Chng 1CC PHNG PHP IU CH C BN Trongcc
bbinibndn,cckhointlmnhimvnigiauraviuvotrong nhngkhong thi giannht
nh, lp litheo mtchuk nhtnh.inp hocdng in to ras bng gi tr trung bnh
ca cc gi tr tc thi theo chu k lp li . Yu cu chnh y l chu k lp li
phi nh hn nhiu ln so vi chu k sng hi c bn ca cc i lng cn quan tm,
nh m to nn in p, dng in u ra v u vo c dng nh mong mun. Hnh dng mong
mun y c th l dng hnhsintheo snghic bn,nul mtchiuth cdng pmchvi
pmchchophp. Quy lut ng ct cc phn t bn dn nh vy gi lcc phng php bin
iu, hay cc phng php iu ch rng xung (Pulse Width Modulation PWM). C
nhiu phng php bin iu khc nhau, tu thuc vo s b bin i v cng ph thuc
vo mc tiu t ra. Tuy vy c th k ra ba phng php c bn nht sau y: -Phng
php iu ch nh b so snh c ngng. -Phng php bin iu b rng xung tuyn tnh.
-Phng php bin iu vect khng gian. Cc phng php iu ch c p dng trong
nhiu loi b bin i khc nhau. Di y, nu ln nhng c tnh c bn ca cc phng
php, ta s a ra cc v d ng dng ch yu cho cc s b bin i DC-AC ngun p,
trn c s cu mt pha, cu ba pha. 1.1.Phng php iu ch nh b so snh c ngng
Theo phng phpnytnhiu cn iuchnh,lyvqua php o, c sosnhvi mttn hiu t.
Tn hiu u ra b so snh s c gi tr, v d l mc lgic 1, nu tn hiu o c ln
hn tn hiu tmtgitr ngng nht nh,lmclgic 0 nutn hiuo nhhnlng tgi tr
ngng.Tn hiu lgic 1 c a n iu khin ng ct cc van trong b bin i tn hiu
iu chnh phi gim i. Tn hiu lgic 0 s lm cho lng iu chnh phi tng ln.
Trn hnh 3.1.a th hin tc ng ca b so snh hai ngng, u ra tn hiu c gi
tr (0, 1) vi c tnh vo ra nh trnhnh 3.1.b. C th s dng nhng b so snh
phc tp hn, gm ba ngng, vi u ra tn hiu c gi tr (-1, 0, 1). I+Ai Ai
AIA Hnh 1.1. (a) Tc ng ca b so snh c ngng; (b) c tnh vo ra ca b so
snh. V d v tc ng ca phng php ny c m t qua s b bin i DC-AC cu mt
pha, lm vicnhmtb nghchlupngun p,ti tr cmRL,chotrn hnh 3.2. Gi sta
mun iuchnh dng u ra pha xoay chiu theo mt lng t hnh sin, theo th
biu din trn hnh 3.3. Trn hnh 3.2, iref l lng t dng hnh sin mong
mun. Tn hiu dng xoay chiu u ra nghch lu o cin cso snh vi lng t qua
khu sosnh ctr,tonntnhiuiukhinchoccvan V1, .., V4. Xt chiu dng in
ang dng. Khi V1, V4 m s lm cho dng tng ln, cn V2, V3 m s lm cho dng
gim i.CRLuninV1V2V3V4o inV1V2V3V4irefD1 D3D2 D4Etin Hnh 1.2. S cu
trc h thng iu khin. I+AIAHnh 1.3. Tc ng ca b iu chnh dng in c ngng.
Khi V2, V3 m, dng ch chy qua it D2, D3. iu tng t xy ra vi chiu dng
in m, khi vai tr ca cc van i cho nhau. Nu mun iu chnh in p ra trn
ti R, phi dng mch lc LC to ra in p ti c dng gn sin. Khi in p trn ti
un o c s a n b iu chnh in p, u ra b iu chnh in p c th l tn hiu thay
i bin ca lng t dng in. Qua hnh 3.3 c th thy rng tn s ng ct ca cc
van khng c nh. y lnhc im chnh ca phng php ny.Khi mc ngng nh, tn s
ng ct c th rt ln. Nu mc ngng ln, dng dng in s xu i vi nhiu thnh phn
sng hi bc cao.u im chnh ca phng php ny l n gin, d p dng, c bit l tc
ng nhanh rt tt. C th thy r u im th ba ny qua hnh 3.3, trong lng cn
iu chnh chnh l dng in in, c o mt cch trc tip, do s phn nh mt cch tc
thi nhng thay i c th xy ra. Trong s trn y tn hiu iu khin l tn hiu
xoay chiu. Trong cc s b bin i khc th lng t c th c dng tn hiu mt
chiu, v d nh trong cc b bin i xung p DC-DC. 1.2.Phng php bin iu b
rng xung (PWM - Pulse Width Modulation).1.2.1.Nguyn l bin iu b rng
xung Hnh 1.4. th m t phng php PWM. Phng php bin iu b rng xung c pht
trin trong k thut iu ch sng radio, sau c p dng cho k thut bin i in
nng. Ni dung ca phng php bin iu b rng xung l so snh mt tn hiu chun,
l tn hiu ra mong mun,vimt inp rngcacchuk cnh,Ts, thng gi lchuk ly
mu.u raca bso snh s l dy xung c rng thay i, tu theo gi tr ca tn hiu
t, tx:0x st T s s . Trong khong thi gian tx cc kho in t s ni u ra
Uo vi u vo Ui ca b bin i. Nh vy trong mi chu k ct mu, gi tr u ra Uo
s c gi tr trung bnh ph thuc gi tr u vo Ui v thay i theo dng iu ca
tn hiu chun. y cng gi l phng php bin iu c sng mang (Carrier based
PWM). v d,ta s xtmttrng hp ngin,mt qua thtrn hnh 3.4. Gis Ui=
E,khng i, cn tn hiu t thay i theo hm sin tn s thp, c bin bng Ur,m:
( ),sinref r mu U t e =(3.1) 2 f e t = , f l tn s sng sin chun. Tn
hiu rng ca c dng tuyn tnh, bin bng Us,m: ( ),, 0,1, 2,...s s m su U
t kT k = = (3.2) Ti chu k th k ca tn hiu rng ca, tx,k c xc nh
bng:tx,k = tk* - kTs , trong : ( ) ( ),,sins mk s r m ksUt kT U
tTe- - = , ngha l tk* l thi im tn hiu chun bng tn hiu rng ca chu k
ct mu th k. Do ta c: ( ) ( ), ,,, ,sin sin ,r m r mx k s k s ks m s
mU Ut T t T tU Ue e - -= = = (3.3) gi l h s bin iu,0 1 s s .
+E-E00ttUs,mUr,mT/2 T+E-E00ttUs,mUr,mT/2 T-Us,m(a)(b)Hnh 1.5. Phng
php bin iu b rng xung PWM. (a) Mt cc tnh; (b) Hai cc tnh. Vy gi tr
trung bnh ca tn hiu ra trong chu k ct mu th k l: ( )( 1),,sinssk Tx
ko k o i i ks kTtU u dt U U tT e+-= = =}(3.4) C th thy rng gi tr
trung bnh ca tn hiu ra sau mi chu k ct mu bm theo dng ca tn hiu sin
chun mong mun. Biu thc dng (3.4) gi l gi tr trung bnh trt. Nu phn
tch ra chui Furie c th thy rng dng in p trung bnh trt thc s cha
thnh phn sng hi c bn nh sng sin chun v cc sng hi bc cao vi tn s lfs
+/- f , l = 1, 2, Nu tn s ct mu fs ln hn nhiu ln tn s f ca sng sin
ra mong mun th cc tn s sng hi bc cao c th d dng loi b nh cc mch lc
n gin hoc di tc dng ca in cm ti.Phng phpbiniubrng
xungcdngmtcctnhvdnghaicctnh. Theodngpra mt cc tnh, trong nhng khong
tn hiu chun cao hn tn hiu rng ca, van c m a in p ra ti, trong nhng
khong tn hiu chun thp hn tn hiu rng ca, van kho li in p ra ti bng
khng. in p ra s c to thnh ring cho na chu k dng v na chu k m. Theo
dng p ra hai cc tnh in p ra s l +E khi tn hiu chun cao hn rng ca v
l -E khi tn hiu chun thp hn. Hnh 3.5 m t nguyn l hot ng PWM cho hai
trng hp trn cho s nghch lu p cu mt pha. Phng php hai cc tnh c dng
tn hiu iu khin ra n gin hn nhng in p ra s c bc nhy inp ln hn,2E. Bc
nhyin plns lmchodngdng inp mch nhiu hn,ni cch khc l dng dng in s xu
hn so vi phng php iu ch mt cc tnh. Tn hiu rng ca c th c dng khng i
xng, nh trn hnh 3.4, hoc c dng i xng, nh trn
hnh3.5.Trongdngkhngixngrnglicthcsniln,nhtrnhnh3.4,hocsni xung. Dng
rng ca i xng l kt hp ca c hai hai dng khng i xng trn. Trong dng rng
ca i xng chu k ct mu c chia lm hai na Ts/2, v vy trn ng in p ra sng
hi bc cao s c tn s l bi ca 2fs, ngha l cht lng in p ra s tt hn. m
bo in p ra c cha t nht thnh phn sng hi bc cao, s phi lm vic trong
ch tuyn tnh, ngha l phi m bo0 1 s s . Hnh 1.6. (a) S xut hin dng m
xuyn; (b) Tn hiu iu khin IGBT. Trong s cc b bin i p dng PWM, in p
ra s cha cc thnh phn sng bc cao vi tn s bng cc bi s ca tn s xung
rng ca. Do tn s xung rng ca rt cao so vi tn s sin chun nn d dng loi
b c cc sng hi bc cao ny. y l u im c bn ca phng php bin iu b rng
xung. u im th hai l tc ng nhanh cao nh bn cht ca cc h thng iu khin
tng t. Nu PWM c xydngtrn b x l tn hius thng qua qutrnhri rc ha
tnhiuth u imny cng mt i. Nhc im ca phng php ny l cc van phi lm vic
vi tn s ng ct cao nn tn hao cng sut do ng ct ln, h thng iu khin cng
phc tp hn. CV1V4D1D4ZtEidin t t tV1V4tt(a)(b)Hai van trn cng mt
nhnh cu phi p dng phng php chuyn mch c thi gian cht trnh dng
mxuyn.Hnh3.6m ts xuthindng mxuyn vyucuivitnhiuiukhin trongs nghchlu
nacu. Thigian trtgiatn hiumV1v V4 phitnht bng thi gian kho ca van.
i vi IGBT gi tr tiu biu1, 5 2 s t = . 1.2.2.B bin i cu ba pha PWM B
bin i cu ba pha, c s cho trn hnh 2.10.c, cn gi l b bin i hai mc, l
mt s c bn, c s dng rng ri trong cc b bin i DC-AC v AC-DC.Trc ht ta
s xem xt s hot ng ca s cu ba pha trong s mt nghch lu ngun p ba pha,
nh c biu din trn hnh 3.7. Mch lc cu to t 6 van iu khin hon ton V1,
V2, , V6 v 6 it ngc D1, D2, , D6. Cc it ngc gip cho qu trnh trao i
cng sut phn khng gia ti vingun. uvomt chiu lmtngun pvictrng ctC,gi
trln.Ph ti3pha i xng, ZA = ZB = ZC, c th u Y hoc. Hnh 1.7. S nghch
lu c lp ngun p ba pha. Phng php c bn to ra h thng in p xoay chiu ba
phatrn ti l iu khin cc van theo th t nh c k hiu trn s , mi van vo
dn cch nhau 60o. Khong iu khin dn ca mi van = 180o. Vi cch iu khin
nh vy in p dy trn ti s ch c hai mc, hoc l +UDC hoc l UDC. V vy y cn
gi l b bin i hai mc. 0 60 u s s60 120 u s s 120 180 u s s Hnh 1.8.
S tng ng mch ti ng vi cc khong dn ca van.(a) V1, V6, V5 dn; (b) V1,
V6, V2 dn; (c) V1, V2, V3 dn.
AStothnhcainpuratrnccphacgiithchquaccsmchtitng ng trong cc khong dn
ca van nh trn hnh 3.8. Xt cc khong dn ca van trong mi 60o na chu k
th nht nh sau: - Trong khong0 60 u s cc in p ra uAn, uBn,uCn s b
gii hn bi +/-UDC/2 v vect khng gian in p ra b gii hn trong hnh lc
gic c nh l cc vect bin. Hnh 1.21. Dng in p bin iu uAn, uBn, uCn,
uZn v in p trn cc pha ti uA, uB, uCvi UDC = 300 V, Urm = 150 V. Hnh
1.22. Dng in p bin iu uAn, uBn, uCn, uZn v in p trn cc pha ti uA,
uB, uCvi UDC = 300 V, Urm = 173 V.
Trnhnh3.21,3.22,3.23minhhaccdnggitrtrungbnhtrt,xcnhbiccbiuthc
(3.44),(3.45),(3.46),cainpracaqutrnhiuchchobatrnghp: 1 1; ;2 3rm DC
rm DC rm DCU U U U U U = = > . th th hin qu trnh qua su sect ca
mt chu k in p ra. Trn hnh 3.21, 3.22 cho thy dng trung bnh trt in p
ra trn ti, UA, UB, UC, c dng sin hon ton. Hnh 1.23. Dng in p bin iu
uAn, uBn, uCn, uZn v in p trn cc pha ti uA, uB, uCvi UDC = 300 V,
Urm = 200 V. th trn hnh 3.23 cho thy cc in p uAn, uBn, uCn u t n gi
tr gii hn v in p ra trn ti khng cn l hnh sin khi 13rm DCU U > .
Hnh 1.24. Vect khng gian in p ra vi UDC = 300 V, Urm = 150 V. Hnh
1.25. Vect khng gian in p ra viUDC = 300 V, Urm = 173 V . Hnh 1.26.
Vect khng gian in p ra viUDC = 300 V, Urm = 200 V. Trn cc hnh 3.24,
3.25, 3.26 th hin dng ca vect khng gian in p ra trn tr khng ti tng
ngvibatrnghp iuchtrn y.Trnhnh 3.24,3.25vectkhnggianquaytheomtng
trn. Hnh 3.26 cho thy vect in p ra t n ht gi tr gii hn l hnh lc gic
c nh l cc vect bin chun. 1.3.4.6.S mch tng ng S mch in tng ng cho
php thit lp nn h phng trnh m t qu trnh in t, t c th kho st h thng,
xy dng cc cu trc iu chnh v xc nh cc tham s ca b iu chnh theo cc
phng php bit. S thay th tng ng ca nghch lu p ba pha cho trn hnh
3.27. Mi pha in p ra c thay th bng mt ngun in p c dng xung gia
+UDC/2 v UDC/2, nh u ra ca mt s na cu.
.UDCiAiBiCZuAuBuCiDCiDCuAnuBnuAn Hnh 1.27. S mch in tng ng ca nghch
lu ba pha. Phn mt chiu c th hin bng mt ngun p UDC. Dng mt chiu id
to bi cc mnh ca dng xoay chiu iA, iB,iC do tc dng ng ct ca cc kha
S1, S2, , S6. iu ny c th gii thch qua hm ng ct ca cc kha. nh ngha
hm ng ct ca mi pha SA,SB, SC nh sau: SA = 1 nu S1 ng; SA = -1 nu S2
ng; SB = 1 nu S3 ng; SB = -1 nu S4 ng; SC = 1 nu S5 ng; SC = -1 nu
S6 ng. Khi c th thy rng: | | | |2DCA B C A B CUu u u S S S = (3.47)
Dng in biu din qua cc hm ng ct nh sau: | | | | .TDC A A B B C C A B
C A B Ci S i S i S i S S S i i i = + + = (3.48) Trong phng php iu
ch vect khng gian, ti mi chu k ct mu Ts php iu ch s la chn bn trng
thi van ng vi cc khong thi gian t0, t1, t2, t7 to nn vect in p ra.
Cc trng thi van sxc nhhon tongi tr gi trcavecthm ng ct[SA SB SC], t
m cc biuthc (3.47), (3.48) c xc nh. Bng phng php iu
chvectkhnggian,b quanhhng catn sctmu vccthnh phn in cm, t k sinh
cng nh qu trnh chuyn mch gia cc van bn dn, gi tr trung bnh trt ca
in p ra c xc nh nh (3.44). in p ra trn cc tr khng ti xc nh bi
(3.45). Thay th cc in p dng xung ca s iu ch hnh 3.26 bng cc gi tr
trung bnh trt ca chng, UAf, UBf, UCf, ta thu c m hnh trn gi tr
trung bnh. Hnh 3.27 th hin m hnh cho nghch lu p ba pha vi mch lc LC
trn u ra. M hnh cho chnh lu ba pha cho trn hnh 3.28. Cc i lng in p,
dng in k hiu bng ch in ln cho gi tr trung bnh. Hnh 1.28. M hnh tn
hiu trung bnh cho nghch lu p ba pha. Hnh 1.29.M hnh tn hiu trung
bnh cho chnh lu ba pha. 1.3.5.M hnh trn h ta ba pha 1.3.5.1.M hnh
nghch lu S dng m hnh tn hiu trung bnh trn hnh 3.28, gi thit ngun mt
chiu UDC l l tng, cc tn hiu in p iu khin UAf, UBf, UCf c th biu din
di dng: Af AfBf DC BfCf CfU dU U dU d (( ((= (( (( (3.49) dAf,dBf,
dCfl cc h s lp y xung ca tn hiu iu ch pha-trung tnh. So vi (3.47)
thy rng cc h s ny l dng trung bnh ca cc hm ng ct SA, SB, SC. Phng
trnh vi phn i vi dng in qua cc cun cm v in p trn cc t uc vit di
dng: 1AfA ADCB Bf BC CCfdI UU dI d Udt L LI Ud ( (( ( ((= ( (( ( ((
(3.50) 1A A LAB B LBC C LCU I IdU I Idt CU I I ((( (((= ` ((( (((
)(3.51) ILA, ILB, ILC : dng ba pha ti. Dng mt chiu biu din di dng:
| |TDC Af Bf Cf A B CI d d d I I I( = (3.52) Cc phng trnh t (3.49)
n (3.52) cho thy y l mt h thng nhiu u vo, nhiu u ra. C su bin trng
thi l dng trn cc cun cm v in p trn cc t. C ba u vo iu khin l cc h s
lp y xung dAf,dBf, dCfv ba u ra l cc in p trn ti UA, UB, UC. Trong
ch xc lp, in p trn ti l h thng in p ba pha: cos2cos32cos3AB rmCUU
UUututu ( ( ( ( (| |( = (| (\ . ( ( (| |+ ( |\ . (3.53) Thay (3.53)
vo (3.50), (3.51), vi iu kin bit c cc thng s ca ti s tnh ton c in p
iu khin t (3.49). C th thy rng tt c cc i lng in p, dng in xoay chiu
u c dng sin. 1.3.5.2.M hnh chnh lu tch cc ba pha Da trn s m hnh tn
hiu trung bnh trn hnh 3.29, gi thit rng in p lui u vo chnh lu UA,
UB, UCl ngun in p ba pha l tng, ta c h phng trnh vi phn sau: 1AfA
ADCB Bf BC CCfdI UU dI d Udt L LI Ud ( (( ( ((= ( (( ( (( (3.54) |
|( )1 TDCAf Bf Cf A B C LdUd d d I I I Idt C( = (3.55) IL l dng ti
pha mt chiu. M hnh c bn bin trng thi l dng qua cun cm IA, IB, IC v
in p trn t mt chiu UDC. Ba bin vo iu khin l dAf, dBf, dCf v mt bin
ra in p UDC. 1.3.6.M hnh trn h ta 0dq 1.3.6.1.M hnh nghch lu ng dng
ma trn bin i T4 nh trong (3.26): 42 2cos cos cos3 32 2 2sin sin
sin3 3 31 1 12 2 2Tt tu u ut tu u u ( | | | | + ||(\ . \ . ( (| | |
|= + (||\ . \ . ( ( ( cho cc php bin i t h ta 0abc sang 0dq, vi lu
cc php o hm c thc hin nh trong (3.56), (3.57): 11 44dqabcdqdXdX dTX
Tdt dt dt= + (3.56) 1440 00 00 0 0dTTdtee( (=( ( (3.57) Cc biuthc
trong hta ba pha t (3.49) n(3.52) c bin ithnhtng ng t(3.58) n
(3.62). 4 40 0df Af Af dfqf Bf DC Bf DC qff Cf Cf fU U d dU T U U T
d U dU U d d (((( ((((= = = (((( (((( (3.58) 0 0 00qd d dq DC q q
dII d UdI U G d G U IdtI d Ue (((( ((((= + (((( (((( (3.59) 0 0
010qd d Ldq d q LqLUU I IdU U I Idt CU I Ie (((( ((((= + ` ((((
(((( )(3.60) 10 010 00 0 0LGL ( ( ( (=( ( ( ( (3.61) Dng mt chiu
bng: 0 03 332 2TDC d q d qI d d d I I I ( ( = ( (3.62) 1L1C} }1L1C}
}IdILqL eL eIqILqC eC eUdUqXXddUDCdq-+++--++-+-- Hnh 1.30. M hnh
nghch lu trong h ta d 0dq.
Mhnhnghchlutronghta0dq,xydngtheo(3.59),(3.60),khngknthnhphn khng,
cho trn hnh 3.30. Trn m hnh c th thy c bn bin trng thi l Id, Iq,
Ud, Uq, hai bin iu khin l cc h s bin iu dd, dq, hai thnh phn nhiu l
cc dng ti ILd, ILq. Hai knh theo hai trc d,q
clinhchovinhauthngquaccthnh phninptrncuncmeLId,eLIq,ccthnhphn dng
in eCUd, eCUq. Cc lin h cho ny ny khng d phn ly to thnh hai knh iu
khin c lp. u vo l in p mt chiu UDC, u ra l in p Ud, Uq. Khi cc thnh
phn ph ti l i xng, tt c cc thnh phn U0, d0, I0 u bng 0, cc biu thc
trn s n gin i ng k. Trong ch xc lp cc o hm trong (3.59), (3.60) cho
bng khng, in p ra s c dng ng nh tn hiu t mong mun: | |00 0TTd q rmU
U U U(= (3.63) Dng in ra trn in cm c dng: 0000d Ldq Lq rmI II I U
CIe (( ( (( (= + (( ( (( ( (3.64) Cc h s bin iu bng: 21100 00 0Lqd
Ldrmq Lq LdDC DC DCId I LCU G d Ld I IU dt U Uee(((( ((((= + + ((((
(((( (3.65) Trong ch xc lp o hm cc thnh phn dng in trong h ta 0dq s
bng khng, v vy cc h s bin iu s bng: 2100 00Lqdrmq LdDC DCId LCU Ld
IU Uee((( ((( = + ((( ((( (3.66) Tuyn tnh ha quanh im lm vic xc lp
bng cch cho cc bin trng thi v cc bin iu khin nhng bin ng nh nh
(3.67).; ; ; ;; ;d d d q q q d d d q q qd d d q q qDC DC DCd d d d
d d I I i I I iU U u U U uU U u= + = + = + = += + = += + (3.67)
Trong cc k hiu c m ng trn ch cc bin ng nh. Tuyn tnh ha c tin hnh
theo cch thng thng bng cch b qua cc bin ng bc hai, v d vi tch hai
bin sau: ( )( )DC d DC DC d d DC d DC d DC dU d U u d d U d U d u d
= + + ~ + + (3.68) p dng cc php gn ng tng t nh (3.68) cho cc phn t
trn s hnh 3.30, b qua phn cn bng gia cc gi tr xc lp, c th thu c m
hnh trn cc tn hiu bin ng nh. Nu m phng s trn SIMULINK qu trnh tuyn
tnh ha c th thc hin mt cch t ng. 1.3.6.2.M hnh chnh lu
pdngmatrnbiniT4chocc phngtrnh(3.54),(3.55)thu cmhnhchochnhlu trong
h ta 0dq nh sau: 0 0 00qd d dq DC q q dII d UdI U G d G U IdtI d Ue
(((( ((((= + + (((( (((( (3.69) 0 01 3 332 2TDCd q d q LdUd d d I I
I Idt C ( ( = ` ( )(3.70)
Mhnhchnhlutronghta0dq,xydngtheo(3.69),(3.70),khngknthnhphn khng,
cho trn hnh 3.30. Trn m hnh c th thy c ba bin trng thi l Id, Iq,
UDC, hai bin iu khin l cc h s bin iu dd, dq, thnh phn nhiu l dng ti
IL. Hai knh theo hai trc d,q c lin h cho vi nhau thng qua cc thnh
phn in p trn cun cm eLId, eLIq. u vo l cc thnh phn in p li Ud, Uq,
u ra l in p mt chiu UDC. 1L}}1L}L eL e32C Hnh 1.31 M hnh chnh lu
trong h ta 0dq. Gi thit rng s c iu khin cho h s cng sut bng mt.
Trong ch xc lp Ud = Ulm, Uq = 0, Ulm l gi tr bin in p pha. Dng in c
gi tr Id = Ilm, Iq = 0, vi Ilm l bin dng in pha. Cho v phi cc phng
trnh (3.66), (3.67) bng khng, c th xc nh cc h s bin iu nh sau:
03230dLqMdIdMd ( ( (( ((= (( (( ( ( (3.71) Trong M l h s bin iu, IL
l dng ti. Thc hin th tc tuyn tnh ha, tng t nh lm cho m hnh nghch
lu, ta s thu c m hnh cho cc tn hiu bin ng nh, lm c s cho vic thit k
cc b iu chnh trong h thng iu khin.
