giao_trinh_bien_tan

8/7/2019 giao_trinh_bien_tan

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Chng IIITNG QUAN V CC LOI

BIN TN

B bin i tn s hay cn gi l cc b bin tn l thit b bin idng in xoay chiu tn s ny thnh dng in xoay chiu c tn skhc m c th thay i c.i vi cc b bin tn dng cho vic iu chnh tc ng c xoaychiu th ngoi vic thay i tn s ca chng cn c th thay i c inp ra khc vi in p li cp vo b bin tn.I. PHN LOI BIN TN :B bin tn c chia lm hai nhm:

+ Bin tn my in.+ Bin tn van.

1.Bin tn my in:


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nguyn l chung ca loi bin tn ny l dng my in xoay chiu lmngun in c tn s bin i.

2 =f1=

~

F F

~f1=

K1

CKF CKU1

BTK

f1 =

10

20 ffr

=

Hnh 3.1. S nguyn ly b bin tn may

Du (+) ng vi trng hp rto BTK quay ngc chiu t trng.Lc ny fr > f1.Du (-) ng vi trng hp rto BTK quay cng chiu t trng.Lc ny fr < f1.Khi rto ng yn th fr = f1.

Nh thay i tc 2 ta c th thay i tn s ra.Vic s dng cng nh iu khin loi ny rt phc tp v phi s dngnhiu my in, din tch lp t ln, hiu sut lm vic thp, gy n,nn mng phi kin c nn gi thnh cao.2. Bin tn van:Nguyn l lm vic ca bin tn van l dng cc tn hiu iu khin ng m cc van ( y thng l tiristor hay transisto ) bin i nng


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lng in xoay chiu tn s ny thnh nng lng in xoay chiu ctn s khc. Bin tn van c chia lm 2 loi :

+ Bin tn trc tip.+ Bin tn gin tip.

Bin tn van c ng dng rng ri v c nhiu u im nh: kch thcnh nh, khng gy n, h s khuch i cng sut ln, hiu sut cao.

II. GII THIU V BIN TN VAN :1. Bin tn trc tip:Thit b bin tn trc tip l loi bin tn c tn s vo f1 c bin i

thnh tn s f2 mt cch trc tip khng phi qua khu trung gian f2 = (00,5)f1, thng dng cho truyn ng c cng sut ln, tc lm victhp. n gin trc ht ta phn tch s mch lc ca bin tn mt pha:

Mach

van

U~

U~f1

Hnh 3.2. S khi va s nguyn ly

Zt

Lcb

Lcb

N

P


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Cc nhm van P, N c th c iu khin ring hoc chung. Khi iukhin ring th khng cn cun khng cn bng. Khi iu khin chung

th cun khng cn bngdng hn ch dng incn bng xut hin do schnh lch in p tc thilc ng nhm ny mnhm kia m qu trnh qu khng xy ra tc thi.

Nhm van P to nachu k dng ca in pti, nhm van N to nachu k m ca in p ti.Trong mch iu khin,ngi ta s dng du ca dng in ti quyt nh nhm van no philm vic. Khi mt nhm van c ch nh lm vic th n lm vic ch chnh lu v ch nghch lu ph thuc.

U,I

t4

t

t3t2t1t0

I

U

Nhom

Nhom

Hnh 3.3. Cac giai oan lam vic cuacac nhom van b bin tn trc

ti .

CLCL

Thi im pht xung m cho cc Thyristor trong mi nhm phi c phnb sao cho in p trn ti l phn hnh sin nht v gi tr trung bnh cain p u ra lun tng thch vi gi tr tc thi ca in p mongmun (U=Umsin2t ). iu chnh tc ng c in xoay chiu ta dng b bin tn ba phagm ba b bin i song song ngcS bin tn trc tip c u iml hiu sut cao khng dng t chuyn mch.

ZcZbZa

Hnh 3.4. S nguyn ly mach lc b bin tn trc tip ba pha chong c in xoay chiu ba pha


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Nhc im ca s l gam tn s hp f2 < 20Hz, phi dng nhiuThyristor v nhy cm vi bin ng ca li in.

2. Bin tn gin tip:S cu trc ca mch:

NghchLoChnh

f1

f1~,u1

=

=

f2

,f2u2~

Hnh 3.5 : S cu trc ca b bin tn gin tip

Trong bin tn ny in p xoay chiu u tin c chuyn thnh mtchiu nh mch chnh lu, qua b lc ri mi bin tr li in p xoaychiu vi tn s f2. in p u ra c iu chnh nh s thay i gc

thng ca cc van trong nhm chnh lu hoc iu ch rng xung.Vic phi bin i nng lng hai ln lm gim hiu sut bin tn songb li loi bin tn ny cho php thay i d dng tn s f2 khng phthuc f1 m n ch ph thuc mch iu khin.

B bin tn gin tip nh nu trn c s chc nng nhhnh sau :

~u1,f1

Chnh

F

K

~u2,f2

iu khin

NghchLo


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Hnh 3.6 : S chc nng b bin tn gin tip.

Ty theo tnh cht ca b chnh lu v dng tn hiu u ra m b bintn c lp li c chia ra lm 2 loi :*B bin tn ngun p (hay l b nghch lu ngun p)*B bin tn ngun dng (hay l b nghch lu ngun dng )

III. CC PHNG PHP BIN TN GIN TIP :A. B NGHCH LU DNG :1. B nghch lu dng mt pha:B nghch lu ngun dng thng dng cho cc h thng cng sut ln,trong cc van bn dn iu khin hon ton khi ti mang tnh cm

khng th cn cc Diod to thnh cu ngc cho dng in phnkhng i qua khi du ca dng ti ngc vi in p cun dy Ld c in

idLd

+

-T3

T2

T4

T1

D4

D1 D2

D3

Ii

t

Hnh 3.7. S nguyn l mch nghch lu dng mt

pha v dng dng ti


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cm ln san bng dng chnh lu v lc cc thnh phn sng hi bccao.

Ld

Hot ng s :Gi s T2 v T ang dn dng chy t B sang A.4 Ti t = 0 cho m T1 v T3 th T2 v T4 b kha bi thit b chuyn mch.V dng khng th thay i t ngt nn dng vn chy theo chiu c.D1 v D3 dn, T1 v T3 vn b kha.T t1t2 th T1 v T3 dn nu cn xung iu khin.T t2t4 cho xung m T2 v T4, T1, T3 b kha nhng t t2t3 th D2, D4

dn cn t3t4 th T2, T4 mi dn dng in p ra trn ti c dng sin chnht "Sinus" n l hm l chu k...2. B nghch lu dng ba pha:Khi nghch lu dng dng bin i dng in mt chiu sau b

lc thnh dng in xoay chiu cung cp cho ng c khng ng bba pha . Trong cc h thng truyn ng in iu chnh th nghch ludng thng dng cho cc h thng cng sut ln v c s cu bapha, trong cc van bn dn l cc van iu khin hon ton . y tadng cc tiristor . Ngun in mt chiu Ud thng qua cun dy c incm ln cung cp cho cu bin tn dng in hng Id .

id+E

T1 T3

Trong cu bin tn , mi tiristor c ni thm mt diode , gi l diodechn. Cc tiristor c iu khin m theo trnh t : 1, 2, 3, 4, 5, 6, 1, ...

T4 T6

D1

D4 D6

R

S

T

C1 C2

C3

C4 C5

C6

-

Hnh 3.8 S nguyn l b bin tn ngun dng 3 pha

A


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Hnh 3.9 S phn phi xung cho cc Thyristor


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Ti bt k thi im no, tr giai on trng dn , ch c hai tiristor dn

dng . Dng in ti c dng sng gn sin ch nht gm hai khi. Cckhi cch nhau mt khong , trng hp l tng , bng /3, trongkhong ny dng in pha ti bng 0.Cc pha stator ca ng c ln lt nhn cc dng in sin ch nhtlch nhau gc 2 /3 , to ra t trng quay m tc ca n quyt nhbi nhp iu cp xung iu khin cu bin tn. ng c in sn sinh ra cc pha cc sc in ng tng ng

tsinU2uR

=

=3

22

tsinUuS

=

3

42

tsinUuT

Hot ng ca b nghch lu dng ba pha:Ngun cung cp cho nghch lu l ngun dng in, ngun in mtchiu khng ph thuc vo tng tr ca ti. thc hin c iu nythng th in cm Ld phi c gi tr ln v phi s dng cc mchvng iu chnh dng in . Dng in ti c dng hnh ch nht v dotrnh t ng ct ca cc van t T1 n T6 quyt nh.Gi tr hiu dng ca dng in ti:

3

2ds II =

Gi tr hiu dng ca thnh phn sng c bn dng in trong phn tchFourie l:

61 ds II =

T y ta suy ra:


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1

1cos63

ds

UU =

Khi nghch lu ngun dng lm vic vi ti l ng c in xoay chiuth trn th in p ti c xut hin cc xung nhn ti cc thi imchuyn mch dng in gia cc pha.Trong thc t k thut thng dng cc van iu khin khng hon tonv vy cn c cc mch kha cng bc cc van ang dn , m bochuyn mch gia cc pha mt cch chc chn trong phm vi iu chnhtn s v dng in rng .Trong s cu ny ngoi cc tiristor lc T1T6 cn s dng cc diodecch ly hay diode chn t D1 D6 nhm cch ly gia cc t inchuyn mch v dy qun cc pha ca ng c khng ng b K chng khng to thnh mch cng hng lm nh hng n qu trnhchuyn mch . xt s hot ng ca b nghch lu dng ba pha ny ta xt qu trnhchuyn dng in t pha R sang pha S , v t pha T sang pha R .


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Hnh 3.11 S chuyn mch t pha R sang pha S

SU

T1

D1

D4

T4

C1 C 2

C3

AId

T3

D3

D6

T6

T5

D5

D2

C'

T2

C4

C6

B C

A'B'

C5

UR

UT

RST

~~

~

t 2

2

2_

/3

t

t

Ed

iR

0

iS

0

iT

0


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* Chuyn dng in t pha R sang pha S:Gi thit T1, D1, D2 v T2 ang m cho dng chy qua. Dng in Id chyvo ti pha R v t ti pha T chy ra. Lc ny , in p trn cc t innh sau:

01 Uuu BAC == 02 == BCC uu

03Uuu CAC ==

Khi t = t1 , cho xung iu khin m T3 .Tiristor ny m , t in puBA=-U0 ln T1 kho T1 . Dng in Id , t ngun , lp tc chuyn quaT3 , ri r thnh hai nhnh . Nhnh th nht , IC1 = 2 Id / 3 , np in choC1 ; nhnh th hai , IC2 = IC3 = Id /3 np in cho C2 ni tip C3 . Dngin hai nhnh hp li chy qua D1 vo ti pha R ri ra ra ti pha Tqua D2 v T2 tr v ngun .T in C1 v C3 c np ngc so vitrc . Lc ny (t=t1) ,D3 vn cha dn dng . Trong mch vngBARSB ta c phng trnh:

RSCD uuu += 13

Khi t t2, uD3 0, diode D3 bt u dn dng . Dng Is t zero tng dn ntr Id cn dng IR t tr Id gim dn xung zero .Khi t = t3 , kt thc qutrnh chuyn mch . Lc ny T3 v T2 dn dng :

UBA= -U0 , UCB= U0 , UCA=0.

Chuyn dng in t pha T sang pha RLc ny T2 v T3 ang dn dng , ta c :

UAB=0 , UBC=U0 , UCA= -U0 .

Khi t=t4 , cho xung iu khin m T4 . Tiristor ny t in p - U0 lnT2 kho T2 . Dng in Id chy qua D2 , chia thnh hai nhnh .Nhnh


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B bin tn ngun p hay l b nghch l in p c t im ldng in p ra ti c nh hnh sn, cn dng dng in ti li ph

thuc tnh cht ti. Ngun cp in cho b bin tn phi l ngun scin ng vi ni tr nh. Nu s dng chnh lu lm ngun cho bnghch lu c lp th cn phi mc thm mt t in C0 u vonghch lu mt mt m bo in p ngun t b thay i, mt khc trao i nng lng phn khng vi in cm ti ( vi ti R hoc ng cin ) . in p ra ca b nghch lu c lp khng c dng hnh sin nhmong mun m a s l dng xung ch nht . nh gi sng hi ca

in p ra ng

i ta th

ng dng h s sau:1U

UK

q

q =

trong Uq , U1 l tr hiu dng ca sng hi bc q v bc 1 ( sng cbn ) .Cc van bn dn dng trong b nghch lu c lp c th l tiristor hoccc transisto ( bipolar , MOSFET, IGBT) , nhng ph hp v u vic hnc l dng transisto do ngi ta trnh dng tiristor . Cc s

nghch lu c lp phn ln c dng tng t nh mch chnh lu ,thng dng nht l cc s cu . V vy di y ch xem xt s bnghch lu c lp loi cu dng van iu khin khoa

1. B nghch lu p cu mt pha:

Trang 38

+

-

id

Zt

U

T1c

it

D1

D4

D2

D3

T1 T1

T3

U BET1,T3

U BET2,T4

U tit

iT

i

id

t

t

t

t

t

t

0C

42TT31TT


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S nghch lu in p mt pha nh hnh gm c 4 van T1,T2,T3,T4 v cc diode chn tng ng D1,D2 ,D3,D4 .Cc van T1 T4 c iu

khin theo cp T1,T3 v T2, T4 lch pha nhau mt gc 1800 . na chuk u iu khin m T1,T3 , in p ngun s t ln ti vi cc tnhnh trn hnh (du trn) .Ta c :

ut = ENDng in chy t cc dng ngun qua T1 - Zt - T3 v cc m ca

ngun.n thi im T/2 hoc ta o trng thi iu khin cho T1 T3 v T2

T4 dn. Nhng do ti c tnh cm nn dng in khng o chiu ngayc. Nng lng lch ly in cm s duy tr dng in theo chiu c, lc dng in but phi thot qua cc diode D2 , D4 v ngun theong D2 , cc dng EN , qua ngun EN xung cc m ( hoc qua tCo ) -D4 ( mt phn dng ti s qua T2, T4 theo chiu ngc) . Nh vy ,do D2 , D4 v T2 , T4 dn , in p ra ti o cc tnh ngay ( du di )nn lc ny ut = - EN , song dng in it vn duy tr chiu c cho n thiim t

2

mi o chiu. n im 2 li o trng thi, qu trnh din ratng t , dng s duy tr chiu c mt on bng t1 nh cc van D1, D3 ,T1, T3 ri mi o chiu . Qua mt chu k ti nhn c in p vdng in l xoay chiu , y chnh l nguyn l nghch lu . xc nh quy lut bin thin ca dng ti ta c th s dng ccphng php gii mch tng t khi phn tch cc b iu chnh xung pmt chiu :Vi hm nh Laplace tc ng trong mch l :

( )2/

2/

11

11)(

pT

pT

NpT

tpTee

pEdtetu

epU

+=

=

Ta suy ra biu thc dng in ti :

( )

+=

2/

/

1

21

T

t

N

te

e

R

Eti

vi =L/R .Biu thc ny hay c vit di dng :( )

+

=30

1

/21

a

QeItit


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Trang 40

trong R

EI N=0 gi l dng c s.

R

L

Q

.

= vi l tn s gc v

T

2= ; Qea 3/1=

Khi c biu thc dng in ti it ta xc nh cc c tham s khcca s Dng in ti cc i c xc nh :

3

3

0max1

1

2 a

aI

TiI t +

=

=

tr hiu dng ca dng ti c xc nh :( )

+

+=

=

1

121

2

13

3

0

0a

aQIdiI

tt

Thi im dng ti v n 0 tng ng vi ( ) 01 =ti l :

311

2ln.

aQ

+=

T y c dng trung bnh qua van iu khin :

+

== QaaI

diI tT 3

3

1

0

11

1

2)(

2

1

Tr hiu dng ca dng ny l :

+

=

= Q

a

aaIdiI thdT

)1(2

23

2

1).(

2

13

63

10

2

Cc tr s tng ng ca dng qua diode :

+

== 13

3

0

1

01

1

2)(

2

1

Q

a

aIdiI tD

( )

+

+=

13

63

012

321

2

1

Q

a

aaIIhdD

Dng in tiu th t ngun EN l:


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Trang 41

( )( )

( )

+

+==

1

121

13

3

0a

aQIdiI td

Cng sut hu ch ti tiu th t ngun :( )

( )

+

+==1

121

3

3

0a

aQIEIEP

NdNd

Cng sut biu kin ly t ngun :( )

( )

+

+==

1

121

3

3

0a

aQIEIUS

Ntt

Suy ra h s cng sut :( )

( )

+

+=

1

121

3

3

a

aQ

S

P

Phn tch dng ut thnh dy Fourier ta c tr s hiu dng ca sng hibc q l :

( )[ ]qNq

q

EU 11=

Nhvy sng hi ch c cc bc l v c h s :qU

UK

q

q

1

1

==

Trng hp dng mch chnh lu lm ngun cho b nghch lu in p,do tnh cht ch cho dng in chy theo chiu xc nh , m boqu trnh phng in v ngun cn c mt t in Co u vo bnghch lu in p.Xut pht t quy nh v n nh in p ngun v qu p chophp trn t Uc khng nn qu 10 % v cho rng ton b dao ngdng in ti do t Co gnh chu , ta rt ra c tr s in dung cn c :

+

+

2/2/

2/

01

2ln

1

1

. TT

T

C

N

ee

e

UR

EC

Biu thc trn cho thy vi tn s lm vic cng thp cn c Co ln hngi tr gi tr Co ln nht khi tn s f 0 v bng :

( )C

d

C

d

UR

E

UR

EC

=

.

.293,02ln1

.max0

Qua biu thc Uq v Kq ta thy bin cc sng hi bc thp kh ln

so vi sng hi c bn .i vi ti l ng c in th iu ny hon ton


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Trang 42

khng mong mun .V vy ngi ta c gng loi tr cc sng hi bcthp.

2. Nghch lu p ba pha:a.S nguyn l :Hot ng ca s :Nguyn tt hot ng ca b nghch lu p ba pha da trn nguyn lhot ng ca b nghch lu p mt pha. b nghch lu p ba pha ctt c su van cc van l S1, S3, S5 nm pha trn cn cc van chn S2,S4, S6 nm pha di, hai van trong cng mt pha th khng ng thi

dn ngha l van ny dn th van kia s kha v ngc li. c dngchy qua ti th nu c mt nhm van c ch s l bt but phi c t nhtmt van thuc nhm chn dn..

Hnh 3. 14 : S nguyn l mch nghch lu pba pha

Nu van c ch s thuc nhm l thng hoc Diod ngc i km nthng th in p u ra tng ng ca pha vi im khng l Ud/2.Ngc li nu van c ch s chn thng hoc Diod i km vi n dn thin p u ra ca pha i vi im khng l -Ud/2.

Ta c:

U10-U30UZ31

U30-U20UZ23

=

=

U20-U10UZ12 =

0321

1331

3223

2112

=++

=

=

=

ZZZ

ZZZ

ZZZ

ZZZ

UUU

UUU

UUU

UUU

+ VR1 S1

VR3 3

S VR5 S5

- VR4 S4

1 UZ31 2

3

UZ12


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Trang 43

( )

( )( )2331312132

31131

31 31

31

ZZZZZZ

ZZZ

UU/UUU/U

UU/U

= =

=

T

Ud

2Ud/3

T/

Uz1

Uz2

Uz3

Uz1

Hnh 3. 15 : Dng in ra trn ti sau b nghch lu.

in p dy v in p pha nh sau:Khai trin Furie in p dy v in p pha:

+++=

=

tSintSintSintSinuu

tSintSintSintSinuu

dA

dAB

1111

17

7

15

5

12

1111

17

7

15

5

132


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Trang 46

Hnh 3.16. S nguyn l v dng sng chnh lu cu 3 pha c iu khina) S b) Dng sng khi gc m nhc)Dng sng khi gc m ln


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DrZt

LcDc

Ta

TpC

-

+b. iu chnh bin in p mtchiu bng b bm xung:

B bm in p mt chiu gm c:Tp: Thyristor chnh; Thyristor ph;Lc iu chnh; C l phn t chuynmch; Dr l Diod hon nng lng.Khi Tp m th Uf = V, t C phngin v c np theo chiu ngc vi cc tnh nhhnh v.

Hnh 3.17. S nguyn ly

Khi ta m th Tp b kha Uf= 0. Ut V

t

T1

Hnh 3.18. Chu ky xung iu

khin m Thyristor

Gi T l chu k bm T = T1 + T2.T1 = T l thi gian ng mchca Tp.T2=T-T1 l thi gian h mch.

= T1/T l t s chu k.Gi tr trung bnh ca in p ti:

Uf= V.

Vy bng cch bin i t s chu k (T = Const) c th iu chnh

cgi tr trung bnh ca in p ra.2. iu chnh thi gian ng ngt ca cc van thay rng xung: lm c iu ny ngi ta tm cch xy dng trong nghch lunhng chuyn mch ph sao cho in p ti s c mt on bng khng.V d i vi b nghch lu p ba pha: trong mt khong = /3ta chiathnh hai khong v . Trong khong th hai van nhm ny v mt

van nhm kia dn nh

bnh th

ng, nh

ng trong khong th c ba

Trang 47Hnh 3.19. Gian

2

2/

Ufa

T4T5T6

T3T4T5

T2T3T4

T1T2T3

T6T1T2

T5T6T1


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Trang 48

van trong mt nhm cng dn in p pha ti trong khong ny bngkhng.

3. iu bin rng xung (PWM):Phng php iu bin rng xung cho php va iu chnh c inp ra va gim nh c nh hng ca cc sng hi bc cao. xcnh khong pht xung chm iu khin cc van, ta to ra mt sng dngSin Ur c tn s bng tn s mong mun gi l sng iu bin. Dngmt khu so snh Ur v Up , cc giao im ca hai sng ny xc nhkhong pht xung.

T s gia bin sng iu bin v bin sng mang gi l t s iubin.M = Ar/Ap

iu chnh rng xung tc l ta iu chnh in p ra trn ti ta iuchnh Ar. iu bin rng xung c chia thnh hai loi:

- iu bin rng xung n cc.- iu bin rng xung lng cc.

a. iu bin rng xung n cc (hnh 3.20a).

in p ra trn ti l mt chui xung, rng khc nhau, c tr s 0 v E.


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Trang 49

Ut Ur

2

2

Hnh 3.20a. Dng in p ra ca iu ch rng xungn cc

b. iu bin rng xung lng cc (hnh3.20b).

in p ra trn ti l mt chui xung, rng khc nhau, c tr s E.


26/26

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2

2

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uE+

Ut Ur

Hnh 3.20b. Dng in p ra ca iu ch rng xung lng cc

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