Do an 6vdc_220vac

1

Li ni u

in t cng sut cn c tn gi l K thut bin i in nng l

mt ngnh k thut in t nghin cu ng dng cc phn t bn dn trong

cc b bin i khng ch bin i ngun nng lng in. Cc b bin

i in t cng sut th h mi ngy cng th hin r cc u vit ni bt

nh: kch thc gn nh, tc ng nhanh, lm vic n nh vi tin cy

cao, gi thnh h

Trong cc b bin i in t cng sut khng th khng nhc n cc

b bin i in p DC/DC, DC/AC. Cc b bin i ny ngy cng c

ng dng rng ri c bit trong lnh vc iu khin ng c, truyn ng

in, tit kim nng lng, s dng trong sinh hot khi mt in li. y

cng chnh l ti ca n ny:

Xy dng h thng bin i DC/AC t n trong trng hp mt

in li. Thng s : UDC= 6V, UAC= 220V, f=50Hz

Bn n gm 3 chng:

Chng 1. Cc b nghch lu.

Chng 2. Xy dng h thng bin i DC/AC t 6VDC ln

220VAC tn s 50Hz.

Chng 3. Xy dng m hnh vt l h thng bin i DC/AC t

6VDC ln 220VAC tn s 50Hz.

Em xin chn thnh cm n GS.TSKH. Thn Ngc Hon cng cc

thy c gio b mn hng dn em hon thnh n ny. Do y l ln

u tin thc hin lm n nn khng th mc phi sai st, em mong c

s ch bo tn tnh ca cc thy.

Hi Phng, ngy 12 thng 07 nm 2010

Sinh vin thc hin

L Vn Kin

127.0.0.1 downloaded 28.LeVanKien_DC1001.pdf at Tue Aug 21 21:53:40 ICT 2012

2

Ch-ng 1 : cc b nghch l-u

Nghch lu c lp l thit b bin i dng in mt chiu thnh dng

in xoay chiu c tn s ra c th thay i c v lm vic vi ph ti c

lp.

Ngun in mt chiu thng thng l in p chnh lu, acquy v cc

ngun in mt chiu c lp khc.

Nghch lu c lp v bin tn c s dng rng ri trong cc lnh

vc nh cung cp in t cc ngun c lp nh acquy, cc h truyn ng

xoay chiu, giao thng, truyn ti in nng, luyn kim

Ngi ta thng phn loi nghch lu theo s , v d nh nghch lu

mt pha, nghch lu ba pha.

Ngi ta cng c th phn loi chng theo qu trnh in t xy ra

trong nghch lu nh: nghch lu p, nghch lu dng, nghch lu cng

hng.

Ngoi ra cn nhiu cch phn loi nghch lu nhng hai cch trn l

ph bin hn c.

1.1. NGHCH LU DNG [3].

1.1.1. Nghch lu dng mt pha.

Nghch lu dng l thit b bin i ngun dng mt chiu thnh dng

xoay chiu c tn s ty .

c im c bn ca nghch lu dng l ngun mt chiu cp in cho

b bin i phi l ngun dng, do in cm u vo Ld thng c gi tr

ln v cng dng in l lin tc.

1.1.1.1. Nguyn l lm vic.

S nghch lu mt pha c trnh by trn hnh 1.1 s cu v

hnh 1.2 s c im trung tnh.


3

Xt s cu : Cc tn hiu iu khin c a vo tng i tiristo

T1, T2 th lch pha vi tn hiu iu khin a vo i T3, T4 mt gc 1800.

in cm u vo nghch lu ln Ld = do dng in u vo

c san phng (hnh 1.3), ngun cp cho nghch lu l ngun dng v dng

dng in ca nghch lu iN c dng xung vung.

Khi a xung vo m cp van T1, T2, dng in iN = id = Id. ng thi

dng qua t C tng ln t bin, t C bt u c np in vi du + bn

tri v du - bn phi. Khi t C np y, dng qua t gim v khng. Do

iN = iC + iZ = Id = hng s, nn lc u dng qua ti nh v sau dng qua

ti tng ln.

Sau mt na chu k t = t1 ngi ta a xung vo m cp van T3, T4.

Cp T3, T4 m to ra qu trnh phng in ca t C t cc + v cc -.

Ld

T1

T4 T2

T3 +

-

C +

Z

-

(-) (+)

iZ

iN id

iC

Hnh 1.1. S nghch lu cu mt pha

T1

C+

Zt

(-) (+)

Ld

+ id

ic -

T2

W1 W1 i1

-

Co

W2

ib

Hnh 1.2. S nghch lu mt pha c im trung tnh

tnh


4

Dng phng ngc chiu vi dng qua T1 v T2 s lm cho T1 v T2 b kha

li.

Qu trnh chuyn mch xy ra gn nh tc thi. Sau t C s c

np in theo chiu ngc li vi cc tnh + bn phi v cc tnh -

bn tri, dng nghch lu iN = id = Id nhng i du. n thi im t = t2

ngi ta a xung vo m T1, T2 th T3, T4 s b kha li v qu trnh c lp

li nh trc.

Nh vy chc nng c bn ca t C l lm nhim v chuyn mch cho

cc tiristo. thi im t1, khi m T3 v T4 , tiristo T1 v T2 s b kha li bi

in p ngc ca t C t ln ( hnh 1.3). Khong thi gian duy tr in p

ngc t1 t1 l cn thit duy tr qu trnh kha v phc hi tnh cht iu

khin ca van v t1 - t1 = tk toff ; toff l thi gian kha ca tiristo hay chnh l

thi gian phc hi tnh cht iu khin.

Trong : .tk = l gc kha ca nghch lu.

Hnh 1.3. Gin xung ca nghch lu cu mt pha

T

Id

iN

0

UT1

iT1

iz

t1 t1 tk

ic

id

t

iT2

t

t

t

t

t


5

1.1.1.2. nh hng ca ph ti i vi ch lm vic ca nghch

lu.

Ta xt trng hp Ld = (in cm v cng ln). S trn hnh 1.2

c th thay th bng s hnh 1.4.

T s thay th c th vit h phng trnh sau :

id = it + ic = Id = const

iC = Cdt

dUC (1.1)

it t

t

R

U

Gii h phng trnh trn i vi U(t) ta c:

Ut(t) = A1 + A2eCRt

1

(1.2)

tm h s A1 v A2 ta s dng cc iu kin sau:

in p trn ti c tnh cht thay i chu k nn:

Ut 0t = -Ut 2/Tt

Gi tr trung bnh ca in p trn in cm Ld ch xc lp

bng khng, tc l :

0)(2/

12/

0

dtUET

T

t

Gii cc phng trnh trn ta tm c:

Hnh 1.4. S thay th ca nghch lu dng mt pha.

id

ic iz

Z +

-


6

A1 CR

T

t

CR

T

CR

T

tt

t

eCReT

eT

E

22

2

114

14

(1.3)

A2 CR

T

t

CR

T

tt eCReT

TE

2211

4

2 (1.4)

Thay cc gi tr A1 v A2 vo (1.2) ta c:

Ut (t) CR

T

tCR

T

CRt

t

CR

T

tt

t

eT

CRe

eeE

22

.2

14

1

21

(1.5)

Biu thc (1.5) cho thy in p trn ti bin thin theo quy lut hm

m c s e. Khi thay i ph ti nh gim dng ti, dng qua t s t thay i

v constC

I

dt

dU CC (ngun dng), do in p trn ti s c dng l nhng

ng gn tuyn tnh, gc kha = .tk 2

, vi tk l thi gian kha ca

nghch lu.

Nghch lu dng khng c kh nng lm vic ch khng ti, v

nu Rt th Ut v id .

Trn thc t khi Rt ln v cng th in p trn ti cng tin n gi tr

rt ln, do qu trnh chuyn mch khng th thc hin c, cng nh

khng c thit b bn dn no chu ng ni qu in p ln nh vy.

Ngc li khi tng ph ti ngha l tng ng vi vic gim Rt, lc

ny dng np cho t s gim, ngc li dng phng ca t qua ti s tng ln.

iu dn n gim nng lng tch tr trong t, dng in p trn

ti s c dng gn vi hnh ch nht, nhng gc cng gim ng k v nh

hng ti qu trnh chuyn mch ca nghch lu.


7

Thi gian tk l thi gian duy tr in p ngc t ln tiristo c xc

nh t biu thc (1.5) nu cho Ut = 0:

Ut tkt = 0 CR

T

tCR

T

CR

t

CR

T

tt

t

k

t

eT

CRe

eeE

22

2

14

1

21

(1.6)

Gii phng trnh (1.6) ta tm c:

tk = Rt.C lnCR

T

te2

1

2 (1.7)

=

e

ktk

1

2ln. (1.8)

k = CRk .. (1.9)

Biu thc (1.8) v (1.9) cho thy gc kha ca nghch lu ph thuc

vo tn s, ph ti v t chuyn mch.

tha mn iu kin lm vic ca nghch lu th min offt. , trong

toff l thi gian kha ca tiristo c trong trong s tay tra cu.

1.1.1.3. c tnh ca nghch lu dng.

Nu ngun l ngun dng th dng dng in ca nghch lu iNL s l

dng xoay chiu hnh xung vung gc (hnh 1.3). Phn tch theo chui

Foruier v ly thnh phn iu ha bc 1 ta c bin ca sng iu ha bc

1 (sng c bn) l:

Im (1) 0

2

0

4sin

2sin

1ddNL IdIdi

Gi tr hiu dng ca sng c bn l:

I (1) dI22

(1.10)


8

S thay th ca nghch lu ngun dng quy i v sng iu ha

bc 1 c dng nh hnh 1.5a.

T s thay th ta dng c th vc t ca nghch lu dng :

I (1) = IC + It (1.11)

Trong s thay th hnh 1.5b UNL chnh l Ut.

Ut - in p trn ti hay l in p ra ca nghch lu UNL.

Nu b qua tn hao trong nghch lu v coi l gc lch pha gia in

p ra ca nghch lu v sng c bn ca dng nghch lu, theo nh lut bo

ton nng lng, cng sut pha xoay chiu s bng pha mt chiu Pd = P1,

tc l: E.Id = n.Ut.I(1).cos (1.12)

Thay (1.10) vo (1.12) ta c:

E.Id = n.Ut.I(1).cos (1.13)

1.1.2. Nghch lu dng ba pha.

Trong thc t nghch lu dng ba pha c s dng ph bin v cng

sut ca n ln v p ng c cc ng dng trong cng nghip.

Cng ging nh nghch lu dng mt pha nghch lu dng ba pha cng

s dng tiristo.

kho c cc tiristo th phi c cc t chuyn mch C1, C3, C5.

I(1) I(t)

Rt IC

C Id I(t)

IC

I(1)

UNL

Lt

a) b)

Hnh 1.5. a) S thay th - b) Biu vc t


9

V l nghch lu dng nn ngun u vo phi l ngun dng, v vy

gi tr cun cm dL .

m bo kho c cc tiristo chc chn v to ra dng in ba pha i

xng th lut dn in ca cc tiristo phi tun theo th nh trn hnh 1.7.

Qua th ta thy mi van ng lc ch dn trong khong thi gian 120 .

Hnh 1.6. S nghch lu dng ba pha

Ld

T1

+

-

-

id

+

C1 C3

C5

+ -

ZA

ZB

ZC

T3 T5

T2 T4 T6

E

t1 t2

t3 t4 t5 t6 T1

T4

T6

T3

T6

T2

T5

T

t

0

Hnh 1.7. Gin xung ca nghch lu dng ba pha.

0

0 T5


10

Qu trnh chuyn mch bao gi cng din ra i vi cc van trong cng mt

nhm.

Trong nghch lu ngun

dng v ti lun mc song song

vi t chuyn mch nn gia ti

v t lun c s trao i nng

lng, nh hng ny lm cho

ng c tnh ngoi kh dc v

hn ch vng lm vic ca

nghch lu dng. lm gim

nh hng ca ti n qu trnh

np ca t C, ngi ta s dng

it ngn cch D1, D2, D3, D4,

D5, D6 (trn hnh 1.8).

Vic s dng cc it ny

i hi pha t chuyn mch chia lm hai nhm :

Nhm C1, C3, C5 dng chuyn mch cho cc van T1, T3, T5 .

Nhm C2, C4, C6 dng chuyn mch cho cc van T2, T4, T6 .

Nghch lu dng nh phn tch trn khng ch tiu th cng sut

phn khng m cn pht ra cng sut tc dng v dng id khng i hng

nhng du ca in p hai u ngun c th o du. iu c ngha l khi

nghch lu lm vic vi ti l ng c in xoay chiu ng c c th thc

hin hm ti sinh.

1.2. NGHCH LU P.

Nghch lu p l thit b bin i ngun p mt chiu thnh ngun p

xoay chiu vi tn s ty .

Ld

ZA

ZB

ZC

T5 +

id T1

C1 C3

T3

C5

D4

C4 C6

D6

C2

D1 D3 D5

D2

T4 T6 T2

E

-

(-) +

(+) -

Hnh 1.8. Nghch lu dng ba pha

c it ngn cch.


11

Ngun p vn l ngun c s dng ph bin trong thc t. Hn na

in p ra ca nghch lu p c th iu ch theo phng php khc nhau

c th gim c sng iu ha bc cao.

Trc kia nghch lu p b hn ch trong ng dng v cng sut ca cc

van ng lc iu khin hon ton cn nh. Hn na vic s dng nghch lu

p bng tiristo khin cho hiu sut ca b bin i gim, s iu khin

phc tp.

Ngy nay cng sut ca cc van ng lc IGBT, GTO, MOSFET cng

tr nn ln v c kch thc gn nh, do nghch lu p tr thnh b bin

i thng dng v c chun ha trong cc b bin tn cng nghip. Do

s nghch lu p trnh by sau y s dng van iu khin hon ton.

Trong qu trnh nghin cu ta gi thit cc van ng lc l cc kha

in t l tng, tc l thi gian ng v m bng khng nn in tr ngun

bng khng.

1.2.1. Nghch lu p mt pha.

1.2.1.1. Cu to.

S nghch lu p mt pha c m t trn hnh 1.9. S gm 4

van ng lc ch yu l: T1, T2, T3, T4 v cc it D1, D2, D3, D4 dng tr

cng sut phn khng v li v nh vy trnh c hin tng qu p u

ngun.

T C c mc song song vi ngun m bo cho ngun u vo l

ngun hai chiu (ngun mt chiu thng c cp bi chnh lu ch cho

php dng i theo mt chiu).

Nh vy t C thc hin vic tip nhn cng sut phn khng ca ti,

ng thi t C cn m bo cho ngun u vo l ngun p.


12

1.2.1.2. Nguyn l lm vic.

na chu k u tin (0 2 ), cp van T1, T2 dn in, ph ti c

u vo ngun. Do ngun l ngun p ln in p trn ti U1 = E, hng dng

in l ng nt m.

Ti thi im = 2 , T1 v T2 b kha, ng thi T3 v T4 m ra ti s

c u vo ngun theo chiu ngc li, tc l du in p trn ti s o

chiu v Ut = - E ti thi im 2 .

Do ti mang tnh tr cm nn dng vn gi nguyn hng c (ng

nt m) T1, T2 b kha nn dng phi khp mch qua D3, D4. Sut in ng

cm ng trn ti s tr thnh ngun tr nng lng thng qua D3, D4 v t C

(ng nt t ).

Tng t nh vy i vi chu k tip theo khi kha cp T3, T4 dng ti

s khp mch qua D1 v D2.

th in p ti Ut, dng in ti it, dng qua it iD v dng qua

tiristo c biu din trn hnh 1.10.

Biu thc in p v dng in trn ti :

Ut tE

.sin4

It ).sin(4

22t

XR

E

tt

.

T1

+

id

T2 T4

T3

D3

D2

D1

D4

Zt

it

C0

E

-

Hnh 1.9. S nghch lu p cu mt pha


13

Trn thc t ngi ta thng dng nghch lu p vi phng php iu

ch rng xung PWM gim bt c kch thc ca b lc. Nguyn l

ca phng php ny s c nghin cu phn sau.

1.2.2. Nghch lu p ba pha.

S nghch lu p ba pha hnh 1.11 c ghp t ba s mt pha

c im trung tnh.

n gin ha vic tnh ton ta gi thit nh sau :

Gi thit cc van l l tng, ngun c ni tr nh v cng v dn

in theo hai chiu.

Van ng lc c bn T1, T2, T3, T4, T5, T6 lm vic vi dn in

180 , Za = Zb = Zc.

Cc it D1, D2, D3, D4, D5, D6 lm chc nng tr nng lng v ngun

v t C m bo ngun cp l ngun p ng thi tip nhn nng lng phn

khng t ti.

Ta xt c th nguyn l v lut iu khin cho cc tiristo nh sau

Hnh 1.10. th nghch lu p cu mt pha

E it

0

Ut Ut

it

1 2 3

4

i

0

iD3,4 iD1,2

0

0

iD1,2

iT1,2


14

m bo to ra in p ba pha i xng lut dn in ca cc van

phi tun theo th nh trn hnh (1.12).

Nh vy T1, T4 dn in lch nhau 180 v to ra pha A. T3, T6 dn in

lch nhau 180 to ra pha B. T5, T2 dn in lch nhau 180 to ra pha C,

v cc pha lch nhau 120 .

t1 t2

t3 t4 T1

T4

T6

T3

T6

T2

T5

T1

T3

T5

T2

t

t

t

Hnh 1.12. Lut iu khin cc tiristo

T1 +

T2 T4

T3

D2

D1

C

E

- D4 D6 T6

T5 D5 D3

Za Zb Zc

Hnh 1.11. S nghch lu p ba pha


15

Dng in p trn cc pha UZA, UZB, UZC c dng nh trn hnh 1.13 v

c gi tr hiu dng c tnh bi cng thc sau :

EdUU phapha3

2)(

2

12

0

2 (1.14)

Suy ra :

tEtU A .sin3

2)( (1.15)

)120.sin(3

2)( tEtUB (1.16)

)120.sin(3

2)( tEtUC (1.17)

Gi tr t C c tnh theo cng thc: )2ln21(3 Ct

t

UR

ETC 1.18)

Hnh 1.13. in p trn ti ca mch nghch lu

p ba pha

-E/3

-2E/3

2E/

3 E/3

-E/3

-2E/3

UZC

UZB

UZA

E/3

2E/

3

2E/

3

-E/3

-2E/3

t

t

t

E/3


16

1.3. NGHCH LU CNG H-ng.

c im c bn ca nghch lu cng hng l qu trnh chuyn mch

ca van da vo hin tng cng hng. Gi tr in cm khng ln nh

nghch lu dng ( Ld = ) v khng nh hn nghch lu p ( Ld = 0 ), m

chim mt v tr trung gian sao cho khi kt hp vi in cm ca ti Lt v t

in C th trong mch s xut hin hin tng dao ng .

1.3.1. Nghch lu cng hng song song.

Xt s hnh 1.14, khi t = 0 cp van T1, T2 c m ra. T C c

np qua mch (+) Ld T1 Zt T2 (-). Dng np cho t s c dng hnh

sin v mch dao ng cng hng.

Ti thi im 1.t dng i qua ti gim v khng do T1 v T2 b

kha li. Trong khong thi gian t 1 n 2 tt c cc tiristo u b kha li

v Lt = 0. in p trn T1, T2 bng na in p trn t Uc v in p ngun E.

in p trn t trong khong thi gian 1 2 phi ln hn ngun E m bo

kha T1 v T2 chc chn. Ti thi im 2.t cp van T3 v T4 c m ra.

in p trn T1 v T2 bng in p nghch ca t C t ln (= Uc), t c np

theo chiu ngc li v o du. Dng np ca t C cng mang tnh dao ng

Hnh 1.14. a) Nghch lu cng hng song song b) Gin xung

Ld

T1

T4 T2

T3 +

- UC=Ut

i

id

C

Zt Lt

E

a)

i iT1=iT2

iT3=iT4

Uc=Ut

0

1 2 3

4 5

b)

0


17

v gim v khng thi im 4 . Lc ny T3, T4 kha li. Dng qua tiristo c

th coi l xung sin :

tII mt .sin. 0 (1.19)

1.3.2. Nghch lu cng hng ni tip.

S gm hai cun cm L1 v L2 c qun trn cng mt li thp

to ra hin tng cm ng, t C c mc ni tip vi ti.

Cc gi tr ca L1, L2, C v Rt c chn sao cho dng qua tiristo l

dng dao ng.

Nghch lu ni tip c ba ch lm vic :

a) Ch kha t nhin : f0 > f , dng qua T1 gim v khng sau mt

thi gian mi m T2, ch ny tng t nh ch lm vic ca nghch

lu song song.

b) Ch gii hn : f0 = f dng qua T1 gim v khng th T2 c

m ra v vy ch ny m bo dng ti it v in p trn ti Ut l hnh sin.

c) Ch chuyn mch cng bc: f0 < f khi T1 cn cha kha

kch xung m cho T2.

S d nghch lu ni tip c th lm vic ch 2 v 3 l do hin

tng cm ng ca hai cun L1 v L2.

Hnh 1.15. Mch nghch lu cng hng ni tip v s thay th.

L

C

rt

K

E i

1

i

2

L1 L2 T1 T2

+

-

E C

Rt

a) b)


18

Khi T1 cn ang dn m cho T2, dng phng qua t C qua L2 v T2

s gy nn hin tng cm ng trong cun L2. Sc in ng ny c du

chng li s tng ca dng, tc l (+) bn tri v (-) bn phi.

Do L1 v L2 qun trn cng mt li thp nn sc in ng ny cm

ng nn L1. Nh vy T1 s chu mt in p UT :

UT = E - ( UL1 + UL2 )

Cc tham s c chn sao cho Ut < 0 nn T1 s b kha li.

Nghch lu ch yu lm vic hai ch trn. Nghch lu ni tip lm

vic vi di ph ti thay i tng i rng.

gi cho in p trn ti l khng i khi ph ti thay i, cn thay

i tn s ca xung iu khin f .

Ch f > f0 l ch m nghch lu cng hng lm vic nh ch

nghch lu dng in.

1.4. nghch l-u iu bin rng xung pwm [1].

Cc b nghch lu trnh by trn c in p ra c cha nhiu sng

hi. nng cao cht lng in p v dng in u ra ca b nghch lu,

b nghch lu iu bin rng xung PWM (Pulse Width Modulation) c

a ra nghin cu v ng dng.

Tiu chun nh gi cht lng ca mt b nghch lu l mc gn

sin chun ca in p v dng in u ra. Trong tt c cc b nghch lu th

b nghch lu iu bin rng xung c nh gi l b nghch lu cho

php a ra dng sng gn sin nht.

Ni dung c bn ca k thut ny l mi na chu k dng in hay

in p ra gm nhiu on hnh ch nht c rng thch hp.

u im ca k thut ny l :

Cc thnh phn iu ho ca in p hoc dng in ra b y sang

pha tn s cao do d lc.


19

Cho php thay i in p ra bng s c hai kho chuyn mch

trong mt pha.

Lut iu khin ca phng php iu bin rng xung PWM c

s dng nhiu nht l lut so snh. Tn hiu iu khin hnh sin c tn s

mong mun s c so snh vi cc xung hnh tam gic. Tn s chuyn

mch ca nghch lu fcm bng tn s xung tam gic fx c gi tr khng i;

tn s xung tam gic cn gi l tn s mang.

Tn s tn hiu iu khin f1 c tn l tn s iu bin s xc nh tn s

c bn ca in p ra nghch lu.

H s iu bin bin c nh ngha l:

xm

dkm

aU

Um (1.20)

Trong :

Udkm bin ca tn hiu iu khin.

Umx bin ca tn hiu xung tam gic.

H s iu bin tn s l :

1f

fm xx (1.21)

Xt mt chu k in p mang ( hnh 1.16).

Khi xp chng udk v ux chng ct nhau ti cc

honh v (2 ). Cc giao im ca

chng quyt nh gi tr trung bnh ca in p ra.

12

22222

12

2

2

0

Ed

Ed

Ed

EU tb (1.22)

Mt khc ta c : am1

2 (1.23)

E

2

Uxm

Uk

Ux

Hnh 1.16.

Lut iu khin

PWM.


20

Do : atb m

E

U2 (1.24)

Qua biu thc (1.24) ta thy rng : gi tr trung bnh ca in p ra

trong mt chu k in p mang t l vi in p iu khin. Nu in p iu

khin c dng hnh sin th Utb dng hnh sin. Ngi ta c th iu chnh bin

in p ra bng cch tc ng vo t s Udkm /Uxm .

Trn hnh 1.17 biu din s khi iu khin cc tiristo ca PWM.

T s cho ta thy: hai tn hiu iu khin Uk v tn hiu sng mang Ux

a vo b so snh. Khi hai in p ny bng nhau s cho mt xung, qua b

chia xung ta a ti iu khin cc tiristo tng ng.

Hnh 1.17. S khi b iu khin cc van ca PWM.

Hnh 1.18. in p ra b nghch lu iu khin bi xung n cc.

Uk

Ux

Iara

uara

Udk Umang


21

Trn hnh 1.17 biu din phng php to in p ra bng so snh in

p iu khin hnh sin v in p tam gic cn. hnh 1.18 l cch to ra in

p bng cc xung n cc (in p mang trong trng hp ny ch c xung

n cc dng hoc m ).

Trong khi hnh 1.19 l phng php to in p ra bng cc xung

lng cc ( in p mang lc ny c xung vi hai cc tnh khc nhau ).

uara Udk

UdkUmang

Hnh 1.19. in p ra b nghch lu iu khin bi xung lng cc.

u im ca s iu bin rng xung in p n cc l tn s

in p ra gp i tn s chuyn mch v in p u ra khi chuyn mch

thay i vi tr s Ud so vi 2Ud s chuyn mch in p lng cc. Do

tn s in p gp i tn s chuyn mch nn di tn s thnh phn sng hi

gp i so vi s nghch lu iu bin vi chuyn mch in p lng cc.

Mt s lu khi chn tri s mf v ma :

Tr s mf

Vi mf l s l, cc thnh phn sng hi bc chn s khng tn ti

v cc h s hm cos s bng khng.


22

La chn tn s chuyn mch v h s iu bin tn s: gim

thnh phn sng hi bc cao, do gim kch thc v gi thnh b lc, tn

s chuyn mch nn chn tr s ln. Tuy nhin tn hao do chuyn mch ca

nghch lu s tng t l vi tn s chuyn mch.

Tr s ma

Khi ma < 1 phng php iu khin c u th to c quan h

tuyn tnh gia bin in p thnh phn c bn v h s tuyn tnh. Tuy

nhin khng th tng tr s in p ln cao c.

Khi ma > 1 th c th tng bin in p tn s c bn, phng

php ny l qu iu bin, so vi phng php ma < 1 th phng php ma >1

c nhiu sng hi hn.

1.00

3.24 ma

1.273

(uAOm)1

ud

2

vng

tuyn

tnh

vng

qu iu

bin

Hnh 1.20. Quan h in p v ma

Mch nghch lu ba pha PWM gm ba mch nghch lu mt pha ghp

li vi nhau.

Trong s nghch lu ba pha ta c th s dng chung mt b pht dao

ng sng mang. Cn in p iu khin so snh th phi c 3 b pht dao

ng hnh sin c cng bin nhng lch pha nhau 120o theo th t pha.


23

Ch-ng 2: xy dng h thng bin i dc/ac t

6vdc ln 220vac tn s 50hz

2.1. la chn h thng bin i dc/ac.

Ta a ra thng s v yu cu b nghch lu cn thit k nh sau:

Ngun cp l Acquy 6VDC/20Ah.

Cng sut 100W.

in p u ra 220VAC/50Hz.

Vi ngun cp l Acquy nn ta s dng mch nghch lu c lp.Nh

vy ta c ba s chn la : Nghch lu c lp ngun p, ngun dng v cng

hng.

Mch nghch lu c lp dng in c cp t ngun dng, y ta

s dng ngun cp l acquy nn khng ph hp.

Mch nghch lu c lp cng hng c dng in p ra gn sin nht,

tuy nhin vi tn s ln t 500Hz tr ln do vy khng ph hp s dng

cho mch m ta cn thit k.

Nh vy ta s dng mch nghchlu c lp ngun p, c hai la chn:

Nghch lu c lp ngun p mt pha.

Nghch lu c lp ngun p ba pha sau ly mt pha s dng.

Nghch lu c lp ngun p ba pha c dng hnh sin hn so vi nghch

lu c lp ngun p mt pha, tuy nhin vi mc ch s dng nh ban u ta

a ra th hon ton khng cn thit phi dng nh vy, bi b nghch lu p

ba pha cho chi ph cao hn v tnh ton iu khin cng phc tp hn rt

nhiu, trong khi ta ch cn s dng mt pha cho nhu cu sinh hot hng

ngy.

Do vy ta s chn mch nghch lu c lp ngun p mt pha vi cc

thng s v yu cu ra.

B bin i DC/AC s gm hai thnh phn chnh nh sau :


24

Mch iu khin : C nhim v pht xung vung dao ng vi tn s

50 Hz cp xung m cho transitor, transitor dn s lm cho mosfet dn.

Mch lc b nghch lu mt pha :c nhim v y ko in p 6V

DC ln 220VAC tn s 50Hz.

2.2. thit k mch bin i in p dc/ac t 6vdc ln

220vac tn s 50hz

2.2.1. Nguyn l mch bin i in p.

Nguyn l mch nng in p acquy c th trnh by nh sau:

Hnh 2.1. S nguyn l mch nng in p.

in p acquy c a ti im trung tnh ca cun s cp bin p T1,

hai Mosfet Q1 v Q2 ni chung cng ngun S ni ti cc m ca acquy,

cc cng mng D ca Q1 v Q2 ni vi cc u cn li ca s cp my bin p

ri c ni vi cc dng ca acquy

2.2.2. Mch khuch i y ko ( push-pull ).

2.2.2.1. Gii thiu v mch push-pull [9].

Nguyn l mch y ko dng xung dng, p c trnh by nh sau:


25

Hnh 2.2. S nguyn l mch Push-pull v th cc dng xung.

a) S nguyn l

b) Xung in p VDS ca van Q1

c) X ung in p VDS ca van Q2

S gm mt my bin p vi mt hoc nhiu cun th cp. Cun

th cp cung cp mt cp xung vung lch nhau 1800 m bin ca n c

xc nh bi s vng dy cun th cp. Hai van ng lc Q1 v Q2 l loi

mosfet. Khi hai van m s lm in p ri trn cun s cp gim i mt lng

l VDS ( l in p ri trn hai cc D v S ca van ).

in p VDS ph thuc vo ni tr RDS-on ca van khi dn v dng chy

qua van.

Khi mt trong hai van m n s t mt xung p hnh vung c tr s

Vg -VDS n na cun s cp.


26

Hnh 2.3. Dng sng in p ra.

2.2.2.2. Nguyn nhn s la chn y ko cho b bin i in p.

nng in p t in p acquy ln thnh in p cao c th dng rt

nhiu mch bin i nh l: b Push-pull nh trnh by trn, b Half

bridge, b Full-bridge, hay b Flyback.

Hnh 2.4. S nguyn l mch Half bridge.

T0

Ts

Q1 dn Ton

Q1 dn

Q1 dn

Q2 dn Ton

Q2 dn

Q1 dn

Q2 dn

Q2 dn

Q1 dn

Q1 dn

E

E/2

E/2L

C

D

+

T1

C1

C2

Q2

Q1


27

D2

D1

T1

L

Q4

Q3

Q2

Q1

C

+VCC

Hnh 2.5. S nguyn l mch Full bridge

Hnh 2.6. S nguyn l mch Flyback

Tuy nhin b Flyback ch dng cho mch cng sut b di 100W. Vi

cng mt li bin p th b Half bridge v b Full bridge c cng sut cao hn

so vi b Push -pull. Nhng trong mch Half bridge th cn c thm hai t v

v in p trn cun dy ch bng na in p ngun cp cho nn vi cng

mt in p ra cun th cp trong bin p ca b Half bridge c s vng dy

ln gp i ca b Push pull.

B Full bridge khc phc c nhc im c s vng th cp ln ca

b half bridge nhng n cn ti 4 Mosfet trong mch lc, khin mch tr nn

phc tp, cng knh, tng chi ph cho sn phm. Vi cng sut khng ln

(150W) ta s s dng mch push pull l hp l, v mch ny tuy c ti hai

cun s cp nhng cun s cp c s vng nh nn s kinh t hn .

Vi V1 V2

Vs Is

S

R C

D

VD ID

Vo


28

2.2.4. Tnh ton bin p ng lc [4].

Thit k bin p ng lc vi tng tn tht nh nht, s gm mt s

bc c bn nh sau:

Bc 1. Xc nh cc thng s tnh ton.

in tr sut dy qun )( cm .

Dng in hiu dng tng quy i v bn s cp Itot (A).

T s bin p N2/N1.

T thng cun s cp 1 (VS).

Tng tn hao Ptot (W).

H s lp y Ku.

Hng s v s m tn hao li KFe (W/cm3.T ).

Bc 2. Chn loi li thch hp.

p dng cng thc sau tnh c Kgfe.

Kgfe 108

2

2

2

012

..4

..

tot

fet

PKu

KI (2.2)

Tra bng chn loi li v tn li.

Bc 3. Kim tra mt t cm nh.

Vi li chn bc 2 ta c cc kch thc hnh hc ca li nh

MTL, AC, lm, WA.

Tnh c mt t cm nh theo cng thc sau:

2

1

3

22

18

.

1.

..

)(.

.2

..10

femcA

totth

KlAW

MTL

Ku

IB (2.3)

Kim tra nu B nh hn mt t cm bo ha ca li th li chn

tha mn. Ngc li th ta phi chn mt li c kch thc ln hn so vi li

chn.

Bc 4. Tnh s vng cc cun dy v kch thc dy qun.


29

S vng cun s cp tnh theo cng thc:

n1 = 104

cAB..2

1 (2.4)

Chn s vng cun th cp theo t s bin p:

n2 = n11

2

n

n (2.5)

n3 = n11

3

n

n

.

Tnh cc h s i theo cc cng thc sau:

totIn

In

.

.

1

111

totIn

In

.

.

1

222

. (2.6)

tot

kkk

In

In

.

.

1

Chn tit din dy qun theo cng thc:

Awl 1

1 ..

n

WK Au

Awl 2

2 ..

n

WK Au (2.7)

Hnh 2.7. Dng xung p v dng ca bin p mch push-pull.

v1(t)

+ D1 i1(t)

D2

n2 n1 i2

i2b(t)

T

-

v1(t)

u1(t) Vg

i1(t) oI

n

n

1

2

0 0

-Vg

sg TDv ..1

0 0

t

t


30

a

b

Vi b nghch lu m chng ta thit k theo thng s thc nghim o

c th cng sut ra ca bin p phi l 110W.

Vi mch push pull ta c gin xung nh hnh 2.7. Bin p thit k

dng cho mch push pull nn bn s cp c hai cun. Tuy nhin d tnh

ton ta quy v mt cun nh hnh v. Thc t dng sng i2b(t) cng ging nh

i2a(t) nhng lch pha 1800.

Trong trng hp ny in p Vg chnh l in p trn hai cc ca

acquy. Acquy dng cho b nghch lu l loi acquy ch 6V-20Ah. Vgmax khi

acquy np y l V . Chn tn s chuyn mch fs = 50 Hz , nh vy tn s hot

ng ca bin p l f0 = 50Hz.

Bin p thc t s dng trong mch:

Bin p c kch thc : a = 3(cm), b = 5,5 (cm)

Cng thc tnh s vng cho mt volt l : 810

4.44N

S F B

Vi : S tnh = cm2

F tnh = Hezt

B tnh = Gausse (chn 10.000)

Bin p c in th ngun l 6 Volt, in th ra l 220 Volt dng th

cp l 0.5 (A), ta s dng st t c li in tch l 16,5 cm2 ,tn s 50 Hz.

Tnh cng sut v dng s cp :


31

Cng sut cun th cp l : 220 Volt x 0,5 Ampere = 110 Watt

Ngun 6 Volt do dng s cp I = 110 Watt / 6 Volt = 18,3 (A)

Tnh s vng dy:

Thay tr s vo cng thc trn ta c :

Do ta qun th cp : 220 volt x 2,73 vng = 600 vng

S cp : 6 volt x 2.73 vng = 16,4 vng

Tnh c dy :

(2)

Thay gi tr vo cng thc (2) tm c c dy th cp l :

Thay gi tr vo cng thc (2) tm c c dy s cp l :

2.2.5. Gii thiu v IC chuyn dng s dng trong mch [13]

Trong mch iu khin b nghch lu ta hon ton c th s dng cc

mch ring r ghp li vi nhau. Mi mt mch s thc hin mt khu ring:

c th l to xung, so snh hoc l mt khu khuch i. Tuy nhin iu ny

s lm cho mch tr nn cng knh, tng chi ph cho sn phm, hn na vic

dng nhiu cc phn t nh vy s lm cho mch thiu tnh n nh. iu ny

l rt quan trng i vi mt mch in t cng sut.

8102,73

4.44 16.5 50 10.000N ng /v volt

( )2

ID mm

0.50.35( )

2mm

18,32,1( )

2mm


32

Da trn nguyn l iu khin chung nh trnh by trn, hin nay

cc hng ch to ra IC chuyn dng iu bin rng xung PWM dng

cho cc ngun chuyn mch. Chng to ra c mt cuc cch mng trong

vic ch to b ngun chuyn mch.

Ngoi IC CD4047BC trn th trng hin nay cn c mt s loi IC

chuyn dng iu bin rng xung nh LT1524, SG3524, HCF4047B,

HCC4047B, SG3525, TL494.

Loi IC chuyn dng ny c nhiu u im vt tri nh :

Lm vic vi di in p rng: 3.0V 15V i vi

CD4047BC , 3.0 18V vi HCC4047B.

C kh nng chng nhiu cao.

Hot ng n nh trong di nhit kh rng: -650C 1500C

vi CD4047BC.

To c sng ra vi tn s kh cao 300 kHz.

Tiu th nng lng rt thp 100 mW.

Mi hng ch to cc IC ny c i cht khc nhau song s cu to

v nguyn l hot ng ca chng u c nhng im ging nhau c bn v

c trnh by nh hnh 2.21. Do vy trong thit k mch iu khin b

nghch lu ta hon ton c th thay th cc IC ny cho nhau khi cn thit.


33

Hnh 2.8 . S khi ca IC CD4047BC.

Hnh 2.9. S logic ca IC CD4047BC.


34

Hnh 2.10 . S cu to v nguyn l hot ng ca IC chuyn dng.

Mt b dao ng rng ca sinh ra mt xung rng ca (hnh 2.21) c

bin khong 3,3V, Vst.

Mc in p mt chiu nn xung rng ca vo khong 0,5V v nh

l 4,5V.

Chu k xung rng ca c xc nh bi thnh phn in tr v t

in bn ngoi Rt v Ct, gi tr xp x : T = Rt.Ct

Sawtooth

oscillator PWM

PWM

T1 Binary

Counter

Vpwm

NAND Gate

Q _

Q

Q2

Q1

G2

G2

E2

C2

E1

C1

Overcurrent

Sensing

Vref

Error

Amplifier

KVo

+

-

+

-

Vst

Vp

Vea

Rt Ct

Vp

Vst

Vpwm

Q

Q

E1

E2

t1 t2 Vea


35

Mt b khuch i sai s so snh mt phn in p ng ra KV0 vi in

p chun Vref v sinh ra in p sai s Vea, Vea c so snh vi in p rng

ca Vst trong b iu bin rng xung PWM. Ch rng trong b khuch

i sai s, mt phn ca in p ng ra KV0 c cp n ng o khi V0

tng th in p sai s Vea gim.

Trong b iu bin rng xung PWM xung rng ca c cp vo

ng vo khng o v Vea c cp n ng vo o. Do ng ra khi

PWM l xung vung Vpwm. Gi tr ca Vpwm m trong sut khong thi gian

m gi tr ca in p rng ca Vst nh hn Vea hay t t1 n t2. Khi in p

ng ra tng, KVo cng tng tng ng v lc Vea s gim, Vea s i xung

phn y ca xung rng ca. Dn ti thi gian m ca Vpwm gim v do

thi gian m ca transitor gim v s lm gim in p ra. Ngc li khi in

p ng ra gim, KV0 gim tng ng v lc Vea s tng, n s i ln phn

nh ca xung rng ca. Dn ti thi gian m ca Vpwm tng v do thi

gian m ca transitor tng v nh vy s lm tng in p ra. T y ta thy

rng in p ra c n nh nh vng hi tip m in p.

IC CD4047BC c thit k cho mch y ko do xung m n c

rng iu chnh c Vpwm xy ra mi ln trong mt chu k xung rng ca

phi c chuyn i thnh hai xung lch pha nhau 1800 vi cng rng.

iu ny thc hin c nh b m nh phn v cng lgic NAND G1, G2.

Xung dng VP xy ra cui mi xung rng ca c sinh ra t b dao ng

rng ca, xung dng ny c s dng khi ng b m nh phn.

Ng ra ca b m nh phn Q v Q gm hai sng vung ngc pha

trong mt chu k xung rng ca. Nhng sng vung ny v Vpwm s c kt

hp trong hai b NAND G1 v G2. V vy cc B v cc E ca hai transitor Q1

v Q2 ch dng trong mt na chu k lun phin.

Thi gian m ca cc transitor cng sut chnh l khong thi gian in

p Vpwm mc thp. Khi Vp mc cao trong khong thi gian rt ngn th c


36

hai cc B ca Q1 v Q2 u mc thp khin c hai transitor lc u b kha.

iu ny m bo rng nu rng xung Vpwm ln nht, tc l Vpwm mc

thp trong c chu k xung rng ca th hai van ng lc khng m ng thi

thi im cui mi chu k. Vic m ng thi hai transitor lc cho d ch

trong thi gian ngn l rt nguy him c th s lm ph hy transitor lc.

2.3. thit k mch to xung b nghch l-u mt pha

Xung vung vi tn s 50Hz t c to ra t IC CD4047BC c a

vo chn B ca 2 transistor C1815 v A1015.

2.3.1. Nguyn l hot ng ca mch to xung dao ng tn s 50Hz.

Hnh 2.11. S mch to xung dao ng tn s 50Hz.

IC CD4047BC c cp ngun 6VDC t bnh Acquy qua tr 330

trc khi cp vo IC. Do khi mch hot ng in p cp cho IC s dao ng

khng n nh. cho IC hot ng vi mt in p n nh v khng qu


37

cao, ta mc song song mt t in c in dung l 100 F/ 16V,diot zener 9V

trc khi cp cho IC.

to ra tn s 50Hz ti chn 1 ca IC CD4047BC ta mc t in c

in dung l 0.1uF, chn s 2 ca IC c mc tr c in tr l 47k v c

ni chung vi chn s 3. Xung vung ra vi tn s 50Hz ti chn s 10 v 11

ca IC. Xung ny s c a v chn 2 chn B ca transistor C1815 v

A1015 c mc nh hnh v trn .

2.3.2. Cu to v nguyn l iu khin ca Mosfet

Hnh 2.12. Cu trc bn dn ca Mosfet .

Khc vi cu trc ca BJT, Mosfet c cu trc bn dn cho php iu

khin bng in p vi dng iu khin cc nh. Trong cc G l cc iu

khin c cch ly hon ton vi cu trc bn dn cn li bi lp in mi

cc mng nhng c cch in cc ln dioxide-silic (SiO2). Hai cc cn li

l cc gc S v cc mng D. Cc mng l cc n cc ht mang in. Nu

knh dn l n th cc ht mang in l in t (electron), do cc tnh in

p ca cc mng s l dng so vi cc gc.

Cu trc bn dn Mosfet kiu p cng tng t nhng cc lp bn dn

s c kiu dn in ngc li. Tuy nhin a s cc Mosfet cng sut l loi

knh dn kiu n. Mt trong cc u im khi dng Mosfet l tn s ng ct


38

ln, mch iu khin n gin v Mosfet iu khin bng in p, dng in

iu khin hon ton cch ly vi dng dn trn cc mng do khi Mosfet

dn khng cn dng in duy tr nh i vi transitor lng cc.

Mt thng s quan trng ca Mosfet cng sut l tn ti in tr t

nhin bn trong Mosfet. in p ri trn cc mng D v cc gc S t l tuyn

tnh vi dng trn knh dn.

Mi lin h c c trng bi thng s RDS(on) c ghi trong cc

datasheet ca Mosfet.

in tr RDS(on) l hng s tng ng vi mt in p Vgs nht nh v

nhit nht nh ca Mosfet.

Khi dng in qua Mosfet tng th nhit trn lp bn dn tng v do

in tr RDS(on) cng tng theo.

Hnh 2.13. K hiu quy c v hnh dng ca Mosfet


39

Cc thng s ca Mosfet cng sut.

Khi ng dng Mosfet trong cc thit b in t cng sut th thng s

quan trng nht m ta quan tm n l thi gian ng ct ca Mosfet,

thng thng thi gian ng ct ca Mosfet t 10ns 60ns.

Bn cnh cn c cc thng s quan trng khc nh:

in p ln nht trn hai cc D, S ca Mosfet : VDS(max) (V).

Dng in ln nht m van chu c : ID (A).

in tr trong ca van : RDS(ON) ( ).

Di nhit hot ng ca van.

Cc thng s ny rt quan trng khi ta thit k mch iu khin van.

2.3.3. Qu trnh m v kha ca Mosfet

Khi cp vo cc G (Gate) ca Mosfet mt in p thng qua mch

Driver th qu trnh m Mosfet c th hin trong th sau:

Hnh 2.14. Qu trnh m ca Mosfet

UGS

UTH

IG

t

t

t

t

UDS

ID

Mc Miller

1 2 3 4


40

2.3.3.1. Qu trnh m ca Mosfet.

Giai on th nht: in dung u vo ca Mosfet c np t in p

0V n gi tr UTH, trong sut qu trnh hu ht dng in vo cc G c

np cho t CGS, mt lng nh np cho t CGD. Qu trnh ny c gi l qu

trnh m tr bi v c dng ID v in p trn cc D (Drain) u khng i..

Sau khi cc G c np ti gi tr in p gi mu UTH, mosfet sn sng

dn dng in.

Giai on th hai: in p cc G tip tc tng t UTH n gi tr UMiller

y l qu trnh tng mt cch tuyn tnh; dng in ID tng t l vi in p

ca cc G trong khi in p gia hai cc UDS vn gi nguyn gi tr.

Giai on th ba: in p cc G gi nguyn mc in p Miller

VGS,Miller trong khi in p trn cc D bt u gim. Dng in ID trn

Mosfet gi nguyn mt gi tr nht nh.

Giai on th t: y l giai on Mosfet dn bo ha khi cp mt in

p cao UDRV (gi tr ca UDVR nm trong khong 10 20V ) vo cc G ca

Mosfet.

Gi tr cui cng ca VGS s quyt nh in tr trong RDS(ON) ca van

trong qu trnh m. Do trong giai on th t in p trn cc Gate tng t

gi tr UMiller n gi tr ca mch Driver UDRV. Trong khi in p gia cc

D, S (UDS) gim mnh gn v gi tr 0V, dng in ID gi khng i.


41

2.3.3.2. Qu trnh kha ca Mosfet.

Hnh 2.15. Qu trnh kha ca Mosfet

Qu trnh kha ca mosfet cng c chia lm bn giai on :

Giai on th nht: L qu trnh x in tch trn t CGS,DS t gi tr ban

u n gi tr miller, in p trn cc D ca Mosfet bt u tng dn nhng

rt nh, dng in trn cc D ( ID) khng i.

Giai on th hai: in p gia hai cc D - S ca Mosfet s tng t gi

tr UDS = ID.RDS(on) ti gi tr cui UDS(off).

Trong sut giai on ny dng in trn cc D vn gi khng i.

Dng in ca cc G hon ton l dng x ca t trn cc cc ca Mosfet.

Giai on th ba: in p cc G gim t gi tr Miller n gi tr gi

mu UTH. Phn ln dng in x trn cc G l phng trn t CGS.

Giai on ny in p UGS v dng in ID u gim tuyn tnh. Trong

khi in p UDS vn gi nguyn gi tr UDS(OFF).

Giai on th t: Giai on ny l qu trnh phng in hon ton ca

t in trn cc cc ca Mosfet, UGS gim n gi tr 0V. Dng in trn cc

D gim v gi tr 0 v khng i.


42

Tm li qu trnh m - kha ca Mosfet l qu trnh chuyn mch gia

trng thi tr khng cao v trng thi tr khng thp c thc hin trong bn

giai on.

di khong thi gian ca cc giai on c quyt nh bi gi tr

in dung gia cc cc, in p t vo cc iu khin, v dng in np x

ca cc t in trn cc G. y l thng s quan trng thit k mch iu

khin Mosfet trong cc ng dng c tn s ng ct ln.

2.3.4. Mch li Mosfet.

Mch khuch i c nhim v to xung ph hp m transitor. S

ph hp y l ph hp v cng sut v cch ly gia mch iu khin vi

mch ng lc khi mch ng lc c in p cao.

Tn hiu li van s c cp t IC iu khin. Vn cch ly gia

mch lc vi mch iu khin l khng cn thit do mch lc c in p thp.

Hnh 2.16. Mch li Mosfet.


43

Trong na chu k tip u cp van Q1, Q2 m vi rng xung nht

nh cp van Q2, Q4 kha, dng in i t VDC qua van Q1, v Q2 ri xung

0V.

Trong cc chu k sau thc hin tng t, ta c dng in p ra trn

ti l dng bc thang. Tn s ng ct ca cc cp van c iu khin sao

cho bng tn s ca ngun in li l 50Hz.

Hnh 2.17. Dng in p u ra ca mch .

rng xung ca mt cp van c tnh ton sao cho in p trung

bnh trn ti Ura = 220VAC.

2.3.5. Tnh ton mch ng lc.

Mch ng lc ca b bin i in p mt chiu thnh in p xoay

chiu cho ti. in p xoay chiu tn s f = 50 Hz trn cun th cp bin p

ng lc c lc qua b lc LC sau a vo ti.

T thng s mch nghch lu nh sau:

P = 100 W

VAC = 220V

Tn s ca in p l : f = 50Hz.

Dng in trn ti : Id 100/220 0,46 A

t

Ton

Toff

50Hz

Ura

+220

V

-220V

0


44

Nh vy vi yu cu thc t v cc thng s mch ta chn van ng

lc loi transitor trng cng sut knh N (Mosfet ): FQA10N60C vi cc

u im nh sau:

Tc ng ct nhanh.

in tr trong rt nh : RDS(on) = 0,6 ( ).

Dng in cc i : IDS = 10 (A).

Tch hp it (DDS) x trn van.

Hnh 2.18. Hnh dng thc v k hiu ca Mosfet FQA10N60C.

Ta s dng 4 Mosfet lm van lc.

Hnh 2.19. S ng lc ca mch bin i in p DC /AC


45

Bo v cc van bn dn ng lc khi cc xung in p nh thng van

v gim tn hao do ng ct trn van ta dng mch RC v it mc song song

vi Mosfet.

Ngoi ra bo v chng ngn mch, qu ti ta mc ni tip cu ch

vo u vo im gia ca bin p ng lc nh hnh v trn.

Chn thng s ca mch bo v nh sau:

Gi tr dng in nh mc ca cu ch c chn ln hn dng

nh mc ca ti: ICC = klv.Iti.

Vi klv l h s dng in lm vic

Chn gi tr klv = 4 5

Gi tr in tr R1, R2 thng thng chn tr 5600 , 2W.

Gi tr C1 nm trong khong: CS = 47 100 F/ 350V.

Gi tr D1, v D2 thng thng chn it FMS IN5408 chu c dng

in 5A.

Nh vy ta chn :

R1, R2 = 5600 /2W.

C1 = 100 F /3500V.

D1, D2 chn :FMS IN5408

2.3.6. Tnh ton mch lc in p u ra ca b bin i [2]

Vi mc ch ci thin c cht lng in p ra ca b bin i in

p c th dng filt lc xoay chiu.

tnh filt lc ta xut pht t cc thng s sau :

in p ra sau filt lc: UAK (V).

Cng sut ra ca b nghch lu: P (W).

Tn s ra ca b nghch lu: f (Hz).

H s cos ca ti.


46

Hnh 2.20. S filt lc xoay chiu

Tnh ton thng s ca filt lc gm 4 bc c bn nh sau:

* Bc 1. Tnh in tr ti :

R P

U AK22 cos.

* Bc 2. Tnh in khng ti:

X 2cos1.cos

R

Z = 22 XR

* Bc 3. Tnh tng tr ca filt lc:

DZ2

Z

* Bc 4. Tnh thng s ca filt lc:

C1 DDZ .6

1

L1 =D

DZ

.2

.9

p dng cc bc trn tnh filt lc cho b bin i in p vi cc

thng s nh sau: Ura = UAK= 220V, Pra = 110W, f = 50Hz, cos = 0.8 (vi

ti cm khng) :

Gi tr in tr ti : 2 2220 0.8

281.6( )110

R .

L1

C1

u ra ca b bin i Ti


47

Gi tr in khng ti : 2281.6

1 0.8 211.20.8

X .

2 2281.6 211.2 111.3Z

Nhn DZ2

Z 111.355.65

2 ( )

Ta ly quy chun : DZ = 56 ( ).

Vi D 2. .f = 2.3,14.50 = 314 (rad/s).

611 1

1.8.10 ( )3. . 3.56.314D D

C FZ

1

9. 9.560.8( )

2. 2.314

D

D

ZL H

2.4. ACQUY

2.4.1.Khi nim acquy

c quy l mt ngun in c tr nng lng in di dng ho.

c quy l mt ngun in mt chiu cung cp in cho cc thit b in

trong cng nghip cng nh trong i sng hng ngy: nh ng c in,

bng n in, l ngun nui ca cc linh kin in t... c quy l ngun

cung cp in cho cc ng c khi ng.

Trong thc t c nhiu loi c qui nhng ph bin nht l hai loi c

qui ch v c qui axit.

2.4.2. Qu trnh bin i nng lng trong c qui

c qui l ngun nng lng c tnh cht thun nghch: n tch tr nng

lng di dng ho nng v gii phng nng lng di dng in nng.

Qu trnh c qui cp in cho mch ngoi c gi l qu trnh phng in,

qu trnh c qui d tr nng lng c gi l qu trnh np in.


48

2.4.2.1. Qu trnh bin i nng lng trong c qui axit:

Trong c qui axit c cc bn cc dng l ixit ch ( PbO2 ), cc bn

m l ch ( Pb ), dung dich in phn l axit sunfuaric ( H2SO4 ) nng d

1,1 1,3 %

(- ) Pb H2SO4 d 1,1 1,3 PbO2 ( + )

Phng trnh ho hc biu din qu trnh phng np ca c qui axit :

Th in ng e 2,1 V.

2.4.2.2 Qu trnh bin i nng lng trong c qui kim:

Trong c qui kim c bn cc dng l Ni(OH)3 , bn cc m l Fe,

dung dch in phn l: KOH nng d 20 %

( - ) Fe KOH d 20% Ni(OH)3 ( + )

Phng trnh ho hc biu din qu trnh phng np ca c qui kim :

Th in ng e 1,4 V.

Nhn xt: T nhng iu trnh by trn ta nhn thy trong cc qu

trnh phng np nng dung dch in phn l thay i. Khi c qui phng

in nng dung dch in phn gim dn. Khi c qui np in nng

dung dch in phn tng dn. Do ta c th cn c vo nng dung dch

in phn nh gi trng thi tch in ca c qui.

2.4.3. Cc thng s c bn ca c qui:

2.4.3.1. Sc in ng ca c qui:

Sc in ng ca c qui kim v c qui axit ph thuc vo nng

dung dch in phn. Ngi ta thng s dng cng thc kinh nghim

E0 0,85 + ( V )

trong : E0 - sc in ng tnh ca c qui ( V )


49

- nng dung dch in phn 15 C ( g/cm3 )

Trong qu trnh phng in th sc in ng Ep ca c qui c tnh

theo cng thc:

Ep Up + Ip.rb

trong : Ep - sc in ng ca c qui khi phng in ( V )

Ip - dng in phng ( A )

Up - in p o trn cc cc ca c qui khi phng in (V)

rb - in tr trong ca c qui khi phng in ( )

Trong qu trnh np in th sc in ng En ca c qui c tnh theo

cng thc:

En Un - In.rb

trong : En - sc in ng ca c qui khi np in ( V )

In - dng in np ( A )

Un - in p o trn cc cc ca c qui khi np in ( V )

rb - in tr trong ca c qui khi np in ( )

2.4.3.2. Dung lng ca c qui:

Dung lng phng ca c qui l i lng nh gi kh nng cung cp

nng lng in ca c qui cho ph ti, v c tnh theo cng thc :

Cp Ip.tp

trong : Cp - dung dch thu c trong qu trnh phng ( Ah )

Ip - dng in phng n nh trong thi gian phng in tp ( A )

tp - thi gian phng in ( h ).

Dung lng np ca c qui l i lng nh gi kh nng tch tr nng

lng ca c qui v c tnh theo cng thc :

Cn In.tn

trong : Cn - dung dch thu c trong qu trnh np ( Ah )

In - dng in np n nh trong thi gian np tn ( A )

tn - thi gian np in ( h ).


50

2.4.4. c tnh phng np ca c qui.

2.4.4.1. c tnh phng acqui.

Hnh 2.21 . c tnh phng ca acquy

c tnh phng ca c qui l th biu din quan h ph thuc ca

sc in ng, in p c qui v nng dung dch in phn theo thi gian

phng khi dng in phng khng thay i .

T c tnh phng ca c qui nh trn hnh v ta c nhn xt sau:

Trong khong thi gian phng t tp 0 n tp tgh, sc in ngin

p, nng dung dch in phn gim dn, tuy nhin trong khong thi gian

ny dc ca cc th khng ln, ta gi l giai on phng n nh hay

thi gian phng in cho php tng ng vi mi ch phng in ca c

qui ( dng in phng ).

T thi gian tgh tr i dc ca th thay i t ngt .Nu ta

tip tc cho c qui phng in sau tgh th sc in ng ,in p ca c qui s

gim rt nhanh .Mt khc cc tinh th sun pht ch (PbSO4) to thnh trong

phn ng s c dng th rn rt kh ho tan ( bin i ho hc) trong qu

trnh np in tr li cho c qui sau ny. Thi im tgh gi l gii hn phng

in cho php ca c qui, cc gi tr Ep, Up, ti tgh c gi l cc gi tr

gii hn phng in ca c qui. c qui khng c phng in khi dung lng

cn khong 80%.

CP = IP.tP

Vng phng in cho php

20

5

10

1,75

1,95

2,11

I (A) E,U (V)

1064 8

t

E

UP

Khong ngh


51

Sau khi ngt mch phng mt khong thi gian no, cc gi tr sc

in ng, in p ca c qui, nng dung dch in phn li tng ln, ta gi

y l thi gian hi phc hay khong ngh ca c qui. Thi gian hi phc ny

ph thuc vo ch phng in ca c qui (dng in phng v thi gian

phng ).

2.4.4.2.c tnh np acqui.

Hnh 2.22 . c tnh np acquy.

c tnh np ca c qui l th biu din quan h ph thuc gia sc

in ng , in p v nng dung dch in phn theo thi gian np khi tr

s dng in np khng thay i .

T th c tnh np ta c cc nhn xt sau :

Trong khong thi gian t tn 0 n tn tgh th sc in ng, in

p, nng dung dch in phn tng dn.

Ti thi im ts trn b mt cc bn cc m xut hin cc bt kh (cn

gi l hin tng" si " ) lc ny hiu in th gia cc bn cc ca c qui

n tng n 2,4 V . Nu vn tip tc np gi tr ny nhanh chng tng ti 2,7

V v gi nguyn. Thi gian ny gi l thi gian np no, n c tc dng cho

phn cc cht tc dng su trong lng cc bn cc c bin i tun hon,

nh s lm tng thm dung lng phng in ca c qui.

1,95

Cn = In.tn

Vng np chnh

5

10

0 2 4

10%C101

6 8 ts 10 12

Vng

np n0

t

I (A) U,E (V)

2,4

2

2,7

U

TE

Khong

ngh


52

Trong s dng thi gian np no cho c qui ko di t 2 3 h trong sut

thi gian hiu in th trn cc bn cc ca c qui v nng dung dch

in phn khng thay i. Nh vy dung lng thu c khi c qui phng

in lun nh hn dung lng cn thit np no c qui.

Sau khi ngt mch np, in p, sc in ng ca c qui, nng

dung dch in phn gim xung v n nh. Thi gian ny cng gi l

khong ngh ca c qui sau khi np.

Tr s dng in np nh hng rt ln n cht lng v tui th ca

c qui. Dng in np nh mc i vi c qui l In 0,1C10 .

Trong C10 l dung lng ca c qui m vi ch np vi dng in nh

mc l In 0,1C10 th sau 10 gi c qui s y.

V d vi c qui C 180 Ah th nu ta np n dng vi dng in bng

10% dung lng ( tc In 18 A ) th sau 10 gi c qui s y.

2.4.5. S khc nhau gia c qui kim v c qui axit.

C hai loi c qui ny u c mt c im chung l tnh cht ti

thuc loi dung khng v sc phn in ng. Nhng chng cn c mt s

c im khc bit sau :

Acquy axit Acquy kim

- Kh nng qu ti khng cao, dng

np ln nht t c khi qu ti l

Inmax = 20%C10

-Hin tng phng ln, do c qui

nhanh ht in ngay c khi khng

s dng.

-S dng rng ri trong i sng,

cng nghip c bit nhng ni c

nhit cao va p ln nhng cng

sut v qu ti va phi.

-Kh nng qu ti rt ln dng in

np ln nht khi c th t ti:

Inmax = 50%C10

-Hin tng t phng nh.

-S dng nhng ni c yu cu

cng sut ln qu ti thng

xuyn, c s dng vi cc thit

b cng sut ln.


53

-Dng trong t, xe my v cc

ng c my n cng sut va v

nh.

-Gi thnh thp

-Dng ph bin trong cng nghip

hng khng, hng hi v nhng ni

nhit mi trng thp.

-Gi thnh cao.

2.4.6.Cc phng php np c qui t ng.

C ba phng php np c qui l.

Phng php dng in.

Phng php in p.

Phng php dng p.

2.4.6.1. Phng php np c qui vi dng in khng i.

y l phng php np cho php chn c dng np thch hp vi

mi loi c qui, bo m cho c qui c no. y l phng php s dng

trong cc xng bo dng sa cha np in cho c qui hoc np s cha

cho cc c qui b Sunfat ho. Vi phng php ny c qui c mc ni tip

nhau v phi tho mn iu kin :

Un 2,7.Naq

Trong : Un - in p np

Naq - s ngn c qui n mc trong mch

Trong qu trnh np sc in ng ca c qui tng dn ln, duy tr

dng in np khng i ta phi b tr trong mch np bin tr R. Tr s gii

hn ca bin tr c xc nh theo cng thc :

n

aqn

I

N0,2UR

Nhc im ca phng php np vi dng in khng i l thi gian

np ko di v yu cu cc c qui a vo np c cng dung lng nh mc.

khc phc nhc im thi gian np ko di, ngi ta s dng phng

php np vi dng in np thay i hai hay nhiu nc. Trong trng hp hai


54

nc, dng in np nc th nht chn bng ( 0,3 0,6 )C10 tc l np cng

bc v kt thc nc mt khi c qui bt u si. Dng in np nc th hai

l 0,1C10

2.4.6.2. Phng php np vi in p khng i.

Phng php ny yu cu cc c qui c mc song song vi ngun np.

Hiu in th ca ngun np khng i v c tnh bng (2,3V 2,5V) cho

mi ngn n. Phng php np vi in p khng i c thi gian np ngn,

dng np t ng gim theo thi gian.Tuy nhin dng phng php ny c

qui khng c np no. V vy np vi in p khng i ch l phng php

np b xung cho c qui trong qu trnh s dng.

2.4.6.3. Phng php np dng p.

y l phng php tng hp ca hai phng php trn. N tn dng

c nhng u im ca mi phng php.

i vi yu cu ca bi l np c qui t ng tc l trong qu trnh

np mi qu trnh bin i v chuyn ho c t ng din ra theo mt trnh

t t sn th ta chn phng n np c qui l phng php dng p.

i vi c qui axit: bo m thi gian np cng nh hiu sut np th

trong khon thi gian tn 8h tng ng vi 75 80 % dung lng c qui ta

np vi dng in khng i l In 0,1. V theo c tnh np ca c qui trong

on np chnh th khi dng in khng i th in p, sc in ng ti t

thay i, do bo m tnh ng u v ti cho thit b np. Sau thi gian 8h

c qui bt u si lc ta chuyn sang np ch n p. Khi thi gian np

c 10 h th c qui bt u no, ta np b xung thm 2 n 3h.

i vi c qui kim : Trnh t np cng ging nh c qui axit nhng do

kh nng qu ti ca c qui kim ln nn lc n dng ta c th np vi dng

np In 0,2C10 hoc np cng bc tit kim thi gian vi dng np In

0,5C10 .


55

Cc qu trnh np c qui t ng kt thc khi b ct ngun np hoc khi

np n p vi in p bng in p trn 2 cc ca c qui, lc dng np s

t t gim v khng.

2.4.7. Tnh ton b cquy.

Ta s chn loai c quy axit loi 6V, in tr trong Raq =0.09 .

p Ucl chnh l in p np cho c quy

Khi

E = 6V

Raq =0.09

UpIp = P

M Up =E Ip.Raq =6 0.09.Ip

Suy ra (6 0.09.Ip).Ip =110 W

Ip =33 A

Gi C l dung lng thc t ca c quy, m bo c quy hot ng

bnh thng ta phi chn h s d tr l 1.5

C =1.5.Ip.tphong =2.33A.0.5h =33Ah

cho b chnh lu nh gn ta chn dng np nh hn nhiu so vi

dng phng,iu c ngha thi gian np ln hn nhiu so vi thi gian

phng, ta chn thi gian np l tnap=10h

Khi : C = In*tnap =3*Ip*tphong = 33 Ah, M tnap=10h In =3,3A


56

CH-ng 2: XY DNG M HNH VT L H THNG

BIN I IN P DC/AC T 6VDC LN 220VAC TN S

50Hz

Trong chng 2 ta tin hnh la chn v tnh ton cc gi tr linh kin

trong b bin i DC/AC Ni dung chng ny ta s xy dng m hnh vt

l v kim tra cc tham s u ra ca b bin i DC/AC bng my hin sng

Oscilloscope.

3.1. xy dng mch in bin i dc/ac t 6vdc ln

220vac tn s 50Hz

S dng phn mm v mch chuyn dng Orcad 9.0 v s nguyn

l mch nng in p Acquy.

Hnh 3.1. S nguyn l mch bin i DC/AC


57

Hnh 3.2. Mch in mch bin i DC/AC

Hnh 3.3. Mch bin i DC/AC t 6VDC ln 220VAC /50Hz.


58

Hnh 3.4. Mch lc LC v Relay iu khin

Hnh 3.5. Bin p ng lc s dng trong b bin i.


59

Hnh 3.6. M hnh vt l h thng bin i DC/AC.


60

bo v qu nhit cho cc van bn dn y ta s dng tn nhit

bng nhm v qut gi lm mt. H thng bin i in p t ng ng, m

trong trng hp mt in li nh relay 12VDC c nui t ngun in

li.

3.2. dng in p ra ca b bin i

Tin hnh cp ngun cho b nghch lu v kim tra cht lng dng

in p ra bng my hin sng Oscilloscope.

Hnh 3.7. Dng in p ra ca b bin i DC/AC thi cng.


61

3.3. thit k mch np acquy [8].

Ngun cp cho b nghch lu mt pha ta s dng loi Acquy ch

6V/32Ah.

V vy cn thit k mt mch np m bo cc thng s k thut ca

Acquy:

in p np acquy: Unp= 6,9V 7,5V.

Dng in np cc i: Inpmax 33

10

Ah 3.3A.

Hnh 3.8. S nguyn l mch np Acquy

m bo cht lng in p np Acquy lun n nh ta s dng IC

n p LM7806.

in p 220VC/50Hz c a ti cun s cp ca bin p T1, in p

ly ra trn cun th cp c gi tr 24V c nn thnh in p mt chiu bng

chnh lu cu, sau a vo chn IN ca IC7806. T C1 v C2 c vai tr l

cc t lc ngun.

Trn thc t LM7806 ch cho c in p ra l 6V . Nhng vi yu

cu in p np cho Acquy 6,5V 7.5V v vy ta cn nng in p ny bng

cch mc thm it zener Dz 1.2V (loi BZX79 ). Lc ny in p mt chiu

np cho Acquy c tnh bng cng thc sau:

Ura = Un + UDz = 6V + 1,2V = 7,2 (V)

Khi np y in p trn hai cc ca Acquy l 7,2V.


62

3.4. nhn xt chung.

Sau qu trnh nghin cu v lp mch bin i in p DC/AC t

6VDC ln 220VAC tn s 50Hz t n trong trng hp mt in.

Bin in p v tn s t c 220VAC/50Hz.

V s dng nhiu phn t IC chuyn dng nn mch hat ng n

nh, kh nng chng nhiu v hiu sut ca mch kh cao.

Dng sng in p ra ca b bin i p ng c yu cu thit

k, st p khng ng k so vi khi khng ti.

Trn th trng hin nay c bn cc sn phm b bin i in p

ca cc hng, tuy nhin gi c cn kh cao, hn na cht lng cn thp. Nh

vy vi mch iu khin hot ng n nh, nng cao kh nng mang

ti ca b bin i thi cng, ta ch cn thit k bin p ng lc vi dung

lng ln hn v chn van lc chu c dng ph hp. Do kinh ph ch

to b bin i in p thp hn so vi cc b bin i cng cng sut hin c

trn th trng, theo tnh ton ch bng 50%.

Trn thc t sai s ca linh kin in tr, t in l khng nh.

khc phc iu ny ta tin hnh mc ni tip, song song, cc linh kin c

th t c ng gi tr nh tnh ton, thit k.


63

KT LUN

Sau ba thng nghin cu v thc hin ti di s hng dn tn tnh

ca GS.TSKH Thn Ngc Hon cng vi s c gng n lc ca bn thn,

em hon thnh n tt nghip ca mnh theo ng k hoch c giao.

Trong ti ny em thc hin c nhng vn nh sau:

1. Nghin cu tng quan v cc b nghch lu.

2. Tnh ton v xy dng thnh cng m hnh thc nghim.

3. ng dng v rn luyn c k nng v mch in bng phn

mm Orcad 9.2 v ra mch in th cng bng tay.

Tuy nhin, do thi gian c hn nn bn cnh nhng kt qu t

c, ti cha thc hin c mt s vn nh : Cha thc hin ch

n p, gim st qu trnh cp in cho ti. Mch thit k v lp rp cha tht

ti u. Nu tch hp trn mt v mch th sn phm b nghch lu s gn nh,

kinh t, v c gi tr thm m cao hn.

ti m ra nhng hng pht trin nh sau :

T b bin i in p DC/AC t n trong trng hp mt

in cng sut nh ta c th pht trin nn thnh b bin i in

p c cng sut ln hn ng dng rng ri hn trong i sng.

Kt hp mch np acquy, ta c th xy dng c b lu in

(UPS) dng cho cc thit b dn dng, c bit l my tnh bn

PC.

Nhng vn cha thc hin c trong ti ny s l nhng gi

cho cc nghin cu tip theo v cho nhng ai quan tm n lnh vc thit k

in t cng sut.

Sinh vin

L Vn Kin


64

TI LIU THAM KHO

[1]. GS.TSKH. Thn Ngc Hon (2004), in t cng sut, Nh xut bn

xy dng.

[2]. GS.TSKH. Thn Ngc Hon (1991), in t cng sut ln, Nh xut

bn giao thng vn ti.

[3]. TS. V Minh Chnh - Phm Quc Hi - Trn Trng Minh (2007),

in t cng sut, Nh xut bn khoa hc v k thut.

[4]. TS. Trn Vn Thnh (2008), Tnh ton thit k thit b in t cng

sut, Nh xut bn gio dc.

[5]. L Vn Doanh Nguyn Th Cng Trn Vn Thnh (2005), in t

cng sut, Nh xut bn khoa hc v k thut.

[6]. Nguyn Bnh (2000), in t cng sut, Nh xut bn khoa hc v k

thut.

[7]. Dng Minh Tr (2007), S chn linh kin bn dn, Nh xut bn

tr.

[8]. TS. xun Th (2002), K thut in t, Nh xut bn gio dc.

[9]. L Vn Doanh (1997), in t cng sut v iu khin ng c in,

Nh xut bn khoa hc v k thut.

[10]. TS. Nguyn Ln Trng (2007), Quy hoch pht trin h thng in,

Nh xut bn khoa hc v k thut.

[11]. Din n in T Vit Nam (www.dientuvietnam.net).

[13]. Datasheet ca cc Linh kin in t (www.datasheetcatalog.com).

[14]. Trang tm kim thng tin (www.google.com).


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