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CHAPTER 1
INTRODUCTION
1.1 GENERALBidirectional dc-dc converters (BDC) have recently received a lot of
attention due to the increasing need to systems with the capability of bidirectional
energy transfer between two dc buses. Apart from traditional application in dc
motor drives, new applications of BDC include energy storage in renewable
energy systems, fuel cell energy systems, hybrid electric vehicles (HEV) and
uninterruptible power supplies (UPS).The fluctuation nature of most renewable
energy resources, like wind and solar, makes them unsuitable for standalone
operation as the sole source of power.
A common solution to overcome this problem is to use an energy storage
device besides the renewable energy resource to compensate for these fluctuations
and maintain a smooth and continuous power flow to the load. As the most
common and economical energy storage devices in medium-power range are
batteries and super-capacitors, a dc-dc converter is always required to allow energy
exchange between storage device and the rest of system. Such a converter must
have bidirectional power flow capability with flexible control in all operating
modes.
In HEV applications, BDCs are required to link different dc voltage buses
and transfer energy between them. For example, a BDC is used to exchange energy
between main batteries (200-300V) and the drive motor with 500V dc link. Highefficiency, lightweight, compact size and high reliability are some important
requirements for the BDC used in such an application. BDCs also have
applications in line-interactive UPS which do not use double conversion
technology and thus can achieve higher efficiency.
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In a line-interactive UPS, the UPS output terminals are connected to the grid
and therefore energy can be fed back to the inverter dc bus and charge the batteries
via a BDC during normal mode. In backup mode, the battery feeds the inverter dc
bus again via BDC but in reverse power flow direction. BDCs can be classified
into non-isolated and isolated types. Non-isolated BDCs (NBDC) are simpler than
isolated BDCs (IBDC) and can achieve better efficiency. However, galvanic
isolation is required in many applications and mandated by different standards. The
complexity of IBDCs stems from the fact that an ac link must be present in their
structure in order to enable power transfer via a magnetically isolating media, i.e. a
transformer.As isolation and/or voltage matching is required in many applications. It
should be stated that in order to improve the efficiency, almost all recently
proposed medium-power IBDC configurations have exploited the benefits of soft-
switching or resonant techniques to increase the switching frequency and achieve
lower size and weight.
1.2 OBJECTIVES OF THE PROJECT
The objective of this project is to get high voltage gain without using
Snubber circuit by using Zero current switching and Zero voltage switching
techniques.
1.3 APPLICATIONS
Fuel cell energy conservation systems Solar cell energy conservation systems Battery back-up system for un interruptiple power supplies.
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CHAPTER 2
DC/DC BOOST CONVERTER
In many industrial applications, it is required to convert a fixed
voltage DC source into a variable voltage dc source. A DC chopper converts
directly from DC to DC and it is also known as a DC to DC converter.
This can be considered as the DC equivalent to an AC transformer with a
Continuous variable turns ratio and like a transformer; this can step up or step
down DC voltage source. This DC to DC converter is used in dc Voltage
regulators.
2.1 MODES OF OPERATION
CCM DCM
2.2 ADVANTAGES
Used in much wider range voltage application. High level dc is converted to desired level with simple diode Circuit
2.3 DISADVANTAGE
Used only for low voltage systems Cost is high
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CHAPTER 3
BI-DIRECTIONAL DC CONVERTERS
BDCs also have applications in line-interactive UPS which do not usedouble conversion technology and thus can achieve higher efficiency. In a line
interactive UPS, the UPS output terminals are connected to the grid and therefore
energy can be fed back to the inverter dc bus and charge the batteries via a BDC
during normal mode. In backup mode, the battery feeds the inverter dc bus again
via BDC but in reverse power flow direction.
BDCs can be classified into non-isolated and isolated types. Non-isolated
BDCs (NBDC) are simpler than isolated BDCs (IBDC) and can achieve better
efficiency. However, galvanic isolation is required in many applications and
mandated by different standards.
3.1 TYPES OF BDC3.1.1 NON-ISOLATED BDC
Basic dc-dc converters such as buck and boost converters (and their
derivatives) do not have bidirectional power flow capability. This limitation is due
to the presence of diodes in their structure which prevents reverse current flow. In
general, a unidirectional dc-dc converter can be turned into a bidirectional
converter by replacing the diodes with a controllable switch in its structure. As an
example, Fig. 1 shows the structure of elementary buck and boost converters and
how they can be transformed into bidirectional converters by replacing the diodes
in their structure. It is noteworthy that the resulted converter has the same structure
in both cases.
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Some of the major limitations associated with the NBDC are:
It can only operate in buck mode in one direction and boost in theother. In technical terms, this means that the voltage ratio d, which is
defined as d= VB/VA, is either smaller or greater than unity in one
direction.
When the voltage ratio becomes large, this structure becomesimpractical.
The lack of galvanic isolation between two sides.
3.1.2 ISOLATED BDC (IBDC):
Galvanic isolation between multi-source systems is a requirement mandated
by many standards. Personnel safety, noise reduction and correct operation of
protection systems are the main reasons behind galvanic isolation. Voltage
matching is also needed in many applications as it helps in designing and
optimizing the voltage rating of different stages in the system. Both galvanic
isolation and voltage matching are usually performed by a magnetic transformer in
power a electronic system, which call for an ac link for proper energy transfer.
Although this approach is similar to unidirectional dc-dc converters, the need to
bidirectional power flow significantly adds to the system complexity. Furthermore,
when high efficiency soft-switching techniques are to be applied, this complexity
tends to be more.
While different terminologies have been proposed and used in the literature,
a unified terminology is introduced and used throughout the project to simplify the
comparison between different structures. A classification is provided which helps
in understanding the conceptual similarities and differences between different
structures.
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CHAPTER 4
ZERO CURRENT SWITCHING (ZCS)
The switches of a zero current switching (ZCS) turn-on and turn-off at zero
current. The resonant circuit that consists of switch S, inductor L and capacitor C.
Inductor L is connected in series with a power switch S to achieve zero current
switching (ZCS). When switch current is zero, there is current flowing through the
internal capacitance due to a finite slope of the switch voltage at turn-off. This
current flow causes power dissipation in the switch and limits the high switching
frequency.
4.1 ZERO CURRENT SWITCHING RESONANT CONVERTERS
The switches of Zero Current Switching (ZCS) resonant converters turn on
and off at zero current. The resonant circuit that consists f switch S1, inductor L,
and capacitor C is shown. The inductor L is connected in series with power switch
S1 to achieve ZCS. It is classified into two typesL type and M type. In both the
types the inductor L limits the di/dt of the switch current and L and C constitute a
series resonant circuit. When the switch current is zero there is a current i=Cj.dvt/dt
flowing through the internal capacitance Cj due to finite slope of switch voltage at
turn off. This current flow causes power dissipation in the switch and limits the
high switching frequency.
The switch can be implemented either in half wave configuration where
diode D1 allows unidirectional current flow or in full-wave configuration where the
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switch current can flow bidirectionally. The practical devices do not turn off at
zero current due to their recovery time.
Lr
CrS
(a)
Lr
CrS
(b)
Figure 4.1 Zero current resonant switching
As a result, an amount of energy can be trapped in inductor L of the m-type
configuration and voltage transients appear across the switch. This normally favors
L type configuration over M type one.
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CHAPTER 5
ZERO VOLTAGE SWITCHING (ZVS)
The switches of a zero voltage switching turn-on and turn-off at zero
voltage. The capacitor C is connected in parallel with the switch S to achieve zero
voltage switching. The internal switch capacitance is added with the capacitor and
it affects resonant frequency only, thereby contributing no power dissipation in the
switch. In Zero voltage switching the switch in converter is turned ON and turned
OFF at zero voltage across the switch. Here capacitor is used as Filter circuit. The
function of capacitor is to produce zero voltage across the switch.
5.1 ZERO-VOLTAGE-SWITCHING RESONANT CONVERTERS
The switches of ZVS resonant converters turn on and off at zero voltage.
The capacitor C is connected in parallel with the switch S1 to achieve ZVS. The
internal switch capacitance Cj is added with the capacitor C and it affects the
resonant frequency only, thereby contributing no power dissipation in the switch. If
the switch is implemented with transistor Q1 and an anti-parallel diode D1 as
shown, the voltage across C is clamped by D1 and the switch is operated in half
wave configuration. If the diode D1 is connected in series with Q1 as shown, the
voltage across C can oscillate freely and the switch is operated in full wave
configuration.
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A ZVS resonant converter is shown in Figure 5.1. A ZVS resonant
converter is the dual of ZCS resonant converter.
Lr
S
(a)
Cr
Lr
CrS
(b)
Figure 5.1 Zero voltage resonant switching
In a ZV resonant switch, a capacitor Cr is connected in parallel with the
switch S for achieving zero-voltage-switching (ZVS). If the switch S is a
unidirectional switch, the voltage across the capacitor Cr can oscillate freely in
both positive and negative half-cycle. Thus, the resonant switch can operate in
full-wave mode. If a diode is connected in anti-parallel with the unidirectional
switch, the resonant capacitor voltage is clamped by the diode to zero during the
negative half-cycle. The resonant switch will then operate in half-wave mode. The
objective of a ZV switch is to use the resonant circuit to shape the switch voltage
waveform during the off time in order to create a zero-voltage condition for the
switch to turn on.
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CHAPTER 6
COMPARISON OF ZCS AND ZVS RESONANT CONVERTERS
ZCS can eliminate switching losses at turnoff and reduce the switching
losses at turn on. Because a relatively large capacitor is connected across the diode
Dm the inverter operation becomes insensitive to the diodes junction capacitance.
When power MOSFETs are used for ZCS the energy stored in the devices
capacitance is dissipated during turn on. This capacitive turn on loss is proportional
to the switching frequency. During turn on a high rate of change of voltage may
appear in the gate drive circuit due to the coupling through the Miller capacitor,
thus increasing switching loss and noise.
Another limitation is that the switches are under high current stress, resulting
in higher conduction loss. By the nature of ZCS, the peak switch current is much
higher. In addition, a high voltage becomes established across the switch in the off
state after the resonant oscillation. When the switch is turned on again, the energystored in the output capacitor becomes discharged through the switch, causing a
significant power loss at high frequency and higher voltages.
This switching loss can be reduced by using ZVS. ZVS eliminates the
capacitive turn on loss. It is suited for high frequency operation. Without any
voltage clamping, the switches may be subjected to excessive voltage stress which
is proportional to the load and the output voltage can be achieved by varying the
frequency.
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CHAPTER 7
PROPOSED CONVERTER
This project proposes a novel and simple ZCS-primary, ZVS-secondary
converter without a need for an active clamp or passive snubbers. In this project,
authors have concentrated on improving the efficiency of the current-fed converter
by ZCS operation of the converter switches as well as reduction in size and cost by
eliminating the need of passive snubbers or active clamp circuit.
It replaces the output rectifier diodes by active switches. However, this ZCS
concept is applicable to half-bridge voltage doubler rectifier on secondary. The
currents through primary and secondary switches start building from zero with a
slope depending on the transformer leakage inductance causing zero-current turn
on of the switches resulting in reduced switching losses. The proposed topology
has reduced circulating current and reduced switching losses and therefore, is
expected to show better part-load efficiency than hard-switching and active-clampcurrent-fed converter
Figure 7.1 Proposed ZCS current-fed half-bridge dc/dc converter
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In forward direction the converter acts as a two-phase isolated boost
(current-fed half-bridge) converter and in reverse directional, the converter acts as
voltage-fed full bridge current doubler dc/dc converter. Electrolytic capacitors
consume a major volume of the converter.
The proposed topology has only one electrolytic capacitor compared to four
large capacitors and two large input capacitors. Due to dual boost topology, it also
needs half if the transformer turns ratio. Due to two phase input, the current is
divided and it reduces the current stresses through the switches and thetransformer, reducing their KVA ratings.
It has low components count. Switching losses are reduced a lot due to soft-
switching of primary and secondary devices and higher efficiency. It allows high
switching frequency operation, which results in compact and low cost system. The
objectives of this project are to present steady-state operation and analysis of the
proposed converter has been reported. The objectives of this project are to present
the analysis and design of the active-clamped current-fed full-bridge dc/dc
converter.
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CHAPTER 8
BLOCK DIAGRAM
Figure 8.1 General block diagram of proposed converter
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8.1 OPERATION AND ANALYSIS OF THE CONVERTER
Before the instant, gating signal of the primary-side switch is removed, a
secondary side switch is turned on. The reflected output voltage Vo/n appears
across the transformer primary. It diverts the current from the primary switch into
the transformer, causing transformer current to rise and the primary switch current
to fall to zero. Then the body diode across the primary switch starts conducting and
the gating signal is removed causing its ZCS turn-off.
The following assumptions are made during analysis of the converter:
InductorsL1 andL2 are assumed large so that the current through themcan be considered constant.
Magnetizing inductance of the transformer is assumed infinitely large. All the components are assumed ideal.Llk is the leakage inductance of the transformer or a series inductor
that includes the transformer leakage inductance.
The steady-state operating waveforms of the proposed converter are Primary
side switches S1 and S2 are controlled by gating signals shifted in phase by 180
with an overlap. The overlap varies with duty cycle. Fixed frequency duty cycle
modulation is used for control.
The duty cycle of the primary switches is always greater than 50%. The
operation of the converter during different intervals ina HF half cycle is explained
using the equivalent circuits for the next half cycle.
The intervals are repeated in the same sequence with other symmetrical
devices conducting to complete the full HF cycle.
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The analysis is done to obtain the design equations to design and select the
components as well as to evaluate the converters performance theoretically. The
operation of the converter during different intervals in a half HF cycle is explained
using the equivalent circuits.
8.2 MODES OF OPERATION
8.2.1 MODE 1 (Interval to < t < t1; Figure 8.2):During this interval, primary side switch S1 and anti-parallel body diodesD4
and D5 of secondary side switches are conducting. Power is fed to the load from
the source through the HF transformer.
Transformer leakage inductance current is negative and constant. Switch S1 is
carrying the entire input current.
Figure 8.2 Mode 1 Operation of proposed converter
is1 =Iin. iS2 = 0, ilk= -Iin/2, iD4 =Iin/n.
Voltage across the switch S2Vs2 = Vo/n.
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At the end of this interval t= t3, switch current iS1 reduces to Iin/2, leakage
current ilk reaches zero, switch current iS2 increases to Iin/2 and secondary
switch/diode current reduces to zero.
8.2.4 MODE 4 (Interval t3< t < t4; Figure 8.5):
In this interval, secondary switches S4 and S5 are turned-on with ZVS. The
current through the components are rising or falling with the same slope. At the
end of this interval, the switch current iS1 naturally reaches to zero attaining zero-
current switching turn-off. Final values are: iS2 =Iin, iS1 = 0, ilk=Iin/2, iS4 =Iin/n.
Figure 8.5 Mode 4 Operation of proposed converter
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8.2.5 MODE 5 (Interval t4< t < t5; Figure 8.6):During this interval, the anti-parallel body diode D1 of switch S1 starts
conducting causing zero voltage across the switch S1 ensuring its ZCS. Still the
current through the components are rising or falling with the same slope. Switch
current iS2 and transformer leakage inductance current ilkattain their peak values.
This interval should be short in order the limit the peak current through the
components reducing the current stress and KVA rating.
The current through the several components are given by
Figure 8.6 Mode 5 Operation of proposed converter
It is clear that peak current through the primary switches is a little higher
thanIinand transformer leakage inductance current is a little higher than Iin/2. This
is a diode conduction interval and is kept short.
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8.2.6 MODE 6: (Interval t5< t < t6; Figure 8.7):In this interval, secondary switches S4 and S5 are turned-off. Other pair of
body diodes of the secondary switches takes over the current immediately.
The current through the several components are given by
Figure 8.7 Mode 6 Operation of proposed converter
The peak current through the switch S2 and transformer leakage inductance
Llkdecreases to values similar to final values of interval 4. Body diodeD1 of switch
S1 commutates at the end of this interval.
Final values are:
iS2 =Iin, iD1 = 0, ilk=Iin/2, iS4 =Iin/n.
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8.2.7 MODE 7 (Interval t6< t < t7; Figure 8.8):
In this interval, device capacitance of switch S1 charges to Vo/n. This interval
is very small, getting the switch into forward blocking mode.
Figure 8.8 Mode 7 Operation of proposed converter
8.2.8 MODE 8:(Interval t7< t < t8; Figure 8.9):In this interval, steady-state is achieved. Constant current is flowing through
switch S2, leakage inductanceLlkand body diode of secondary switch.
Figure 8.9 Mode 8 Operation of proposed converter
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Half HF switching cycle ends here with the end of this interval. For the next
half cycle, the intervals are repeated in the same sequence with other symmetrical
devices conducting to complete the full HF cycle.
7.3 OPERATING WAVEFORMS
The operating waveforms for the proposed converter is shown in Figure
8.10.
Fig 8.10 Operating waveforms of the proposed converter
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CHAPTER 9
HARDWARE DESCRIPTION
9.1 MOSFET
The symbol diagram and pin diagram of the Mosfet are shown in
Figure 9.1
Figure 9.1 Symbol and pin diagram of MOSFET
The metaloxidesemiconductor field-effect transistor (MOSFET,
MOS-FET, or MOS FET) is a transistor used for amplifying or switching
electronic signals. Although the MOSFET is a four-terminal device with source
(S), gate (G), drain (D), and body (B) terminals,[1] the body (or substrate) of the
MOSFET often is connected to the source terminal, making it a three-terminal
device like otherfield-effect transistors. Because these two terminals are normally
connected to each other (short-circuited) internally, only three terminals appear in
electrical diagrams. The MOSFET is by far the most common transistor in both
digital and analog circuits, though the bipolar junction transistorwas at one time
much more common.
http://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Signal_%28electrical_engineering%29http://en.wikipedia.org/wiki/MOSFET#cite_note-SPICE-1http://en.wikipedia.org/wiki/MOSFET#cite_note-SPICE-1http://en.wikipedia.org/wiki/MOSFET#cite_note-SPICE-1http://en.wikipedia.org/wiki/Field-effect_transistorhttp://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Digital_circuithttp://en.wikipedia.org/wiki/Bipolar_junction_transistorhttp://en.wikipedia.org/wiki/Bipolar_junction_transistorhttp://en.wikipedia.org/wiki/Digital_circuithttp://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Field-effect_transistorhttp://en.wikipedia.org/wiki/MOSFET#cite_note-SPICE-1http://en.wikipedia.org/wiki/Signal_%28electrical_engineering%29http://en.wikipedia.org/wiki/Transistor7/28/2019 02 Report Datas
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9.1.1 GENERAL DESCRIPTION:
In our project the MOSFET switch is connected to the main circuit.Here we
have two switches namely
Primary switches S1, and S2. Secondary switches Sr1, Sr2, Sr3, and Sr4.
9.1.2 TYPES OF MOSFET:
9.1.2.1 CMOS:
The MOSFET is used in digital complementary metaloxidesemiconductor
(CMOS) logic, which uses p- and n-channel MOSFETs as building blocks.
Overheating is a major concern in integrated circuits since ever more transistors
are packed into ever smaller chips. CMOS logic reduces power consumption
because no current flows (ideally), and thus no poweris consumed, except when
the inputs to logic gates are being switched. CMOS accomplishes this currentreduction by complementing every N-MOSFET with a P-MOSFET and connecting
both gates and both drains together.
A high voltage on the gates will cause the N-MOSFET to conduct and the
P-MOSFET not to conduct and a low voltage on the gates causes the reverse.
During the switching time as the voltage goes from one state to another, both
MOSFETs will conduct briefly. This arrangement greatly reduces power
consumption and heat generation.
http://en.wikipedia.org/wiki/CMOShttp://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Power_%28physics%29http://en.wikipedia.org/wiki/Logic_gatehttp://en.wikipedia.org/wiki/Logic_gatehttp://en.wikipedia.org/wiki/Power_%28physics%29http://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/CMOS7/28/2019 02 Report Datas
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9.1.2.2 NMOS and PMOS:
N-channel MOSFETs are smaller than p-channel MOSFETs and producing
only one type of MOSFET on a silicon substrate is cheaper and technically
simpler. These were the driving principles in the design ofNMOS logic which uses
n-channel MOSFETs exclusively. However, unlike CMOS logic, NMOS logic
consumes power even when no switching is taking place. With advances in
technology, CMOS logic displaced NMOS logic in the mid-1980s to become the
preferred process for digital chips.
In the case of a P-MOS, the body is connected to the most positive voltage,
and the gate is brought to a lower potential to turn the switch on. The P-MOS
switch passes all voltages higher than VgateVtp (threshold voltage Vtp is negative in
the case of enhancement-mode P-MOS).A P-MOS switch will have about three
times the resistance of an N-MOS device of equal dimensions because electrons
have about three times the mobility of holes in silicon.
9.1.3 FEATURES:
Single pulse avalanche energy ratedNano second switching speeds Linear transfer characteristics High input impedance
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9.2 INDUCTOR
A coil of wire that generates a magnetic field when current is passed
through it. The strength of the magnetic field is measured in henrys (H). When the
current is removed, as the magnetic field disintegrates, it "induces" a brief current
in the opposite direction of the original. Thus "induction" is caused by the opening
and closing of a DC circuit or the continuous changing of directions in an AC
circuit.
Figure 9.2 Symbol of Inductor
Inductance (measured in henries, symbol H) is a measure of the generated
emf for a unit change in current. For example, an inductor with an inductance of 1
H produces an emf of 1 V when the current through the inductor changes at the
rate of 1 As1.
An inductor is a passive electrical device used in electrical circuits for its
property of inductance. An inductor is usually made as a coil (or solenoid) of
conducting material, typically copper wire, wrapped around a core either of air or
of ferromagnetic material.
Electrical current through the conductor creates a magnetic flux proportional
to the current. A change in this current creates a change in magnetic flux that, in
turn, generates an emf that acts to oppose this change in current.
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The inductance of an inductor is determined by several factors:
The shape of the coil; a short, fat coil has a higher inductance than onethat is thin and tall.
The material that the conductor is wrapped around. How the conductor is wound; winding in opposite directions will
cancel out the inductance effect, and you will have only a resistor.
The inductance of a solenoid is defined by:
Where is the permeability of the core material (in this case air), A is the
cross-sectional area of the solenoid, N is the number of turns and l is the length of
the solenoid.
9.2.1 TYPES OF INDUCTORS:
1. WIREWOUND INDUCTORbobbin inductor toroidal inductor
2. MULTILAYER FERRITE INDUCTORbead inductor
3. MULTILAYER CERAMIC INDUCTOR4. FILM INDUCTOR5. LASER CUT INDUCTOR
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9.3 CAPACITORA capacitor is an electronic component used for storing charge and energy.
The usual capacitor is a pair of parallel plates separated by a small distance. When
a steady voltage is applied across a capacitor, a charge +Q is stored on one plate
while -Q is stored on the opposite plate. The amount of charge is determined by the
capacitance Cand the voltage difference Vapplied across the capacitor:
Figure 9.3 Various type of Capacitors
Since the charge cannot change instantaneously, the voltage across a
capacitor cannot change instantaneously either. Thus capacitors can be used to
guard against sudden losses of voltage in circuits, among other uses that we will
study later. Capacitance is measured in farads. One farad (F) equals one coulomb
per volt.
One of the many uses for capacitors is in computer memories. A typical
computer memory chip might contain 16,777,216 capacitors; each capacitor is
charged to approximately 5 volts to store the binary digit 1 or 0 volts to store the
binary digit 0.
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Another use of capacitors is to store energy for relatively brief times; for
example, the calculator I use is powered by light energy instead of a battery, and it
has a capacitor to provide power during brief intervals in which a shadow passes
across its photocell.
9.4 HIGH FREQUENCY TRANSFORMER:
A high frequency transformers transfer electric power. Its mechanical size
depends on the power to be transferred and on the operating frequency. The higherthe frequency the smaller the mechanical size. Usually frequencies are from 20 to
100 kHz. The material of the core is ferrite.
Data books for appropriate cores provide information about the possible
transfer power for various cores. The first step to calculate a high frequency
transformer is to choose an appropriate core with the help of the data book, the size
of the core is dependent on the transfer power and the frequency. The second step
is to calculate the number of primary turns.
This number determines the magnetic flux density within the core. The
number of secondary turns is the ratio of primary to secondary voltage. Following
this the diameters of the primary and secondary conductors can be calculated
depending on the RMS-values of the currents.
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The magnetizing current can be neglected in this calculation. The current
density can be chosen in a range of 2 to 5 A/mm, depending on the thermal
resistance of the choke.
If good coupling is important, the primary and secondary winding should be
placed on top of each other. Improved coupling is achieved if the windings are
interlocked.
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CHAPTER 10
CONTROL CIRCUIT
10.1 GATE PULSE CIRCUIT
In this project, Gate pulse for power switches is generated by Integrated by
PWM IC TL494. The TL494 is a fixed frequency, pulse width modulation control
circuit designed primarily for switch mode power supply control.
Figure 10.1 Gate pulse generation circuit using TL494
The TL494 is a fixedfrequency pulse width modulation control circuit,
incorporating the primary building blocks required for the control of a switching
power supply. An internallinear saw tooth oscillator is frequencyprogrammable
by two external components, RT and CT.
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This is desirable when the output transformer has a ring back winding with a
catch diode used for snubbing. When higher outputdrive currents are required for
singleended operation, Q1 and Q2 may be connected in parallel, and the output
mode pin must be tied to ground to disable the flipflop. The output frequency will
now be equal to that of the oscillator.
Table 10.1 Functional table for TL494
10.1.1 PULSE-WIDTH MODULATION
Pulse-width modulation (PWM) or pulse-duration modulation (PDM) is amodulation technique that conforms the width of the pulse, formally the pulse
duration, based on a modulator signal information. Although this modulation
technique can be used to encode information for transmission, its main use is to
allow the control of the power supplied to electrical devices, especially to inertial
loads such as motors.
The average value of voltage (and current) fed to the load is controlled by
turning the switch between supply and load on and off at a fast pace. The longer
the switch is on compared to the off periods, the higher the power supplied to the
load.
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The PWM switching frequency has to be much faster than what would affect
the load, which is to say the device that uses the power. Typically switching have
to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer,
from few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or
hundreds of kHz in audio amplifiers and computer power supplies.
Figure 10.2 Waveform of PWM signal
The term dutycycle describes the proportion of 'on' time to the regular
interval or 'period' of time; a low duty cycle corresponds to low power, because the
power is off for most of the time. Duty cycle is expressed in percent, 100% being
fully on.
The main advantage of PWM is that power loss in the switching devices is
very low. When a switch is off there is practically no current, and when it is on,
there is almost no voltage drop across the switch. Power loss, being the product of
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voltage and current, is thus in both cases close to zero. PWM also works well with
digital controls, which, because of their on/off nature, can easily set the needed
duty cycle.
PWM has also been used in certain communication systems where its duty
cycle has been used to convey information over a communications channel.
10.2 DRIVER CIRCUIT
The driver circuit for the proposed converter is shown in Figure 10.3. In this
project, IR2110 IC is used as a driver circuit.
Figure 10.3 Gate driver circuit of IR2110
Figure shows the isolator/driver circuit used in the control circuit. It has the
combined property of isolation and MOSFET driver. This IC gets gate pulse from
the optocoupler in and gives the pulses to the MOSFET, which gives the isolation
between gate and source.
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The IR2110 is a high voltage ,high speed power MOSFET and IGBT driver
with independent high and low side referenced output channels. Proprietary HVIC
and latch immune CMOS technologies enable ruggedized monolithic construction.
Logic inputs are compatible with standard CMOS or LSTTL outputs.
Figure 10.4 Various configurations of IR2110
The output drivers feature high pulse current buffer stage designed for
minimum driver cross-conduction.Propagation delays are matched to simplfy use
in high frequency applications.The floating channel can be used to drive an N-
channel power MOSFET or IGBT in the high side configuration which operates
upto 5oo volts.
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CHAPTER 11
POWER SUPPLY UNIT
All the electronic circuits such as transistor, integrated circuits generally
required DC electrical power for the operation. For the operation most of the
electronic devices, AC power must be converted into DC Power. This process
commonly called rectification.
Alternating current differ from DC in the direction of electron flow, first in
one direction for a short time, then reverse direction and flow again in opposite
direction for short time. The flow of electrons in one direction and then in another
direction is called a cycle of AC. The number of cycles that occur in one second of
time is called Cycles/ Second. In our country the standard power line frequency
is 50Hz.
The major blocks of the power supply units are:
Step down transformer Rectifier Diodes Filters Voltage regulators
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11.1 STEP DOWN TRANSFOMER
The instrument transformer for power supply in this project is to convert AC
from 230V to required low level such as 5V AC. This transformer apart from
stepping down AC voltage gives isolation between power source and power supply
circuitries.
11.2 RECTIFIER UNIT
In a power supply unit, rectification is normally achieved by a solid state
diode. Diode contains two electrodes called the anode and the cathode. A diode has
the property that will let electron flow easily in one direction. As a result when AC
is applied to a diode, electrons only flow when the anode is positive and cathode is
negative. Reversing the polarity of voltage applied to a diode will not permit
electron flow.
The various method of rectifying AC to DC are half wave, full wave and
bridge rectifications. This project employs a full wave bridge rectifier which is
most commonly used in industries. A bridge structure of four diodes is commonly
used in power supply units to achieve full wave rectification. When AC voltages
applied to the primary winding of power transformer. It is stepped down to 5V AC
across the secondary winding of the transformer.
Normally one alteration of the input voltage will cause the polarities to
reverse. Opposite end of the transformer will therefore, always be 1800 - out of
face with each other. For positive cycle, two diodes connected to the top winding
gets positive voltage and only one diode conducts for that cycle due to forward
bias. At the same time one out of the other two diodes conducts, for the negative
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voltage being applied form the bottom winding due to forward bias for that diode.
Due to positive half cycle diodes D1 & D3 conduct to give10.8V pulsating DC of
frequency 100Hz.In the next alteration the two diodes conducted form top winding
and bottom winding as they are forward biased in this cycle. It is to be noted that
the current flow through the load is always in one direction for each alteration of
the applied AC input.
This is of course, means that AC is rectified into DC. This DC output, in this
case, and has a ripple frequency of 100Hz, since each alternation producers a
resulting output pulse, the ripple frequency or 2*50 Hz =100Hz. The output DC is
not a pure DC. It is pulsating DC voltage.
11.3 FILTER UNIT
After pulsating DC has been produced by our rectifier, it must be filtered in
or for it to be usable in a power supply. Filtering involves the ripple frequency. The
power supply unit employed in this project used 7805 voltage regulator (for
positive output voltages) and a 7905 regulator, (for negative output voltages).
Resistors R1 and R2 maintain line load regulation. Capacitors C2 and C4 act as high
frequency suppressors.
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CHAPTER 12
SIMULATION STUDIES
12.1 INTRODUCTION
Computer simulation is the discipline of designing a model of an actual or
theoretical physical system, executing the model on a digital computer and
analysing the execution output. Simulation embodies the principle of learning by
doing to learn about the system we must first a model of some sort and then
operate the model.
12.2 MATLAB
Matlab is a high-performance language for technical computing. It integrates
computation, visualization and programming in an easy-to-use environment where
problems and solutions are expressed in familiar mathematical notation. Typical
uses include
Math and computation Algorithm development Data acquisition Modeling, simulation, and prototyping Data analysis, exploration, and visualization Scientific and engineering graphics Applications development, including graphical user interface building
Matlab is an interactive system whose basic data element is an array that
does not require dimensioning. This allows you to solve many technical computing
problems, especially those with matrix and vector formulations, in a fraction of the
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time it would take to write a program in a scalar non interactive language such as C
or FORTRAN. Matlab features a family of add-on application-specific solutions
called toolboxes.
12.2.1 SIMULINK
Simulink is a software package for modeling, simulating, and analysing
dynamic systems. It supports linear and nonlinear systems, modeled in continuous
time, sampled time or a hybrid of two. Systems can also be multi rate, i.e., have
different parts that are sampled or updated at different rates. For modeling,
Simulink provides a graphical user interface (GUI) for building models as block
diagrams, using click-and-drag mouse operations. This is a far cry from previous
simulation packages that require formulating differential equations and difference
equations in a language or program. Simulink includes a comprehensive block
library of sinks, sources, linear and nonlinear components, and connectors. It is
possible to customize and create blocks as required.
12.2.2 ROLE OF SIMULATION
Sim Power System is a modern design tool that allows scientist and
engineers to rapidly and easily build models that simulate power systems. A sim
power system uses the simulink environment, allowing us to build a model using
simple click and drag procedures. The circuit topology can be drawn rapidly, but
the analysis of the circuit can include its interactions with mechanical, thermal,
control, and other disciplines. This is possible because all the electrical parts of the
simulation interact with the extensive simulink modeling library, since simulink
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uses matlab as its computational engine, designers can also use MATLAB
toolboxes and Simulink block sets. Sim power systems and sim mechanics share a
special physical modeling block and connection line interface.
12.3 SIMULATION OF PROPOSED CONVERTER
The simulation diagram or the proposed converter is shown in Figure 12.1.
Figure 12.1 Simulation of proposed converter
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12.4 SIMULATION RESULTS
The simulation results for proposed converter at various locations are shownin Figures 12.2, 12.3, & 12.4.
Figure 12.2 Simulation result of Inductors L1, L2, and Leakage inductance
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Figure 12.3 Simulation results of Gate pulses for switches
Figure 12.4 Simulation results of input and output voltages
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CHAPTER 13
CONCLUSION
Current-fed topologies are suitable for low voltage higher current
applications. However, these topologies suffer from higher voltage stress across
the power semiconductor devices. So far, active-clamp, passive and resonant
snubbers have been proposed to improve absorb the turn-off voltage spike across
the switches during turn off to avoid high voltage rating devices. However, it does
results in need of extra components, increased PCB or foot size, and additional
cost.
Therefore, it affects the overall volume and cost of the system. Also, there
are some losses associated with the auxiliary snubber circuitry as well as it owes
the contribution of undesired circulating current through the devices and
components, which increases their peak current. The proposed bi-directional
current-fed converter provides a switching based solution to this problem. It avoids
the needs of such extra snubber circuitry for the solution making it novel and
snubberless. Steady-state analysis and design of the proposed converter have been
presented. Experimental results demonstrate the accuracy of the proposed analysis
and design. This topology is suitable for low voltage high current such as fuel cell,
PV and battery based applications.
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APPENDIX-I
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APPENDIX-II
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APPENDIX-III
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REFERENCES
1. S. Aso, M. Kizaki, and Y. Nonobe, Development of hybrid fuel cellvehicles in Toyota, inProc. IEEE PCC2007, pp. 1606-1611.
2. A. Emadi, and S. S. Williamson, Fuel cell vehicles: opportunities andchallenges,IEEE PES meeting2004, pp. 1640-1645.
3. K. Rajashekhara, Power conversion and control strategies for fuel cellvehicles, inProc. IEEE IECON2003, 2865-2870.
4. A. Emadi, S. S. Williamson, and A. Khaligh, Power electronics intensivesolutions for advanced electric, hybrid electric, and fuel cell vehicular power
systems,IEEE Trans. on Power Electronics, 2006,pp. 567-577.
5. A. Emadi, K. Rajashekara, S. S. Williamson, and S. M. Lukic,Topologicaloverview of hybrid electric and fuel cell vehicular power system
architectures and configurations IEEE Trans. on Vehicular Technology,
2005, pp. 763-770.
6. A. Khaligh and Z. Li, Battery, Ultra capacitor, Fuel Cell, and HybridEnergy Storage Systems for Electric, Hybrid Electric, Fuel Cell, and Plug-In
Hybrid Electric Vehicles: State of the Art, IEEE Trans. On Vehicular
Technology, 2010, pp. 2806-2814.
7. G-J Su, D. J. Adams, F. Z. Peng, and H. Li, Experimental evaluation of asoft-switching DC/DC converter for fuel cell vehicle applications IEEEPower Electronics in Transportation, 2002, pp. 39-44.
8. S.Han and D.Divan, Bi-directional dc/dc converters for plug-in hybridelectric vehicle (PHEV) applications, in Proc. IEEE APEC2008, pp. 784-
789.
9. P. J. Wolfs, A current-sourced dc-dc converter derived via duality principleform half bridge inverter, IEEE Trans. on Industrial Electronics, Vol. 40,
1993, pp. 139-144.
10. W.Song, and B. Lehman, Current-fed dual-bridge DCDC converter,IEEE Trans.on Power Electronics, vol. 22, March 2007, pp. 461-469.
11. A. Averberg, K. R. Meyer, and A. Mertens, Current-fed full-bridgeconverter for fuel cell systems,Proc. IEEE PESC 2008,pp. 866-872.
12. V. Yakushev, V. Meleshim, and S. Fraidlin, Full bridge isolated currentfed converter with active-clamp, inProc. IEEE APEC, 1999,pp. 560-566.
7/28/2019 02 Report Datas
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63
13. E. S. park, S. J. Choi, J. M. Lee, and B. H. cho, A soft-switching active-clamp scheme for isolated full-bridge boost converter, inProc.IEEE APEC
2004, 1067-1070.
14. J-T. Kim, B-K Lee, T-W.Lee, S-J.Jang, S-S.Kim, and C-Y. Won , An activeclamping current-fed half-bridge converter for fuel-cell generation systems,
inProc. IEEE PESC, 2004, pp. 4709-4714.
15. S. Han, H. Yoon, G. Moon, M. Youn, Y. Kim, and K. Lee, A new activeclamping zero-voltage switching PWM current-fed half bridge converter,
IEEE Trans. on Power Electronics, 2006, pp 1271-1279.
16. S. J. Jang, C. Y. Won, B. K. Lee and J. Hur, Fuel cell generation systemwith a new active clamping current-fed half-bridge converter,IEEE Trans.
on Energy Conversion, vol. 22, June 2007, pp. 332-340.
17. A. K. Rathore, A. K. S. Bhat and R. Oruganti, A Comparison of soft switched dc-dc converter for fuel cell to utility interface application,
inProc.IEEE Power Conversion Conf., Japan, 2007, pp. 588-594.
18. A. K. Rathore, A. K. S. Bhat, and R. Oruganti, Analysis, design, and experimental results of wide range ZVS active-clamped L-L type current-fed
dc/dc converter for fuel cells to utility interface, IEEETrans. on
Ind.Electronics, DOI:10.1109/TIE.2011.2146214,2011.
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