EE-321 NPOWER ELECTRONICS-I

credits:4Lecture-1

Introduction

About this Course

• Power Electronics deals with efficient power(energy) conversion using different circuittopologies.

• Very interesting and useful course but alsoneeds a bit of hardwork

• Also important for competitive exams (GATE,IES, PSUs)

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Learning Outcomes

• To introduce the basic theory of powersemiconductor devices and passivecomponents, their practical application inpower electronics.

• To familiarize the operation principle of AC-DC, DC-DC, DC-AC conversion circuits and theirapplications.

• To provide the basis for further study of powerelectronics circuits and systems.

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Interdisciplinary Nature of Power Electronics

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Brief Contents

Unit 1: Power SC Devices and their CharacteristicsUnit 2: Triggering CircuitsUnit 3: 1-ph Phase Controlled ConvertersUnit 4: 3-ph Controlled ConvertersUnit 5: Misc. Converters

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Me

Dr. AT

Venue of Classes

• Your Classroom (ML-10) obviously!• Teaching mainly with the help of slides• You are requested to arrange for the projector

cord in advance from the principal office andreturn the same after the lecture.

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Learning Resources• Books:1. M. H. Rashid, “Power Electronics:Circuits,

Devices & Applications”, 3/e, Pearson-PH.2. M. S. Jamil Asghar, “Power Electronics”, PHI.3. Ned Mohan et. al., “Power Electronics:

Converters, Applications and Design”, 3/e, JohnWiley and Sons.

4. P. S. Bimbhra, “Power Electronics”, KhannaPublishers.

5. And many more!!!!

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Learning Resources…contd.• This was more than enough, but still you can

explore more material• Browse web and search for lecture notes, other

e-books… also inform me if you find some goodmaterial.

• http://www.nptel.iitm.ac.in• Relevant Journals: IEEE Transactions on Power

Electronics, Industrial Electronics, EnergyConversion etc.

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Discipline Issues1. Attendance:

Not necessary but desirable. Rememberthat 75% attendance is essential toappear in the final exam.

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Issues…contd1

2. Coming late• Try to come on time• 5-7 minutes max.• If you come within this limit …good enough

and come quietly without seeking permission• Once I start the lecture do not even peep into

the classroom!

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Issues…contd2

3. Mobile Phones• Use of mobile phones is not expected during

the class. However, emergency calls may beresponded to.

• Kindly turn your mobiles to silent mode beforethe lecture begins.

• Students found playing with/or using mobilesunnecessarily are liable to disciplinary action!

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Issues…contd3

4. Leaving/ Bunking Classes• Bunking is NOT acceptable• If for some reason(bored/tired) you don’t

wanna study, grab me in the corridor before entering the classroom.

• But arrange for the compensating lecture also!

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Issues…contd45. Home Assignment• Make a neat & legible assignment• Original work is recommended…may work out

in groups of 3-4, try to understand what you arewriting

• I like creativity…but avoid too much of it likedecorating with flower patterns

• Give proper references of books, websitesthat helped you, at the end (IMPORTANT)

• Submit the assignment in person on/beforedue date

• Submission after due date: PLAIN ZERO

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Lets Begin!

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Introduction

• Electrical Power is a fundamental requirementfor residential and industrial applications

• However, the nature of requirements may bevariable for different consumers or application

• The electric utility supplies at a fixed voltageand frequency and thus can’t meet the aboverequirement

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Introduction

• Hence, a power modulator (Power electronicconverter) is needed which will act as aninterface between the utility system andconsumer load.

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Electric Utility

PE Converter Load

A General Power Electronic System Configuration

Historical Review

• Mercury arc rectifiers in 1900.• Used up to 1950, limited use• Silicon transistor in 1948 Bell Labs―First

Electronic Revolution• The first Thyristor (Silicon Controlled Rectifier)

developed by Bell labs in 1956.• Commercial grade SCR developed by GE in

1958 ―Second Electronic Revolution

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Applications

• Commercial Applications (AC, UPS, elevators)• Domestic Applications (Lighting & heating ckts,

cooking equipments)• Telecommunications (Battery chargers)• Transportation (Traction control of• electric vehicles)• Utility Systems (HVDC, SVC, Renewable Energy)• See Rashid/Mohan for further listing

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Types of PE Converters

• DC to DC (Choppers, Regulators)

• DC to AC (Inverters)

• AC to DC (Rectifier)

• AC to AC (Cycloconverter, Regulator,Matrix converter)

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Advantages of PE Converters

• High Efficiency (> 90%, sometimes up to 99%) • Compactness (Small size and weight)• Ease and speed (faster response)• Reliability & long life (lesser failure rates)

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Disadvantages of PE Converters

• Requirement of elaborate control andprotection circuitry

• Generation of unwanted harmonics• Associated electromagnetic interference (EMI)

and electromagnetic compatibility (EMC)issues

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Ideal Switch

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Real Switch

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Real Switch

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Real Switch

• However, for most analysis purposes switchesare assumed to be ideal.

• Practical behavior is to be considered whiledesigning an actual power electronicconverter (You will not face this!!)

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Desirable Characteristics of a Switch

Please see yourself in Rashid/Mohan/JA

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Power Diodes

• A pn junction diode is the most basic type ofpower semiconductor device

• A diode acts as a switch to perform variousfunctions, such as switches in rectifiers andfreewheeling in switching regulators.

• Similar to signal diode but have higher v and iratings

• Up to 6000 V and 4500 A !

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Device Structure

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P+

N- epi

N+ substrate

v

iAnode

Cathode

N = 10 cm19

19250 microns

10 microns

breakdown vol tage dependent

N = 10 cm

-3

-3D

14N = 10 cm

-3D

A

Physical Layout

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Signal Diode

Device Symbol

Power Diode

i-v characteristics

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Forward Conduction Region

Breakdown Region

IDEALREAL

/( 1)D TV nVD sI I e= −Shockley Diode Equation

Reverse Recovery Characteristics

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Reverse Recovery Characteristics

• Current in forward-biased junction diode is dueto the net effect of majority and minority carriers.

• Once its forward current is reduced to zero, thediode continues to conduct due to minoritycarriers that remain stored in pn-junction and thebulk semiconductor material.

• The minority carriers require a certain time torecombine with opposite charges and to beneutralized.

• This time is called reverse recovery time of thediode.

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Contd...• The reverse recovery time, trr , is measured from the

initial zero crossing of the diode current to 25% ofthe peak reverse current.

• Softness Factor (SF) = tb/ta

• For practical purposes, we need to be concernedwith the total recovery time trr and the peak value ofthe reverse current IRR.

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barr ttt +=

dtditI aRR =

• The reverse recovery charge QRR is the amountof charge carriers that flow across the diode inthe reverse direction due to changeover fromforward conduction to reverse blockingcondition.

• Its value is determined from the area enclosedby the path of the reverse recovery current.

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• Therefore:

• Equating the two IRR equations will yield:

rr

RRRR

rrRRbRRaRRRR

tQI

tItItIQ

221

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21

=

=+=

dtdiQtt RR

arr /2

=35

• If tb is negligible as compared to ta, which is usually the case, then the above equation will be reduced to:

• Finally,

0,/

2≈= b

RRrr t

dtdiQt

0,2 ≈= bRRRR tdtdiQI

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• It can be concluded that the reverse recoverytime trr and the peak reverse current IRR dependon QRR and di/dt.

• The peak reverse recovery current, reversecharge, and the softness factor are all of interestto the circuit designer.

• These parameters are commonly included in thespecification sheets of diodes.

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