tiểu luận Ðtcs

8/2/2019 Tiu Lun TCS

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Tiu Lun TCS_NC Phn A: Tng quan v b nghch luup da bc

PHN A: TNG QUAN V B NGHCH LUU A BC1. Tng quan1.1. t vn dTrong nhng nam gn dy, h thng din t cng sut duc pht trin rt mnh. Vi nhiul do,th nht: cc thit b din t cng sut ngy cng duc s dng nhiu, khng nhngtrong linh vc cng nghip m cn thm nhp vo c linh vc thuong mi v dn dng. Ldo th hai: do nhu cupht trin cc thit b s dng hiu qu v tit kim nang lung dng thi vi vic s dngngunnang lung mi nhu nang lung gi, nang lung mt tri.v.v trc tip noi tiu th.Cc b chuyn di ACDC (chnh luu, nghch luu, bin tn) ngy cng duc quan tmnghin

cu. dp ng cc nhu cu cng sut ln, cn phi nng cao din p v dng din. Tuynhin dokh nang chu dng v p ca cc linh kin din t cng sut c gii hn, nn song songvi vicpht trin cc linh kin cng sut ln, ngui ta dng gii php mc song song d to dngdin caov mc ni tip d tang din p. Gii php mc ni tip cho ra di cc cu trc mchnghch luu pda bc thay cho nghch luu p hai bc truyn thng. Mch nghch luu p da bc c nhiu uudim

nhu cng sut cao hon, cht lung din p v dng din ng ra tt hon, mch lc du ranh hon.so vi nghch luu p hai bc. Tuy nhin n cung c nhiu nhuc dim nhu cn nhiu linhkin hon,gii thut diu khin phc tp hon v v vy gi thnh cung dt hon.Nam 1980, Navae v cc cng s ca ng bt du nghin cu v nghch luu p da bc. Vdnnam 1981 ng d ngh cu hnh NPC (Neutral Point Clamped) cho nghch luu p 3 bc. Vsau, cuhnh ny duc pht trin cho nghch luu p da bc vi tn chung l cu hnh diode-clamped

converter (diode kp). Cu hnh ny c dng cu vi mi nhnh gm nhiu linh kinchuyn mchmc ni tip. Mt s cu hnh khc ra di mun hon gm floating capacitor converter (tkp) vcascade H-dridge converter. Cu hnh t kp c cu trc tuong t nhu cu hnh diode kp;cu hnhH-dridge duc xy dng bng cch ni tip cc mch nghch luu 2 bc co bn. Trong dcu hnh


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diode kp l cu hnh duc nghin cu v c nhiu ng dng nht.1.2 ng dng ca b nghch luu.ng dng trong cng nghipng dng trong dn dngng dng trong truyn ti h thng din

ng dng trong thuong ming dng trong phng th nghimDng lm ti liu trong ging dy2. Gii thiu b nghch luu p.B nghch luu p c nhim v chuyn di nang lung t ngun din mt chiu khng disangdng nang lung din xoay chiu d cung cp cho ti xoay chiu.GVHD: PGS. TS. Nguyn Van Nh Trang 5 HVTH: TruongMinh TriuTiu Lun TCS_NC Phn A: Tng quan v b nghch luu

p da bci lung duc diu khin ng ra l din p hoc dng din. Nu di lung duc diukhin ng ra l din p th b nghch luu duc gi l b nghch luu p, nguc li gi l b nghchluudng.Cc b nghch luu to thnh b phn ch yu trong b bin tn. ng dng quan trng vtuongdi rng ri ca chng nhm vo linh vc truyn dng din dng co xoay chiu vi dchnh xccao.Trong linh vc tn s cao, b nghch luu duc dng trong cc thit b l cm ng trung tn,thitb hn trung tn. B nghch luu cn ng dng lm ngun din xoay chiu cho nhu cu giadnh, lmngun din lin tc UPS, diu khin chiu sng v cn duc ng dng trong linh vc bnhuyncng sut phn khng2.1 Khi nim.B nghch luu p l mt b nghch luu c ngun mt chiu cung cp l ngun p v ditung

diu khin ng ra l din p. B nghch luu dng l b nghch luu c ngun mt chiucung cp lngun dng v di tung diu khin ng ra l ngun dng. Trn thc t ngun mt chiul ngunp v di tung nghin cu l b nghch luu p.B nghch luu p cung cp v diu khin din p xoay chiu ng ra, ngun din p mtchiu


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c th l: pin din, c quy, din p mt chiu duc chnh luu t din p xoay chiu c lcphng.Cc ti xoay chiu thung mang tnh cht cm khng (dng co xoay chiu, l cm ng),dngdin qua cc linh kin khng th dng ngt bng qu trnh chuyn mch t nhin. Do d,

linh kintrong b nghch luu p phi c kh nang kch dng, ngt dng qua n. Trong cc ng dngvi cngsut nh v va th c th s dng Transitor BJT, MOSFET, IGBT. Trong phm vi cngsut ln cth dng GTO, IGCT hoc SCR kt hp vi b chuyn mch. Vi ti tng qut, mi linhkin cnmc thm mt diode di song song d hn ch din p pht sinh khi kch ngt linh kin.2.2 Phn loi.B nghch luu p c nhiu loi cung nhu c nhiu phuong php diu khin khc nhau:

Theo s pha din p du ra: nghch luu p mt pha, ba pha.Theo s cp gi tr din p: d l s din p gia mt du pha ti dn mt dim din thchuntrn mch DC c: hai bc (two level), da bc (multilevel t ba bc tr ln).Khi nim b bin tn hai bc xut pht t din p mt du pha ti (pha a, b, c) vi dimchun(v tr ni dt) trn mch DC thay di gia hai bc khc nhau (Vv 0). B nghch luu p hai bcc nhuc dim l to din p cung cp cho cun dy dng co dv/dt kh ln v gy ra hintung

din p common mode (VN0DC

0) rt nghim trng. B nghch luu p da bc duc pht trin dgii quyt cc vn d gy ra nu trn ca b nghch luu p hai bc v thung duc s dngcho ccng dng din p cao v cng sut ln.Uu dim ca b nghch luu p da bc l cng sut ca b nghch luu tang ln, din p dtln cclinh kin gim xung nn cng sut tn hao do qu trnh dng ngt ca linh kin cung gimtheo

(switching losses); vi cng tn s dng ngt, cc thnh phn sng hi bc cao ca din pra gimnh hon so vi b nghch luu p hai bc.GVHD: PGS. TS. Nguyn Van Nh Trang 6 HVTH: TruongMinh TriuTiu Lun TCS_NC Phn A: Tng quan v b nghch luup da bcTheo cu hnh b nghch luu: dng cascade (cascade inverter), dng nghch luu cha cp


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diode kp NPC (neutral point clamped multilevel inverter)2.3. Cc phuong php diu khin b nghch luu p.Phuong php diu ch d rng xung sin (Sin PWM-sin pulse width modulation).Phuong php diu khin theo bin d.Phuong php diu ch d rng xung (SH-PWM).

Phuong php diu ch d rng xung ci bin (Modified PWM).Phuong php diu ch vector khng gian (SVPWM-space vector pulse width modulation).3. Cu trc co bn ca b nghch luu p da bc.3.1. Cu trc b nghch luu NPC.S dng thch hp khi cc ngun DC to nn t h thng din AC. B nghch luu da bcchacc cp diode kp c mt mch ngun DC duc phn chia thnh mt s cp din p nhhon nhchui cc t din mc ni tip.Gi s nhnh mch DC gm n ngun c d ln bng nhau mc ni tip. in p pha - tm

ngunDC (dim 0) c th dt duc (n+1) gi tr khc nhau v t d b nghch luu duc gi l bnghchluu p (n+1)bc.V d: xt hnh 1.1 bn dui, chn mc din th 0 cui dy ngun, cc mc din p cth dtduc gm (0, VDC

/2, 2VDC

/2, 3VDC/2,nV/2). in p t mt pha ti (v d pha a) thng dnmt v tr bt k trn nhnh DC (v d M) nh cp diode kp ti dim d (VD: D+

-

+

-

-

-

-

V

d

c

/

5

V

d

c

/

5

V

d

c

/

5

V

d

c

/

5

V

d

c

/

5

DC

din p pha tm ngun DC dt duc mc din p U0

a0

= V


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/5, tt c cc linh kin b kpgia hai diode (Da4Da2

Da3

Da4

D'a1

D'a2

D'a3

D'a4

, Da4S

5

a

S

3

a+

b

+

M

+

Da1

S

4

a

S

2

a

S

1

a

S

'

5

a

S

'

4

a

S

'

3

aS

'

2

a

S

'

1

a

Hnh 1.1 B nghch luu NPC) gm n linh kin mc ni tip lin tc k nhau SDC1a

GVHD: PGS. TS. Nguyn Van Nh Trang 7 HVTH: TruongMinh Triua4

, S

phi duc kch dng, cc linh kin cn li phi duc kho theo nguyn tc kch di nghch.Nhuhnh v trn, to ra su mc din p pha tm ngun DC (dim 0) nn mch nghch luu ptrn gil b nghch luu p su bc.a

c

, D5aa4

, S)4aN

, S3a

, S2a

Tiu Lun TCS_NC Phn A: Tng quan v b nghch luup da bc


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B nghch luu p da bc dng diode kp ci tin dng sng din p ti v gim Shock dinptrn linh kin n ln.Vi b nghch luu ba bc, dv/dt trn linh kin v tn s dng ct gimdi mtna. Tuy nhin vi n > 3, mc d chu gai p trn cc diode s khc nhau. Ngoi ra, cn

bng dinp gia cc ngun DC (p trn t) tr nn kh khan, dc bit khi s bc ln.3.1.1. Cc trng thi dng ngt ca b nghch luu NPC.Xt b nghch luu p nbc dng cha cp diode kp NPC (hnh 1.1). Gi V/5 l d ln din ptrong mi ngun ring l ph thuc d ln din p pha ngun VDC cn thit lp, cc linhkin bkp gia cc cp diode ni dn mt din th trn mch DC cn thit lp s trng thi kchdng.in p pha tm ngun DC tnh t dim du dy ca mt pha ti dn mt din th chun

(dim 0)trn mch DC.DC

Trng thi kch ngt ca cc kha bn dn trn mt nhnh pha ti ca cc pha a, b, c phithamn diu kin kch di nghch. Nu cc kha bn dn trn mt nhnh pha cng kch dngth gyngn mch ngun hoc khng duc php cng kch ngt.S

ja

+ Sja=1; S

jb

+Sjb

=1; Sjc

+ S=1 (1.1)Vi: j = 1, 2,3 (n-1)Gi n l dim nt ba pha ti dng sao di xng. Ta c din p ba pha ti:

u u u 00ta aN

;u u u 00tb bN


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;u u u

in p ua0

, ub0, uc000tc cN

gi l din p pha tm ngun ca pha a, b, c.Gi thit ti ba pha di xng, tho mn h thc:

u u u ta tb tc

u u u u in p Common mode:0 0 0 0a b c N

Ta c p ti :

030

u u uu0 0 00abcN

3

23u u uu u u0 0 000a b cta a N


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23u u uu u u

jc

(1.2)0000b ao ctb b N

23u u uu u u0 0 000c a btc c N

(1.3)

T d ta thy qu trnh din p v qu trnh dng din ng ra ca b nghch luu p ba phasduc xc dnh khi ta xc dnh duc cc din p nghch luu ua0

, ub0

, u.Nu ba pha ti dng tam gic, din p pha ti bng din p dy do b nghch luu cung cp:u u u ;00tab a bu u u ;00tbc b c

u u u (1.4)

3.1.2 Trng thi dng ngt b nghch luu NPC 5 bc.00tca c a


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c0

GVHD: PGS. TS. Nguyn Van Nh Trang 8 HVTH: TruongMinh TriuTiu Lun TCS_NC Phn A: Tng quan v b nghch luup da bcVdc/4

Vdc/4

0

S'4a

Vdc/4

Vdc/4pha a

S4a

S3bS3a

S2a

S1a S1b

S'3a

S'2a

S'1apha b

S4b

S2b

S'4b

S'3b

S'2b

S'1bpha c

S4cS3c

S2c

S1c

S'4c

S'3c

S'2c

S'1c

Xt pha a ca b nghch luu p nam bc dng diode kp. Gi V/4 l d ln din p trn mingun din ring l. Chn dim 0 tm ngun DC v tr gia, din p pha tm ngun DCdt cc

gi tr nhu trong bng sau:DCBng 1.1 Trng thi dng ngt ca b nghch luu p NPC 5 bcMc din p nghch luu V0

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

4Vd

234VV

(dd


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Hnh 1.2 So d nguyn l nghch luu NPC 3 pha 5 bcA0

Cc trng thi dng ngttuong ng(

((VVVV44d

4dd

4d,,,

GVHD: PGS. TS. Nguyn Van Nh Trang 9 HVTH: TruongMinh Triua

b

c

Trng thi dng ngt ca cclinh kin

,0,0,0)(1,0,0,0)VVV44dd

4d

,

,,0,0)(1,1,0,0)VV4d

4d


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,,0)(1,1,1,0)V)

(1,1,1,1)Ta thy c 5 mc din p ra tuong ng vi cc trng thi dng ngt cho mi pha. Vy c 5trngd

4thi dng ngt linh kin cho mi pha, nhu vy c 125 trng thi dng ngt cho ba pha. Vb nghchluu p c th to ra nam mc din p nn duc gi l b nghch luu p 5 bc3.1.3. Nhn xtVi cu trc nhu trn nn tn s dng ngt gim dn dn s ln chuyn mch trn cc phabnghch luu p gim, tn tht ca b nghch luu gim t d c kh nang nng cao cng sutca bnghch luu. V vy b nghch luu p da bc ngy cng duc s dng rng ri trong cc linhvccng sut cao, nhung bn cnh d vn cn c nhng uu v khuyt dim nhu sau:

Tiu Lun TCS_NC Phn A: Tng quan v b nghch luup da bcUu dim.Khi s bc d cao, thnh phn hi bc cao s d thp d khi s dng cc b lc.

Hiu sut cao v cc kho c th duc diu khin tn s dng ngt co bn (phuong phpPWMl ti uu).C th diu khin lung cng sut phn khng.Phuong php diu khin don gin cho h thng ni kt dng di song (back-to-back).Khuyt dim.Yu cu s dng qu nhiu diode khi s bc din p cao.Kh diu khin lung cng sut tch cc cho cc b bin di don.3.1.4. Cc cng thc lin quan.in p Offset:V V M V Min

(1.5)ax(u , u , u ), (u , u , u )ax t1 t2 t3 min t1 t2 t3om d o

Ch d medium common mode: V

o

=


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V

oMin

+ V

oMax

2(1.6)

Ch d gin don (Discontinuos): Vo

= VoMin

hoc Vo

= V(1.7)

in p diu khin:VVV V V nnV 00 dki dkidii

(vi n: s bc ca b nghc luu)

.( 1)

1dc

oMax

3.2. Cu trc b nghch luu Cascade H-dridge.S dng cc ngun DC ring, thch hp trong trung hp s dng ngun DC c sn, v dacquy,battery. Cascade inverter gm nhiu b nghch luu p cu mt pha ghp ni tip, cc bnghch luup dng cu mt pha ny c cc ngun DC ring.S kt hp hot dng ca nb nghch luu p trn mt nhnh pha ti s to nn n kh nang

mcdin p theo chiu m (-VDC

, -2VDC

, -3VDC

, -4V


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DC

, -nV), n kh nang mc din p theo chiuduong (VDC

, 2VDC

, 3VDC

, 4VDC

,nVDCDC

) v mc din p 0. Nhu vy, b nghch luu p dngcascade gm nb nghch luu p mt pha trn mi nhnh s to thnh b nghch luu (2n+1)bc.

GVHD: PGS. TS. Nguyn Van Nh Trang 10 HVTH: TruongMinh TriuTiu Lun TCS_NC Phn A: Tng quan v b nghch luup da bc

3.2.1. Cc trng thi dng ct ca b ngch luu Cascade 7 bc.Xt pha a ca b nghch luu p 7 bc dng Cascade H-dridge. Gi Vl d ln din p trn mingun din ring l. Chn dim 0 nhu trn th, din p pha Va0

DCdt cc gi tr nhu trong bng sau:Va0

(Va1

, Va2

, Va3

) (Va10

, Va11, Va20

, Va21

, Va30

, V


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a31

) (Saj

, S) 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(Vd,0,0);(0,Vd,0);(0,0,Vd)(Vd,Vd,-Vd)(Vd,-Vd,Vd)(-Vd,Vd,Vd)0(0,0,0)

VV

Va10a20a30

SSa1

S`a1

SS

Sa3

S`a3

SSS


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VVa11a21a5

Sà5

SVa31

Hnh 1.3 B nghch luu Cascade H-dridge 1 pha 7 bc(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)(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).a2à2a4à4a6à6

(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);VVVVa1a2a3

V0aàj

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


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(1,0,0,0,1,0);(1,0,1,1,1,0)(0,0,1,0,1,0);(1,1,1,0,1,0)(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);(0,0,0,0,1,1);(0,0,1,1,0,0);(0,0,1,1,1,1)(1,1,0,0,0,0);(1,1,0,0,1,1);GVHD: PGS. TS. Nguyn Van Nh Trang 11 HVTH: Truong

Minh TriuTiu Lun TCS_NC Phn A: Tng quan v b nghch luup da bc-Vd

(0,Vd,-Vd)(0,-Vd,Vd)(Vd,0,-Vd)(-Vd,0,Vd)(Vd,-Vd,0)(-Vd,Vd,0)(-Vd,0,0);(0,-Vd,0);(0,0,-Vd)(-Vd,-Vd,Vd)(-Vd,Vd,-Vd)(Vd,-Vd,-Vd)-2Vd

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


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(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).(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,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).

(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).(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).(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 xtVi cu trc nhu trn nn tn s dng ngt gim dn dn s ln chuyn mch trn cc phabnghch luu p gim, tn tht ca b nghch luu gim t d c kh nang nng cao cng sutca bnghch luu. V vy b nghch luu p da bc ngy cng duc s dng rng ri trong cc linhvccng sut cao, nhung bn cnh d vn cn c nhng uu v khuyt dim nhu sau:


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Uu dim.Cn s lung cc cu phn t nht d dt duc s bc din p cao nht.Vic ch to mch duc m dun ho do b nghch luu co bn c cu trc nhu nhau vkhng cnmc thm diode cung nhu t cn bng p nhu cc so d d k trn.

C th s dng chuyn mch mm d trnh mch bo v chng dV/dt cng knh v tnhao.Khuyt dim.Cn ngun DC dc lp cho vic chuyn di cng sut thc, do vy vic ng dng cn bhn ch.3.2.3. Cc cng thc lin quan.in p Offset :V nV M V nV Min (1.8)

(vi n: l s ngun c trong mch)

. ax(u , u , u ), . (u , u , u )ax t1 t2 t3 min t1 t2 t3om d o d

Ch d medium common mode: V

o

=V

oMin

+ V

oMax

2(1.9)

Ch d gin don (Discontinuos): Vo

= VoMin

hoc Vo

= V(1.10)

oMaxGVHD: PGS. TS. Nguyn Van Nh Trang 12 HVTH: TruongMinh TriuTiu Lun TCS_NC Phn A: Tng quan v b nghch luup da bc3.3. Nhn xt chung.


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C th diu khin b nghch luu p (bng cch diu khin tn hiu dng ngt ln cc linhkin)bng nhiu phuong php, mi phuong php thch hp vi mi loi ti khc nhau. Bnghch luu pda bc c phm vi hot dng vi ti cng sut ln do d vn d dt ra l gim bt tn s

dng ngtv gim shock din p trn linh kin cng sut c nghia quan trng. Chuong sau s mphng bnghch luu p da bc NPC, qua d s thy r duc tn s dng ngt ca cc linh kin bndn ducgim thiu dng k so vi cc phuong php diu khin b nghch luu p hin nay. Tn sdng ngtgim dn dn s ln chuyn mch trn cc pha b nghch luu p gim, tn tht ca bnghch luugim t d c kh nang nng cao cng sut ca b nghch luu . B nghch luu ngy cng

duc sdng rng ri trong cc linh vc cng sut cao.

4. Cc phuong php diu ch d rng xung.4.1 Phuong php diu ch d rng xung Sine (SH-PWM).Phuong php SH-PWM c tn nay d l Subharmonic Pulse Width Modulation . thchinto gin d kch dng cc linh kin trong cng mt pha ti, ta s dng mt s sng mang(dng tamgic) v mt tn hiu diu khin (dng sin). i vi b nghch luu p n bc, s sng mang

duc sdng l (n-1). Chng c cng tn s fc, v cng c bin d dnh dnh Ac. Sng diu ch(hay sngdiu khin) c bin d dnh dnh Am

v tn s f, dng sg ca n thay di chung quanh trc tmca h thng (n-1) sng mang. Nu sng diu khin ln hon sng mang no d th linh kintuongng duc sng mang d diu khin s duc kch dng. Trong trung hp sng diu khinnh hon

sng mang no d th linh kin s b kha kch.m

i vi b nghch luu p da bc ch s diu ch duc dnh nghia nhu sau:Vi: U: bin d thnh phn hi co bn to nn do phuong php diu ch.U

(1)m

: bin d thnh phn hi co bn dt duc.


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4.2 Phuong php diu ch d rng xung ci bin (SFO-PWM).base

UmU

(1.11)im khc bit so vi phuong php diu ch d rng xung d trnh by l sng diu ch(din pdiu khin) duc ci bin. Theo d mi sng diu ch duc cng thm tn hiu th tkhng (snghi bi ba). Tn ti nhiu kh nang to nn thnh phn th t khng, mt trong cc tn hiuth tkhng c th chn bng gi tr trung bnh ca gi tr tn hiu ln nht trong ba tn hiu diuch vitn hiu nh nht trong ba tn hiu diu ch- Phuong php SFO - PWM.Gi Va

, Vb

, Vl cc tn hiu diu khin ca phuong php diu ch PWM. Tn hiu diu khintheo phuong php SFO-PWM va duc m t c th biu din dui dng ton hc nhu sau:offsetc

(1.12)ax( , , ) min( , , )2M V V V V V VVa b c a b c

4.3. Phuong php diu ch vector khng gian.4.3.1. Khi nim vector khng gian.Ta gi s cho di lung 3 pha va

, v

b, vc

cn bng, tho h thc: va

+ vb

+ vc


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GVHD: PGS. TS. Nguyn Van Nh Trang 13 HVTH: TruongMinh Triu(1)bmase

=0 (1.13)

Tiu Lun TCS_NC Phn A: Tng quan v b nghch luup da bcThc hin php bin hnh t cc di lung ba pha vthc :13.( . . ),2 2 / 3

ja b c

(1.14)v k v a v a v a e ja

, v22

b

, vc

sang di lung vector theo hPhp bin hnh thc hin nhu trn duc gi l php bin hnh vector khng gian v dilung

duc gi l vector khng gian ca di lung ba pha.Hng s k c th chn vi cc gi tr khc nhau. Vi k = 2/3 ta c php bin hnh khngbo toncng sut. Vi2/ 3kphp bin hnh bo ton cng sut. minh ho c th cho khi nim ny ta xt cc di lung ba pha dng cosin nhu sau:(1.15)

Vector khng gian theo dnh nghia s l :Nhu vy, trong to d vung gc,

, vector khng gian c bin d V

s quay quanh trc to d vi tn s gc .4.3.2. Vector khng gian ca b nghch luu p da bc.Qu trnh dng ngt cc linh kin to ra din p ba pha ti. Theo l thuyt v khng gianvector


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th din p ba pha d c th biu din dui dng vector khng gian. V n s thay di nhycp trnhnh lc gic da bc. V tr ca mi vector din p trong khng gian s ph thuc vo cctrng thidng ngt kinh kin. Tin hnh kho st c th cho cc b nghch luu ba v nam bc d xc

dnhgin d vector khng gian din p.4.3.3. Gin d vector din p ca b nghch luu 5 bc.Vi b nghch luu nam bc, kh nang diu khin kch dn linh kin to nn 125 trng thikhcnhau. Ta xt mi trng thi minh ho bi t hp (ka

k), vi:k

=-2,-1,0,1,2ka

=-2,-1,0,1,2k

b

=-2,-1,0,1,2Cc h s trng thi kca

, kb

, kcb

kc

ph thuc vo cch quy uc truc. Ta tin hnh quy uc nhu sau:(s quy uc ny da vo bng trng thi dng ngt)

2 1 2 11 1 1 1

0 1, 0 1khi S S S S khi S S S Skhi S S S S khi S S S S1 2 3 4 1 2 3 4''a a a a b b b b 1 2 3 4 1 2 3 4' ' ' 'a a a a b b b b


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k khi S S S S k khi S S S Skhi S S S Skhi S S S S

1 2 3 4 1 2 3 4' ' 'a a a a a b b b b b

11211 2 3 4' ' ' 'a a a a

1 2 3 4a a a a

GVHD: PGS. TS. Nguyn Van Nh Trang 14 HVTH: TruongMinh Trium

bt du t v tr

2111khi S S S Skhi S S S S1 2 3 4

'c c c c 1 2 3 4''c c c c

, 0 11 1 1 12 1 2 1k khi S S S Skhi S S S S khi S S S S

khi S S S S khi S S S S

1 2 3 4' ' ' ' ' 'c c c c c 1 2 3 4 1 2 3 4' ' ' ' ' ' ' 'b b b b c c c c


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1 2 3 4 1 2 3 4b b b b c c c c

Tiu Lun TCS_NC Phn A: Tng quan v b nghch luup da bcTrong qu trnh kch, quy lut dng ngt di nghch phi tun th:

'11

SSSSxx

11,'22xx

;

'33

SSSSxx

11,'44

xxVi x = a, b, c.Theo dnh nghia vector khng gian, tuong ng 125 trng thi kch dn linh kin ta thu duc61v tr vector khng gian ca vector din p to thnh. Ti tm ca lc gic c nam trngthi khcnhau cho cng v tr ti d l vector khng. Cc v tr cn li ng vi cc trng thi ducbiu dintrong gin d vector din p b nghch luu p 5 bc.-222-221-212-220-202-22-1-210-121-211-122-111-200022-201-112-2-12-21-2


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-12-1-120-21-1021-110012-2-11-102-20-1020-20-2-11-1-210-101122011100121010112001

22-212-202-2-12-2-22-2-10-1-2-1-2-2-1-1-2-2-2

000111002102220120-10-201-122111000-1-1-1-2222211100-1-1-1101212-1-10

-2-2-1 -1-2-1-1-11-2-20-2-21-1-12-2-22-1-22-11-202-1-1-200-11-1-210-12

5. Cc dng sng mang trong k thut diu ch PWM.Cc sng mang dng tam gic c tn s cao (f12-101-211-100-2-1-2-20-1001-10-1-210-10-201-110-211-120-22


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1-22

sm11-222-12022101110-2-20-2-1

1-102011-212-1210-221-12002-111-20

Hnh 1.4. Gin d vector din p b nghch luu p 5 bccc di2-2220-121-21-1-21-2-12-101-2-22-1-12-21

< 9500Hz). C th chia thnh ba loi nhu sau:5.1. B tr cng pha PD (Phase Dispostion).Tt c cc loi sng mang du cng pha nhau:

Hnh 1.5: Sng mang dng PDcc diGVHD: PGS. TS. Nguyn Van Nh Trang 15 HVTH: TruongMinh Triu20-22-202-1-22-2-12-2-2

Tiu Lun TCS_NC Phn A: Tng quan v b nghch luup da bc5.2. B tr k tip nhau APOD ( Alternative Phase Opposition Disposition).Hai sng mang k tip nhau s dch 18005.3. B tr di 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 dui trc 0 s bdchdi 1800

.


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5.4. Nhn xt.Trong cc phuong php b tr sng mang, th thuong php b tr cc sng mang da bccng pha(dng PD) cho d mo dng p dy nh nht. Ring di vi b nghch luu p ba bc,

phuong phpPOD v APOD c cng kt qu dng sng mang. Trong cc phn m phng sau, ta ch sdngphuong php sng mang dng PD.

Hnh 1.6: Sng mang dng APODcc diHnh 1.7: Sng mang dng PODcc diGVHD: PGS. TS. Nguyn Van Nh Trang 16 HVTH: Truong

Minh Triu


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