02 report datas

7/28/2019 02 Report Datas

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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.



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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


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


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.


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.



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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/Transistor


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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/CMOS


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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
http://en.wikipedia.org/wiki/NMOS_logichttp://en.wikipedia.org/wiki/NMOS_logic


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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.
http://en.wikipedia.org/wiki/Electrical_loadhttp://en.wikipedia.org/wiki/Electrical_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
http://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Duty_cyclehttp://en.wikipedia.org/wiki/Duty_cyclehttp://en.wikipedia.org/wiki/File:PWM,_3-level.svghttp://en.wikipedia.org/wiki/Duty_cyclehttp://en.wikipedia.org/wiki/Hertz


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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.
http://en.wikipedia.org/wiki/Signalling_%28telecommunication%29http://en.wikipedia.org/wiki/Signalling_%28telecommunication%29


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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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