ABSTRACT

A bidirectional dc-dc converter is used for dc-dc power conversion

applications. The power converter includes two full bridge converters (one serving as

inverter and other as rectifier). This Bidirectional dc–dc converter is best for electrical

vehicle applications. The topology proposed in the thesis has advantages of simple

circuit topology with soft switching implementation without additional devices, high

efficiency and simple control.

This advantages make the converter promising for medium and high power

applications especially for auxiliary power supply in fuel cell vehicles and power

generation where the high power density, low cost, lightweight and high reliability

power converters are required.

PIC Micro Controller is used to generate pulses implementing PWM technique

for making MOSFETS devices to operate and control. PWM technique is used for

reducing the harmonic in the circuit.

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CHAPTER-1

INTRODUCTION

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1.1 PROJECT OVERVIEW

In Recent years, growing concerns about environmental issues have

demanded more energy efficient nonpolluting vehicles. The rapid

advances in fuel cell technology and power electronics have enabled the

significant developments in fuel cell powered electric vehicles. The fuel

cells have numerous advantages such as high density current output

ability, clean electricity generation, and high efficiency operation.

However, the fuel cell characteristics are different from that of the

traditional chemical-powered battery. The fuel cell output voltage drops

quickly when first connected with a load and gradually decreases as the

output current rises.

The fuel cell also lacks energy storage capability. Therefore, in

electric vehicle applications, an auxiliary energy storage device (i.e.,

lead-acid battery) is always needed for a cold start and to absorb the

regenerated energy fed back by the electric machine. In addition, a dc–dc

converter is also needed to draw power from the auxiliary battery to boost

the high-voltage bus during vehicle starting.

Until the fuel cell voltage raises to a level high enough to hold the

high-voltage bus, the excess load from the battery will be released. The

regenerated braking energy can also be fed back and stored in the battery

using the dc–dc converter.

A full-bridge isolated bidirectional dc–dc converter is considered

one of the best choices for these applications.

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1.2 INTRODUCTION TO DC-DC CONVERTER:

DC-DC converters are devices which change one level of direct current voltage to

another (either higher or lower) level. They are primarily of use in battery-powered

appliances and machines which possess numerous sub circuits, each requiring

different levels of voltage. A DC-DC converter enables such equipment to be

powered by batteries of a single level of voltage, preventing the need to use numerous

batteries with varying voltages to power each individual component.

1.2.2. BUCK CONVERTER STEP-DOWN CONVERTER

In this circuit the transistor turning ON will put voltage Vin on one end of the

inductor. This voltage will tend to cause the inductor current to rise. When the

transistor is OFF, the current will continue flowing through the inductor but now

flowing through the diode. We initially assume that the current through the inductor

does not reach zero, thus the voltage at Vx will now be only the voltage across the

conducting diode during the full OFF time. The average voltage at Vx will depend on

the average ON time of the transistor provided the inductor current is continuous.

Fig. 1: Buck Converter

Fig. 2: Voltage and current changes

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To analyse the voltages of this circuit let us consider the changes in the inductor

current over one cycle. From the relation

Vx – Vo = L (di/dt)

the change of current satisfies

For steady state operation the current at the start and end of a period T will not

change. To get a simple relation between voltages we assume no voltage drop across

transistor or diode while ON and a perfect switch change. Thus during the ON time

Vx= Vin and in the OFF Vx=0. Thus

Which simplifies to

Or

and defining "duty ratio" as

the voltage relationship becomes Vo=D Vin Since the circuit is lossless and the input

and output powers must match on the average Vo* Io = Vin* Iin. Thus the average input

and output current must satisfy Iin =D Io These relations are based on the assumption

that the inductor current does not reach zero.

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1.2.1.1Transition between continuous and discontinuous

When the current in the inductor L remains always positive then either the transistor

T1 or the diode D1 must be conducting. For continuous conduction the voltage Vx is

either Vin or 0. If the inductor current ever goes to zero then the output voltage will

not be forced to either of these conditions. At this transition point the current just

reaches zero as seen in Figure 3. During the ON time V in-Vout is across the inductor

thus

(1)

The average current which must match the output current satisfies

(2)

Fig. 3: Buck Converter at Boundary

If the input voltage is constant the output current at the transition point satisfies

(3)

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1.2.1.2 Voltage Ratio of Buck Converter (Discontinuous Mode)

As for the continuous conduction analysis we use the fact that the integral of voltage

across the inductor is zero over a cycle of switching T. The transistor OFF time is

now divided into segments of diode conduction ddT and zero conduction doT. The

inductor average voltage thus gives

(Vin - Vo ) DT + (-Vo) dT = 0 (4)

Fig. 4: Buck Converter - Discontinuous Conduction d

(5)

for the case . To resolve the value of consider the output current which is

half the peak when averaged over the conduction times

(6)

Considering the change of current during the diode conduction time

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(7)

Thus from (6) and (7) we can get

(8)

using the relationship in (5)

(9)

and solving for the diode conduction

(10)

The output voltage is thus given as

(11)

defining k* = 2L/ (Vin T), we can see the effect of discontinuous current on the

voltage ratio of the converter.

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Fig. 5: Output Voltage vs Current

As seen in the figure, once the output current is high enough, the voltage ratio

depends only on the duty ratio "d". At low currents the discontinuous operation tends

to increase the output voltage of the converter towards Vin.

1.2.2 BOOST CONVERTER STEP-UP CONVERTER

The schematic in Fig. 6 shows the basic boost converter. This circuit is used when a

higher output voltage than input is required.

Fig. 6: Boost Converter Circuit

While the transistor is ON Vx =Vin, and the OFF state the inductor current flows

through the diode giving Vx =Vo. For this analysis it is assumed that the inductor

current always remains flowing (continuous conduction). The voltage across the

inductor is shown in Fig. 7 and the average must be zero for the average current to

remain in steady state

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Vin ton + (Vin - Vo) toff =0

This can be rearranged as

and for a lossless circuit the power balance ensures

Fig. 7: Voltage and current waveforms (Boost Converter)

Since the duty ratio "D" is between 0 and 1 the output voltage must always be higher

than the input voltage in magnitude. The negative sign indicates a reversal of sense of

the output voltage.

1.2.3. BUCK-BOOST CONVERTER

Fig. 8: schematic for buck-boost converter

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With continuous conduction for the Buck-Boost converter Vx =Vin when the transistor

is ON and Vx =Vo when the transistor is OFF. For zero net current change over a

period the average voltage across the inductor is zero

Fig. 9: Waveforms for buck-boost converter

Vin ton + Vo toff = 0

which gives the voltage ratio

and the corresponding current

Since the duty ratio "D" is between 0 and 1 the output voltage can vary between lower

or higher than the input voltage in magnitude. The negative sign indicates a reversal

of sense of the output voltage.

CONVERTER COMPARISON

The voltage ratios achievable by the DC-DC converters is summarised in Fig.

10. Notice that only the buck converter shows a linear relationship between the

control (duty ratio) and output voltage. The buck-boost can reduce or increase the

voltage ratio with unit gain for a duty ratio of 50%.

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Fig. 10: Comparison of Voltage ratio

1.2.4. CUK CONVERTER

The buck, boost and buck-boost converters all transferred energy between input and

output using the inductor, analysis is based of voltage balance across the inductor.

The CUK converter uses capacitive energy transfer and analysis is based on current

balance of the capacitor. The circuit in Fig. 11 is derived from DUALITY principle on

the buck-boost converter.

Fig. 11: CUK Converter

If we assume that the current through the inductors is essentially ripple free we can

examine the charge balance for the capacitor C1. For the transistor ON the circuit

becomes

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Fig. 12: CUK "ON-STATE"

and the current in C1 is IL1. When the transistor is OFF, the diode conducts and the

current in C1 becomes IL2.

Fig. 13: CUK "OFF-STATE"

Since the steady state assumes no net capacitor voltage rise, the net current is zero

IL1tON + (-IL2) tOFF = 0

which implies

The inductor currents match the input and output currents, thus using the power

conservation rule

Thus the voltage ratio is the same as the buck-boost converter. The advantage of the

CUK converter is that the input and output inductors create a smooth current at both

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sides of the converter while the buck, boost and buck-boost have at least one side with

pulsed current.

1.4.5 Isolated DC-DC Converters

In many DC-DC applications, multiple outputs are required and output

isolation may need to be implemented depending on the application. In addition, input

to output isolation may be required to meet safety standards and / or provide

impedance matching. The above discussed DC-DC topologies can be adapted to

provide isolation between input and output.

1.4.5.1 Fly back Converter

The fly back converter can be developed as an extension of the Buck-Boost

converter. Fig 14a shows the basic converter; Fig 14b replaces the inductor by a

transformer. The buck-boost converter works by storing energy in the inductor during

the ON phase and releasing it to the output during the OFF phase. With the

transformer the energy storage is in the magnetization of the transformer core. To

increase the stored energy a gapped core is often used. In Fig 14c the isolated output

is clarified by removal of the common reference of the input and output circuits.

Fig. 14(a): Buck-Boost Converter

Fig. 14(b): Replacing inductor by transformer

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Fig. 14(c): Fly back converter re-configured

1.4.5.2 Forward Converter

The concept behind the forward converter is that of the ideal transformer converting

the input AC voltage to an isolated secondary output voltage. For the circuit in Fig.

15, when the transistor is ON, Vin appears across the primary and then generates

The diode D1 on the secondary ensures that only positive voltages are applied to the

output circuit while D2 provides a circulating path for inductor current if the

transformer voltage is zero or negative.

Fig. 15: Forward Converter

The problem with the operation of the circuit in Fig 15 is that only positive

voltage is applied across the core, thus flux can only increase with the application of

the supply. The flux will increase until the core saturates when the magnetizing

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current increases significantly and circuit failure occurs. The transformer can only

sustain operation when there is no significant DC component to the input voltage.

While the switch is ON there is positive voltage across the core and the flux increases.

When the switch turns OFF we need to supply negative voltage to reset the core flux.

The circuit in Fig. 16 shows a tertiary winding with a diode connection to permit

reverse current. Note that the "dot" convention for the tertiary winding is opposite

those of the other windings. When the switch turns OFF current was flowing in a

"dot" terminal. The core inductance act to continue current in a dotted terminal, thus

Fig. 16: Forward converter with tertiary winding

1.3 BI-DIRECTIONAL DC-TO-DC CONVERTER

A DC/DC converter which can be operated alternately as a step-up

converter in a first direction of energy flow and as a step-down converter in a second

direction of energy flow is disclosed. Potential isolation between the low-voltage side

and the high-voltage side of the converter is achieved by a magnetic compound

unit, which has not only a transformer function but also an energy store function. The

converter operates as a push-pull converter in both directions of energy flow. The

DC/DC converter can be used for example in motor vehicles with an electric drive fed

by fuel cells.

A bi-directional converter for converting voltage bi-directionally between a

high voltage bus and a low voltage bus, comprising a switching converter connected

across the high voltage bus, the switching converter comprising first and second

switching modules connected in series across the high voltage bus, a switched node

disposed between the switching modules being coupled to an inductor, the inductor

connected to a first capacitor, the connection between the inductor and the first

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capacitor comprising a mid-voltage bus, the first and second switching modules being

controllable so that the switching converter can be operated as a buck converter or a

boost converter depending upon the direction of conversion from the high voltage bus

to the low voltage bus or vice versa; the mid-voltage bus being coupled to a first full

bridge switching circuit comprising two pairs of series connected switches with

switched nodes between each of the pairs of switches being connected across a first

winding of a transformer having a preset turns ratio; and a second full bridge

switching circuit comprising two pairs of series connected switches with switched

nodes between each of the pairs of switches being connected across a second winding

of the transformer, the second full bridge switching circuit being coupled to a second

capacitor comprising a low voltage node.

1.3.1 USES OF DC-DC CONVERTER:

DC-DC converters are used to fill the gaps left by the limitations of direct and

alternating currents. Direct current (DC) is a steady flow of electric energy in the

same direction, while alternating current (AC) is a flow of energy which frequently

changes in direction and intensity. Alternating current is used for the vast majority of

electric transmission, because it is far easier to harness and dispense, and because it

can be easily stepped up or down in intensity by use of transformers, devices which

produce higher or lower levels of voltage by transferring currents into windings of

varying lengths. Because transformers work by means of time delays, they are unable

to work with direct current, due to direct current's constant rate of flow.

Alternating current has thus become far more commonly used simply because it is

far more flexible, and it is the preferred form of current for all forms of transmission

save one: batteries, which are unable to alternate their electrical flow and thus work

on direct current alone. For this reason, the DC-DC converter has become an

important electrical component, acting as the direct current equivalent of a

transformer for battery-operated devices, enhancing or reducing intensity as needed.

1.3.3 WORKING OF DC-DC Converters

In its simplest form, a DC-DC converter simply uses resistors as needed to

break up the flow of incoming energy – this is called linear conversion. However,

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linear conversion is a wasteful process which unnecessarily dissipates energy and can

lead to overheating. A more complex, but more efficient, manner of DC-DC

conversion is switched-mode conversion, which operates by storing power, switching

off the flow of current, and restoring it as needed to provide a steadily modulated flow

of electricity corresponding to the circuit's requirements. This is far less wasteful than

linear conversion, saving up to 95% of otherwise wasted energy.

1.3.2 BIDIRECTIONAL DC-DC CONVERTERS TOPOLOGIES

There are many circuit topologies for bidirectional dc-dc converter. Some of

them are

I. Non isolated (Without transformer):

a. Full bridge bidirectional dc-dc converter (shown in fig)

b. Half bridge bidirectional dc-dc converter

II. Isolated (with transformer):

a. Full bridge bidirectional dc-dc converter ( shown in fig)

b. Half bridge bidirectional dc-dc converter

1.3.2.1 NON-ISOLATED BIDIRECTIONAL DC/DC CONVERTER:

Fig17: Full bridge bidirectional dc-dc converter

Interleaved operation for both boost and buck modes →

• Smaller passive components;

• Less battery ripple current

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1.3.2.2 ISOLATED BIDIRECTIONAL DC-DC CONVERTER (PROPOSED

CONVERTER):

Fig18: lv-side “current source” and hv-side “voltage source”

The above converter has the following features

Simple voltage clamp circuit implementation

Simple transformer winding structure and low turns ratio

High choke ripple frequency (2fs)

start up problem will be present in this circuit

1.4 SEMICONDUCTOR SWITCHING:

Semi conductor switching types are 1. Hard Switching and 2. Soft Switching

1.4.1Hard Switching

Traditional high frequency switch-mode supplies, which rely on generating an

AC waveform in the range of 100 kHz to 200 kHz to drive the main power

transformer, have used power transistors to “hard-switch” the unregulated input

voltage at this rate. This means that a transistor turning on will have the whole raw

input voltage, typically in the range of 350 V, across it as it changes state. During the

actual switching interval (less than 0.5US) there is a finite period as the transistor

begins to conduct where the voltage begins to fall at the same time as current begins

to flow. This simultaneous presence of voltage across the transistor and current

through it means that, during this period, power is being dissipated within the device.

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A similar event occurs as the transistor turns off, with the full current flowing through

it.

Designers that use a hard-switching topology are in a no-win situation

when they try to reduce wasted power, and still meet the European EMC directive. As

the switching period is reduced through the use of improved driving circuitry, the

faster rise and fall times generate more high frequency energy that is radiated and

conducted out of the unit as unacceptable radio frequency interference (RFI). If the

rise and fall times are intentionally slowed to reduce the radio frequency interference,

the power losses in the transistor increase proportionally, increasing the thermal stress

on the part, thus reducing its lifespan. In this way, older hard switching topologies are

a compromise between electrical efficiency reduction and EMC “noise” trade-offs.

1.4.2 SOFT SWITCHING

More recently, new power conversion topologies have been developed which

dramatically reduce the power dissipated by the main power transistors during the

switching interval, while at the same time nearly eliminating much of the generated

radio frequency energy, or high frequency “noise”. The most common technique

employed has been a constant frequency resonant switching scheme, which ensures

that the actual energy being dissipated by the active device is reduced to nearly zero.

This method, commonly called “Zero Voltage Switching” (ZVS) or “Soft Switching”

uses the parasitic output capacitance of the power transistors (typically MOSFETs)

and the parasitic leakage inductance of the power transformer as a resonant circuit.

Using this resonant circuit, the output inductance, the parasitic drain-source body

diodes of the MOSFETs, and an appropriate switching sequence allows the voltage

across each transistor to swing to zero before the device turns on and current flows.

Likewise, at turn-off, the voltage differential across the transistor swings to zero

before it is driven to a non-conductive state. With this scheme, current is only fl

owing through the transistors when they are fully “on”, and doing useful work

transferring energy to the output of the supply. The power dissipation within the

transistor that would normally occur during the switching interval has effectively been

eliminated. Unwanted high-frequency voltage and current transients during the

switching period the culprits that supply much of the RF noise radiated and conducted

out of the power supply – are also dramatically reduced due to the smooth resonant

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transition. With the noise effectively reduced at its source, enhancing filtering at the

input and output of the unit ensures that the unit is well within the noise limits set by

international standards.

With “soft switching” techniques, reduction in wasted power will often improve

the efficiency of a unit by more than 2%. While this does not sound significant, it can

account for a saving of more than 20 W in a 1000 W power supply. This 20 W is

power that would have been dissipated by the main power transistors, the most critical

and most heavily stressed semi-conductors in any switch mode power supply.

Reducing the power here lowers their junction temperature, giving increased thermal

operating margins and, hence, a longer life for the power supply. Not only does a

“soft switching” power supply generate significantly less electrical noise, it achieves

greater efficiency, longer mean time between failures (MTBF), and higher immunity

to the effects of other equipment operating nearby.

It is desirable for power converters to have high efficiencies and high power

densities. Packaging and cost limitations require that the converter have a small

physical size and weight. Power density and electrical performance are dependent on

the switching frequency as it determines the values of the reactive components in the

converter. Thus, high frequency operation of the converter is highly desired.

However, operation at high frequency results in higher switching losses and higher

switching stresses caused by the circuit parasitics (stray inductance, junction

capacitance).

The main factors that contribute to the high-frequency switching losses are:1) Semiconductor devices have non-zero turn-on and turn-off times and thus

there is a finite time during the transitions wherein the devices are conducting

a significant current while a large voltage is applied across it. This results in

large energy dissipation. This energy loss increases with increasing frequency.

2) At high frequencies, high dv/dt and di/dt induce voltage and current

oscillations in parasitic capacitors and inductors during switching transitions.

These oscillations result in higher peak current and voltage in the devices and

thus the switching loss increases. Furthermore, these oscillations create EMI

noise, which can interfere with other parts of the circuit or surrounding

electronic equipment.

3) When a device is turned on while having a voltage across it, the energy stored

in the parasitic capacitance across the switch is dissipated in it. This loss

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increases with the frequency and is proportional to the square of the voltage

across the device before turn-on. Soft-switching techniques force the switch

voltage or current to zero before the device switching, thus avoiding current

and voltage overlap during the switching transition.

The advantages of soft switching are as follows:

Lower switching losses due to smaller overlap of switch voltage and

current.

Lower dv/dt and di/dt and thus lower voltage spike and EMI emissions.

Higher reliability due to reduced stresses on the switching components.

Reduced voltage and current ratings for the devices.

Smaller reactive elements.

Soft switching for the power devices can be achieved by either zero-voltage

switching (ZVS) or zero-current switching (ZCS). ZVS consists of turning on the

switches while the voltage across them is zero. ZCS consists of turning off the

switches when the current through them is zero.

Soft switching has been proven to be an effective means of reducing switching losses

and for attaining higher overall efficiencies. Various soft-switching techniques have

been developed in the recent years.

SOFT SWITCHING

Fig19 (a)HARD SWITCHING

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Fig19 (b)

Fig.20 Typical switching trajectories of power switches.

Fig.21. Typical switching waveforms of (a) hard-switched & (b) soft-switched

devices

1.5 PULSE WIDTH MODULATION (PWM) TECHNIQUE

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The energy that a switching power converter delivers to a

motor is controlled by Pulse Width Modulated (PWM) signals, applied to the gates of

the power transistors. PWM signals are pulse trains with fixed frequency and

magnitude and variable pulse width. There is one pulse of fixed magnitude in every

PWM period. However, the width of the pulses changes from period to period

according to a modulating signal.

When a PWM signal is applied to the gate of a power

transistor, it causes the turn on and turns off intervals of the transistor to change from

one PWM period to another PWM period according to the same modulating signal.

The frequency of a PWM signal must be much higher than that of the modulating

signal, the fundamental frequency, such that the energy delivered to the motor and its

load depends mostly on the modulating signal.

FIG 22. TWO TYPES OF PWM SIGNALS

Figure22 shows two types of PWM signals, symmetric and asymmetric

edge-aligned. The pulses of a symmetric PWM signal are always symmetric with

respect to the center of each PWM period. The pulses of an asymmetric edge-aligned

PWM signal always have the same side aligned with one end of each PWM period.

Both types of PWM signals are used in this application.

It has been shown that symmetric PWM signals generate fewer

harmonic in the output current and voltage. Different PWM techniques, or ways of

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determining the modulating signal and the switch-on/switch-off instants from the

modulating signal, exist. The Technique that we use is Natural PWM technique. This

technique is commonly used with three phase Voltage Source power inverters for the

control of three-phase AC induction motors.

(a) 1.5.1 Natural PWM Method

So as to feed the stator windings with a 3-phase sinusoidal voltage

through an inverter, a first solution is to use a sine table to generate three sine waves

with 120 degrees phase shift to each other. For this, the stator pulsation s is used to

feed three discrete-time integrators, which compute the instantaneous phase of each

stator voltage,

1[k] = 1[k-1] + s [k] Ts

2[k] = 2[k-1] + s [k] Ts

3[k] = 3[k-1] + s [k] Ts

With 1[0]=0, 2[0]= -2π /3, 3[0]= - 4π/3, Ts, being the sampling period of the

control algorithm. When one of these angles becomes higher than 2π, 2π is subtracted

to it to keep it between 0 and 2π.

A sine table is the used to compute the three voltages that should be

applied to the stator, Va[k] = Vsm(s[k]) sita (1[k])

Vb[k] = Vsm(s[k]) sita(2[k])

Vc[k] = Vsm(s[k]) sita(3[k])

Where Vsm(s) is the stator voltage magnitude deduced from the constant

Volts per Hertz principle and sita () = sin ().

A slight improvement can be obtained by adding to the pure sine wave of

the sine table a third harmonic, sita() = sin() + 1/6 sin(3) , since it has no effect on

the motor behavior and it allows to generate a signal whose first harmonic has an

amplitude which is 15.47% higher (2/3 ) than the signal maximum. With this

improvement, we can generate more AC voltage with the same DC bus voltage, so we

can increase the speed of the motor with keeping constant the V/F ratio.

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These values are compared to the output of an up/down counter (used as

a triangle generator). When the up/down counters output oversteps one of these

values, the corresponding output of the comparator toggles. As a result, the duty cycle

of each PWM channel is proportional to the corresponding stator voltage value. Since

this up/down counter with three comparators would be very heavy to implement by

software, such a device must be included in a microcontroller so as to suit AC motor

control applications. Taking the first phase as an example, the duty cycle stored in the

compare register of the corresponding PSC’s will be proportional to

Ts/ 2(1 + Va[k] / Vs max), with = 1- 2/Ts, Vs max and are respectively

the highest value of the stator voltage magnitude and the dead time of the inverter

switches. The resulting data-flow diagram is shown on Figure 23.

Fig 23: data flow diagram of pwm method

CHAPTER-2 HARDWARE

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2.1 PRINTED CIRCUIT BOARD DESIGN

A printed circuit board, or PCB, is used to mechanically support and

electrically connect electronic components using conductive pathways, or traces,

etched from copper sheets laminated onto a non-conductive substrate. Alternative

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names are printed wiring board (PWB), and etched wiring board. A PCB

populated with electronic components is a printed circuit assembly (PCA).

MANUFACTURING

The manufacturing process consists of two methods; print and etch, and print,

plate and etch. The single sided PCBs are usually made using the print and etch

method. The double sided plate through – hole (PTH) boards are made by the print

plate and etch method. The production of multi layer boards uses the methods. The

inner layers are printed and etch while the outer layers are produced by print, plate

and etch after pressing the inner layers.

SOFTWARE:

The software used in our project for obtaining schematic layout is ORCAD.

PATTERNING (ETCHING)

The vast majority of printed circuit boards are made by bonding a layer of

copper over the entire substrate, sometimes on both sides, (creating a "blank PCB")

then removing unwanted copper after applying a temporary mask (eg. by etching),

leaving only the desired copper traces. A few PCBs are made by adding traces to the

bare substrate (or a substrate with a very thin layer of copper) usually by a complex

process of multiple electroplating steps.

DRILLING

Holes, or vias, through a PCB are typically drilled with tiny drill bits made of

solid tungsten carbide. The drilling is performed by automated drilling machines with

placement controlled by a drill tape or drill file. These computer-generated files are

also called numerically controlled drill (NCD) files or "Excellon files". The drill file

describes the location and size of each drilled hole.

EXPOSED CONDUCTOR PLATING AND COATING

The places to which components will be mounted are typically plated, because

bare copper oxidizes quickly, and therefore is not readily solderable. Traditionally,

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any exposed copper was plated with solder by hot air solder leveling (HASL). This

solder was a tin-lead alloy, however new solder compounds are now used to achieve

compliance with the RoHS directive in the EU, which restricts the use of lead. Other

plantings used are OSP (organic surface protectant), immersion silver (IAg),

immersion tin, electroless nickel with immersion gold coating (ENIG), and direct

gold. Edge connectors, placed along one edge of some boards, are often gold plated.

SOLDER RESIST

Areas that should not be soldered to may be covered with a polymer solder

resist (solder mask) coating. The solder resist prevents solder from bridging between

conductors and thereby creating short circuits. Solder resist also provides some

protection from the environment.

SCREEN PRINTING

Screen print is also known as the silk screen, or, in one sided PCBs, the red print.

Lately some digital printing solutions have been developed to substitute the traditional

screen printing process. This technology allows printing variable data onto the PCB,

including serialization and barcode information for traceability purposes.

POPULATING

After the printed circuit board (PCB) is completed, electronic components must

be attached to form a functional printed circuit assembly, or PCA(sometimes called a

"printed circuit board assembly" PCBA). In through-hole construction, component

leads are inserted in holes. In surface-mount construction, the components are placed

on pads or lands on the outer surfaces of the PCB. In both kinds of construction,

component leads are electrically and mechanically fixed to the board with a molten

metal solder.

2-2–POWER SUPPLY UNIT

All electronic circuits works only in low DC voltage, so we need a power

supply unit to provide the appropriate voltage supply for their proper

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functioning .This unit consists of transformer, rectifier, filter & regulator. AC voltage

of typically 230v rms is connected to a transformer voltage down to the level to

the desired ac voltage. A diode rectifier that provides the full wave rectified voltage

that is initially filtered by a simple capacitor filter to produce a dc voltage. This

resulting dc voltage usually has some ripple or ac voltage variation . A regulator

circuit can use this dc input to provide dc voltage that not only has much less ripple

voltage but also remains the same dc value even the dc voltage varies some what, or the

load connected to the output dc voltages changes.

Fig 24.General Block of Power Supply Unit

2.2.1 DIODE BRIDGE RECTIFIER

Fig25 : Diode Bridge Rectifier

A diode bridge or bridge rectifier is an arrangement of four diodes

connected in a bridge circuit as shown below, that provides the same polarity of

output voltage for any polarity of the input voltage. When used in its most common

application, for conversion of alternating current (AC) input into direct current (DC)

output, it is known as a bridge rectifier. The bridge rectifier provides full wave

rectification from a two wire AC input (saving the cost of a center tapped transformer)

29

but has two diode drops rather than one reducing efficiency over a center tap based

design for the same output voltage.

Fig 26: Schematic Of A Diode Bridge Rectifier

The essential feature of this arrangement is that for both polarities of the voltage at the

bridge input, the polarity of the output is constant.

BASIC OPERATION OF DIODE BRIDGE RECTIFIER

When the input connected at the left corner of the diamond is positive with

respect to the one connected at the right hand corner, current flows to the right along

the upper colored path to the output, and returns to the input supply via the lower one.

Fig27: operation of diode bridge rectifier

When the right hand corner is positive relative to the left hand corner, current flows

along the upper colored path and returns to the supply via the lower colored path.

30

Fig 28: AC, half-wave and full wave rectified signals

In each case, the upper right output remains positive with respect to the lower

right one. Since this is true whether the input is AC or DC, this circuit not only

produces DC power when supplied with AC power: it also can provide what is

sometimes called "reverse polarity protection". That is, it permits normal functioning

when batteries are installed backwards or DC input-power supply wiring "has its

wires crossed" (and protects the circuitry it powers against damage that might occur

without this circuit in place).

Prior to availability of integrated electronics, such a bridge rectifier was

always constructed from discrete components. Since about 1950, a single four-

terminal component containing the four diodes connected in the bridge configuration

became a standard commercial component and is now available with various voltage

and current ratings.

2.2.2 TRANSFORMER: A transformer is a static piece of which electric power in

one circuit is transformed into electric power of same frequency in another circuit. It can

raise or lower the voltage in the circuit, but with a corresponding decrease or increase in

current. It works with the principle of mutual induction. In our project we are using a

31

step down transformer to providing a necessary supply for the electronic circuits. Here we

step down a 230v ac into 12v ac.

2.2.3 RECTIFIER: A dc level obtained from a sinusoidal input can be improved 100%

using a process called full wave rectification. Here in our project for full wave

rectification we use bridge rectifier. From the basic bridge configuration we see that two

diodes(say D2 & D3) are conducting while the other two diodes (D1 & D4) are in off

state during the period t = 0 to T/2.Accordingly for the negative cycle of the input the

conducting diodes are D1 & D4 .Thus the polarity across the load is the same.

In the bridge rectifier the diodes may be of variable types like 1N4001, 1N4003,

1N4004, 1N4005, IN4007 etc… can be used . But here we use 1N4007, because it can

withstand up to 1000v.

2.2.4 FILTERS: In order to obtain a dc voltage of 0 Hz, we have to use a low pass filter.

so that a capacitive filter circuit is used where a capacitor is connected at the rectifier

output& a dc is obtained across it. The filtered waveform is essentially a dc voltage with

negligible ripples & it is ultimately fed to the load.

2.2.5 REGULATORS: The output voltage from the capacitor is more filtered & finally

regulated. The voltage regulator is a device, which maintains the output voltage constant

irrespective of the change in supply variations, load variations & temperature changes.

Here we use fixed voltage regulator namely LM7805.The IC LM7805 is a +5v regulator

which is used for microcontroller.

2.2.6 Circuit Diagram:

Fig29 power supply unit

32

2.2.7 FEATURES & DESCRIPTION OF REGULATORS

• Output Current up to 1A

• Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V

• Thermal Overload Protection

• Short Circuit Protection

• Output Transistor Safe Operating Area Protection

The KA78XX/KA78XXA series of three-terminal positive regulator are

available in the TO-220/D-PAK package and with several fixed output voltages,

making them useful in a wide range of applications. Each type employs internal

current limiting, thermal shut down and safe operating area protection, making it

essentially indestructible. If adequate heat sinking is provided, they can deliver over

1A output current. Although designed primarily as fixed voltage regulators, these

devices can be used with external components to obtain adjustable voltages and

currents.

2.3 GATE DRIVER CIRCUIT

Driver performs three operations.

1: Amplification

2: Isolation

3: Impedance matching

R 1

1 k

R 2

R 3 R 4

R 5

R 61 k

R 81 k

U 1

O P -0 7 C / 3 0 1 / TI Q 1

B D X3 7

Q 2

Q 3

D 1

D 1 N 1 1 9 0

C 11 n

0

FROM MICRO CONTROLLER

1K

100100

100

S

G500mA

230/12VMCT2E

Fig 30

The buffer IC used here IC 4050 is used for pulse generation to generate triggering

pulse. There are pull up resistors to provide a resistance in series with the

33

microcontroller which acts as a current source here. This IC acts as an impedance

improvement buffer IC. Voltage follower concept is used and the signal is getting

inverted. Now it is given to the isolator.

Since the microcontroller is a sensitive device and MOSFET carries high

current, in order to provide isolation between the two, isolation is being provided by

the optocoupler.

2.4 OPTOCOUPLER

Fig 31: An opto-isolator integrated circuit & Schematic diagram

In electronics, an opto-isolator (or optical isolator, optocoupler or photo

coupler) is a device that uses a short optical transmission path to transfer a signal

between elements of a circuit, typically a transmitter and a receiver, while keeping

them electrically isolated — since the signal goes from an electrical signal to an

optical signal back to an electrical signal, electrical contact along the path is broken.

A common implementation involves an LED and a light sensor, separated so

that light may travel across a barrier but electrical current may not. When an electrical

signal is applied to the input of the opto-isolator, its LED lights, its light sensor then

activates, and a corresponding electrical signal is generated at the output. Unlike a

transformer, the opto-isolator allows for DC coupling and generally provides

significant protection from serious overvoltage conditions in one circuit affecting the

other.

34

With a photodiode as the detector, the output current is proportional to the

amount of incident light supplied by the emitter. The diode can be used in a

photovoltaic mode or a photoconductive mode.

In photovoltaic mode, the diode acts like a current source in parallel with a

forward-biased diode. The output current and voltage are dependent on the load

impedance and light intensity. In photoconductive mode, the diode is connected to a

supply voltage, and the magnitude of the current conducted is directly proportional to

the intensity of light.

An opto-isolator can also be constructed using a small incandescent lamp in

place of the LED; such a device, because the lamp has a much slower response time

than an LED, will filter out noise or half-wave power in the input signal. In so doing,

it will also filter out any audio- or higher-frequency signals in the input. It has the

further disadvantage, of course, (an overwhelming disadvantage in most applications)

that incandescent lamps have finite life spans. Thus, such an unconventional device is

of extremely limited usefulness, suitable only for applications such as science

projects.

The optical path may be air or a dielectric waveguide. The transmitting and

receiving elements of an optical isolator may be contained within a single compact

module, for mounting, for example, on a circuit board; in this case, the module is

often called an optoisolator or opto-isolator. The photo sensor may be a photocell,

phototransistor, or an optically triggered SCR or Triac. Occasionally, this device will

in turn operate a power relay or contactor.

2.4.1 Device rating:

OPTOCOUPLER MCT2E – 1 K, 100 Ω resistance

Here the LED glows and current flows through the base of the transistor, so

the signal will be got across a resistance and given to another transistor CK 100 which

is a PNP transistor to provide inversion again. In order to improve the voltage and the

current gain we go for the Darlington amplifier, which amplifies the voltage.

35

2.5 DARLINGTON AMPLIFIER

Fig 32 Circuit diagram of Darlington configuration

In electronics, the Darlington transistor is a semiconductor device which

combines two bipolar transistors in tandem (often called a "Darlington pair") in a

single device so that the current amplified by the first is amplified further by the

second transistor. This gives it high current gain (written β or hFE), and takes up less

space than using two discrete transistors in the same configuration. The use of two

separate transistors in an actual circuit is still very common, even though integrated

packaged devices are available. This configuration was invented by Bell Laboratories

engineer Sidney Darlington. The idea of putting two or three transistors on a single

chip was patented by him, but not the idea of putting an arbitrary number of

transistors, which would have covered all modern integrated circuits.

A similar transistor configuration using two transistors of opposite type (NPN

and PNP) is the Sziklai pair, sometimes called the "complementary Darlington".

Finally the amplified signal is sent to the multilevel inverter and the output is

obtained.

2.6 SEMICONDUCTOR DEVICES

The electronic semiconductor device act as a switching device in the

power electronic converters. In general, the characteristics of the device are utilized in

such a way that it acts as a short circuit when closed. In addition to, an ideal switch

also consumes less power to switch from one state to other.

36

Semiconductor is defined as the material whose conductivity depends

on the energy (light, heat, etc.,) falling on it. They don’t conduct at absolute zero

temperature. But, as the temperature increases, the current conducted by the semi

conductor increases as it gets energy in the form of heat. The increase in current is

proportional to the temperature rise. Semiconductor switches are diodes, SCR,

MOSFET, IGBT, BJT, TRIAC etc.,

2.6.1 CLASSIFICATION OF SEMICONDUCTOR DEVICE

Based on controllability:

Uncontrolled switching device (SCR)

Semi control switching device

Fully control switching device

Based on control modes:

Current control devices(SCR ,BJT)

Voltage control device(MOSFET ,IGBT)

Based on current direction:

Unidirectional device (SCR,MOSFET ,IGBT)

Bi- Unidirection device(TRIAC)

2.6.2 MOSFET

The component that is used as the switch in the inverter unit is the MOSFET which is a voltage controlled device. They are the power semi conductor devices that have a fast switching property with a simple drive requirement.

Fig 33: MOSFET symbol

Vdss= 500 V

Rds (on) = 0.27 ohm

Id= 20 A

37

This MOSFET provide the designer with the best combination of fast switching,

ruggedixed device design, low on-resistance and cost-effectiveness. This package is

preferred for commercial and industrial applications where higher power levels are to

be handled.

2.6.3. MOSFET OPERATING PRINCIPLE

CONSTRUCTION N Channel depletion type N Channel enhancement type

Fig 34: construction of MOSFET

N CHANNEL DEPLETION

The N channel depletion type of MOSFET is constructed with p -Substrate. it

has two n doped regions , which forms the drain and source. It has sio2 insulating layer

between the channel and the metal layer. Thus it has three terminals namely drain

source and gate.

When negative voltage applied between the gate and source (VGS) , The

positive charge induced in the channel and the channel is depleted of electrons. Thus

there is no flow of current through this terminal.

When appositive voltage is applied between the gate and source, more electros

are induced in the channel by capacitor action. So there is a flow of current from drain

to source. As the gate source voltage increases, the channel gets wider by

accumulation of more negative charges and resistance to the channel decreases. Thus

more current from drain to source. As there is a current flow through device for zero

Gate Source Voltage, it is called as normally ON MOSFET.

38

N CHANNEL ENHANCEMENT

The N channel enhancement MOSFET is similar to the depletion type in the

construction except that there is no physical existence of the channel when it is

unbiased.

When the positive voltage is applied between the gate and the source, the

electron get accumulated in the channel by capacitive induction in the channel formed

out of electrons allowing the flow of current. This channel gets widened as more

positive voltage is applied between gate and source. There will not be any condition

through the device if the gate source voltage is negative.

Setting VGS to a constant value, varying VDS and nothing the corresponding

changes into give the drain characteristic. VGS ≤0, the device does not conduct drain

current and the device is considered to be in the off state. In this state, the entire

voltage drop across the device i.e., between drain and source.

In the ON state of the device, gate source voltage is positive and the drain

current is increased with the increase in the gate source voltage. It is understood

clearly in the transfer characteristics. As the enhancement type mosfet conduct only

after applying positive gate voltage, it is also called as normally OFF MOSFET. For

this reason it becomes easily controllable and is used in power electronics as a switch.

2.7 MICRO CONTROLLER PIC 16f877A

MICROCONTROLLER

Microcontrollers versus Microprocessors

Microcontroller differs from a microprocessor in many ways. First and the

most important is its functionality. In order for a microprocessor to be used, other

components such as memory, or components for receiving and sending data must be

added to it. In short that means that microprocessor is the very heart of the computer.

On the other hand, microcontroller is designed to be all of that in one. No other

external components are needed for its application because all necessary peripherals

are already built into it. Thus, we save the time and space needed to construct devices.

39

2.7.1 MICROCONTROLLER

The main controlling unit of the proposed system is the microcontroller. The

main features of microcontroller and particularly PIC Microcontroller is discussed

here.

A microcontroller consists of a powerful CPU tightly coupled with memory

[RAM,ROM or EPROM],various I/O features such as serial ports, parallel

ports ,timer/counters, interrupt controller ,data requisition interface , Analog to digital

converter[ADC],digital to analog converter, everything integrated into a single

silicon chip.

It does not mean that any microcontroller should have all the above said

features on a single chip, depending on the need and area of application for which it is

designed, the on chip features present in it may or may not include all the individual

section said above.

Any microcomputer systems requires memory to store a sequence of

instructions making up a program ,parallel port or serial port for communicating with

an external system timer/counter for control purpose like generating time delay.

2.7.2 PIC MICROCONTROLLER

The PIC micro was originally designed around 1980 by General Instrument

as a small, fast, inexpensive embedded microcontroller with strong I/O capabilities.

PIC stands for "Peripheral Interface Controller". General Instrument recognized the

potential for the little PIC and eventually spun off Microchip, headquartered in

Chandler, AZ to fabricate and market the PICmicro.

The PICmicro has some advantages in many applications over the older chips

such as the Intel 8048/8051/8052 and its derivatives, the Motorola MC6805/6hHC11,

and many others. Its unusual architecture is ideally suited for embedded control.

Nearly all instructions execute in the same number of clock cycles, which makes

timing control much easier. The PICmicro is a RISC (Reduced Instruction Set

Computer) design, with only thirty-odd instructions to remember; its code is

40

extremely efficient, allowing the PIC to run with typically less program memory than

its larger competitors.

Very important, though, is the low cost, high available clock speeds, small

size, and incredible ease of use of the tiny PIC. For timing-insensitive designs, the

oscillator can consist of a cheap RC network. Clock speeds can range from low speed

to 20MHz. Versions of the various PICmicro families are available that are equipped

with various combinations ROM, EPROM, OTP (One-Time Programmable) EPROM,

EEPROM, and FLASH program and data memory. An 18-pin PICmicro typically

devotes 13 of those pins to I/O, giving the designer two full 8-bit I/O ports and an

interrupt. In many cases, designing with a PICmicro is much simpler and more

efficient than using an older, larger embedded microprocessor.

2.7.3 FEATURES OF PIC CONTROLLER:

High performance RISC CPU

• Only 35 single word instructions to learn

• All single cycle instructions except for program branches which are two cycle

• Operating speed: DC - 20 MHz clock input DC - 200 ns instruction cycle

• Up to 8K x 14 words of FLASH Program Memory, Up to 368 x 8 bytes of Data

Memory (RAM) Up to 256 x 8 bytes of EEPROM Data Memory

• Pinout compatible to the PIC16C73B/74B/76/77

• Interrupt capability (up to 14 sources)

• Eight level deep hardware stack

• Direct, indirect and relative addressing modes

• Power-on Reset (POR)

• Power-up Timer (PWRT) and Oscillator Start-up Timer (OST)

• Watchdog Timer (WDT) with its own on-chip RC oscillator for reliable peration

• Programmable code protection

• Power saving SLEEP mode

• Selectable oscillator options

• Low power, high speed CMOS FLASH/EEPROM technology

• Fully static design

• In-Circuit Serial Programming (ICSP) via two pins

41

• Single 5V In-Circuit Serial Programming capability

• In-Circuit Debugging via two pins

• Processor read/write access to program memory

• Wide operating voltage range: 2.0V to 5.5V

• High Sink/Source Current: 25 mA

• Commercial, Industrial and Extended temperature ranges

• Low-power consumption:

2.7.4 ADVANTAGES OF MICROCONTROLLER

If a system is developed with a microprocessor the designer has to go for

external memory such as RAM ,ROM or EPROM and peripherals and hence

the size of the PCB will large enough to

hold all the required peripheral. But, the microcontroller has got all there

peripheral facilities on a single chip so developed of a similar system with a

microcontroller reduces PCB size and cost of the design.

One of the major difference between a microcontroller and a microprocessor is

that a controller. often deals with bits,not bytes as in the real world

application, for example switch contacts can only be open or close ,indicators

should be lit or dark and motors can be either turned on or off and so forth.

The microcontroller has two 16 bits timer/counters built within it, which

makes it more suitable to this application since, we need to produce some

accurate time delays.

This microcontroller has a 8 bit internal Analog to digital converter with a 10

bit resolution, which will after the usage of external ADC and the circuit and

hardware complexity.

These controllers also have an higher erase cycle of 10,000 and for the

EEPROM its 1 lakh number of time. This controllers other advantage is it’s a

RISC computing system.

42

2.7.2 PIN DIAGRAM OF 16F877A PIC CONTROLLER

Fig35: pin diagram of PIC

2.7.3 I/O PORTS

Some pins for these I/O ports are multiplexed with an alternate function for the

peripheral features on the device. In general, when a peripheral is enabled, that pin

may not be used as a general purpose I/O pin. Additional information on I/O ports

may be found in the PICmicro™ Mid-Range Reference Manual, (DS33023).

PORTA AND THE TRISA REGISTER

43

PORTA is a 6-bit wide, bi-directional port. The corresponding data direction

register is TRISA. Setting a TRISA bit (= 1) will make the corresponding PORTA pin

an input (i.e., put the corresponding output driver in a Hi-Impedance mode). Clearing

a TRISA bit (= 0) will make the corresponding PORTA pin an output (i.e., put the

contents of the output latch on the selected pin). Reading the PORTA register reads

the status of the pins, whereas writing to it will write to the port latch. All write

operations are read-modify-write operations. Therefore, a write to a port implies that

the port pins are read, the value is modified and then written to the port data latch. Pin

RA4 is multiplexed with the Timer0 module clock input to become the RA4/T0CKI

pin. The RA4/T0CKI pin is a Schmitt Trigger input and an open drain output. All

other PORTA pins have TTL input levels and full CMOS output drivers. Other

PORTA pins are multiplexed with analog inputs and analog VREF input. The

operation of each pin is selected by clearing/setting the control bits in the ADCON1

register (A/D Control Register1).

PORTB AND THE TRISB REGISTER

PORTB is an 8-bit wide, bi-directional port. The corresponding data direction

register is TRISB. Setting a TRISB bit (= 1) will make the corresponding PORTB pin

an input (i.e., put the corresponding output driver in a Hi-Impedance mode). Clearing

a TRISB bit (= 0) will make the corresponding PORTB pin an output (i.e., put the

contents of the output latch on the selected pin). Three pins of PORTB are

multiplexed with the Low Voltage Programming function: RB3/PGM, RB6/PGC and

RB7/PGD. The alternate functions of these pins are described in the Special Features

Section. Each of the PORTB pins has a weak internal pull-up. A single control bit can

turn on all the pull-ups. This is performed by clearing bit RBPU (OPTION_REG<7>).

The weak pull-up is automatically turned off when the port pin is configured as an

output. The pull-ups are disabled on a Power-on Reset.

Four of the PORTB pins, RB7:RB4, have an interrupton- change feature. Only

pins configured as inputs can cause this interrupt to occur (i.e., any RB7:RB4 pin

configured as an output is excluded from the interrupton- change comparison). The

input pins (of RB7:RB4) are compared with the old value latched on the last read of

PORTB. The “mismatch” outputs of RB7:RB4 are OR’ed together to generate the RB

Port Change Interrupt with flag bit RBIF (INTCON<0>).

44

PORT C AND THE TRISC REGISTER

PORTC is an 8-bit wide, bi-directional port. The corresponding data direction

register is TRISC. Setting a TRISC bit (= 1) will make the corresponding PORTC pin

an input (i.e., put the corresponding output driver in a Hi-Impedance mode). Clearing

a TRISC bit (= 0) will make the corresponding PORTC pin an output (i.e., put the

contents of the output latch on the selected pin). PORTC is multiplexed with several

peripheral functions (Table 3-5). PORTC pins have Schmitt Trigger input buffers.

When the I2C module is enabled, the PORTC<4:3> pins can be configured with

normal I2C levels or with SMBus levels by using the CKE bit (SSPSTAT<6>). When

enabling peripheral functions, care should be taken in defining TRIS bits for each

PORTC pin. Some peripherals override the TRIS bit to make a pin an output, while

other peripherals override the TRIS bit to make a pin an input. Since the TRIS bit

override is in effect while the peripheral is enabled, read-modify write instructions

(BSF, BCF, XORWF) with TRISC as destination, should be avoided. The user should

refer to the corresponding peripheral section for the correct TRIS bit settings.

PORTD and TRISD Registers

PORTD and TRISD are not implemented on the PIC16F873 or PIC16F876.

PORTD is an 8-bit port with Schmitt Trigger input buffers. Each pin is individually

configurable as an input or output. PORTD can be configured as an 8-bit wide

microprocessor port (parallel slave port) by setting control bit PSPMODE

(TRISE<4>). In this mode, the input buffers are TTL.

PORTE AND TRISE REGISTER

PORTE has three pins (RE0/RD/AN5, RE1/WR/AN6 and RE2/CS/AN7) which

are individually configurable as inputs or outputs. These pins have Schmitt Trigger

input buffers. The PORTE pins become the I/O control inputs for the microprocessor

port when bit PSPMODE (TRISE<4>) is set. In this mode, the user must make certain

that the TRISE<2:0> bits are set and that the pins are configured as digital inputs.

Also, ensure that ADCON1 is configured for digital I/O. In this mode, the input

buffers are TTL. Register 4-1 shows the TRISE register which also controls the

Parallel Slave Port operation. PORTE pins are multiplexed with analog inputs. When

45

selected for analog input, these pins will read as ‘0’s. TRISE controls the direction of

the RE pins, even when they are being used as analog inputs. The user must make

sure to keep the pins configured as inputs when using them as analog inputs.

2.7.4 DATA EEPROM AND FLASH PROGRAM MEMORY

The Data EEPROM and FLASH Program Memory are readable and writable during

normal operation over the entire VDD range. These operations take place on a single

byte for Data EEPROM memory and a single word for Program memory. A write

operation causes an erase-then-write operation to take place on the specified byte or

word. A bulk erase operation may not be issued from user code (which includes

removing code protection). Access to program memory allows for checksum

calculation. The values written to program memory do not need to be valid

instructions. Therefore, up to 14-bit numbers can be stored in memory for use as

calibration parameters, serial numbers, packed 7-bit ASCII, etc. Executing a program

memory location containing data that form an invalid instruction, results in the

execution of a NOP instruction. The EEPROM Data memory is rated for high erase/

writes cycles (specification D120). The FLASH program memory is rated much lower

(specification D130), because EEPROM data memory can be used to store frequently

updated values. An on-chip timer controls the write time and it will vary with voltage

and temperature, as well as from chip to chip. Please refer to the specifications for

exact limits (specifications D122 and D133). A byte or word write automatically

erases the location and writes the new value (erase before write). Writing to EEPROM

data memory does not impact the operation of the device. Writing to program memory

will cease the execution of instructions until the write is complete. The program

memory cannot be accessed during the write. During the write operation, the

oscillator continues to run, the peripherals continue to function and interrupt events

will be detected and essentially “queued” until the write is complete. When the write

completes, the next instruction in the pipeline is executed and the branch to the

interrupt vector will take place, if the interrupt is enabled and occurred during the

write. Read and write access to both memories take place indirectly through a set of

Special Function Registers (SFR). The six SFRs used are:

• EEDATA

46

• EEDATH

• EEADR

• EEADRH

• EECON1

• EECON2

TIMER0 MODULE

The Timer0 module timer/counter has the following features:

• 8-bit timer/counter

• Readable and writable

• 8-bit software programmable prescaler

• Internal or external clock select

• Interrupt on overflow from FFh to 00h

• Edge select for external clock

Additional information on the Timer0 module is available in the PICmicro™

Mid-Range MCU Family Reference Manual (DS33023). Timer mode is selected by

clearing bit T0CS (OPTION_REG<5>). In Timer mode, the Timer0 module will

increment every instruction cycle (without prescaler). If the TMR0 register is written,

the increment is inhibited for the following two instruction cycles. The user can work

around this by writing an adjusted value to the TMR0 register

TIMER1 MODULE

The Timer1 module is a 16-bit timer/counter consisting of two 8-bit registers

(TMR1H and TMR1L), which are readable and writable. The TMR1 Register pair

(TMR1H:TMR1L) increments from 0000h to FFFFh and rolls over to 0000h. The

TMR1 Interrupt, if enabled, is generated on overflow, which is latched in interrupt

flag bit TMR1IF (PIR1<0>). This interrupt can be enabled/disabled by

setting/clearing TMR1 interrupt enable bit TMR1IE (PIE1<0>). Timer1 can operate

in one of two modes:

• As a timer

• As a counter

47

The operating mode is determined by the clock select bit, TMR1CS (T1CON<1>). In

Timer mode, Timer1 increments every instruction cycle. In Counter mode, it

increments on every rising edge of the external clock input. Timer1 can be

enabled/disabled by setting/clearing control bit, TMR1ON (T1CON<0>). Timer1 also

has an internal “Reset input”. This Reset can be generated by either of the two CCP

modules. Register 6-1 shows the Timer1 Control register. When the Timer1 oscillator

is enabled (T1OSCEN is set), the RC1/T1OSI/CCP2 and RC0/T1OSO/T1CKI pins

become inputs. That is, the TRISC<1:0> value is ignored and these pins read as ‘0’.

TIMER2 MODULE

Timer2 is an 8-bit timer with a prescaler and a postscaler. It can be used as the

PWM time-base for the PWM mode of the CCP module(s). The TMR2 register is

readable and writable, and is cleared on any device RESET. The input clock

(FOSC/4) has a prescale option of 1:1,1:4, or 1:16, selected by control bits

T2CKPS1:T2CKPS0 (T2CON<1:0>). The Timer2 module has an 8-bit period

register, PR2. Timer2 increments from 00h until it matches PR2 and then resets to 00h

on the next increment cycle. PR2 is a readable and writable register. The PR2 register

is initialized to FFh upon RESET. The match output of TMR2 goes through a 4-bit

postscaler (which gives a 1:1 to 1:16 scaling inclusive) to generate a TMR2 interrupt

(latched in flag bit TMR2IF, (PIR1<1>)). Timer2 can be shut-off by clearing control

bit TMR2ON (T2CON<2>), to minimize power consumption.

2.7.5 CRYSTAL OSCILLATOR

Every PIC needs a clock. The PIC uses four clock cycles to complete one

instruction cycle. Since the PIC is fully static, the clock rate can vary from DC

(nothing) to the maximum rated speed, which is currently around 20MHz for some

parts. What do we mean by "fully static"? Some microprocessors use some dynamic

circuitry internally, which operate similar to dynamic RAM. These processors have a

certain specified minimum clock frequency which must be maintained, just like a

minimum power supply voltage. The PIC has no such limitation; the processor clock

can be completely stopped. In fact, the SLEEP instruction does just that - shuts down

48

the clock oscillator! This leads to enormous power savings. A PIC in sleep mode

will draw just a few microamperes.

There are several methods of clocking a PIC. These are:

LP - Low power crystal

XT - Crystal or ceramic resonator

HS - High Speed crystal or resonator

RC - Resistance/capacitance

We are using crystal oscillator in our project. The first three methods use either

a parallel-cut crystal or a ceramic resonator. LP mode is generally used for low-

power applications using watch-type crystals or ceramic resonators in the 32 kHz to

200 kHz range. XT mode is used from typically 455 kHz to 4MHz, and HS mode is

usually used above 4MHz. The modes are very similar except for the amount of drive

supplied to the crystal. In these three modes, an external clock source can also be

used instead of a crystal or resonator. If you have an existing clock signal of the

desired frequency in your circuit, you can connect this signal to the OSC1 pin and

leave the OSC2 pin open.

When using a crystal or resonator, it is good practice to connect a small

capacitor from each OSC lead to ground. This helps assure stable oscillator operation

and reliable start-up. Consult the Microchip data sheet for your processor and the

specs for your crystal for the recommended values, but 15pF to 33pF seems to be

adequate for most clock frequencies over 400kHz or so.

The last mode is RC mode. If your application is not at all timing sensitive, RC

mode is simple and inexpensive. To use this mode, you simply connect and external

resistor ranging from 5K to 100K Ohms from Vdd to OCS1, and an external capacitor

from OSC1 to Vss. The external capacitor can be eliminated, but Microchip warns

that the frequency can vary widely and change often. They recommend at least 20pF

of external capacitance for anything resembling stable operation. Of course, RC

mode will be affected much more than any of the crystal or resonator modes by

temperature, part to part variations, etc.

49

2.7 LEAD ACID BATTERY

Battery specifications

Fig36:A valve-regulated, sometimes called "sealed", lead acid battery

Energy/weight 30-40 Wh/kg

Energy/size 60-75 Wh/L

Power/weight 180 W/kg

Charge/discharge efficiency 70%-92%

Energy/consumer-price 7(sld)-18(fld) Wh/US$ [1]

Self-discharge rate 3%-20%/month [2]

Cycle durability 500-800 cycles

Nominal Cell Voltage 2.105 V

50

Lead-acid batteries are the oldest type of rechargeable battery. Despite having

the second lowest energy-to-weight ratio (next to the nickel-iron battery) and a

correspondingly low energy-to-volume ratio, their ability to supply high surge

currents means that the cells maintain a relatively large power-to-weight ratio. These

features, along with their low cost, makes them attractive for use in cars, as they can

provide the high current required by automobile starter motors. They are also used in

vehicles such as forklifts, in which the low energy-to-weight ratio may in fact be

considered a benefit since the battery can be used as a counterweight. Large arrays of

lead-acid cells are used as standby power sources for telecommunications facilities,

generating stations, and computer data centers. They are also used to power the

electric motors in diesel-electric (conventional) submarines.

Electrochemistry

Each cell contains (in the charged state) electrodes of lead metal (Pb) and lead (IV)

oxide (PbO2) in an electrolyte of about 37% w/w (5.99 Molar) sulfuric acid (H2SO4).

In the discharged state both electrodes turn into lead (II) sulfate (PbSO4) and the

electrolyte loses its dissolved sulfuric acid and becomes primarily water. Due to the

freezing-point depression of water, as the battery discharges and the concentration of

sulfuric acid decreases, the electrolyte is more likely to freeze.

The chemical reactions are (charged to discharged):

Anode (oxidation):

Cathode (reduction):

Because of the open cells with liquid electrolyte in most lead-acid batteries,

overcharging with excessive charging voltages will generate oxygen and hydrogen

gas by electrolysis of water, forming an explosive mix. This should be avoided.

Caution must also be observed because of the extremely corrosive nature of sulfuric

acid.

51

Practical cells are usually not made with pure lead but have small amounts of

antimony, tin, or calcium alloyed in the plate material. These are general voltage

ranges for six-cell lead-acid batteries:

Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10-2.13V per cell)

Open-circuit at full discharge: 11.8 V to 12.0 V

Loaded at full discharge: 10.5 V.

Continuous-preservation (float) charging: 13.8 V for gelled electrolyte; 13.5 V

for AGM (absorbed glass mat) and 13.4 V for flooded

1. All voltages are at 20 °C, and must be adjusted -0.022V/°C for temperature

changes. (note: this value seams far too high: it's usually -0.003V/°C)

2. Float voltage recommendations vary, according to the manufacturer's

recommendation.

3. Precise (±0.05 V) float voltage is critical to longevity; too low (sulfation) is

almost as bad as too high (corrosion and electrolyte loss)

Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's

recommendation)

Equalization charging (for flooded lead acids): 15 V for no more than 2 hours.

Battery temperature must be monitored.

Gassing threshold: 14.4 V

After full charge the terminal voltage will drop quickly to 13.2 V and then

slowly to 12.6 V.

CONSTRUCTION OF BATTERY

Plates

The principle of the lead acid cell can be demonstrated with simple sheet lead

plates for the two electrodes. However such a construction would only produce

around an amp for roughly postcard sized plates, and it would not produce such a

current for more than a few minutes.

52

Gaston Planté realized that a plate construction was required that gave a much

larger effective surface area. Planté's method of producing the plates has been largely

unchanged and is still used in stationary applications.

The Faure pasted-plate construction is typical of automotive batteries. Each plate

consists of a rectangular lead grid alloyed with antimony or calcium to improve the

mechanical characteristics. The holes of the grid are filled with a mixture of red lead

and 33% dilute sulfuric acid. (Different manufacturers have modified the mixture).

The paste is pressed into the holes in the plates which are slightly tapered on both

sides to assist in retention of the paste. This porous paste allows the acid to react with

the lead inside the plate, increasing the surface area many fold. At this stage the

positive and negative plates are similar; however expanders and additives vary their

internal chemistry to assist in operation when in use. Once dry, the plates are then

stacked together with suitable separators and inserted in the battery container. An odd

number of plates is usually used, with one more negative plate than positive. Each

alternate plate is connected together. After the acid has been added to the cell, the cell

is given its first forming charge. The positive plates gradually turn the chocolate

brown color of lead dioxide, and the negative turn the slate gray of 'spongy' lead. Such

a cell is ready to be used.

One of the problems with the plates in a lead-acid battery is that the plates

change size as the battery charges and discharges, the plates increasing in size as the

active material absorbs sulfate from the acid during discharge, and decreasing as they

give up the sulfate during charging. This causes the plates to gradually shed the paste

during their life. It is important that there is plenty of room underneath the plates to

catch this shed material. If this material reaches the plates a shorted cell will occur.

Separators

Separators are used between the positive and negative plates of a lead acid

battery to prevent short circuit through physical contact, mostly through dendrites

(‘treeing’), but also through shedding of the active material. Separators obstruct the

flow of ions between the plates and increase the internal resistance of the cell. Various

materials have been used to make separators:

53

wood

rubber

glass fiber mat

cellulose

sintered PVC

Microporous PVC/polyethylene.

An effective separator must possess a number of mechanical properties;

applicable considerations include permeability, porosity, pore size distribution,

specific surface area, mechanical design and strength, electrical resistance, ionic

conductivity, and chemical compatibility with the electrolyte. In service, the separator

must have good resistance to acid and oxidation. The area of the separator must be a

little larger than the area of the plates to prevent material shorting between the plates.

The separators must remain stable over the operating temperature range of the battery.

BY APPLICATION

Stand-by (stationary) batteries

Motor vehicle starting, lighting and ignition (SLI) batteries

Traction (propulsion) batteries

54

CHAPTER-3

SOFTWARE CODING

55

CODING FOR PIC CONTROLLER:

The following is the code used for PIC controller for giving delay time to switches,

#include<pic.h>#include<stdio.h>#include "delay.c"

__CONFIG(0x3f71);

unsigned char n=1;void main() RBPU=0; TRISC=0x00; PORTC=0x00;

while(1) if(RB0==0) n=1; if(RB1==0) n=2; if(n==1)

PORTC=0x09; DelayMs(10); PORTC=0x06; DelayMs(10); else if(n==2)

PORTC=0x90; DelayMs(10); PORTC=0x60; DelayMs(10);

56

CHAPTER-4

CIRCUIT DIAGRAM

57

FULL BRIDGE BIDIRECTIONAL DC-DCCONVERER:

Fig37: circuit diagram for bidirectional dc-dc converter

DRIVER CIRCUIT TO THE SOURCE OF MOSFET

58

Fig38: driver circuit

PIC CONTROLLER:

Fig39: circuit for PIC

BLOCK DIAGRAM OF BIDIRECTIONAL DC-DC CONVERTER:

59

Fig40: Boost operation of bidirectional dc-dc converter

Fig41: Buck operation of bidirectional dc-dc converter

60

CHAPTER-4

CIRCUIT OPERATION

61

The circuit topology of the proposed bidirectional isolated converter is shown

in Fig. . According to the power flow directions, there are two operation modes for the

proposed converter. When power flows from the low-voltage side (LVS) to the high-

voltage side (HVS), the circuit operates in boost mode to draw energy from the

battery. In the other power flow direction, the circuit operates in buck mode to

recharge the battery from the high-voltage dc bus. Based on the symbols and signal

polarities introduced in Fig. 2, the theoretical waveforms of the two operation modes

are shown in Fig. (a) and (b), respectively.

62

Fig42: Theoretical waveform under (a) boost and (b) buck operation

A. Boost Mode (Discharging Mode) Operation

When the dc bus voltage in the HVS is not at the desired high level, such as

during a cold start, the power drawn from the low-voltage battery flows into the high-

voltage dc bus. During this mode, the proposed converter is operated as a current-fed

circuit to boost the HVS bus voltage. The LVS switches Q1, Q4 and Q2, Q3 operate

at asymmetrical duty ratios and 1- which require a short overlapping conduction

interval. Referring to the equivalent circuits for the boost mode operation in Fig. 43,

the detailed operating principle can be explained as follows.

63

Fig43: modes of operation in boost mode

Stage 1 (t0–t1): At t0, the LVS switch Q2, Q3 is turned off and the HVS switch Q5,

Q8 is turned on. The current from the inductor L1 flows through Q1, Q4 and the

transformer LVS winding, closing the loop via the battery. Therefore, the transformer

LVS winding carries only IL1. The voltage amplitude across the transformer HVS

winding, V2 can be clamped to the dc voltage. Thus, the voltage across the

transformer LVS winding, V1 is clamped to (-VA/n). The “n” is the transformer turn

ratio.

64

Stage 2 (t1–t2): At t1, the LVS switch Q2, Q3 is turned on and the HVS switch Q5,

Q8 is turned off. During this interval, the switches Q1, Q4 and Q2, Q3 are on

simultaneously. The voltage across the transformer winding become zero

Stage 3 (t2–t3): The voltage Vds6 & Vds8 across the HVS switch, Q6, Q7 continues

to decrease to zero at t3.

Stage 4 (t3–t4): At t3, as long as the switch Q6, Q7 is turned on at t4, zero-voltage

switching can be assured.

Stage 5 (t4–t5): At t4, the LVS switch Q1, Q4 is turned off and the HVS switch Q6,

Q7 is turned on. The current from the inductor L1 flows through Q2, Q3 and the

transformer LVS winding, closing the loop via the battery. Therefore, the transformer

LVS winding carries only IL1. The voltage amplitude across the transformer HVS

winding, V2 can be clamped to (VBus-VA). Thus, the voltage across the transformer

LVS winding, V1 is clamped to (VBus-VA) /n.

Stage 6 (t5–t6): At t5, the LVS switch Q1, Q4 is turned on and the HVS switch Q6,

Q7 is turned off. During this interval, the switches Q1, Q4 and Q2, Q3 are

simultaneously on. The voltage across L1 also becomes negative and its’ amplitude

equals the battery voltage. The inductance current, IL1 decreases linearly. The voltage

across the transformer winding become zero.

Stage 7 (t6–t7): The voltage Vds5 & Vds8 across the HVS switch, Q5,Q8 continues

to decrease to zero at t7.

Stage 8 (t7–t8): At t7, as long as the switch Q5, Q8 is turned on at t8, zero-voltage

switching can be assured. The circuit will then proceed back to stage 1 after

completing one operating cycle T8.

Based on the above analysis, the voltage and current stresses

of the LVS switches can be found

Although the LVS switches subject to higher voltage stress, this is an advantage

because the battery voltage is low. Because the overlapping interval for the LVS

switches Q1, Q4 and Q2, Q3 is very short, the LVS transformer current flows through

65

only one LVS switch at most time. Thus, the conduction losses for Q1, Q4 and Q2,

Q4 can be greatly reduced to improve the conversion efficiency. Moreover, the LVS

circuit produces a relatively ripple free battery current that is desirable for the low

voltage battery. The voltage transfer ratio Mboost for the boost mode operation for the

proposed dc–dc converter can be derived from the volt-second balance condition

across the inductor L1 represented by (7). The current stresses of the inductor

windings can be also determined as (6).The inductances of the power inductor L1 can

be determined for their given peak-to-peak current ripples, ΔI1

Where λ (%) is the ripple percentage of the inductor currents IL1

B. Buck Mode (Charging Mode) Operation

Different from the traditional electric vehicle driving system, the fuel cell

powered system needs an additional energy storage device to absorb the feedback

power from the electric machine. This energy storage device may be a lead-acid

battery as shown in Fig. . The proposed circuit works in buck mode to recharge the

battery from high-voltage dc bus. During this mode, the proposed converter is

operated as an asymmetrical half bridge circuit with synchronous rectification current

doubler to recharge the battery from high-voltage dc bus. The HVS switches Q5, Q8

and Q6, Q7 operate at asymmetrical duty ratios and 1- which require short and

well-defined dead time between the conduction intervals. Referring to the equivalent

circuits in Fig. , the detailed operating principle of this mode can be explained as

follows.

66

Fig44: modes of operation in buck mode

Stage 1(t0–t1): At t0, the HVS switch Q6, Q7 and the LVS switch Q2, Q3 stay on.

The inductance current is equal to –IL1/n. The current from the inductor L1 flows

through Q2, Q3 and the transformer LVS winding, closing the loop via the battery.

Therefore, the transformer LVS winding carries only –IL1. The current –IL1

increases. Since the recharging current, -IBat.

Stage 2 (t1–t2): At t1, the LVS switch Q1, Q4 is turned on and the HVS switch Q6,

Q7 is turned off. During this interval, the switches Q1, Q4 and Q2, Q3 are

simultaneously on. The recharging current, -IBat , freewheels through both the

switches, Q1, Q4 and Q2, Q3. The voltage across L1 also becomes negative and

equals the battery voltage. Therefore, the inductance current –IL1 decreases. The

67

voltage across the transformer winding becomes zero. The voltage Vds5 & Vds8

across the switch, Q5, Q8 continues to decrease to zero at t2.

Stage 3 (t2–t3): At t2, as long as the HVS switch Q5, Q8 is turned on before the

inductor current changes its direction at t3, zero voltage switching can be assured.

Stage 4 (t3–t4): While the HVS switch, Q5, Q8 is zero-voltage turned on, the LVS

switch, Q2, Q3 is turned off.

The stages 5–8 are similar to stages 1–4, respectively.

The circuit will then proceed back to stage 1 after completing one operating cycle

TS.

While the LVS switches, Q1, Q4 and Q2, Q3, share unequal voltage and current

stresses, the HVS switches, Q5, Q8 and Q6, Q7, share equal voltage stresses as (8).

Then the current stresses of the HVS switches can be found as

DESIGN CONSIDERATIONS FOR KEY COMPONENTS

To verify the feasibility of the proposed scheme, a 2-kW laboratory prototype

operated at 20 kHz was built. The simulation and experimental results will be shown

and discussed in the next section. The LVS of the design example was connected to a

12-V lead-acid battery whose terminal voltage could swing from 10–15 V. The

nominal voltage on the HVS dc bus was designed to 300 V, with an operating range

from 150–400 V. The design considerations

A. Power Switches

The power switch voltage and current ratings are very important converter

design topics. When the duty ratio is chosen in the operating range of from 0.2 to

0.5, the LVS device rating can be calculated by using (1)–(4) as follows:

68

Based on (5), the turn-ratio selection of transformer can be calculated as (15). The

HVS device ratings can then be calculated using (8)–(10) as follows:

B. Power Inductors

Let the peak-to-peak current ripples be 20% of the inductor currents under full

power. The current rating and the inductance of the power inductor L1 can be

determined using (6)– (7) as follows:

Because of the ripple cancellation on the battery current, a larger ripple current in

inductor L1 and can be allowed in practical applications. Thus, the inductance and the

size of the inductors L1 might be smaller.

69

CHAPTER-5

SIMULATION &

RESULTS

70

To verify the theoretical operating principles, a 2-kW design example was

simulated by using MATLAB. There is a good agreement between the simulation

results and theoretical analysis. In this research, a 2-kW laboratory prototype was

implemented and tested to evaluate the performance of the proposed bidirectional

isolated dc–dc converter. Fig47, 48, 49 shows the waveforms in the boost mode

operations for the laboratory prototype & Fig 49, 50, 51 shows the waveforms for

buck mode operation. The gating signals for the LVS switches Q1, Q4, & Q2, Q3 and

HVS switches Q5,Q8 & Q6, Q7 are shown in Fig. . The ripple cancellation between

two inductor currents can be observed. This is desirable for a low-voltage battery. In

Fig 48 and 50, the zero-voltage turn-on details of the LVS switch Q3 and HVS switch

Q5 shown. For the full-bridge topology, the peak voltage across the LVS switches is

around 45 V, allowing 75-V MOSFET to be used.

5.1 BOOST OPERATION FOR BIDIRECTIONAL DC-DC

CONVERTER

71

Fig45

5.1.1SUBCIRCUIT:

5.2 BUCK OPERATION:

Fig46

72

5.2.1SUBCIRCUIT:

5.3 RESULTANT WAVE FORM:

5.3.1 BOOST OPERATION:

Input wave form:

Fig 47

73

Output waveform:

Fig48

ZVS Waveform:

74

Fig49

Current & Voltage Wave Form of Primary Side Transformer:

Fig50

Input pulses to mosfet

75

Fig 51

5.4 BUCK OPERATION:

Input voltage waveform

Fig 52

Out put voltage:

76

Fig53

ZVS Wave Form:

Fig54

Current & Voltage Waveform Of Primary Side Of Transformer:

77

Fig55

Input pulses to mosfet:

Fig 56

78

CHAPTER-6

CONCLUSION

79

A soft-switched isolated bidirectional dc–dc converter has been

implemented in this project. The operation, analysis, features and design

consideration were illustrated. Simulation and experimental results for the

200W, 20 kHz prototype was shown as per principle. It is shown that

ZVS in either direction of power flow is achieved with no lossy

components involved, no additional active switch, no additional TDR

exhibited. Thanks to the dual functions (simultaneous boost conversion

and inversion) provided by the low voltage side half bridge, current

stresses on the switching devices and transformer are kept minimum. As

results, advantages of the new circuit including ZVS with full load range,

decreased device count, high efficiency (measured more than 94% at

rated power), and low cost as well as less control and accessory power

needs, make the proposed converter very promising for medium power

applications with high power density.

80

FUTURE SCOPE

The bidirectional dc-dc converter instead of full bridge isolated

configuration can be made as half bridge isolated configuration using several half

bridge configurations. This half bridge will have less device count and simple circuit,

therefore it is more economic and we can achieve high efficiency than full bridge

configuration. This circuit will have more advantages than full bridge configuration.

81

BIBILOGRAPHY

The bibliography used fro the project “A BIDIRECTIONAL DC-DC

CONVERTER USED FOR ELECTRICAL VEHICLE DRIVING SYSTEM” is as

follows.

ARTICLES:

1. A Bidirectional DC–DC Converter for Fuel Cell Electric Vehicle

Driving System

By Huang-Jen Chiu, Member, IEEE, and Li-Wei Lin,

IEEE Transactions on Power Electronics, Vol. 21, No. 4, July 2006

BOOKS:

Power Electronics P.S. Bimbra

&

Vedam

Subramanyam

Micro controllers A.K. Ray

WEBSITE:

1. GOOGLE

2. Wikipedia

3. Other Websites

82

APPENDIX:

_ Advanced Process Technology_ Dynamic dv/dt Rating_ 175°C Operating Temperature_ Fast Switching_ Fully Avalanche Rated_ Ease of ParallelingSimple Drive Requirements

Description:

Fifth Generation HEXFETs from International Rectifier utilize advanced

processing techniques to achieve extremely low on-resistance per silicon

area. This benefit, Combined with the fast switching speed and ruggedized

device design thatHEXFET Power MOSFETs.The TO-247 package is

preferred for commercial-industrial applications where Higher power levels

preclude the use of TO-220 devices.

83

84

PIC CONTROLLER 16F877A:

PIC BLOCK DIAGRAM

85

Fig 57

86

87

88

89