sổ tay cdt chuong 20(1-3)-cc chap hanh

8/6/2019 s tay cdt Chuong 20(1-3)-Cc Chap Hanh

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20C cu chp hnh

Rymantas Tadas TolockaKaunas University of Technology

Stefano PastorelliPolitecnico di Torino

20.1 C cu chp hnh C in ............................................1

20.2 My in .....................................................................25

20.3 C cu chp hnh p in ...........................................39

20.1 C cu chp hnh C inGeorge T.-C. Chiu

Gii thiu

Nh tm tt trong cc chng trc, mt h thng C in t c th c chia thnh cc khi chc nng nh tronghnh 20.1. Trong chng ny, chng ti s tp trung vo phn c cu chp hnh ca h thng. c bit, chng ti s a racc tho lun chung v cc dng c cu chp hnh c in v nhng nh hng ca ti trng hay mi trng vt l nchng. Tip theo, chng ta s xem xt cc thnh phn in t c bn cn thit cho vic iu chnh nng lng in.

HNH 20.1 H thng C in t HNH 20.2 S chc nng ca c cu chp hnh

HNH 20.3 C cu chp hnh thu lc v c in

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S tay C in tMt h thng C in t c th c chia mt cch tng i thnh phn nng lng cao hn tng tc vi mi trng

vt l v phn nng lng thp hn x l d liu, hnh 20.1. Cm bin v c cu chp hnh l nhng thit b thc hin nhimv iu chnh v chuyn ho nng lng. Bi vy cu trc ca mt c cu chp hnh c th c m t nh trong hnh 20.2.Thng thng cc c cu chp hnh ch l cc thit b chuyn i nng lng. Tuy nhin, vi s pht trin ca in t cngsut, mt cch tng quan c th coi c cu chp hnh bao gm c phn khuch i cng sut. Mt c cu chp hnh thu lctuyn tnh, hnh 20.3, cng c th phn loi tng t, van cun (spool valve) l khi khuych i/iu chnh cng sut vi vtr van l tn hiu iu khin v p sut/lu lng cht lng l ngun nng lng. Xi lanh thu lc hot ng nh mt thit bchuyn i t thy nng sang dng c nng. Vi mt h c cu chp hnh c in thng thng nh ng c in mt chiu(hnh 20.3), khi khuch i cng sut l phn truyn ng cho ng c, khuch i mc tn hiu iu khin (dng in/cngsut nh) ti tn hiu cng sut cao hn (dng in ln), c dng chuyn nng lng in thnh nng lng c da trnnguyn l in t.

Trong chng ny, phn u s l khi qut cc dng c cu chp hnh c in. Chng c chia thnh cc nhm c ccu chuyn i nng lng tng ng. Cc thnh phn in t cng sut nh it, thyristor, transitor, dng khuch icng sut v iu chnh s c gii thiu thng qua vic xy dng cc khi khuch i cng sut. Cui cng l kt lun vmt s vn lin quan ti cc c cu chp hnh c in.

Cc dng c cu chp hnh c in - Nguyn l hot ng

Nguyn l chung ca cc c cu chp hnh c in l chuyn nng lng in sang nng lng c. C nhiu dng c cukhc nhau, v d c cu chuyn i trc tip nh chuyn i p in hoc c cu chuyn i qua trung gian nh t trng.Cc c cu chp hnh c in ph bin s c gii thiu mt cch khi qut sau s c cp chi tit hn trong ccmc nh.

in t - T trng

in t l phng php chuyn i nng lng ng dng ph bin nht cc c cu chp hnh c in. Mt trong nhngl do s dng t trng thay v in trng l do mt nng lng trong t trng cao hn. Vng khng kh chia phn tnh(stator) v phn chuyn ng ca mt c cu chp hnh c in l ni din ra s chuyn i nng lng c in. Tng snng lng trn mt n v trong vng t trng ny c th l bc 5 ca lng nng lng trn mt n v tng ng cain trng.

Lut Lorentz v lc in t v lut Faraday v cm ng in t l hai nguyn tc c bn chi phi cc c cu chp hnhin t. Trc khi i vo chi tit v in t, chng ti s gii thiu cc nh ngha ca t trng v t thng.

T thng tn ti khi c t trng. ln ca t trng H (A/m) v mt t thng B (tesla [T]) lin quan vi nhaubi t thm ca vt liu. Trong chn khng, mt t thng t l vi ln t trng nh cng thc sau:

0B Hm= (20.1)

Trong 0m = 4 [T m/A] l hng s thm t. Vi cc vt liu t hoc st t khc, cng thc tnh nh sau:

0( )rB H Hm m= (20.2)

Trong , rm ( H ) l t thm ng vi tng loi vt liu. Hnh 20.4 l cc ng cong c trng B-H v - H.

Lut Lorentz ca lc in t

Khi mt vt dn mang dng in c t trong t trng, n s chu tc ng ca mt lc cm ng theo cng thc

F i B= (20.3)

HNH 20.4 Biu - H v biu B-H HNH 20.5 Lc in t Lorentz

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C cu chp hnh

Trong F vect lc, i l vect dng in, B l mt t thng. Lc ny c gi l lc in thay lc Lorentz. Numt vt dn c di L mang dng in i khng i t trong vng t thng B khng i, nh trong hnh 20.5, ln calc Lorentz c tnh theo cng thc:

F F BLi= = (20.4)

nh lut Faraday v cm ng in t

Chuyn ng ca mt vt dn trong t trng s sinh ra mt sut in ng (emf), hay hiu in th, hai u vt dn:

demf E

dt

f= = - (20.5)

Trong .B dAf = l t thng. Vi mt vt dn c di L chuyn ng vi tc hng v trong t trng khng ivung gc vi b mt A, nh hnh 20.6, ln ca sut in ng cm ng (hiu in th) l:

emf E BLv = = (20.6)

HNH 20.6 Sut in ng cm ng

C 2 phng php to ra t trng H , hay mt mt t thng B mong mun l dng nam chm vnh cu hocs dng lut BoitSavart.

Lut BoitSavart

Mt vt dn mang in di (v hn), thng, cm ng mt t trng quanh vt dn hnh 20.7. Mt t thng khongcch r vung gc t vt dn tnh theo cng thc:

0

2rB i

r

mm

p= (20.7)

HNH 20.7 T trng sinh ra bi vt dn mang dng in HNH 20.8 T trng cm ng ca cun cmTrong , i l

dng in. Nu ta b cong vt dn mang dng in thnh

dng cun cm xon c vi N vng (solenoid), n s cm

ng mt t trng tng ng nh m t trong hnh 20.8.

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S tay C in tNu di cun cm L ln hn ng knh D ca n, mt t thng xc nh theo quy tc bn tay phi v ln xp x

bng

NB i

Lm= (20.8)

trong 0.rm m m= l t thm ca vt liu trong cun cm v i l dng in qua cun dy. i lng ny c th ckhuch i bng cch ci mt li st t trong cun cm tng thm t. Cun cm c s dng rng ri trong cc thitb in t cho vic to ra cc t trng iu khin c v thng lin quan ti nam chm in.

HNH 20.9 Phn loi cc c cu chp hnh kiu cun cm(Courtesy of Shih Hsing Industrial Co., Ltd.)

HNH 20.10 Mt cun cm thng thng

Thit b kiu cun cm (Solenoid Type Devices)

Cun cm (nam chm in c li), hnh 20.9, l dng c cu chp hnh in t n gin nht c dng cc b phtng dng thng hoc quay cho cc van, kho chuyn mch (cng tc) v rle. Nh tn gi ch ra, mt cun cm solenoidbao gm mt khung st tnh (stator), mt cun cm, v mt li st t c dng nh pittng (phn ng) gia cun cm hnh20.10.

Khi cun cm c cung cp nng lng, mt t trng c cm ng trong cun cm. Phn li di chuyn thu hp khe

h khng kh gia pittng v khung st stato tnh lm tng t thng mc vng. Lc t sinh ra xp x t l vi bnh phngdng in i v t l nghch vi bnh phng din tch khe h khng kh , c gi l hnh trnh ca cun cm:

2

2

iF

d (20.9)

Nh ch ra trong hnh 20.11, vi cc hnh trnh nh hn 0.060 in., pittng dng mt phng cn lc ko hoc y ln hncc pittng 60 t 3-5 ln. Vi cc hnh trnh ln hn khong 0.750 in., pittng 60 c li th ln nht hn pittng thng. Khicun cm khng c cp nng lng, t trng gim v pittng s tr v v tr c nh ti trng bn thn hoc nh mt l xoko tr li.

Tt c cc cun cm tuyn tnh s ko pittng vo trong cun cm khi n c cung cp nng lng. Cun cm dng ythc hin bng cch ko di pittng qua mt l v tr dng cui (back-stop), hnh 20.12. Do khi c cp nng lng,pittng tip tc c y trong cun cm, nhng phn ko di sinh ra mt chuyn ng y t phn cui ca cun cm. Khi

cun cm khng cp nng lng pittng t chuyn ng tr v v tr ban u nh ti bn thn n (trng lng ca ti) hocnh lc l xo, n c cung cp nh mt phn khng th thiu ca cun cm.

HNH 20.11 ng cong lc-hnh trnh ca cc cun cm (Courtesy of Magnetic Sensor Systems)

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C cu chp hnh

HNH 20.12 Cc dng cun cm y v ko (Curtesy of Ledex & Dormeyer Products)

HNH 20.13 Cc cun cm dng quay (Courtesy of Ledex & Dormeyer Products)

Cc cun cm dng quay s dng cc bi di chuyn xung theo hng ng vng bi bin chuyn ng tnh tinthnh chuyn ng quay. Khi cun cm c cp nng lng, pittng c ko v pha stator v quay mt gc xc nh bing vng bi, Hnh 20.13. Mt rle c in (EMR) l mt thit b s dng mt cun cm ng hay m mt lin kt ckh (cng tc) gia dy dn in chnh cng sut ln. Mt rle thc hin chc nng tng t mt transitor cng sut, dngnng lng in nh iu khin dng in ln. im khc nhau l mt rle c kh nng iu khin mc dng in ln hnnhiu. S khc nhau ca c cu ny c th l: mt s rle c nhiu im tip xc, mt s th li b kt nang (encapsulated),mt s li c mch in gn lin lm tr s tip xc khp kn sau khi khi ng v mt s khc v d nh trong mch inthoi, li di chuyn qua mt lot vi tr tng bc mt khi n (c kch hot v khng c kch hot) cung cp nng lngv khng c cung cp nng lng.

Thit k/la chn. Lc, hnh trnh, nhit v vng qut l 4 im chnh cn cn nhc khi thit k/la chn cun cm.Mt cun cm tuyn tnh c th cp ti a lc 30lb t mt n v t hn 2 in. di. Mt cun cm quay cng c th cung

cp mt momen hn 100lb t 1 n v nh hn 2 in. chiu di. Nh trong hnh 20.11, quan h gia lc v hnh trnh c thsa bng cch thay i thit k ca mt s b phn bn trong. Tng dng in ti cun cm c th t c lc u ra.Tuy nhin dng in ln li c xu hng lm tng nhit cun dy, in tr dy dn tng. iu ny dn ti gim lc u ra.Cc cun cm thng c mt di hot ng vi vng qut lin tc hoc khng lin tc. Mt cun cm vi 100% vng qut cth c cp nng lng in p nh mc ca n lin tc bi v tng nhit cun cm s khng c vt qua di ti acho php, trong khi mt cun cm c vng qut khng lin tc c mt thi gian "on" cho php khng c vt qu. Cuncm vng khng lin tc cung cp lc ln hn cun cm lin tc. Nhit hot ng ti a ca mt cun cm quyt nh bidi nhit ca vt liu cch in dng trong cun dy (Bng 20.1).

BNG 20.1 Di nhit ca cc vt liu cch in

Phn loi Di nhit

Loi (lp) A Loi (lp) 105 1050C 2210F

Loi (lp) E Loi (lp) 120 1200C 2480F

Loi (lp) B Loi (lp) 130 1300C 2660F

Loi (lp) F Loi (lp) 155 1550C 3110F

Loi (lp) H Loi (lp) 180 1800C 3560F

Loi (lp) N Loi (lp) 200 2000C 3920F

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S tay C in t

HNH 20.14 ng c cun dy ng

ng c cun dy ng (Voice-Coil Motors) (VCMs)

ng c cun dy ng (voice-coil motor) c ng dng bt ngun t cc loa pht thanh. Hin nay n dng rng ri trongcc u c/ghi trong cc a cng. Khi cun cm chuyn ng, VCM cng nh mt c cu chp hnh cun cm ng.VCM bao gm mt cun cm (phn ng) gia khe v nam chm vnh cu (stator) ni cung cp t trng trong khe, Hnh20.14. Khi dng in qua cun cm, cun cm chu mt lc in t tc ng theo lut Lorentz bng:

F i B=

Hu ht cc cun cm ng c thit k c t thng vung gc vi chiu dng in nn lc Lorentz c th c tnhnh sau:

VCM F VCMF BNl i K i F ig= = (20.10)

Trong l l di cun cm/mt vng, B l mt t thng, N l s vng dy ca cun cm v l h s s dng cacun cm. Cng thc trn ch ra lc t l vi ln dng in cp v hng s t l KF thng c gi l hng s lc.

Cun cm thng c treotrong khe nh cc l so v ni vi ti nh trong s ca loa radio, ng cun ca van thulc hay u c/ghi a. Quan h tuyn tnh gia lc u ra v dng in cung cp, kh nng thun nghch hai chiu lmcun cm ng u im hn cc cun cm. Tuy nhin khi iu khin lc u ra ca cun cm ng, cn dng iu khinvng kn hoc cc l xo gim chn.

Thit k/la chn. T cng thc (20.10) ta thy rng hng s lc ph thuc vo mt t thng v s lng dy dn cth t trong khe. C 2 cch tng hng s lc. Mt l tng mt t thng, c th t c bng cch dng vt liu t

mnh v tng cc thng s khc nh N hoc l, tc l b nhiu dy hn hoc lm cun cm c ng knh ln hn.Vi mt khe cng th tch, dng loi dy dn nh hn l cch duy nht tng s vng dy. Tuy nhin, tng s vng dy

s dn ti in tr cao hn v n s lm tng nhit ca cun dy v gii hn cho php ca dng in. Thm vo , phn cchly thm vo s chim nhiu th tch hn v c xu hng gim hiu qu ca vic tng s vng dy N. Tm li, tng hiusut ca cun cm ng, ngi thit k c th hoc l chn vt liu t tt hn hoc tng kch c ng c bng cch tng ln cun cm (tng D) hay tng di cun cm (tng N).

ng c in

Cc ng c in c s dng rng ri nht trong cc c cu chp hnh c in. N c th c phn loi theo chcnng hoc theo c tnh in t. S khc nhau ch yu cc ng c in l thit k rto v phng php to t trng. Hnh20.15 m t cc thnh phn cu to ca mt ng c mt chiu nam chm vnh cu. Mt s thut ng chung cho cc ng cin l:

Stator: l phn tnh bn trong hoc bn ngoi ca ng c lm bng vt liu to t trng stator thch hp. N c th clm bng nam chm vnh cu hoc cc cun dy cm.

H thng kch t: l mt phn ca stator, to t thng stator.

Rotorl phn quay ca ng c. Tu theo cu trc, n c th l nam chm vnh cu hay li st t vi cc cun dy (phnng) cung cp t trng phn ng tng tc vi t trng stato to mmen.

Phn ngl cun dy roto mang in v cm ng t trng rotor. Khe h khng kh l khe h nh gia rotor v stator nihai t trng tng tc v sinh ra m men u ra.

Chi than l b phn cho dng in cung cp cho phn ng (rotor) ca ng c mt chiu i qua. cc ng c xoaychiu ng b, vic ny c thc hin bi cc vnh trt.

Vnh i chiu l mt phn ca rotor ng c mt chiu c ni vi chi than dng iu khin chiu dng in phnng. Vnh i chiu dng iu khin chiu dng in trong stato v/hoc cun cm phn ng duy tr chiu t thngstator v rotor. Vi cc ng c xoay chiu, vic chuyn mch c thc hin bi cc dng in xoay chiu cung cp v s u ni cc cun dy. Vi cc ng c bc v ng c mt chiu khng chi than (BLDC), s chuyn mch c thchin bi cc mch in t v/hoc cc lnh ti ng c.

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C cu chp hnh

HNH 20.15. ng c mt chiu nam chm vnh cu (T. Keujo and S. Nagamori, ng c mt chiu nam chm vnh cukhng chi than, 1985, Nh xut bn i hc Oxford)

M men sinh ra trong ng c in c th do tng tc gia dng in phn ng vi t trng stator (nh lut Lorentz)hoc tng tc gia t trng stator v t trng phn ng. Bng 20.2 tng kt cch phn loi chung ca ng c in. Phnsau s nu chi tit hn v hot ng ca cc loi ng c in v nhng c im cn cn nhc khi thit k.

BNG 20.2 Phn loi ng c in

Phn loiM t

Loi ng c T trng

ng c mtchiu

Nam chm vnh cuNam chm vnh cu sinh t trng stator, Dng in cp trc tip ti cun dyphn ng ca rotor qua cc chi than v cc chuyn mch

Nam

chmin

Kch t songsong

Cun dy stator (kch t) chnh l nam chm in. Cun dy kch t c nisong song vi cun dy phn ng

Kch t nitip

Cun dy stator (kch t) chnh l nam chm in. Cun dy kch t c ni nitip vi cun dy phn ng

Kch t hnhp

2 cun dy stator (kch t) chnh l nam chm in. Mt cun dy kch t cni ni tip, mt ni song song vi cun dy phn ng

Kch t clp

Cun dy stator (kch t) chnh l nam chm in. T trng stator v t trngphn ng c cp in c lp

ng c xoay chiu

Mtpha

Cm ng(khng ngb)

Gm mt cun dy stator v rotor lng sc. Khng c s kt ni bn ngoi virotor. M men sinh ra do s cm ng in t gia stator v rotor. Dng in xoaychiu quy nh s i chiu ca cc t trng. Tc rotor chm hn so vi tc t trng quay stator ( trt)

ng bRotor nam chm vnh cu hoc rotor dy qun cng cc vnh i chiu. Tc quay ng b vi tn s ca ngun in xoay chiu

Nhiupha

Cm ng(khng ng b)

Tng t nh ng c cm ng mt pha nhng c nhiu cun dy stator. T khing

ng bTng t ng c ng b mt pha nhng c nhiu cun dy hn, hot ng mhn

Vnnng

V bn cht ging ng c xoay chiu cm ng 1 pha, vi s ni nh ng cmt chiu kch t ni tip. C th c iu khin bi ngun xoay chiu hoc mtchiu

ng c bc Nam chm vnh cu

Rotor nam chm vnh cu vi dy qun stator sinh ra mt t trng tng ng.Khi cung cp trnh t (cc tnh) dng in cun cm khc nhau, t trng namchm vnh cu rotor s ng b vi t trng cm ng stator.

T tr bin thin Rotor bng st t dng rng ca v cc cun dy stator. Chuyn ng ca rotor lkt qu ti thiu t tr gia cc cc rotor v stator

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S tay C in t

LaiRotor rng ca vi dy qun stator. Rotor bao gm hai rng st t phn ng kthp vi mt nam chm vnh cu

ng c mtchiu khngchi than

Nhiupha

ng bV c bn ging ng c xoay chiu nhiu pha nhng dng chuyn mch in t,t trng rotor v stator ng b. Chuyn mch in t c th dng ngun mtchiu iu khin ng c ng b

HNH 20.16 C cu truyn ng rng lc MEMS s dng kch ng tnh in. (Courtesy of Sandia National Laboratories,MEMS and Novel Si Science and Technology Department, SUMMIT Technologies, www.mems.sandia.com.)

Tnh in hc - in trng

Do in trng c mt nng lng thp hn t trng, cc ng dng in hnh ca lc in trng gii hn trong ccthit b o v gia tc cc phn t tch in, trong mt nng lng yu cu nh. Gn y, vi s pht trin nhanh cacng ngh ch to siu nh (microfabrication), c th cung cp lc tnh in nh cho cc c cu chp hnh vi c in nh ccu chp hnh kiu rng lc (hnh 20.16). u im ca cc b pht ng da trn tnh in hc l c tc chuyn mchcao hn v tiu hao nng lng t hn khi so snh vi s pht ng in t. Tuy nhin, cn tnh n gii hn lc, di chuyn,v in p lm vic cao. B pht ng tnh in l b khi ng chnh cho vic di chuyn cc phn t tch in trong qu

trnh sao chp kh tnh in, v d cc my in laser.p in

p in l thuc tnh ca tinh th m c th sinh ra mt in p khi chu mt bin dng c hc hoc chu s b bin dngc hc khi c mt in p. Khi mt vt liu p in chu mt tc ng c hc, n c s dch chuyn khng i xng trongcu trc tinh th v trong in tch trung tm ca cc tinh th ion b tc ng. Kt qu l c s phn in tch sinh ra in pc th o c theo t l vi bin dng c hc. l hiu ng p in thun. Ngc li, vt liu s bin dng vi th tchkhng i khi cung cp mt in p. l hiu ng p in ngc v dng sinh ra tc ng c hc. C 2 loi vt liu pin: gm nung nh l lead-zirconate-titinate (PZT), v nha (polymers) nh l polyvinylidence fluoride (PVDF). S p inc lc u ra ln hn v c s dng nhiu nh cc c cu chp hnh. PVDF c xu hng to bin dng ln hn v dngnhiu trong cc ng dng cm bin.

S lin h gia c tnh in v c ca vt liu c th c m hnh bi cc cng thc tuyn tnh c bn sau:8

HNH 20.17 Cc dng c cu p inph bin (Courtesy of Piezo Systems,

Inc.)


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C cu chp hnh

1( )TE

T D

E g T DS s T d E

D d T E S s T g D

e

e

- = - + = + = + = + (20.11)

Trong :

E = ln in trng [V/m]

D = mt in tch (dielectric) trn mt n v din tch [C/m2]

T = ng sut [N/m2]S = sc cng

s = mm

= hng s in mi [F/m]

d, g= h s lin h p in

Thit k/la chn

Hnh 20.17 m t nhng c cu p in ph bin. Thng h s gii hn ca cc c cu p in nh hn 0.3% tng cong hoc bin dng. Cu trc ph bin nht l dng ngn xp v dng un. Cc c cu chp hnh p in thch hp vi ccng dng yu cu di thng cao, lc ln, ctc ng v bin dng nh. Chng c s dng rng ri trong lnh vc mthanh, cng nh cc ng dng quang hc, trong chuyn ng chnh xc l quan trng.

Cc c cu p in thng nh r bin dng t do v lc ngng ca chng. Bin dng t do (X f) tng ng vi dch chuyn t c mc in p ti a yu cu khi c cu hon ton t do chuyn ng m khng cn bt k lc no khc.Lc ngng (Fb) tng ng vi lc mc in p ti a khi c cu khng chuyn ng. Hnh 20.18 ch ra cc ng congc tnh tnh ca mt c cu chp hnh p in ph bin. (lc i vi bin dng).

Thng thng, c cu p in c mt bin dng tng ng mt lc xc nh, quyt nh bi im hot ng trnng c tnh lc-bin dng. Mt c cu c coi l ti u vi tng ng dng ring nu n a ra lc yu cu bng mt na bin dng t do ca n. Khi thit k cn cn nhc cc yu t quan trng l in p lm vic cao, hin tng tr, trt,kh nng chu hao mn.

HNH 20.18 ng cong c tnh tnh ca mt c cu chp hnh p in ph bin. (Courtesy of Piezo Systems, Inc.)

Hiu sut

Hiu sut l mt trong nhng thng s chnh cn cn nhc la chn ca cc qu trnh chuyn i nng lng. Trong huht cc trng hp, nng lng tiu hao u chuyn thnh nhit v lm tng nhit ca thit b. Vi cc c cu chp hnhc in, nhit (nhit ) l mt trong cc h s gii hn ni bt nht tng ng vi ch hng hc. Khi nhit thit btng, hiu sut chuyn i nng lng gim dn n tng lng nng lng chuyn thnh nhit, v li lm tng nhit thitb hn na. y l hin tng qu nhit. Do , vn quan trng khi thit k cc c cu chp hnh c in l ngn nga squ nhit (tht thot nhit) v bo m di iu kin hot ng bnh thng h thng c cu chp hnh cn bng nhit. Cnbng nhit nn c gi di di nhit thp nht ca cc thnh phn, v d nh cch in cho cc cun dy. Di nhit cho phn cch in c lit k trong bng 20.1.

Khuch i cng sut v iu bin - Chuyn mch in t cng sut

Nh trnh by trong phn trc v m t trong hnh 20.2, c 2 phn chnh trong nh ngha m rng ca mt c cuchp hnh cho cc h thng C in t. Chng ti gii thiu mt s c cu chuyn i nng lng v cc c cu chphnh. Trong phn 2 ca chng ny, chng ti s tp trung vo phn khuch i cng sut v iu bin ca c cu chp hnh.Tn gi truyn thng ca b phn ny l khuch i cng suthay iu khin cng sut ca c cu chp hnh tng ng. Tuynhin khi s thu nh v tch hp h thng tr nn ph bin hn, phn cng sut in hoc c nhng trong b iu khin(n v x l thng tin) hoc c cu chp hnh. Phn chc nng/c tnh thng minh v b sung c th kt hp vi nhau. Vicc c cu chp hnh c in, in l ngun nng lng khng iu chnh. B khuch i cng sut hot ng nh mt b

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S tay C in tm gia phn nng lng thp ca h thng, trong cc lnh c a ra mc tn hiu in nng lng thp, v cnc chuyn i thnh tn hiu in nng lng cao.

Khuch i cng sut nhn chung c th chia theo 2 phng php: tuyn tnh v chuyn mch. u im chnh ca khuchi cng sut tuyn tnh l "s sch" ca tn hiu cleanness so vi khuch i chuyn mch. im hn ch chnh l hiusut, khuch i tuyn tnh c xu hng b nng hn khuch i chuyn mch cng kch thc. Tuy nhin bt k mt k sthit k no u phi nm chc quy tc l cn phn tch ng dng v la chn hoc thit k phn iu khin cng sut thchhp.

Khuch i chuyn mch c lm bng cc thnh phn bn dn nh cc it v transitor. Cc thit b bn dn ny c

chc nng nh l cc phn t chuyn mch, iu khin dng in ti cc phn t chuyn i nng lng nh cun cm hocnh cc phn t khuch i iu bin ln dng in chy trong cun cm. Mt u im khc ca khuch i cng sutdng chuyn mch l vi cc chuyn mch, tng khuch i c th iu khin trc tip bi mt tn hiu s t mt thit b xl thng tin (Hnh 20.1) nh mt b vi iu khin hoc mt b vi x l.

HNH 20.19 ng c 1 chiu vi cng tc iu khin DC HNH 20.20 it

Hn ch s dng ADC, tr nhng trng hp cn thit nhm gim chi ph v kch thc yu cu ca mch in t. iubin rng xung (PWM) l mt v d in hnh dng tn hiu nh phn iu khin cc c cu chp hnh c in. Hnh20.19 ch ra mt v d n gin dng mt cng tc iu khin ni vi mt ng c mt chiu nam chm vnh cu PMDC.Nh nu trong cc phn trc, mmen c sinh ra khi dng in chy trong cun cm phn ng ca ng c mt chiunam chm vnh cu. bt hoc tt mt ng c, chng ta c th ni ng c vi ngun mt chiu ni tip vi mt khochuyn mch. Khi kho chuyn mch c ng li, dng in chy qua ng c v ng c quay. Nu kho m, dng inngt, ng c s dng li. Vi nhng mch phc tp hn, cn phi c thit k chuyn mch. Tuy nhin, v d ny minh honguyn l c bn ca chuyn mch khuch i cng sut. Phn di y a ra cc nguyn tc c bn xy dng cc khi cakhuch i chuyn mch.

Cc cht bn dn

Cc cht bn dn l cc vt liu cu thnh t cc nguyn t thuc nhm IV trong bng tun hon ho hc v d: silicon

(Si), germanium (Ge), v cadmium sulfide. Khc vi cht dn in v cch in, kh nng mang in ca cc cht bn dnchu tc ng ng k bi nhit v khi lng ca cc photon ti, dng v khi lng cc tp cht trong vt liu. Khi acc nguyn t nhm V hoc nhm III (dopants) vo trong cc cht bn dn, s dn ti tng hoc gim s in t ho tr trongcc cht bn dn. Tu theo dng nguyn t thm vo, cht bn dn c th chia thnh cc nhm:

Bn dn dng n: Thm cc nguyn t tha in t (nguyn t cho) vo cht bn dn (v d arsenic hay phosphor cc

nguyn t nhm V), li tinh th c thm mt in t (in t t do), tr thnh cht dn in.

Bn dn dng p: Thm cc nguyn t thiu in t (nguyn t nhn) vo cht bn dn (v d boron hoc gallium cc

nguyn t nhm III), dn n thiu mt in t trong cu trc tinh th (l trng). Cc l trng c th c xem nh l

cc ht mang in dng hay ch nhn cc in t t do.

Nh ni trn, c s cho tt c cc thit b in t bn dn l s kt hp di cc dng khc nhau cc cht bn dn

dng n v dng p. im mnh ca in t hin i l cc tnh nng a dng c gi trong mt thit b chuyn mch n ginc th ng hoc m cc mch iu khin. Phn di y s nu mt s phn t in t c s dng rng ri, ch yu l ccphn t chuyn mch cho vic thit k cc b khuych i cng sut/truyn ng ca cc c cu chp hnh c in.

it

it l thit b in t hai cc c thit k bng cch ghp mt bn dn dng p v mt bn dn dng n to thnh mt lptip gip pn. Hnh 20.20 l s biu din mt it thng thng. Cc vi vt liu dng p gi l ant v vi dng n l catt.Nu ant c mc in th ln hn (> 0.7 V) so vi catt, it c gi l it thun, VD>0.7V. Ngc li, nu VD


11/47

C cu chp hnh

HNH 20.21 Cc c tnh it

HNH 20.22 Mch tng ng ca mt it

Nh ch ra trong hnh 20.21, tu thuc vo in p cung cp, mt it c th lm vic c 3 vng khc nhau:

Vng th hiu thun: VD>V , trong V c gi l in p th hiu thun v thng ln cn mc 0.7V vi

silicon v 0.3 V vi germanium. it hot ng nh mt kho ng mch, ngn mch ant v catt vi mt in th

ngc nh bng V (in p thun ri trn it), hnh 20.22.

Vng th hiu ngc: VZ


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S tay C in t

HNH 20.23 S tng ng gia it v van kim sot

HNH 20.24 Cc ng dng ph bin ca it

Vi cc ng dng chuyn mch, thi gian phc hi (reverse-recovery time) cng l mt thng s thit k quan trng khc.Thi gian phc hi quy nh gii hn trn cho tn s chuyn mch m it c th ng hoc m. Nu it lm vic qu tn sny s lm gim hiu sut chuyn mch v c th l nguyn nhn gy qu nhit. it c s dng rng ri trong cc mchin t cng sut. Chng c dng nhiu nht cho vic chnh lu v tch sng nh. Hnh 20.24 minh ho mt s cc ngdng ph bin ca it. Thng thng thut ng mng it bao gm 4 it hoc nhiu it trong mt v n. Thng thngc 8 it tr ln c ng gi trong mt v dng DIP (dual inline package). Cc gi kiu khc l dng SIP (single inlinepackage), mch thng v thm ch l mt mng it. D c th c nhiu dng mng it kt hp cc loi it khc nhau, dngmng kh ph bin l s dng it tn hiu nh v nhanh nh l 1N4148 v cc mng it truyn ng vi nhim vchuyn mch nhanh, dng cao, 100 mA.

it Zener

Tr li ng cong c tnh in p-dng in ca mt it trong hnh 20.21. Nu t mt th hiu in p ngc nmtrong vng nh thng, it s phi chu mt in p ngc ln. Vi hu ht cc it, in p ny thng ln hn 50V v cth ti kilovolt. it Zener (Thc) l loi it c ng cong nh thng dc ng vi mt in p ngc, nh thng honton xc nh VZ

HNH 20.25 it Zener

c tnh nh thng c bit ny khin it Zener l s la chn tt cho vic xy dng cc b iu chnh in p, do chng c th gi mt ngun in p n nh d ngun cung cp thay i cng nh s thay i ca ti v tr khng. Hnh20.25 l k hiu ring biu din mt it Zener.

dng it Zener nh b iu chnh in p, n nn c th hiu in p ngc vi mt ngun in p cung cp ln hndi in p ngc nh thng VZ, hnh 20.26. Vi mt it Zener l tng, trong hnh 20.26, V S >VZ, in p hai u ti sbng VZ; Do dng in qua ti i ti v dng in qua it Zener c th tnh nh sau:

Ztai

tai

ViR

= vS Z

Z

S

V ViR-=

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C cu chp hnh

Cc it thng tiu hao cng sut, vi cng thc

max max. Z Z Z P i V=

Do khi la chn it Zener cc ng dng iu chnh in p, cn chc chn rng i zmax khng vt qu gii hn chophp. Di in p nh thng ca cc it Zener l t 3.3 V ti 75 V. Tuy nhin u ra cc in p ca di ny u sn sng dng c. Mt s di cng sut thng thng ca cc it Zener l , , 1, 5, 10, v 50 W.

HNH 20.26 Dng it zener nh b iu chnh in p n gin

Thyristor

Mt thyristor, hoc mt chnh lu bn dn c iu khin (SCR), l mt kho bn dn 4 lp, tng t nh mt it, nhng

thm mt cc iu khin vic dn in. Mt thyristor c 3 cc: Mt ant, mt catt, v mt cng, hnh 20.27. C th coimt thyristor nh mt it iu khin c trong cc cng nh mt b phn iu khin chnh xc tc thi khi thyristorm, ni cch khc l mt kho iu khin c.

HNH 20.27 Thysistor v k hiu ca n

HNH 20.28 Cc c tnh thysistor (SCR)

Hnh 20.28 biu din c tnh in p-dng in ca mt thyristor. Thyristor m cho dng in i qua (ngn mch haydn in) khi hai iu kin sau tho mn:

1. Cc ant (A) v catt (K) phi c th hiu p thun, in p ant cn cao hn in p catt.

2. Dng in cc cng IGphi mt khong thi gian thng thng l mt vi giy. Dng in cc cng c th tora bi mt xung in p dng cp cho cc cng (G) v cc catt (K). Dng in cc cng ti thiu yu cu mmt thyristor gi l dng in cht.

Khi thyristor dn, gi tr dng in qua chng ISCR b gii hn bi phn cn li ca tr khng mch in. Khi m thyristorm cc cng mt quyn iu khin, ngha l khng th s dng cng dng hot ng ca thit b. Thyristor s ch ng

nu dng in ant ISCR tin ti khng, sau cc cng mi c th xc lp li quyn iu khin. R rng, thyristor cng cth dn khi in p vt qua in p nh thng V FB. Tuy nhin, thng s ny thng l ch s gii hn cn tnh ton n khithit k, cn thng thng vic chuyn mch thng c iu khin bi in p cc cng. Nu cc cng (G) ngn mch vi

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S tay C in tcatt (K), thyristor khng th m c, thm ch c khi VAK l th hiu in p thun. C th coi thyristor nh mt khothng m c hm. Khi kho ng khng cn iu khin thm. Hnh 20.29 m t cc hot ng ca mt thyristor trong mtmch ti thun tr n gin vi mt ngun in p sin V S. Hnh 20.31, in p cc cng VG l u vo iu khin.

Khi thyristor c th hiu in p ngc (ang kho), khng nn t th hiu thun ln cc cng (G) v catt (K) ngns nh thng ca lp tip gip pn th nht ca thyristor, Hnh 20.27. in p nh thng VRB, dng in cht, dng in vcng sut nh mc, v t l tng in p l cc thng s quan trng khi thit k la chn mt thysistor. Khi t ngt cung cphoc tng nhanh in p hai u thyristor, thyristor c th m ngay c khi dng in (in p) cc cng bng khng.

HNH 20.29 Thyristor vi mch cha ti thun tr

HNH 20.30 Mch bo v (Snubber circuit)

HNH 20.31 Chnh lu iu khin (thyristor) v chnh lu khng iu khin (it)

Mc thay i in p thng thng s kch m thyristor l khong 50 V/ s. trnh s dn in khng mong mun dotn s thay i in p ln, thng dng mt mch bo v ni song song vi thysistor (snubber circuit), hnh 20.30, lc sbin thin in p tn s cao. Mch ny v bn cht c bn l mt b lc thng thp RC. Vic la chn in tr RS v dung

khng CS c th dng cng thc sau:2

max

2max

2( / )

A Ls s L

L s

V LC R R

L dV dt C= = - (20.12)trong RL v LL l phn ti cm v ti tr

tng ng. VAmax l in p ant ti a v (dV/dt)max l t l in p ant - catt tng ti a mong mun.

Khng ging cc it dng trong mch chnh lu ch c th chnh lu in p xoay chiu u vo thnh in p mt chiutrung bnh, cc thyristor c th dng xy dng cc mch chnh lu c iu khin c th chnh lu ngun xoay chiu AC viu bin in p u ra mt chiu trung bnh bng cch iu chnh thi gian ca in p/dng in cc cng, Hnh 20.31.

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C cu chp hnh

HNH 20.32 c tnh Triac

Triac

Thyristor ch c th m theo chiu in p thun. Triac l mt loi kho iu khin c tng ng mt cp thysistorni song song v ngc nhau Hnh 20.32. Nh m t trong hnh 20.32, mt triac c th m theo c hai chiu thun v ngc.

Transistors

Transitor l mt thit b bn dn c 3 cc hoc nhiu hn v c th ng dng trong khuch i cng sut v chuyn mch.Nh nu trong phn trc, chuyn mch in t c th dng it hoc thysistor. Chuyn mch it khng iu khinc, thyristor l thit b c 3 cc v cc th 2 (cc cng) c th dng iu khin v chuyn mch tc thi. Tuy nhin,mt hn ch ca chuyn mch thysistor l ch iu khin c theo mt chiu. Tc lcc cng ch c th dng mthysistor. Ch c th kho thyristor bi cch h dng in ant ti khng.

Transistor l mt thit b bn dn c bit dng cho khuch i cng sut, c th iu chnh dng in hoc in p khln gia hai cc bng mt dng in hay in p iu khin nh, vic chuyn mch c thc hin bi vic m hoc nghai cc transistor dng mt tn hiu iu khin cc th 3.

Cc transistor l cc phn t c bn ca thit b in t hin i v l cc khi ch yu trong in t s, ton t khuchi v in t cng sut. C 3 dng transistor ph bin l transitor lng cc tip gip (bipolar junction transistors - BJTs),transistor hiu ng trng metal-oxide (metal-oxide field effect transistors - MOSFETs), v transistor lng cc cch ly(insulated gate bipolar transistors -IGBTs).

HNH 20.33 Transistor lng cc tip gip (BJTs)

Cc transistor lng cc tip gip (BJTs)

Mt transistor lng cc tip gip l mt thit b vi 3 lp kt hp 2 dng bn dn p-n-p v n-p-n, hnh 20.33. Cc BJT c3 cc tng ng vi tng lp gi l colect (collector - C), emitt (emitter - E), baz (base - B). Hnh 20.34 m t hot ngca mt BJT dng n-p-n vi dng cc emitt chung. Cc BJTs c th hot ng 3 ch :

HNH 20.34 c tnh ca mt transitor n-p-n BJT c emit chung

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S tay C in tNgng: Khi in p BE (base-emitter) nh hn in p m V , dng in baz iB nh khng ng k. Transistor

hot ng vng ngng, khng c dng qua cc colect v emitt (C v E). Thng thng, V = 0.6 - 0.7V.

ch ny, transitor tng t mt van ng, C v E coi nh h mch.

Tuyn tnh tch cc: Khi VBE =V , transistor hot ng ch tuyn tnh tch cc, ch ny, transistor c

xem nh b khuch i dng in iu khin trong dng in colectCi t l vi dng in baz iB. Hng s t l

(h s khuch i dng in) = 20 ~ 200, thng c gi l h, hf, hay h FE trong bng d liu thng tin ca chng.

ch ny, transistor c xem nh van m mt phn, trong dng in t l vi m ca van ( ln dng

in baz). Cng sut tiu hao trn transistor

BJ T C CEP i V=

Trng thi bo ho: Khi dng in baz iB ln hn dng in ti a c th iC, transistor ri vo vng bo ho, trong

/0.2

B C

CE SAT

BE

i iV V V

V Vg

b > = =(20.13)

ch ny, transistor m thng t C n E. Dng in colectCi c xc nh bi mch colect. Transistor tng t

mt van m hon ton, dng in tu thuc ngun v ti. Lu rng, khi transistor bo ho, in p CE (collector-emitter)gi gi tr rt nh gi l in p bo ho VSAT.

HNH 20.35 Mt s v d dng BJT

HNH 20.36 BJT vi vai tr mt kho iu khin dng

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C cu chp hnh

HNH 20.37 Cc c tnh chuyn mch ca BJT

Tm li, khi bo ho, transistor thng mch (ng cng tc). Khi ch ngng, n khng cho dng qua, transitor lmmch h (m cng tc). Khi vng tch cc, n l b khuch i i C nh dng in iu khin iB . Mc d phn ny ch m tmt cch tng i n gin nhng n gip ta c nhng hiu bit c bn v in t cng sut v rt c ch cho vic thit kv tip cn vi h c in. Hnh 20.35 minh ho mt s v d v cc ng dng ca BJT .

Khi iu khin in p BE (base-emitter) VBE v dng in baz iB, transistor c th hot ng gia 2 vng ngng vbo ho, nh mt chuyn mch, hnh20.38. Thc t, chuyn mch transistor khng tc thi (hnh 20.37). Thi gian m t ON

ca transistor bng tng ca thi gian tr tD v thi gian qu (khong sn ln pha trc) tR (rise time). Tng t, thigian ng tOFFbng tng thi gian lu tS (storage time) v thi gian gim tF (fall time - sn dc sau). Thi gian ng v mca mt transistor gii hn tn s chuyn mch ti a. Tn s chuyn mch thng thng cho mt BJT cng sut l khonggia 2 v 20 kHz. Ta thng ni, cc BJT c th chuyn mch tn s cao hn cc thysistor, s dng cng sut nh hn. CcBJT cng sut c th iu khin dng in ti hng trm ampe v in p VCE ti khong 1 kV.

HNH 20.38 Hai dng ca cc cp transistor Darlington

Cng sut tiu hao l mt hn ch khi thit k la chn BJT. Khi BJT lm vic vng tuyn tnh tch cc (khuych ituyn tnh), cng sut tiu hao l PBJT = iC . VCE viVCE > V . Vi dng in colect ln trn n v th tch v nhit khi nhca thit b, transistor hot ng khng hiu qu ch tuyn tnh tch cc. Ni cch khc, khi BJT chuyn gia bo ho vngng, dng in colect s nh (trong ch ngng) v VCE s nh (trong ch bo ho). Tn hao cng sut chuynmch nh hn nhiu so vi hot ng ch tuyn tnh tch cc. Do vy lm tng kh nng chuyn mch.

Khi BJT lm vic, cn cung cp dng baz tng xng, c bit l khi transistor lm vic vng bo ho, cng thc(20.13). iu ny yu cu mt nng lng u vo ln v c th qu ti tng u vo. Nh s tho lun sau, y l nguynnhn chnh khin cc BJT t s dng hn trong chuyn mch in t cng sut v thng c thay th bi cc thit b nhMOSFET v IGBT, yu cu dng in iu khin nh hn nhiu. Mt gii php cho hn ch ny l tng h s khuch idng in . Mt cch thc hin n gin v hiu qu tng h s khuch i dng in hiu qu ca cc BJT l dng cp

transistor Darlington.Cp transistor Darlington

Mt cp transistor Darlington ni 2 transistor BJT thnh mt dng phn t 3 cc, lm tng h s khuch i dng inmt cch hiu qu, hnh 20.38. Trong hnh 20.38, 1 v 2 l h s khuch i dng in ca 2 transistor, quan h giadng in baz ca transistor Q1 v dng in colect ca transistor Q2 c m t bi:

2 2 2 2 1 1 2 1 1 1( ) ( )C B B B D Bi i i i ib b b b b b= = = =

Do , h s khuch i dng in cho cp transistor bng tch ca 2 h s khuch i dng in ring l tc l, D = 1. 2. vi mt cp Darlington in hnh, h s ny c th nm trong di 50010,000. Cn c s phi hp tt v cp transistorDarlington s dng 2 transistor thay cho mt.

Transistor cng sut hiu ng trng (MOSFET)

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S tay C in tMOSFET l mt dng transistor hiu ng trng (FET). Cc FET l cc phn t 3 cc iu khin in p, cc cc tng

ng l cc mng (drain (D)), ngun (source (S)) v cc cng gate (G). Cc thut ng bt ngun t s tng t gia hotng ca transistor v h thng thng t pha trn cao dng 1 van cng iu khin dng nc t ngun ti mng.MOSFET dng mt ming kim loi l cc cng v n c cch in vi cht nn silicon dng n hoc p bi mt lp oxitmng (Hnh. 20.39).Khi cung cp mt in p cng VG, s cm ng mt in tch m so vi in tch ca cc cng v chtnn. in tch ca cht nn to nn cc dng c tnh transistor bi s nh hnh ca hoc knh dng n hoc knh dng p. Do, phn thnh 2 dng MOSFET n hoc p (Hnh. 20.39).

HNH 20.39 Transistor cng sut (MOS) hiu ng trng (FET)

HNH 20.40 Cc c tnh ca MOSFET

Vi phn ln l ng dng khuch i cng sut v iu bin, cc MOSFET c thit k hot ng ch tngcng (enhancement). Hnh 20.42 minh ho cc c tnh ca ch tng cng (enhancement) ca mt MOSFET knh n:

Ngng - Cutoff : Khi in th qua cc cng v cht nn (cc ngun) V GS nh hn in p m (ngng - threshold) V T,MOSFET s vng ngng c dng din khng ng k chy qua cc mng (D), tc l:

D

0

0

DGS T

G DS D

iV V

i V V

VT, MOSFET trong vng tch cc, trong :

VGS>VT v( )

2

D GS T

DS GS T

i V V

V V V

- > -

ch ny, transistor c th c xem nh mt khuch i dng in in p iu khin c, trong dng in cc

mngCi t l thun vi bnh phng chnh gia in p cng - ngun v in p ngng. Dng in mng c iu

khin bi in p cng-ngun VGS. Cng sut tiu tn qua transistor PFET l:

PFET = iD . VDS

Trng thi mc (Ohmic): Khi VGS ln, dng in mng c xc nh bi mch mng-ngun, MOSFET t bo hov

/

( )

D DD D

GS T

DS D ON DS GS T

i V RV V

V i R V V V

= < -

? (20.14)

ch ny, transistor c th c xem nh mt kho ng gia cc cc D v S vi mt in tr iu khin c inp RON. Dng in mng iD c xc nh bi mch mng. Vi dng in nh mc, VDS gim xung trong di bo ho t 2

ti 5 V.

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C cu chp hnh

HNH 20.41 MOSFET nh mt kho iu khin in p

Khi hot ng ch tng cng (enhancement), mt MOSFET hot ng tng t vi mt BJT. Nhng thay v dngin baz, hot ng ca MOSFET c quyt nh bi in p cng. Khi iu khin in p cng ca 1 MOSFET,transistor c th hot ng nh 1 kho in p iu khin c (Hnh. 20.41) hot ng gia 2 ch ngng (im A) vbo ho mc (im B).

Mt u im ca MOSFET l c tr khng u vo ln ng k so vi BJT. Vic n gin ho mch in iu khinMOSFET l iu cn thit do ln ca dng in cng khng phi l mt h s. Vic ny cng gip MOSFET c hiu sutcao hn cc BJT do n c th chuyn mch mt tn s cao hn nhiu. Thng thng tn s chuyn mch ca MOSFET gia 20 v 200 kHz, cao hn cc BJT. Cc MOSFET cng sut c th mang dng in mng ti vi trm ampe v V DS ti500 V. Hiu ng trng l mt trong nhng nguyn nhn chnh ti sao MOSFET c chuyn mch tt hn BJT. Tuy nhin,in trng tnh cng l mt trong nhng nguyn nhn chnh gy hng.Cc MOSFET rt nhy cm vi in p tnh. Do lp

oxit cch in cng v cht nn ch l mt lp film mng (khong chng mt ti vi micro mt), in p tnh cao c th ddng nh thng lp oxit cch in. in p nh thng ca mt cng thng thng l khong 50 V. Do iu khin intnh hoc cch in th rt quan trng khi iu khin cc MOSFET.

So snh BJT v MOSFET:

C hai c th dng nh cc khuch i dng in.

BJT l mt khuch i iu khin dng in trong dng in colect iC t l vi dng in baz iB.

MOSFET l khuch i iu khin in p trong dng in cc mng iD t l vi bnh phng in p cng VG.

C 2 c th dng lm kho chuyn mch 3 cc hoc nghch lu in p

BJT: chuyn mch vi logic TTL. MOSFET: chuyn mch vi logic CMOS.

BJT thng c in dung ln hn MOSFET cng kch c.

MOSFET c tr khng vo cao hn nhiu so vi BJT v thng thng ng, cng sut hot ng thp hn.

Cc MOSFET d ch to hn trong cc mch tch hp.

MOSFET thng t xy ra hin tng qu nhit hn.

MOSFET d b nh hng in p tnh (in p vt qu in p nh thng 50 V).

BJT c thay th bi cc MOSFET cc ng dng in p thp (


20/47

S tay C in t

HNH 20.43 Hai b khuch i tuyn tnh c bn

Transistor lng cc cch in (IGBT)

IGBT l mt dng transistor iu khin in p cc cc tng t nh cc BJT. IGBT l thit b 4 lp c cu trc tng tMOSFET cng thm vi mt lp p.

Hnh 20.42 biu din k hiu v mch tng ng cho mt IGBT. IGBT c cc c tnh kt hp ca BJT v MOSFET.Tng t MOSFET, n c tr khng vo v tn s chuyn mch cao. N cng c cng sut iu khin nh BJT.

Cc b khuch i cng sut in hnh ca cc c cu chp hnh c in

Khuch i cng sut v iu bin cho cc c cu chp hnh c in c chia thnh 2 loi c bn, da trn cc phngphp in t cng sut tng ng. Cc b khuch i tuyn tnh iu khin BJT hot ng ch tch cc. Cc b khuchi chuyn mch iu khin cc transistor ch bt tt. Tu thuc vo i tng iu khin, tn hiu (Hnh. 20.2) tikhuch i c th l in p hoc dng in, dng iu chnh nng lng in phn ti cc thit b chuyn i nng lng.Hu ht cc c cu chp hnh c in l ti c tnh cm nh cun dy ca nam chm in hoc rto ca ng c mt chiu.Phn sau y s a ra v d vi ng c mt chiu DC l ti ca b khuch i cng sut.

Cc b khuch i tuyn tnh

Hnh 20.43 m t mch truyn ng c bn dng cho cc b b khuch i in p tuyn tnh v iu khin dng in. Chai s c cc im chung sau:

1. in p vo Vi(t) cung cp cho baz ca transistor.

2. Cng sut in cn thit iu khin ti cung cp bi in p mt chiu.

3. Transistors hot ng ch tuyn tnh tch cc.

B b khuch i iu khin in p

Trong hnh 20.43(a), ng c c iu khin l ti ca mch emit. Nu b qua in p baz-emit, in p qua ng cVM c iukhin trc tip bi in p vo V IN v dng in ngun cung cp. ln dng in, ni mt cch khc, phthuc vo in p cung cp, tc v thng s ng c.

HNH 20.45 B khuch i in p lng cc

20

HNH 20.44 B b khuch i inp c h s khuch i thay i


21/47

C cu chp hnh

HNH 20.46 B khuch i in p lng cc c h s khuch i thay i

Hnh 20.44 l s b khuch i in p c h s khuch i in p iu chnh c, trong h s khuch i in pbiu kin u vo VIN so vi in p cung cp cho ng c (cun cm) V M c th xp x bng (RA+RB)/RA, Nu yu cu mtdng in qua ng c ln, transistor Q2 c th thay th bi mt cp transistor Darlington. Cc b khuch i m t trong20.43 v 20.44 ch c th iu khin dng in qua ng c (ti) theo mt chiu. Do chng cng c gi l cc bkhuch i n cc. cung cp dng in i theo 2 chiu, 2 transistor c th ni vi ng c theo cu trc ko-y, nh mt trong hnh 20.45. Hai it trong mch c dng loi vng cht (dead-zone) to bi in p baz-emit hi cho cctransistor. Ch rng mt ngun in p lng cc th cn thit cho s ny. Hnh 20.46 m t mt ch in p lngcc vi bin h s khuch i (RA+RB)/RA. Tng t, nu cn dng in ng c ln 2 transistor Q3 v Q4 c th c thayth bi cc cp transistor Darlington.

B khuch i iu khin dng in

Nh nu phn trc, trong nhiu c cu chp hnh in t, lc v mmen u ra ca thit b c s tng quan lnvi dng in cun dy, v d vi 1 ng c mt chiu nam chm vnh cu v c cu chp hnh kiu cun cm (voice coil),m men v lc u ra t l vi dng in u vo. Do trong nhiu ng dng iu khin chuyn ng, rt cn c 1 chuyni in p - dng in (ch khuch i dng in) tng cng sut, trong in p u vo t l vi dng in chytrong/ngoi ng c (cun dy). Hnh 20.43(b) m t mt mch in c bn cho ch khuch i dng in. Quan h gia

dng in emit (ng c) iM v in p vo VIN l:

SRIN BE

M

V Vi

-=

HNH 20.47 B khuch i dng in lng cc c h s thay i

Nu in p baz-emit c b qua, in p dng in qua ng c i M t l vi in p vo VIN, tc l, iM (1/RS).VIN.

Hnh 20.47 m t mt b khuch i lng cc dng c bn. Mt b khuch i thut ton (Op-Amp) c dng iukhin dng in theo vng kn. in tr RS, thng c gi l in tr o, dng o dng in ng c phn hi ti bkhuch i thut ton. Tu thuc vo cng dng in, in tr Rs c cng sut tiu tn nhit ( 2 .M Si R ) tng ng gy rabi dng in qua in tr. Vi xp x bc khng, trng thi n nh , b khuch i thut ton s cn bng in th ccdng v cc m, tc l n s to ra:

21


22/47

S tay C in t

2

1

.S INR

V VR

= -

a n

2

1

..M INS

Ri V

R R

-

Mc d 1 b khuch i dng c xu hng c 1 quan h tuyn tnh gia u vo v dng in cun dy, nhng trn thct c gii hn do c ngun in p gii hn. Trong hnh 20.47, in p cung cp l V. Gi thit rng cun dy ng c cin tr RM, dng in ti a iMAX ngun c th cung cp c gii hn trn bi:

Max

M S

Vi

R R3W>3T

31

W

gV F= 31

T

d Ll VD = 3 W

T

TLC

e=

41


42/47

S tay C in t

Dch chuyn theo dy: D>5T 332

4

D

T gV F

p= 33

T d VD = 23

4T

TDC

pe=

Theo vng trn: D>5T Khng 31T

d DD VD =

2

3 04 TT DC K

pe=

Theo chiu dc: L>3D332

4

D

LV g F

p= 33

L d VD = 23 0

D4

TC KL

pe=

Trt theo chiu dy W>5T, L>5T 15W

g

V F=15x d V D =

1 0

W TLC KT e=

Ch thch: F l lc v 3Te l hng s in mi ca vt liu vi ng sut hng s theo phng 3, TiK l hng s in mi

tng i ( 0/T Ti iK e e= ), v 0e l hng s in mi trong chn khng.

Cu trc ny cho php dch chuyn nhng khong ln in p thp hn. Thng cc tm mng c dy 0.31 mm.Cc c cu dng ngn thng tng ng vi ch hot ng d 33. Tng dch chuyn c th ti 200m, v trong trng hpny l t l vi s cc tm, nu khng c ti ph c cung cp:

33l Vnd D = (20.37)

trong n l s phn t..Cu trc dng ngn thng sinh ra lc y mnh:

33

lAF

Ls Y

D= (20.38)

Trong L l di ngn, A l din tch cc phn t, s33, Y l b v moduleYoung, tng ng. Tham kho thm trongbng 20.7, c tnh ca mt s c cu chp hnh ngn (nhiu lp) trch theo catalog ca nh cung cp s p in [6].

BNG 20.7 c tnh ca cc c cu chp hnh ngn (nhiu lp)

STTchun

Vtliu

Hnhdng

Di x rng x dy (mm)hoc ng knh ngoi x

ng knh trong x dy(mm)

Vmm(V)

Hnhtrnh

( m)

Fmax(kN)

A01 Pz26 Ch nht 2.5 x 2.0 x 2.0 200 1.8 0.5

A06 Pz26 Vung 10 x 10 x 2.0 200 2.0 10

A16 Pz27 Vung 10 x 10 x 2.0 200 3.2 5.0

A21 Pz26 Trn 6.0 x 2.0 x 2.0 200 1.7 2.5

A27 Pz26 Trn 25 x15 x 2.0 200 2.2 31

A37 Pz27 Trn 25 x15 x 2.0 200 3.4 16

Nu yu cu bin dng di, phn t p in c th m rng bng cch ghp. Ghp l vic kt hp hai lp khc nhau

(Hnh. 20.82(b)). Mt lp l vt liu xy dng, mt lp l vt liu p in. Vt liu p in c th dng cho c hai lp. Trongtrng hp ny, lp u tin s gin, lp th hai co. Tuy nhin, dng ny c cng thp.

42


43/47

C cu chp hnh

ng dng

Do c tnh vn c ca vt liu p in, cc c cu chp hnh vi kh nhiu u im k thut c xy dng. V d nh l rn chc v nh, lc ln, di tn s hot ng rng, cng vng cao, chu c nn v c dch chuyn t l vi inp cung cp, hiu sut chuyn i nng lng 50%. Chng c dng trong cc c cu nh, cc h thng gim dao ng,van, laser v quang, ng c sng siu m, cm bin v tr, rle, my bm, trong cng nghip t ng ha, vin thng, mytnh,... Mt vi ng dng c k ra, hnh. 20.83.

a) Gim dao ng: Vt liu p in - cc phn gim chn c bn chuyn dao ng c sang nng lng in. Nng lngsinh ra sau c tiu hao di dng nhit, nng lng dao ng b kh. S nguyn l c a ra trong [2].

b) Vi rbt. Cc chn rbt l cc c cu p in. Bng vic cp in p ti cc in cc, cc chn p in (piezolegs)c di ra, ngn i, hoc cong theo mi hng ca qu trnh dch chuyn.

c) Bm siu nh. Mng ngn, mng chn c tc ng bi cc c cu chp hnh p in, cc van kim tra u vo vu ra ln lt m bm cht lng v kh. u im l chuyn mch nhanh v cng sut nn kh cao.

d) Bn kp siu nh. C cu chp hnh p in lm vic trn s co gin ca chuyn ng kp da trn c cu hp l. Bnkp thng c kch thc rt nh v c hu ht cc dng hnh hc yu cu.

e) Tay my siu nh: Do c phn gii khng hn ch, c cu chp hnh p in thng dng trong cc ng dngnhiu v tr.

f) Thit b vi lng. C cu chp hnh p in c chnh xc v lng cao vi nhiu cht lng trong di nan lt nhiu ng dng.

ng c p in (ng c siu m)

ng cVibromotors [4] c ng dng rng ri nh cc c cu chp hnh da trn vic chuyn i cc dao ng c tns cao (nhiu kHz) sang cc chuyn ng lin tc [7,8]. Cc phn t p in c th dng nh cc my to do ng v trongtrng hp vibromotors c gi l ng c p in [5,7,8]. u im ca ng c p in l mmen ln, phn giicao, d kim sot, hng s thi gian nh, n gin, hiu sut cao, khng gy n, khng cm ng in t.

Cc dng chnh ca ng c p in

Cc ng c p in khc vi cc phng php chuyn dao ng sang chuyn ng tuyn tnh. Cc dng c bn c ara trong bng 20.8.

Cc ng c p in sinh ra chuyn ng ellip trong vng tip xc gia cc u ni vo v ra c s dng chnh. Vimc ch ny, cc tc ng xin, cho c c nh vo cc u ra hoc cc sng dch chuyn. cc ng c p in, sdng cc tc ng xin, lc ma st truyn chuyn ng v nng lng gia ng ni u vo v ra. C th nhn ra bi 2 daong (thnh phn php tuyn v tip tuyn) uy and ux trong vng tip xc vi gc lch pha , c dng thay i chiuchuyn ng ca u ra. C 2 chuyn ng c th nhn ra bi mt hoc hai phn lin kt tch cc dao ng cng hng. Ccdao ng c th pht trin cc dng khc nhau: theo chiu dc, chiu ngang, chiu dch chuyn v xon. Cc ng c p intn dng cc tc ng cho chim mt di tn s rt rng. Gii hn thp hn ca n l tn s siu m thp (loi tr tc ngca m thanh), 1620 kHz, v gii hn trn ca n vi MHz. S truyn sng trong piezomotors da trn ma st qua li giachuyn ng ca sng trn cc vt n hi v lin kt u ra, tc l nguyn tc hot ng ca n tng t nh s truyn sngiu ha. Sng truyn dc b mt (sng Rayleigh) ca cc dng u vo c dng chuyn ng ellip trong vng tip xc. SngRayleigh l sng kt hp ca sng dc v sng di chuyn; do vy mi im b mt mi trng n hi di chuyn dc theoqu o ellip. Cc dng sng gp khc, xin, xon v dc c dng trong. Sng chy trong s p in c kch thch biin trng. Cc c tnh chuyn ng sng ca ng c p in (ABB Corporate Research ITCRC/AS) c nu ra trongbng 20.9. (a) (b) (c) (d) (e) (f)

43


44/47

S tay C in tHNH 20.83

BNG 20.8 Nguyn l hot ng ca ng c p in

Khi nim c bn S thc hin Ch

A. Chuyn ng Elip trongvng tip xc: 2 chuynng thnh phn c lch

pha

1. Mt khp tch cc 0

0

sin( )

sin

y y

x x

u u t

u u t

w j

w

= +

=

2. Hai khp tch cc 0

0

sin( )

siny y

x x

u u t

u u t

w j

w

= +

=

trong : uy0, ux0, v ln lt lbin , tn s gc v pha ca ccchuyn ng dao ng ca cc phnt p in.

B. Chuyn ng Elip trongvng tip xc: sng dchchuyn

*0 cos2 / ( )yu u u ct p l= -

trong : u0, v c ln lt l bin, di v vn tc ca sng tngng

C. Tnh khng ng hngca ma st ti vng tip xc

a)

Thng thng 0.05T

ct trong

ct , T ln lt l khong thi giantip xc v dao ng.

b)

c)

D. Cc chu k dao ngkhng i xng

a)

b)

BNG 20.9 c tnh ca mt s dng sng chy ca cc ng c p in

ng c n v USR60 USR45 USR30

Tn s lm vic kHz 40 43 42

in p lm vic Vrms 100 100 100

M men nh mc Nm 0.38 0.15 0.04

u ra nh mc W 4 2.3 1.0

Tc quay nh mc rpm 100 150 250

44


45/47

C cu chp hnh

Hng s thi gian ms 1 1 1

Khi lng G 175 69 33

quay khng u % 2 2 2

Tui th H 1000 1000 1000

Nhit lm vic, di 0C -10+50 -10+50 -10+50

Vic kch thch sng chy c thc hin ng thi bi cc dao ng kch thch lch pha cng tn s v ch . Vicny c thc hin bng cch chia cc in cc ca b chuyn i thnh n phn bng nhau v ni vi n pha ca my phtdao ng in, trong n3 lun phin 2 in cc lin k mt gc 2 /n, hoc bng cch dng cc chuyn i khng lintc.

Cc ng c p in vi ma st khng ng hng ca tip xc da trn c s s bin thin cc dao ng trong phn tipxc tip tuyn trong chu k dao ng. Vic ny c thc hin bi cc tc ng iu ha b tr chng cht trn vng tipxc. c tnh phn bit l thi gian c/T t l ca khong thi gian rt gn tn ti ca tip xc vi chu k dao ng trong ccthng s lin h. Tip xc khng ng hng c th thc hin theo 2 cch: (a) bng cch kha lin kt tch cc trong mton ring bit ca qu o (Bng 20.8, trng hp C, a), (b) bng cch thm dao ng tn s cao hn (Bng 20.8, Trnghp C, b), theo hng ca dao ng c s, hoc theo hng vung gc ca dao ng c s (Bng 20.8, Trng hp C, c) trnmt phng php tuyn hoc tip tuyn.

ng c p in vi dao ng khng i xng da trn s khng i xng ca cc lc qun tnh trong cc dao ngkhng iu ha tn s cao, cc dao ng a tn (Bng 20.8, trng hp D, a), hoc lc ca ma st tnh vi quan h phi tuyngia lc v vn tc (Bng 20.8, trng hp D, b). Chu k khng i xng ca cc dao ng c sinh ra bng iu ha tnga tn. Bin ca mi iu ha c chn bng cch thay i hnh dng in cc v din tch ca cc in cc ring bithoc bin thin bin ca in p cung cp. C khi l s thay i lun phin pha ca in p cung cp. Hiu sut ca ngc p in trong trng hp ny thp nhng cc thit k ca thit b c phn gii cao ti 0,002 m trong truyn ng tnhtin. Do , cho php ng c p in gii hn v kch thc theo c hai ta , vic ny quan trng trong mt s ng dng.Cc ng c p in c th d dng ti thiu kch thc, o cc vi ng c pht trin kh mnh. ng c quay [5] l mtv d in hnh ca dng ny. N c ng knh 2 mm, cao 0.3 mm, th tch 0.49 mm 3. ng c quay n nh mt vi vtr v mmen khi ng khong 3.2 Nm.

ng c p in nhiu bc t do

ng c p in nhiu bc t do l mt dng cu trc mi c th thay i cc thng s hoc cu trc ng hc ca chngkhi iu chnh. Nu mt hoc hai lin kt ca cp ng hc c lm t vt liu p in, n c th to ra dch chuyn tnhgia cc phn t ca n, gi tnh hoc dao ng cng hng, kt qu l sinh ra cc lc hoc momen ti vng din tch tipxc ca lin kt. Chuyn ng tng i ca mt lin kt vi nhng phn khc cng c m bo. Cc cp ng hc nhvy c th c xc nh l tch cc. Cc cp ng hc tch cc c c trng bi cc kh nng:

iu khin s bc t do. n gin nht l iu khin s va chm ca tng cp, c dng khi cc phn t ca cp

khp kn lc. y c h s va chm hay bin ca lc tc ng c th thay i. Vic ny c c khi kch

thch cc dao ng tip tuyn v php tuyn tn s cao trong vng tip xc ca cc cp.

Sinh lc hoc mmen trong vng tip xc gia cc lin kt. Phng ca cc lc sinh ra hoc mmen c iu

khin bi s thay i ca cc dao ng, v d, tc ng ring n cc in cc ca b chuyn i.

C cc c tnh ph: t chun on, a chc nng, t sa cha, t thch nghi.V d mt ca robot (Hnh. 20.84(a))trong c 1 CCD camera 1 c t trong cu th ng 2, lin kt vi vng p in 3. p sut hng trong vng

lin kt c xc nh bi nam chm vnh cu 4. H thng ny c 3 bc t do.

(a)

45


46/47

S tay C in t

(b)

HNH 20.84

(a)

(b)

HNH 20.85

in cc 5 trong vng p in c chia vng (trong trng hp ny c chia thnh 3 phn i xng); tch cc mtvi in cc trong s vi tn s cng hng AC s c kt qu l hnh cu s quay xung quanh trc ca n, v tr cachng c iu khin bng cch thay i tc ng cc in cc khc nhau. Cc dao ng sng dch chuyn trong vnh(bng cch cung cp in 3 pha xoay chiu ti c 3 in cc) s lm cu quay vng quanh trc ca vnh. Cc dng ng cny c phn gii xp x 2 gc giy theo mi phng, cao hn yu cu ca h thng th gic robot. Vi nhng phng phphin c, cc dng iu khin v cc loi dao ng cng hng, c th cho php thit k cc c cu my vi lin kt linh hotc s dng trong hai cp ng hc nhm lm tng d tha trong h thng. Mt robot p in loi ny c ch trong

hnh 20.84(b). N bao gm cc vt liu th ng (nh thp) - cu 1 v 3, vi chuyn i p in 2 gia chng. L xo lin htt c cc lin kt. Mt robot vi 2 cu c 6 bc t do. Cc cp ng hc di chuyn tu thuc phng php thit k ng cp in. Cc in cc trn cc khp tch cc c chia nh. Hnh 20.84(b) ch ra cc dng ca chng v s phn phi ca badao ng thnh phn trong vng lin kt. Cc dao ng nhiu thnh phn tn s cao sinh ra im lin kt (cc in cc nhtnh A ca lin kt 2 c tc ng) quay thanh ni 2 lin h vi thanh ni 1. A /3 thay i trong v tr ca cc dao ngmu (S thay i v tr ca cc nt dao ng trong cc im lin kt) s khin thanh ni 3 quay trong mi lin h vi thanhni 2. Dng hiu ng p in thun, c th thu c cc thng tin ph (vi in cc B) v lc v mmen, tc ng lnthanh 2 ln trng thi ca cc b mt tip xc. Cc thng tin ny c dng gim sai s v tr v hiu chnh qu ochuyn ng. Bng cch tng chnh xc v cng vng ca cc phn t h thng, sai s tnh v ng trong hp s, ctchng, thanh dn gim hoc loi b hon ton. Kt hp cc c tnh ca chuyn i p in v cc c cu chp hnh trong hthng iu khin c th gim nh nhn thm ch loi b hon ton hu ht cc sai s trong hp s, ct chng v thanh dndng trong cc thit b o c chnh xc cao. Nguyn nhn l do cc hp s, ct chng nhiu bc t do vi mt hai phn tc lm t vt liu p in tch cc vi cc vng kch thch xc nh. lch tm hoc trc, khe h v vng cht, cc sai

s thng thng c ti thiu ho trong cc thit b . S ca trc tch cc c ch ra trong hnh 20.85(a) trong strc n v bn knh m vng in cc l n = m = 3. Cc trc tch cc dng trong cc h thng o chnh xc b mt thnh phnv nghing qut b mt. V d c lng sai s vng ngoi ca cc trc bi chnh xc cao. y o lun phin ng46


47/47

C cu chp hnh

thi mt nghing v mt thng. iu ny c th do cc chuyn i p in (Hnh. 20.85(b)) tip xc vi cc thnh phn trong2 vng vi cng kiu phn b dao ng v s chuyn lun phin gia cc thnh phn dao ng tip tuyn v php tuyn.Khng c lc suy rng, r rng sai s gy ra bi mmen trong vng lin kt l khng ng k.

Ti liu tham kho

[1] Cady, W. G.,Piezoelectricity, Dover Publications, New York, 1964.

[2] Volkov, V., Some Theoretical Problems in Modern Techniques of Diagnostics in Mechanical Systems , in Proc. Int.AMSE Conf. Systems Analysis, Control and Design, Lyon, France, 205.

[3] Uchino, K.,Piezoelectric Actuators and Ultrasonic Motors, Kluwer Academic Publishers, MA, 1997, 349.

[4] Ragulskis, K., Bansevicius, R., Barauskas, R., Kulvietis, G., Vibromotors for Precision Microrobots, HemispherePublishing Corporation, 1988, 310.

[5] Suzuki, Y., Tani, K., Sakuhara, T., Development of new type piezoelectric micromotor, J. Sensors & Actuators, 83,244, 2000.

[6] Catalog Ceramic Multilayer Actuator CMA d33 & d31, July 2000.

[7] Sashida, T., Kenjo T., An Introduction to Ultrasonic Motors, Oxford Science Publications, 1993, Oxford UniversityPress, New York, 242.

[8] Ueha S., Tomikawa Y., Ultrasonic Motors, Theory and Application, Oxford Science Publications, Oxford Press,Oxford, 1993, 298.

sổ tay cdt chuong 20(1-3)-cc chap hanh

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