1  

Power Electronics

Prof. B.G. Fernandes

Department of Electrical Engineering

Indian Institute of Technology, Bombay

Lecture - 1

Power Electronics

Hello, I am B.G. Fernandez. I am with the department of electrical engineering, IIT Bombay. For another forty lectures or so, I will be dealing with various aspects of power electronics. Now, what is the definition of power electronics and what is the goal of power electronics, I will tell you sometime later. Power electronics is one of the basic courses in electrical engineering. It is a very interesting course, an important course and relatively easier to understand. So, all 3, in 1 course, very interesting, very important and relatively easy to understand. So, it is a very basic course in electrical engineering, it can be termed as course on circuits. I will be using Kirchhoff’s voltage law, that is KVL, Kirchhoff’s current law, that is KCL and behavior of inductor and capacitor for DC excitation and AC excitation. So, these are the prerequisites. Definitely, all this topics you would have studied in your eleventh or twelfth standard. Having said, that power electronics is a basic course, to appreciate this course, you need to know or you need to have reasonably a good knowledge on circuit theory, good knowledge on electrical machines, power systems, power semi conductor devices, little bit of device physics. So, if there are devices, definitely you need to know, little bit of analog electronics, digital electronics, control theory and microprocessor or micro controllers. So, in this sense, power electronics is a multi disciplinary course. So, little bit of almost all the branches and all the subjects in electrical engineering is been covered or you need to know the various topics to appreciate this course. So, I will not talk much on this course, I expect you to explore more about it, during the course. So, the outline of the course, I have divided into 6 parts.

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Time: 04:59)

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Time: 13:36)

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responsibilio come. We end this perioal energy vUse the elecrom one forefficiency o

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Time: 19:37)

ow you a cyne is drivingloss at the sl. Power is blevels. So, gtion takes plhere is bein

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o, if the inpus around jusnput of fuel 0%. So the

when the lossonversion efs at the fronilo watt of los saved hereilo watt here

Time: 21:26)

ut is 100 kilt 15 to 20 kenergy. Ho

question is, ses are at thefficiency of tt end or at toss saved at results in s

e is equal to

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o watt of fuekilo watts ofow much the

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kilowatts of here.

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f fuel energy

att is the inppeat, 100 kiof the orderand their eq

nversion, imen the bulk ois very simplo watts of py here, 6 kilo

put, output ilo watt is r of 15 to quipment,

mprove the of the loss ple. Every power that o watts. 1

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o, that is fficiency. Sexplore moreuclear or the

Nuclear poweWhat about bmonoxide, niwarming, tem

ne of the neight at the ational daily

That is becaffects agricuapan. The def gasses, a s

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We all know,nd what are ither a fan tyhe power thaan types ofnduction mohe machineslmost constonsumptions

Time: 22:35)

the reason econd is usee on renewabermal powerer plant, waburning of fitrogen diox

mperature is ational dailirate of 10 cy. Every yeuse of glob

ulture and veveloped coupecific type

e the urban pehicles. Can e there is a w, bulk of thethe majority

ype of load oat is being cof loads, pumtor, the spee

s that we hatant speed. s is by ligh

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I told youe the electrible. What ar plants or b

aste handlingfossil fuel? Txide NO2. Cgoes on inc

ies. It says centimeter. Tear Mount Ebal warmingegetation. Suntries, whas. In other w

pollution. Noyou do som

way or looke power that y of the loador a pump tyonsumed glomp or comped is approxiave, separateSpeed doeshting. Light

u that, imprcal energy e

are the problburning of fg is still a prThey give ouoal burningreasing. Glothat every y

This was repEverest heigg. That has o in 1997, t

at they decidwords, try to ow, major comething abos like there is being con

ds? Major loype of load. obally is, indpressor typeimately consely excited Ds not changting consum

rove the efefficiently alems that arfossil fuel? Wroblem, safeut carbon di

g, it give ouobal warminyear Mount ported the otght decrease

resulted to there was a

ded was to cureduce the b

oncern in urbout reducing

is a solutionnsumed by eoads are indFan, pump,duction mace of loads. stant for all pDC machinege much anmes another

fficiency, cand if possibre associatedWhat is the ety of nucleaioxide, ozon

ut the fly asng, other day

Everest is ther day in oes by 10 cen

climatic chconference

ut down theburning of fban pollutiothe urban p

n to all this pelectric moto

duction motocompressors

chines drivinAnd we k

practical pure, induction

nd not a bugood perce

onversion ble, try to d with the problem? ar plants?

ne, carbon h. Global

y I read in losing its

one of the ntimeters. hanges. It

at Quito, e emission fossil fuel. n is again pollution? problems. ors. Bulk,

or, driving s. Bulk of

ng either a know that rposes, all machine,

ulk power entage of

9  

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Refer Slide T

Now, if you whe air deliverbout high kiischarge, whrovide a reseduce a dischrottling walo reduce, theolved. You he dampers, nput, remaipproximately0% or 50% utput. Insteable to regulahe case of pu

as been prowell as power

be significato save 1

y fuel can by inductionBut, sort of portional to

ok here, fan tportional to o

Time: 28:45)

want to redured by the failo watt fan hat will you sistance to tcharge. So, bll for the pume air suppliecan reduce toutlet damp

ins approxy the same ior fully ope

ad, if we tryate the air in ump. Then w

oduce globalr that is bein

ant reductionkilo watt o

be saved at n motors af torque spee

square of thtype of TL isomega cube.

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uce the dischans. I am notthat are useddo? Either

the flow of by the usingmps, you med or the outhe pump dipers, you caimately coinput, whethen, approxim to reduce ththe case of f

what happens

lly. So, if yng consumedn on this oveof power atthe input. I nd that are

ed characterihe speed. TL

s proportion.

harge throught talking abod in a indusyou use damair or use a

g the dampemay be able tutput of the ischarge by

an regulate thonstant. Thher you havemately the sahe speed itsefan or we ares to the input

you try to sad by motorserall saving t the load said bulk o

e driving eistics of theL is proporti

nal to omega

h the pump oout the 60 wstry. If you wmpers or in oa throttling wers in the cato reduce. Sopump dischthrottling th

the air flow,e drive, te closed the ame. We areelf, speed ofe able to reg

ut then? See h

ave on this s if you try tof the electrend, 6 kilo

of the powereither fan

ese loads. TL

ional to squaa square. So,

or you want atts fans, I awant to reduother wordswall for the

ase of fans oorry, you wiharge. The phe wall, by at what costhe motor throttle wal

e able to regf the rotation

gulate the dishere.

power on to reduce, ric power. o watt of r is being pump or

L the load are of the therefore

to reduce am talking uce the air , dampers

e pump to or using a ill be able purpose is providing st? Power

taking ll whether gulate the n. We are scharge in

10 

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Refer Slide T

ower inputsatio is 1 oveonsumed, if o, you are tischarge dep

Nothing comhe machinesonstant spee

want to channergy I wan

machine, we motor runs appeed of the requency coonstant volpproximatelyrequency souf now, becahat voltage a

we require a sing the frenergy. Whatirectly switc0 hertz, induraws a largeo come from

Time: 31:27)

, suppose ther 8. So, thef you reducetrying to acpending upo

mes for free. s or for thated motors, apge or regula

nt to vary thhave to chanpproximatelrotor, how

onverter bectage, assumy constant. urce, there i

ause I want band frequencfrequency co

equency cont are the othch on to the suction machie current, cou

m a source, at

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e ratio of twere is a sign

e the speed ohieve both,

on the procesI told you int separately pproximatelyate or vary thhe speed of rnge the frequly at the synto reduce thause voltag

med to be Variation is

is available. be change thcy will haveonverter to v

nverter, I tolher advantagesupply voltaine, what hauld be of thet force throu

wo speeds is nificant reduof rotation, osame energ

ss requiremenduction maexcited DCy constant she output dirotation. Deuency of thenchronous sphe synchrone that has bconstant v

s very smalBut then, I

he speed of , we will seevary the speld you that es? What ha

age and suppappens if I die order of 6 augh the cable

point 5, omuction in theone-eighth,

gy as well aent. But thenachine, almo

C machine, ispeed motorsischarge. Soefinitely, ine input voltapeed. So, if

nous speed ibeen supplievoltage andl. So, constneed to charotation. Noe some timeed, of the inwe are able

appens the inply rated freqirectly start ias or rated. e to the mach

ega 1 to ome power thatsignificant r

as regulate tn again, at wost for that minduction ms. Here is a

o, in order tothe case of

age, because f I want to ritself? So, I ed by the u

d frequencytant voltage,ange the freqow, what rele later. So, anduction mace to save onduction maquency. So, 4it or DOL stNow, that cuhine. So, the

ega 2, the t is being reduction. the output what cost? matter, all

machine or process, I

o save the induction induction

reduce the require a

utilities is y remains , constant quency as lationship

as of now, chine. So,

on electric achine if I 415 volts, tarting? It urrent has

ere will be

1 

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voltage dipmomentarily,s a large curlow. So, a slowing throncreases. In

What happenecreases, Nshe speed of ta and at startarting. Now

(Refer Slide

told you, aeducing the

will tell you.requency of nd output voutput frequerequency, I homes down.liminated, stooks like, tholtage dip gef the machined by a contably, deliveeen applied.nd it is the r

p. That is w, the intensitrrent shouldstress on theugh the maother words

ns if I try ts minus Nr. Nthe rotor. Sorting, slip is

w, if I reduce

Time: 36:35

as of now, Ifrequency, I. As of nowthe output.

oltage, we wency can be rhave to redu. So, if the tress on the

here are lot oets eliminatene improves

nstant voltagering some l. So, b is corated flux be

why, in the sty of the buld flow throue cable is aachine winds, life of theto reduce thNs is the syn

o, Ns minus Nequal to 1. the frequen

5)

I am just taI have to redw, I just saiSo, what is

will see somereduced, Ns uce applied vmagnitude o

e cable reduof benefits. ed, stress on s. So, what nge and frequload torque. onstant. If because am a

sense, whenelk comes dowugh the cablalso more ifding. Stresse machine che frequencnchronous spNr is nothinSo, Ns minucy, Ns has c

alking aboutduce a voltagd a frequenthe relation

e time later. Scomes down

voltage alsoof inrush co

uces and impOne is unabthe cable ge

next? What uency supply

Input voltais constant,

applying the

ever you puwn, then the

le. 6 times af I directly s on the mcomes downcy itself? If peed, 120 F

ng but SNS.us Nr is equ

come down.

t reducing tge also. Reasncy converteship what bSo, if I am trn. It so happ. So, magnitomes down,proves the lble to save tets eliminatehappens in y? Say 415

age is 415, r, flux in the rated voltag

ut on large he voltage dipa rated currestart. That

machine windn, if I directlf the input f

by P minusS is slip, slid

ual to Ns itse

the frequencsons, sometier. It has toetween the frying to redupens that as Itude of inrus the voltagelife of machthe power, sed, reduces rthe machine, 50 hertz irated voltage machine, isge at rated f

hp motor, p. Second ent it can current is ding also ly start it. frequency

s Nr. Nr is de me hai elf during

cy. While ime later I o vary the frequency uce, if the I reduce a sh current e dip gets hines. So, second is, rather, life e is being s running e that has s constant frequency.

12 

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o, area flux The core losshat load of torque. If the

Assume that lso keep chlux remains osses also vaor maximal eow, am negirectly fromnd if the looaded, efficifficiency of ondition forosses. Whenosses have cemained samy reducing to the motor.here is an auhe size of thes well as aut

By the way, hegulate the seduced voltaegulators.

(Refer Slide

is the rated ses, core losthe motor ise load of thit is changianging. Youconstant, co

ary. Now whefficiency isglecting the

m utility suppoad of the miency of thef the motor r maxima en the load oncome down, me. Now, I wthe air gap f. How do I uto transforme machine itto transforme

how are we vspeed of theage to the m

Time: 43:25

flux. Therefsses remain s varying. Inhe machineng, the variu have kept ore losses rehat are the cs constant lo

frictional aply, wherein motor is of e motor is vwhen it is fficiency is n the motor

constant lowant to reducflux density.vary the inp

mer. The siztself. So defier, plus it is

varying the e fan. What otor, in orde

5)

fore, the conconstant, b

n other word is varyingable lossesthe input v

emain constaconditions fosses should

and wind aginput voltagvariable typ

very poor. Slightly loadvariable lo

is varying,osses have rece the core lo That I can put voltage ze of the autinitely, it is bexpensive.

speed of theexactly are

er to reduce

nstant losses because flux ds, motor is , that is a which are f

voltage consant. Load is

or maximal ebe equal to

ge. So, if I ge is assumepe, when thSo, it is posded by decross should bmotor is lig

emained samosses. I can rdo by reducto the moto

to transformbulky, entire

e fan? We arwe doing?

the speed. S

also remain is constantsupplying aprocess req

function of lstant. Theres varying, soefficiency? Cvariable lossam feeding ed to remainhe machine ssible to impeasing the fbe equal toghtly loadedme or core lreduce the ccing the inpuor? In the la

mer could be e, overall set

re using a reWe are app

See here, her

n constant. t. Assume a variable

quirement. load, they fore, area o variable Condition ses. As of a motor,

n constant is lightly prove the flux. See,

o constant d, variable losses are ore losses ut voltage ab, maybe

as big as t of motor

gulator to plying the re are two

13 

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This is a old ofter sometim

we have to mir to flow, sohis regulatorhe motor is ircuit, it beco

Refer Slide T

ee, here is aan have a vteps, it is a unction, reguan see just witchboard, f it gets hot,ow, very eleegulator to, ometime late

one, very rume this regulmount it on th

o that to coor, these are tvery low. Inomes hot. V

Time: 44:27)

another reguvery smooth

contacted tulate the spethe knob, smdefinitely, h

, definitely wegant. How such a smaler.

ugged. Variatlator becomehe switch bool the entire the openingsn other word

Very raged, m

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ulator. You h control, vetype. Here,eed of the famooth contr

heat dissipatiwe have to mis this poss

ll elegant reg

tion is in stees very hot, oard and therset up. Thers and it becods, when yo

may be.

could have ery smoothlyvery smooth

an. It is mourol. So, if ition is negligmount it outible, from sgulator? Ma

eps. If I keepextremely hre are lot of re got a resisomes very hou introduce

seen a smaly varying sh, both of t

unted inside tt is so smal

gible. If thereutside. So hesuch of masay be this qu

p it in very lohot. That is t

openings hestance inside

hot when thee the resistan

ll elegant respeed. Here,them doing the switchboll mounted ie is a heat dieat dissipatiosive regulatuestion, I wi

ow speed, the reason ere for the e. To cool e speed of nce in the

egulator. I , just see, the same

oard. You inside the issipation, on is very tor, heavy ill answer

14 

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Refer Slide T

o, here is ans a power selectronic equonducted deesistor. This ome, very efficiencies sariation in s

Overall conve

o, coming bwhich is drivhe machine. t lighted loa

What is thirdhe speed itserequency hase variable she US. Why

Time: 46:01)

n internal stremi conductuipment. Thevice, this is

is a power selegant, lighhould be vespeed, dissipersion efficie

ack to the thing a load oSo, we can

aded conditid benefit? Seelf is varyins been chanspeed drives? May be en

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ructure of thted device. I

his is one typs the one, Lsemi conducht weight, vry high becapates powerency is low.

heory, if I canf variable lohave eta is eions. How tee, I was tolng. Speed ofnged, in 70%. Whereas, inergy, cost p

he regulator. I told you spe of a pow

L, C and smcted device …very small, ause there isr, so definiteSo, this is a

n try to reduoad, it is posequal to eta to do this? Wld that in Japf the motor

% of the air cinstead of thper unit may

May be a csuppose, it i

wer electronicmall small re…… So, thino heat di

s no heat disely, power c

another exam

uce the inputsible to impmax, of maxWho will apan 70 % ofitself is varyconditioners

hat thing justy be very low

coil, a capacis a heart ofc device, poesistors, higis is being usssipation, cossipation. Heconsumption

mple.

t voltage to trove the effiximal efficie

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15  

must be very expensive. Looks like, everything has been driven by economics. What is the use of using a variable speed in air conditioners? Or to understand that what happens in the window air conditioners that are been directly switched on or off. There is thermostat inside. Temperature is being controlled within a band, hysteresis band. When the temperature falls below a certain value, AC is put off, temperature starts increasing and when it crosses upper limit, AC is again switched on. What is a problem here? Same problems, direct online starting of induction machine, voltage dip, voltage cable wire or stress on the cable and machine life comes down. Instead, can you vary the speed itself, slowly accelerated, so you can now, you can control the temperature, very smoothly. Very smooth, control of temperature is possible, air conditioners as well as refrigerators. What next? slip ring induction machine. When do you go for slip ring induction machine? When the power rating is high. For low power motors it is invariably, squirrel cage is the constructions, cage rotor. As the power rating increases, slip ring induction motors can be used. So, in any induction machines, s times the air gap power input is dissipated as heat in the rotor. So, air gap power input is approximately equal to input power itself. So, s times the input power is dissipated as heat. Now, instead of dissipating as heat, can this power be fed back to the source? Yes. Can I recover? What are the power that is there in the power that has been dissipated as heats? Can it be fed back to the source or is it possible to increase the starting torque and decrease the starting current electronically? Yes, our machines teacher has told, connect a resistor r to the slip rings, whereby, reducing the starting current and increasing the starting torque. Can you do this electronically? See, I am posing various problems to you and at the end. We will see, whether this problems can be addressed using power electronics. More on this, we will see in the next class. Thank you.