cascade inverters awesome

8/3/2019 Cascade Inverters Awesome

1/19

Tiu Lun TCS_NC Phn A: Tng quan v b nghch lu p a bc

PHN A: TNG QUAN V B NGHCH LU A BC1. Tng quan

1.1. t vn

Trong nhng nm gn y, h thng in t cng sut c pht trin rt mnh. Vi nhiu l do,th nht: cc thit b in t cng sut ngy cng c s dng nhiu, khng nhng trong lnh vc

cng nghip m cn thm nhp vo c lnh vc thng mi v dn dng. L do th hai: do nhu cu

pht trin cc thit b s dng hiu qu v tit kim nng lng ng thi vi vic s dng ngun

nng lng mi nh nng lng gi, nng lng mt tri.v.v trc tip ni tiu th.

Cc b chuyn i AC DC (chnh lu, nghch lu, bin tn) ngy cng c quan tm nghin

cu. p ng cc nhu cu cng sut ln, cn phi nng cao in p v dng in. Tuy nhin do

kh nng chu dng v p ca cc linh kin in t cng sut c gii hn, nn song song vi vic

pht trin cc linh kin cng sut ln, ngi ta dng gii php mc song song to dng in cao

v mc ni tip tng in p. Gii php mc ni tip cho ra i cc cu trc mch nghch lu p

abc thay cho nghch lu p hai bc truyn thng. Mch nghch lu p a bc c nhiu u im

nh cng sut cao hn, cht lng in p v dng in ng ra tt hn, mch lc u ra nh hn.

so vi nghch lu p hai bc. Tuy nhin n cng c nhiu nhc im nh cn nhiu linh kin hn,

gii thut iu khin phc tp hn v v vy gi thnh cng t hn.

Nm 1980, Navae v cc cng s ca ng bt u nghin cu v nghch lu p a bc. V n

nm 1981 ng ngh cu hnh NPC (Neutral Point Clamped) cho nghch lu p 3 bc. V sau, cuhnh ny c pht trin cho nghch lu p a bc vi tn chung l cu hnh diode-clamped

converter (diode kp). Cu hnh ny c dng cu vi mi nhnh gm nhiu linh kin chuyn mch

mc ni tip. Mt s cu hnh khc ra i mun hn gm floating capacitor converter (t kp) v

cascade H-dridge converter. Cu hnh t kp c cu trc tng t nh cu hnh diode kp; cu hnh

H-dridge c xy dng bng cch ni tip cc mch nghch lu 2 bc c bn. Trong cu hnh

diode kp l cu hnh c nghin cu v c nhiu ng dng nht.

1.2 ng dng ca b nghch lu.

ng dng trong cng nghipng dng trong dn dng

ng dng trong truyn ti h thng in

ng dng trong thng mi

ng dng trong phng th nghim

Dng lm ti liu trong ging dy

2. Gii thiu b nghch lu p.

B nghch lu p c nhim v chuyn i nng lng t ngun in mt chiu khng i sang

dng nng lng in xoay chiu cung cp cho ti xoay chiu.

GVHD: PGS. TS. Nguyn Vn Nh Trang 5 HVTH: Trng Minh Triu


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i lng c iu khin ng ra l in p hoc dng in. Nu i lng c iu khin

ng ra l in p th b nghch lu c gi l b nghch lu p, ngc li gi l b nghch lu

dng.

Cc b nghch lu to thnh b phn ch yu trong b bin tn. ng dng quan trng v tng

i rng ri ca chng nhm vo lnh vc truyn ng in ng c xoay chiu vi chnh xccao.

Trong lnh vc tn s cao, b nghch lu c dng trong cc thit b l cm ng trung tn, thit

b hn trung tn. Bnghch lu cn ng dng lm ngun in xoay chiu cho nhu cu gia nh, lm

ngun in lin tc UPS, iu khin chiu sng v cn c ng dng trong lnh vc b nhuyn

cng sut phn khng

2.1 Khi nim.

B nghch lu p l mt b nghch lu c ngun mt chiu cung cp l ngun p v i tng

iu khin ng ra l in p. B nghch lu dng l b nghch lu c ngun mt chiu cung cp lngun dng v i tng iu khin ng ra l ngun dng. Trn thc t ngun mt chiu l ngun

p v i tng nghin cu l b nghch lu p.

B nghch lu p cung cp v iu khin in p xoay chiu ng ra, ngun in p mt chiu

c th l: pin in, c quy, in p mt chiu c chnh lu t in p xoay chiu c lc phng.

Cc ti xoay chiu thng mang tnh cht cm khng (ng c xoay chiu, l cm ng), dng

in qua cc linh kin khng th ng ngt bng qu trnh chuyn mch t nhin. Do , linh kin

trong b nghch lu p phi c kh nng kch ng, ngt dng qua n. Trong cc ng dng vi cng

sut nh v va th c th s dng Transitor BJT, MOSFET, IGBT. Trong phm vi cng sut ln cth dng GTO, IGCT hoc SCR kt hp vi b chuyn mch. Vi ti tng qut, mi linh kin cn

mc thm mt diode i song song hn ch in p pht sinh khi kch ngt linh kin.

2.2 Phn loi.

B nghch lu p c nhiu loi cng nh c nhiu phng php iu khin khc nhau:

Theo s pha in p u ra: nghch lu p mt pha, ba pha.

Theo s cp gi tr in p: l s in p gia mt u pha ti n mt im in th chun

trn mch DC c: hai bc (two level), a bc (multilevel t ba bc tr ln).

Khi nim b bin tn hai bc xut pht t in p mt u pha ti (pha a, b, c) vi im chun

(v tr ni t) trn mch DC thay i gia hai bc khc nhau (V DC v 0). B nghch lu p hai bc

c nhc im l to in p cung cp cho cun dy ng c dv/dt kh ln v gy ra hin tng

in p common mode (VN0 0) rt nghim trng. B nghch lu p a bc c pht trin

gii quyt cc vn gy ra nu trn ca b nghch lu p hai bc v thng c s dng cho cc

ng dng in p cao v cng sut ln.

u im ca b nghch lu p a bc l cng sut ca b nghch lu tng ln, in p t ln cc

linh kin gim xung nn cng sut tn hao do qu trnh ng ngt ca linh kin cng gim theo(switching losses); vi cng tn s ng ngt, cc thnh phn sng hi bc cao ca in p ra gim

nh hn so vi b nghch lu p hai bc.



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Theo cu hnh b nghch lu: dng cascade (cascade inverter), dng nghch lu cha cp

diode kp NPC (neutral point clamped multilevel inverter)

2.3. Cc phng php iu khin b nghch lu p.

Phng php iu ch rng xung sin (Sin PWM-sin pulse width modulation).

Phng php iu khin theo bin .Phng php iu ch rng xung (SH-PWM).

Phng php iu ch rng xung ci bin (Modified PWM).

Phng php iu ch vector khng gian (SVPWM-space vector pulse width modulation).

3. Cu trc c bn ca b nghch lu p a bc.

3.1. Cu trc b nghch lu NPC.

S dng thch hp khi cc ngun DC to nn t h thng in AC. B nghch lu a bc cha

cc cp diode kp c mt mch ngun DC c phn chia thnh mt s cp in p nh hn nh

chui cc t in mc ni tip.Gi s nhnh mch DC gm n ngun c ln bng nhau mc ni tip. in p pha - tm ngun

DC (im 0) c th t c (n+1) gi tr khc nhau v t b nghch lu c gi l b nghch

lu p (n+1)bc.

V d: xt hnh 1.1 bn di, chn mc in th 0 cui dy ngun, cc mc in p c th t

c gm (0, VDC/2, 2VDC/2, 3VDC/2,nVDC/2). in p t mt pha ti (v d pha a) thng n

mt v tr bt k trn nhnh DC (v d M) nh cp diode kp ti im (VD: Da4, Da4)

+ Vdc/5

-

Da1

Da2

S5a

S4a

+ Vdc/5

-

Da3

Da4

S3a

S2a

+ Vdc/5

-

D'a1

S1aa

b N

S'5a c

Vdc/5+ D'a2

S'4a

-

M D'a3

S'3a

+ Vdc/5S'2a

- D'a4

S'1a

0 Hnh 1.1 B nghch lu NPC in p pha tm ngun DC t c mc in p Ua0 = VDC/5, tt c cc linh kin b kp

gia hai diode (Da4, Da4) gm n linh kin mc ni tip lin tc k nhau S1a, S5a, S4a, S3a, S2aphi c kch ng, cc linh kin cn li phi c kho theo nguyn tc kch i nghch. Nh

hnh v trn, to ra su mc in p pha tm ngun DC (im 0) nn mch nghch lu p trn gi

l b nghch lu p su bc.



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+ +

3


B nghch lu p a bc dng diode kp ci tin dng sng in p ti v gim Shock in p

trn linh kin n ln.Vi b nghch lu ba bc, dv/dt trn linh kin v tn s ng ct gim i mt

na. Tuy nhin vi n > 3, mc chu gai p trn cc diode s khc nhau. Ngoi ra, cn bng in

p gia cc ngun DC (p trn t) tr nn kh khn, c bit khi s bc ln.

3.1.1. Cc trng thi ng ngt ca b nghch lu NPC.Xt b nghch lu p nbc dng cha cp diode kp NPC (hnh 1.1). Gi VDC/5 l ln in p

trong mi ngun ring l ph thuc ln in p pha ngun VDC cn thit lp, cc linh kin b

kp gia cc cp diode ni n mt in th trnmch DC cn thit lp s trng thi kch ng.

in p pha tm ngun DC tnh t im u dy ca mt pha ti n mtin th chun (im 0)

trn mch DC.

Trng thi kch ngt ca cc kha bn dn trn mt nhnh pha ti ca cc pha a, b, c phi tha

mn iu kin kch i nghch. Nu cc kha bn dn trn mt nhnh pha cng kch ng th gy

ngn mch ngun hoc khng c php cng kch ngt.Sja+ Sja =1; Sjb +Sjb =1; Sjc + Sjc =1 (1.1)

Vi: j = 1, 2,3 (n-1)

Gi n l im nt ba pha ti dng sao i xng. Ta c in p ba pha ti:

u = u u ; u = u u ; u = u uta a 0N0 tb b 0 N0 tc c 0 N0

in p ua0, ub0, uc0 gi l in p pha tm ngun ca pha a, b, c.

Gi thit ti ba pha i xng, tho mn h thc:

u +u +u = 0ta tb tcua0 +ub0+uc0 3uN0 = 0

in p Common mode:

u = u

a 0 b 0 c0

(1.2)N0 3

u = u u=

2ua 0 ub 0 uc 0

ta a0 N0 3

u = u u

=

2ub 0 uao uc 0

Ta c p ti : tb b0 N0 3

(1.3)

u = u u=

2uc 0 ua 0 ub 0

tc c0 N0

T ta thy qu trnh in p v qu trnh dng in ng ra ca b nghch lu p ba pha s

c xc nh khi ta xc nh c cc in p nghch lu ua0, ub0, uc0.Nu ba pha ti dng tam gic, in p pha ti bng in p dy do b nghch lu cung cp:

utab = ua0 ub0;

utbc = ub0 uc0;

utca = uc0 ua0

(1.4)


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3.1.2 Trng thi ng ngt b nghch lu NPC 5 bc.



6/19

Mc in p nghch lu VA0Cc trng thi ng ngt

tng ng

Trng thi ng ngt ca cc

linh kin

0 (0,0,0,0) (0,0,0,0)

Vd

4(

Vd ,0,0,0)4

(1,0,0,0)

Vd

2(

Vd ,Vd ,0,0)

4 4(1,1,0,0)

3Vd

4Vd Vd Vd (1,1,1,0)

Vd

Vd Vd Vd Vd4 4 4 4

(1,1,1,1)


S4aS4b S4c

V dc/4

S3a S3b S3c

S2a S2b S2c

V dc/4

S1a S1b S1c

abc

0

Vdc/4

S'4a S'4b S'4c

S'3aS'3b S'3c

V dc/4S'2a S'2b S'2c

S'1aS'1b S'1c

pha aphab pha c

Hnh 1.2 S nguyn l nghch lu NPC 3 pha 5 bc

Xt pha a ca b nghch lu p nm bc dng diode kp. Gi VDC/4 l ln in p trn mi

ngun in ring l. Chn im 0 tm ngun DC v tr gia, in p pha tm ngun DC t cc

gi tr nh trong bng sau:

Bng 1.1 Trng thi ng ngt ca b nghch lu p NPC 5 bc

( , , , )

Ta thy c 5 mc in p ra tng ng vi cc trng thi ng ngt cho mi pha. Vy c 5 trng

thi ng ngt linh kin cho mi pha, nh vy c 125 trng thi ng ngt cho ba pha. V b nghch

lu p c th to ra nm mc in p nn c gi l b nghch lu p 5 bc

3.1.3. Nhn xt

Vi cu trc nh trn nn tn s ng ngt gim dn n s ln chuyn mch trn cc pha b

nghch lu p gim, tn tht ca b nghch lu gim t c kh nng nng cao cng sut ca b

nghch lu. V vy b nghch lu p a bc ngy cng c s dng rng ri trong cc lnh vc

cng sut cao, nhung bn cnh vn cn c nhng u v khuyt im nh sau:


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8/19


u im.

Khi s bc cao, thnh phn hi bc cao s thp khi s dng cc b lc.

Hiu sut cao v cc kho c th c iu khin tn s ng ngt c bn (phng php PWM

l ti u).

C th iu khin lng cng sut phn khng.Phng php iu khin n gin cho h thng ni kt dng i song (back-to-back).

Khuyt im.

Yu cu s dng qu nhiu diode khi s bc in p cao.

Kh iu khin lng cng sut tch cc cho cc b bin i n.

3.1.4. Cc cng thc lin quan.

in p Offset: Vomax = Vd Max(ut1,ut2 ,ut3 ),Vo min = Min(ut1,ut2,u

t3)

VoMin + VoMa x

(1.5)

Ch medium common mode: Vo = 2(1.6)

Ch gin on (Discontinuos): Vo = VoMin hoc Vo = VoMax (1.7)

in p iu khin: V = Vd VV =

Vi 0.(n1)i 0

n1 dki dki Vdc

(vi n: s bc ca b nghc lu)

3.2. Cu trc b nghch lu Cascade H-dridge.

S dng cc ngun DC ring, thch hp trong trng hp s dng ngun DC c sn, v d acquy,

battery. Cascade inverter gm nhiu b nghch lu p cu mt pha ghp ni tip, cc b nghch lu

p dng cu mt pha ny c cc ngun DC ring.

S kt hp hot ng ca nb nghch lu p trn mt nhnh pha ti s to nn n kh nng mc

in p theo chiu m (-VDC, -2VDC, -3VDC, -4VDC, -nVDC), n kh nng mc in p theo chiu

dng (VDC, 2VDC, 3VDC, 4VDC,nVDC ) v mc in p 0. Nh vy, b nghch lu p dng

cascade gm nb nghch lu p mt pha trn mi nhnh s to thnh b nghch lu (2n+1) bc.


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10/19

S S

S` a4

S`

`


VaSa1 Sa2

`Va10 a1 Va11 a2

Va1

Sa3 Sa4

a3 S`

Va2

Va20 Va21

Sa5 Sa6

a5 S`

Va3

Va30 Va31 a6V0

Hnh 1.3 B nghch lu Cascade H-dridge 1 pha 7 bc

3.2.1. Cc trng thi ng ct ca b ngch lu Cascade 7 bc.

Xt pha a ca b nghch lu p 7 bc dng Cascade H-dridge. Gi VDC l ln in p trn mingun in ring l. Chn im 0 nh trn th, in p pha Va0 t cc gi tr nh trong bng sau:

Va0 (Va1, Va2, Va3) (Va10, Va11, Va20, Va21, Va30, Va31) (Saj, S`aj) vi j=1,2.. 6.

3Vd (Vd,Vd,Vd) (Vd,0,Vd,0,Vd,0). (1,0,1,0,1,0).

2Vd

(Vd,Vd,0);

(Vd,0,Vd);

(0,Vd,Vd)

(Vd,0,Vd,0,0,0);(Vd,0,Vd,0,Vd,Vd)

(Vd,0,0,0,Vd,0);(Vd,0,Vd,Vd,Vd,0)

(0,0,Vd,0,Vd,0);(Vd,Vd,Vd,0,Vd,0)

(1,0,1,0,0,0);(1,0,1,0,1,1);

(1,0,0,0,1,0);(1,0,1,1,1,0)

(0,0,1,0,1,0);(1,1,1,0,1,0)

Vd

(Vd,0,0);

(0,Vd,0);

(0,0,Vd)

(Vd,Vd,-Vd)

(Vd,-Vd,Vd)

(-Vd,Vd,Vd)

(Vd,0,0,0,0,0); (Vd,0,0,0,Vd,Vd);

(Vd,0,Vd,Vd,0,0);(Vd,0,Vd,Vd,Vd,Vd);

(0,0,Vd,0,0,0); (0,0,Vd,0,Vd,Vd);

(Vd,Vd,Vd,0,0,0);(Vd,Vd,Vd,0,Vd,Vd);

(0,0,0,0,Vd,0); (0,0,Vd,Vd,Vd,0);

(Vd,Vd,0,0,Vd,0);(Vd,Vd,Vd,Vd,Vd,0);

(Vd,0,Vd,0,0,Vd);

(Vd,0,0,Vd,Vd,0);

(0,Vd,Vd,0,Vd,0).

(1,0,0,0,0,0); (1,0,0,0,1,1);

(1,0,1,1,0,0);(1,0,1,1,1,1);

(0,0,1,0,0,0); (0,0,1,0,1,1);

(1,1,1,0,0,0);(1,1,1,0,1,1);

(0,0,0,0,1,0); (0,0,1,1,1,0);

(1,1,0,0,1,0);(1,1,1,1,1,0);

(1,0,1,0,0,1);

(1,0,0,1,1,0);

(0,1,1,0,1,0).

0

(0,0,0) (0,0,0,0,0,0);(0,0,0,0,Vd,Vd);

(0,0,Vd,Vd,0,0);(0,0,Vd,Vd,Vd,Vd)

(Vd,Vd,0,0,0,0);(Vd,Vd,0,0,Vd,Vd);

(0,0,0,0,0,0);(0,0,0,0,1,1);

(0,0,1,1,0,0);(0,0,1,1,1,1)

(1,1,0,0,0,0);(1,1,0,0,1,1);



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(0,Vd,-Vd)

(0,-Vd,Vd)

(Vd,0,-Vd)

(-Vd,0,Vd)

(Vd,-Vd,0)

(-Vd,Vd,0)

(Vd,Vd,Vd,Vd,0,0);(Vd,Vd,Vd,Vd,Vd,Vd)

(0,0,Vd,0,0,Vd);(Vd,Vd,Vd,0,0,Vd);

(0,0,0,Vd,Vd,0);(Vd,Vd,0,Vd,Vd,0);

(Vd,0,0,0,0,Vd);(Vd,0,Vd,Vd,0,Vd);

(0,Vd,0,0,Vd,0);(0,Vd,Vd,Vd,Vd,0)

(Vd,0,0,Vd,0,0);(Vd,0,0,Vd,Vd,Vd)

(0,Vd,Vd,0,0,0);(0,Vd,Vd,0,Vd,Vd).

(1,1,1,1,0,0);(1,1,1,1,1,1);

(0,0,1,0,0,1);(1,1,1,0,0,1);

(0,0,0,1,1,0);(1,1,0,1,1,0);

(1,0,0,0,0,1);(1,0,1,1,0,1);

(0,1,0,0,1,0);(0,1,1,1,1,0)

(1,0,0,1,0,0);(1,0,0,1,1,1)

(0,1,1,0,0,0);(0,1,1,0,1,1).

-Vd

(-Vd,0,0);

(0,-Vd,0);

(0,0,-Vd)

(-Vd,-Vd,Vd)(-Vd,Vd,-Vd)

(Vd,-Vd,-Vd)

(0,Vd,0,0,0,0); (0,Vd,0,0,Vd,Vd);

(0,Vd,Vd,Vd,0,0);(0,Vd,Vd,Vd,Vd,Vd);

(0,0,0,Vd,0,0); (0,0,0,Vd,Vd,Vd);

(Vd,Vd,0,Vd,0,0);(Vd,Vd,0,Vd,Vd,Vd);

(0,0,0,0,0,Vd); (0,0,Vd,Vd,0,Vd);

(Vd,Vd,0,0,0,Vd);(Vd,Vd,Vd,Vd,0,Vd);(0,Vd,0,Vd,Vd,0);

(0,Vd,Vd,0,0,Vd);

(Vd,0,0,Vd,0,Vd).

(0,1,0,0,0,0); (0,1,0,0,1,1);

(0,1,1,1,0,0);(0,1,1,1,1,1);

(0,0,0,1,0,0); (0,0,0,1,1,1);

(1,1,0,1,0,0);(1,1,0,1,1,1);

(0,0,0,0,0,1); (0,0,1,1,0,1);

(1,1,0,0,0,1);(1,1,1,1,0,1);(0,1,0,1,1,0);

(0,1,1,0,0,1);

(1,0,0,1,0,1).

-2Vd

(-Vd,-Vd,0);

(-Vd,0,-Vd);

(0,-Vd,-Vd)

(0,Vd,0,Vd,0,0);(0,Vd,0,Vd,Vd,Vd);

(0,Vd,0,0,0,Vd);(0,Vd,Vd,Vd,0,Vd);

(0,0,0,Vd,0,Vd);(Vd,Vd,0,Vd,0,Vd).

(0,1,0,1,0,0);(0,1,0,1,1,1);

(0,1,0,0,0,1);(0,1,1,1,0,1);

(0,0,0,1,0,1);(1,1,0,1,0,1).

-3Vd (-Vd,-Vd,-Vd) (0,Vd,0,Vd,0,Vd). (0,1,0,1,0,1).3.2.2. Nhn xt

Vi cu trc nh trn nn tn s ng ngt gim dn n s ln chuyn mch trn cc pha b

nghch lu p gim, tn tht ca b nghch lu gim t c kh nng nng cao cng sut ca b

nghch lu. V vy b nghch lu p a bc ngy cng c s dng rng ri trong cc lnh vc

cng sut cao, nhung bn cnh vn cn c nhng u v khuyt im nh sau:

u im.

Cn s lng cc cu phn t nht t c s bc in p cao nht.

Vic ch to mch c m un ho do b nghch lu c bn c cu trc nh nhau v khng cnmc thm diode cng nht cn bng p nh cc s k trn.

C th s dng chuyn mch mm trnh mch bo v chng dV/dt cng knh v tn hao.

Khuyt im.

Cn ngun DC c lp cho vic chuyn i cng sut thc, do vy vic ng dng cn b hn ch.

3.2.3. Cc cng thc lin quan.

in p Offset : Vomax = n.Vd Max(ut1,ut2 ,ut3 ),Vo min = n.Vd Min(ut1,u

t2,u

t3)

(vi n: l s ngun c trong mch)

(1.8)

Ch medium common mode: Vo =VoMin + VoMa x (1.9)

2

Ch gin on (Discontinuos): Vo = VoMin hoc Vo = VoMax (1.10)


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13/19


3.3. Nhn xt chung.

C th iu khin b nghch lu p (bng cch iu khin tn hiu ng ngt ln cc linh kin)

bng nhiu phng php, mi phng php thch hp vi mi loi ti khc nhau. B nghch lu p

a bc c phm vi hot ng vi ti cng sut ln do vn t ra l gim bt tn s ng ngt

v gim shock in p trn linh kin cng sut c ngha quan trng. Chng sau s m phng b

nghch lu p a bc NPC, qua s thy r c tn s ng ngt ca cc linh kin bn dn c

gim thiu ng k so vi cc phng php iu khin b nghch lu p hin nay. Tn s ng ngt

gim dn n s ln chuyn mch trn cc pha b nghch lu p gim, tn tht ca b nghch lu

gim t c kh nng nng cao cng sut ca b nghch lu . B nghch lu ngy cng c s

dng rng ri trong cc lnh vc cng sut cao.

4. Cc phng php iu ch rng xung.

4.1 Phng php iu ch rng xung Sine (SH-PWM).Phng php SH-PWM c tn nay l Subharmonic Pulse Width Modulation . thc hin

to gin kch ng cc linh kin trong cng mt pha ti, ta s dng mt s sng mang (dng tam

gic) v mt tn hiu iu khin (dng sin). i vi b nghch lu p n bc, s sng mang c s

dng l (n-1). Chng c cng tn s fc, v cng c bin nh nh Ac. Sng iu ch (hay sng

iu khin) c bin nh nh Am v tn s fm, dng sg ca n thay i chung quanh trc tm

ca h thng (n-1) sng mang. Nu sng iu khin ln hn sng mang no th linh kin tng

ng c sng mang iu khin s c kch ng. Trong trng hp sng iu khin nh hn

sng mang no th linh kin s b kha kch.

i vi b nghch lu p a bc ch s iu ch c nh ngha nh sau:U

m =(1)m

Ubase

(1.11)

Vi: U(1)m: bin thnh phn hi c bn to nn do phng php iu ch.

Ubase: bin thnh phn hi c bn t c.

4.2 Phng php iu ch rng xung ci bin (SFO-PWM).

im khc bit so vi phng php iu ch rng xung trnh by l sng iu ch (in p

iu khin) c ci bin. Theo mi sng iu ch c cng thm tn hiu th t khng (snghi bi ba). Tn ti nhiu kh nng to nn thnh phn th t khng, mt trong cc tn hiu th t

khng c th chn bng gi tr trung bnh ca gi tr tn hiu ln nht trong ba tnhiu iu ch vi

tn hiu nh nht trong ba tn hiu iu ch- Phng php SFO - PWM.

Gi Va, Vb, Vc l cc tn hiu iu khin ca phng php iu ch PWM. Tn hiu iu khin

theo phng php SFO-PWM va c m t c th biu din di dng ton hc nh sau:

Voffset =

Max(Va ,Vb ,Vc )+ min(Va ,Vb,Vc )

2

(1.12)

4.3. Phng php iu ch vector khng gian.

4.3.1. Khi nim vector khng gian.

Ta gi s cho i lng 3 pha va, vb, vc cn bng, tho h thc: va+ vb+ vc=0 (1.13)


14/19



15/19

==

=

=

=

=

a1 ' b1

'

c1

'

a 2


Thc hin php bin hnh t cc i lng ba pha va, vb, vc sang i lng vector theo h

thc : v = k.(v

+a.v

+a2 .v ),a = e

j 2 / 3=

1+j3

(1.14)

a b c2 2

Php bin hnh thc hin nh trn c gi l php bin hnh vector khng gian v i lngc gi l vector khng gian ca i lng ba pha.

Hng s k c th chn vi cc gi tr khc nhau. Vi k = 2/3 ta c php bin hnh khng bo ton

cng sut. Vi k= 2/3

php bin hnh bo ton cng sut.

minh ho c th cho khi nim ny ta xt cc i lng ba pha dng cosin nh sau:

Vector khng gian theo nh ngha s l :

(1.15)

Nh vy, trong to vung gc , , vector khng gian c bin Vm bt u t v tr

s quay quanh trc to vi tn s gc .

4.3.2. Vector khng gian ca b nghch lu p a bc.

Qu trnh ng ngt cc linh kin to ra in p ba pha ti. Theo l thuyt v khng gian vector

th in p ba pha c th biu din di dng vector khng gian. V n s thay i nhy cp trn

hnh lc gic a bc. V tr ca mi vector in p trong khng gian s ph thuc vo cc trng thi

ng ngt kinh kin. Tin hnh kho st c th cho cc b nghch lu ba v nm bc xc nh

gin vector khng gian in p.

4.3.3. Gin vector in p ca b nghch lu 5 bc.Vi b nghch lu nm bc, kh nng iu khin kch dn linh kin to nn 125 trng thi khc

nhau. Ta xt mi trng thi minh ho bi t hp (ka kb kc), vi:

ka =2,1,0,1,2

kb =2,1,0,1,2

kc =2,1,0,1,2

Cc h s trng thi ka, kb, kc ph thuc vo cch quy c trc. Ta tin hnh quy c nh sau:

(s quy c ny da vo bng trng thi ng ngt)

2 khi S a1 = Sa 2 = Sa 3 = Sa 4= 1

2 khi S b1 = Sb 2 = Sb3 = Sb 4= 1

2 khi S c1 = Sc 2 = Sc 3 = Sc 4 = 1

1 khi S

= Sa

2

= Sa 3 a 4

=1

1 khi S

= Sb

2

= Sb3 b 4

=1

1 khi S

= Sc

2

= Sc 3 c 4

= 1

ka = 0 khi S a1 = Sa 2'

'

a 3

a 4= 1,kb = 0 khi S b1 = Sb 2


16/19

= = ==

= = = = = = = =

a1

== = b1

= == c1 = = =

=

' = ' ='

=

= b 2 =

c 2

=

' 'b 3 b 4 = 1,kc = 0 khi S c1 = Sc 2

''

c 3 c 4

1

khi S a1 a 2

' 'a 3 a 4

1

khi S b1 b 2

' 'b3 b 4

1

khi S c1 c 2

' 'c 3 c 4

2

khi S' ' ' 'a 3 a 4

2

khi S' ' ' 'b3 b 4

2

khi S' ' ' 'c 3 c 4



17/19

Trong qu rnh kch, quy lut ng ngt i nghch phi tun th

S +S'= 1 S +S

'= 1x1 x1

;x 3 x 3

Vi x = a, b, c.S +S

'= 1, S +S

'= 1,x 2 x 2 x 4 x 4

Theo nh ngha vecto khng gian, ng ng 125 trng thi kch dn linh kin ta thu c 61

v tr vector khng gian ca vector in p to thnh. Ti tm ca c gic c nm trng hi khcnhau cho cng v tr ti l vector khng. Cc v tr cn li ng v cc trng thi c biu din

trong gin vecto in p b nghch lu p 5 bc.


t :

r t

l ti

r

- 22-2- 12-

2

02-

2

12 -222- 2

-22 -1

-12-1-11-

2

12-

1

22-

1

21-2- 21-2 02-

1

01-2 11-2

- 220-

120

020 - 10-

212000-2

22021-

120-2

- 21-1 - 20-2 -11-1

01 -111-1 10-2

- 221021 - 10-

1121221 00-1

10-1210 20-1 2-1-2

- 121

- 210

- 111

- 110

-20 -

1

-2-1-1

010 - 2-1-2 -1-1-2110

-2-2-2 1-2-20-1-2

-2

1-1-2

- 222

-12 2

- 211

-112

022

-20 0

-

101

122

011100

112

000111

222- 1-1-1

212

-211

10001-

1

0-2111

200

0-2-1

1-2-2

2-1-1

1-2-1

2-2-2

-21 2-

201

012

-

210

- 1-10001 101

0-

10

- 2-2-1 -1-2-1201

1-10 2-10 2-2-1

- 202

-

102

- 1-

11002

0-

11 1-11

0-

20

1-20-2-11 -2-

20

102 202

- 1-20 2-11 2-20

- 1-120-12 1-12 1-21

- 2-12 -2-21

-1-21

0-21 2-122-21

- 2-22 -1-22 0-22 1-22 2-22

Hnh 1.4. Gin vector in p b nghch lu p 5 bc

5. Cc dng sng mang trong k thut iu ch PWM.

Cc sng mang dng tam gic c tn s cao (fsm < 9500Hz). C th chia thnh ba loi nh sau:

5.1. B tr cng pha PD (Phase Dispostion).

Tt c cc loi sng mang u cng pha nhau:


18/19

Hnh 1.5: Sng mang dngPD



19/19


5.2. B tr k tip nhau APOD ( Alternative Phase Opposition Disposition).

Hai sng mang k tip nhau s dch 1800

Hnh 1.6: Sng mang dng APOD5.3. B tr i xng nhau qua trc 0 POD (Phase Opposition Disposition).

Tt c cc sng mang trn trc 0 s cng pha nhau v cc sng mang nm di trc 0 s b dch

i 1800.

5.4. Nhn xt.

Hnh 1.7: Sng mang dng POD

Trong cc phng php b tr sng mang, th thng php b tr cc sng mang a bc cng pha

(dng PD) cho mo dng p dy nh nht. Ring i vi b nghch lu p ba bc, phng php

POD v APOD c cng kt qu dng sng mang. Trong cc phn m phng sau, ta ch s dng

phng php sng mang dng PD.

cascade inverters awesome

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