A PROJECT REPORT

ON

FORCED COMMUTATION TECHNIQUES USING

ARDUINO

“SUBMITTED IN PARTIAL FULFILLMENT REQUIREMENTS FOR

THE AWARD OF THE DEGREE OF”

ELECTRICAL AND ELECTRONICS ENGINEERING

Submitted by

BANOTH SUDHAKAR-(11245A0209)

UNDER THE ESTEEMED GUIDANCE OF

B.VASANTH REDDY, M.TECH (Assistant Professor)

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING

AND TECHNOLOGY

Hyderabad, Andhra Pradesh

2013-2014

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING

AND TECHNOLOGY

Hyderabad, Andhra Pradesh

CERTIFICATE

This is to certify the major project entitled FORCED COMMUTATION USING ARDUINO that

is being submitted by B.SUDHAKAR in the partial fulfillment for the award of the Degree of Bachelor of

Technology in Electrical and Electronics Engineering in the Jawaharlal Nehru Technological University is

a record of bona-fide work carried out by them under my guidance and supervision. The results embodied

in this project report have not been submitted to any other University or Institute for the award of any

Graduation degree.

Under the Guidance of H.O.D

B.VASANTH REDDY, M.TECH Dr.M.CHAKRAVARTHY

(Assistant professor)

External Examiner

GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING

AND TECHNOLOGY

Hyderabad, Andhra Pradesh

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

Batch No.B13

K.VINAY KUMAR (10241A0292)

N.VIJAY KUMAR (10241A02A3)

P.SIVAIAH (10241A02A5)

B.SUDHAKAR (11245A0209)

Under the Guidance of

B.VASANTH REDDY

M.TECH (NIT), (Assistant professor)

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING

AND TECHNOLOGY

Hyderabad, Andhra Pradesh

2013-2014

ACKNOWLEDGEMENT

This is to place on record my appreciation and deep gratitude to the persons without whose support

this project would never see the light of day. I have immense pleasure in expressing my thanks and deep sense of gratitude to my guide Mr.

B.Vasanth reddy, Assistant Professor, Department of Electrical and Electronics Engineering, G.R.I.E.T for his guidance throughout this project.

I wish to express my profound sense of gratitude to Mr. P. S. Raju, Director, and G.R.I.E.T for his guidance, encouragement, and for all facilities to complete this project.

I also express my sincere thanks to Dr. M. Chakravarthy, Head of the Department, G.R.I.E.T and

for extending their help. Finally I express my sincere gratitude to Mr. E. Venkateshvarulu, Associate Professor, Professor,

Department of Electrical and Electronics Engineering, G.R.I.E.T and all the members of the faculty and my friends who contributed their valuable advice and helped to complete the project successfully.

BY

BANOTH SUDHAKAR

ABSTRACT

This project mainly focus on various forced commutation techniques used in various DC to DC

converters operating at high voltages, thyristors based inverters. The name forced commutation means

turning off of the device by applying reverse voltage across device and making current through device zero

using auxiliary devices, capacitors and inductors.

These techniques are used only for DC supply operated converters which does not have natural current

zero. In order to control output voltage of converter to desired level converter switches are on and off by

forced commutation. The various forced commutation techniques used in choppers and inverters are self

commutation or load commutation (class A), resonant commutation or current commutation (class B),

complimentary commutation (class C), impulse or voltage commutation (Class D).

In this project forced commutation is obtained by turning on and off of main and auxiliary thyristors by

generating gating pulses using software coding in Arduino UNO. This pulses are generated based on

switching times of devices in order obtain desired output voltages.

i

CONTENTS

Abstract i

Contents ii

List of figures iii

Tables iv

Legends v

Abbreviation and acronyms vi

Result vii

Date sheet of devices viii

ii

CHAPTER-1

COMPONENTS OF CIRCUIT

1.1. Introduction 1

1.2. Resistance 3

1.3. Inductor 4

1.4. Capacitor 5

1.5. thyristor

1.5.1. Introduction 8

1.5.2. thyristor symbol and operation 9

1.5.3. Triggering characteristics 11

1.5.4. Latch and hold characteristics 12

1.5.5. Switching characteristics 12

CHAPTER-2

DC POWER SUPPLY DESIGN

2.1 Introduction 16

2.2 Circuit component 16

2.2.1 Voltage regulator 17

2.2.2 Transformer 18

2.2.3 Diode 19

2.2.4 Bridge rectifier 22

CHAPTER-3

TRIGGERING CIRCUIT DESIGN

3.1 Introduction 24

iii

3.2 opto -isolator 24

3.3 photo diode opto-isolator 25

3.4 photo transistor opto-isolator 27

3.5 silicon controlled rectifier (SCR) 28

CHAPTER-4

ARDUINO

4.1 Introduction 31

4.2 digital arduino 31

4.3 analog arduino 32

4.4 output signals 33

4.5 input signals 34

4.6 Serial setup 36

CHAPTER-5

COMMUTATION TECHNIQUES

5.1 Introduction 38

5.2 line commutation 38

5.3 forced commutation 40

5.3.1 Voltage commutation 40

5.3.2 Current commutation 42

5.3.3 Load commutation 42

CHAPTER-6

CONCLUSION AND FUTURE WORK

6.1 Conclusion 49

6.2 Future work 49

iv

6.3 Reference 49

LIST OF FIGURES

CHAPTER-1

Fig no. Name of figure page no

1.1 Resistance symbol. 1

1.2 Inductor symbol. 3

1.3 Capacitor symbol and circuit diagram. 4

1.4 Representation of capacitor symbol. 5

1.5 Representation of diode symbol and schematic diagram. 8

1.6 Characteristics of diode in forward and reverse bias. 9

1.7 Silicon controlled rectifier. 11

1.8 SCR Triggering characteristics. 12

1.9 Switching characteristics of SCR. 12

CHAPTER-2

2.1 Voltage regulator with filtering capacitor. 17

2.2 Voltage regulator symbol and pin configuration. 17

2.3 Two winding Transformer. 18

2.4 Representation of diode symbol and schematic diagram. 20

2.5 Characteristics of forward and reverse bias. 21

2.6 Operating during negative half cycle. 22

2.7 DC power supply design circuit diagram. 23

v

CHAPTER-3

3.1 An opto- isolator. 24

3.2 Photo diode opto- isolator. 25

3.3 Opto-isolator. 27

3.4 Basic operating principle of a thyristor. 28

CHAPTER-4

4.1 Arduino 31

CHAPTER-5

5.1 Voltage commutation DC-DC chopper and most 40

Significant waveforms

5.2 A current commutated DC-DC chopper and 42

Most significant waveforms

5.3 Load commutation circuit 43

5.4 Output waveforms of load commutation 44

LIST OF TABLES

1. TYN612 data sheet regulator

2. 7824 date sheet regulator

vi

LEGENDS

µH - Micro Hendry

µc - Micro coulomb

R - Resistance

Ω - Ohms

VBO - Forward break over voltage

VBR - Reverse break over voltage

trr - Reverse recovery voltage

tq - circuit turn off time

β1 - Base current time1

β2 - Base current time 2

NP - Primary turn of a transformer

Ns - Secondary turns of a transformer

Ix - Internal current

Vm - Peak inverse voltage

RθJC - Thermal Resistance Junction-Cases (TO-220)

TSTG - Storage Temperature Range

TOPR - Operating temperature range

RθJA - Thermal Resistance Junction-Air (TO-220)

ITSM - Non-repetitive surge peak on-state current

IT (RMS) - RMS on-state current

VDRM - Repetitive peak off-state voltages

Vcc - common collector voltage

vii

Abbreviation and acronyms

SCR - Silicon controlled rectifier

PWM - Pulse Width Modulation

DC - Direct current

AC - Alternating current

R - Resistor

C - Capacitor

L - Inductor

1

Chapter-1

COMPONENTS OF CIRCUIT

1.1. INTRODUCTION:

Basic components in forced commutation techniques for voltage commutation, current commutation

and load commutation techniques are.

Resistor

Inductor

Capacitor

Diode

Thyristor

1.2 RESISTOR:

A resistor is a passive two-terminal electrical component that implements electrical resistance as a

circuit element. Resistors act to reduce current flow, and, at the same time, act to lower voltage levels

within circuits. Resistors may have fixed resistances or variable resistances, such as those found

in thermistors, varistors, trimmers, photoresistors and potentiometers.

Figure 1.1: Resistance symbol

The current through a resistor is in direct proportion to the voltage across the resistor's terminals. This

relationship is represented by Ohm's law:

Where I is the current through the conductor in units of amperes, V is the potential difference

measured across the conductor in units of volts, and R is the resistance of the conductor in units

of ohms (symbol :).

2

The ratio of the voltage applied across a resistor's terminals to the intensity of current in the circuit is called

its resistance, and this can be assumed to be a constant (independent of the voltage) for ordinary resistors

working within their ratings.

Resistors are common elements of electrical networks and electronic circuits and are ubiquitous

in electronic equipment. Practical resistors can be composed of various compounds and films, as well

as resistance wires (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors are also

implemented within integrated circuits, particularly analog devices, and can also be integrated

into hybrid and printed circuits.

The electrical functionality of a resistor is specified by its resistance: common commercial resistors

are manufactured over a range of more than nine orders of magnitude. When specifying that resistance in

an electronic design, the required precision of the resistance may require attention to the manufacturing

tolerance of the chosen resistor, according to its specific application.

The temperature coefficient of the resistance may also be of concern in some precision applications.

Practical resistors are also specified as having a maximum power rating which must exceed the anticipated

power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics

applications. Resistors with higher power ratings are physically larger and may require heat sinks. In a

high-voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the

resistor. While there is no minimum working voltage for a given resistor, failure to account for a resistor's

maximum rating may cause the resistor to incinerate when current is run through it.

Practical resistors have a series inductance and a small parallel capacitance; these specifications can

be important in high-frequency applications. In allow-noise amplifier or pre-amp, the noise characteristics

of a resistor may be an issue. The unwanted inductance, excess noise, and temperature coefficient are

mainly dependent on the technology used in manufacturing the resistor. They are not normally specified

individually for a particular family of resistors manufactured using a particular technology. A family of

discrete resistors is also characterized according to its form factor, that is, the size of the device and the

position of its leads (or terminals) which is relevant in the practical manufacturing of circuits using them.

3

1.2. INDUCTOR:

An inductor, also called a coil or reactor, is a passive two-terminal electrical

component which resists changes in electric current passing through it. It consists of a conductor such as a

wire, usually wound into a coil. When a current flows through it, energy is stored temporarily in a magnetic

field in the coil. When the current flowing through an inductor changes, the time-varying magnetic field

induces a voltage in the conductor, according to Faraday‟s law of electromagnetic induction, which

opposes the change in current that created it.

Figure 1.2: inductor symbol

An inductor is characterized by its inductance, the ratio of the voltage to the rate of change of current,

which has units of henries (H). Inductors have values that typically range from 1 µH (10-6H) to 1 H. Many

inductors have a magnetic core made of iron or ferrite inside the coil, which serves to increase the magnetic

field and thus the inductance. Along with capacitors and resistors, inductors are one of the three

passive linear circuit elements that make up electric circuits. Inductors are widely used in alternating

current (AC) electronic equipment, particularly in radio equipment. They are used to block the flow of AC

current while allowing DC to pass; inductors designed for this purpose are called chokes. They are also

used in electronic filters to separate signals of different frequencies, and in combination with capacitors to

make tuned circuits, used to tune radio and TV receivers.

4

1.3. CAPACITOR:

A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to

store energy electro statically in an electric field. The forms of practical capacitors vary widely, but all

contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator). The conductors

can be thin films of metal, aluminum foil or disks, etc. The 'none conducting' dielectric acts to increase the

capacitor's charge capacity. A dielectric can be glass, ceramic, plastic film, air, paper, mica, etc. Capacitors

are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, a

capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic

field between its plates

.

Figure 1.3: capacitor symbol and circuit diagram

When there is a potential difference across the conductors (e.g., when a capacitor is attached across a

battery), an electric field develops across the dielectric, causing positive charge (+Q) to collect on one plate

and negative charge (-Q) to collect on the other plate. If a battery has been attached to a capacitor for a

sufficient amount of time, no current can flow through the capacitor. However, if an accelerating or

alternating voltage is applied across the leads of the capacitor, a displacement current can flow.

An ideal capacitor is characterized by a single constant value for its capacitance. Capacitance is

expressed as the ratio of the electric charge (Q) on each conductor to the potential difference (V) between

them. The SI unit of capacitance is the farad (F), which is equal to one coulomb per volt (1 C/V). Typical

capacitance values range from about 1 pF (10−12 F) to about 1 mF (10−3 F).

The capacitance is greater when there is a narrower separation between conductors and when the

conductors have a larger surface area. In practice, the dielectric between the plates passes a small amount

5

of leakage current and also has an electric field strength limit, known as the breakdown voltage. The

conductors and leads introduce an undesired inductance and resistance

.

Figure 1.4: representation of capacitor symbol

Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating

current to pass. In analog filter networks, they smooth the output of power supplies. In resonant

circuits they tune radio to particular frequencies. In electric power transmission systems they stabilize

voltage and power flow.

1.4. DIODE:

A diode is the simplest sort of semiconductor device. Broadly speaking, a semiconductor is a material

with a varying ability to conduct electrical current. Most semiconductors are made of a poor conductor that

has had impurities added to it. The process of adding impurities is called doping.

In the case of LEDs, the conductor material is typically aluminum-gallium-arsenide (AlGaAs). In

pure aluminum-gallium-arsenide, all of the atoms bond perfectly to their neighbors, leaving no free

electrons (negatively charged particles) to conduct electric current. In doped material, additional atoms

change the balance, either adding free electrons or creating holes where electrons can go. Either of these

alterations makes the material more conductive.

6

Figure 1.5: representation of diode symbol and schematic diagram

A semiconductor with extra electrons is called N-type material, since it has extra negatively charged

particles. In N-type material, free electrons move from a negatively charged area to a positively charged

area.

A semiconductor with extra holes is called P-type material, since it effectively has extra positively

charged particles. Electrons can jump from hole to hole, moving from a negatively charged area to a

positively charged area. As a result, the holes themselves appear to move from a positively charged area to

a negatively charged area.

A diode consists of a section of N-type material bonded to a section of P-type material, with electrodes

on each end. This arrangement conducts electricity in only one direction. When no voltage is applied to the

diode, electrons from the N-type material fill holes from the P-type material along the junction between the

layers, forming a depletion zone. In a depletion zone, the semiconductor material is returned to its original

insulating state -- all of the holes are filled, so there are no free electrons or empty spaces for electrons, and

charge can't flow.

7

1.6 Characteristic of diode in forward and reverse bias

To get rid of the depletion zone, you have to get electrons moving from the N-type area to the P-type

area and holes moving in the reverse direction. To do this, you connect the N-type side of the diode to the

negative end of a circuit and the P-type side to the positive end. The free electrons in the N-type material

are repelled by the negative electrode and drawn to the positive electrode. The holes in the P-type material

move the other way. When the voltage difference between the electrodes is high enough, the electrons in

the depletion zone are boosted out of their holes and begin moving freely again. The depletion zone

disappears, and charge moves across the diode.

If you try to run current the other way, with the P-type side connected to the negative end of the circuit

and the N-type side connected to the positive end, current will not flow. The negative electrons in the N-

type material are attracted to the positive electrode. The positive holes in the P-type material are attracted

to the negative electrode. No current flows across the junction because the holes and the electrons are each

moving in the wrong direction. The depletion zone increases.

8

1.5. Thyristor:

1.5.1. Introduction

Thyristors can take many forms, but they have certain things in common. All of them are solid state

switches which act as open circuits capable of withstanding the rated voltage until triggered. When they are

triggered, thyristors become low−impedance current paths and remain in that condition until the current

either stops or drops below a minimum value called the holding level. Once a thyristor has been triggered,

the trigger current can be removed without turning off the device.

Silicon controlled rectifiers (SCRs) and triacs are both members of the thyristor family. SCRs are

unidirectional devices where triacs are bidirectional. An SCR is designed to switch load current in one

direction, while a triac is designed to conduct load current in either direction.

Structurally, all thyristors consist of several alternating layers of opposite P and N silicon, with the

exact structure varying with the particular kind of device. The load is applied across the multiple junctions

and the trigger current is injected at one of them. The trigger current allows the load current to flow

through the device, setting up a regenerative action which keeps the current flowing even after the trigger is

removed.

These characteristics make thyristors extremely useful in control applications. Compared to a

mechanical switch, a thyristor has a very long service life and very fast turn on and turn off times. Because

of their fast reaction times, regenerative action and low resistance once triggered, thyristors are useful as

power controllers and transient overvoltage protectors, as well as simply turning devices on and off.

Thyristors are used in motor controls, incandescent lights, home appliances, cameras, office equipment,

programmable logic controls, ground fault interrupters, dimmer switches, power tools, telecommunication

equipment, power supplies, timers, capacitor discharge igniters, engine ignition systems, and many other

kinds of equipment.

Although thyristors of all sorts are generally rugged, there are several points to keep in mind when

designing circuits using them. One of the most important is to respect the devices‟ rated limits on rate of

change of voltage and current (dv/dt and di/dt). If these are exceeded, the thyristor may be damaged or

destroyed. On the other hand, it is important to provide a trigger pulse large enough and fast enough to turn

the gate on quickly and completely. Usually the gate trigger current should be at least 50 percent greater

than the maximum rated gate trigger current. Thyristors may be driven in many different ways, including

9

directly from transistors or logic families, power control integrated circuits, by opto- isolated triac drivers,

programmable unijunction transistors (PUTs) and SIDACs. These and other design considerations are

covered in this manual.

Of interest too, is a new line of Thyristor Surge Suppressors in the surface mount SMB package

covering surge currents of 50, 80 and 100 amps, with break over voltages from 77 to 400 volts. NP Series

Thyristor Surge Protector Devices (TSPD) protects telecommunication circuits such as central office,

access, and customer premises equipment from overvoltage conditions. These are bidirectional devices so

they are able to have functionality of 2 devices in one package, saving valuable space on board layout.

These devices will act as a crowbar when overvoltage occurs and will divert the energy away from circuit

or device that is being protected. Use of the NP Series in equipment will help meet various regulatory

requirements including: GR−1089−CORE, IEC 61000−4−5, ITU K.20/21/45, IEC 60950, TIA−968−A,

FCC Part 68, EN 60950, UL 1950. See ON Semiconductor application note AND8022/D for additional

information.

1.5.2. Thyristor symbol and operation

Figure 1.7: silicon controlled rectifier

The bistable action of thyristors is readily explained by analysis of the structure of an SCR. This

analysis is essentially the same for any operating quadrant of triac because a triac may be considered as two

parallel SCRs oriented in opposite directions. Figure shows the schematic symbol for an SCR, and Figure

shows the P−N−P−N structure the symbol represents. In the two−transistor model for the SCR shown in

Figure, the interconnections of the two transistors are such that regenerative action occurs. Observe that if

current is injected into any leg of the model, the gain of the transistors (if sufficiently high) causes this

10

current to be amplified in another leg. In order for regeneration to occur, it is necessary for the sum of the

common base current gains () of the two transistors to exceed unity.

Therefore, because the junction leakage currents are relatively small and current gain is designed to be

low at the leakage current level, the PNPN device remains off unless external current is applied. When

sufficient trigger current is applied (to the gate, for example, in the case of an SCR) to raise the loop gain to

unity, regeneration occurs and the on−state principal current is limited primarily by external circuit

impedance. If the initiating trigger current is removed, the thyristor remains in the on state, providing the

current level is high enough to meet the unity gain criteria. This critical current is called latching current.

In order to turn off a thyristor, some change in current must occur to reduce the loop gain below unity.

From the model, it appears that horting the gate to cathode would accomplish this. However in an actual

SCR structure, the gate area is only a fraction of the cathode area and very little current is diverted by the

short. In practice, the principal current must be reduced below a certain level, called holding current, before

gain falls below unity and turn−off may commence. In fabricating practical SCRs and Triacs, a “shorted

emitter” design is generally used in which, schematically, a resistor is added from gate to cathode or gate to

MT1. Because current is diverted from the N−base through the resistor, the gate trigger current, latching

current and holding current all increase. One of the principal reasons for the shunt resistance is to improve

dynamic performance at high temperatures. Without the shunt, leakage current on most high current

thyristors could initiate turn−on at high temperatures.

Sensitive gate thyristors employ a high resistance shunt or none at all; consequently, their

characteristics can be altered dramatically by use of an external resistance. An external resistance has a

minor effect on most shorted emitter designs.

Junction temperature is the primary variable affecting thyristor characteristics. Increased temperatures

make the thyristor easier to turn on and keep on. Consequently, circuit conditions which determine turn−on

must be designed to operate at the lowest anticipated junction temperatures, while circuit conditions which

are to turn off the thyristor or prevent false triggering must be designed to operate at the maximum junction

temperature.

Thyristor specifications are usually written with case temperatures specified and with electrical

conditions such that the power dissipation is low enough that the junction temperature essentially equals

the case temperature. It is incumbent upon the user to properly account for changes in characteristics

caused by the circuit operating conditions different from the test conditions.

11

1.5.3. Triggering characteristics:

Figure 1.8: SCR triggering characteristics

Turn−on of a thyristor requires injection of current to raise the loop gain to unity. The current can take

the form of current applied to the gate, an anode current resulting from leakage, or avalanche breakdown of

a blocking junction. As a result, the break over voltage of a thyristor can be varied or controlled by

injection of a current at the gate terminal. Figure 1.8 shows the interaction of gate current and voltage for

an SCR.

When the gate current Ig is zero, the applied voltage must reach the break over voltage of the SCR

before switching occurs. As the value of gate current is increased, however, the ability of a thyristor to

support applied voltage is reduced and there is a certain value of gate current at which the behavior of the

thyristor closely resembles that of a rectifier. Because thyristor turn−on, as a result of exceeding the

breakover voltage, can produce high instantaneous power dissipation non−uniformly distributed over the

die area during the switching transition, extreme temperatures resulting in die failure may occur unless the

magnitude and rate of rise of principal current (di/dt) is restricted to tolerable levels. For normal operation,

therefore, SCRs and triacs are operated at applied voltages lower than the break over voltage, and are made

to switch to the on state by gate signals high enough to assure complete turn−on independent of the applied

voltage. On the other hand, diacs and other thyristor trigger devices are designed to be triggered

12

1.5.4. Latch and hold characteristics

In order for the thyristor to remain in the on state when the trigger signal is removed, it is necessary to

have sufficient principal current flowing to raise the loop gain to unity. The principal current level required

is the latching current, IL. Although triac show some dependency on the gate current in quadrant II, the

latching current is primarily affected by the temperature on shorted emitter structures.

In order to allow turn off, the principal current must be reduced below the level of the latching

current. The current level where turn off occurs is called the holding current, IH. Like the latching current,

the holding current is affected by temperature and also depends on the gate impedance. Reverse voltage on

the gate of an SCR markedly increases the latch and hold levels. Forward bias on thyristor gates may

significantly lower the values shown in the data sheets since those values are normally given with the gate

open. Failure to take this into account can cause latch or hold problems when thyristors are being driven

from transistors whose saturation voltages are a few tenths of a volt. Thyristors made with shorted emitter

gates are obviously not as sensitive to the gate circuit conditions as devices which have no built- in shunt.

1.5.5. Switching characteristics

When triacs or SCRs are triggered by a gate signal, the turn−on time consists of two stages: a delay

time, td, and arise time, tr, as shown in Figure. The total gate controlled turn−on time, tgt, is usually

defined as the time interval between the 50 percent point of the leading edge of the gate trigger voltage and

90 percent point of the principal current. The rise time tr is the time interval required for the principal

current to rise from 10 to 90 percent of its maximum value. A resistive load is usually specified.

Figure 1.8: switching characteristic of scr

Delay time decreases slightly as the peak off−state voltage increases. It is primarily related to the

magnitude of the gate−trigger current and shows a relationship which is roughly inversely proportional.

The rise time is influenced primarily by the off−state voltage, as high voltage causes an increase in

regenerative gain. Of major importance in the rise time interval is the relationship between principal

13

voltage and current flow through the thyristor di/dt. During this time the dynamic voltage drop is high and

the current density due to the possible rapid rate of change can produce localized hot spots in the die. This

may permanently degrade the blocking characteristics. Therefore, it is important that power dissipation

during turn−on be restricted to safe levels.

Turn−off time is a property associated only with SCRs and other unidirectional devices. (In triacs of

bidirectional devices a reverse voltage cannot be used to provide circuit−commutated turn−off voltage

because a reverse voltage applied to one half of the structure would be a forward−bias voltage to the other

half.) For turn−off times in SCRs, the recovery period consists of two stages, a reverse recovery time and a

gate or forward blocking recovery time, as shown in Figure 1.9

When the forward current of an SCR is reduced to zero at the end of a conduction period, application

of reverse voltage between the anode and cathode terminals causes reverse current flow in the SCR. The

current persists until the time that the reverse current decreases to the leakage level. Reverse recovery time

(trr) is usually measured from the point where the principal current changes polarity to a specified point on

the reverse current waveform as indicated in Figure 1.9. During this period the anode and cathode junctions

are being swept free of charge so that they may support reverse voltage. A second recovery period, called

the gate recovery time, tgr, must elapse for the charge stored in the forward−blocking junction to

recombine so that forward−blocking voltage can be reapplied and successfully blocked by the SCR. The

gate recovery time of an SCR is usually much longer than the reverse recovery time. The total time from

the instant reverse recovery current begins to flow to the start of the forward−blocking voltage is referred

to as circuit− commutated turn−off time tq.

Turn−off time depends upon a number of circuit conditions including on−state current prior to turn−off,

rate of change of current during the forward−to−reverse transition, reverse−blocking voltage, rate of

change of reapplied forward voltage, the gate bias, and junction temperature. Increasing junction

temperature and on− state current both increase turn−off time and have a more significant effect than any

of the other factors. Negative gate bias will decrease the turn−off time.

For applications in which an SCR is used to control ac power, during the entire negative half of the

sine wave a reverse voltage is applied. Turn off is easily accomplished for most devices at frequencies up

to a few kilohertz. For applications in which the SCR is used to control the output of a full−wave rectifier

bridge, however, there is no reverse voltage available for turn−off, and complete turn−off can be

accomplished only if the bridge output is reduced close to zero such that the principal current is reduced to

14

a value lower than the device holding current for a sufficiently long time. Turn−off problems may occur

even at a frequency of 60 Hz particularly if an inductive load is being controlled.

In triacs, rapid application of a reverse polarity voltage does not cause turn−off because the main

blocking junctions are common to both halves of the device. When the first triac structure (SCR−1) is in

the conducting state, a quantity of charge accumulates in the N−type region as a result of the principal

current flow. As the principal current crosses the zero reference point, a reverse current is established as a

result of the charge remaining in the N−type region, which is common to both halves of the device.

Consequently, the reverse recovery current becomes a forward current to the second half of the triac. The

current resulting from stored charge causes the second half of the triac to go into the conducting state in the

absence of a gate signal. Once current conduction has been established by application of a gate signal,

therefore, complete loss in power control can occur as a result of interaction within the N−type base region

of the triac unless sufficient time elapses or the rate of application of the reverse polarity voltage is slow

enough to allow nearly all the charge to recomb ine in the common N−type region. Therefore, triacs are

generally limited to low−frequency −60 Hz applications.

Turn−off or commutation of triacs is more severe with inductive loads than with resistive loads

because of the phase lag between voltage and current associated with inductive loads. Figure 2.8 shows the

waveforms for an inductive load with lagging current power factor. At the time the current reaches zero

cross over (Point A), the half of the triac in conduction begins to commutate when the principal current

falls below the holding current. At the instant the conducting half of the triac turns off, an applied voltage

opposite the current polarity is applied across the triac terminals (Point B). Because this voltage is a

forward bias to the second half of the triac, the suddenly reapplied voltage in conjunction with the

emaining stored charge in the high−voltage junction reduces the over−all device capability to support

voltage. The result is a loss of power control to the load, and the device remains in the conducting state in

absence of a gate signal. The measure of triac turn−off ability is the rate of rise of the opposite polarity

voltage it can handle without remaining on. It is called commutating dv/dt (dv/dt). Circuit conditions and

temperature affect dv/dt(c) in a manner similar to the way tq is affected in an SCR. It is imperative that

some means be provided to restrict the rate of rise of reapplied voltage to a value which will permit triac

turn−off under the conditions of inductive load. A commonly accepted method for keeping the

commutating dv/dt within tolerable levels is to use an RC snubber network in parallel with the main

terminals of the triac. Because the rate of rise of applied voltage at the triac terminals is a function of the

load impedance and the RC snubber network, the circuit can be evaluated under worst−case conditions of

15

operating case temperature and maximum principal current. The values of resistance and capacitance in the

snubber area then adjusted so that the rate of rise of commutating dv/dt stress is within the pecified

minimum limit under any of the conditions mentioned above. The value of snubber resistance should be

high enough to limit the snubber capacitance discharge currents during turn−on and dampen the LC

oscillation during commutation. The combination of snubber values having highest resistance and lowest

capacitance that provides satisfactory operation is generally preferred.

16

Chapter-2

DC POWER SUPPLY DESIGN

2.1. INTRODUCTION:

A rectifier is an electrical device that converts alternating current (AC), which periodically reverses

direction, to direct current (DC), which flows in only one direction. The process is known as rectification.

Physically, rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves, copper

and selenium oxide rectifiers, semiconductor diodes, silicon-controlled rectifiers and other silicon-based

semiconductor switches. Historically, even synchronous electromechanical switches and motors have bee n

used. Early radio receivers, called crystal radios, used a "cat's whisker" of fine wire pressing on a crystal of

galena (lead sulfide) to serve as a point-contact rectifier or "crystal detector".

Rectifiers have many uses, but are often found serving as components of DC power supplies and high-

voltage direct current power transmission systems. Rectification may serve in roles other than to generate

direct current for use as a source of power. As noted, detectors of radio signals serve as rectifiers. In gas

heating systems flame rectification is used to detect presence of flame.

Because of the alternating nature of the input AC sine wave, the process of rectification alone

produces a DC current that, though unidirectional, consists of pulses of current. Many applications of

rectifiers, such as power supplies for radio, television and computer equipment, require a steady constant

DC current (as would be produced by a battery). In these applications the output of the rectifier is

smoothed by an electronic filter to produce a steady current.

A more complex circuitry device that performs the opposite function, converting DC to AC, is called

an inverter.

2.2. CIRCUIT COMPONENTS

The following circuit components are requires to designing a dc power supply are:

Bridge rectifier

230/48 volts single phase transformer

Voltage regulator

Capacitors

Variable pot ( variable resistor )

17

2.2.1 VOLTAGE REGULATOR:

A Voltage regulator is designed to automatically maintain a constant voltage level. A voltage

regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may

use an electromechanical mechanism, or electronic components. Depending on the design, it may be

used to regulate one or more AC or DC voltages.

Figure 2.1: voltage regulator with filtering capacitors

A simple voltage regulator can be made from a resistor in series with a diode. Due to the

logarithmic shape of diode V-I curves, the voltage across the diode changes only slightly due to changes in

current drawn or changes in the input. When precise voltage control and efficiency are not important, this

design may work fine.

Figure 2.2: voltage regulator symbol and pin configuration

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Feedback voltage regulators operate by comparing the actual output voltage to some fixed reference

voltage. Any difference is amplified and used to control the regulation element in such a way as to reduce

the voltage error. This forms a negative feedback control loop increasing the open- loop gain tends to

increase regulation accuracy but reduce stability (avoidance of oscillation, or ringing during step changes).

There will also be a trade-off between stability and the speed of the response to changes.

If the output voltage is too low (perhaps due to input voltage reducing or load current increasing),

the regulation element is commanded, up to a point, to produce a higher output voltage–by dropping less of

the input voltage, or to draw input current for longer periods if the output voltage is too high, the regulation

element will normally be commanded to produce a lower voltage.

However, many regulators have over-current protection so that they will entirely stop sourcing

current (or limit the current in some way) if the output current is too high, and some regulators may also

shut down if the input voltage is outside a given range.

2.2.2. TRANSFORMER:

A transformer is an electrical device that transfers energy between two circuits

through electromagnetic induction. A transformer may be used as a safe and efficient voltage converter to

change the AC voltage at its input to a higher or lower voltage at its output. Other uses include current

conversion, isolation with or without changing voltage and impedance conversion.

Figure 2.3: two winding transformer

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A transformer most commonly consists of two windings of wire that are wound around a common

core to provide tight electromagnetic coupling between the windings. The core material is often a

laminated iron core. The coil that receives the electrical input energy is referred to as the primary winding,

while the output coil is called the secondary winding.

An alternating electric current flowing through the primary winding (coil) of a transformer generates

a varying electromagnetic field in its surroundings which causes a varying magnetic flux in the core of the

transformer. The varying electromagnetic field in the vicinity of the secondary winding induces an

electromotive force in the secondary winding, which appears a voltage across the output terminals. If a load

impedance is connected across the secondary winding, a current flows through the secondary winding

drawing power from the primary winding and its power source.

A transformer cannot operate with direct current; although, when it is connected to a DC source, a

transformer typically produces a short output pulse as the current rises

2.2.3. DIODE:

A diode is the simplest sort of semiconductor device. Broadly speaking, a semiconductor is a material

with a varying ability to conduct electrical current. Most semiconductors are made of a poor conductor that

has had impurities added to it. The process of adding impurities is called doping.

In the case of LEDs, the conductor material is typically aluminum-gallium-arsenide (AlGaAs). In

pure aluminum-gallium-arsenide, all of the atoms bond perfectly to their neighbors, leaving no free

electrons (negatively charged particles) to conduct electric current. In doped material, additional atoms

change the balance, either adding free electrons or creating holes where electrons can go. Either of these

alterations makes the material more conductive.

20

Figure 2.4: representation of diode symbol and schematic diagram

A semiconductor with extra electrons is called N-type material, since it has extra negatively charged

particles. In N-type material, free electrons move from a negatively charged area to a positively charged

area.

A semiconductor with extra holes is called P-type material, since it effectively has extra positively

charged particles. Electrons can jump from hole to hole, moving from a negatively charged area to a

positively charged area. As a result, the holes themselves appear to move from a positively charged area to

a negatively charged area.

A diode consists of a section of N-type material bonded to a section of P-type material, with electrodes

on each end. This arrangement conducts electricity in only one direction. When no voltage is applied to the

diode, electrons from the N-type material fill holes from the P-type material along the junction between the

layers, forming a depletion zone. In a depletion zone, the semiconductor material is returned to its original

insulating state -- all of the holes are filled, so there are no free electrons or empty spaces for electrons, and

charge can't flow.

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2.5. Characteristic of diode in forward and reverse bias To get rid of the depletion zone, you have to get electrons moving from the N-type area to the P-

type area and holes moving in the reverse direction. To do this, you connect the N-type side of the diode to

the negative end of a circuit and the P-type side to the positive end. The free electrons in the N-type

material are repelled by the negative electrode and drawn to the positive electrode. The holes in the P-type

material move the other way. When the voltage difference between the electrodes is high enough, the

electrons in the depletion zone are boosted out of their holes and begin moving freely again. The depletion

zone disappears, and charge moves across the diode.

If you try to run current the other way, with the P-type side connected to the negative end of the

circuit and the N-type side connected to the positive end, current will not flow. The negative electrons in

the N-type material are attracted to the positive electrode. The positive holes in the P-type material are

attracted to the negative electrode. No current flows across the junction because the holes and the electrons

are each moving in the wrong direction. The depletion zone increases.

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2.2.4: bridge rectifier

During the positive half cycle both D3 and D1 are forward biased. At the same time, both D2 and

D4 are reverse biased. Note the direction of current flow through the load. During the negative half cycle

D2 and D4 are forward biased and D1 and D3 are reverse biased. Again note that current through the load

is in the same direction although the secondary winding polarity has reversed.

2.6. Operation during negative half cycle Peak Inverse Voltage:

In order to understand the Peak Inverse Voltage across each diode, look at figure below. It is a

simplified version of figure showing the circuit conditions during the positive half cycle. The load and

ground connections are removed because we are concerned with the diode conditions only. In this circuit,

diodes D1and D3 are forward biased and act like closed switches. They can be replaced with wires. Diodes

D2 and D4 are reverse biased and act like open switches.

The circuit of redrawn below. We can see that both diodes are reversing biased, in parallel, and

directly across the secondary winding. The peak inverse voltage is therefore equal to Vm.

23

Fig 2.7. Dc power supply design circuit diagram

Therefore,

Peak inverse voltage = Vm

24

Chapter-3

TRIGGERING CIRCUIT DESIGN

1.1 Introduction:

The following components are required to trigger a thyristor. They are:

Opto-isolator

5 volts dc supply

Arduino

Current limiting resistor

1.2 OPTO-ISOLATOR:

Figure 3.1 an opto-isolator

In electronics, an opto-isolator, also called an optocoupler, photocoupler, or optical isolator,

is a component that transfers electrical signals between two isolated circuits by using light.Opto- isolators

prevent high voltages from affecting the system receiving the signal. Commercially available opto- isolators

withstand input-to-output voltages up to 10 kV and voltage transients with speeds up to 10 kV/μs.

A common type of opto- isolator consists of an LED and a phototransistor in the same opaque

package. Other types of source-sensor combinations include LED-photodiode, LED-LASCR, and lamp-

photo resistor pairs. Usually opto-isolators transfer digital (on-off) signals, but some techniques allow them

to be used with analog signals.

History:

The value of optically coupling a solid state light emitter to a semiconductor detector for the purpose

of electrical isolation was recognized in 1963 by Akmenkalns, et al. (US patent 3,417,249). Photo resistor-

based opto- isolators were introduced in 1968. They are the slowest, but also the most linear isolators and

25

still retain a niche market in audio and music industry. Commercializat ion of LED technology in 1968

to1970 caused a boom in optoelectronics, and by the end of the 1970s the industry developed all principal

types of opto-isolators. The majority of opto- isolators on the market use bipolar silicon phototransistor

sensors. They attain medium data transfer speed, sufficient for applications

like electroencephalography. The fastest opto- isolators use PIN diodes in photoconductive mode.

Operation:

An opto- isolator contains a source (emitter) of light, almost always a near infrared light-emitting

diode (LED), that converts electrical input signal into light, a closed optical channel (also called dielectrical

channel, and a photo sensor, which detects incoming light and either generates electric energy directly,

or modulates electric current flowing from an external power supply. opto- isolator can transfer the light

signal not transfer the electrical signal . The sensor can be a photo resistor, a photodiode, a phototransistor,

a silicon-controlled rectifier (SCR) or a triac. Because LEDs can sense light in addition to emitting it,

construction of symmetrical, bidirectional opto- isolators is possible. An optocoupled solid state

relay contains a photodiode opto-isolator which drives a power switch, usually a complementary pair

of MOSFETs. A slotted optical switch contains a source of light and a sensor, but its optical channel is

open, allowing modulation of light by external objects obstructing the path of light or reflecting light into

the sensor.

3.3 Photodiode opto-isolators:

Fig3.2 photodiode opto- isolator

Diode opto- isolators employ LEDs as sources of light and silicon photodiodes as sensors. When

the photodiode is reverse-biased with an external voltage source, incoming light increases the reverse

current flowing through the diode. The diode itself does not generate energy; it modulates the flow of

energy from an external source. This mode of operation is called photoconductive mode. Alternatively, in

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the absence of external bias the diode converts the energy of light into electric energy by charging its

terminals to a voltage of up to 0.7 V. The rate of charge is proportional to the intensity of incoming light.

The energy is harvested by draining the charge through an external high- impedance path; the ratio of

current transfer can reach 0.2%. This mode of operation is called photovoltaic mode.

The fastest opto- isolators employ PIN diodes in photoconductive mode. The response times of PIN

diodes lie in the sub-nanosecond range; overall system speed is limited by delays in LED output and in

biasing circuitry. To minimize these delays, fast digital opto- isolators contain their own LED drivers and

output amplifiers optimized for speed. These devices are called full logic opto-isolators: their LEDs and

sensors are fully encapsulated within a digital logic circuit.] The Hewlett-Packard 6N137/HPCL2601

family of devices equipped with internal output amplifiers was introduced in the late 1970s and attained

10 MBd data transfer speeds. It remained an industry standard until the introduction of the 50 MBd Agilent

Technologies 7723/0723 family in 2002. The 7723/0723 series opto- isolators contain CMOS LED drivers

and a CMOS buffered amplifiers, which require two independent external power supplies of 5 V each.

Photodiode opto- isolators can be used for interfacing analog signals, although their non-

linearity invariably distorts the signal. A special class of analog opto-isolators introduced by Burr-Brown

uses two photodiodes and an input-side operational amplifier to compensate for diode non- linearity. One of

two identical diodes is wired into the feedback loop of the amplifier, which maintains overall current

transfer ratio at a constant level regardless of the non- linearity in the second (output) diode.

A novel idea of a particular optical analog signal isolator was submitted on 3, June 2011. The

proposed configuration consists of two different parts. One of them transfers the signal, and the other

establishes a negative feedback to ensure that the output signal has the same features as the input signal.

This proposed analog isolator is linear over a wide range of input voltage and frequency.

Solid-state relays built around MOSFET switches usually employ a photodiode opto- isolator to drive

the switch. The gate of a MOSFET requires relatively small total charge to turn on and its leakage current

in steady state is very low. A photodiode in photovoltaic mode can generate turn-on charge in a reasonably

short time but its output voltage is many times less than the MOSFET's threshold voltage. To reach the

required threshold, solid-state relays contain stacks of up to thirty photodiodes wired in series.

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3.4 Phototransistor opto-isolators:

Phototransistors are inherently slower than photodiodes. The earliest and the slowest but still

common 4N35 opto- isolator, for example, has rise and fall times of 5 μs into a 100 Ohm load and its

bandwidth is limited at around 10 kilohertz - sufficient for applications

like electroencephalography] or pulse-width motor control. Devices like PC-900 or 6N138 recommended in

the original 1983 Musical Instrument Digital Interface specification allow digital data transfer speeds of

tens of kilo Bauds. Phototransistors must be properly biased and loaded to achieve their maximum speeds,

for example, the 4N28 operates at up to 50 kHz with optimum bias and less than 4 kHz without it.

Fig3.3: opto- isolator

Design with transistor opto- isolators requires generous allowances for wide fluctuations of

parameters found in commercially available devices. Such fluctuations may be destructive, for example,

when an opto- isolator in the feedback loop of a DC-to-DC converter changes its transfer function and

causes spurious oscillations, or when unexpected d1elays in opto- isolators cause a short circuit through one

side of an H-bridge. Manufacturers' datasheets typically list only worst-case values for critical parameters;

actual devices surpass these worst-case estimates in an unpredictable fashion. Bob Pease observed that

current transfer ratio in a batch of 4N28's can vary from 15% to more than 100%; the datasheet specified

only a minimum of 10%. Transistor beta in the same batch can vary from 300 to 3000, resulting in 10:1

variance in bandwidth. Opto-isolators using field-effect transistors (FETs) as sensors are rare and, like

vectors, can be used as remote-controlled analog potentiometers provided that the voltage across the FET's

output terminal does not exceed a few hundred mV. Opto-FETs turn on without injecting switching charge

in the output circuit, which is particularly useful in sample and hold circuits.

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3.5 SILICON CONTROLLED RECTIFIER (SCR):

Constructional Features of SCR

As shown in FIG (b) the primary crystal is of lightly doped n- type on either side of which two p type

layers with doping levels higher by two orders of magnitude are grown. As in the case of power diodes and

transistors depletion layer spreads mainly into the lightly doped n-region. The thickness of this layer is

therefore determined by the required blocking voltage of the device. However, due to conductivity

modulation by carriers from the heavily doped p regions on both side during ON condition the “ON state”

voltage drop is less. The outer n+ layers are formed with doping levels higher then both the p type layers.

The top p layer acts as the “Anode” terminal while the bottom n+ layers acts as the “Cathode”. The “Gate”

terminal connections are made to the bottom p layer.

As it will be shown later, that for better switching performance it is required to maximize the peripheral

contact area of the gate and the cathode regions. Therefore, the cathode regions are finely distributed

between gate contacts of the p type layer. An “Involutes” structure for both the gate and the cathode

regions is a preferred design structure.

3.4 Basic operating principle of a thyristor

The SCR is a four- layer, three-junction and a three-terminal device and is shown in fig. The end P-

region is the anode, the end N-region is the cathode and the inner P-region is the gate. The anode to

cathode is connected in series with the load circuit. Essentially the device is a switch. Ideally it remains off

(voltage blocking state), or appears to have an infinite impedance until both the anode and gate terminals

have suitable positive voltages with respect to the cathode terminal. The thyristor then switches on and

29

current flows and continues to conduct without further gate signals. Ideally the thyristor has zero

impedance in conduction state. For switching off or reverting to the blocking state, there must be no gate

signal and the anode current must be reduced to zero. Current can flow only in one direction.

In absence of external bias voltages, the majority carrier in each layer diffuses until there is a built- in

voltage that retards further diffusion. Some majority carriers have enough energy to cross the barrier

caused by the retarding electric field at each junction. These carriers then become minority carriers and can

recombine with majority carriers. Minority carriers in each layer can be accelerated across each junction by

the fixed field, but because of absence of external circuit in this case the sum of majority and minority

carrier currents must be zero.

A voltage bias, as shown in figure, and an external circuit to carry current allow internal currents

which include the following terms:

The current Ix is due to

Majority carriers (holes) crossing junction J1

Minority carriers crossing junction J1

Holes injected at junction J2 diffusing through the N-region and crossing junction J1 and

Minority carriers from junction J2 diffusing through the N-region and crossing junction J1.

Similarly I2 is due to six terms and I3 is due to four terms. The two simple analogues to explain the basic

action for the thyristor are those of the diode and the two transistor models.

1. Diode Model. The thyristor is similar to three diodes in series as there are three P-N junctions. Without

gate bias, there is always at least one reverse biased junction to prevent conduction irrespective of the

polarity of an applied voltage between anode and cathode. If the anode is made positive and the gate is also

biased positively with respect to cathode, the P-layer at the gate is flooded by the electrons from the

cathode and loses its identity as a P-layer. Accordingly the thyristor becomes equivalent to a conducting

diode.

2. Two Transistor Model: Imagine the SCR cut along the dotted line, as shown in fig. a. Then we can have

two devices. These two devices can be recognized as two transistors. The upper left one is P-N-P transistor

and the lower right N-P-N type. Further it can be recognized that the base of the P-N-P transistor is joined

to the collector of the N-P-N transistor while the collector of P-N-P is joined to the base of N-P-N

30

transistor, as illustrated in fig. c. The gate terminal is brought out from the base of the N-P-N material. This

construction has been conceived merely to explain the working of SCR; otherwise in physical shape the

SCR has four solid layers of P-N-P-N type only.

Now we can see that the two transistors are connected in such a manner that the collector of Q 1 is

connected to the base of Q2 i.e. the output collector current of Q t becomes the base current for Q2. In the

similar way the collector of Q2 is joined to the base of Q1 which shows that the output collector current of

Q2 is fed to Q1as input base current. These are back to back connections of transistors in such a way that

the output of one goes into as input of other transistor and vice-versa. This gives net gain of loop circuit as

β1 x β2 where β1 and β2 are current gains of two transistors respectively.

When the gate current is zero or the gate terminal is open, the only current in circulation is the leakage

current, which is very small in case of silicon device specially and the total current is a little higher than

sum of individual leakage currents. Under these conditions P-N-P-N device is said to be in its forward

blocking or high impedance „off state. As soon as a small amount of gate current is given to the base of

transistor Q2 by applying forward bias to its base-emitter junction, it generates the collector current as

β2 times the base current. This collector current of Q2 is fed as input base current to Q : which is further

multiplied by β1 times as ICl which forms input base current of Q2 and undergoes further amplification. In

this way both transistors feedback each other and the collector current of each goes on multiplying. This

process is very quick and soon both the transistors drive each other to saturation. Now the device is said to

be in on-state. The current through the on-state SCR is controlled by external impedance only.

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Chapter-4

ARDUINO

4.1 Introduction

Fig4.1 Arduino

All of the electrical signals that the Arduino works with are either Analog or Digital. It is extremely

important to understand the difference between these two types of signal and how to manipulate the

information these signals represent

4.1 Digital arduino:

And low voltages or short pulses at a particular frequency. Humans perceive the world in analog, but

robots, computers and circuits use Digital. A digital signal is a signal that has only two states. These states

can vary depending on the signal, but simply defined the states are ON or OFF, never in between. In the

world of Arduino, Digital signals are used for everything with the exception of Analog Input. Depending

on the voltage of the Arduino the ON or HIGH of the Digital signal will be equal to the system voltage,

while the OFF or LOW signal will always equal 0V. This is a fancy way of saying that on a 5V Arduino

32

the HIGH signals will be a little under 5V and on a 3.3V Arduino the HIGH signals will be a little under

3.3V.

To receive or send Digital signals the Arduino uses Digital pins # 0 - # 13. You may also setup your

Analog pins to act as Digital pins. To set up Analog In pins as Digital pins use the command: pin Mode

(pin Number, value);where pin Number is an Analog pin (A0 – A5) and value is either INPUT or

OUTPUT. To setup Digital pins use the same command but reference a Digital pin for pin Number instead

of an Analog In pin. Digital pins default as input, so really you only need to set them to OUTPUT in pin

Mode. To read these pins use the command: digital Read (pin Number); where pin Number is the Digital

pin to which the Digital component is connected. The digital Read command will return either a HIGH or a

LOW signal. To send a Digital signal to a pin uses the command: digital Write (pin Number, value);

where pin Number is the number of the pin sending the signal and value is either HIGH or LOW. The

Arduino also has the capability to output a Digital signal that acts as an Analog, signal, this signal is called

Pulse Width Modulation (PWM). Digital Pins # 3, # 5, # 6, # 9, # 10 and #11 have PWM capabilities. To

output a PWM signal use the command: analog Write (pin Number, value); where pin Number is a

Digital Pin with PWM capabilities and value is a number between 0 (0%) and 255.

4.3 Analog:

A continuous stream of information with values between and including 0% and 100%. Unmans

perceive the world in analog. Everything we see and hear is a continuous transmission of information to

our senses. The temperatures we perceive are never 100% hot or 100% cold, they are constantly changing

between our ranges of acceptable temperatures. This continuous stream is what defines analog data. Digital

information, the complementary concept to Analog, estimates analog data using only ones and zeros. In the

world of Arduino an Analog signal is simply a signal that can be HIGH (on), LOW (off) or anything in

between these two states. This means an Analog signal has a voltage value that can be anything between

0V and 5V (unless you mess with the Analog Reference pin). Analog allows you to send output or receive

input about devices that run at percentages as well as on and off. The Arduino does this by sampling the

voltage signal sent to these pins and comparing it to a voltage reference signal (5V). Depending on the

voltage of the Analog signal when compared to the Analog Reference signal the Arduino then assigns a

numerical value to the signal somewhere between 0 (0%) and 1023 (100%). The digital system of the

Arduino can then use this number in calculations and sketches.

To receive Analog Input the Arduino uses Analog pins # 0 - # 5. These pins are designed for use with

components that output Analog information and can be used for Analog Input. There is no setup necessary,

33

and to read them use the command: analog Read (pinNumber);where pin Number is the Analog In pin to

which the Analog component is connected. The analog Read command will return a number including or

between 0 and 1023. The Arduino also has the capability to output a digital signal that acts as an Analog

signal; this signal is called Pulse Width Modulation (PWM). Digital Pins # 3, # 5, # 6, # 9, # 10 and #11

have PWM capabilities. To output a PWM signal use the command : analogWrite(pinNumber,

value);where pin Number is a Digital Pin with PWM capabilities and value is a number between 0 (0%)

and 255 (100%).

4.4 Output Signals:

A signal exiting an electrical system, in this case a microcontroller. Output to the Arduino pins is

always digital, however there are two different types of Digital Output; regular Digital Output and Pulse

Width Modulation Output (PWM). Output is only possible with Digital pins # 0 - # 13. The Digital pins are

preset as Output pins, so unless the pin was used as an Input in the same sketch, there is no reason to use

the pin Mode command to set the pin as an Output. Should a situation arise where it is necessary to reset a

Digital pin to Output from Input use the command: pin Mode (pin Number, OUTPUT); where Number

pin is the Digital pin number set as Output. To send a Digital Output signal use the command:

digitalWrite(pinNumber, value);where pin Number is the Digital pin that is outputting the signal and

value is the signal. When outputting a Digital signal value can be either HIGH (On) or LOW (Off). Digital

Pins # 3, # 5, # 6, # 9, # 10 and #11 have PWM capabilities. This means you can Output the Digital

equivalent of an Analog signal using these pins. To Output a PWM signal use the command: analog Write

(pin Number, value); where pin Number is a Digital Pin with PWM capabilities and value is a number

between 0 (0%) and 255 (100%). For more information on PWM see the PWM worksheets or S.I.K. circuit

12. Output can be sent too many different devices, but it is up to the user to figure out which kind of Output

signal is needed, hook up the hardware and then type the correct code to properly use these signals.

Things to remember about Output:

• Output is always digital

• There are two kinds of Output: regular Digital or PWM (Pulse Width Modulation)

• To send an Output signal use analog Write (pin Number, value);(for analog) or digital Write(pin

Number, value);(for digital)

• Output pin mode is set using the pin Mode command: pinMode(pinNumber, OUTPUT);

• Regular Digital Output is always either HIGH or LOW

• PWM Output varies from 0 to 255

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Examples of Output:

Light Emitted Diodes (LED‟s), Piezoelectric Speakers, Servo Motors

4.5 Input Signals:

A signal entering an electrical system, in this case a microcontroller. Input to the Arduino pins can

come in one of two forms; Analog Input or Digital Input. Analog Input enters your Arduino through the

Analog In pins # 0 - # 5. These signals originate from analog sensors and interface devices. These analog

sensors and devices use voltage levels to communicate their information instead of a simp le yes (HIGH) or

no (LOW). For this reason you cannot use a digital pin as an input pin for these devices. Analog Input pins

are used only for receiving Analog signals. It is only possible to read the Analog Input pins so there is no

command necessary in the setup ( ) function to prepare these pins for input. To read the Analog Input pins

use the command: analog Read (pin Number); where pin Number is the Analog Input pin number. This

function will return an Analog Input reading between 0 and 1023. A reading of zero corresponds to 0 Volts

and a reading of 1023 corresponds to 5 Volts. These voltage values are emitted by the analog sensors and

interfaces. If you have an Analog Input that could exceed Vcc + .5V you may change the voltage that 1023

corresponds to by using the Aref pin. This pin sets the maximum voltage parameter your Analog Input pins

can read. The Aref pin‟s preset value is 5V. Digital Input can enter your Arduino through any of the Digital

Pins # 0 - # 13. Digital Input signals are either HIGH (On, 5V) or LOW (Off, 0V). Because the Digital pins

can be used either as input or output you will need to prepare the Arduino to use these pins as inputs in

your setup ( ) function. To do this types the command: pin Mode (pin Number, INPUT); inside the curly

brackets of the setup ( ) function where pin Number is the Digital pin number you wish to declare as an

input. You can change the pin Mode in the loop ( ) function if you need to switch a pin back and forth

between input and output, but it is usually set in the setup ( ) function and left untouched in the loop(

)function. To read the Digital pins set as inputs use the command: digital Read (pin Number); where pin

Number is the Digital Input pin number. Input can come from many different devices, but each device‟s

signal will be either Analog or Digital, it is up to the user to figure out which kind of input is needed, hook

up the hardware and then type

the correct code to properly use these signals.

Things to remember about Input:

• Input is either Analog or Digital, make sure to use the correct pins depending on type.

• To take an Input reading use analog Read (pin Number); (for analog)

• Or digital Read (pin Number); (for digital)

35

• Digital Input needs a pin Mode command such as pin Mode (pin Number, INPUT);

• Analog Input varies from 0 to 1023

• Digital Input is always either HIGH or LOW

Examples of Input:

Push Buttons, Potentiometers, Photo resistors, Flex Sensors

Serial is used to communicate between your computer and the Arduino as well as between Arduino boards

and other devices. Serial uses a serial port also known as UART, which stands for universal asynchronous

receiver/transmitter to transmit and receive information. In this case the computer outputs Serial

Communication via USB while the Arduino receives and transmits serial using, you guessed it, the RX and

TX pins. You use serial communication every time you upload code to your Arduino board.

You will also use it to debug code and troubleshoot circuits. Basic serial communication is outlined in the

following pages along with a simple activity to help you understand the concepts.

Serial Monitor: This is where you monitor your serial communication and set baud rate.

Activating the Serial Monitor:

When the activated Serial Monitor looks like

36

4.6 Serial setup:

The first thing you need to know to use Serial with your Arduino code is Serial setup. To setup Serial

you simply type the following line inside your setup( ) function: Serial.begin (9600); This line establishes

that you are using the Digital Pins # 0 and # 1 on the Arduino for Serial communication. This means that

you will not be able to use these pins as Input or Output because you are dedicating them to Serial

communication. The number 9600 is the baud rate; this is the rate at which the computer and the Arduino

communicate. You can change the baud rate depending on your needs but you need to make sure that the

baud rate in your Serial setup and the baud rate on your Serial Monitor are the same. If your baud rates do

not match up the Serial Monitor will display what appears to be gibberish, but is actually the correct

Communication incorrectly translated. Using Serial for code debugging and circuit trouble shooting: Once

Serial is configured using the basic communication for debugging and troubleshooting is pretty easy.

Anywhere in your sketch you wish the Arduino board to send a message type the line Serial. println

(“communication here”);. This command will print whatever you type inside the quotation marks to the

Serial Monitor followed by a return so that the next communication will print to the next line. If you wish

37

to print something without the return use Serial.print(“communication here”);. To display the value of a

variable using println simple remove the quotation marks and type the variable name inside the parenthesis.

For example, type Serial. println( i );to display the value of the variable named i. This is useful in many

different ways, if, for example, you wish to print some text followed by a variable or you want to display

multiple variables before starting a new line in the Serial Monitor.

These lines are useful if you are trying to figure out what exactly your Arduino code is doing. Place a

println command anywhere in the code, if the text in the println command shows up in your Serial

Monitor you will know exactly when the Arduino reached that portion of code, if the text does not show up

in the Serial Monitor you know that portion of code never executed and you need to rewrite.To use Serial

to troubleshoot a circuit use the println command just after reading an input or changing anoutput. This

way you can print the value of a pin signal. For example, type Serial.print(“Analog pin 0 reads:”); and

Serial.println(analogRead(A0));to display the signal on Analog Input Pin # 0. Replace the second portion

with Serial.println(digitalRead(10));to display the signal on Digital Pin # 10.

1. If Serial is displaying gibberish check the baud rates.

2. Use Serial.print(“communication here”);to display text.

3. Use Serial. println (“communication here”);to display text and start a new line.

4. Use Serial. print(VariableName);to display the value stored in Variable Name.

5. Use Serial. print(digitalRead (10));to display the state of Digital Pin #

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Chapter-5

COMMUTATION TECHNIQUES

1.1 Introduction

Commutation:

Within the context of HVDC converters, the definition of commutation is the transfer of dc current

from one valve to another in the same row is termed “commutation”.

It is important to realize that the commutation process is a function of both circuit-dependent and

switch-dependent parameters: Circuit-dependent parameters depend on circuit topology, and include

components such as transformer leakage (inductor), commutation capacitor, auxiliary switching device, etc.

For the 6-pulse bridge configuration, the most important circuit-dependent parameter for commutation is

the finite transformer leakage (inductance); assuming typical values for this, an overlap angle degree is

necessary, and more than two valves will conduct during the commutation period. Switch-dependent

parameters include device turn-on and turn-off times, di/dt and dv/dt limitations, etc. The most significant

switch

Types of commutation techniques:

There are two types of commutation to turn off the thyristor .they are.

1. Line (or) natural commutation.

2. Forced commutation.

5.2 Line commutation:

This technique relies on the natural reversal of the sinusoidal ac line voltage across the valves of

the converter. To initiate commutation, the firing pulse from the outgoing valve is removed and an alternate

incoming valve in the same row is triggered to take up the dc current. During the commutation (overlap)

period, the dc current is shared between the outgoing and incoming valves as a result of the leakage

inductance of the transformer. Once current is transferred to the incoming valve, the reverse voltage across

the outgoing valve is maintained for a time period toff (equivalent to gamma angle); the outgoing valve

must be reverse biased for a period greater than tq, the turn-off time of the device. During this period a

small reverse current is drawn from the device to deplete the charge carriers within the pn-junction of the

39

device. The time difference between toff and tq is required to provide a margin of security for the device to

achieve its voltage blocking capability. Typical valves of toff and tq are 350us and 700 us respectively.

It is important to note that the voltage blocking capability of the device is a function of the (reverse-

voltage * time period) product, and not the reverse voltage alone. For example, low reverse-voltage for a

long time period may not achieve successful blocking; similarly, high reverse-voltage for a short time

period may fail to achieve voltage blocking capabilities of the valve due to high dv/dt stress. With line

commutation, because of the direct dependence of the firing angle alpha to the ac voltage, it is only feasible

to delay the firing angle; it is not possible to advance the firing angle with reference to the ac system

voltage. This means that alpha can vary only from 0 to 180 degrees; as is well known from converter

theory; operation within these angles by a line commutated converter can only absorb reactive power from

the ac system.

Limitations of Line Commutation:

The fundamental limitation of a LC converter is its dependence on an adequate stiff ac voltage source

for commutation purposes. Power systems are subject to disturbances, voltage regulation difficulties and

harmonic pollution which cause commutation problems for such converters. As a result, LC converters

have difficulties to feed into weak ac systems and may take prohibitively long times to recover from

disturbances. Furthermore, the ability of the LC converter to control reactive power is limited.

These limitations can be overcome by the use of forced commutation employing either circuit- or self-

commutation techniques.

40

5.3 Forced commutation techniques:

5.3.1 Voltage Commutation In a voltage commutated thyristor circuit a voltage source is impressed across the SCR to be turned

off, mostly by an auxiliary SCR. This voltage is comparable in magnitude to the operating voltages. The

current in the conducting SCR is immediately quenched; however the reverse-biasing voltage must be

maintained for a period greater than that required for the device to turn-off. With a large reverse voltage

turning it off, the device offers the fastest turn-off time obtainable from that particular device. It is an

exposition of „hard‟ turn-off where the reverse biasing stress is maximum.

Fig. 5.1 A voltage commutated DC-DC Chopper and most significant

Wave forms Fig. 20.5 illustrates voltage commutation. ThM is the main SCR and ThAux is the Auxiliary. As a

consequence of the previous cycle, Capacitor C is argued with the dot as positive. When the Main SCR is

triggered, it carries the load current, which is held practically level by the large filter inductance, LF and

the Free-wheeling diode. Additionally, the charged Capacitor swings half a cycle through ThM, L and D

ending with a negative at the dot. The reverse voltage may be less than its positive value as some energy is

41

lost in the various components in the path. The half cycle capacitor current adds to the load current and is

taken by the Main SCR.

With the negative at the dot C-ThAux is enabled to commutate ThM. When ThAux is triggered the

negative charge of the capacitor is impressed onto ThM and it immediately turns off. The SCR does take

the reverse recovery current in the process. Thereafter, the level load current charges the capacitor linearly

to the supply voltage with the dot again as positive.

The Load voltage peaks by the addition of the capacitor voltage to the supply when ThAux is

triggered. The voltage falls as the capacitor discharges both changes being linear because of the level load

current. When the Capacitor voltage returns to zero, the load voltage equals supply voltage. The turn-off

time offered by the commutation circuit to the SCR lasts till this stage starting from the triggering of

ThAux. Now the capacitor is rogressively positively charged and the load voltage is equally diminished

from the supply voltage. ThAux is naturally commutated when the capacitor is fully charged and a small

excess voltage switches on the freewheeling diode. With the positive at the dot the capacitor is again ready

for the next cycle. Here ThAux must be switched before ThM to charge C to desired polarity.

Voltage commutation may be chosen for comparatively fast switching and it can be identified from the

steep fall of the SCR current. There is no overlapping operation between the incoming and the outgoing

devices and both currents fall and rise sharply. Stresses on all the three semiconductors can be expected to

be high here.

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5.3.2 Current commutation:

The circuit of Fig. 20.6 can be converted into a current commuted one just by Inter changing the

positions of the diode and the capacitor. Here the Capacitor is automatically charged through D-L-LF-Load

with the dot as positive. Any of the SCRs can thus be switched on first.

Fig. 5.2 A current commutated DC-DC Chopper and most significant waveforms

If ThM is triggered first, it immediately takes the load current turning off DF. When ThAux is

triggered, it takes a half cycle of the ringing current in the L-C circuit and the polarity of the charge across

the capacitor reverses. As it swings back, ThAux is turned off and the path through D-C-L shares the load

current which may again be considered to be reasonably level. The Current-share of THM is thus reduced

in a sinusoidal (damped) manner. Turn-off process is consequently accompanied by an overlap between

ThM and the diode D in the D-C-L path. Once the main SCR is turned off, the capacitor current becomes

43

level and the voltage decreases linearly. A voltage spike appears across the load when the voltage across

the commutating Inductance collapses and the capacitance voltage add to the supply voltage.

The free-wheeling diode also turns on through an overlap with D when the capacitor voltage just

exceeds the supply voltage and this extra voltage drives the commutating current through the path D-

Supply-DF-L. Thus there is soft switching of all devices during this period.

Further an additional diode may be connected across the main SCR. It ensures „soft‟ turnoff by

conducting the excess current in the ringing L-C circuit. The low forward voltage appearing across the

SCR causes it to turn-off slowly. Consequently switching frequencies have to be low. Note that such a

diode cannot be connected across the Main SCR in the voltage commutated circuit.

5.3.3 Load Commutation:

Figure 5.3: load commutation circuit

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Figure 5.4: Output wave forms of load commutation

For achieving load commutation of a thyristor, the commutating components L and C are connected as

shown in fig. Here R is the load resistance. For high value of R, load R is connected across C Fig. the

essential requirement for both the circuits of Fig. is that the overall circuit must be under damped. Wheb

these circuits are energized from dc, current waveforms as shown onn the right hand side of Fig. are

obtained. It is seen that current I first rises to maximum value and then begins to gall. When current decays

to zero and tends to reverse, thyristor T in Fig. is turned-off on its own at instant A.

Load, or class-A, commutation is prevalent in thyristor circuits supplied from a dc source. The nature

of the circuit should be such that when energized from a dc source, current must have a natural tendency to

decay to zero for the load commutation to occur in a thyristor circuit. Load commutation is possible in dc

circuits and not in ac circuits. Class A, or load, commutation is also called resonant commutation or self-

commutation. A practical circuit employing load commutation is a series inverter.

45

RESULTS

VOLTAGE COMMUTATION:

CIRCUIT DIAGRAM:

OUTPUT WAVE FORM:

Across load:

46

Across capacitor:

CURRENT COMMUTATION:

CIRCUIT DIAGRAM:

47

OUTPUT WAVE FORMS:

Across the load

Across thyristor

48

LOAD COMMUTATION:

OUPUT WAVE FORMS:

49

Chapter-6

CONCLUSION AND FUTURE WORKS

6.1 CONCLUSIONS:

Analysis of different forced commutation techniques to commutate the thyristor. For effectiveness of the

study arduino is used Main thyristor is commutated with the help of triggering the auxiliary thyristor by

giving 5 volts DC with the help of opto- isolator. Among load commutation, current commutation and

voltage commutation, load commutation is easiest one and current commutation is effective one

6.2 REFERENCE BOOK

1. Dr.P.S.Bimbhra ph.D.,M.E.(Hons.), F.I.E. (India), M.I.S.T.E. Ex-Dean, Ex-prof. and Head of Electrical

And electronics Engg. Dept. Thapar Institute of Engineering and Technology PATIALA-147004

By khanna publishers

2. Google web we had took the image

3.PDF took from wikipadia

50

DATE SHEET OF DEVICES

TYN612:

SYMBOL PARAMETER VALUE UNIT

VDRM Repetitive peak off-state voltages 600 V

IT (RMS) RMS on-state current 12 A

ITSM Non-repetitive surge peak on-state current 140 A

Table1. TYN612 data sheet

7824:

ABSOLUTE MAXIMUM RATINGS

Absolute maximum ratings are those values beyond which damage to the device may occur. The

datasheet Specifications should be met, without exception, to ensure that the system design is reliable over

its power supply, temperature, and output/input loading variables. Fairchild does not recommend operation

outside datasheet specifications.

Symbol Parameter value unit

VI Input Voltage VO=5v to 18v

VO=24 V

35

40

V

V

RθJC Thermal Resistance Junction-Cases (TO-220) 5 °C/w

RθJA Thermal Resistance Junction-Air (TO-220) 65 °C/w

TOPR Operating Temperature LM78xx

Range LM78xxA

-40 to +125

0 to +125

°C

TSTG Storage Temperature Range -65 to 150 °C

Table2 data sheet of 7824 regulator