An AC-AC Converter for Doubly Fed Induction Generator Driven By Wind Turbine

8/10/2019 An AC-AC Converter for Doubly Fed Induction Generator Driven By Wind Turbine

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International Journal of Scientific and Research Publications, Volume 4, Issue 12, December 2014 1ISSN 2250 !15!

An AC-AC Converter for Doubly Fed InductionGenerator Driven By Wind Turbine

Chetan S. Rawal ! Dr. Anwar ". "ulla

"Post#raduate Student in Po$er S%stem from De&artment of 'lectrical 'n#ineerin#,"" P( (uide, P)D in )i#h Volta#e 'n#ineerin# from De&artment of 'lectrical 'n#ineerin#**+nnasaheb Dan#e olle#e of 'n#ineerin# and -echnolo#%, +shta, San#li, .aharashtra, India

Abstract - -his &a&er deals $ith a D/I( model em&lo%in# nines$itches + + con erter* +s com&ared to the con entionalD/I( em&lo%in# ac3 to ac3 &o$er con erter the nine s$itchcon erter re uires fe$er s$itches and #ate dri e circuits*-herefore &ro&osed to&olo#% results in reduction of installationarea and cost* -he nine s$itch con erter D/I( is a&&lied to the$ind turbine and inte#rated $ith the #rid* -he results re eal thate en thou#h chan#e in $ind s&eed occurred, the #enerator terminal olta#e and fre uenc% remain same* -he #enerator out&ut &o$er follo$s the $ind s&eed and deli ers the more

&o$er to the #rid*

Index Terms D/I( Doubl% /ed Induction (enerator6, RSRotor Side on erter6, (S (rid Side on erter6, P7.Pulse 7idth .odulator6, Nine S$itch on erter

I* I N-R8D9 -I8N

s con entional ener#% sources are #oin# to be de&leted er%soon, $ind &o$er is the most reliable and de elo&ed

rene$able ener#% source o er &ast decades* -he 7' S utili:in#ariable s&eed ariable &itch $ind turbine $ith D/I( is the most

&o&ular in the $ind &o$er industr% es&eciall% for multi me#a$attsi:e* -he &o$er con erters bein# utili:ed in the D/I( &la% er%im&ortant role in maintainin# the constant olta#e and fre uenc%*)armonics $ill be certainl% &roduced $hene er con erter &artsare bein# used* )o$e er &resence of this harmonic le el can bereduced b% reducin# the si:e of the con erter* )ence there isneed to reduce the si:e of the &o$er con erters in the Doubl%/ed Induction (enerators s%stem in order to reduce theharmonics &roduced* 9suall% in the con entional D/I( s%stemtotall% 12 number of s$itches are bein# utili:ed i*e* si; number of s$itches for rectification and another si; number of s$itchesfor in ertification* )ence there is need to minimi:e the number of s$itches b% de elo&in# a ne$ model $hich must consist of

less number of s$itches as com&ared to con entional ac3 toac3 con erter* So b% de elo&in# ne$ less number of s$itches

bein# utili:ed con erter the cost and s&ace re uirement of &o$er con erters can be reduced*

+

-he main reason for the &o&ularit% of the doubl% fedinduction #enerators connected to the national net$or3s is their abilit% to su&&l% &o$er at constant olta#e and fre uenc% $hilethe rotor s&eed aries of rated #eneration &o$er i*e* the sli&

&o$er in the rotor circuit and remainin# &o$er is directl% fed tothe #rid from the stator &art


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conce&t is to inter&ose a fre uenc% con erter bet$een theariable fre uenc% induction #enerator and fi;ed fre uenc% #rid*

-he D ca&acitor lin3in# stator and rotor side con erters allo$sthe stora#e of &o$er from induction #enerator for further #eneration* -o achie e full control of #rid current, the D lin3

olta#e must be boosted to a le el hi#her than the am&litude of #rid line to line olta#e* -he sli& &o$er can flo$ in bothdirections, i*e* to the rotor from the su&&l% and from su&&l% to the

rotor and hence the s&eed of the machine can be controlled fromeither rotor or stator side con erter in both su&er and subs%nchronous s&eed ran#es* +s a result, the machine can becontrolled as a #enerator or a motor in both su&er and subs%nchronous o&eratin# modes reali:in# four o&eratin# modes*

elo$ the s%nchronous s&eed in the motorin# mode and abo ethe s%nchronous s&eed in the #eneratin# mode, rotor sidecon erter o&erates as a rectifier and stator side con erter as anin erter, $here sli& &o$er is returned to the stator* elo$ thes%nchronous s&eed in the #eneratin# mode and abo e thes%nchronous s&eed in the motorin# mode, rotor side con erter o&erates as an in erter and stator side con erter as a rectifier,$here sli& &o$er is su&&lied to the rotor* +t the s%nchronouss&eed, sli& &o$er is ta3en from su&&l% to e;cite the rotor $indin#s and in this case machine beha es as a s%nchronousmachine*

Fi#.'% (ower flow dia#ra) of DFIG

-his &a&er &resents a control strate#% b% means of al#ebraicanal%tical relationshi&s #i en b% the mathematical model of themachine to the &erformances of doubl% fed induction #eneratorsusin# bac3 to bac3 con erter, thereb% ma;imi:in# the efficienc%of the #eneration s%stem* -he main &roblem usin# rene$ableener#% sources is to ma3e them $or3 at full &o$er for differento&eratin# conditions of the source* -his is usuall% achie ed b%means of the im&lementation of control al#orithms 3no$n as.PP- al#orithms* /or $ind &lants it is not so eas% because $ind

chan#es ra&idl% and randoml%* -he out&ut &o$er of a $indturbine can be $ritten asA

PB C** CCCCC* 16

-he &o$er co efficient & is a function of the &itch an#le and ti& s&eed ratio * -he results re eal that the out&ut &o$er re#ulation of a $ind turbine can be achie ed in t$o $a%sA actin#on the ti& s&eed ratio and actin# on the &itch an#le*

-his &a&er #i es information about the controllin# of D/I($ind turbines usin# bac3 to bac3 ariable fre uenc% con erter* -he mechanical &o$er and the stator electric &o$er out&utare com&uted as follo$s

CCCCCCCCCCC* 26

CCCCCCCC*******C** !6

/or a loss less #enerator the mechanical e uation is

J CCCCCCCC**CC** 46 In stead% state at fi;ed s&eed for a loss less #enerator

+nd CCC********CC** 56

+nd it follo$s thatB CC*C* ?6

7here,

SB is defined as the sli& of the #enerator

(enerall% the absolute alue of sli& is much lo$er than 1and, conse uentl%, P r is onl% a fraction of P s* Since - m is &ositi efor &o$er #eneration and since is &ositi e and constant for aconstant fre uenc% #rid olta#e, the si#n of P r is a function of thesli& si#n* Pr is &ositi e for ne#ati e sli& s&eed #reater thans%nchronous s&eed6 and it is ne#ati e for &ositi e sli& s&eedlo$er than s%nchronous s&eed6* /or su&er s%nchronous s&eedo&eration, P r is transmitted to D bus ca&acitor and tends to raisethe D olta#e* /or sub s%nchronous s&eed o&eration, P r is ta3enout of D bus ca&acitor and tends to decrease the D olta#e*

#rid is used to #enerate or absorb the &o$er P #c in order to 3ee&

the D olta#e constant* In stead% state for a lossless + D +con erter P #c is e ual to P r and the s&eed of the $ind turbine isdetermined b% the &o$er P r absorbed or #enerated b% rotor * -he

&hase se uence of the + olta#e #enerated b% rotor is &ositi efor sub s%nchronous s&eed and ne#ati e for su&er s%nchronouss&eed* -he fre uenc% of this olta#e is e ual to the &roduct of the#rid fre uenc% and the absolute alue of the sli&* rotor and #ridha e the ca&abilit% for #eneratin# or absorbin# reacti e &o$er and could be used to control the reacti e &o$er or the olta#e atthe #rid terminals*

A. Steady State Characteristics -he stead% state e ui alent circuit of D/I( is sho$n in

belo$ fi#*2*+

Fi#.'.A% Steady &tate e*uivalent circuit of DFIG

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International Journal of Scientific and Research Publications, Volume 4, Issue 12, December 2014 !ISSN 2250 !15!

-o obtain the tor ue e uation from the e ui alent circuit, $ecan sim&lif% the stead% state induction motor circuit b% mo in#

to the stator terminal *-he rotor current is e;&ressed asA

CCCCCCCCCCC* E6

-he electrical tor ue -e, from the &o$er balance across thestator to rotor #a&, can be calculated fromA

CCCCCCCCC***CCC F6

7here the &o$er su&&lied or absorbed b% the controllablesource inGectin# olta#e into the rotor circuit, that is the rotor acti e &o$er, can be calculated from

CCCCCCCCCCCC H6

**CCCCCCCCCCCCC 106

III* 8 P'R+-I8N 8/ N IN' S7I- ) 8NV'R-'R

+s sho$n in /i#*1*2 ondition 1 Se1 then S +8 is onondition 2 Se2K then S +I is on

Table.$% Switchin# &tate& and converter out+ut volta#e&

"ode ,Switche&

In+ut and ,ut+ut node volta#e&

1 S+8, S+. V+R BVdc , V R BVdc

2 S+., S+I V+R B0, V R B0

! S +8 , S+I V+R BVdc, V R B0

Se1 and Se2 can be e;&ressed asSe1B CCCC* 116Se2B CCCCC*** 126

7here,

, is the out&ut and in&ut fre uenc% res&ecti el%*, are the modulation inde; and , are the offset

of out&ut and in&ut references si#nals res&ecti el%*In this to&olo#% ;, %, : are connected to the #rid and lo$er

s$itches S +I , S I , S I 6 o&erate as a rectifier or (rid Sideon erter* +, , are connected to the rotor, therefore u&&er

s$itches S +8 , S 8 , S 8 6 o&erate as an in erter or Rotor Sideon erter*

IV* 8N-R8@ 8/ N IN' S7I- ) 8NV'R-'R

In the D/I( based $ind turbines rotor current re#ulation onthe stator flu; oriented reference frame* -herefore the d a;is isali#ned $ith the stator flu; lin3a#e ector L s , namel%, L sBLdand L sB0* -his results in follo$in# relationshi&s


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and 6 to form the d olta#e si#nals and * 7here

and are assumed as

CCCCCCCCCC 216

6 **CCCC** 226

-he% are then used b% the carrier based P7. method to#enerate .8S/'- #ate control si#nals of the RS *

-he obGecti e of the (S is to 3ee& the D lin3 olta#econstant re#ardless of the ma#nitude and direction of the rotor

&o$er* -he control of D lin3 olta#e, and D/I( stator terminals olta#e, Vs, are achie ed b% current re#ulation on as%nchronousl% rotatin# reference frame* -he out&ut olta#e

si#nals and from the current controllers are used b% thecarrier based P7. al#orithm to s$itch the #rid side of nines$itch con erter* /i#ure 4*1 sho$s the o erall ector controlscheme of the (rid Side on erter


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/i#*1E sho$s the simulation model of nine s$itch con erter*It consists of totall% three le#s, each le# consistin# of threes$itches* -hen total number of s$itches is nine* -he abo e si;s$itches act as Rectifier i*e* the con ersion of + D and the

belo$ si; s$itches act as In erter i*e* the con ersion of D + *-he &ulses for all the .8S/'- #ates are #enerated usin# the

olta#e si#nals #enerated from RS and (S com&arin# $iththe carrier $a e si#nal*

Fi#./.B% Si)ulation )odel of nine &witch converter

VI* SI.9@+-I8N R 'S9@-S

-he D/I( &arameters are #i en in -able 2*

Table.'% (ara)eter& of the DFIG &i)ulated

Rated Po$er 2.7Stator Volta#e ?H0VRs 0*010F&uRr 0*0121&u referred to the

stator6@m !*!?2&u@s 0*102&u@r 0*11&u referred to the

stator6 Number of &ole &airs

2

In order to e aluate the d%namic &erformance of the &ro&osed D/I(, sudden ariation in the $ind s&eed is made*

A. Generator output power/i#*?*+ sho$s the #enerator out&ut &o$er* It is obser ed that

$hen the $ind s&eed is increased at 12 sec, the &o$er out&ut of the #enerator also sli#htl% increased* In means the #enerator out&ut &o$er follo$s the $ind s&eed and deli ers more &o$er tothe #rid $hene er $ind s&eed increases

Fi#.0.A% Generator out+ut +ower

B. Stator output reactive power/i#*?* sho$s the stator out&ut reacti e &o$er* +t 12 sec

there is sudden ariation in the $ind s&eed i*e* initiall% $ind

blo$in# at 12m s increased to 15m s at 12 sec* -he referencealue of reacti e &o$er is set to :ero and stator reacti e &o$er &roduced b% #enerator is tried to 3ee& around :ero* In the abo efi#ure it is obser ed that at the time of $ind s&eed chan#e thereacti e &o$er #enerated b% stator is maintained constant around:ero*

Fi#.0.B% Stator out+ut reactive +ower

C. Generator terminal voltage

/i#*?* sho$s the stator each &hase out&ut olta#e* It isobser ed that, initiall% $hen the $ind is blo$in# at 12 m s stator terminal each &hase olta#e is around ?H0 olts* -hen at 12 sec,$hen $ind s&eed chan#es to 15m s the ma#nitude of stator out&ut each &hase olta#e is not affected and is maintainedalmost constant i*e* around ?H0 olts* It means irres&ecti e of the$ind s&eed chan#es and rotor s&eed ariation the stator out&uteach olta#e remains almost constant in order to ma3e it &ossibleto inte#rate the $ind turbine #enerated &o$er $ith the #rid* -hisis one of the er% essential controllin# as&ects in doubl% fedinduction #enerators achie ed throu#h nine s$itch con erter*

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International Journal of Scientific and Research Publications, Volume 4, Issue 12, December 2014 ?ISSN 2250 !15!

Fi#.0.C% Generator ter)inal volta#e&

D. Generator terminal current /i#*?*D sho$s the each &hase #enerator terminal current* 7e3no$ that $hen $ind s&eed increases the &o$er deli ered to the#rid also increases* +s stator terminal olta#e is #oin# to remainconstant durin# $ind chan#es, the current dra$n b% the #ridincreases in order to increase the &o$er deli ered to the #rid* Itcan be obser ed in /i#*22 that $hen there is sudden chan#e in

the $ind s&eed at 12 sec the ma#nitude of each &hase stator out&ut current increases sli#htl%* Stator out&ut terminal each &hase olta#e and current are in &hase* It means that the#enerator is o&eratin# a&&ro;imatel% at its unit% &o$er factor*

Fi#.0.D% Generator ter)inal current

E. Generator rotor speed /i#*?*' sho$s the #enerator rotor s&eed* It is obser ed that

before the ste& chan#e in $ind s&eed occurred i*e* $ind blo$in#at 12m s, the rotor is rotatin# at 0*55&u but $hen the $ind s&eedincreases to 15m s the rotor s&eed also increases* +fter a fractionof second the rotor s&eed a#ain #ains its stead% state at 0*?E&u*/rom /i#*21 and 2! it can be clearl% obser ed that e en thou#hthere is chan#e in rotor s&eed in course of time &eriod because of

chan#e in $ind s&eed the stator terminal each &hase out&utolta#es remains almost constant* /rom /i#*1H and 2! it is clear

that the &o$er deli ered to the #rid from the #enerator increases$ith increase in rotor s&eed because of chan#e in $ind s&eed*

Fi#.0.1% Generator rotor &+eed

VII* 8N @9SI8N

-his thesis &resented a D/I( model em&lo%in# ne$ nines$itches + + con erter* +s com&ared to the con entionalD/I( em&lo%in# ac3 to ac3 &o$er con erter the ne$ nine

s$itch con erter re uires fe$er s$itches and #ate dri e circuits*-herefore &ro&osed to&olo#% results in reduction of installationarea and cost* -he ne$ nine s$itch con erter D/I( is a&&lied tothe $ind turbine and inte#rated $ith the #rid* -he results re ealthat e en thou#h chan#e in $ind s&eed occurred, the #enerator terminal olta#e and fre uenc% remain same* -he #enerator out&ut &o$er follo$s the $ind s&eed and deli ers the more

&o$er to the #rid* It means &ro&osed D/I( $ill o&erateaccordin# to control strate#ies aims in the $ind s&eed sudden

ariations

R '/'R'N 'S


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International Journal of Scientific and Research Publications, Volume 4, Issue 12, December 2014 EISSN 2250 !15!

+ 9-)8RS

Fir&t Author hetan S* Ra$al, Post#raduate Student in Po$erS%stem , +nnasaheb Dan#e olle#e 8f 'n#ineerin# and-echnolo#%, +shta, San#li, .aharashtra, India,rchetan1441U#mail*com*

Second Author Dr* +n$ar .* .ulla, P( (uide, P)D in )i#hVolta#e 'n#ineerin# from De&artment of 'lectrical'n#ineerin#**, +nnasaheb Dan#e olle#e 8f 'n#ineerin# and-echnolo#%, +shta, San#li, .aharashtra, India

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An AC-AC Converter for Doubly Fed Induction Generator Driven By Wind Turbine

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