CNG S B bi : iu khin tc ng c mt chiu bng b bin i xung p Li ni u Chng 1 : Tng quan v ng c mt chiu1.1.

Cu to v c tnh c ca ng c mt chiu kch t c lp Cc ch lm vic ca ng c in mt chiu kch t c lp Cc phng php iu chnh tc ca ng c mt chiu kch t c lp * Phng php iu chnh in p phn ng * Phng php iu chnh t thng kch t

1.2. 1.3.

Chng 2 : Tng quan v b bin i xung p 2.1. Cu trc v phn loi b bin i xung p * B bin i xung p ni tip ( xung p gim p ) * B bin i xung p song song ( xung p tng p ) * B bin i xung p tng-gim p * La chn b bin i 2.2. Phng php iu khin b bin i xung p * Phng php thay i rng xung * Phng php thay i tn s bm xung * La chn phng php iu khin Chng 3 : Thit k mch iu khin 3.1. 3.2. S mch ng lc S cu trc mch iu khin * Khu to in p tam gic * Khu so snh to xung iu khin van * Khu to xung chm * Khu khuch i xung chm

* Bin p xung 3.3. Nguyn l hot ng ca mch iu khin Chng 4 : M phng mch iu khin Kt lun Ti liu tham kho GV hng dn SV thc hin

Li ni u Cng vi s pht trin ngy cng mnh m ca cc ngnh cng nghip c v chiu rng ln chiu su,in v cc my in ng mt vai tr rt quan trng , khng th thiu c trong phn ln cc ngnh cng nghip v i sng sinh hot ca con ngi. N lun i trc mt bc lm tin nhng cng l mi nhn quyt nh s thnh cng ca c mt h thng sn xut cng nghip. Khng mt quc gia no, mt nn sn xut no khng s dng in v my in. Do tnh u vit ca h thng in xoay chiu: d sn xut, d truyn ti..., c my pht v ng c in xoay chiu u c cu to n gin v cng sut ln, d vn hnh... m my in (ng c in) xoay chiu ngy cng c s dng rng ri v ph bin. Tuy nhin ng c in mt chiu vn gi mt v tr nht nh nh trong cng nghip giao thng vn ti, v ni chung cc thit b cn iu khin tc quay lin tc trong phm vi rng (nh trong my cn thp, my cng c ln, u my in...). Mc d so vi ng c khng ng b ch to ng c in mt chiu cng c th gi thnh t hn do s dng nhiu kim loi mu hn, ch to bo qun c gp phc tp hn ... nhng do nhng u im ca n m my in mt chiu vn khng th thiu trong nn sn xut hin i. u im ca ng c in mt chiu l c th dng lm ng c in hay my pht in trong nhng iu kin lm vic khc nhau. Song u im ln nht ca ng c in mt chiu l iu chnh tc v kh nng qu ti. Nu nh bn thn ng c khng ng b khng th p ng c hoc nu p ng c th phi chi ph cc thit b bin i i km (nh b bin tn....) rt t tin th ng c in mt chiu khng nhng c th iu chnh rng v chnh xc m cu trc mch lc, mch iu khin n gin hn ng thi li t cht lng cao. Ngy nay hiu sut ca ng c in mt chiu cng sut nh khong 75% 85%, ng c in cng sut trung bnh v ln khong 85% 94% .Cng sutln nht ca ng c in mt chiu vo khong 100000kw in p vo khongvi trm cho n 1000v. Hng pht trin l ci tin tnh nng vt liu,

nng cao ch tiu kinh t ca ng c v ch to nhng my cng sut ln hn l c mt vn rng ln v phc tp v vy vi vn kin thc cn hn hp ca mnh trongphm vi ti ny em khng th cp nhiu vn ln m ch cp ti vn thit k b bm xung mt chiu iu chnh tc c o chiu ca ng c mt chiu kch t c lp theo nguyn tc i xng . y l mt trong nhng phng php c dng ph bin nht hin nay iu chnh ng c in mt chiu kch t c lp vi yu cu o chiu quay ng c theo phng php i xng .y l mt phng php mang li hiu qu kinh t cao v c s dng rng ri bi nhng tnh nng v c im ni bt

Chng 1 : TNG QUAN V NG C MT CHIU1.1. Cu to v c tnh c ca ng c mt chiu ng c mt chiu bao gm 2 phn phn cm (phn tnh) v phn ng (phn quay). * Phn cm (stator) Phn cm gi l stator, gm li thp lm bng thp c, va l mch t va l v my v cc cc t chnh c dy qun kch t (hnh 1.1), dng in chy trong dy qun kch t sao cho cc cc t to ra c cc tnh lin tip lun phin nhau. Cc t chnh gn vi v my nh cc bulng. Ngoi ra my in mt chiu cn c np my, cc t ph v c cu chi than.

Hnh 1.1 Cc t chnh * Phn ng (rotor) Rto gm li thp, dy qun phn ng, c gp v trc my.

Hnh 1.2 L thp rto

Hnh 1.3 Dy qun phn ng my in 1 chiu

1. Li thp phn ng: Hnh tr lm bng cc l thp k thut in dy 0,5 mm, ph sn cch in ghp li. Cc l thp c dp cc l thng gi v rnh t dy qun phn ng (hnh 1.2). 2. Dy qun phn ng: Gm nhiu phn t mc ni tip nhau, t trong cc rnh ca phn ng to thnh mt hoc nhiu vng kn. Phn t ca dy qun l mt bi dy gm mt hoc nhiu vng dy, hai u ni vi hai phin gp ca vnh gp (hnh 1.3a). hai cnh tc dng ca phn t t trong hai rnh di hai cc t khc tn (hnh 1.3b). 3. C gp (vnh gp) hay cn gi l vnh i chiu gm nhiu phin ng hnh ui nhn c ghp thnh mt khi hnh tr, cch in vi nhau v cch in vi trc my. Cc b phn khc nh trc my, qut lm mt my 1.2- Nguyn l lm vic ca ng c in mt chiu Trn hnh 1.4 khi cho in p mt chiu U vo hai chi in A v B, trong dy qun phn ng c dng in. Cc thanh dn ab v cd mang dng in nm trong t trng s chu lc tc dng tng h ln nhau to nn mmen tc dng ln rto, lm quay rto. Chiu lc tc dng c xc nh theo quy tc bn tay tri (hnh 1.4a).

Hnh 1.4 M t nguyn l lm vic ca ng c in mt chiu Khi phn ng quay c na vng, v tr thanh dn ab, cd i ch nhau (hnh 1.4b), nh c phin gp i chiu dng in, nn dng in mt chiu bin i thnh dng in xoay chiu a vo dy qun phn ng, gi cho chiu lc tc

dng khng i, do lc tc dng ln rto cng theo mt chiu nht nh, m bo ng c c chiu quay khng i. Ch lm vic nh mc ca my in ni chung v ca ng c in mt chiu ni ring l ch lm vic trong nhng iu kin m nh ch to quy nh. Ch c c trng bng nhng i lng ghi trn nhn my gi l nhng i lng nh mc.1. 2. 3. 4.

Cng sut nh mc Pm (kW hay W). in p nh mc Um (V). Dng in nh mc Im (A). Tc nh mc nm (vng/ph). Ch : Cng sut nh mc ch cng sut a ra ca my in. i vi

Ngoi ra cn ghi kiu my, phng php kch thch, dng in kch t my pht in l cng sut a ra u cc my pht, cn i vi ng c l cng sut a ra trn u trc ng c. 1.3. Cc phng php iu chnh tc ca ng c mt chiu kch t c lp V phng din iu khin tc ng c in mt chiu c nhiu u vit hn so vi loi ng c khc, khng nhng n c kh nng iu chnh tc d dng m cu trc mch lc, mch iu khin n gin hn ng thi li t cht lng iu chnh cao trong di iu chnh tc rng. Thc t c hai phng php c bn iu chnh tc ng c in mt chiu ni chung v ng c mt chiu kch t c lp ni ring : iu chnh in p cp cho phn ng ng c. iu chnh in p cp cho mch kch t ng c. Cu trc phn lc ca h truyn ng iu chnh tc ng c in mt chiu bao gi cng cn c b bin i. Cc b bin i ny cp cho mch phn ng ng c hoc mch kch t ng c. Trong cng nghip thng s dng bn loi b bin i chnh:

nh:

B bin i my in gm: ng c s cp ko my pht mt chiu B bin i in t: Khuch i t (KT) B bin i chnh lu bn dn: Chnh lu tiristo (CLT) B bin i xung p mt chiu: tiristo hoc tranzito (BBXA)

hoc my in khuch i (KM)

Tng ng vi vic s dng cc b bin i m ta c cc h truyn ng H truyn ng my pht-ng c (F-) H truyn ng my in khuch i - ng c (MK-) H truyn ng khuch i t - ng c (KT-) H truyn ng chnh lu tiristor-ng c (T-) H truyn ng xung p-ng c (XA-)

Theo cu trc mch iu khin cc h truyn ng, iu chnh tc ng c mt chiu c loi iu khin theo mch kn (ta c h truyn ng iu chnh t ng) v loi iu khin theo mch h (h truyn ng iu khin h). H iu chnh t ng truyn ng in c cu trc phc tp, nhng c cht lng iu chnh cao v di iu chnh rng hn so vi h truyn ng h. Ngoi ra cc h truyn ng iu chnh tc ng c in mt chiu cn c phn loi theo truyn ng c o chiu quay v khng o chiu quay. ng thi tu thuc vo cc phng php hm, o chiu m ta c truyn ng lm vic mt gc phn t, hai gc phn t v bn gc phn t.

Nguyn l iu chnh in p phn ng:

iu chnh in p phn ng ng c mt chiu cn c thit b ngun nh my pht in mt chiu kch t c lp, cc b chnh lu iu khin vv... Cc thit b ngun ny c chc nng bin nng lng in xoay chiu thnh mt chiu c sc in ng Eb iu chnh c nh tn hiu iu khin Uk.

Lk Rb Uk BB

I

Ru U Eu

Eb (Ud k)

Hnh II-1. S khi v s thay th ch xc lp. V l ngun c cng sut hu hn so vi ng c nn cc b bin i ny c in tr trong Rb v in cm Lb khc khng. ch xc lp c th vit c phng trnh c tnh ca h thng nh sau: Eb - E = I.Rb + RI

=

Eb R + Rud b Iu K dm K dm

(II-2-1)

= 0 (U dk )

M

V t thng ca ng c c gi khng i nn cng c tnh c cng khng i, cn tc khng ti l tng th tu thuc vo gi tr in p iu khin Uk ca h thng, do c th ni phng php iu chnh ny l trit . xc nh gii iu chnh tc ta rng tc ln nht ca h thng b chn bi c tnh c bn, l c tnh ng vi in p phn ng nh mc v t thng cng c gi gi tr nh mc. Tc nh nht ca di iu chnh b gii hn bi yu cu v sai s tc v v m men khi ng. Khi m men ti l nh mc th cc gi tr ln nht v nh nht ca tc l:

max = 0 max

M dm

(II-2-2)

min = 0 min

M dm

tho mn kh kh nng qu ti th c tnh thp nht ca di iu chnh phi c m men ngn mch l: Mnmmin = Mcmax = KM.Mdm Trong KM l h s qu ti v m men. V h c tnh c l cc ng thng song song nhau, nn theo nh ngha v cng c tnh c ta c th vit: min = ( M nm min M dm )M 1 = dm ( K M 1)

0 max D= (K MW

M dm 0 max . 1 M dm = (II-2-3) M dm KM 1 1)

Wo max Wmax Wk1 Wk1 Wo min Wmin 0 M m M nm min

M,I

Hnh II-2. Xc nh phm vi iu chnh Vi mt c cu my c th th cc gi tr 0max, Mm, KM l xc nh, v vy phm vi iu chnh D ph thuc tuyn tnh vo gi tr ca cng ? Khi iu chnh in p phn ng ng c bng cac thit b ngun iu chnh th in tr tng mch phn ng gp khong hai ln in tr phn ng ng c. Do c th tnh s b c:

o max / M dm 10

V th vi ti c c tnh m men khng i th c gi tr phm vi diu chnh tc cng khng vt qu 10. i vi cc my c yu cu cao v di iu chnh v chnh xc duy tr tc lm vic th vic s dng cc h thng h nh trn l khng tho mn c. Trong phm vi ph ti cho php c th coi cc c tnh c tnh ca truyn ng mt chiu kch t c lp l tuyn tnh. Khi iu chnh in p phn ng th cng cc c tnh c trong ton di iu chnh l nh nhau, do st tc tng i t gi tr ln nht ti c tnh thp nht ca di iu chnh. Hay ni cch khc , nu ti c tnh c thp nht ca di iu chnh m sai s tc khng vt qu gi tr sai s cho php, th h truyn ng s lm vic vi sai s lun nh hn sai s cho php trong ton b di iu chnh. Sai s tng i ca tc c tnh c thp nht l:

s=s=

o min min = o min o minM dm scp o min(II-2-4)

V cc gi tr Mdm, min, Scp la xc nh nn c th tnh c gi tr ti thiu ca cng c tnh c sao cho sai s khng vt qu gi tr cho php. lm vic ny, trong a s cc trng hp cn xy dng cc h thng truyn ng in kiu vng kn. Trong sut qu trnh iu chnh in p phn ng th t thng kch t c gi nguyn, do m men ti cho php ca h s l khng i: Mc.cp=K m.Im=Mm. Phm vi iu chnh tc v m men nm trong hnh ch nht bao bi cc ng thng = m , M = Mm v cc trc to . Tn hao nng lng chnh l tn hao trong mch phn ng nu b qua cc tn hao khng i trong h. E = E + I(Rb + R) IEb = I E + I2(Rb + R)

Khi lm vic ch xc lp ta c m men do ng c sinh ra ng bng m men ti trn trc: M* = Mc* v gn ng coi c tnh c ca ph ti l Mc* = (?* )x th

u =

* + R * ( * )

*

x 1

(II-2-5)

m

1x= 0

mti khc nhau

1

u

Hnh II-3 Quan h gia hiu sut truyn ng v tc vi cc loi

Hnh II-3 m t quan h gia hiu sut v tc lm vic trong cc trng hp c tnh ti khc nhau. iu chnh tc bng cch thay i in p phn ng l rt thch hp trong trng hp m men ti l hng s trong ton di iu chnh. Cng thy rng khng nn ni thm in tr ph vo mch phn ng v nh vy s lm gim ng k hiu sut ca h. Nguyn l iu chnh t thng ng c: iu chnh t thng kch ca ng c in mt chiu l iu chnh m men in t ca ng c M = K I v sc in ng quay ca ng c E = K . Mch kch t ca ng c l mch phi tuyn, v vy h iu chnh t thngcng l h phi tuyn:

ik =

ek d + k rb + rk dt

trong : rk - in tr dy qun kch thch,

x= -1

(II-3-1)

rb - in tr ca ngun in p kch thch,

k s vng dy ca dy qun kch thch,Trong ch xc lp ta c quan h:

= f [ik]Thng khi iu chnh t thng th in p phn ng c gi nguyn bng gi tr nh mc, do c tnh c thp nht trong vng iu chnh t thng chnh l c tnh c in p phn ng nh mc,t thng nh mc v c gi l c tnh c bn (i khi chnh l c tnh t nhin ca ng c). Tc ln nht ca di iu chnh t thng b hn ch bi kh nng chuyn mch ca c gp in. Khi gim t thng tng tc quay ca ng c th ng thi iu kin chuyn mch ca c gp cng b xu i, v vy m bo iu kin chuyn mch bnh thng th cn phi gim dng in phn ng cho php, kt qa l m men cho php trn trc ng c gim rt nhanh. Ngay c khi gi nguyn dng in phn ng th cng c tnh c cng gim rt nhanh khi gim t thng kch thch:

( K ) 2 =Ru

hay

* = ( * )

2

ik U k rbk Lk a , ikk rk kE I

max

0

t cb c nh n

m

b,

L k(U ) k 0 c,

Hnh II-4 S thay th (a) c tnh iu chnh khi iu chnh t thng ng c (b) Quan h ?(ikt),(c) Do iu chnh tc bng cch gim t thng nn i vi cc ng c m t thng nh mc nm ch tip gip gia vng tuyn tnh v vng bo ho ca c tnh t ho th c th coi vic iu chnh l tuyn tnh v hng s C ph thuc vo thng s kt cu ca my in: Kt lun Phng php iu chnh tc bng cch thay i t thng c nhiu hn ch so vi phng php iu chnh in p phn ng phng php thay i t thng b hn ch bi cc iu kin c kh: chnh l iu kin chuyn mch ca c gp in. C th phng php iu chnh in p phn ng c cc u im hn nh sau : 1 - Hiu sut iu chnh cao (phng trnh iu khin l tuyn tnh, trit ) hn khi ta dng phng php iu chnh in p phn ng nn tn hao cng sut iu khin nh. 2 - Vic thay i in p phn ng c th l lm gim U dn n mmen ngn mch gim, dng ngn mch gim. iu ny rt c ngha trong lc khi ng ng c. 3 - st tc tuyt i trn ton di iu chnh ng vi mt mmen iu chnh xc nh l nh nhau nn di iu chnh u, trn, lin tc. Tuy vy phng php ny i hi cng sut iu chnh cao v i hi phi c ngun p iu chnh c xong n l khng ng k so vi vai tr v u Im ca n. Vy nn phng php ny c s dng rng ri.

Chng 2 : TNG QUAN V B BIN I XUNG P2.1. Cu trc v phn loi b bin i xung p * B bin i xung p gim p S nguyn l :

Nguyn l hot ng : Phn t iu chnh quy c l kha S ( van bn dn iu khin c ) c im ca s ny l kha S, cun cm v ti mc ni tip. Ti c tnh cht cm khng hoc dung khng. B lc L & C. it mc ngc vi Ud thot dng ti khi ngt kha K. + S ng th U c t vo u ca b lc. Nu b qua tn tht trong cc van v cc phn t th Ud=U + S m th h mch gia ngun v ti, nhng vn c dng id do nng lng tch ly trong cun L v cm khng ca ti, dng khp kn qua D, do vy Ud=0 Nh vy, Ud U. Tng ng ta c b bin i h p. * B bin i xung p tng p S nguyn l :

c im: L ni tip vi ti, kho S mc song song vi ti. Cun cm L khng tham gia vo qu trnh lc gn sng m ch c t C ng vai tr ny. + S ng, dng in t +U qua L S -U. Khi D tt v trn t c UC ( c tch in trc ). + S ngt, dng in chy t +U qua L D Ti. V t thng trong L khng gim tc thi v khng do trong L xut hin sut in ng t cm c cng cc tnh vi U. Do tng in p: ud =U + eL. Vy ta c b bin i tng p. c tnh ca b bin i l tiu th nng lng t ngun U ch lin tc v nng lng truyn ra ti di dng xung nhn. * B bin i xung p tng-gim p S nguyn l:

Ti l ng c mmt chiu c thay bi mch tng ng R-L-E. L1 ch ng vai tr tch lu nng lng. C ng vai tr lc. Nguyn l hot ng : + S ng, trn L1 c U, dng chy t +U S L1 -U. Nng lng tch lu trong cun cm L1; i-t D tt; Ud =UC, t C phng in qua ti. + S ngt, cun cm L1 sinh ra sc in ng ngc chiu vi trng hp ng D thng nng lng t trng np v C, t C tch in; ud s ngc chiu vi U. Vy in p ra trn ti o du so vi U. Gi tr tuyt i |Ud| c th ln hn hay nh hn U ngun.

* B bm xung mt chiu c o chiu

y ta s dn van bn dn IGBT B BXM dng van iu khin hon ton IGBT c kh nng thc hin iu chnh in p v o chiu dng in ti Trong cc h trngruyn ng t ng c yu cu o chiu ng c do b bin i ny tthng hay dng cp ngun cho ng c mt chiu kch t c lp c nhu cu o chiu quay. Cc van IGBT lm nhim v kho khng tip im .Cc it 1,2,3,4 dng tr nng lng phn khng v ngun v thc hin qu trnh hm ti sinh. C cc phhng php iu khin khc nhau nh : iu khin c lp, iu khin khng i xng v iu khin i xng * La chn b bin i - La chn mch lc Qua cc mch phn tch trn ta thy ph hp o chiu ng c (mt cch ch ng) ta chn b bm xung mt chiu c o chiu (cu BXDC), mch ny cho php nng lng i theo 2 chiu Ud, Id c th o chiu mt cch c lp. Hn na mch ny rt thng dng (dng trong DC-DC, DC-AC converter) do vic tm mua cc phn t cng d dng hn. - La chn van bn dn Chn van IGBT bi :

+ IGBT l phn t kt hp kh nng ng ct nhanh ca MOSFET v kh nng chu qu ti ln ca transistor thng, tn s bm in p cao th lm cho ng c chy m hn. + Cng sut iu khin yu cu cc nh nn lm cho n gin ng k thit k ca cc b bin i v lm cho kch thc h thng iu khin nh, hn na n cng lm tit kim nng lung (iu khin). + IGBT l phn t ng ct vi dng p ln, n ang dn thay th transistor BJT n ngy cng thng dng hn do vic mua thit b cng n gin hn.Cng vi s pht trin ca IGBT th cc IC chuyn dng iu khin chng (IGBT Driver) ngy cng pht trin v hon thin do vic iu khin cng chun xc v vic thit k cc mch iu khin cng n gin, gn nh. 2.2. Phng php iu khin b bin i xung p in th trung bnh u ra s c iu khin theo mc mong mun mc d in th u vo c th l hng s (c qui, pin) hoc bin thin (u ra ca chnh lu), ti c th thay i.Vi mt gi tr in th vo cho trc, in th trung bnh u ra c th iu khin theo hai cch: - Thay i rng xung. - Thay i tn s bm xung.

* Phng php thay i rng xung Ni dung ca phng php ny l thay i t1, gi nguyn T. Gi tr trung bnh ca in p ra khi thay i rng l:

Ud =Trong t :

t1.U = . U T

=

t1 T

l h s lp y, cn gi l t s chu k. Nh vy theo phng php ny th di iu chnh ca Ura l rng(0 < 1). * Phng php thay i tn s bm xung Ni dung ca phng php ny l thay i T, cn t1 = const. Khi :

Ud =

t1.U = t1. f .U T

Ngoi ra c th phi hp c hai phng php trn. Thc t phng php bin i rng xung c dng ph bin hn v n gin hn, khng cn thit b bin tn i km. y ta chn cch thay i rng xung, phg php ny gi l PWM (Pulse Width Modulation).Theo phng php ny tn s bm xung s l hng s.Vic iu khin trng thi ng m ca van da vo vic so snh mt in p iu khin vi mt sng tun hon (thng l dng tam gic (Sawtooth)) c bin nh khng i.N s thit lp tn s ng ct cho van,tn s ng ct ny l khng i vi di tn t 400Hz n 200kHz.Khi Uctl >Ust th cho tn hiu iu khin m van, ngc li kha van. Phng php iu khin b bm xung c o chiu Nguyn tc iu khin Theo phng php iu khin ny cc cp van S1 v S2; S3 v S4 lp thnh hai cp van m trong mi cp th hai van c iu khin ng ct ng thi. Tn hiu iu khin c to ra bng cch so snh in p iu khin vi

in p ta (thng l dng xung tam gic): -Nu Udk>utua th S1 v S2 c kch dn; S3 v S4 c kch tt. -Nu Udk toff . Da vo phng trnh ca Uta theo thi gian, ta c: Uta = 8*104.t (V) Thi gian tr cn thit l ttr =1s nn im chuyn i trn in p ta phi chnh nhau gi tr: 8*104 * 1* 10-6 = 0.08 (V) Cp in tr R32, R42 cn chn sao cho Uk2 bin thin trong khong Chn R42=44k v R32=81k, R42=44k v R32=81k * Khu o chiu ng c (dng cng tc 2 v tr): Nguyn tc o chiu ng c l : - u tin gim tc ng c v khng. - n nt chuyn tc theo chiu ngc li. Nt bm y

c thit k l mt cng tc lin ng thc hin chuyn mch 2 tn hiu iu khin. - Theo tnh cht Uk c trnh by trn, b phn to tr m bo an ton cho van c quyt nh bi b phn p nh 2 cp in tr R31, R41 v R32, R42. Do , khi in p iu khin i chiu th ng cp Uk1 bin thnh ng cp Uk2 th mi m bo nhm van ny ng th nhm van kia mi m. - Khu o chiu in p Uk l mt b o du s dng khuch thut ton. B o du ny ch o du mt gi tr khng i v khng i hi tn s lm vic cao. Tuy nhin, ng b cc thit b yu cu tn s cao, ta chn b o du l khuch thut ton LM7131A/NS. S b o du nh sau:

Thc cht ca b o du l mt b khuch i o, do ta chn R1=R2=1k, Rcb c tc dng cn bng in tr vo nn ta chn l 0.5k. * Khu so snh to xung iu khin van

Gii thch nguyn l hot ng: Vi 2 gi tr Uk ta em so snh vi gi tr Uta to ra 4 xung a n b trn xung pha sau. Hai xung Um1 v Ukha1 ng b vi nhau, xung ny mc cao th xung kia mc thp. Tr hn mt khong l hai xung Um2 v Ukha2 cng ng b vi nhau. Khuch thut ton c s dng l loi c thi gian tc ng nhanh to iu kin cho xung ra c sn ln, sn xung dc. Ta dng loi LM7131A/NS ca hng National Semiconductor sn xut. - S chn:

* Khu to xung chm

Gii thch nguyn l hot ng: y l mch to dao ng dng khuch thut ton, rt thng dng hin nay. Khuch thut ton c s dng nh b so snh hai ca. T C lin tc phng, np lm cho khuch thut ton o trng thi mi ln in p trn t t tr s b chia in p R1, R2. Chu k dao ng c tnh theo cng thc sau:T = 2RC ln(1+ 2R 1 ) R2

Tnh ton: - Khuch thut ton dng loi c tc cao l LM318 nu trn. - Ta chn sao cho (R2 + R1) c 20 (k). Thng thng ta chn R2 < R1. Vy ta chn cc gi tr nh sau: R1=15k v R2=4.7k T cng thc rng buc trn ta c R . C2 = 12.5 * 10-6. Ta chn R=5.6k v C2 = 0.0022F - Chn D1 l Diode FJT1100 * Khu trn xung Mch trn xung dng cc cng logic AND, c 4 tn hiu cn trn xung nn mch cn 4 cng AND, ta dng 1 IC 7408 do hng Texas Instrument sn xut c tch hp 4 cng AND trong mt IC

* Khu khuch i xung chm Nguyn tc: cch ly gia mch lc v mch iu khin ta dng bin p xung. Tuy nhin do tnh cht vi phn ca bin p xung nn khng cho php truyn cc xung rng vi miligiy. Chnh v tnh cht ny m ta phi truyn xung rng di dng xung chm bin p xung hot ng bnh thng. n gin mch dng thi bo m h s

khuch i dng cn thit tng khuch i ta dng l kiu Dalinton. S mch nh hnh v trn. m bo in p bn cun s cp ca BAX l 15(V) ta chn ngun nui c gi tr Vcc = 20 (V). (V cn phi tnh n st p trn in tr). Khi c tn hiu xung i vo th bng T2 s m ng thi lm m lun T1. Lc ny xut hin dng in chy t ngun nui qua R20, qua cun s cp v T1 ri i xung t v thnh lp trn cun s cp mt in p U1. in tr R20 c tc dng bo v T1 trnh dng I1 vt qu gi tr IC1max. * Bin p xung My bin p xung thc hin cc nhim v: - Cch li mch lc v mch iu khin. - Phi hp tr khng. - Nhn thnh nhiu xung (BAX nhiu cun th cp) cho van cn m ng thi. Mch iu khin gm c 4 bin p xung, trong 2 ci to xung m cho cc van, 2 ci to xung kha cho cc van. * Khu chun ha tn hiu iu khin: Khu ny t sau bin p xung, c nhim v bin i cc tn hiu t bin p xung thnh cc tn hiu in p ph hp ng m cc van. ng m c cc van, yu cu in p m l +15V v in p kha l -5V. Ta iu ch bng cch o du in p +5V thnh -5V bng mt mch o du nh trnh by trn, sau dng mt mch cng tng ng cng in p +15V vi -5V tng ng. S mch cng nh sau:

Chn R51 = R55 = R53 = R54 = 1k

Khuch thut ton vn chn loi c tc nhanh l LM7131A/NS Tn hiu in p t sau khu chun ha ny s c a vo cc iu khin ca IGBT. 3.3. Nguyn l hot ng ca mch iu khin Khu to in p tam gic s cho ta mt in p ta c dng tam gic thun tin cho khu so snh tip theo. Khu to in p ta ny thc cht bao gm 2 khu l khu pht xung ng b v khu to xung rng ca (dng tam gic). Khu ny s quyt nh lun tn s iu khin cc IGBT. S d ta chn in p ta dng ny l v c 2 u im sau: m bo an ton cho vic ng m cc van bn dn. Vi 2 in p iu khin lch nhau c 0.2V a vo 2 mch so snh tng ng 2 knh iu khin 2 nhm IGBT ta c th tin tng rng trong ton b qu trnh hot ng, nhm van ny kha chc chn th nhm van cn li mi c pht xung m. Gii php ny u im hn cch s dng khu tr m bo an ton cho cc van bn dn. in p ta dng tam gic gm c min m ln min dng cho php ta o chiu ng c n gin bng cch o du in p iu khin a vo mch so snh. - in p ta c a vo cc b so snh (Comparator) cng vi in p iu khin thu c in p dng xung Ubh thch hp vi cc knh iu khin m lut ng m v lut iu khin i xng t ra. m bo phm vi iu chnh tc l 25:1 ta cn a in p iu khin vo vi bin bin thin 25 ln. Cng vic ny c thc hin nh b n p dng IC LM317. y ta cn dng 2 b n p LM317 a vo 2 in p iu khin chnh lch nhau c 0.2V. - Vic o chiu quay ng c c thc hin nh b o du in p iu khin. Nguyn l ca b o du ny thc cht l mch t hp tuyn tnh mt thnh phn dng khuch thut ton.

- Ta s dng phng php cch ly t cch ly mch lc v mch iu khin bng bin p xung. Tuy nhin do tnh cht vi phn ca my bin p nn khng cho php truyn cc xung rng vi ms. Chnh v tnh cht ny m ngi ta phi truyn xung rng di dng xung chm bin p xung hot ng c bnh thng. Nguyn tc y l tn hiu (hay xung c rng c ms) sau b so snh i ra c coi l cc tn hiu cho php hay cm xung chm vi tn s cao i vo BAX dng cc phn t logic AND. - Xung chm c to ra bi Khu to xung chm vi tn s 20 kHz, sau khi c trn vi in p so snh s c dng cc chm xung i ra t mch logic vi cng sut nh. Do m bo m c cc van lc n phi i qua khu khuch i xung. Khu khuch i xung ph bin nht v cng c s dng trong n ny l phng php dng tng khuch i Dalinton.

Chng 4 M phng mch iu khin 4.1. 4.2. Ta c: Hnh 2.1. Cu trc mch vng dng in tng qut S cu trc: trong : T = R : Hng s thi gian in t ca mch phn ng u S tng ng:Lu

M hnh ng c mt chiu trn MatLab Cu trc mch vng dng in

Hnh 2.2. Cu trc mch vng dng in rt gn T s trn ta c hm truyn ca i tng : Soi(p) = ng vi iu kin : Tsi = Ti + TV +Tk Ri(p) = 2 p(1 + 2 p).S Oi => Ri(p) = 2 pK K / R (1 + 2 p) cl i u Chn = min(Tsi,Tu) = Tsi Rt gn ta c hm truyn:1 + pT R .T 1 (1 + pTsi )(1 + pTu )1

1

Ri ( p ).Soi

FMoi

u u u Ri(p) = 2 pK .K .T / R = 2 K .K .T (1 + pT ) cl i si u cl i si u

Vy Ri(p) l khu t l tch phn (PI) 4.3. Tng hp b iu chnh tc . Cu trc ca h iu chnh tc :

Hnh 2.3. Cu trc ca mch iu khin tc tng qut Trong ly hm truyn ca mch vng dng in l khu qun tnh bc nht, b qua cc thnh phn bc cao. Vit gn s ta c:

Hnh 2.4. Cu trc mch iu chnh tc rt gn Trong : So = K .( K )T . p(1 + pT ) i c s Vi TS = 2Tsi + T rt nh Theo tiu chun Modul ti u ta c hm truyn h kn nh sau: FMo = 1 + 2 . p + 2 2 . p 2 Mt khc ta c:R ( p).So1

Ru .K

FMo(p) = 1 + R ( p).So

=> R(p) = So (1 F ) Mo => R(p) = 2 p(1 + 2 p).S O => R(p) = 2 pR .K (1 + 2 p) u K i .( K )Tc . p (1 + pTs )1

FMo

Chn = Ts Rt gn ta c hm truyn: R(p) = 2T R .K s u Vy R(p) l khu t l tch phn (P) Sau khi tng hp ra cc b iu chnh, ta c s cu trc ca h thng iu khin tc ng c in mt chiu nh hnh v.K i .( K )Tc

Hnh 2.5. Cu trc h thng iu khin tc ng c in mt chiu 4.4. Tnh ton m phng Cc thng s cho trc: Pm : cng sut ng mc ca ng c 2,5 kw Um : in p nh mc phn ng nm : Tc quay nh mc L : in cm phn ng Ti : Hng s thi gian my bin dng TV : Hng s ti gian b chnh lu 400 V 1750 V/ph 0,2 H

dm : Hiu sut danh nh ca ng c 90%

0,002 S 0,0025 S

Tk : Hng s thi gian mch iu khin b chnh lu 0,0001 S

T : Hng s thi gian my pht tc 0,001 S=2 n n 1750 = => dm = = 183rad / s 60 9,55 9,55

dm Mm = = 183 = 13.6 Nm dm dm Im = U = 400 = 6, 25( A) dm

P

2500

P

2500

K =

M dm 13, 6 = = 2,18 I dm 6, 25

Tnh R gn ng theo cng thc:dm R = 0,5(1-dm ) I = 0,5(1 0,9) 6, 25 = 3, 2 dm u T = R = 3, 2 = 0,0625s u

U

400

L

0, 2

Mt khc ta c : U = Uk.Kcldm Chn Uk = 10V => Kcl = U = 10 = 40 dk

U

400

Hm truyn ca b iu chnh:u u Ri(p) = 2 K .K .T (1 + pT ) cl i si u

R .T

1

C Tsi = Ti + Tv+Tk = 0,002 + 0,0025 + 0,0001 = 0,0046 S Chn Ui = 7Vid => Ki = I = 6, 25 = 1,12 dm

U

7

=> Ri = 2.40.1,12.0, 0046 (1 + 0, 625 p ) = 0, 485(1 + 0, 625 p )u Tc = ( K )2 = 2,07 2

3, 2.0, 0625

1

1

JR

2,45.1,31

= 0,75 S

Ru 3, 2 = = 1, 95 ( K ).TC 2,18.0, 75

U d = .K Chn U d = 10 V =>K =10 = 0,055 183

Vi TS = 2Tsi + T = 2.0,0046 +0,001 = 0,01 S R (p) = 1,31.0,055.2.0,01 = 519 S m phng :0,482.2,07.0,75

Kt qu m phng Tc ng c

Dng in ng c

Kt lun Ti liu tham kho 1.Phm Quc Hi,Dng Vn Nghi.Phn tch v gii mch in t cng sut Nh xut bn Khoa hc v k thut H Ni ,1997 2.Phm Quc Hi,Trn Trng Minh ,V Minh Chnh.in t cng sut Nh xut bn Khoa hc v k thut H Ni ,2004 3.Nguyn Bnh .in t cng sut Nh xut bn Gio dc ,2000 4.Nguyn Vn Lin ,Nguyn Th Hin .Truyn ng in Nh xut bn Khoa hc v k thut H Ni ,2000 5.Phm Quc Hi ,Dng Vn Nghi,Nguyn Vn Lin,Nguyn Th Hin . iu chnh t ng truyn ng in 6.Bo T ng ho Ngy nay- S thng 1&2 7.L Vn Doanh ,Trn Vn Thnh .in t cng sut L thuyt v ng dng Nh xut bn Khoa hc v k thut H Ni ,2005 8.Trn Trng Minh .Bi ging in t cng sut Nh xut bn Gio dc ,2002 9. Nguyn Phng Quang. Matlab v Simulink cho k s iu khin t ng Nh xut bn Khoa hc v k thut H Ni ,2004 10.Nhm pht trin phn mm tin hc v in t EDA. Hng dn s dng ORCAD 9.2 Nh xut bn tr 2000 11.Matlab.Users guide. Prentice Hall,1995 12.Bi nh Tiu .C s truyn ng in Nh xut bn Khoa hc v k thut H Ni 13.L Vn Doanh ,Cyril Lander .in t cng sut v iu khin ng c in

Nh xut bn Khoa hc v k thut H Ni ,2004 V cc trang Web : 14.Alldatasheet.com 15.INF.com 16.IGBT.com 17.IGBT-scaledriver.com

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