gt_dtcs 1 thay nguyen van nho (bk hcm)

7/29/2019 Gt_dtcs 1 Thay Nguyen Van Nho (Bk Hcm)

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CHNG M AU:

CAC HE THC VA KHAI NIEM C BAN

TR TRUNG BNH CUA MOT AI LNG:Goi i (t) la ham bien thien tuan hoan theo thi gian vi chu ky Tp. Tr trung bnh cua ai lngi, viet tat la IAV c xac nh theo he thc:

+

=Tp0t

0tpAV dt).t(i

T

1I

Vi t0 la thi iem au cua chu ky c lay tch phan.

Ta thng hay gap cac ai lng tr trung bnh c bieu dien vi ch so I d (Direct mot chieu) hoac IAV (Average .... tr trung bnh), v du ien ap trung bnh UAV, dong ien trungbnh IAV.

V du 0-1

Xet qua trnh dong ien tren hnh ve H0.1 , tr trung bnh dong ien cho bi he thc:

]A[6dt.105.0

1dt).t(i

5.0

1I

3.0

0

5.0

0

d ===

Trong nhieu trng hp, thc hien tch phan theo ham bien thi gian phc tap hn thc hien

tch phan theo bien goc X vi X cho bi he thc:X=.t vi la tan so goc nao o xac nh.

Khi ay, tr trung bnh ai lng theo goc X tnh theo he thc:

++ Xp0XTp0t11


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Tnh tr trung bnh ien ap chnh lu cua bo chnh lu cau 1 pha khong ieu khien. Ham ien

ap chnh lu co dang u=Um.sin(.t) ; vi Um=220 2 [V]; =314[rad/s].

Giai:

De dang thay rang, chu ky cua dang ap tren la Tp=0.01[s]. at X=314.t;Xp=314.0 ,01=[rad].

Ta co:

]V[198dX.Xsin.22201

dX).X(uX

1U

0

Xp0X

0Xpd =

== +

Cac trng hp thng gap:Tai R:Quan he gia ien ap va dong ien tc thi qua ien tr R cho bi:uR=R.iRLay tr trung bnh hai ve ta co:URAV=R.IRAVTai L:

Ta co: dtdi. LL Lu =

che o xac lap iL(t0)=iL(t0+Tp), tr trung bnh ien ap tren L c xac nh bangcach lay tch phan hai ve cua he thc tren trong thi hian (t0.t0+Tp). Ket qua thu c:

ULAV=0

Tai RL:


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Tr trung bnh dong khong phu thuoc vao gia tr L ma ch phu thuoc vao R va ien aput.

Tai RLE:E

dt

di.Li.Ru ttt ++=

Vi E la sc ien ong khong oi: E=const.Ket qua: UtAV=R.ItAV+E hay ItAV=(UtAV-E)/R

CONG SUAT TRUNG BNHCong suat tc thi cua mot tai tieu thu c xac nh bang tch ien ap va dong ien tc thidan qua tai o, tc la:

)t(i).t(u)t(p =

Cong suat trung bnh c xac nh bang cach ap dung cach tnh trung bnh vao ai lngcong suat tc thi p(t), tc la:

==PP T

0P

T

0PAV dt).t(i).t(u

T

1dt).t(p

T

1P

hoac theo bien goc X=wt:

PP

X

0P

X

0PAV T.X;dX).X(i).X(u

X

1dX).X(p

X

1P

PP

===

Trng hp dong qua tai khong oi theo thi gian i=const=IAV , cong suat trung bnhqua tai bang tch cua ien ap trung bnh va dong ien:

PAV=UAV.I=UAV.IAV

Trng hp ien ap at tren tai khong oi theo thi gian u=const=UAV, cong suattrung bnh cua tai bang tch ien ap va dong ien trung bnh:PAV=U.IAV=UAV.IAV

Cac trng hp ac biet:Tai R:

==PP T

0

2R

P

T

0

RRP

AV dt).t(i.RT

1dt).t(i).t(u

T

1P

==PT

0

2Rrms

2R

PAV I.Rdt).t(i

T

1RP

Tu ien va cuon khang la cac phan t co kha nang d tr va khong tieu hao cong suat. Dedang dan giai he thc cho cac tai L va C nh sau.Tai L: PAV=0


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Dong qua tai trung bnh:ItAV=(198-50)/1=148A

Cong suat trung bnh qua tai: do L ln vo cung nen dong qua tai khong oi trong suotchu ky. T o: it=ItAV=148A. Ta ap dung c trong trng hp nay cong thc:

Pt=UtAV.ItAV=198.148= 29304W=29,3kW

TR HIEU DUNG CUA MOT AI LNGGia thiet ai lng i bien thien theo thi gian theo mot ham tuan hoan vi chu ky Tp hoac vichu ky theo goc Xp= .T p. Tr hieu dung cua ai lng i c tnh theo cong thc:

++

==Xp0X

0X

2

p

Tp0t

0t

2

pRMS dX.i.

X1dt.i.

T1I

Ch so RMS ...Root Mean Square co ngha la tr hieu dung.

V du 0-4Cho mot ien ap dang ]V)[t.314sin(.2220)t.314sin(.Uu m == .

a.Tnh tr hieu dung cua ien ap tren ?Cho ham u1 va u2 vi tnh chat sau:

=2 va I(1) la tr hieu dung thanh phanhai c ban dong ien.Quan he gia DF va THD:

2)THD(1

1DF

+=

Bai tap:0.1 ien ap at tren tai ien tr 10 co ham bieu dien ]V)[t.100sin(.170u = .

Hay xac nh:

a. ham cong suat tc thi cua taib. cong suat tc thi ln nhatc. cong suat trung bnh cua tai

0.2 ien ap va dong ien tren tai la nhng ham tuan hoan theo thi gian vi chuky T=100ms.


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0.3 Xac nh cong suat trung bnh tren tai. Cho biet ien ap tai khong oiu=12VDC va dong ien qua tai tuan hoan co ham bieu dien trong moi chu ky T=100ms

nh sau:


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CHNG MOT

CAC LINH KIEN BAN DAN

Ban dan: la chat ma trong nhiet o bnh thng no co o dan ien gia chat dan ienva chat cach ien. Hien nay, ban dan thng dung la Silic, Silic tinh khiet co cau truc tinh therat ben vng. nhiet o thap, no khong co cac ien tch t do. V the, Silic tinh khiet hoatong nh chat cach ien.

Hon hp Silic vi cac nguyen to khac co anh hng rat ln en o dan ien cua Silic.

Mot cua hon hp cua Silic cha tha ien tch t do va cac ien tch nay tr thanh hat danien, hon hp nay tao thanh chat ban dan loai N. Mot so hon hp cua Silic thieu ien t-chung co lo hong. Cac lo hong tao thanh thanh phan dan ien chu yeu. Hon hp loai nay taothanh ban dan loai P vi o dan ien loai P.

Lp tiep xuc PN: la vung trong ban dan ma vung dan ien loai P c chuyen thanhloai N.

ac tnh V-A: bieu dien quan he gia dong ien i qua hai cc cua linh kien va ienap at gia cac cc o. Cac gia tr ien ap va dong ien nay c hieu la gia tr ap va dong

mot chieu khong oi.

1.1 - PHAN LOAI LINH KIEN BAN DAN THEO KHA NANG IEU KHIEN

Cac linh kien ban dan cong suat trong lanh vc ien t cong suat co hai chc nang cban: ong va ngat dong ien i qua no. Trang thai linh kien dan ien (ong) la trang thai linhkien co tac dung nh mot ien tr rat be (gan bang khong). o ln dong ien qua linh kien

phu thuoc trang thai mach ien luc linh kien ong va o sut ap tren linh kien nho khong angke (toi a khoang vai volt).Trang thai linh kien khong dan ien (ngat dong ien) la trang thai linh kien co tac

dung trong mach nh mot ien tr rat ln. Dong ien i qua linh kien co o ln khong angke; o ln ien ap at len linh kien phu thuoc vao trang thai hoat ong cua mach ien benngoai.

Do o, linh kien ban dan hoat ong vi hai che o lam viec ong va ngat dong ienc xem la ly tng neu trang thai dan ien no co o sut ap bang khong va trang thai

khong dan ien, dong ien qua no bang khong.Cac linh kien ban dan co the chuyen oi trang thai lam viec cua mnh , v du t trang

thai khong dan ien (ngat) sang trang thai dan ien (ong) va ngc lai thong qua tac dungkch thch cua tn hieu len cong ieu khien (ngo vao) cua linh kien. Ta goi linh kien co tnhieu khien. Tn hieu ieu khien co the ton tai di dang dong ien, ien ap, anh sang vi

t th h h t hi i t t i


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Ngc lai, cac linh kien co the thay oi trang thai t dan ien sang ngat ien vangc lai thong qua tac dung cua tn hieu ieu khien , c goi la linh kien co kha nang kch

ngat (Self commutated device-tam dch linh kien t chuyen mach). ai dien cho nhom linhkien nay la transistor (BJT,MOSFET,IGBT), GTO(Gate-Turn-Off thyristor),IGCT,MCT,MTO.

Tren ay, ta cha e cap en tac dung ien ap va dong ien cua mach cong suatlen qua trnh chuyen oi trang thai lam viec cua linh kien. Tn hieu ieu khien len manhcong ieu khien ch co tac dung khi trang thai ien ap at vao hai cc chnh ngo ra cua linhkien co chieu phan cc va o ln phu hp.

Vi nhng nhan xet tren, cac linh kien ban dan cong suat, theo chc nang ongva ngat dong ien va theo kha nang ieu khien cac chc nang nay, co the chia lam 3 nhomchnh:

- Nhom mot: gom cac linh kien khong ieu khien nh diode, diac;- Nhom hai: gom cac linh kien ieu khien kch ong c nh thyristor, triac;- Nhom ba: gom cac linh kien khien kch ngat c nh transistor

(BJT,MOSFET,IGBT), GTO.Ngoai ra, dang mach phc hp gom thyristor va bo chuyen mach cung co kha nang

ong dong ien cung nh ngat dong ien qua no nh tac dung cua cac tn hieu ieu khien lencac cong ieu khien. Ve kha canh ieu khien, mach phc hp nay cung vi cac linh kiennhom ba tao thanh nhom cong tac t chuyen mach.

1.2 - DIODE

Mo ta va chc nangDiode c cau tao thanh bi moi noi PN. Lp p thieu ien t va cha phan t mangien dang lo hong. Tng t, lp n tha ien t. Cac lp pn trong cau truc diode at cbang cach them tap chat vao trong phien silic. e tao qua trnh dan ien i qua moi noi p-n,cac hat mang ien c tao thanh va tham gia qua trnh dan ien, mot ien ap c ap dungsao cho lp p mac vao cc dng va lp n vao cc am. Lc ien trng lam cho lo hong t


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ac tnh V-Aac tnh V-A cua diode c ve hnh H1.1 gom hai nhanh. Nhanh thuan: tng ng

vi trang thai dan ien. Cac thong so quan trong cua no la ien ap u (TO) (turn on) va ien trrF (differential forward resistance) c xac nh tai mot iem tnh nao o cua ac tnh

F

FF

di

dur =

Nhanh nghch: tng ng vi trang thai nghch, diode khong dan ien. Cac thong soquan trong cua no la ien tr rR (differential reverse resistance) xac nh tai mot iem naoo cua ac tnh V-A.

r

du

diRR

R=

va ien ap anh thung chieu nghch u (Br) (Breaking). Sau khi ien ap vt qua giatr u(BR) th gia tr uR giam i rat nhieu lan. Gia tr dong sau o se phu thuoc chu yeu vao ienap va ien tr mach co cha diode trong o. Neu nh dong tang qua ln diode se b hong.

CAC TNH CHAT ONGTrong cac hien tng qua o cua diode, qua trnh diode chuyen t trang thai dan sang

trang thai nghch co y ngha quan trong. Hien tng nay goi la ngat diode hoac qua trnh

chuyen mach cua diode.Khi dong thuan qua diode tat nhanh (chang

han 10A/us), qua trnh ngat se khong dien ra theo actnh V-A. Qua trnh ngat dong nhanh co the theo doitren hnh H1.2. Sau khi ong khoa S, nhanh chadiode thong en ien ap chuyen mach U : U tac dungtat nhanh dong qua diode. Sau khi dong ien thuan iF

giam ve 0, dong ien qua diode khong tat ngay vatiep tuc dan theo chieu ngc lai vi toc o giam banau. Sau mot thi gian ngan, kha nang dan ien theo chieu nghch b mat va dong ien giamot ngot en gia tr cua dong ien nghch (nho khong ang ke ) - diode co kha nang chu apnghch, ien tr nghch rR cua no c khoi phuc.

Tren hnh ve H1.2 thi gian trr (reverse recovering) la thi gian phuc hoi tnh nghch.Dong irr i qua diode trong thi gian trr la dong chuyen mach hoac dong phuc hoi .

Thi gian phuc hoi tnh nghch cang ln neu nh gia tr ien tch chuyen mach Qr

cang ln. ien tch Qr cua diode c nh ngha nh sau:

Qr = rrt

rrdti

0

o ln Q phu thuoc vao cau truc cua phien ban dan Si va cong nghe san xuat no


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Mot he qua quan trong la cong suat ton hao khi ngat diode. Gia tr cong suat tc thinay c tnh bang tch cua dong va ap cua diode. Trong thi gian ien ap nghch tang len,

dong chuyen mach i qua diode ln. Gia tr cong suat ton hao tc thi v the se ln.Kha nang chu taiien ap nh mc: c xac nh bi ien the nghch cc ai URRM. o la ien ap

nghch ln nhat co the lap lai tuan hoan tren diode.Khi thiet ke mach bao ve chong lai qua ap nghch ngau nhien, ta nh mc theo ien

the nghch khong the lap lai uRSM. Khi diode lam viec, ta khong cho phep xuat hien ap lnhn uRSM.

Dong ien nh mc: diode khi hoat ong phat sinh ton hao. Ton hao chu yeu dodong thuan gay ra. Ton hao do dong nghch gay ra khong ang ke va cong suat ton hao doqua trnh ngat se co o ln ang ke khi tan so ong ngat ln hn khoang 400Hz. Cong suatton hao tong khong c phep lam nong mach diode len qua nhiet o cc ai VjM, neu khonglp PN se b pha hong . V the diode c lam mat va kha nang chu dong cua no b gii hanbi tr trung bnh cc ai cua dong thuan iF(AV)M . oi vi tng loai diode va ieu kien lammat, cac nha san xuat thng a ra cac ac tnh IFAVM = f (Tamb) (Tamb la nhiet o moitrng). oi vi nhng ac tnh khac nhau nay, thong so c chon la hnh dang cua dong

qua diode. Gia tr IFAV ng vi nhiet o Tamb va ieu kien lam mat cho trc va ng vi dangna song sin cua dong (50Hz) c goi la dong ac trng cua diode. Kha nang chu dong cuadiode hien nay khoang vai ngan ampere.

Kha nang chu qua dong: c cho dang o th qua dong IFSM = f(t), ng vi motgia tr dong vt qua mc bnh thng, o th cho biet khoang thi gian ma diode co khanang chu c ma khong b hong. Gia tr qua dong cho phep c goi la dong thuan cc aikhong the lap lai c IFSM. ng vi nhiet o ban au cho trc cua ban ban dan va tr cuaap nghch, gia tr IFSM cho biet o ln cua dong thuan chu c trong thi gian xac nh.

Mot thong so khac anh hng len kha nang qua dong la nang lng tieu hao , xacnh bang tch phan theo thi gian cua ham IF bnh phng. Lng nang lng nay t le vinang lng ma ban ban dan co kha nang hap thu di dang nhiet trong thi gian qui nh

(khoang 10ms) ma khong b hong. T ac tnh IFSM(t) va , ta co the thiet ke mach bao

ve qua dong cho diode.

dtIF. 2

Ghep noi tiep va song song cac diode c thc hien khi kha nang chu ap va dongcua cac diode khong ap ng c nhu cau at ra. Khi ghep noi tiep , ta can am bao tnhphan bo ien the eu tren cac diode.

Cac diode ac biet1. Schottky diode: o sut ap theo chieu thuan thap (khoang 0,3V). Do o, no c s

dung cho cac mach ien ap thap. ien ap ngc chu c khoang 50- 100V2. Diode phuc hoi nhanh: c ap dung trong cac mach hoat ong tan so cao. Kha


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ln nhat nh mcDiode phuc hoi nhanh1N3913 400V 30A 1.1V 400ns

SD453N25S20PC 2500V 400A 2,2V 3 s Diode phuc hoi ac bietnhanhMUR815 150V 8A 0,975V 35nsMUR1560 600V 15A 1.2V 60nsRHRU100120 1200V 100A 2.6V 60nsDiode SchottkyMBR6030L 30V 60A 0.48V444CNQ045 45V 440A 0.69V30CPQ150 150V 30A 1.19V

1.3-TRANSISTOR BJT CONG SUAT (BIPOLAR JUNCTION TRANSISTOR)

Transistor co hai lp PN, da theo cau tao lp nay ta phan biet hai loai transistor:transistor PNP va transistor NPN. Cac lp PN gia tng ien cc c goi la lp emitter J1va lp collector J2. Moi lp co the c phan cc theo chieu thuan hoac chieu nghch ditac dung cua ien the ngoai. S dch chuyen cua dong collector ic khi qua lp b phan ccnghch chu anh hng rat ln cua dong kch iB dan qua lp phan cc thuan. Hien tng naytao thanh tnh chat c ban c s dung nhieu cua transistor va c goi la hien tng ieuche o dan ien cua lp b phan cc nghch.

Trong lanh vc ien t cong suat, transistor BJT c s dung nh cong tac (khoa)ong ngat cac mach ien va phan ln c mac theo dang mach co chung emitter.

Tren ien cc B,E la ien ap ieu khien uBE. Cac ien cc C.E c s dung lamcong tac ong m mach cong suat. ien the ieu khien phai tac dung tao ra dong iB u lne ien ap gia cong CE at gia tr bang zero ( uCE 0).


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ac tnh V-A trong mach co chung emitter

ac tnh V-A ngo ra cua transistor mac chung cc emitter.ac tnh ngo ra (output characteristic) -hnh H1.4a,b -bieu dien quan he cua cac ai

lng ngo ra IC = f(UCE). Thong so bien thien la dong kch iB. Cac ac tnh ngo ra c vecho cac gia tr khac nhau cua iB trong vung 1 cua he toa o. Trong vung toa o nay con veng thang bieu dien ac tnh tai UCE = U - R.IC. Giao iem cua ng thang nay va actnh ngo ra (ng vi tr thiet lap iB) se xac nh iem lam viec gom dong IC va ien the uCE.

Trong vung cha cac ac tnh ngo ra, ta phan biet vung nghch, vung bao hoa vavung tch cc.Vung nghch: ac tnh ra vi thong so iB = 0 nam trong vung nay. Transistor che o

ngat. Dong collector iCO co gia tr nho khong ang ke i qua transistor va tai. Khi uBE < 0,khong co dong ien kch, transistor trang thai ngat va o ln dong iCO giam nho hn na.Tuy nhien, kha nang chu ap ngc cua lp cong emitter kha nho. Do o, can han che ienap am tren BE e no khong vt qua gia tr cho phep.

Vung bao hoa: nam gia ng thang gii han a va gii han bao hoa b. ng thang

gii han a xac nh ien the uCE nho nhat co the at c ng vi gia tr iC cho trc. Giihan bao hoa la ng thang xac nh ranh gii cua cac trang thai uCB = 0 va uCB > 0. Neu nhiem lam viec nam trong vung bao hoa (xem iem ONG), transistor se ong, dong iC danva ien the uCE at gia tr uCESAT nho khong ang ke (khoang 1-2 V) va nh vay, khi thchien tang dong ien kch IB>IBsat, dong ien qua collector hau nh khong thay oi. ien theuCESAT goi la ien the bao hoa va ta noi rang transistor trang thai bao hoa.

Vung tch vc: la vung ma transistor hoat ong che o khuech ai tn hieu, tng

ng vi cac gia tr lam viec uCE > uCESAT va dong iC>IC0. Moi quan he gia hai ai lng uCEva IC phu thuoc vao tai va dong iB. Khi transistor lam viec nh mot cong tac ong m(switching), iem lam viec cua no se khong nam trong vung nay.

He so khuech ai trong mach co chung emitterHe so khuech ai tnh cua dong: c nh ngha tai mot iem lam viec (IC,IB)UCE=const

(khi UCE = hang so ) bi tham so hFE:


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Khi tnh toan dong ien kch ong transistor, ta dung he so hFESAT xac nh cho iemlam viec nam trong vung bao hoa. Gia s trong vung bao hoa, ONG (hnh H1.4a) la iem

lam viec vi dong ien qua collector ICS va he so hFESAT c thiet lap tng ng vi iem B.Dong ien kch ong transistor c xac nh theo he thc:

FESAT

CSBS

h

II =

Dong ICS c xac nh t phng trnh ien ap mach tai:

R

UUi CESATCS

=

Mach kch phai tao dong IB u ln sao cho :

FESAT

CSBSB

h

III =>

Trong thc te, o ln dong kch c thiet lap vi he so an toan ks.

FESAT

CSB

h

I.kI =

He so ks =2 5 c chon e viec kch ong an toan khi xet en cac anh hng khacnhau lam thay oi thong so cua transistor va cac transisor cung loai cung co s sai biet tham

so do ieu kien che tao thc te. Viec a he so nay am bao cac transistor cung loai euat c trang thai bao hoa.

Ton hao phat sinh khi transistor dan ien:CCEBEBET I.UI.UP +=

Viec tang he soks qua ln se khong lam giam ien ap UCE bao nhieu nhng no cothe lam tang ang ke ien ap UBEva cong suat ton hao mach cong nay.

Cac transistor cong suat ln co he so hFE ch khoang 10- 20. Do o, e giam bt dong


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Khao sat cac hien tng qua o khi ong va ngat transistor co y ngha quan trong.Qua trnh dong collector IC khi kch ong co dang xung vuong ve tren hnh H1.5. Thi gian

ong ton keo dai khoang vai s. Thi gian ngat toffvt qua 10s.Mot he qua bat li trong cac hien tng qua o la viec tao nen cong suat ton hao doong va ngat transistor. Cong suat ton hao lam gii han day tan so hoat ong cua transistor.Gia tr tc thi cua cong suat ton hao trong qua trnh ong ngat tng oi ln, v dong ien iqua transistor ln va ien ap tren transistor trang thai cao. e theo doi mot cach n gian,ta co the hnh dung qua trnh ong ngat nh s chuyen oi iem lam viec t v tr NGAT env tr 0NG (hoac ngc lai) xuyen qua vung tch cc (hnh H1.5). Qua trnh nay keo daitrong thi gian ton hoac toff.

Kha nang chu tai :nh mc ien ap: phu thuoc vao ien ap anh thung cac lp ban dan va xac nh bi

gia tr uCEOM -gia tr ien the cc ai at len lp collector-emitter khi i B = 0 va gia tr cc aiuEBOM - ien the lp emitter-base khi iC = 0. Cac gia tr nay la nhng tr tc thi. Ta can phanbiet chung trong trng hp tai dang mot chieu khong oi theo thi gian va cac tai xung, macdau thong thng trong ca hai trng hp cac ien ap c thiet lap giong nhau.

nh mc dong ien: gia tr cc ai cua dong collector iCM, dong emitter iEM va dong

kch iBM. o la cac gia tr cc ai tc thi cua transistor khi ong trong trang thai bao hoa. Khithiet lap chung, ta xet en anh hng cua cac moi tiep xuc, day dan ti ien cc va cac gia trhFEsat, uCEsat.

Cong suat ton hao: cong suat ton hao tao nen trong hoat ong cua transistor khongc phep lam nong ban dan vt qua gia tr nhiet o cho phep TjM (TjM =150

0C). V the, canlam mat transistor va toan bo cong suat ton hao phai nho hn P totM. Cong suat ton hao chu yeudo cong suat ton hao tren collector, PC= UCE.ICE tao ra (cac thanh phan khac cua Ptot thng boqua ). Gia tr PtotM phu thuoc vao phng phap lam mat va c cho di dang ham so Ptot

=f(Tamb) (Tamb la nhiet o moi trng ), thong so la UCE . Cong suat ton hao hnh thanh khitransistor dan bao hoa, ngay ca khi IC = ICM, rat nho so vi gia tr PtotM. Cong suat ton hao khitransistor ngat thng khong ang ke. Trong che o xung, khi tan so ong ngat cao va vtqua gia tr chang han 2000 Hz th cong suat ton hao trung bnh do ong ngat co the at gia trang ke va lam cho cong suat ton hao tong co the vt hn PtotM.

Mach kch Transistor BJTe tang tan so ong ngat cua transistor cong suat, can giam thi gian ton,toff. e giam

ton ta co the a xung dong kch IB vi nh kha ln au giai oan kch. Sau khi transistor dan,co the giam dong kch IB en gia tr dong bao hoa.ieu khien kch ong:Gai dong ien kch co the at c bang mach (H1.7). Khi xung ien ap UB a vao,

dong ien qua cong B b gii han bi ien tr R1.


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ien t cong suat 1

1

1

R

UUI BEBO

=

Sau thi gian qua o, dong IB co gia tr:

21

1

1RR

UUI BEB +

=

Tu C1 c nap en o ln

21

2

BC RR

RUU

+

Hang so thi gian nap tu:

21

121

1 RR

CRR

+=

..

Neu nh ta cho ien ap UB ve 0, lp BE b phan cc ngc va tu C1 phong qua R2 .Hang so thi gian xa tu la 2 = R2.C1.. e u thi gian nap va xa tu, o rong xung phai thoaman :

t1 5.1t2 5.2Do o, tan so ong ngat ln nhat

2121

3

2011

+=

+==

,

ttTf

ieu kien kch ngat:Neu ien ap UB giam xuong gia tr am U2 < 0, ien ap ngc at len BE bang tong

ien ap UB va UC.Gai dong IB xuat hien, sau khi tu C1 xa het, ien ap tren BE xac lap bang U2. Neu can

thiet lap qua trnh kch ong va kch ngat rieng biet, ta co the s dung mach sau (H1.8):


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Diode D1 bao ve mach cong cua transistor trong thi gian kch ngatMach cach ly tn hieu ieu khien va mach kch :Cac mach phat ra tn hieu e ieu khien mach cong suat dung ban dan thng yeu

cau cach ly ve ien. ieu nay co the thc hien bang optron hoac bang bien ap xung.Bien ap xung: gom mot cuon s cap va co the nhieu cuon th cap. Vi nhieu cuon

day pha th cap, ta co the kch ong nhieu transistor mac noi tiep hoac song song. S onguyen ly mach cach ly tn hieu ieu khien dung bien ap xung c ve tren hnh H1.9.

Bien ap xung can co cam khang tan nho va ap ng nhanh. Trong trng hp xungieu khien co canh tac ong keo dai hoac tan so xung ieu khien thap, bien ap xung sm attrang thai bao hoa va ngo ra cua no khong thoa man yeu cau ieu khien.

Optron: gom nguon phat tia hong ngoai dung diode (ILED) va mach thu dungphototransistor. Tn hieu xung ieu khien c a vao LED va ngo ra c dan t

phototransistor (H1.10).


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Thi gian ton cua phototransistor khoang 2-5s, toff= 300ns.Mach dung optron oi hoi phai tao nguon rieng cho no. Do o, mach phc tap va ton

kem hn.Mach bao ve BJT

Dang mach bao ve BJT tieu bieu c ve tren hnh H1.11.

Tac dung cua mach nham bao ve transistor trc cac hien tng tang qua nhanh cua

ien apdt

du va dong iendt

di qua transistor.

Mach RC co tac dung han che o docdt

du gia hai cc CE. Cuon khang LS thc hien

giam s tang nhanh dong dtdi qua BJT.

1.4 - MOSFET (METAL - OXIDE - SEMICONDUCTOR FIELD EFFECTTRANSISTOR)

Loai transistor co kha nang ong ngat nhanh va ton hao do ong ngat thap c goi laMetal Oxide Semiconductor Field Effect Transistor(MOSFET) vi cong ieu khien bang ientrng (ien ap). MOSFET c s dung nhieu trong cac ng dung cong suat nho (vai kW) vakhong thch hp s dung cho cac ng dung co cong suat ln. Tuy nhien, linh kien MOSFET

khi ket hp vi cong nghe linh kien GTO lai phat huy hieu qua cao va chung ket hp vinhau tao nen linh kien MTO co ng dung cho cac tai cong suat ln.

MOSFET co hai loaipnp va npn. Tren hnh H1.12 mo ta cau truc MOSFET loai npn.Gia lp kim loai mach cong va cac moi noi n+ va p co lp ien moi silicon oxid SiO. iemthuan li c ban cua MOSFET la kha nang ieu khien kch ong ngat linh kien bang xung


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ac tnh V-A linh kien loai n c ve tren hnh H1.12, co dang tng t vi ac tnhV-A cua BJT. iem khac biet la tham so ieu khien la ien ap kch U GS thay cho dong ien

kch IBE.

MOSFET trang thai ngat khi ien ap cong thap hn gia tr UGS.e MOSFET trang thai ong, oi hoi ien ap cong tac dung lien tuc. Dong ien ivao mach cong ieu khien khong ang ke tr khi mach trang thai qua o, ong hoac ngatdong. Luc o xuat hien dong phong va nap ien cho tu cua mach cong. Thi gian ong ngatrat nho, khoang vai ns en hang tram ns phu thuoc vao linh kien. ien tr trong cua MOSFETkhi dan ien Ron thay oi phu thuoc vao kha nang chu ap cua linh kien. Do o, cac linh kienMOSFET thng co nh mc ap thap tng ng vi tr khang trong nho va ton hao t.

Tuy nhien, do toc o ong ngat nhanh, ton hao phat sinh thap. Do o, vi nh mc ap

t 300V- 400V MOSFET to ra u iem so vi BJT tan so vai chuc kHz.MOSFET co the s dung en mc ien ap 1000V, dong ien vai chuc amper va vi

mc ien ap vai tram volt vi dong cho phep en khoang 100A. ien ap ieu khien toi a20V (2V,5V,10V.. tuy theo loai), mac du thong thng co the dung ap en 5V e ieu khien

c no.

Cac linh kien MOSFET co the au song song e m rong cong suat.Mach kch MOSFET

e giam thi gian kch ong ton cua MOSFET ta co the s dung dang mach (H1.13a)Khi tac dung ien ap uG , dong ien tch ien ban au cho tu mach cong G:

S

GG

R

UI =

Sau o ien ap xac lap tren cong laRU


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ien t cong suat 1

S o mach kch c cai thien tren hnh H1.13b s dung cau truc totem-pole gom 2

transistor NPN va PNP. Khi ien ap kch U1 mc cao, Q1 dan va Q2 khoa lam MOSFETdan. Khi tin hieu U1 thap, Q1 ngat, Q2 dan lam cac ien tch tren mach cong c phongthch va MOSFET tr nen ngat ien. Tn hieu U1 co the lay t mach collector m (open-collector TTL) va totem-pole ong vai tro mach em (buffer).

Tng t nh BJT, mach kch cong G cua MOSFET co the c cach ly vi mach taotn hieu ieu khien thong qua bien ap xung, optron hoac cap quang (H1.14a,b).

Mach bao ve MOSFET

Cau tao khac biet cua MOSFET so vi BJT lam cho linh kien hoat ong tot makhong can bao ve nhieu nh BJT. Tuy nhien, ta co the s dung mach RC nho mac song songvi ngo ra cua linh kien e han che tac dung cac gai ien ap va cac xung nhieu dao ongxuat hien khi linh kien ong.


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ien t cong suat 1

IRF510 100V 5.6A 0.54 8.3nCIRF540 100V 28A 0.077 72nCAPT10M25BNR 100V 75A 0.025 171nCIRF740 400V 10A 0.55 63nCMTM15N40E 400V 15A 0.3 110nCAPT5025BN 500V 23A 0.25 83nCAPT1001RBNR 1000V 11A 1.0 150nC

*Qg: lng ien tch c nap va phong t ien dung ngo vao khi thc hien kchong va ngat transistor. Cong suat ton hao mach cong phu thuoc vao ai lng Qg theo hethc: sGSgG f.U.QP = ; fs la tan so ong ngat transistor.

1.5 - IGBT ( INSULATED GATE BIPOLAR TRANSISTOR )IGBT co ky hieu, mach ien tng ng ve tren hnh H1.15.IGBT la transistor cong suat hien ai, che tao tren cong nghe VLSI, cho nen kch

thc gon nhe. No co kha nang chu c ien ap va dong ien ln cung nh tao nen o sutap va phai khi dan ien.

IGBT co phan t MOS vi cong cach ien c tch hp trong cau truc cua no. Giongnh thyristor va GTO, no co cau tao gom hai transistor. Viec ieu khien ong va ngat IGBTc thc hien nh phan t MOSFET au noi gia hai cc transistor npn.

Viec kch dan IGBT c thc hien bang xung ien ap a vao cong kch G. ac tnhV-A cua IGBT co dang tng t nh ac tnh V-A cua MOSFET.

Khi tac dung len cong G ien the dng so vi emitter e kch ong IGBT, cac hatmang ien loai n c keo vao kenh p gan cong G lam giau ien tch mach cong p cuatransistor npn va lam cho transistor nay dan ien. ieu nay se lam IGBT dan ien. Viec ngatIGBT co the thc hien bang cach khoa ien the cap cho cong kch e ngat kenh dan p. Machkch cua IGBT v the rat n gian.


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Cong nghe che tao IGBT phat trien tang nhanh cong suat cua IGBT a giup no thaythe dan GTO trong mot so ng dung cong suat ln. ieu nay con dan en cac cai tien hn na

cong nghe cua GTO va tao nen cac dang cai tien cua no nh MTO,ETO va IGCT.Giong nh MOSFET, linh kien IGBT co ien tr mach cong ln lam han che congsuat ton hao khi ong va ngat. Giong nh BJT, linh kien IGBT co o sut ap khi dan ien thap(23V; 1000V nh mc) nhng cao hn so vi GTO. Kha nang chu ap khoa tuy cao nhngthap hn so vi cac thyristor. IGBT co the lam viec vi dong ien ln. Tng t nh GTO,transistor IGBT co kha nang chu ap ngc cao.

So vi thyristor, thi gian ap ng ong va ngat IGBT rat nhanh, khoang mot vai sva kha nang chu tai en 4,5kV-2.000A. Hien nay cong nghe che tao IGBT ang c ac biet

phat trien e at den mc ien ap vai ngan Volt (6kV) va dong ien vai ngan Amper.IGBT co kha nang hoat ong tot khong can en mach bao ve. Trong trng hp ac

biet, co the s dung mach bao ve cua MOSFET ap dung cho IGBT.Modul IGBT thong minh (Intelligent Power Modul): c che tao bi cong nghe tch

hp cao. Tren modul cha ng phan t IGBT, mach kch lai, mach bao ve, cam bien dongien. Cac modul nay at o tin cay rat cao.

Mach kch IGBT t thiet ke tng t nh mach kch cho MOSFET. Do gia thanh

IGBT cao, va ac biet cho cong suat ln, mach kch lai IGBT c che tao di dang IC congnghiep. Cac IC nay co kha nang t bao ve chong qua tai, ngan mach, c che tao tch hpdang modul rieng (1,2,4,6 driver) hoac tch hp tren ca modul ban dan (hnh thanh dangcomplex (bao gom mach lai, IGBT va mach bao ve) )

Tren bang B1.3 mo ta thong so mot so linh kien IGBT bao gom ien ap nh mc,dong ien nh mc, o sut ap khi dan ien (VTM) va thi gian ap ng khi kch dan linh kien(ton). Bang B1.9 so sanh cac thong so cua IGBT vi mot so linh kien cong suat ln nhGTO,GCT va ETO

Bang 1.3 Cac thong so ac trng cua IGBTLoai ien ap nh

mc ln nhatDong trung bnhnh mc

VTM ton (ac trng)

Linh kien riHGTG32N60E2 600V 32A 2.4V 0.62sHGTG30N120D2 1200V 30A 3.2V 0.58sLinh kien dang

moduleCM400HA-12E 600V 400A 2.7V 0.3sCM300HA-24E 1200V 300A 2.7V 0.3sModule ap thap

30V 60A 0.48V45V 440A 0 69V


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1.6 THYRISTOR (SCR- SILICON CONTROLLED RECTIFIER)

Mo ta va chc nangThyristor gom 3 lp PN va mac vao mach ngoai gom 3 cong: ien cc anode

A, cathode C va cong ieu khien G. Ve mat ly thuyet ton tai cau truc thyristor: PNPNva NPNP, trong thc te ngi ta ch phat trien va s dung loai PNPN. S o thay thethyristor bang mach transistor c ve hnh H1.16. Gia s anode cua thyristor chutac dung cua ien ap dng so vi cathode (uAK > 0). Khi a vao mach G, K cuacathode (tng ng vi mach base- emitor cua tranristor NPN) xung dong IG, transistorNPN se ong. Dong ien dan tiep tuc qua mach emitor -base cua transistor PNP vaong no. Cac transistor se tiep tuc ong ngay ca khi dong i G b ngat. Dong qua

collector cua mot transistor cung chnh la dong i qua base cua transistor th hai vangc lai. Cac transistor v vay cung nhau duy tr trang thai ong.Cac tnh chat va trang thai c ban:Neu transistor b ngat, th anode co the chu c ien ap dng so vi

cathode.- trang thai khoa ;hoac ien ap am so vi cathode - trang thai nghch.Hien tng ong SCR tc chuyen t trang thai khoa sang trang thai dan ien

co the thc hien neu thoa man ca hai ieu kien sau:

1/- Thyristor trang thai khoa.2/-co xung dong ien kch iG > 0 u ln.Hien tng ngat SCR : qua trnh chuyen t trang thai dan ien sang khong

dan ien (tc trang thai nghch hoac trang thai khoa). Qua trnh nay gom hai giaioan:


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ac tnh V-A ngo ra: quan he gia ien ap va dong ien i qua hai ccanode, cathode (xem hnh H1.17). ac tnh ngo vao quan he gia ien ap va dong

cong G (cong ieu khien).ac tnh V-A ngo ra gom 3 nhanh :

- nhanh thuan (1): thyristor trang thai dan ien. o sut ap gia anode cathode nho khong ang ke.

- Nhanh nghch (3): ng vi trang thai nghch tng t nh diode.-Nhanh khoa (2): ng vi trang thai khoa. Neu dong iG = 0 th dang nhanh

khoa tng t nh nhanh nghch. Thay v ien tr rR th ay la ien tr rD(differential block resistance). Tng t ta co ien ap ong uBO thay v uBR. Khi ienap at en gia tr uBO, thyristor khong b pha hong ma se b ong (chuyen t trang thaikhoa sang trang thai dan ien). Khi iG thay oi, tuy thuoc vao o ln cua iG ma gia trcua ien the khoa thay oi theo (ien the khoa giam khi iG tang). Hien tng thyristordan ien do tac dung ien ap vt qua uBO (iG=0) la s co gay ra do qua ien ap xuathien tren li.

Thong thng, ta ong thyristor bang xung dong qua mach G,K. ien trthuan rT va ien ap thuan uTO c nh ngha tng t nh trng hp cua diode.Khac vi diode, cac nhanh thuan cua thyristor khong bat au t goc zero cua he trucma t gia tr IH (holding current) dong duy tr trang thai dan. Neu gia tr donggiam nho hn iH th thyristor tr ve trang thai khoa. Ngay sau khi ong thyristor, trckhi dong cong iG tat, oi hoi dong thuan phai at en hoac vt hn gia tr dong chotiL, iL > iH (L: Latching).


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Fotothyristor cach ly nguon xung kch va mach cong suat, cac dang cua noc ve tren hnh H1.20. Trong o phng an hnh a/- s dung dang vi mach giuptan dung nguon tia sang kch thch, phng an b/- va c/- bao am cach ly tot gianguon xung kch va mach cong suat, do o han che nhieu tac dung cua song nhieu,dang c/- ch can cong suat kch cua nguon sang khong ang ke.

Bang B1.4 Cac thong so ac trng cua thyristor SKKT 41/12E (SEMIKRON)

VRRM 1200V ien ap ngc cc ai lap lai cho phep -Repetitive peakReverse voltage

VDRM 1200V ien ap khoa lap lai cc ai cho phep -Repetitive peakoff-state voltage

VRSM 1300V ien ap ngc cc ai khong lap lai cho phep -Non-repeative peak reverse voltage

(dV/dt)crit 1000V/ s o tang ien ap khoa cho phep

ITRMS 75A dong ien hieu dung -RMS-on-state current

ITAV 48A dong ien trung bnh -Mean on state current

(di/dt)crit 150A/ s o tang dong ien cho phep khi linh kien ong

VT Max. 1,95V ien ap thuan -Direct on- state voltageVGT 3V ien ap cong kch -Gate trigger voltage

IGT 150mA Dong ien cong kch -Gate trigger current

IH 150mA dong ien duy tr -Holding current-

IL 300A dong ien chot -Latching current

Mach kch thyristorTrong cac bo bien oi cong suat dung thyristor, thyristor va mach tao xung

kch vao cong ieu khien cua no can cach ien. Tng t nh cac mach kch chotransistor, ta co the s dung bien ap xung hoac optron, xem hnh H1.22


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g

P[W] 7 15 30 60 100 150

500V C[ F] 0.1 0.22 0.33 0.68 1.5 2.2R[ ] 120 68 33 22 22 18P[W] 10 25 40 70 150 250

690V C[ F] 0.33 0.47 1.0 1.0R[ ] 47 33 33 22P[W] 70 100 100 300

1.7 TRIAC

Triac la linh kien co the dan dong ien theo ca hai chieu. V vay nh nghadong thuan va dong ngc khong co y ngha, tng t cho khai niem ien ap ngc.Viec kch dan triac thc hien nh xung dong ien a vao cong ieu khien G. ieu

kien e triac ong ien la a xung dong kch vao cong ieu khien trong ieu kienton tai ien ap tren linh kien khac zero.

Giong nh thyristor, khong the ieu khien ngat dong qua triac. Triac se ngattheo qui luat a c giai thch oi vi thyristor.

Mo ta va chc nangViec ong triac theo ca hai chieu c thc hien nh 1 cong duy nhat G va

xung dong kch vao cong G co chieu bat ky. Bi v triac dan ien ca hai chieu nen ch

co hai trang thai, trang thai dan va khoa. Mac du vay co the nh ngha triac co chieuthuan va chieu nghch.

ac tnh V-Aac tnh V-A cua triac tng t nh thyristor. Do kha nang dan ien theo ca

hai chieu, ac tnh triac co dang oi xng qua tam toa o. Can noi them ve trnghp ac tnh cong ieu khien. Viec kch ong triac co the chia ra lam cac trng hp:

uV > 0a/- uG > 0 , iG > 0b/- uG < 0 , iG < 0

uVR > 0c/ u > 0 i > 0

ien t cong suat 1


33/262

max

VR

max

V

critidt

di

dt

diS

=

=

Viec ngat(xem thyristor): thi gian ngat c tnh t luc giam dong dan theomot hng ve 0 en khi co the at ien ap khoa cung chieu o len triac. Neu ta ngatdong dan cua triac trong mot chieu nao o, ien the khoa chieu ngc lai tang len cuoi qua trnh chuyen mach vi toc o ln co the gay ra viec ong ngoai y muon. Vthe, toc o tang cua ien the khoa khi chuyen mach b gii han bi gia tr:

max

VR

max

V

critudt

du

dt

duS

=

=

Cac gia tr Sucrit thng nho hn 20V/s. Toc o gii han cua ien the khoaSucrit oi vi triac ien trang thai khong dan ien co gia tr cao hn - khoang vaitram V/s.

Kha nang chu tainh mc ien ap: Xac nh theo ien ap khoa cc ai co the lap lai, no bang

nhau cho ca hai hng uDRM = uRRM. ien ap cc ai khong lap lai khong c biet .nh mc dong ien: Xac nh theo gia tr hieu dung ln nhat cua dong dan

iVM. Thng c nh ngha cho dong hnh sin oi vi nhiet o cho trc va van toc

lam mat cho trc.

Bang B1.6 Cac thong so c ban cua triac BCR5AS (Mitsubishi )VDRM 600A ien ap khoa lap lai cc ai- repetitive peak off-state voltage

ITRMS 5A Tr hieu dung dong ien dan- RMS on-state current

IFGT,IRGT 30mA Dong ien kch

VDSM 720V ien ap khoa khong lap lai cc ai- non-repetitive peak off-statevoltage

ITSM 50A Dong ien nh khong lap lai cc ai qua linh kien-dang sin- surge on-

state currentVGM 10V ien ap kch cc ai peak gate voltage

IGM 2A Dong ien kch cc ai- peak gate current

VTM Max. 1,8V ien ap tren triac khi dan ien- on state voltage

VFGT,VRGT Max. 1,5V ien ap kch cong

IFGT,IRGT Max. 30mA Dong ien kch cong

(dV/dt)crit 5V/ s o tang ien ap khoa critical-rate of rise off-state commutatingvoltage

(diT/dt)crit 100A/ s o tang dong ien qua linh kien cc ai-Critical rate of rise of on-statecurrent

ien t cong suat 1


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g

1.8 GTO (GATE TURN OFF THYRISTOR )

ien t cong suat 1


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g

cau truc tng t mach mo ta SCR nhng co them cong kch ngat mac song songcong kch ong. Ky hieu linh kien GTO ve tren hnh H1.26c. Cau truc thc te (loaiGTO oi xng) ve tren hnh H1.26d.

GTO c kch ong bang xung dong ien tng t nh khi kch ongthyristor thong thng. Dong ien kch ong c tang en gia tr IGM va sau o giamxuong en gia tr IG . iem khac biet so vi yeu cau xung kch ong SCR la dongkch iG phai tiep tuc duy tr trong suot thi gian GTO dan ien.

e kch ngat GTO, xung dong ien am ln c a vao cong G cathodevi o doc (diGQ/dt) ln hn gia tr qui nh cua linh kien, no ay cac hat mang ien

khoi cathode, tc ra khoi emitter cua transistor pnp va transistor npn se khong thehoat ong che o tai sinh. Sau khi transistor npn tat, transistor pnp con lai se hoatong vi cong kch ong trang thai m va linh kien tr ve trang thai khong danien. Tuy nhien, dong ien yeu cau mach cong G e tat GTO co gia tr kha ln. Trongkhi xung dong ien can a vao cong e kch ong GTO ch can at gia tr khoang3 5% t kh 30A i 10 i i l i li h ki d h


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du nh ngan mach) gay nen hien tng qua dong, he thong bao ve phai c thiet kee nhan biet s co va ngat GTO e bao ve linh kien. Neu nh gia tr dong qua GTOkhi s co xay ra thap hn tr so dong cc ai th co the ngat GTO bang xung dongcong am ieu khien vi bien o thch hp. Nhng neu gia tr dong s co vt qua giatr bao ve bang xung dong am, can s dung mach bao ve kieu on bay (gom khoacong suat mac song song vi linh kien GTO). Nguyen ly hoat ong cua mach bao vela tao ngan mach nguon cap ien cho GTO bang cach kch ong mot SCR mac songsong vi linh kien GTO. Dong ngan mach lam chay cau ch va cat linh kien GTO khoinguon. ieu o c minh hoa tren H1.29.

Trong nhng nam gan ay, GTO tr thanh linh kien ong ngat c s dungrong rai cho cac mach cong suat ln: mot GTO loai noi tat anode co gia tr nhmc ap khoang 4500V va nh mc dong 6000A. Cac gia tr tng ng cua loai GTOcho phep dan dong ngc la 4500V va 3000A (Mitsubishi 1998). ien ap at trenGTO khi dan ien thng cao hn SCR (2-3V). Toc o ong ngat t vai s en 25s.Tan so ong ngat khoang 100Hz en 10kHz.

Linh kien cong suat se tr nen chat lng cao neu cho o sut ap thap khi danien (nh thyristor), yeu cau mach ieu khien n gian va kha nang ngat dong nhanh(nh IGBT). Hien nay, mot so linh kien nh vay a xuat hien tren th trng va chungco kha nang thay the dan GTO. Chung co the xem la nhng dang cai tien cua GTO,che tao theo nguyen ly khoi tch hp (Power Electronics Building Block- PEBB) nhamgiam bt cac yeu cau ve mach kch va lam tang kha nang ngat nhanh. Cac linh kien

nay gom MTO (MOS Turn-Off Thyristor), ETO (Emitter Turn-Off Thyristor) va IGCT(Integrated Gate-Commutated Thyristor).

Bang B1.7: Cac thong so c ban cua GTO FG1000BV-90DA (Mitsubishi)

Thong so o ln Ghi chu

V 4 500V i kh h l l i t h i (R titi k ff t t

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IRRM Max. 100mA Dong ngc cc ai (tng ng i VRRM)

IDRM Max. 100mA Dong thuan cc ai trang thai khoa.

tgt Max. 10 s Thi gian tre khi ong

tgq Max. 20 s Thi gian tre khi ngat.IGQM 300A Dong kch ngat qua cong G

VGT Max. 1,5V ien ap cong khi kch ong

IGT Max.2500mA

Dong ien cong khi kch ong

1.9 IGCT (INTEGRATED GATE COMMUTATED THYRISTOR)Cau tao va chc nang:

S cai tien cong nghe che tao GTO thyristor a dan en phat minh congnghe IGCT.

GCT Gate Commutated Thyristor la mot dang phat trien cua GTO vi khanang keo xung dong ien ln bang dong nh mc dan qua cathode ve mach congtrong 1 e am bao ngat nhanh dong ien. Cau truc cua GCT va mach tng

ng cua no giong nh cua GTO.

s

IGCT la linh kien gom GCT va co them mot so phan t ho tr, bao gom ca

board mach ieu khien va co the gom ca diode ngc.e kch ong GCT, xung dong ien c a vao cong kch lam ong GCT

tng t nh trng hp GTO.e kch ngat GCT, moi noi pn base-emitter c phan cc ngc bang

cach cung cap ien ap nguon ngc chieu. ieu nay lam triet tieu dong ien quacathode v toan bo dong ien i qua cathode se c ay sang mach cong vi toc orat nhanh va bien GCT tr thanh mot transistor pnp.

e co the tao dong ien qua mach cong tang nhanh va u ln, GCT (IGCT)c che tao ac biet e giam cam khang mach cong (mach vong cong ieu khien cathode) en gia tr nho nhat.

Van e mau chot cua GCT la tao kha nang tang nhanh dong ien qua cong.ieu nay at c bang ong dan ien ong truc qua mach cong- cathode va congnghe mach ieu khien nhieu lp (multilayer). Chung cho phep dong cong tang vitoc o 4kA/ khi ien the cong- cathode mc 20V. Trong thi gian 1 ,

transistor npn cua GTO b ngat hoan toan va cc cong cua transistor pnp con lai bm lam GCT b ngat. Do viec ngat thc hien bang xung dong rat ngan nen cong suatton hao mach cong c giam en mc toi thieu. Cong suat tieu thu cua GCT giami khoang 5 lan so vi trng hp GTO.

s s

Lp p pha anode c lam mong va lam giau hat mang ien chut t e chophep kh cac hat mang ien pha anode nhanh hn trong thi gian ngat IGCT co the

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u iem chnh cua IGCT the hien cac mat sau:-kha nang chu ap khoacao en 6kV ( d kien se tang len en 10kV) vi o tin cay cao; ton hao thap khi danien bi co kha nang dan nh thyristor; kha nang gii han dong ngan mach s dungmach bao ve cha cuon khang han che di/dt (turn on snubber) va gia thanh thap dotan dung cong nghe silicon vi mc tch hp nang lng cao.

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Bang B1.8 Cac thong so c ban cua GCT oi xng FGC800A-130DS (Mitsubishi)

ien ap khoa VDRM 6500V vi VGK= -2V

ien ap ngc VRRM 6.500V

Dong ien thuan cc ai malinh kien co the kch ngat

ITQRM 800A vi diGQ/dt=1200A/ s , khong mach bao ve

Dong thuan trung bnh IT(AV) 330A- dang sin, f=60Hz, goc dan 1800

Thi gian lu tr (storagetime)

ts 3 s vi diGQ/dt=1200V/ s ,

Cs=0,1 F ,Rs=10

Toc o tang ti han cuadong ien

dit/dt 1000A/ s vi IGM=90A,

diG/dt=50A/ s ,Cs=0,1 F ,Rs=10

Thi gian ong (turn ontime)

Tgt Max. 5 s vi iGM=90A va diG/dt=50A/ s

o sut ap khi dan VTM Max. 8V vi IT=800A

Dong ngc cc ai IRRM Max. 150mA

Dong ien trang thai khoa IDRM Max. 100mA

Toc o tang ien ap khoa dV/dt Min. 3000V/ s

Dong ien kch ong IGT Max. 0,5A

ien ap xung kch ong VGT Max. 1,5V

1.10 MCT (MOS CONTROLLED THYRISTOR)

Cau tao va chc nang

MCT co cau tao ket hp cong nghe cua thyristor vi u iem ton hao danien thap va kha nang chu ap cao va cua MOSFET vi kha nang ong ngat nhanh


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Linh kien MTO thyristor c phat trien bi hang SPCO (Silicon PowerCoperation) tren c s cong nghe GTO va MOSFET. Chung khac phuc cac nhciem cua GTO lien quan en cong suat mach kch, mach bao ve va cac han che cua

tham so dv/dt. Khong giong nh IGBT tch hp cau truc MOS phu len toan bo tietdien ban dan, MTO at MOS FET tren phien silicon.

Cac linh kien co cau truc tng t thyristor nh MTO (xem hnh H1.34) vaGTO thng c s dung trong cac trng hp co yeu cau cong suat ln nh khanang hoat ong gan nh mot cong tac 2 trang thai ly tng co ton hao thap ca haitrang thai on va off.

Cau truc MTO gom 4 lp va hai cong ieu khien- mot cong ieu khien kch

ong va mot cong ieu khien kch ngat. Tai hai cong nay, lp kim loai c gheptren lp p.

MTO c kch ong bang xung dong ien trong khoang thi gian 5-10 s

vao cong turn on-G1, tng t nh khi kch GTO. Xung dong nay se cung cap dongien vao lp em cua transistor NPN Q1 ma dong qua collector cua no se cung capdong em cho transistor NPN Q2 va qua trnh tai sinh dien ra sau o tao thanh trangthai dan ien cua MTO.

e ngat dong qua MTO, mot xung ien ap khoang 15V can a vao congoff G2- tng t nh khi ngat MCT. Xung ien ap tren se lam cau truc mach FETdan ien, lam noi tat mach emitter va cong kch cua transistor npn Q1. Do o, lamgiam kha nang dan lp emitter va lp em cua transistor Q1 va qua trnh tai sinh sedng lai. So vi trng hp GTO phai s dung xung dong am rat ln e dap tat qua

h i i h i Q h d MTO di h h h hi

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MTO thch hp s dung cho cac truyen ong cong suat ln, ien ap cao(>3kV cho en 10kV), dong ien ln hn 4000A, o sut ap thap (thap hn so viIGBT) va cho cong suat tai trong pham vi 1MVA en 20MVA do kha nang ieu

khien n gian va chu c ap khoa ln. MTO co the s dung cho cac thiet b ieukhien cong suat trong he thong ien (FACTS Controller) lam viec tren nguyen lyieu che o rong xung PWM. Cac nguon ien d phong cong suat ln (UPS) cung lamot hng ap dung cua MTO. Kha nang ieu khien cat nhanh va de dang cua MTOlam cho no co the ng dung thuan li lam cac thiet b cat dong ien dc va dong ienac.

1.12 ETO (EMITTER TURN-OFF THYRISTOR)Giong nh MTO, ETO c phat trien tren c s ket hp cac cong nghe cuaGTO va MOSFET. ETO c phat minh bi Trung tam ien t cong suat Virginia(Virginia Power Electronics Center) hp tac vi hang SPCO. Ky hieu ETO va machtng ng cua no c ve tren hnh H1.35

Linh kien MOSFET T1 mac noi tiep vi GTO va linh kien MOSFET T2 macnoi tat gia cong kch cua GTO va linh kien MOSFET T1. Thc te, T1 bao gom motso n-MOSFET va T2 gom mot so p-MOSFET, chung c thiet ke bao quanh GTOe giam toi a cam khang gia cac linh kien MOSFET va cong cathode cua GTO.

ETO co hai cong ieu khien: mot cong cua rieng GTO c s dung e ongno va cong th hai la cong kch vao cong MOSFET noi tiep e ngat ETO.

Khi ap at mot ien the e kch ngat ETO len cong n-MOSFET, n-MOSFETb tat va no ay toan bo dong ien ang dan qua mach cathode (lp emitter n cuatransistor npn trong cau tao GTO) sang mach cong kch cua ETO vi s ho tr cuaMOSFET T2. Do o, qua trnh tai sinh trong linh kien ket thuc lam linh kien b ngat.

iem thuan li do cau truc cha MOSFET noi tiep mang lai la no tao ieukien e chuyen dong ien t cathode sang mach cong thc hien hoan toan va nhanhchong, cho phep ngat ong thi tat ca cac cathode trong cau hnh linh kien. iemkhong thuan li la linh kien MOSFET noi tiep nay phai dan toan bo dong ien qua

cathode cua GTO, v the lamtang them o sut ap va ton hao.Tuy nhien, cac MOSFET nay coien ap thap khi dan (0,3-0,5V)nen cac he qua neu tren khongquan trong.

ETO ve c ban gomGTO co trang b them linh kienphu dang MOSFET no giup

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Bang B1.9. So sanh thong so cua cac linh kien IGBT, GCT,ETO

IGBT

MitshubishiCM1200HA-66H

GCT

MitsubishiFGC4000BX-90DS

ETO4060

(Toshiba GTO)SG4000JX26

ETO1045

(Westcode GTO)WG10045S

ien ap khoa 3300V 4500V 6000V 4500V

ien ap hoatong

1750VDC 3000VDC 3600VDC 3000VDC

Dong ien hoatong

2400A 4000A 4000A 1500A

o sut ap khidan

6.5/2400 4.0/4000 5.0/4000 4.6/1500 1250C

o sut ap khidan

4.1/800 2.6/1200 3.2/1200 2.6/500 1250C

Thi gian ngat[ s ]

10 3 7 7

Cong suat machkch [W]

1 179 35 10 500Hz

1.13 SO SANH KHA NANG HOAT ONG CUA CAC LINH KIEN

Kha nang hoat ong cua cac linh kien ban dan cong suat c so sanh theohai kha canh cong suat mang tai va toc o ong ngat c minh hoa tren hnh H1.36va H1.37 da theo so lieu tra cu nam 98-99 cua hang EUPEC va so lieu [44],[57].

Linh kien GTO cong suat ln c san xuat vi kha nang chu c ien ap/dong ien t 2,5-6kV/1-6kA. GTO con c che tao cha diode ngc vi ton haothap, kha nang chu ien ap/ dong ien cua no at en 4,5kV/3kA.

Linh kien GCT c che tao gan ay co kha nang chu c ien ap/ dongien 6kV/6kA vi kha nang chuyen mach gan nh toan bo dong ien sang mach

cong khi kch ngat. Cam khang mach cong giam en 1/100 so vi loai GTO thongthng, cho phep toc o tang dong ien cong khi kch ngat en diGQ/dt=6.000A/ s .

Thi gian lu tr ts giam con khoang 1/10 so vi cua GTO. Cac tnh chat cho phepGCT rat thuan tien khi mac song song hoac noi tiep va kha nang ieu khien ongngat cong suat ln ngay ca khong s dung mach bao ve.

Cac diode cho nhu cau thong thng c che tao vi kha nang chu cien ap thay oi t 500V en 4kV va dong ien t 60A en 3,5kA. oi vi nhu cau

ong ngat nhanh kha nang dong at en 800-1.700A va ien ap 2.800-6.000V,Cac thyristor cho nhu cau thong thng c che tao vi kha nang chu

c ien ap thay oi t 400V en 12kV va dong ien t 1000A en 5kA. oi vinhu cau ong ngat nhanh, kha nang dong at en 800-1.500A va ien ap 1.200-2.500V,

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H1.36

ien t cong suat 1


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CHNG HAI

BO CHNH LU

Bo chnh lu co nhiem vu bien oi dong ien xoay chieu thanh dong ienmot chieu. Bo chnh lu c ap dung lam nguon ien ap mot chieu; lam nguonien mot chieu co ieu khien cap cho cac thiet b ma, thiet b han mot chieu ;nguon ien cho cac truyen ong ong c ien mot chieu ; nguon cung cap chomach kch t cua may ien mot chieu hoac may ien ong bo. Bo chnh lu condung e chuyen oi ien xoay chieu thanh dang mot chieu e truyen tai i xa

(HVDC). Bo chnh lu con tao thanh mot bo phan trong thiet b bien tan,cycloconverter dung trong truyen ong ien ong c xoay chieu.Cong suat cua cac bo chnh lu co the t vai tram W en hang chuc MW.

2.1 - BO CHNH LU MACH TIA BA PHA KHONG IEU KHIEN

S o cau tao


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ien t cong suat 1


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*6

13

2

3


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Gia thiet V3 dan ien va ta muon kch ong V1 . Muon vay ta xet dau ienap tren V1 theo he thc :

uv1 = u1 - u3 + uv3 = u1 - u3 (do uv3 = 0)

Do u1 - u3 > 0 (tc co ap khoa tren V1) khi6

7

6


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ien t cong suat 1

V d 2 2


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V du 2.2:Tnh tr trung bnh ap va dong chnh lu, cong suat tai tieu thu cua bo chnh

lu mach tia ba pha ieu khien.

Tai co R= 10 [], E=50 [V] va L=0. Ap nguon U=220 [V]; goc ieu khien

3

= [rad].

Giai:

Phan tch: gia s luc au dong qua tai bang 0. Ta co :

Ud = R.Id + E =E Khi 0 < X< 3

=

Tai X =, uv1 =u 1 04219503

22203

>=

=

][,sin Vu

d

la ap khoa, lai co xung kch (IG1 >0) nen V1 ong. Dong ien khep kn quamach (u 1,V1,RE). Luc o: uv1 =0 va ud = -uv1 + u1 = u1

iv1 =id =R

Eu

R

Eud

=

1

Dong V1 sau o giam ve 0 tai X= X1 khi u1 =E

iv1(X1) =0 iv1 b ngat.Dong tai id b gian oan (trang thai 0), phng trnh mo ta mach:id =0

ien t cong suat 1

55


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( )

+== +

++

+

1

16

6

5

6

5

62

3

3

2

1 X

Xmdd

dxExdxUdxuU

.sin.

( ) { }

++

+=

116

5

62

3XEXUU

md

coscos

{ ( ) }

V472

9826

5

350982

632220

3

2

,

,,coscos.

=

++

+=

Tr trung bnh dong tai xac lap:

AR

EU

I

d

d 24210

50472

,

,

=

=

= b. Cong suat trung bnh tren tai:

=

=

=

+ ++

+

+

1 11 X

6

X

6d

2d

X

6

d

dd

6

5

6

ddd

dxu.R

E

dxR

u

2

3

dx.R

Eu

.u2

3

P

dxi.u

3

2

1P

Thay X1 =2,98 [rad], xurad d sin],[ 22203

==

E =50 [V], R = 10[] va lay tch phan ta thu c:Pd =5.553W=5,55kW

2.3 - BO CHNH LU CAU BA PHA IEU KHIEN HOAN TOAN

ien t cong suat 1

ud = udA udK


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ud = udA - udKTa se chng minh rang neu dong tai lien tuc, ien ap udA se ch phu thuoc

vao goc kch ong cua nhom linh kien ( V1 ,V3 ,V5 ) va ien ap nguon ; va ap udK

phu thuoc goc kch ong cua nhom (V2 ,V4 ,V6 )That vay, xet nhom anode (V1 ,V3 ,V5 ), gia s rang V1 ong va V3, V5 b

ngat, ta co:iV1 = id ; iV3 = 0 ; iV5 = 0uV1 = 0 ; uV3 = u2 - u1 ; uV5 = u3 - u1 ; udA = u1

Ro rang, cac he thc mo ta ien ap nhom anode khong phu thuoc vao trangthai kch ong cua cac thyristor nhom cathode. Do o, e khao sat ien ap udA, ta

ch can xet en trang thai kch ong cua cac thyristor (V1 ,V3 ,V5 ).

Cac he thc mo ta ien ap nhom anode co dang giong nh mach chnh lutia ba pha vi ap chnh lu udA, (hnh H2.5). Goc ieu khien v du cua V1, ctnh t v tr xuat hien ap khoa tren V1 tc uv1 = u1 - u3 > 0

Tng t, hoat ongnhom cathode co the phan tchdi dang chnh lu mach tia

ba pha vi ap chnh lu udK.Goc ieu khien, v du cua V2c tnh t v tr xuat hienien ap khoa tren V2, tc la:

uV2 = u2 - u3 > 0Phng trnh ien ap tai

va dong tai:

ud = udA - udK E

dt

diLi

d

d++ .Rud = .

Tong hp cac ket quaphan tch tren, ta co the vietphng trnh mo ta trang thaimach, v du khi V1 ,V2 ong :

uV1= 0 ; uV2 = 0 ; uV3 =

u2 - u1 ; uV4 = u3 - u1iV1 = id ; iV2 = id ; iV3 = 0

; iV4 = 0uV5 = u3 - u1 ; uV6 = u3 -

u2


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ien t cong suat 1

I dI

(2 19)


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ITAV =3

d (2.19)

ien ap khoa va ap ngc cc ai xuat hien tren linh kien

UUUU mRRMDRM 63 === . (2.20)- Dong ien qua nguon ien ap, v du qua pha 1:

i1 = iV1 - iV4Tri hieu dung dong ien qua nguon c xac nh vi gia thiet dong tai

khong oi:

d2

12

0

21

I.3

2]dX.i

2

1[I =

=

(2.21)

Bang cach phan tch Fourier dong ien qua nguon cho trng hp goc kch0= , ta xac nh bieu thc dong ien qua pha th nhat:

....)t13sin13

1t11sin

11

1t7sin

7

1t5sin

5

1t.(sinI

32)t(i da ++++

= (2.22)

Ket qua cho thay dong ien qua nguon bao gom ngoai thanh phan c bancon co cac song hai bac 6k 1, k=1,2,3

Cac thanh phan song hai dong ien gay ra nhieu anh hng bat li trong he

thong ien li nen chung can c kh bo. Mach loc c ban c lap at giahe thong li ien va bo chnh lu bao gom cac bo loc cong hng LC va machloc thong cao RLC. Mach loc cong hng c hieu chnh chu yeu cho cac songhai bac 5 va 7 v chung co bien o ln nhat.

V du 2.3:Cho bo chnh lu cau 3 pha ieu khien hoan toan vi cac tham so sau: ap

day nguon ac 480V, f=50Hz. Tai R=10, L=50mH. Xac nh goc kch e dong taitrung bnh bang 50A

Giai:

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2.4 - BO CHNH LU CAU MOT PHA IEU KHIEN HOAN TOAN

S o mach ve tren hnh H2.8:Bang cach chia nguon ien ap u lam 2 na bang nhau, ta tao nen he thong nguon xoay chieu2 pha oi xng u1, u2

( )==

==

XUu

u

XUu

u

m

m

sin

sin

22

22

2

1

(2.25)

Bai toan phan tch hoat ong mach chnh lu cau mot pha c qui oi thanh phantch hai nhom mach chnh lu tia hai pha (hnh H2.9).

Nhom anode gom V1,V3. Goc ieu khien c tnh t thi iem bat au xuat hien ap khoa

tren linh kien en khi a xung kch vao cong ieu khien cua no, v du, oi vi V 1, ap khoaton tai khi u1 - u2 = u > 0 hay u1 > 0. Khi V1 dan:uV1 = 0 ;uV3 = u2 - u1 = -uudA = u1

Khi V3 dan:uV3 = 0 ;uV1 = u1 - u2 =u

udA = u2

Tng t nhom cathode gom V2,V4, goc cho V4 c tnh t thi iem:u2 -u1 = - u >0, tc u >0

Khi V4 dan :uV4 = 0 ; uV2 = u1 - u2 =u ; udA = u1

Khi V d

ien t cong suat 1

Tong hp cac ket qua phan tch, ta co the bieu dien trang thai hoat ong cua machh h l d khi V V b h h h


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chnh lu, v du khi V1V2 ong bang he phng trnh sau :uv1 = 0 ; iv1 = id

uv2 = 0 ; iv2 =id ; uv3 = - u ; iv3 = 0 (2.26)uV4 = -u ; iV4 = 0ud = u

Edt

diL dd ++ .iRud = .

Ket qua phan tch di dang oth c ve tren hnh H2.10

Cac he qua:

- Neu dong qua tai lien tuc,ien ap tai co dang ch phu thuoc vaogoc ieu khien va ap nguon. Dang apchnh lu co hai xung trong mot chu kyap nguon vi chu ky xung chnh lubang 1/2 chu ky ap li Tp = T/2

- V du khi V1 dan, ap khoa

xuat hien tren V3 khi uV3 = -u > 0, tctrong na chu ky am cua ap nguon. To suy ra, pham vi goc ieu khien la( 0, )

- Tr trung bnh ien ap chnhlu :

( )

( )

cos

cossin.

UU

UXdXUdXuU

d

mmdd

22

211

=

=== ++

(2.27)

Vi 0 < < , ien ap chnh lu trung bnh c ieu khien thay oi trongkhoang:

( ) UUU d ..

2222+


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Cho bo chnh lu cau 1 pha ieu khien hoan toan vi cac tham so sau: ap pha nguonac 120V, f=50Hz. Tai R-L mac noi tiep R=10 , L=100mH. Goc kch . Xac nh che

o dong ien tai va tr trung bnh cua no

060=

Giai:

Co the kiem chng e thay rang dong ien tai lien tuc.

Tr trung bnh ap tai: VUUd 54601202222 0 === cos.cos.

2.5 CAC BO CHNH LU IEU KHIEN CHA DIODE QUI TAC PHANTCH MACH BO CHNH LU TONG QUAT

Cac diode xuat hien trong bo chnh lu ieu khien di dang mach ieu khien banphan hoac dang diode khong (diode zero), hoac trong dang bo chnh lu khong ieu khien.Cac diode dung thay thyristor trong mach lam giam gia thanh mach ong lc lan mach ieukhien, han che thanh phan xoay chieu cua dong chnh lu, ieu nay dan en chat lngdong ien phang hn. Do o, tang hieu suat cung nh he so cong suat nguon ien. mot

vai dang mach, viec a them diode vao mach lam tang kha nang ieu khien goc trongthc te at en gia tr ly tng (v du max = )

Phan tch hoat ong cua cac bo chnh lu cha diode co the da tren ba bc chnh1/ -Tach dang mach chnh lu cau thanh hai nhom mach tia mac noi tiep. Moi nhom

mach tia gom hai hai nhieu nhanh mach tia mac song song. Moi nhanh cua mach tia co thegom:

a. nguon ien mac noi tiep vi linh kien. Linh kien co the dang ieu khien(SCR) hoac khong ieu khien (diode)

b. linh kien. Trng hp nay, nguon ien c gia thiet bang 0.2/- Vi gia thiet dong ien qua tai lien tuc va bo qua tac dung cam khang trong cua

nguon, thc hien phan tch gian o ong ngat cac linh kien trong tng nhom mach tia theoqui tac phan tch bo chnh lu mach tia nh sau:

Qui tac 1: Dau qui c chon cho cac ien ap pha nguon co cc dng tiep xuc vianode linh kien.

Trong nhom mach chnh lu mach tia nhieu pha, tai thi iem ang xet gia cac

thyristor c kch ong thi, diode va linh kien ang dan ien th linh kien nao mac vaonguon ap pha co tr tc thi ln nhattrong tat ca cac pha nguon se chuyen sang trang thaiong, tat ca cac linh kien con lai b ngat. (Diode c xem nh mot dang ac biet cuathyristor co che o kch ong lien tuc).

Qui tac 2: Trong trng hp dau ien ap pha nguon ngc lai vi qui tac 1


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ien t cong suat 1

)cos()cos()(

+=+= 12

1UU

U md (2.29)


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Neu gia thiet dong qua tai c loc phang id=Id, ta co:

- Tr trung bnh dong qua linh kien: dSCRAV II ..

2

= ; dDAV II ..

2

+= (2.30)

- Tr hieu dung dong ien qua nguon: dI.I

= (2.31)

V du 2.6:Ap dung qui tac phan tch bo chnh lu e xac nh qua trnh ien ap va dong ien cho

bo chnh lu cau 1 pha ieu khien ban phan dang oi xng. Gia thiet dong tai lien tuc.Hng dan:

ien t cong suat 1

Nhom mach tia anode V1,V3 vi cac pha nguon tng ng la u va 0, dau qui c thoaman qui tac 1.


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man qui tac 1.Nhom cathode gom V2,V4 vi cac pha nguon tng ng la u va 0, dau nguon thoa man

qui tac 2. Gian o ong ngat linh kien V1V2V3V4 c suy ra tren hnh H2.14.Tong hp gian o ong ngat linh kien cua hai nhom mach tia, ta co gian o ong ngatcho mach cau- xem hnh ve H2.14. T o, qua trnh ien ap va dong ien c dan giai nhsau:

Trang thai V1V2: ud=uTrang thai V2V3: ud=0Trang thai V3V4: ud=-uTrang thai V4V1: ud=0

Phng trnh dong ien chung cho cac khoang la:E

dt

diLiRu ddd ++= ..

Tr trung bnh ien ap tai:

)cos()cos()(

+=+= 12

1UU

U md (2.32)

Neu gia thiet dong qua tai loc phang id=Id, ta co:

- Tr trung bnh dong qua linh kien: .2dDAVSCRAV III == (2.33)

-Tr hieu dung dong ien qua nguon: dI.I

= (2.34)

V du 2.7:

Ap dung qui tac phan tch mach bo chnh lu, hay phan tch machbo chnh lu cau 3pha ieu khien ban phan (hnh H2.15). Ve hnh cac ai lng ap, dong ien trongmach. Xac nh tr trung bnh ap tai, xac nh ap va dong qua cac linh kien. Ap dung

ien t cong suat 1

)cos1(2

U.63)(Ud +

=


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2

Tnh toan ien ap va dong ien qua linh kien giong nh mach cau 3 pha ieu khien

hoan toan.

V du 2.8:Ap dung qui tac phan tch mach bochnh lu, hay phan tch mach bochnh lu cau 3 pha ieu khienhoan toan vi hai diode khong V01va V02 (hnh H2.16). Ve hnh cac

ai lng ap, dong ien trongmach. Xac nh tr trung bnh aptai, xac nh ap va dong qua caclinh kien, chu y bien luan theo giatr goc kch . Nhan xet vai tro cuacac diode khong. Ap dung vi cacgia tr sau: tr hieu dung ap pha

nguon 220V, f=50Hz. Tai R=10 ,E=100V, L . Goc ieu khien ][rad4

=

Hng dan:

Thc hien tach mach chnh lu cau ba pha vi hai diode khong tren hnh H2.16 thanhhai nhom mach tia ba pha: nhom mach tia vi diode khong V01 (V1V3V5, V01) va nhom mach tiavi diode V02 (V2V4V6V02). Sau o ap dung qui tac 1 va 2 e giai bai toan tren. Chu y pham vico anh hng cua cac diode khong.

V du 2.9:ong c DC co phan ng va mach kch t c cung cap ien bi bo chnhlu cau 3 pha ieu khien ban phantheo s o H2.17. Cho biet tr hieudung ap pha nguon 220V, f=50Hz.Mach phan ng: R=0,1 ,E=100V, L . Goc ieu khien

][rad4

= . Mach kch t:

Rkt=15 , Lkt . Phan tch quatrnh ien ap va dong ien quamach phan ng va cuon kch t.Xac nh tr trung bnh dong ien

ien t cong suat 1

So sanh he so cong suat gia bo chnh lu cau mot pha ieu khien toan phan va bochnh lu cau mot pha ieu khien ban phan. Cho biet ap nguon xoay chieu, cong suat tai va


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p p p g y gdong tai trong hai trng hp la nh nhau U = 220V, P d= 10kW. Dong tai id lien tuc va phang id

= Id = 100AGiai:Cong suat tai dang mach ieu khien toan phan

dtptpdtpdtpd IUIUP

cos...22

==

va mach ieu khien ban phan

dbp

bp

dbpdbpd IUIUP .

cos

... 2

122

+

== Cong suat bieu kien cua nguon trong hai trng hp:

dbp

bp

bpbp

dtptptp

I..UI.US

I.UI.US

==

==

T o he so cong suat :

4545,0100.220

000.10

I.U

P

S

P

dbp

tp

tp

tptp ====

dbpbp

d

bp

bpbp

I..U

P

S

P

==

Xac nh bp:

56105,1

00974,01

100.220.2

000.10.1

I.U.2

P.cos

bp

d

dbp

=

=

=

=

6408,0

100.561,1

.220

10000

S

P

bp

bpbp =

==

T o: mach chnh lu ieu khien ban phan at gia tr he so cong suat cao hn.

V du 2.11:Mach kch t cho ong c mot chieu c mac vao bo chnh lu mach tia mot pha vidiode zero (hnh H2.18a). Ap nguon u= 220 2 sin314t [V], tham so mach kch t L = 0,1H, R =

10 . Goc ieu khien2

= [rad]

ien t cong suat 1


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Ap dung qui tac tong quat phan tch bo chnh lu, vi diode c xem nh mot dang

SCR c kch lien tuc va no co ap nguon tng ng bang 0. Do trong khoang thi gian diodeong, phng trnh mach tai :

dt

di.Li.R0 dd +=

co nghiem xac lap id = 0 khi t nen ro rang dong id lien tuc trong khoang nay.Khi V1 ong :

dt

diLiRuu ddd .. +==

Dong tai id tangKet qua:Tr trung bnh ap tai:

( ) ]V[5,492

cos12

2.220cos1

2

U

dx.xsin.u2

1dx.u.

2

1U

m

m

2

dd

=

+

=+

=

=

=

+

Tr trung bnh dong kch t.

][,,

AR

U

R

EUI ddd 954

10

549===

=

ien t cong suat 1

2.6 CAC CHE O LAM VIEC CUA BO CHNH LU VA HE QUA2.6.1 CHE O CHNH LU VA CHE O NGHCH LU


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Trong che o chnh lu (hnh H2.19a), cong suat tieu thu a t nguon xoay chieu

sang mach mot chieu. Gia thiet dong ien tai c loc phang, cong suat do bo chnh lucung cap co gia tr Pd=Ud.Id, ieu kien cua che o chnh lu la Pd 0. Do dong ien tai luondng, nen ieu kien tren ong ngha Ud 0. Cac bo chnh lu ieu khien hoan toan, ienap chnh lu khong am xay ra vi cac goc kch ieu chnh trong pham vi:

20 . Cac

bochnh lu ieu khien ban phan, ieu kien e Ud>0 xay ra vi goc kch nam trong phamvi 0 .

Tai tieu thu cong suat Pd>0 co the la tai thuan tr R hoac dang noi tiep RL hoac tai

gom RLE vi E la sc ien ong mot chieu E>0 .

Trong che o nghch lu, cong suat phat ra t tai se a tra ve nguon xoay chieu qua

bo chnh lu. V cong suat bo chnh lu nhan ve bang Pd=Ud.Id, ieu kien cua che onghch lu xay ra khi Pd 0. Do dong ien tai luon dng, nen ieu kien tren ong nghaUd 0. oi vi cac bo chnh lu ieu khien hoan toan, ien ap chnh lu se am neu gockch thay oi trong pham vi:

2

.oi vi cac bo chnh lu ieu khien ban phan,

ieu kien e Ud


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ien t cong suat 1


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V du 2.13:Giai thch cac che o lam viec cua cac bo chnh lu theo cau hnh H2.22 a/-b/-c/- khi

thay oi goc kch trong pham vi)(

2

0 va

)( 2 . Khi nao ton tai che o

nghch lu trong cac cau hnh tren. Trang thai cong suat gia nguon va tai nh the nao?


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ien t cong suat 1

ap chnh lu va khong con la duy nhat. Trong ieu khien, v du ong c ien mot chieu,khi dong tai bang 0, moment tac ong triet tieu va viec ieu khien tai khong co tac dung.Tac dung dong tai gian oan lam ac tnh ieu khien tr nen phi tuyen hien tng qua o


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Tac dung dong tai gian oan lam ac tnh ieu khien tr nen phi tuyen, hien tng qua ocua he ieu khien kho hieu chnh, do o trong ky thuat ngi ta co gang han che vung lamviec cua bo chnh lu che o dong gian oan.

Tren hnh H2.24 ve qua trnh ien ap va dong ien tai khi chuyen t che o dong lientuc (t


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vi 22 )L(RZ += ;R

Larctan

= ;

R

L=

Hang so A xac nh t ieu kien ban au 0)(id = . T o:

= e.)sin(.Z

UA m

Ket qua la qua trnh dong ien tai trong mot chu ky ien ap li co the bieu dien didang ham tong quat sau:


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Tr trung bnh dong ien tai chnh lu:

dx).x(i2

1I dd

=

Tr hieu dung dong ien qua nguon bang vi tr hieu dung dong qua linh kien va quatai co the xac nh theo ham tch phan sau:

dx).x(i2

1I 2drms

=

Trng hp tai RLE: (xem hnh H2.26)Thyristor co the kch dan neu xung kch thc hien trong ieu kien ap tren thyristor

dng. Ro rang ieu kien goc kch phai thoa man la:

=>

mmin

U

Earcsin va min


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[ ]rad3

/b =

Giai:

Trng hp [rad9

= ] dong qua tai lien tuc (hnh H2.27a)

Trng hp [rad3

2 = ] , dong qua tai b gian oan. o th cac qua trnh c ve tren

hnh H2.27b

a/-

]V[78,2419

cos.220.2

63cos.U.

2

63Ud =

=

=

]A[178,2410

78,241

R

UI dd ===

b/-

++

=

= + 6cos1.2

U3dx.xsin.U.

3

21U m

6

md

]V[9192

cos1220.23

U =

+

+=

ien t cong suat 1

Bo chnh lu mach tia ba pha ieu khien mac vao nguon U =220 V, = 314 rad/s. Taico RE, R = 10, E = 50 V. Ve cac qua trnh ap va dong tai va ket luan. Cho biet goc ieukhien :


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]rad[2

/b

]rad[6/a

=

=

Hng dan

e y rang:

,R

Eui

d

d

=

Do o, khoang thi gian xuat hien (ud - E) < 0 theo qui tac dong lien tuc se c thaybang che o dong gian oan id = 0.

Ap tai luc o;ud = R.id +E = R.0 + E = E

hay ud = 50 VKet qua ap cho tren hnh ve H2.28a khi 6= va H2.28b khi 2=

ien t cong suat 1

V du: Trong khoang


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Um.sinX1=EGiai ra va chon nghiem X1=170,70

Dong ien tai cho bi

R

Eui

d

d

=

Tr trung bnh ap tai

+

+

+=

=

1

11

1

X

X

dd

dd

dxEdxuU

dxuU

..

.

Ket qua Ud=224 [V] khi 6= va Ud=257[V] khi 2= .

V du 2.17Cho bo chnh lu mach cau mot pha ieu khien hoan toan tai R. Goc ieu khien

( )rad2

=

Ap nguon u = 220 2 sin314t [V], R = 10 . Tnh Ud ,Id va cong suat Pd .Giai :Trc het, ta ap dung qui tac phan tch tong quat bo chnh lu vi dong tai lien tuc va

xac nh ien ap ud . T gia tr cua ap ud , ta kiem chng nghiem dong id xem co thoa man tnhchat linh kien khong (id > 0). Neu khong thoa man ieu kien dong, th khoang xuat hien dong id< 0 khong the ap dung qui tac cho dong lien tuc c. Luc o, dong tai gian oan id = 0 va taxac nh lai ien ap ud

trong khoang o.

oi vi tai R, vR

ui

d

d = nen ro rang dong tai gian oan trong khoang thi gian ap ud

xac nh theo qui tac dong lien tuc co gia tr am tc ud


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][..

cos.sin.

.

V

UxdxUU

dxuU

m

md

dd

992

0122022

2

121

1

=+

=

+==

=

+

Tr trung bnh dong tai :

][, AR

UI dd 99

10

99

===

Cong suat trung bnh tren tai :

( )dx.

R

sinU1dx

R

u1dxi.u

1P

2

m2d

ddd

+

=

=

=

Ket qua:

WR

UP

m

d2420

4

2

==

V du 2.18Cho bo chnh lu mach cau mot pha ieu khien toan phan. Ap nguon u = 220 2 sin314t.

Tai R=1 , L = 0,01 H va E. Mach trang thai xac lap vi goc ieu khien (rad3

2 = ) . Ket

luan g ve trang thai ap va dong tai neu :a./- E=150[V]>0 b/- E = - 150[ V] < 0

Giai: trang thai xac lap :

Ud = R.Id + EGia s dong tai lien tuc , tr trung bnh ien ap va dong ien chnh lu:

][cos.cos. VUUd

993

2220

2222=

==

R

EUI

d

d

=

a/- Neu E = 150 V

AId

92410

15099,=

=

ieu nay khong the xay ra

ien t cong suat 1

vi id()=0X1 la goc tng ng thi iem dong ien id at gia tr 0.Khoang X1


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id=0ud=E=150V

b/- Neu E = - 150 V( )

AId

1510

15099,=

=

Do o, dong tai lien tuc va bo chnh lu lam viec che o nghch lu. Dang dong ienva ien ap cho hai trng hp c ve tren hnh H2.30.

2.7 - MACH LOC AP TAI VA DONG TAI.

e han che thanh phan xoay chieu cua ap chnh lu va do o lam giam o nhap nhodong ien tai, ta co the:

1. Tang so xung ien ap chnh lu, v du s dung mach nhieu pha, dang cau.

2. Dung tu loc.3. Dung cam khang loc.4. Dung diode khong, mach ieu khien ban phan.

ien t cong suat 1

RC)x(

md e).sin.U(u

=

Goc , tai v tr dong qua diode b ngat, c xac nh theo he thc:+== )RCarctan()RCarctan(


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)()(

ien ap ln nhat tren tai bang bien o ap nguon va ien ap nho nhat xay ra tai thiiem ( ), ta co:+

)sin(.Ue).sin.U( mRC

)(

m += +

T o: 0)sin(e).(sin RC)(

=+ +

Gia tr can xac nh bang phng phap tnh so.o chenh lech gia ien ap ln nhat va nho nhat ien ap tai bang:

)sin1.(U)sin(.UUU mmmd =+= Vi cac gia tr R, dU cho trc, ta co the xac nh o ln tu C.

Thong thng: ;>>RC2

;2

. ien ap thap nhat cua tai co the gia s bang

gia tr ap tai thi iem x= . Ta co:

ien t cong suat 1


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RCmRC/)2/2/(md e.Ue.U)(U + ==+ T o:

)

RC1(1.U)e1.(UU m

RCmd

RC.f.2

U

RC

U.U mmd =

Dong ien qua tai trong v du tren co tnh gian oan. e cho dong ien tai lien

tuc, cam khang loc can c s dung (hnh H2.32). Trong trng hp ket hp vi tu C,mach loc LC c ve tren hnh kem theo. Viec chon cac gia tr can thiet cua mach locco the thc hien bang giai tch, da theo phan tch song hai bang chuoi Fourier. Tuynhien, viec tnh toan co the n gian hn nh s dung phan mem mo phong. Tren hnhve H2.32, cac o th minh hoa ket qua ap va dong ien tai vi hai gia tr khac nhau cuacuon khang loc.

ien t cong suat 1

2.8 - HIEN TNG CHUYEN MACH

Trong cac phan trc ay, bo chnh lu c phan tch vi gia thiet bo qua


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cam khang trong cua nguon ap. He qua la qua trnh chuyen mach gia cac nhanhcha thyristor dien ra tc thi. Trong thc te, nguon co cam khang trong lamdong ien qua no khong the thay oi ot ngot. V the, hien tng chuyen machgia cac nhanh cha cac thyristor khong dien ra tc thi ma keo dai mot khoangthi gian, hnh thanh trang thai cac nhanh cha thyristor cung dan ien. Hientng nay c goi la hien tng trung dan (overlapping) hoac hien tngchuyen mach (commutation).

Xet bo chnh lu mach tia ba pha ieu khien (hnh H2.33)

Nguon xoay chieu co cam khang trong Lb.Trang thai V3:Gia thiet dong qua tai lien tuc va V3 dan dong ien. Khi o, dong ien tai

dan qua mach (u3,Lb,V3,RLE ). Phng trnh mo ta mach:uv3 = 0 ; iv3 = iduv1 = u1 - u3 ; iv1 = 0 ; uv2 = u2 - u3 ; iv2 = 0 (2.43)ud = u3

Edt

diLiRu ddd ++= ..

Trang thai (V1V3):Tai thi iem a xung kch ong cho V1 (goc ), do tac dung ong thi

cua ien ap khoa va xung kch ong, V1 ong .Do V mac noi tiep vi L nen dong qua no tang lien tuc t gia tr 0 Tng

ien t cong suat 1

dt

diLuu Vbd

1

1 += (2.44)

Edt

diLiRu ddd ++= ..


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dt

uV1 = 0 ; uV3 = 0Gia s khoang thi gian trung dan nho hn nhieu so vi hang so thi gian

cua tai chnh lu, co the xem dong ien tai khong thay oi o ln. Do o:iv1 + iv3 = Id = const

031 =+

dt

di

dt

di VV (2.45)

T o dan giai:

dXL

uudib

V2

311 = (2.46)

Bieu dien cac he thc trong he truc toa o mi O X vi O dch sang phai

cua iem O va6

OO

= , ta co: XdXUuu m = sin331 (2.47)

T o:

( )

( )

dXXsinL2

U3di

X

bm

Xi

i1V

1V

1V=

(2.48)

( ) ( ) ( XcoscosL.2

U3iXi

b

m1V1V

= ) (2.49)

Do iV1()= 0 , nen

( ) ( )'XcoscosL.2

U3'Xi

b

m1V

= (2.50)

1Vd1Vd3V iIiii == (2.51)o th bieu dien cac he thc dong ien cho thay iv1 tang dan t gia tr 0 vadong iv3 giam dan t gia tr Id .

Trang thai V1:

Trang thai V1 ,V3 cung dan se keo dai en v tr Xk thoa man:

iV1(X k' ) = IdiV3(Xk

) = 0 (2.52)Luc o, V3 b ngat v khong cho phep dong qua no oi dau. Hien tng

chuyen mach ket thuc, dong ien tai khep kn qua mach cha (u1,Lb ,V1,RLE),phng trnh mo ta mach co dang:

diL

ii;0u

1V

d1V1V ==

ien t cong suat 1

o ln goc chuyen mach c suy ra t ieu kien ket thuc hien tng

chuyen mach:( ) ( ) +==+= ',' XIiXi dVV 11 (2.54)


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Ket qua la:

=

m

db

U

IL

3

2cosarccos (2.55)

Goc chuyen mach (va thi gian chuyen mach) phu thuoc vao goc ieukhien , vao o ln dong ien tai va cam khang trong cua nguon ap

Cac he qua:

1. Hien tng chuyen mach lam giam ap tai. V du, trong thi gian chuyenmach gia V3, va V1, t he phng trnh (2.44) ta suy ra ap tai co dang:

22

231 uuuud =+

= (2.56)

Tren hnh ve H2.34, ta thay dang ap chnh lu b mat i mot phan so vitrng hp ap ly tng (Lb = 0). Do o, trong mot chu ky ap chnh lu, tr trungbnh ien ap tai b giam i Udx .

( ) +

+

== Xd2

uu

2

3

Xd.uu

3

2

1

U

31

d1dx (2.57)

T (2.46) ta suy ra:

( )

( )

db

i

i1Vbdx I.

2

L3diL

2

3U

1V

1V

=

=

+

Neu at: bcm L2

3R

=

Ta co: dcmdx IRU = ien ap tren tai thc te co o ln:

dcm0ddx IRcos.UU = (2.58)

Vi

=2

X.pR bcm (2.59a)

hoac

= bcmX.p

R (2.59b)

Cong thc (2.59a) ap dung cho:- bo chnh lu tia mot xung vi diode khong (p=1);- bo chnh lu cau mot pha ieu khien ban phan khi 0> (p=2);- cac bo chnh lu tia m pha ieu khien hoac khong ieu khien, co hoac

khong co diode khong (p=m);

ien t cong suat 1

- bo chnh lu cau mot pha ieu khien hoan toan va khong ieu khien(p=2);

- bo chnh lu cau mot pha ieu khien ban phan khi 0= (p=2)-


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bo chnh lu cau ba pha ieu khien hoan toan vi mot diode khong va3> (p=6).

- bo chnh lu cau ba pha ieu khien ban phan (p=3).2. Hien tng chuyen mach han che pham vi goc ieu khien va do o

han che pham vi ieu khien ien ap chnh lu .Khi phan tch qua trnh ien ap va dong ien cua thyristor trong cac dang

mach chnh lu c ban, vi goc ieu khien va bo qua hien tng chuyen mach(Lb= 0), ta co goc an toan cua thyristor :

== qt. (2.60)tq la thi gian khoi phuc kha nang khoa cua thyristor.Neu thyristor co gia tr cho trc, gia tr goc ieu khien cc ai cho phep

co o ln bang:

max= (2.61)

Neu xet ca hien tng chuyen mach vi la o ln goc chuyen mach, oln goc an toan con lai cua thyristor bang:

(2.62)( ) = + = Vi gia tr cho trc cua thyristor, goc ieu khien ln nhat cho phep co

gia tr:max = - - (2.63)

Ro rang, pham vi goc ieu khien che o nghch lu b han che. Gocchuyen mach cang ln (v du khi dong tai ln , Lb ln), goc max cang giam. Trenthc temax thng lay gia tr khoang 160

01650.

Do max giam nen tr trung bnh ap chnh lu trong che o nghch lu bgiam theo:

Udmin = Udo.cosmax - Xcm.Id (2.64)Trong trng hp mach tia ba pha, ta de dang suy ra:

( ) dcmdm

bdd IXI

U

LUU .

.cos.min

=

3

20

(2.65)

Vi cho trc, ien ap trung bnh nho nhat cua tai phu thuoc vao dong tai.

3. Hien tng chuyen mach lam bien dang ien ap nguon .

Phan tch ien

ien t cong suat 1

hien cac gai va lom ien ap. Cac lom va gai ien ap co o ln t le vi gia tr camkhang Lb va dong ien tai. Do o, neu mac cac tai tieu thu khac vao mach nguonchung vi bo chnh lu, s bien dang ap nguon gay ra do tac dung chuyen machcua bo chnh lu co the khong chap nhan c.


84/262

g p e han che o bien dang cua ap nguon, ngi ta khong mac trc tiep bo

chnh lu vao li ien ma thong qua may bien ap hoac cuon khang. May bien aptrong hoat ong mach tac dung nh cuon khang loc vi o ln xac nh bi camkhang tan cua cac cuon day. Cau truc mach nguon au vao bo chnh lu co dangthay the ve tren hnh H2.36.

Hien tng chuyen mach tac dung lam ngan mach gia cac pha nguon. Camkhang hoac may bien ap mac noi tiep vi bo chnh lu co tac dung tng ngcam khang LT. Do co LT, ien ap ngan mach tai iem A phu thuoc vao t so cam

khang Lb va LT trong mach, neuL

L

T

b

rat ln, ien ap li cang t bien dang. Tuy

nhien, viec tang LT lai khong co li ve kha canh s dung may bien ap va ien apchnh lu giam nhieu do chuyen mach.o ln ien ap tai cac v tr A luc chuyen mach xac nh theo he thc gan

ung :

UA = UTb

T

XX

X

+; XT = LT , Xb = Lb (2.66)

Trong thc te, gia tr XT thng chon trong khoang

XT = ( 0,04 0,1). ff

I

U

2

2

(2.67)

U2f , I 2f la tr hieu dung ien ap va dong ien nh mc cua nguon capcho tai (v du ien ap va dong ien pha th cap may bien ap).

ien t cong suat 1

b/- Tnh ien ap ln nhat do bo chnh lu cung cap cho tai

c/- Tnh o tang max

dt

diV


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d/- Tnh o ln goc chuyen mach khi =0e/- Tnh goc ieu khien max, gia thiet thi gian khoi phuc kha nang khoa cuaSCR la tq = 50S

Giai:

a/- Gia s V3,V4 ang dan, V1,V2 b ngat. Trong na chu ky dng cua apnguon, tai v tr tng ng goc kch , xung kch a vao V1,V2 lam cho chung ong.Do tac dung Lb, hnh thanh trang thai ong dan ien cua V1,V2,V3,V4 vi he phng

trnh mo ta sau:

041

3141

31

==

==

=

=+

VVd

VVVV

b

dVV

uuu

iiiii

dt

diLu

Iii

.

Giai he phng trnh tren ta thu c goc chuyen mach:

=

U

LI bd

.

...cosarccos

2

2

o tang dong ien qua SCR (v du khi ong V1,V2):

ien t cong suat 1

][,.,..

. VIRU dxxb 91910000103142

===

ien ap trung bnh ln nhat bo chnh lu cap cho tai :Udmax= Ud0 - (UV +URb+Uxb )


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( ) ][,,.max VUd 73179191438022

=++=

c/- Tnh o tang dong qua SCR khi ong:

sin.

.

b

V

L

U

dt

di

2

2=

o doc at cc ai khi =2

. Luc o:

]./[,]/[.,,.max

sAsAdt

diV268701026870

00102

2380 6 ===

d/- Goc chuyen mach khi = 0

0284880

0

3802

001031410020

2

2

=

=

=

][,

.

,...coscos

.

...cosarccos

rad

arcc

U

LI bd

e.-

( )

0

06

152653288300

015700010314

3802

1002

90015705010314

==

+=

===

][,,cos

,cos,...

.cos

,][,...

maxmax

max

rad

radtq

2.9 MAY BIEN AP CAP NGUON CHO CAC BO CHNH LU2.9.1 CHC NANG CUA MAY BIEN APMay bien ap dung lam nguon xoay chieu cho cac bo chnh lu co cac chc

nang sau:1. Cung cap ien ap nguon co o ln phu hp vi yeu cau cua tai.2. Cach ly ap nguon cua bo chnh lu vi li ien. Do o, tai co the chay

ngan mach trong thi gian ngan.3. Tac dung loc cac song hai bac cao.4. Tao thanh cam khang chuyen mach, do o han che s bien dang gay ra

t qua trnh chuyen mach.5. Tao he thong nguon xoay chieu nhieu pha e cung cap cho bo chnh lu

ien t cong suat 1

Phan tch chnh xac qua trnh ien ap va dong ien mach may bien ap cothe at c bang cach giai bai toan mach ien t. Tuy nhien, viec giai toantng oi phc tap. Trong thc te, ngi ta thng giai bai toan di dang cn gian hoa. Trong vai trng hp n gian, dong


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ien t hoa c bo qua.ien ap pha s cap va th cap c xem co

dang sin va t so cac ien ap nay bang t so vongday cuon s cap va th cap.

Dong ien qua cuon th cap c xac nh phuthuoc vao cau hnh bo chnh lu. Dong ien cuon thcap c xac nh phu thuoc vao thanh phan xoay

chieu cua dong qua cuon s cap. Thanh phan dongien mot chieu qua cuon th cap co tac dung atrang thai mach t vao che o bao hoa nen can chan che.

V du, xet may bien ap ba pha mac vao bo chnh lu tia ba xung nh trenhnh H2.39. Bo qua dong ien t hoa, sc t ong F1, F2 va F3 (hnh H2.39) trencac tru may bien ap at gia tr nh nhau:

F1=F2=F3 (2.66)Gia thiet cac cuon day c quan cung chieu, ta co:

ppssppssppss iNiNiNiNiNiN 332211 ...... == (2.67)

N

gt_dtcs 1 thay nguyen van nho (bk hcm)

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