted
while braking. Generally we uses brake shoe and hydraulic systems are used in
locomotives, so the maintenance cost is high and also those system will create
noises and pollution. In our project we can reduce the wastage of energy
during the braking time. This is simple and cost effective way of braking. It
can perform a fast and controlled braking. The locomotives are normally
designed for gradual braking.If we apply this mechanism in electrical
locomotives, we can obtain very good braking with less maintenance cost and
we gather electricity as byproduct from the system, then the electricity is fed
into the bus.
51
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[3]. Cikanek, S. and Bailey, K., “Regenerative braking system for a hybrid electric
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Regenerative braking

  • 1. 1 CHAPTER - 1 INTRODUCTION The issue of calculating the energy saving amount due to regenerative braking implementation in modern AC and DC drives is of great importance, since it will decide whether this feature is cost effective. However, as the increase of the electric energy cost at the industrial sector, the need for advanced energy saving techniques emerged in order to cut down operational costs. To this direction, this project presents a theoretical, simulation and experimental investigation on the quantization of energy recovery due to regenerative braking application in industrial rotating loads. Finally, a power conversion scheme is proposed for the storage/exploitation of the recovered energy amount. Fossil fuels become each time less abundant and expensive, and with the problems of worldwide pollution, they also become inadequate to be used in such a large scale. The automotive industry is one of the biggest spenders of this limited resource. This fact may be changed with the use of electronic propelling systems, such as the appliance of a three-phase induction motor driven by a controlled inverter, replacing the internal combustion engine. The objective of this project is to research, design and implement the most effective regenerative system . The extra energy obtained from braking is used for light the bulb. 1.1 BRAKING SYSTEM All electric machines have two mechanical operations, motoring and braking. The nature of braking can be regenerative, where the kinetic energy of the rotor is converted into electricity and sent back to the power source or non-
  • 2. 2 regenerative, where the source supplies electric power to provide braking. This project investigates several critical issues related to regenerative braking in both DC and AC electric machines, including the re generative braking capability region and the evaluation of operating points within that capability region that result in maximum regenerative braking recharge current. Electric machines are used in the power trains of electric and hybrid-electric vehicles to provide motoring or braking torque in response to the driver’s request and power management logic. Since such vehicles carry a limited amount of electrical energy on-board their energy storage systems (such as a battery pack), it is important to conserve as much electrical energy as possible in order to increase the range of travel. Therefore, the concept of regenerative braking is of importance for such vehicles since operating in this mode during a braking event sends power back to the energy storage system thereby replenishing its energy level. Since the electric machine assists the mechanical friction braking system of the vehicle, it results in reduced wear on components within the mechanical friction brake system. As both mechanical friction braking and electric machine braking are used to provide the requested vehicle braking torque, braking strategies which relate to splitting of the braking command between the two braking mechanisms are discussed. 1.2 GENERALDISCRIPTION The most common form of regenerative brake involves using an electric motor as an electric generator. In electric railways the generated electricity is fed back into the supply system. In battery electric and hybrid electric vehicles, the energy is stored chemically in a battery, electrically in a bank of capacitors, or mechanically in a rotating flywheel. Hydraulic hybrid vehicles use hydraulic motors to store energy in form of compressed air Vehicles driven by electric
  • 3. 3 motors use the motor as a generator when using regenerative braking: it is operated as a generator during braking and its output is supplied to an electrical load; the transfer of energy to the load provides the braking effect. Regenerative braking is used on hybrid gas or electric automobiles to recoup some of the energy lost during stopping. This energy is saved in a storage battery and used later to supply AC power. 1.3 PROJECTMETHODS This project has various different design paths to complete our product while meeting the majority objectives. This means we will have to implement and compare our different designs to insure the best product based on our set of objectives. These paths have changed as we progressed through our project, and there were a few foreseen methods that we expand upon in the design section. The basic design for the regenerative braking is to have an induction motor, alternator, rectifier, battery, relay, step up transformer and load.While an alternator is easier to find and purchase with many functioning units available in scrap yards, they also tend to be less efficient in the output of DC power compared to a dynamo. One option is to use two contacting wheels to connect the two components. There are bound to be various other obstacles and design methods to be implemented as the project progresses, and will be observed and recorded as they occur.
  • 4. 4 CHAPTER -2 DESIGN AND METHODOLOGY 2.1 BLOCK DIAGRAM A simple block diagram of the overall project design is shown in Fig 2.1 Fig 2.1 Block diagram of overall project design In our project, we consider single phase induction motor as prime mover. Prime mover is directly coupled with an alternator by using belt and pulley arrangement. Output of the alternator is connected to a step-up transformer. The transformer step up into 230 V AC supply and this is fed into an incandescent lamp. While we applying the brake, giving DC supply to rotor. The rotor will produce flux. Due to the kinetic energy, the rotor will slowly rotate and come to rest. During this time an emf will produce in the stator winding and fed to the step-up transformer and then fed to the load The DC supply is provided with 12 V battery and this battery is charging by using rectified output of alternator. Three phase diode bridge rectifier is used as rectifier. PRIME MOVER ALTERNATOR STEP-UP TRANSFORMER LOAD RECTIFIER BATTERY
  • 5. 5 The relay circuit is used to control the braking system properly. Here we used a 12 V single pole double throw relay. In an ordinary system, during braking energy will lost in the form of heat and noise. If we use this system, we can conserve the energy loss due to braking. 2.2 PRIME MOVER All generators, large and small, ac and dc, require a source of mechanical power to turn their rotors. This source of mechanical energy is called a prime mover. The type of prime mover plays an important part in the design of alternators since the speed at which the rotor is turned determines certain characteristics of alternator construction and operation. Here we use an induction motor as prime mover for alternator and braking is applied to this motor itself. 2.2.1 BELT AND PULLEY ARRANGMENT Fig 2.2 Belt and pulley arrangement
  • 6. 6 A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a cable or belt along its circumference. Pulleys are used in a variety of ways to lift loads, apply forces, and to transmit power. In nautical contexts, the assembly of wheel, axle, and supporting shell is referred to as a "block."A pulley may also be called a sheave or drum and may have a groove between two flanges around its circumference. The drive element of a pulley system can be a rope, cable, belt, or chain that runs over the pulley inside the groove. Hero of Alexandria identified the pulley as one of six simple machines used to lift weights. Pulleys are assembled to form a block and tackle in order to provide mechanical advantage to apply large forces. Pulleys are also assembled as part of belt and chain drives in order to transmit power from one rotating shaft to another. Here we use motor shaft as driver pulley and alternator shaft as driven pulley 2.3 SINGLE PHASE INDUCTION MOTOR An induction or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. An induction motor therefore does not require mechanical commutation, separate- excitation or self-excitation for all or part of the energy transferred from stator to rotor, as in universal, DC and large synchronous motors.
  • 7. 7 Fig 2.3 Single phase Induction Motor Like any other electrical motor asynchronous motor also have two main parts namely rotor and stator. Stator: As its name indicates stator is a stationary part of induction motor. A single phase ac supply is given to the stator of single phase induction motor. Rotor: The rotor is a rotating part of induction motor. The rotor is connected to the mechanical load through the shaft. The rotor in single phase induction motor is of squirrel cage rotor type. The construction of single phase induction motor is almost similar to the squirrel cage three phase motor except that in case of asynchronous motor the stator have two windings instead of one as compare to the single stator winding in three phase induction motor.
  • 8. 8 2.3.1 STATOR OF SINGLE PHASE INDUCTION MOTOR The stator of the single phase induction motor has laminated stamping to reduce eddy current losses on its periphery. The slots are provided on its stamping to carry stator or main winding. In order to reduce the hysteresis losses, stamping are made up of silicon steel. When the stator winding is given a single phase ac supply, the magnetic field is produced and the motor rotates at a speed slightly less than the synchronous speed Ns which is given by The construction of the stator of asynchronous motor is similar to that of three phase induction motor except there are two dissimilarity in the winding part of the single phase induction motor. Firstly the single phase induction motors are mostly provided with concentric coils. As the number of turns per coil can be easily adjusted with the help of concentric coils, the mmf distribution is almost sinusoidal. Except for shaded pole motor, the asynchronous motor has two stator windings namely the main winding and the auxiliary winding. These two windings are placed in spacequadrature with respectto each other. 2.3.2 ROTOR OF SINGLE PHASE INDUCTION MOTOR The construction of the rotor of the single phase induction motor is similar to the squirrel cage three phase induction motor. The rotor is cylindrical in shape and has slots all over its periphery. The slots are not made parallel to each other but are bit skewed as the skewing prevents magnetic locking of stator and rotor teeth and makes the working of induction motor more smooth and quieter.
  • 9. 9 The squirrel cage rotor consists of aluminium, brass or copper bars. These aluminium or copper bars are called rotor conductors and are placed in the slots on the periphery of the rotor. The rotor conductors are permanently shorted by the copper or aluminium rings called the end rings. In order to provide mechanical strength these rotor conductor are braced to the end ring and hence form a complete closed circuit resembling like a cage and hence got its name as “squirrel cage induction motor”. As the bars are permanently shorted by end rings, the rotor electrical resistance is very small and it is not possible to add external resistance as the bars are permanently shorted. The absence of slip ring and brushes make the construction of single phase induction motor very simple and robust. 2.3.3 WORKING PRINCIPLE When single phase ac supply is given to the stator winding of single phase induction motor, the alternating current starts flowing through the stator or main winding. This alternating current produces an alternating flux called main flux. This main flux also links with the rotor conductors and hence cut the rotor conductors. According to the Faraday’s law of electromagnetic induction, emf gets induced in the rotor. As the rotor circuit is closed one so, the current starts flowing in the rotor. This current is called the rotor current. This rotor current produces its own flux called rotor flux. Since this flux is produced due to induction principle so, the motor working on this principle got its name as induction motor. Now there are two fluxes one is main flux and another is called rotor flux. These two fluxes produce the desired torque which is required by the motor to rotate. According to double field revolving theory, any alternating quantity can be resolved into two components, each component have magnitude equal to the half of the maximum magnitude of the alternating quantity and both these
  • 10. 10 component rotates in opposite direction to each other. For example – a flux, φ can be resolved into two components Each of these components rotates in opposite direction i. e if one φm / 2 is rotating in clockwise direction then the other φm / 2 rotates in anticlockwise direction. When a single phase ac supply is given to the stator winding of single phase induction motor, it produces its flux of magnitude, φm. According to the double field revolving theory, this alternating flux, φm is divided into two components of magnitude φm /2. Each of these components will rotate in opposite direction, with the synchronous speed, Ns. Let us call these two components of flux as forward component of flux, φf and backward component of flux, φb. The resultant of these two component of flux at any instant of time, gives the value of instantaneous stator flux at that particular instant. Now at starting, both the forward and backward components of flux are exactly opposite to each other. Also both of these components of flux are equal in magnitude. So, they cancel each other and hence the net torque experienced by the rotor at starting is zero. So, the single phase induction motors are not self starting motors.
  • 11. 11 2.3.4 SINGLE PHASE INDUCTION MOTOR AS SELF STARTING MOTOR From the above topic we can easily conclude that the single phase induction motors are not self starting because the produced stator flux is alternating in nature and at the starting the two components of this flux cancel each other and hence there is no net torque. The solution to this problem is that if the stator flux is made rotating type, rather than alternating type, which rotates in one particular direction only. Then the induction motor will become self starting. Now for producing this rotating magnetic field we require two alternating flux, having some phase difference angle between them. When these two fluxes interact with each other they will produce a resultant flux. This resultant flux is rotating in nature and rotates in space in one particular direction only. Once the motor starts running, the additional flux can be removed. The motor will continue to run under the influence of the main flux only. Depending upon the methods for making asynchronous motor as Self Starting Motor, there are mainly four types of single phase induction motor namely,  Split phase induction motor,  Capacitor start inductor motor,  Capacitor start capacitor run induction motor,  Shaded pole induction motor.
  • 12. 12 2.3.5 CAPACITOR START INDUCTION MOTOR This motor is similar to the three-phase motor except that it has only two windings (a-a′ and b-b′) on its stator displaced 90° from each other. The a-a′ winding is connected directly to the single-phase supply. For starting, the b-b′ winding (commonly called the auxiliary winding) is connected through a capacitor (a device that stores electric charge) to the same supply. The effect of the capacitor is to make the current entering the winding b-b′ lead the current in a-a′ by approximately 90°, or one-quarter of a cycle, with the rotor at standstill. Thus, the rotating field and the starting torque are provided. Fig 2.4 Internal Diagram of Capacitor Start Induction Motor As the motor speed approaches its rated value, it is no longer necessary to excite the auxiliary winding to maintain the rotating field. The currents produced in the rotor squirrel-cage bars as they pass the winding a-a′ are retained with negligible change as they rotate past the winding b-b′. The rotor can continue to generate the rotating field with only winding a-a′connected. The winding b-b′ is usually disconnected by a centrifugal switch that opens when the speed is about 80 percent of rated value.
  • 13. 13 Power ratings for these capacitor-start induction motors are usually restricted to about two kilowatts for a 120-volt supply and 10 kilowatts for a 230-volt supply because of the limitations on voltage drop in the supply lines, which would otherwise occur on starting. Typical values of synchronous speed on a 60-hertz supply are 1,800 or 1,200 revolutions per minute for four- and six-pole motors, respectively. Lower-speed motors can be constructed with more poles but are less common. The efficiency of the motor can be somewhat increased and the line current decreased by the use of two capacitors, only one of which is taken out of the circuit (by means of a centrifugal switch) as the rated speed is approached. The remaining capacitor continues to provide a leading current to phase b-b′, approximating a two-phase supply. This arrangement is known as a capacitor-start, capacitor-run motor. Capacitor induction motors are widely used for heavy-duty applications requiring high starting torque. Examples are refrigerator compressors, pumps, and conveyor. 2.4 ALTERNATOR An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature. Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, but usually the term refers to small rotating machines driven by automotive and other internal combustion engines. An alternator that uses a permanent magnet for its magnetic field is called a magneto.
  • 14. 14 Alternators in power stations driven by steam turbines are called turbo- alternators. A conductor moving relative to a magnetic field develops an electromotive force (EMF) in it, (Faraday's Law). This emf reverses its polarity when it moves under magnetic poles of opposite polarity. Typically, a rotating magnet, called the rotor turns within a stationary set of conductors wound in coils on an iron core, called the stator. The field cuts across the conductors, generating an induced EMF (electromotive force), as the mechanical input causes the rotor to turn. The rotating magnetic field induces an AC voltage in the stator windings. Since the currents in the stator windings vary in step with the position of the rotor, an alternator is a synchronous generator. The rotor's magnetic field may be produced by permanent magnets, or by a field coil electromagnet. Automotive alternators use a rotor winding which allows control of the alternator's generated voltage by varying the current in the rotor field winding. Permanent magnet machines avoid the loss due to magnetizing current in the rotor, but are restricted in size, due to the cost of the magnet material. Since the permanent magnet field is constant, the terminal voltage varies directly with the speed of the generator. Brushless AC generators are usually larger machines than those used in automotive applications.
  • 15. 15 2.4.1 ALTERNATOR COMPONENTS A typical rotating-field ac generator consists of an alternator and a smaller dc generator built into a single unit. The output of the alternator section supplies alternating voltage to the load. The only purpose for the dc exciter generator is to supply the direct current required to maintain the alternator field. This dc generator is referred to as the exciter. A typical alternator is shown in fig Fig 2.5 AC generator schematic drawings.
  • 16. 16 Main parts of the alternator obviously consist of stator and rotor. But, the unlike other machines, in most of the alternators, field exciters are rotating and the armature coil is stationary. Stator: Unlike in DC machine stator of an alternator is not meant to serve path for magnetic flux. Instead, the stator is used for holding armature winding. The stator core is made up of lamination of steel alloys or magnetic iron, to minimize the losses. Armature winding is stationary in an alternator because;  At high voltages, it easier to insulate stationary armature winding, which may be as high as 30 kV or more.  The high voltage output can be directly taken out from the stationary armature. Whereas, for a rotary armature, there will be large brush contact drop at higher voltages, also the sparking at the brush surface will occur.  Field exciter winding is placed in rotor, and the low dc voltage can be transferred safely.  The armature winding can be braced well, so as to prevent deformation caused by the high centrifugal force. Rotor: There are two types of rotor used in an AC generator / alternator: (i) Salient and (ii) Cylindrical type  Salient pole type: Salient pole type rotor is used in low and medium speed alternators. Construction of AC generator of salient pole type rotor is shown in the figure above. This type of rotor consists of large number of projected poles (called salient poles), bolted on a magnetic wheel. These poles are also laminated to minimize the eddy current losses. Alternators featuring this type of rotor are large in diameters and short in axial length.
  • 17. 17  Cylindrical type: Cylindrical type rotors are used in high speed alternators, especially in turbo alternators. This type of rotor consists of a smooth and solid steel cylinder havingg slots along its outer periphery. Field windings are placed in these slots. The armature is wound for a three-phase output. Remember, a voltage is induced in a conductor if it is stationary and a magnetic field is passed across the conductor, the same as if the field is stationary and the conductor is moved. The alternating voltage in the ac generator armature windings is connected through fixed terminals to the ac load. 2.5 VOLTAGE REGULATOR Fig 2.6 Alternator with voltage regulator A voltage regulator circuit for an alternator includes voltage responsive circuitry having a zener diode. The regulator will maintain a pre-determined charging system voltage level. When the system voltage decreases the regulator strengthens the magnetic field and thereby increases the alternator output voltage. When the system voltage increases the regulator weakens the magnetic field and thereby decreases the alternator output voltage.
  • 18. 18 Zener diodes are especially used on applications with sensitive electronic components. These can prevent major damage caused by voltage peaks due to sudden discharges. In 12V systems, Zener diodes with a voltage range 24V - 32V are used and in 28V systems the range is 36V - 44V. When ac generators are operated in parallel, frequency and voltage must both be equal. Where a synchronizing force is required to equalize only the voltage between dc generators, synchronizing forces are required to equalize both voltage and speed (frequency) between ac generators. On a comparative basis, the synchronizing forces for ac generators are much greater than for dc generators. When ac generators are of sufficient size and are operating at unequal frequencies and terminal voltages, serious damage may result if they are suddenly connected to each other through a common bus. To avoid this, the generators must be synchronized as closely as possible before connecting them together. The output voltage of an alternator is best controlled by regulating the voltage output of the dc exciter, which supplies current to the alternator rotor field. This is accomplished as shown in Fig 2.5, by a zener diode regulator of a 28 volt system connected in the field circuit of the exciter. The zener diode regulator controls the exciter field current and thus regulates the exciter output voltage applied to the alternator field. The only difference between the dc system and the ac system is that the voltage coil receives its voltage from the alternator line instead of the dc generator. In this arrangement, a three phase, step down transformer connected to the alternator voltage supplies power to a three phase, full wave rectifier. The 28 volt, dc output of the rectifier is then applied to the zener diode voltage regulator. Changes in alternator voltage are transferred through the transformer rectifier unit to the zener diode. This controls the exciter field current and the
  • 19. 19 exciter output voltage. The exciter voltage antihunting or damping transformer is similar to those in dc systems and performs the same function. The DC output voltage from the half or full-wave rectifiers contains ripple superimposed onto the DC voltage and that as the load value changes so to does the average output voltage. By connecting a simple zener stabilizer circuit as shown below across the output of the rectifier, a more stable output voltage can be produced. 2.5.1 ZENER DIODE REGULATOR Fig 2.7 Zener Diode Regulator Zener Diodes can be used to produce a stabilized voltage output with low ripple under varying load current conditions. By passing a small current through the diode from a voltage source, via a suitable current limiting resistor, the zener diode will conduct sufficient current to maintain a voltage drop of output voltage. The resistor, RS is connected in series with the zener diode to limit the current flow through the diode with the voltage source, VS being connected across the combination. The stabilized output voltage Vout is taken from across the zener diode. The zener diode is connected with its cathode terminal connected to the positive rail of the DC supply so it is reverse biased and will
  • 20. 20 be operating in its breakdown condition. Resistor RS is selected so to limit the maximum current flowing in the circuit. With no load connected to the circuit, the load current will be zero, ( IL = 0 ), and all the circuit current passes through the zener diode which in turn dissipates its maximum power. Also a small value of the series resistor RS will result in a greater diode current when the load resistance RL is connected and large as this will increase the power dissipation requirement of the diode so care must be taken when selecting the appropriate value of series resistance so that the zener’s maximum power rating is not exceeded under this no-load or high-impedance condition. The load is connected in parallel with the zener diode, so the voltage across RL is always the same as the zener voltage, ( VR = VZ ). There is a minimum zener current for which the stabilization of the voltage is effective and the zener current must stay above this value operating under load within its breakdown region at all times. The upper limit of current is of course dependent upon the power rating of the device. The supply voltage VS must be greater than VZ. One small problem with zener diode stabilizer circuits is that the diode can sometimes generate electrical noise on top of the DC supply as it tries to stabilize the voltage. Normally this is not a problem for most applications but the addition of a large value decoupling capacitor across the zener’s output may be required to give additional smoothing. Then to summarize a little. A zener diode is always operated in its reverse biased condition. A voltage regulator circuit can be designed using a zener diode to maintain a constant DC output voltage across the load in spite of variations in the input voltage or changes in the load current. The zener voltage regulator consists of a current limiting resistor RS connected in series with the
  • 21. 21 input voltage VS with the zener diode connected in parallel with the load RL in this reverse biased condition. The stabilized output voltage is always selected to be the same as the breakdown voltage VZ of the diode. 2.6 RECTIFIER Rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification. Physically, rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves, copper and selenium oxide rectifiers, semiconductor diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches. Historically, even synchronous electromechanical switches and motors have been used. Early radio receivers, called crystal radios, used a "cat's whisker" of fine wire pressing on a crystal of galena (lead sulfide) to serve as a point-contact rectifier or "crystal detector". Rectifiers have many uses, but are often found serving as components of DC power supplies and high-voltage direct current power transmission systems. Rectification may serve in roles other than to generate direct current for use as a source of power. Because of the alternating nature of the input AC sine wave, the process of rectification alone produces a DC current that, though unidirectional, consists of pulses of current. Many applications of rectifiers, such as power supplies for radio, television and computer equipment, require a steady constant DC current (as would be produced by a battery). In these applications the output of the rectifier is smoothed by an electronic filter (usually a capacitor) to producea steady current. Rectifier circuits may be single-phase or multi-phase (three being the most common number of phases). Most low power rectifiers for domestic
  • 22. 22 equipment are single-phase, but three-phase rectification is very important for industrial applications and for the transmission of energy as DC (HVDC). 2.6.1 THREE PHASE DIODE RECTIFIER Single-phase rectifiers are commonly used for power supplies for domestic equipment. However, for most industrial and high-power applications, three-phase rectifier circuits are the norm. As with single-phase rectifiers, three-phase rectifiers can take the form of a half-wave circuit, a full- wave circuit using a center-tapped transformer, or a full-wave bridge circuit. Fig 2.8 –Three phase AC full-wave rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification. Physically, rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves, copper and selenium oxide rectifiers, semiconductor diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches. Historically, even synchronous electromechanical switches and motors have been used. Early radio receivers, called crystal radios, used a "cat's whisker" of fine wire pressing on a crystal of galena (lead sulfide) to serve as a point-contact rectifier or "crystal detector". Rectifiers have many uses, but are often found serving as
  • 23. 23 components of DC power supplies and high-voltage direct current power transmission systems. Rectification may serve in roles other than to generate direct current for use as a source of power. As noted, detectors of radio signals serve as rectifiers. In gas heating systems flame rectification is used to detect presence of a flame. Because of the alternating nature of the input AC sine wave, the process of rectification alone produces a DC current that, though unidirectional, consists of pulses of current. Many applications of rectifiers, such as power supplies for radio, television and computer equipment, require a steady constant DC current (as would be produced by a battery). In these applications the output of the rectifier is smoothed by an electronic filter (usually a capacitor) to produce a steady current. A more complex circuitry device that performs the opposite function, converting DC to AC, is called an inverter For a three-phase full-wave diode rectifier, the ideal, no-load average output voltage is
  • 24. 24 2.6.2 RECTIFIER OPERATION Fig 2.9 rectification circuit • Two diodes are connected to each stator lead. One positive the other negative. • Because a single diode will only block half the the AC voltage. • Six or eight diodes are used to rectify the AC stator voltage to DC voltage. • Diodes used in this configuration will redirect both the positive and negative polarity signals of the AC voltage to produce DC voltage. This process is called ‘Full - Wave Rectification’.
  • 25. 25 At first you can see current pass through to the rectifier as it goes to the battery. In the second, you can see the return path. Now, current passes through to the rectifier however, this time current has the opposite polarity. In second circuit you can see the new return path. Even though it enters the rectifier at a different location, current goes to the battery in the same direction. 2.7 BATTERY Battery is essential to supply DC power for the alternator rotor and for the storage of generated power. An electric battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy. Each cell contains a positive terminal, or cathode, and a negative terminal, or anode. Electrolytes allow ions to move between the electrodes and terminals, which allows current to flow out of the battery to perform work. Battery we used is 12V, 10 Ah rating. Fig 2.10 Internal diagram of lead acid battery
  • 26. 26 The battery is a two-terminal device that provides DC supply to the inverter section when the AC mains are not available. This DC is then converted into 220V AC supply and output at the inverter output socket. It is pertinent to state that lead-acid batteries used in automobiles are very good for this purpose as they provide good quality power for a long duration and can be recharged once the power stored in them are consumed. The backup time provided by the inverter depends on the battery type and its current capacity Primary (single-use or "disposable") batteries are used once and discarded; the electrode materials are irreversibly changed during discharge. Common examples are the alkaline battery used for flashlights and a multitude of portable devices. Secondary (rechargeable batteries) can be discharged and recharged multiple times; the original composition of the electrodes can be restored by reverse current. Examples include the lead-acid batteries used in vehicles and lithium ion batteries used for portable electronics. The battery was selected based on the amount of time we wanted to operate the system at full load. As mentioned in the specifications, we wanted to be able to power the lights. Fulfilling the 12 V DC battery requirements, we found a unit from Universal Battery with 18 Ah. If the battery is discharged to 50% at most, this battery leaves us with 9 Ah. Our load of lighting, music, and an iPod charger uses about 20 watts, but with an alternative appliance connected (e.g. phone), the total power consumed could be estimated at 25 watts. With a 12 VDC battery and a 25 W load, we have about 2 A of current, which gives us about 4.5 hours of use at full load – this is consistent with our design specifications. The exact battery we selected is UB12180 (12V 10Ah). An electric battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy. Each cell contains a positive terminal, or cathode, and a negative
  • 27. 27 terminal, or anode. Electrolytes allow ions to move between the electrodes and terminals, which allows current to flow out of the battery to perform work. A lead-acid battery charger is most popular though it will very large size than others battery type. But them have advantage are : cheap, easy to buy and long life if correctly uses. 2.7.1 CHARGING AND DISCHARGING Over charging with high charging voltages generates oxygen and hydrogen gas by electrolysis of water, which is lost to the cell. Periodic maintenance of lead-acid batteries requires inspection of the electrolyte level and replacement of any water that has been lost. Due to the freezing-point depression of the electrolyte, as the battery discharges and the concentration of sulfuric acid decreases, the electrolyte is more likely to freeze during winter weather when discharged. Fig 2.11 Fully discharged: two identical lead sulfate plates In the discharged state both the positive and negative plates become lead (II) sulfate (PbSO4), and the electrolyte loses much of its dissolved sulfuric acid and becomes primarily water. The discharge process is driven by the conduction of electrons from the negative plate back into the cell at the positive plate in the external circuit.
  • 28. 28 2.7.2 ION MOTION During discharge, H+ produced at the negative plates moves into the electrolyte solution and then is consumed into the positive plates, while HSO−4 is consumed at both plates. The reverse occurs during charge. This motion can be by electrically driven proton flow or Grotthuss mechanism, or by diffusion through the medium, or by flow of a liquid electrolyte medium. Since the density is greater when the sulfuric acid concentration is higher, the liquid will tend to circulate by convection. Therefore a liquid-medium cell tends to rapidly discharge and rapidly charge more efficiently than an otherwise similar gel cell. 2.7.3 BATTERYCHARGER A battery charger is a device used to put energy into a cell or (rechargeable) battery by forcing an electric current through it. Lead-acid battery chargers typically have two tasks to accomplish. The first is to restore capacity, often as quickly as practical. The second is to maintain capacity by compensating for self discharge. In both instances optimum operation requires accurate sensing of battery voltage. When a typical lead-acid cell is charged, lead sulphate is converted to lead on the battery’s negative plate and lead dioxide on the positive plate. Over-charge reactions begin when the majority of lead sulphate has been converted, typically resulting in the generation of hydrogen and oxygen gas. At moderate charge rates, most of the hydrogen and oxygen will recombine in sealed batteries. In unsealed batteries however, dehydration will occur. The onset of over-charge can be detected by monitoring battery voltage.
  • 29. 29 Over charge reactions are indicated by the sharp rise in cell voltage. The point at which over-charge reactions begin is dependent on charge rate, and as charge rate is increased, the percentage of returned capacity at the onset of over-charge diminishes. For overcharge to coincide with 100% return of capacity, the charge rate must typically be less than 1/100 amps of its amp- hour capacity. At high charge rates, controlled over-charging is typically as quickly as possible. To maintain capacity on a fully charged battery, a constant voltage is applied. The voltage must be high enough to compensate for self discharge, yet not too high as to cause excessive over-charging. 2.8 RELAY A relay is an electrically operated switch. Many relays Automotive-style miniature relay, dust cover is taken off use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid state relays. Relays are used where it is necessary to control a circuit by a low- power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults.
  • 30. 30 Fig2.12 Relay 2.9 CAPACITOR-INPUT FILTER The capacitor-input filter, also called the pi filter due to its shape that looks like the Greek letter π, is a type of electronic filter. Filter circuits are used to remove unwanted or undesired frequencies from a signal .A simple pi filter, containing a pair of capacitors, an inductor, and a load .A typical capacitor input filter consists of a filter or reservoir capacitor C1, connected across the rectifier output, an inductor L, in series and another filter or smoothing capacitor, C2, connected across the load, RL. A filter of this sort is designed for use at a particular frequency, generally fixed by the AC line frequency and rectifier configuration. When used in this service, filter performance is often characterized by its regulation and ripple. 1. The capacitor C1 offers low reactance to the AC component of the rectifier output while it offers infinite resistance to the DC component. As a result the capacitor shunts an appreciable amount of the AC component while the DC component continues its journey to the inductor L. 2. The inductor L offers high reactance to the AC component but it offers almost zero resistance to the DC component. As a result the DC component
  • 31. 31 flows through the inductor while the AC componentis blocked. 3. The capacitor C2 bypasses the AC component which the inductor had failed to block. As a result only the DC componentappears across the load RL. The component value for the inductor can be estimated as an inductance that resonates the smoothing capacitor(s) at or below one tenth of the minimum AC frequency in the power supplied to the filter (100 Hz from a full-wave rectifier in a region where the power supply is 50Hz). Thus if reservoir and smoothing capacitors of 2200 microfarads are used, a suitable minimum value for the inductor would be that which resonates 2200 microfarads (μF) to 10 Hz, i.e. 115 mH. A larger value is preferable provided the inductor can carry the required supply current. In general, the relationship between the resonant frequency (in hertz), which should be less than or equal to one tenth of the minimum AC frequency, in this case 100 Hz, the capacitance (in farads), and the inductance (in henries) can be characterized by the following resonance equation: f_0 = {1 over {2 pi sqrt{LC}}}.Comparison with other filters Capacitor input filters can provide extremely pure DC supplies, but have fallen out of favour because inductors tend to be unavoidably heavy, which has led to the often-preferred choice of voltage regulators instead.
  • 32. 32 Fig 2.13 Capacitor-Input Filter Fig 2.14 Capacitor-Input Filter -Charging and Discharging
  • 33. 33 Advantages of pi filters:  More output voltage  Ripple-free output Disadvantages of pi filters:  Large size  Heavy  High cost 2.10 STEP-UP TRANSFORMER The output of the alternator is 12V ac supply with a frequency of 50 Hz . This Ac supply is step up to 230 V by using step-up transformer. The Voltage Transformer can be thought of as an electrical component rather than an electronic component. A transformer basically is very simple static (or stationary) electro-magnetic passive electrical device that works on the principle of Faraday’s law of induction by converting electrical energy from one value to another. On a step-up transformer there are more turns on the secondary coil than the primary coil. The induced voltage across the secondary coil is greater than the applied voltage across the primary coil or in other words the voltage has been “stepped-up”.
  • 34. 34 Fig 2.15 Step up transformer The transformer does this by linking together two or more electrical circuits using a common oscillating magnetic circuit which is produced by the transformer itself. A transformer operates on the principals of “electromagnetic induction”, in the form of Mutual Induction. Mutual induction is the process by which a coil of wire magnetically induces a voltage into another coil located in close proximity to it. Then we can say that transformers work in the “magnetic domain”, and transformers get their name from the fact that they “transform” one voltage or current level into another. Transformers are capable of either increasing or decreasing the voltage and current levels of their supply, without modifying its frequency, or the amount of electrical power being transferred from one winding to another via the magnetic circuit. A single phase voltage transformer basically consists of two electrical coils of wire, one called the “Primary Winding” and another called the “Secondary Winding”. We will define the “primary” side of the transformer as the side that usually takes power and the “secondary” as the side that usually
  • 35. 35 delivers power. In a single-phase voltage transformer the primary is usually the side with the higher voltage. These two coils are not in electrical contact with each other but are instead wrapped together around a common closed magnetic iron circuit called the “core”. This soft iron core is not solid but made up of individual laminations connected together to help reduce the core’s losses. The two coil windings are electrically isolated from each other but are magnetically linked through the common core allowing electrical power to be transferred from one coil to the other. When an electric current passed through the primary winding, a magnetic field is developed which induces a voltage into the secondary winding .The output of the transformer is 230 V, 50 Hz ,single phase AC, which is fed to the load.
  • 36. 36 CHAPTER- 3 LITERATURE REVIEW 3.1 A BRIEF HISTORY REGENERATIVE BRAKING Regenerative Braking for an Electric Vehicle Using Ultra capacitors and a Buck-Boost Converter:An ultra capacitor bank control system for an Electric Vehicle has been simulated. The purpose of this device is to allow higher accelerations and decelerations of the vehicle with minimal loss of energy, and minimal degradation of the main battery pack. The system uses an IGBT Buck- Boost converter, which is connected to the ultra capacitor bank at the Boost side, and to the main battery at the Buck side. The control of the system measures the battery voltage, the battery state-of-charge, the car speed, the instantaneous currents in both the terminals (load and ultra capacitor), and the actual voltage of the ultra capacitor. This last indication allows to know the amount of energy stored in the ultra capacitor. A microcomputer control manipulates all the variables and generates the PWM switching pattern of the IGBTs. When the car runs at high speeds, the control keeps the capacitor discharged. If the car is not running, the capacitor bank remains charged at full voltage. Medium speeds keep the ultra capacitors at medium voltages, to allow future accelerations or decelerations. The battery voltage is an indication of the car instantaneous situation. When the vehicle is accelerating, the battery voltage goes down, which is an indication for the control to take energy from the ultra capacitor. In the opposite situation(regenerative braking), the battery voltage goes up, and then the control needs to activate the Buck converter to store the kinetic energy of the vehicle inside the ultra capacitor. The measurement of the currents in both sides allows to keep the current levels inside maximum ratings. The battery state-of charge is used to change the
  • 37. 37 voltage level of the ultra capacitor at particular values. If the battery is fully charged, the voltage level of the capacitors is kept at lower levels than when the battery is partially discharged. The converter also has an IGBT controlled power resistor, which allows to drop energy when in some extreme situations cannot be accepted neither for the ultra capacitors nor for the battery pack. The car that will be used for future implementation of this experiment is a Chevrolet LUV truck, similar in shape and size to a Chevrolet S-10. This vehicle was already converted to an electric car at the Catholic University of Chile. Fully Regenerative braking and Improved Acceleration for Electrical Vehicles:Generally, car brake systems use hydraulic brake technology, which converts the excess of kinetic energy into heat, effectively resulting in an energy loss. Regenerative braking technology focuses on converting this kinetic energy of the decelerating vehicle back into electrical energy that can then be reused for example during acceleration. Current hybrid vehicles are equipped with such regenerative braking technology, which makes them particularly interesting for situations with frequent deceleration, like city traffic. However, the technology used in these vehicles has its limitations and therefore does not stand on its own, but is always assisted with conventional hydraulic brakes. This paper looks at removing this limitation and allowing a vehicle to fully rely on regenerative braking technology to deal with any braking situation ranging from simple slow down to emergency stops. To enable this, multiple generators with different gear ratios are used. The additional benefit of this construction is that, by introducing the appropriate control circuit, the generators can be used as electrical engines. Since these motors are connected with different gear ratios there is a more consistent acceleration at any speed. The paper shows that the overall efficiency of the
  • 38. 38 system is very close to the efficiency of the generators used while achieving braking performance similar to conventional braking mechanisms. Study on Regenerative Braking of Electric Vehicle: In this paper, a control scheme for a constant regenerative current is given based on the analysis of several regenerative braking schemes. The three main control strategies discussed are maximum regenerative efficiency control, maximum regenerative power control and the constant regenerative current control. Analysis is performed for two modes, the continuous current mode and the discrete current mode. Using the above analysis, a formula for regenerative efficiency of a control scheme is derived. The analysis of the braking system is done to find out two aspects, the electric loop efficiency and the regenerative energy efficiency. Using the results of the analysis, the paper concludes that the constant regenerative current control scheme is better than the maximum regenerative power control scheme and the maximum regenerative efficiency control scheme. Also, the paper concludes that the used method gives a higher regenerative braking efficiency and better controlperformance. Regenerative Braking for Electric Vehicle based on Fuzzy Logic Control Strategy: In this paper to recycle more energy during regenerative braking, a regenerative braking force calculation controller is designed based on fuzzy logic. Here, Sugeno's fuzzy logic controller is used which has 3 inputs and the output is the braking force. The three inputs are vehicle speed; driver’s braking requirements and the battery’s state of charge. Fuzzy membership functions are defined for the above inputs and outputs and the output is found out in the range of 0 to 1. Each input has a membership value of high, medium and low based on which the fuzzy rules are developed. The simulations which are carried out show a substantial improvement in energy efficiency of an electric vehicle. Benchmarking of Regenerative Braking for a Fully Electric Car:
  • 39. 39 Short range of electric vehicles is one of the stumbling blocks in the way of electric cars to gaining wide user acceptance and becoming a major market player. The possibility to recover vehicle energy otherwise lost as heat during braking is an inherent advantage of a hybrid electric or a fully electric vehicle. Regeneration has the potential to answer this problem by aiding in range extension with recuperation of vehicle energy during braking. The control and dynamics of braking undergoes a major change as compared to a conventional vehicle with friction braking, due to the addition of motor-generator. In this research two regenerative braking concepts namely serial and parallel have been studied and implemented on an electric vehicle. Also a point of interest is to find if any additional states are required from the TNO Vehicle state estimator (VSE) which would aid in regeneration. From the results obtained we try to draw a conclusion on the difference in energy recuperation level in the two strategies with consistent pedal feel in mind. The proposed brake torque distribution strategy has been tested through the simulation on the New European Driving Cycle (NEDC) drive cycle and straight line braking scenario. Care has been taken to observe and adjust brake torque such that wheel lock up is prevented and hence regeneration is un-interrupted. The research couldn’t come with any additional parameters to be added to VSE. However, it would be worthwhile to employ VSE to achieve a more accurate estimation of the braking force, which may aid in prolonging regeneration time and hence more energy recuperation. The results provide a good case to invest more time and money into developing serial regenerative braking as it clearly out-performs parallel regenerative braking strategy. The simulation tests conducted in this research are for a longitudinal braking scenario. Further investigation is required to study effects with lateral motion and cornering manoeuvres
  • 40. 40 A Flywheel Regenerative Braking System : This thesis presents a flywheel based mechanical regenerative braking system (RBS) concept for a Formula SAE type race car application, to improve the performance and/or efficiency of the race car. A mechanical system is chosen to eliminate losses related to energy conversion while capturing the rotational braking energy. The Flywheel-Regenerative Braking System (f-RBS) concept consists of a metal flywheel design of truncated cone geometry for the energy storage system (ESS) component and a V-belt CVT with a fixed gear for the transmission component of the RBS system. Race car lap data and race car specifications are used for designing/sizing the components. Mathematical models are developed for design, integration and operation of the f-RBS system. It was observed that a maximum of 27 % of energy requirements of the race car can be supplied by the f-RBS. Also, a Virtual test rig model is created using MSC ADAMS, an advanced dynamics/virtual prototyping software, in order to test the whole f-RBS system for performance, as a preliminary alternative to experimental testing. Initial testing is performed to validate the regenerative braking principle employed, to establish the actual operating limits of the virtual test rig and for an initial analysis of performance improvement by utilization of the f-RBS system. From the results, it was inferred that using the f-RBS concept can have a significant impact in recycling wasteful the braking energy and provide additional energy to the racecar. 3.2 REGENERATIVE BREAKING IN TRAINS In 1886, the Sprague Electric Railway & Motor Company, founded by Frank J. Sprague, introduced two important inventions: a constant-speed, non-sparking motor with fixed brushes, and regenerative braking, the method braking that uses the drive motor to return power to the main supply system. During braking, the traction motor connections are altered to turn them into electrical generators. The motor fields are connected across the main traction
  • 41. 41 generator (MG) and the motor armatures are connected across the load. The MG now excites the motor fields. The rolling locomotive or multiple unit wheels turn the motor armatures, and the motors act as generators, either sending the generated current through onboard resistors (dynamic braking) or back into the supply (regenerative braking). Compared to electro-pneumatic friction brakes, braking with the traction motors can be regulated faster improving the performance of protection. For a given direction of travel, current flow through the motor armatures during braking will be opposite to that during motoring. Therefore, the motor exerts torque in a direction that is opposite from the rolling direction Braking effort is proportional to the product of the magnetic strength of the field windings, multiplied by that of the armature windings. Savings of 17% are claimed for Virgin Trains Pendolinos. There is also less wear on friction braking components. It is expected that the Delhi Metro will save over 100,000tonsof CO2 from being emitted per year once its phase II is complete through the use of regenerative braking. The train is slowed by the climb, and then leaves down a slope, so kinetic energy is converted to gravitational potential energy in the station. This is normally found on the deep tunnel sections of the network and not generally above ground or on the cut and cover sections of the Metropolitan and District Lines. Electricity generated by regenerative braking may be fed back into the traction power supply; either offset against other electrical demand on the network at that instant, used for head end power loads, or stored in line side storage systems for later use.
  • 42. 42 3.3 EXISTING SYSTEM In the existing system it uses mechanical breaking and it also needs break shoes. In the existing system the wear and tear is more. The existing system consist of brake shoes, which is very costly. The noise produced is more in this system. In this system break shoes needs to be frequently changed due to the mechanical friction. In the existing system the energy during breaking is lost in the form of heat 3.4 PROPOSED SYSTEM In the proposed system it uses electrical energy. In this system during the breaking time the electrical energy is produced. In this system the noise is less. Frequent replacement of brake shoes is not required in this system It is more advantageous than the existing system, it produces electrical energy during the breaking time. It is a cost effective system and it is a flexible system The energy during breaking is converted to electrical energy
  • 43. 43 CHAPTER-4 ANALYSIS AND RESULT 4.1 ELECTRICALSCHEMATIC DIAGRAM Fig.4.1.ELECTRICALSCHEMATIC DIAGRAM
  • 44. 44 4.2 CIRCUIT DISCRIPTION In our design we use 230V, ¼ HP Capacitor start- run single phase induction motor as prime mover. Prime mover is directly coupled with an alternator by using belt and pulley arrangement. 120VA, 12V, 10A, 300 rpm alternator is used. Output of the alternator is connected to a step-up transformer. The transformer step up 12V AC into 230 V AC supply and this is fed into an incandescent lamp. While we applying the brake, giving DC supply to rotor. The rotor will produce flux. Due to the kinetic energy, the rotor will slowly rotate and come to rest. During this time an emf will produce in the stator winding and fed to the step-up transformer and then fed to the load The DC supply is provided with 12 V 10Ah deep cycle lead acid battery and this battery is charging by using rectified output of alternator. Three phase diode bridge rectifier is used as rectifier. The relay circuit is used to control the braking system properly. Here we used a 12 V single pole double throw relay. In an ordinary system, during braking energy will lost in the form of heat and noise. If we use this system, we can conserve the energy loss due to braking. During braking, the traction motor connections are altered turn the electrical generators. The motor fields are connected across the main traction generator(MG) and the motor armatures are connected across the load. The MG now excites the motor fields. The rolling locomotive or multiple unit wheels turn the motor armatures, and the motors act as generators, either sending the generated current through onboard resistors (dynamic braking) or
  • 45. 45 back into the supply (regenerative braking).Compared to electro-pneumatic friction brakes, braking with the traction motors can be regulated faster improving the performance of wheel slide protection. For a given direction of travel, current flow through the motor armatures during braking will be opposite to that during motoring. Therefore, the motor exerts torque in a direction that is opposite from the rolling direction. Braking effort is proportional to the product of the magnetic strength of the field windings, multiplied by that of the armature windings. Savings of 17% are claimed for Virgin Trains. There is also less wear on friction braking components. The Delhi Metro saved around 90,000 tons of carbon dioxide (CO2) from being released into the atmosphere by regenerating112,500 megawatt hours of electricity through the use of regenerative braking systems between 2004 and2007. It is expected that the Delhi Metro will save over100,000 tons of CO2 from being emitted per year once its phase II is complete through the use of regenerative braking. Another form of regenerative braking is used on some parts of the London Underground, which is achieved by having small slopes leading up and down from stations. The train is slowed by the climb, and then leaves down a slope, so kinetic energy is converted to gravitational potential energy in the station. This is normally found on the deep tunnel sections of the network and not generally above ground or on the cut and cover sections of the Metropolitan and District Lines.
  • 46. 46 4.3 COMPARISON OF DYNAMIC BRAKING AND REGENERATIVE BRAKING Dynamic brakes unlike regenerative brakes, dissipate the electric energy as heat by passing the current through large banks of variable resistors. Vehicles that use Dynamic brakes ("rheostatic brakes" in the UK), unlike regenerative brakes, dissipate the electric dynamic brakes include forklifts, diesel-electricl ocomotives, and streetcars. This heat can be used to warm the vehicle interior, or dissipated externally by large radiator-like cowls to house the resistor banks. The main disadvantage of regenerative brakes when compared with dynamic brakes is the need to closely match the generated current with the supply characteristics and increased maintenance cost of the lines. With DC supplies, this requires that the voltage be closely controlled. The AC power supply and frequency converter pioneer Miro Zoric and his first AC power electronics have also enabled this to be possible with AC supplies. The supply frequency must also be matched (this mainly applies to locomotives where an AC supply is rectified for DC motors).In areas where there exists a constant need for power unrelated to moving the vehicle such as electric train heat or air conditioning, this load requirement can be utilized as a sink for the recovered energy via modern AC traction systems. This method has become popular with North American passenger railroads where Head End Power loads are typically in the area of 500 kW year round. Using HEP loads in this way has prompted recent electric locomotive designs such as the ALP- 46 andACS-64 to eliminate the use of dynamic brake resistor grids and also eliminates any need for any external power infrastructure to accommodate power recovery allowing self-powered vehicles to employ regenerative braking as well. A small number of steep grade railways have used 3-phase power supplies and 3-phase induction motors. This results in a near constant speed for
  • 47. 47 all trains as the motors rotate with the supply frequency both when motoring and braking. 4.4 FEASIBILITY OF TECHNOLOGY AND OPERATIONAL NECESSITIES Various types of trains can be equipped with regenerative braking: electric trains, hybrid diesel locomotives and subway trains The more frequently a train stops, the more it can benefit from regenerative breaking. Therefore the technique is especially valuable for commuter trains and subways, which both stop frequently. Electric railway systems can be either DC or AC powered. It is much easier to implement regenerative breaking for AC powered systems. For DC powered systems, there are two main barriers. Most DC powered systems use relatively low voltages and often the generated electricity cannot be fed back into the public electricity grid. In very dense suburban DC powered networks, however, regenerative breaking can be an effective way to reduce the electricity demand. In all other cases, the effectiveness of regenerative braking is rather low but may be enhanced by technological upgrades of vehicles and/or substations. These upgrades are associated with relatively high investment costs. Railway systems working with AC power can implement regenerative braking with almost no additional costs. Also the implementation of regenerative braking in diesel powered locomotives poses no obstacle. Virtually all locomotives are diesel-electric, so the capacity to do regenerative braking is available
  • 48. 48 4.5 STATUS OF THE TECHNOLOGY AND ITS FUTURE MARKET POTENTIALTOP Regenerative braking is a mature technology. Within Europe, there is still a considerable difference between countries in the share of rolling stock that is equipped with regenerative braking, but the share is relatively high already. Regenerative breaking is relatively standard in new trains. It is also used in major new high-speed trains. However, friction brakes are still needed as backup in the case that the regenerative brakes fail. It is possible to use regenerative braking on these high speed trains because most cars have their own electric motors, this is in contrast to trains in which only the locomotive has electric motors. The fourth generation TGVs in France, which are expected to be commissioned in 2010, will also be equipped with regenerative brakes, as will the German ICE 3 trains which are to be commissioned in 2012. 4.6 CONTRIBUTION OF THE TECHNOLOGY TO SOCIAL DEVOLEPMENTTOP Contribution by the use of regenerative breaking to socio- economic development is expected to be low. The Delhi Metro CDM project (DMRC, 2007) argues for marginally improved local employment in the operation and maintenance of the trains, but does not go into details on this. The effects of regenerative braking on air quality depend mainly on the way the electricity is produced. In general, the introduction of regenerative braking on electric trains and subway trains will have no direct effect on the local air quality. However, lowering the electricity demand will lower the emission of air pollutants, like NOx, SO2 and particulate matter in power generation, if power generation is based on fossil fuels. For diesel powered locomotives, hybridization can have a positive direct effect on air quality, depending on the usage pattern. Locomotives used solely on a marshalling yard can achieve very
  • 49. 49 high reductions in emissions, due to frequent need for braking. However, the reduction in local air pollution will be limited when the locomotive is used in long-haul freight trains. 4.7 ELEMENT SPECIFICATIONS Our design will provide all of the following:  Single Phase Induction Motor: 230V, ¼ HP Capacitor start- run single phase induction motor  Belt and pulley arrangement  Alternator: 120VA, 12V, 10A, 300 rpm alternator  Voltage Regulator: Zener diode is used to regulate the output voltage  Rectifier: Three phase bridge rectifier. Diode used IN4007  Battery: 10Ah 12VDC deep cycle lead acid battery for compatibility, convenience, and cost.  Relay: 12V single pole double throw.  Step-up transformer: 12V to 230V AC single phase transformer  Load: 40W 230V incandescent bulb is connected as load. 4.8 RESULT We construct the regenerative braking system by using the induction motor, alternator, rectifier, battery, step-up transformer, relay and incandescent lamp. We successfully take the energy lost due to braking and convert to 230 V single phase 50 Hz output supply and it is fed to the load.
  • 50. 50 CHAPTER 5 CONCLUSION In ordinary braking system there is a huge amount of energy wasted while braking. Generally we uses brake shoe and hydraulic systems are used in locomotives, so the maintenance cost is high and also those system will create noises and pollution. In our project we can reduce the wastage of energy during the braking time. This is simple and cost effective way of braking. It can perform a fast and controlled braking. The locomotives are normally designed for gradual braking.If we apply this mechanism in electrical locomotives, we can obtain very good braking with less maintenance cost and we gather electricity as byproduct from the system, then the electricity is fed into the bus.
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