bao cao lvtn tranquoc hoan0

Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh

SVTH: Trn Quc Hon 1/102

Mc lc

Mc lc ............................................................................................................................1

Tm tt lun vn..............................................................................................................4

Chng 1

TNG QUAN V B NGHCH LU P ....................................................................5

1. Gii thiu tng qut..............................................................................................5

1.1 B nghch lu p ...........................................................................................6

1.2 Phn loi b nghch lu p............................................................................6

2. Cc dng cu trc c bn ca b nghch lu p a bc........................................7

2.1 Cu trc dng Diode kp NPC (Diode Clamped Multilevel Inverter) .........7

2.2 Cu trc dng t in thay i (Flying Capacitor Multilevel Inverter)........9

2.3 Cu trc dng ghp tng (Cascade Inverter)...............................................10

2.4 So snh s linh kin s dng trong 3 dng nghch lu p a bc trn........12

3. Nhn xt..............................................................................................................12

Chng 2

CU TRC B NGHCH LU P A BC DNG CASCADE............................13

1. B nghch lu p cu 1 pha ................................................................................13

2. B nghch lu p a bc dng cascade...............................................................14

Chng 3

IU KHIN B NGHCH LU P A BC DNG CASCADE PHNG

PHP IU CH RNG XUNG (Carrier based PWM).....................................17

1. Tng qut v k thut iu ch rng xung PWM ......................................17

1.1 Mt s ch tiu nh gi k thut PWM ca b nghch lu .......................17

1.2 Cc dng sng mang dng trong k thut PWM ........................................18

2. Phng php iu ch rng xung Sin (Sin PWM)........................................20

2.1 Nguyn tc thc hin ..................................................................................20

2.2 M phng cho b nghch lu p cascade 5 bc ..........................................21

2.3 Kt qu m phng .......................................................................................26

2.4 Nhn xt ......................................................................................................29



3. Phng php iu ch rng xung ci bin ....................................................30

3.1 M phng cho b nghch lu p cascade 5 bc ..........................................31

3.2 Kt qu m phng .......................................................................................33

3.3 Nhn xt ......................................................................................................37

Chng 4

IU KHIN B NGHCH LU P A BC DNG CASCADE - PHNG

PHP IU CH VECTOR KHNG GIAN (Space Vector PWM) ..........................38

1. Khi nim vector khng gian .............................................................................38

1.1 Vector khng gian v php bin hnh vector khng gian ...........................38

1.2 Vector khng gian ca b nghch lu p a bc.........................................39

2. Phng php iu ch vector khng gian ..........................................................41

3. Nhn xt..............................................................................................................44

Chng 5

IU KHIN B NGHCH LU P A BC DNG CASCADE PHNG

PHP IU CH VECTOR KHNG GIAN DNG SNG MANG ........................45

1. Tng qut v phng php iu ch vector khng gian dng sng mang.........45

1.1 tng tng qut ca phng php...........................................................45

1.2 Gii thut iu ch ca phng php..........................................................47

2. ng dng cho b nghch lu p a bc dng cascade........................................54

3. M phng cho b nghch lu cascade 5 bc ......................................................57

3.1 Ch Medium common mode SVPWM...............................................57

3.2 Ch Minimum common mode SVPWM ............................................63

3.3 Ch Minimum common mode DPWM...............................................63

3.4 Ch Medium common mode DPWM .................................................63

4. Nhn Xt.............................................................................................................63

Chng 6

IU KHIN B NGHCH LU A BC DNG CASCADE VI NGUN DC

KHNG CN BNG...................................................................................................63

1. M phng cho trng hp ngun DC khng cn bng......................................63

1.1 Thc hin m phng ...................................................................................63

1.2 Kt qu m phng .......................................................................................63



2. Phng php iu khin b nghch lu p a bc vi ngun DC khng cn bng

............................................................................................................................63

2.1 Nguyn l iu ch .....................................................................................63

2.2 ng dng cho b nghch lu a bc dng cascade.....................................63

3. M phng iu khin b nghch lu cascade vi ngun DC khng cn bng...63

3.1 Chng trnh trong khi DLL.....................................................................63

3.2 M phng trong trng hp ngun khng cn bng l ngun DC.............63

3.3 M phng trong trng hp ngun khng cn bng c ly t b chnh

lu cu 3 pha diode................................................................................................63

4. Nhn xt..............................................................................................................63

Kt lun..........................................................................................................................63

Ti liu tham kho .........................................................................................................63



Tm tt lun vn

Lun vn thc hin nhim v nghin cu k thut iu ch rng xung - PWM

(Pulse Width Modulation) cho b nghch lu a bc ghp tng (Cascade inverter).

Thng qua m phng trong Psim nh gi cht lng in p v dng in ti t

c theo tng phng php.

Chng 1: Gii thiu tng qut v cu to, u nhc im v phn loi cc dng

mch ca b nghch lu p a bc.

Chng 2: Gii thiu cu to b nghch lu p cu 1 pha, b nghch lu p 5 bc

dng cascade v dng in p ti.

Chng 3: Trnh by k thut iu ch rng sung sin cho b nghch lu p

dng cascade 5 bc.

Chng 4: Gii thiu l thuyt v phng php iu ch vector khng gian cho

b nghch lu p a bc.

Chng 5: Trnh by phng php iu ch vector khng gian dng sng mang

cho b nghch lu p a bc, thc hin m phng iu khin b nghch lu p dng

cascade 5 bc trong trng hp ngun cn bng.

Chng 6: Trnh by phng php iu ch vector khng gian dng sng mang

cho b nghch lu p a bc vi ngun DC khng cn bng.



Chng 1

TNG QUAN V B NGHCH LU P

1. Gii thiu tng qut

B nghch lu 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.

i lng c iu khin ng ra l in p hoc dng in, tng ng ta c b

nghch lu c gi l b nghch lu p v b nghch dng.

Ngun mt chiu cung cp cho b nghch lu p c tnh cht ngun in p v

ngun cho b nghch lu dng c tnh cht l ngun dng in. Cc b nghch lu

tng ng c gi l b nghch lu p ngun p v b nghch lu dng ngun dng

hoc gi tt l b nghch lu p v b nghch lu dng.

Trong trng hp ngun in u vo v i lng ng ra khng ging nhau,

v d b nghch lu cung cp dng in xoay chiu t ngun in p mt chiu, ta gi

chng l b nghch lu iu khin dng in t ngun in p hoc b nghch lu

dng ngun p.

Cc b nghch lu to thnh b phn ch yu trong cu to ca 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 xc cao. 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. B nghch lu

cn c dng lm ngun in xoay chiu cho nhu cu gia nh, lm ngun in lin

tc UPS, iu khin chiu sng, b nghch lu cn c ng dng vo lnh vc b

nhuyn cng sut phn khng.

Cc ti xoay chiu thng mang tnh cm khng (v d ng c khng ng b,

l cm ng), dng in qua cc linh kin khng th ngt bng qu trnh chuyn mch

t nhin. Do , mch b nghch lu thng cha linh kin t kch ngt c th iu

khin qu trnh ngt dng in.

Trong cc trng hp c bit nh mch ti cng hng, ti mang tnh cht dung

khng (ng c ng b kch t d), dng in qua cc linh kin c th b ngt do qu



trnh chuyn mch t nhin ph thuc vo in p ngun hoc ph thuc vo in p

mch ti. Khi linh kin bn dn c th chn l thyristor (SCR).

1.1 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 dng n gin nh acquy, pin in hoc dng phc tp

gm in p xoay chiu c chnh lu v lc phng.

Linh kin trong b nghch lu p c kh nng kch ng v kch ngt dng in

qua n, tc ng vai tr mt cng tc. Trong cc ng dng cng sut va v nh, c

th s dng transistor BJT, MOSFET, IGBT lm cng tc v phm vi cng sut ln

c th s dng GTO, IGCT hoc SCR kt hp vi b chuyn mch.

Vi ti tng qut, mi cng tc cn trang b mt diode mc i song vi n. Cc

diode mc i song ny to thnh mch chnh lu cu khng iu khin c chiu dn

in ngc vi chiu dn in ca cc cng tc. Nhim v ca b chnh lu cu diode

l to iu kin thun li cho qu trnh trao i cng sut o gia ngun mt chiu v

ti xoay chiu, qua hn ch qu in p pht sinh khi kch ngt cc cng tc.

1.2 Phn loi b nghch lu p

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

nhau.

Theo s pha in p u ra: 1 pha, 3 pha. Theo s bc in p gia mt u pha ti v mt im in th chun trn

mch (phase to pole voltage): 2 bc (two level), a bc (multi level , t 3

bc tr ln).

Theo cu hnh ca b nghch lu: dng cascade (Cascade inverter), dng diode kp NPC (Neutral Point Clamped Multilevel Inverter), hoc dng

dng t in thay i (Flying Capacitor Multilevel Inverter)

Theo phng php iu khin: Phng php iu rng. Phng php iu bin. Phng php iu ch rng xung sin (Sin PWM). Phng php iu ch rng sung sin ci bin (Modifield SPWM).



Phng php iu ch vector khng gian (Space vector modulation, hoc Space vector PWM).

Phng php Discontinuous PWM. 2. Cc dng cu trc c bn ca b nghch lu p a bc

C 3 dng thng c s dng trong b nghch lu p a bc:

Dng diode kp NPC (Diode Clamped Multilevel Inverter). Dng dng t in thay i (Flying Capacitor Multilevel Inverter). Dng ghp tng cascade (Cascade Inverter).

2.1 Cu trc dng Diode kp NPC (Diode Clamped Multilevel Inverter)

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 - ngun DC (phase to pole voltage) 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 (nh hnh 1.1) chn

mc in th 0 cui dy ngun, cc mc in p c th t c gm (0, U, 2U,

3U,nU). in p t mt pha ti (v d pha a) thng n mt v tr bt k trn mch

DC (v d M) nh cp diode kp ti im (v d D1, D1). in p pha - ngun

DC t c mc in p nu trn (Uao = U), tt c cc linh kin b kp gia hai diode

(D1, D1) - gm n linh kin mc ni tip lin tc k nhau, phi c kch ng (v d

S1, S5, S4, S3, S2), cc linh kin cn li phi c kho theo nguyn tc kch i

nghch. Tng ng vi su trng hp kch ng linh kin b kp gia su cp diode,

ta thu c su mc in p pha - ngun DC: 0, 1U, 2U, 3U, 4U, 5U. V c kh nng

to ra su mc in p pha - ngun DC nn mch nghch lu trn H1.1 gi l b

nghch lu 6 bc.

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.



Hnh 1.1: Diode Clamped Multilevel Inverter NPC.

Bng 1.1: in p ra ca B nghch lu NPC ng vi cc trng thi kch ng.

Vout=Vxo Sx5 Sx4 Sx3 Sx2 Sx1 Sx5 Sx4 Sx3 Sx2 Sx1

Vxo = 5U 1 1 1 1 1 0 0 0 0 0

Vxo = 4U 0 1 1 1 1 1 0 0 0 0

Vxo = 3U 0 0 1 1 1 1 1 0 0 0

Vxo = 2U 0 0 0 1 1 1 1 1 0 0

Vxo = U 0 0 0 0 1 1 1 1 1 0

Vxo = 0 0 0 0 0 0 1 1 1 1 1

Vi x = a, b, c.



2.2 Cu trc dng t in thay i (Flying Capacitor Multilevel Inverter)

Hnh 1.2: Flying Capacitor Multilevel Inverter.

u im chnh ca nghch lu dng ny l:

Khi s bc tng cao th khng cn dng b lc. C th iu tit cng sut tc dng v phn khng nn hin c vic

iu tit cng sut.

Mi nhnh c th c phn tch c lp vi cc nhnh khc. Khng nh nghch lu a bc dng NPC khi phn tch phi quan tm n cn

bng in p ba pha ng vo.

Nhc im:

S lng t cng sut ln tham gia trong mch nhiu, dn n gi thnh tng v tin cy gim.

Vic iu khin s kh khn khi s bc ca nghch lu tng cao.



2.3 Cu trc dng ghp tng (Cascade Inverter)

Hnh 1.3: Cascade Inverter.

S dng cc ngun DC ring, thch hp trong trng hp s dng ngun DC c

sn, v d di dng 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.

Bng cch kch ng cc linh kin trong mi b nghch lu p mt pha, ba mc

in p (-U, 0, U) c to thnh. S kt hp hot ng ca n b nghch lu p trn

mt nhnh pha ti s to nn n kh nng mc in p theo chiu m (-U, -2U, -3U,

-4U,... nU), n kh nng mc in p theo chiu dng (U, 2U, 3U, 4U,nU) v mc

in p 0. Nh vy, b nghch lu p dng cascade gm n b nghch lu p mt pha

trn mi nhnh s to thnh b nghch lu (2n+1) bc.



Tn s ng ngt trong mi module ca dng mch ny c th gim i n ln v

dv/dt cng gim i nh vy. in p trn p t ln cc linh kin gim i 0,57n ln,

cho php s dng IGBT in p thp.

Ngoi dng mch gm cc b nghch lu p mt pha, mch nghch lu p a bc

cn c dng ghp t ng ra ca cc b nghch lu p ba pha. Cu trc ny cho php

gim dv/dt v tn s ng ngt cn 1/3. Mch cho php s dng cc cu hnh nghch

lu p ba pha chun. Mch nghch lu t c s cn bng in p cc ngun DC,

khng tn ti dng cn bng gia cc module. Tuy nhin, cu to mch i hi s

dng cc my bin p ng ra.

Hnh 1.4: Cascade Inverter s dng b nghch lu p ba pha.



2.4 So snh s linh kin s dng trong 3 dng nghch lu p a bc trn

Bng 1.2 so snh s linh kin c s dng trong mi pha ca 3 dng nghch lu

k trn. Ta thy, s cng tc IGBT v s diode mc i song c s dng trong mi

dng nghch lu cng bc l nh nhau. Diode kp th khng cn trong dng t thay i

v dng cascade inverter, trong khi t cn bng th khng cn cho dng diode kp

v cascade inverter. Tm li, dng cascade inverter l s dng t linh kin nht.

Bng 1.2: So snh s linh kin trong 1 pha ca 3 dng nghch lu.

Cu hnh

nghch lu Diode kp NPC T thay i Cascade inverter

Cng tc IGBT 2(n-1) 2(n-1) 2(n-1)

Diode i song 2(n-1) 2(n-1) 2(n-1)

Diode kp (n-1)(n-2) 0 0

T trn ngun DC (n-1) (n-1) (n-1)/2

T cn bng 0 (n-1)(n-2)/2 0

Mt u im khc ca cascade inverter l cu hnh c th thay i linh hot, ta c

th tng hoc gim s bc mt cch d dng, bng cch thm hoc bt s b nghch

lu cu 1 pha tng ng.

3. Nhn xt

u im ca b nghch lu p a bc: cng sut ca b nghch lu p tng ln;

in p t ln cc linh kin b gim xung nn cng sut tn hao do qu trnh ng

ngt cc linh kin cng gim theo; vi cng tn s ng ngt, cc thnh phn sng hi

bc cao ca in p ra gim nh hn so vi trng hp b nghch lu p 2 bc.

i vi ti cng sut ln, in p cung cp cho cc ti c th t gi tr tng i

ln.



Chng 2

CU TRC B NGHCH LU P A BC DNG CASCADE

1. B nghch lu p cu 1 pha

B nghch lu p mt pha dng mch cu (cn c gi l b nghch lu p dng

ch H) cha bn cng tc v bn diode mc i song.

Hnh 2.1: B nghch lu p cu 1 pha.

Quy tc kch ng i nghch: cp cng tc trn cng mt nhnh khng c kch

ng ng thi, tc l 2 cng tc trn cng mt nhnh lun trong trng thi mt

c kch ng v mt c kch ngt. Trng thi c 2 cng kch ng (trng thi

ngn mch in p ngun) hoc cng kch ngt khng c php xy ra.

Nu biu din trng thi c kch ng ca linh kin l 1 v trng thi c kch

ngt l 0 th ta c:

S1 + S4 = 1 (2.1)

S2 + S3 = 1

Bng cch iu khin ng ngt cc kha ta c th thu c in p xoay chiu

ng ra ca b nghch lu. in p ng ra trn 2 im A, B ca b nghch lu thay

i gia 3 trng thi +V, 0, -V. in p ca b nghch lu c to ra nh sau: kha

S1 v S2 ng thi c kch ng s to ra in p VAB = +V, kha S3 v S4 ng

thi kch ng s to ra in p VAB = -V v khi (S1, S3) hoc (S4, S2) c kch

ng s to ra mc in p 0.



Hnh 2.2: Dng in p ng ra b nghch lu cu 1 pha.

2. B nghch lu p a bc dng cascade

B nghch lu p a bc dng cascade nh gii thiu trn, c cu to gm

nhiu b nghch lu p cu mt pha ghp ni tip vi nhau. Mt b nghch lu p

dng cascade n bc th trn mi nhnh pha s c (n-1)/2 b nghch lu p cu mt pha

ghp ni tip vi nhau.

Ta xt b nghch lu p 5 bc dng cacade: cu to gm 2 b nghch lu p cu 1

pha ghp ni tip, mi b c cung cp bi 1 ngun in p DC ring bit. in p

ng ra ca mi b nghch lu p cu mt pha c 3 bc (V, 0, +V), do in p ng

ra ca b nghch lu cascade s c 5 bc (-2V, -V, 0, +V, +2V).

Hnh 2.3: Cu trc mch ca b nghch lu p 5 bc dng cascade.



Trng thi ng ngt cc cng tc trong 1 nhnh pha phi tha mn iu kin kch

ng i nghch:

S1x + S4x = 1; S2x + S3x = 1 (2.2)

S1x + S4x = 1; S2x + S3x = 1

Ty theo trng thi ng ngt, in p pha tm ngun DC (phase to pole

voltage) ca b nghch lu c tnh theo cng thc sau:

Vx out = Vxo = Vx 01 + Vx 02 (2.3)

Vi x = A, B, C

Hnh 2.4: Biu din 1 pha ca cascade inverter 5 bc.

in p pha ti trong trng hp 3 pha ti i xng u dng sao Y c th c

thit lp tng t nh trng hp b nghch lu p 2 bc:

Uta = 32 000 cba uuu ; Utb = 3

2 000 acb uuu ; Utc = 32 000 bac uuu (2.4)

Trong trng hp 3 pha ti dng tam gic, in p pha ti bng in p dy do b

nghch lu cung cp:

Ut ab = uao ubo ; Ut bc = ubo uco ; Ut ca = uco uao (2.5)

V tng in p t cc pha n tm ngun DC (common mode voltage):

UNO = 3coboao uuu ++ (2.6)



Hnh 2.5: Dng in p ng ra ca b nghch lu cascade 5 bc.

Bng 2.1: in p ng ra ng vi cc trng thi ng ngt ca cascade inverter 5 bc.

Vout = Vx0 V01 V02 Sx1 Sx2 Sx3 Sx4 Sx1 Sx2 Sx3 Sx4 Vx0 = +2V +V +V 1 1 0 0 1 1 0 0

+V 0 1 1 0 0 1 0 1 0

+V 0 1 1 0 0 0 1 0 1

0 +V 1 0 1 0 1 1 0 0 Vx0 = +V

0 +V 0 1 0 1 1 1 0 0

+V -V 1 1 0 0 0 0 1 1

-V +V 0 0 1 1 1 1 0 0

0 0 1 0 1 0 1 0 1 0

0 0 1 0 1 0 0 1 0 1

0 0 0 1 0 1 1 0 1 0

Vx0 = 0

0 0 0 1 0 1 0 1 0 1

-V 0 0 0 1 1 1 0 1 0

-V 0 0 0 1 1 0 1 0 1

0 -V 1 0 1 0 0 0 1 1 Vx0 = -V

0 -V 0 1 0 1 0 0 1 1

Vx0 = -2V -V -V 0 0 1 1 0 0 1 1



Chng 3

IU KHIN B NGHCH LU P A BC DNG

CASCADE PHNG PHP IU CH RNG

XUNG (Carrier based PWM)

Cc b nghch lu p thng c iu khin da theo k thut iu ch rng

xung PWM (Pulse Width Modulation) v qui tc kch ng i nghch. Qui tc kch

ng i nghch m bo dng p ti c iu khin tun theo gin kch ng

cng tc v k thut iu ch rng xung c tc dng hn ch ti a cc nh hng

bt li ca sng hi bc cao xut hin pha ti.

Ph thuc vo phng php thit lp gin kch ng cc cng tc trong b

nghch lu p, ta c th phn bit cc dng iu ch rng xung khc nhau.

1. Tng qut v k thut iu ch rng xung PWM

1.1 Mt s ch tiu nh gi k thut PWM ca b nghch lu

Ch s iu ch (Modulation Index) m: c nh ngha nh t s gia bin thnh phn hi c bn to nn bi phng php iu khin v bin

thnh phn hi c bn t c trong phng php iu khin su bc

(sixstep)

m = sixstepsm

m

UU

11 =

d

m

V

U

2

1 (3.1)

vi Vd _ tng in p cc ngun DC.

mo dng tng do sng hi THD (Total Harmonic Distortion) L i lng dng nh gi tc dng ca cc sng hi bc cao (2,3) xut

hin trong ngun in, c tnh theo:

THDI = )1(

1

2)(

I

Ij

j (3.2)

mo dng trong trng hp dng in khng cha thnh phn DC c tnh

theo h thc sau:



THDI = )1(

2

2)(

I

Ij

j= =

)1(

2)1(

2

III

(3.3)

Trong I(j): tr hiu dng sng hi bc j, j 2. I(1): tr hiu dng thnh phn hi c bn ca dng in.

Tn s ng ngt v cng sut tn hao do ng ngt: Cng sut tn hao xut hin trn linh kin bao gm hai thnh phn: tn hao cng

sut khi linh kin trng thi dn in Pon v tn hao cng sut ng Pdyn. Tn hao

cng sut Pdyn tng ln khi tn s ng ngt ca linh kin tng ln. Tn s ng ngt

ca linh kin khng th tng ln ty v nhng l do sau:

Cng sut tn hao trn linh kin tng ln t l vi tn s ng ngt. Linh kin cng sut ln thng gy ra cng sut tn hao ng ngt ln

hn. Do , tn s kch ng ca n phi gim cho ph hp, v d cc

linh kin GTO cng sut MW ch c th ng ngt tn s khong

100Hz.

Cc qui nh v tng thch in t (Electromagnet Compatibility EMC) qui nh kh nghim ngt i vi cc b bin i cng sut

ng ngt vi tn s cao hn 9KHz.

1.2 Cc dng sng mang dng trong k thut PWM

Hai sng mang k cn lin tip nhau s b dch 180 - APOD (Alternative Phase Opposition Disposition)

Hnh 3.1: Hnh dng sng mang APOD.



B tr cng pha PD (In Phase Disposition): tt c cc sng mang u cng pha.

Hnh 3.2: Hnh dng sng mang PD.

B tr i xng qua trc zero POD (Phase Opposition Disposition): cc sng mang nm trn trc zero s cng pha nhau, ngc li cc sng mang

cng nm di trc zero s b dch i 180 .

Hnh 3.3: Hnh dng sng mang POD.

Trong cc phng php b tr sng mang, phng php b tr cc sng mang a

bc cng pha PD cho mo dng p dy nh nht. i vi b nghch lu p ba

bc, phng php POD v APOD cho cng kt qu dng sng mang.



2. Phng php iu ch rng xung Sin (Sin PWM)

Phng php cn c tn Subharmonic PWM (SH PWM), hay Multi carrier

based PWM.

2.1 Nguyn tc 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).

V nguyn l, phng php c thc hin da vo k thut analog. Gin

kch ng cc cng tc ca b nghch lu da trn c s so snh hai tn hiu c bn:

Sng mang up (carrier signal) tn s cao, c th dng tam gic. Sng iu khin ur (reference signal) hoc sng iu ch (modulating

signal) dng sin. V d, cng tc l c kch ng khi sng iu

khin ln hn sng mang (ur > up). Trong trng hp ngc li, cng

tc chn c kch ng.

Tn s sng mang cng cao, lng sng hi bc cao xut hin trong dng in p

v dng in ti b kh cng nhiu.

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 bin nh - nh Ac. Sng iu ch (hay sng iu khin) c

bin nh bng Am v tn s fm, dng sng ca n thay i xung quanh trc tm ca

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

kin tng ng vi sng mang s c kch ng, ngc li nu sng iu khin

nh hn sng mang th linh kin s b kho kch.

Gi mf l t s iu ch tn s ( frequency modulation ratio):

mf = reference

carrier

ff =

m

c

ff (3.4)

Vic tng gi tr mf s dn n vic tng gi tr tn s cc sng hi xut hin.

im bt li ca vic tng tn s sng mang l vn tn hao do s ln ng ct ln

Tng t, gi ma l t s iu ch bin (amplitude modulation ratio):

ma = carrierm

referencem

UU

= c

m

AnA

).1( (3.5)



Nu ma 1 (bin sng sin nh hn tng bin sng mang) th quan h gia thnh phn c bn ca in p ra v in p iu khin l tuyn tnh.

Hnh 3.4: Quan h gia bin sng mang v sng iu khin.

Khi gi tr ma > 1, bin tn hiu iu ch ln hn tng bin sng mang th

bin hi c bn ca in p ra tng khng tuyn tnh theo ma. Lc ny, bt u xut

hin lng sng hi bc cao tng dn cho n khi t mc gii hn cho bi phng

php 6 bc. Trng hp ny cn c gi l qu iu ch (overmodulation) hoc

iu ch m rng.

Phng php Sin PWM t c ch s iu ch ln nht trong vng tuyn tnh

khi bin sng iu ch bng tng bin sng mang :

mSPWM_max = stepsixm

m

UU

_)1(

)1(

=

U

U

2

2/ = 4 = 0.785 (3.6)

trong U_tng in p cc ngun DC.

2.2 M phng cho b nghch lu p cascade 5 bc

2.2.1 Phn tch cch to xung kch Phn tch cho mt pha (v d pha a), xung kch cho cc linh kin c thit lp

da trn c s so snh sng iu khin Udka v cc sng mang Vp1, Vp2, Vp3, Vp4, c

th nh sau:



Udka > Vp1 S1 = 1; S4 = 0 Udka > Vp2 S2 = 1; S3 = 0 Udka > Vp3 S1 = 1; S4 = 0 (3.7) Udka > Vp4 S2 = 1; S3 = 0

Ta xc nh c in p pha tm ngun (phase to pole voltage):

Uao =

d

d

d

d

VV

VV

2

0

2

(3.8)

T y ta hon ton c th xc nh c in p ti trn cc pha nh trnh

by trong (2.4) v (2.5).

Hnh 3.5: S xung kch 1 pha ca BNL p 5 bc.



2.2.2 Phn tch cc trng hp iu khin iu khin b nghch lu p dng cascade phi tha mn yu cu l cng sut tn

hao trn cc linh kin trong mt chu k phi tng i bng nhau, tc l cc b nghch

lu cu mt pha cn phi t c trng thi cn bng cng sut (khong thi gian dn

v ngt phi tng i u nhau). Mun vy ta phi b tr cc sng mang sao cho t

c cc yu cu trn. Di y phn tch cc trng hp ng ngt ca b nghch lu

cu mt pha trong mt chu k p iu khin: c 4 trng hp tng ng vi 4 khong

gi tr ca in p iu khin.

Hnh 3.6: Cc khong gi tr ca Vref.

Trng hp 1: 2Vd Vd Vref 0 C 2 cch iu khin:

C nh in p ng ra ca b nghch lu H1 vi V01 = 0, iu khin b nghch lu H2 sao cho in p ng ra thay i ty theo Vref .

iu khin b nghch lu H1 sao cho in p ng ra thay i theo gi tr Vref, c nh in p ng ra ca b nghch lu H2 sao cho V02 = 0.

Trng hp 2: 2Vd Vref Vd 0 C 2 cch iu khin:



C nh in p ng ra ca b nghch lu H1 sao cho V01 = Vd, iu khin b nghch lu H2 sao cho in p tng ca c 2 b nghch lu

t c gi tr mong mun V0 = V01 + V02 = Vref.

iu khin b nghch lu H1 sao cho tng in p V0 = Vref , c nh in p ng ra ca b nghch lu H2 sao cho V02 = Vd.

Trng hp 3: 0 Vref -Vd -2Vd C 2 cch iu khin:

C nh in p ng ra ca b nghch lu H1 sao cho V01 = 0, iu khin b nghch lu H2 sao cho tng in p ng ra l V0 = Vref.

iu khin b nghch lu H1 sao cho tng in p ng ra V0 = Vref, c nh in p ng ra b nghch lu H2 sao cho V02 = 0.

Trng hp 4: 0 -Vd Vref -2Vd C 2 cch iu khin:

C nh in p ng ra ca b nghch lu H1 sao cho V01 = -Vd, iu khin b nghch lu H2 sao cho tng in p ng ra l V0 = Vref.

iu khin b nghch lu H1 sao cho tng in p ng ra ca c 2 b l V0 = Vref , c nh in p ca b nghch lu H2 sao cho V02 = -Vd.

Vy t c s cn bng cng sut gia cc b nghch lu cu mt pha, ta

chn phng n iu khin nh sau:

Trng hp 1 (2Vd Vd Vref 0): c nh in p ca b nghch lu H2 sao cho V02 = 0, iu khin b nghch lu H1 sao cho V01 = Vref.

Trng hp 2 (2Vd Vref Vd 0): c nh in p ng ra ca b nghch lu H1 sao cho V0 = Vd , iu khin b nghch lu H2 sao cho tng in p

t c V0 = Vref.

Trng hp 3 (0 Vref -Vd -2Vd): c nh in p ca b nghch lu H2 sao cho V02 = 0, iu khin b nghch lu H1 sao cho V02 = Vref.

Trng hp 4 (0 -Vd Vref -2Vd): c nh in p ng ra ca b nghch lu H1 sao cho V01 = -Vd, iu khin b nghch lu H2 sao cho tng in

p ca 2 b nghch lu V0 = Vref.

Do ta b tr sng mang vi dng nh sau:



Hnh 3.7: Dng b tr cc sng mang PD.

2.2.3 Cc thng s m phng trong Psim so snh kt qu gia cc phng php iu ch, t y v sau ta thng nht

kho st cc phng php vi ch s iu ch m t (0 1) quy chun nh sau:

Khi m = 1 th in p ti t cc i Ut(1)m = Ud / 3 . Vy ng vi m bt k ta c Ut(1)m = m.

3dU

Khi bin tn hiu iu khin udk = (n-1)/2 th Ut(1)m = Ud/2. Vy ng vi Ut(1)m = m.

3dU th bin tn hiu iu khin c tnh theo:

udk = 3

)1.( nm (3.9)

vi n l s bc ca b nghch lu.

Ud l tng in p cc ngun DC (v d i vi b nghch lu cascade 5 bc

nh trn th Ud = 4Vd).

S m phng b nghch lu p 5 bc dng cascade theo phng php PWM

(bn v A3). Cc thng s m phng:

Ch s iu ch m = 0.7. Sng iu khin c tn s 50Hz, sng mang dng PD tn s 2000 Hz. Cc ngun DC c gi tr Vd = 200V. Ti RL u dng sao (Y) c R = 5 , L = 0.01H (cos = 0.85), hng s

thi gian =RL = 2 ms.



2.3 Kt qu m phng

Hnh 3.8: Tn hiu in p iu khin trn 3 pha A, B, C.

Hnh 3.9: in p pha tm ngun trn pha A (phase to pole voltage).

Hnh 3.10: in p pha tm ngun DC ca pha B.



Hnh 3.11: in p pha tm ngun DC trn pha C.

Hnh 3.12: in p ti trn pha A.

Hnh 3.13: in p ti trn pha B.



Hnh 3.14: in p ti trn C.

Hnh 3.15: Phn tch Fourier cho in p ti trn pha A.

Hnh 3.16: Dng in ti trn pha A.



Hnh 3.17: Dng in ti trn 3 pha A, B, C.

Hnh 3.18: in p ng ra ca 2 b nghch lu cu mt pha.

2.4 Nhn xt

in p ng ra ca b nghch lu c dng 5 bc, gn vi dng sin hn so vi in

p ng ra ca b nghch lu cu 1 pha (dng ch H, ba bc).

Sng hi bc cao vn cn tn ti trong dng in p trn ti, nu tn s sng

mang cng ln th lng sng hi xut hin s gim.

Thi gian qu ca dng in trn 3 pha nh, do dng in nhanh chng t

c trng thi xc lp.



Dng in ti trn 3 pha trong trng thi xc lp l cn bng.

Trong 1 chu k khong ng v ngt ca mi b nghch lu cu 1 pha l tng

i u nhau.

3. Phng php iu ch rng xung ci bin

Phng php cn c tn l Modified PWM hoc Switching Frequency optimal

PWM method SFO PWM.

K thut iu khin tng t nh phng php iu ch rng xung va trnh

by, im khc bit l sng iu ch c ci bin. Theo , mi sng iu ch c

cng thm tn hiu th t khng (sng hi 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 tr

trung bnh ca gi tr tn hiu ln nht trong 3 tn hiu iu ch vi tn hiu nh nht

trong 3 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 c th biu din di dng ton hc

nh sau:

Voffset = 2),,min(),,max( cbacba VVVVVV + (3.10)

VaSFO = Va Voffset ; VbSFO = Vb Voffset ; VcSFO = Vc - Voffset (3.11)

Phng php ny cho php thc hin iu khin tuyn tnh in p ti vi ch s

iu ch nm trong phm vi 0 m 0.907, bin sng hi in p t gi tr cc i bng U/ 3 v tng ng ch s iu ch lc l:

mSFO_PWM = U

U

2

3/ = 32

= 0.907 (3.12)



Hnh 3.19: Quan h gia bin p iu khin v bin sng mang.

3.1 M phng cho b nghch lu p cascade 5 bc

3.1.1 Phn tch cch to p iu ch Qua vic phn tch l thuyt nh trn, ta thy cn phi to mt hm tnh in

p Voffset, tuy nhin trong phn mm Psim khng c khi trc tip tnh c Voffset. V

vy ta phi dng khi DLL (Dynamic Link Library) trong Psim kt hp vi vic vit

chng trnh trong Microsoft Visual C++ hoc trong Borland C++. u tin ta vit

chng trnh bng ngn ng C/C++, ri dch sang nh dng file .dll, sau chp

(copy) file .dll ny vo th mc Psim. Trong Psim ta dng khi DLL vi tn khi l

file .dll va to m phng.

Chng trnh tnh in p iu ch theo SFO PWM nh sau: namespace SFOPWM { #include void_declspec(dllexport)ham(double t,double delt,double *in,double *out) { double a,b,c; double vmax,vmin,voffset; double vasfo,vbsfo,vcsfo; a = in[0]; b = in[1]; c = in[2]; // Tinh gia tri Voffset, VaSFO, VbSFO, VcSFO



if(a>b) { if(a>c) { vmax = a; if(b>c) { vmin = c;} else { vmin = b;} } else { vmin = b; vmax = c;} } else { if(b>c) { vmax = b; if(a>c) { vmin = c;} else { vmin = a;} } else { vmax = c; vmin = a;} } voffset = (vmax + vmin)/2; vasfo = a - voffset; vbsfo = b - voffset; vcsfo = c - voffset; // Gan gia tri cho cac ngo ra out[0] = vmax; out[1] = vmin; out[2] = voffset; out[3] = vasfo; out[4] = vbsfo; out[5] = vcsfo; } } 3.1.2 Cc thng s m phng trong Psim

S m phng b nghch lu p 5 bc dng cascade theo phng php SFO

PWM (bn v A3). Cc thng s trong m phng:

Ch s iu ch m = 0.8. Sng iu khin c tn s 50Hz, sng mang dng PD tn s 2000Hz. Cc ngun DC c gi tr Vd = 200V. Ti RL u dng sao c R = 5 , L = 0.01H (cos =0.85), hng s thi

gian =RL = 2 ms.

S dng khi DLL vi chng trnh nh trn.



3.2 Kt qu m phng

Hnh 3.20: Tn hiu in p iu ch ban u (ging PWM).

Hnh 3.21: Tn hiu in p Vmax, Vmin, Voffset.

Hnh 3.22: Tn hiu iu ch VaSFO trn pha A.



Hnh 3.23: in p pha tm ngun trn pha A.

Hnh 3.24: in p pha tm ngun trn pha B.

Hnh 3.25: in p pha tm ngun C.





Hnh 3.28: in p ti trn pha C.




Hnh 3.30: Dng in ti trn A.




3.3 Nhn xt

Ta thy phng php SFO PWM c p ng ti tng t nh phng php

PWM thng thng, tuy nhin s xut hin ca sng hi bc cao trong dng in p ti

c t hn.

Tn tht do chuyn mch trn cc linh kin cng gim v loi bt thnh phn

th t khng trong dng sng in p iu ch.

Dng in ti 3 pha trng thi xc lp l cn bng.

Qua phng php ny, ta thy c mt hng pht trin mi trong iu khin

b nghch lu p a bc, l tp trung nghin cu hm offset nhm t c mc

ch ti u trong iu ch.



Chng 4


CASCADE - PHNG PHP IU CH VECTOR

KHNG GIAN (Space Vector PWM)

Phng php iu ch vector khng gian (Space vector modulation hoc Space

vector PWM) xut pht t nhng ng dng ca vector khng gian trong my in

xoay chiu, sau c m rng trin khai trong cc h thng in ba pha. Phng

php iu ch vector khng gian v cc dng ci bin ca n c tnh hin i, gii

thut ch yu da vo k thut s v l cc phng php c s dng ph bin nht

hin nay trong lnh vc in t cng sut lin quan n iu khin cc i lng xoay

chiu ba pha nh iu khin truyn ng in xoay chiu, iu khin cc mch lc tch

cc, iu khin cc thit b cng sut trn h thng truyn ti in.

1. Khi nim vector khng gian

1.1 Vector khng gian v php bin hnh vector khng gian

Cho i lng ba pha cn bng va, vb, vc, tc tha mn h thc:

va + vb + vc = 0 (4.1)

Php bin hnh t cc i lng 3 pha va, vb, vc sang i lng vector v theo h

thc:

v = k.(va + a .vb +2

a .vc) (4.2)

trong : a = e 3/2j = -21 + j

23 (4.3)

c gi l php bin hnh vector khng gian v i lng vector v c 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 php bin hnh

khng bo ton cng sut v vi k = 3/2 php bin hnh bo ton cng sut.

V d, ta c i lng ba pha dng cos nh sau:



va = Vm.cos(x- ) vb = Vm.cos(x- 3

2 - )

vc = Vm.cos(x- 34 - )

Vector khng gian theo nh ngha s l:

v = k.(va + a .vb +2

a .vc)

v = 32 [Vm.cos(x- ) + a .Vm.cos(x- 3

2 - ) + 2a .Vm.cos(x- 34 - )]

v = Vm.[cos(x- ) + j.sin(x- )] = Vm.e )( xj Nh vy trong h ta vung gc _ , vector khng gian v c bin Vm bt

u t v tr Vm.e j s quay chung quanh trc toa vi tn s gc . 1.2 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 ca linh kin.

Ta xt b nghch lu p 5 bc dng cascade nh sau:

Hnh 4.1: Cu hnh b nghch lu p 5 bc dng cascade.

Vi b nghch lu p 5 bc, kh nng kch dn linh kin to nn 125 trng thi

khc nhau, mi trng thi c minh ha bi t hp (ka kb kc) vi:



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

kb = -2, -1, 0, 1, 2 (4.4)

kc = -2, -1, 0, 1, 2

Cc h s ka, kb, kc ph thuc vo cch ta quy c trc, cc quy c ny da vo

bng trng thi ng ngt. Chng hn, ta quy c nh sau:

ka = -2 khi S3a = S4a = S3a = S4a = 1

ka = -1 khi

================

14'2'4313'1'4314'3'4214'3'31

aSaSaSaSaSaSaSaSaSaSaSaSaSaSaSaS

ka = 0 khi

========================

14'2'4213'1'4214'2'3113'1'3112'1'4314'3'21

aSaSaSaSaSaSaSaSaSaSaSaSaSaSaSaSaSaSaSaSaSaSaSaS

(4.5)

ka = 1 khi

================

12'1'4212'1'3114'2'2113'1'21

aSaSaSaSaSaSaSaSaSaSaSaSaSaSaSaS

ka = 2 khi S1a = S2a = S1a = S2a tng t cho kb, kc.

Trong qu trnh ng ngt, quy lut ng ngt i nghch phi c tun th:

S1x + S4x = 1; S2x + S3x = 1

S1x + S4x = 1; S2x + S3x = 1 (4.6)

Vi x = a, b, c.

Theo nh ngha vector khng gian, tng 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 lc gic

c nm trng thi khc nhau cho cng v tr ti l vector khng. Cc v tr cn li

ng vi cc trng thi c biu din trong gin vector sau:



200

210

220120020

021

022

012

002102 202

201

000111

222211100

221110

121010

122011

112001 101

212

-1-1-1

-2-2-2

01-1

-1-2-2

00-1-1-1-2

-10-1-2-1-2

100

-2-1-1

-1-10-2-2-1 -1-2-1

0-10

-111

-200

-110-20-1

-20-2 -11-1-10-2

01-1 11-100-2

0-1-210-1

1110-2-2

0-2-11-10

0-201-11

-1-20

0-11-1-11

-2-20

-210

-101

-1-210-12

0-211-12 1-21

2-12

2-111-20

-2-21-1-12

-2-11-102

-201-112

-211

-122

-210-121

-120-21-1

-21-2-12-1 -11-2

02-112-1

01-2 11-222-1

10-221-1

1-1-220-1

1-2-22-1-1

1-2-12-10

2-2-2

2-1-2

20-2

21-2

22-212-202-2-12-2-22-2

-22-1

-220

-221

-222

-212

-202

-2-12

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

2-21

2-20

2-2-1

Hnh 4.2: Gin vector in p ca b nghch lu p 5 bc.

2. Phng php iu ch vector khng gian

Phng php iu khin su bc (six step) to nn s dch chuyn nhy cp tun

hon ca vector khng gian gia su v tr nh ca hnh lc gic. iu ny lm qu

trnh in p pha ti nghch lu hnh thnh cha nhiu thnh phn sng hi bc cao.

H qu l qu o vector khng gian b bin i v pha v bin so vi trng hp

p ba pha ti dng sin. Mt khc, phng php iu ch rng xung dng sin d to

ra in p pha ti gn dng sin nhng ch c th m bo phm vi iu khin tuyn

tnh thnh phn in p c bn ca pha ti n bin Ud /2.

Phng php iu ch vector khng gian khc phc cc nhc im ca hai

phng php nu trn.

tng ca phng php iu ch vector khng gian l to nn s dch chuyn

lin tc ca vector khng gian tng ng trn qu o ng trn ca vector in p

b nghch lu, tng t nh trng hp vector khng gian ca i lng sin ba pha



to c. Vi s dch chuyn u n ca vector khng gian trn qu o trn, cc

sng hi bc cao c loi b v quan h gia tn hiu iu khin v bin p ra tr

nn tuyn tnh. Vector tng ng y chnh l vector trung bnh trong thi gian

mt chu k ly mu Ts ca qu trnh iu khin b nghch lu p.

Nguyn l iu ch vector khng gian i vi b nghch lu p a bc c thc

hin tng t nh nghch lu hai bc. to vector trung bnh tng ng vector v

cho trc cn xem xt vector v nm v tr no ca hnh lc gic. thun tin, thng

thng din tch hnh lc gic c chia nh thnh cc hnh tam gic con. V d, gc

phn su th nht ca hnh lc gic gii hn bi ba vector 0v , 2v v 5v c chia nh

thnh cc din tch (1), (2), (3), v (4) nh hnh v:

Hnh 4.3: Gc phn su c gii hn bi 0v , 2v v 5v .

Vector v ang kho st cn iu khin t c c v tr nm trn phn din

tch (2). Bc tip theo, ta xc nh cc vector khng gian cn thit gi l cc vector

c bn, cn s dng to nn vector trung bnh nm trong din tch (2). Ta nhn thy

chnh l cc vector 1v , 2v v 3v . Nh vy, vector tng ng vi vector v c th

thc hin bng cch iu khin duy tr tc dng theo trnh t vector 1v trong thi gian

T1, vector 2v trong thi gian T2 v vector 3v trong thi gian T3 theo h thc:

V .Ts = 1v .T1 + 2v .T2 + 3v .T3 (4.7)

trong Ts = T1 + T2 + T3 l chu k ly mu.



Vn cn li l xc nh thi gian tc dng T1, T2 v T3 ca cc vector c bn.

Nu ta bit c vector v di dng cc thnh phn vung gc V , V trong h ta

ng yn (stationary frame), quan h gia cc thnh phn vector V , V vi thi gian duy tr trng thi vector 1v , 2v v 3v c th biu din di dng ma trn sau:

(4.8)

Vi V 1 , V 2 , V 3 ,V 1 , V 2 , V 3 l cc thnh phn theo trc ta v ca cc vector trn hnh lc gic 1v , 2v v 3v .

T , thi gian c xc nh (p dng ma trn ngc):

(4.9)

Hay dng thi gian tng i: d j = T j / Ts ; j = 1, 2, 3

(4.10)

p dng c th vo bn din tch hnh tam gic trong gc phn su th nht ca

hnh lc gic, ch n vector c bn trong mi din tch trn, ta thu c kt qu:

Trong din tch (1), vector v bn 0v , 1v v 4v :

d1 = d 0v = 1 - d 2 - d 3 = 1- m a .(sin + 3 .cos ) d 2 = d 1v = m a .(-sin + 3 .cos ) (4.11) d 3 = d 4v = 2.m.sin

Trong din tch (2), vector c bn 1v , 2v v 3v :

d1 = d 1v = 2 - m a .(sin + 3 .cos ) d 2 = d 2v = -1 + m a .(-sin + 3 .cos ) (4.12) d 3 = d 3v = 2.ma.sin



Trong din tch tam gic (3), vector c bn 1v , 3v v 4v :

d1 = d 1v = 1- 2.ma.sin d 2 = d 3v = -1 + ma. (sin + 3 .cos ) (4.13) d 3 = d 4v = 1 + ma.(sin - 3 .cos )

Trong din tch tam gic (4), vector c bn 5v , 3v v 4v :

d1 = d 4v = 2 ma.(sin + 3 .cos ) d 2 = d 5v = -1 + 2.ma.sin (4.14) d 3 = d 3v = ma.(-sin + 3 .cos )

Nu vect nm V gc phn su th i so vi gc phn su th nht ca hnh lc

gic tnh t v tr trc thc , ta c th qui i n v gc phn su th nht xc nh thi gian tc ng ca cc vector c bn theo h thc:

Vi V = 22 VV + ; =

VV

(4.15)

3. Nhn xt

Phng php iu ch vector khng gian cho php iu khin tuyn tnh tt, hiu

qu cao, rt cn thit cho cc h t ng iu khin. N m ra mt l thuyt thc

hnh iu khin mi c cht lng cao cho vic chuyn i nng lng in t cc

ngun DC sang AC. Tuy nhin, phng php iu ch vector khng gian vn cn tn

ti mt s nhc im nh: i hi b vi x l c kh nng tnh ton cao v b nh

ln, vic tnh ton cng phc tp khi s bc ca b nghch lu tng ln, lp trnh gii

thut kh phc tp



Chng 5


CASCADE PHNG PHP IU CH VECTOR

KHNG GIAN DNG SNG MANG

Trong cc nghin cu gn y, nhiu tc gi tm ra c mi quan h gia

phng php iu ch rng xung sin v phng php iu ch vector khng gian.

Vi nhng khm ph ny, mt phng php mi da trn mi quan h ca hai phng

php trn c ngh: Phng php iu ch vector khng gian dng sng mang

(Carrier based Sapce vector PWM). Theo , phng php ny s tp hp nhng u

im ca hai phng php trn: qu trnh tnh ton n gin hn, m rng c phm

vi iu ch

Phng php iu ch vector khng gian dng sng mang (Carrier based

SVPWM) c ngh bi hai tc gi: Nguyn Vn Nh v Hong Hee Lee [2] [4].

Cc tc gi phn tch mi quan h gia phng php iu ch vector khng gian v

k thut PWM dng sng mang, t a ra thut ton v m phng cho b nghch

lu p a bc dng diode kp (NPC multilevel inverter). Lun vn ny tp trung tm

hiu, nghin cu phng php trn nhng a ra cch m phng ng dng cho b

nghch lu p a bc dng cascade (Cascade inverter).

1. Tng qut v phng php iu ch vector khng gian dng sng mang

1.1 tng tng qut ca phng php

Da trn c s l thuyt phn tch tng quan gia SVPWM v sng mang n

cc (carrier based unipolar PWM), phng php iu ch vector khng gian dng

sng mang thc cht l to ra mt sng iu ch mi c nhiu u im hn so vi cc

sng iu ch c.

Cc tc gi a ra gii thut iu ch da trn phn tch cho b nghch lu p

a bc dng diode kp NPC.

in p iu ch ca b nghch lu p a bc c th c phn tch thnh cc

thnh phn nh sau:



Hnh 5.1: B nghch lu p 5 bc dng diode kp v phn tch in p iu ch.

Reference phase to pole voltages (in p pha tm ngun DC hay cn gi n gin l in p iu ch) l ln in p gia mt u pha ti ca b

nghch lu v mt im in th chun trn mch DC (thng chn l im

trung tnh O, nh trn hnh), bao gm in p thnh phn th t thun

nghch (active voltages) Vx12 v in p thnh phn th t khng (reference

common mode) V0ref :

Vxref = Vx12 + V0ref , vi x = a, b, c (5.1)

Gii hn ca in p iu ch:

0 Vxref Vs (5.2) Vi Vs l tng in p ca cc ngun DC.

Active voltages (in p thnh phn th t thun nghch): trong biu vector, in p ba pha th t thun nghch c xc nh bi bin Vref

v gc pha ca vector in p tng ng, hoc t in p phase to pole voltages sau khi loi tr thnh phn offset.

Va12 = Vref.cos Vb12 = Vref.cos( 32 ) (5.3) Vc12 = Vref.cos( 34 )

nh ngha hai gi tr ln nht v nh nht ca in p ba pha th t thun nghch:



Vmax = Max(Va12, Vb12, Vc12)

Vmin = Min(Va12, Vb12, Vc12) (5.4)

Reference common mode voltage (in p thnh phn th t khng) V0ref: c s dng lm gim s ln chuyn mch v gi cn bng ngun DC,

c gi tr thay i trong gii hn V0max v V0min

V0max = (n 1).Vdc Vmax

V0min = - Vmin (5.5)

V Vk = k.Vdc , vi k = 0, 1, 2, 3... (n-1) l bc ca in p DC.

nh ngha hai bc in p gn nht vi in p iu ch Vxref : 0 VLx Vxref VHx Vs VHx = VLx + Vdc (5.6)

Additional common mode (in p offset) V0add: c ngh cng thm vo in p iu ch nhm thu c mt in p iu ch mi ti u hn

Vxref

Vxref = Vxref + V0add = Vx12 + V0ref + V0add (5.7)

Hnh 5.2: Mi quan h gia cc thnh phn in p.

1.2 Gii thut iu ch ca phng php

thun tin cho qu trnh tnh ton v m phng, tt c cc i lng in p s

c chuyn v dng tn hiu theo php tham chiu:



dcxx VvV .= ; vi x = a, b, c (5.8) T y ta s c cc tn hiu tng ng: vxref, vxref, vx12, v0ref, v0add.

Gii thut ca phng php iu ch vector khng gian dng sng mang c th

c biu din tng qut thng qua s khi sau:

Hnh 5.3: S khi tng qut ca phng php.

Gm 2 khi chnh, vi cc chc nng nh sau:

Khi Primitive voltages Generator c chc nng to ra in p Primitive phase to pole voltages Vxp(tng ng reference phase to

pole voltages Vxref ).

Khi Additional common mode Generator dng tnh ton v a ra mt in p offset_V0add thch hp cho tng ch iu ch PWM

(lin tc hay gin on).

Tn hiu in p cui cng thu c l Reference modulating signals_vxref s

c a vo so snh vi cc tn hiu sng mang sinh ra cc trng thi chuyn

mch ca b nghch lu.

Khi Primitive voltages Generator: c chc nng sinh ra tn hiu iu ch s cp primitive phase to pole voltages vxp :

vxp = vx12 + vop ; x = a, b, c (5.9)



nh ngha hai bc iu ch c gi tr gn nht vi tn hiu primitive voltages vxp:

L(x) vxp H(x) (5.10)

H(x) = =

b) { if(a > c) { Max = a; if(b > c) { Min = c;} else { Min = b;} } else { Max = c; Min = b;} } else { if(b > c) { Max = b; if(a > c) { Min = c;} else { Min = a;} } else { Max = c;Min = a;} } vomax = 4 - Max; vomin = -Min; // Medium common mode vop = (vomax + vomin)/2; vap = a + vop; vbp = b + vop; vcp = c + vop; // Tinh cac gia tri vHx, vxL if (vap == 4) { Ha = 4; La = 3; } else { Ha = int(vap) + 1; La = Ha - 1; } vHa = Ha - vap; vaL = vap - La; if (vbp == 4) { Hb = 4; Lb = 3; } else { Hb = int(vbp) + 1; Lb = Hb - 1; } vHb = Hb - vbp; vbL = vbp - Lb; if (vcp == 4) { Hc = 4;



Lc = 3; } else { Hc = int(vcp) + 1; Lc = Hc - 1; } vHc = Hc - vcp; vcL = vcp - Lc; // Tinh gia tri dminH if(vHa < vHb) { if(vHa < vHc) { dminH = vHa; } else { dminH = vHc;} } else { if(vHb < vHc) { dminH = vHb; } else { dminH = vHc;} } // Tinh gia tri dminL if(vaL < vbL) { if(vaL < vcL) { dminL = vaL; } else { dminL = vcL;} } else { if(vbL < vcL) { dminL = vbL; } else { dminL = vcL;} } // Tinh gia tri Additional common mode va Modulating signals voadd = (dminH - dminL)/2; vaSVM = vap + voadd; vbSVM = vbp + voadd; vcSVM = vcp + voadd; // Gan gia tri cho cac ngo ra out[0] = vap; out[1] = vaSVM; out[2] = vbp; out[3] = vbSVM; out[4] = vcp; out[5] = vcSVM; out[6] = vop;



out[7] = vomax; out[8] = vomin; out[9] = voadd; } } 3.1.2 Kt qu m phng

Hnh 5.15: Cc thnh phn in p trn pha A.

Vi: Va_SVM l tn hiu in p iu ch ca phng php

Va12 l tn hiu in p thnh phn th t thun nghch

Vop l tn hiu in p thnh phn th t khng

Voadd l tn hiu in p cng thm vo.





Hnh 5.18: in p pha tm ngun trn pha C.




Hnh 5.23: Dng in ti trn pha A


3.2 Ch Minimum common mode SVPWM

Ch PWM l lin tc (SVPWM) v minimum common mode:

v0p =

>

b) { if(a > c) { Max = a; if(b > c) { Min = c;} else { Min = b;} } else { Max = c; Min = b;} } else { if(b > c) { Max = b; if(a > c) { Min = c;} else { Min = a;} } else { Max = c;Min = a;} }



vomax = 4-Max; vomin = -Min; // Minimum common mode if(vomax < 2) {vop = vomax;} if((vomax >= 2)&&(vomin 2) {vop = vomin;} vap = a + vop; vbp = b + vop; vcp = c + vop; // Tinh cac gia tri vHx, vxL if (vap == 4) { Ha = 4; La = 3; } else { La = int(vap); Ha = La + 1; } vHa = Ha - vap; vaL = vap - La; if (vbp == 4) { Hb = 4; Lb = 3; } else { Lb = int(vbp); Hb = Lb + 1; } vHb = Hb - vbp; vbL = vbp - Lb; if (vcp == 4) { Hc = 4; Lc = 3; } else { Lc = int(vcp); Hc = Lc + 1; } vHc = Hc - vcp; vcL = vcp - Lc; // Tinh gia tri dminH if(vHa < vHb) { if(vHa < vHc) { dminH = vHa; } else { dminH = vHc;} } else



{ if(vHb < vHc) { dminH = vHb; } else { dminH = vHc;} } // Tinh gia tri dminL if(vaL < vbL) { if(vaL < vcL) { dminL = vaL; } else { dminL = vcL;} } else { if(vbL < vcL) { dminL = vbL; } else { dminL = vcL;} } // Tinh gia tri Additional common mode va Modulating signals if(dminH < dminL) { voadd = dminH; } if(dminL < dminH) { voadd = -dminL; } if(dminH == dminL) { if(vop < 2) { voadd = dminH; } else { voadd = -dminL; } } vaDPWM = vap + voadd; vbDPWM = vbp + voadd; vcDPWM = vcp + voadd; // Gan gia tri cho cac ngo ra out[0] = vap; out[1] = vaDPWM; out[2] = vbp; out[3] = vbDPWM; out[4] = vcp; out[5] = vcDPWM; out[6] = vop; out[7] = vomax; out[8] = vomin; out[9] = voadd; } }



3.3.2 Kt qu m phng

Hnh 5.31: Cc thnh phn in p trn pha A.






3.4 Ch Medium common mode DPWM

Ch PWM gin on v medium common mode:

v0p = (v0max + v0min) / 2

v0add =

> Va2 ta

c:

Hnh 6.16: Cc mc in p c th t c ca b nghch lu cascade 5 bc.

Ty theo tng cch b tr sng mang c th m mi b nghch lu cascade 5 bc

cng ch c th to ra c in p dng 5 bc ng ra. V d mt s cch b tr sng

mang v in p to c tng ng nh sau:



a)

b)

Hnh 6.17: Mt s trng hp b tr sng mang v mc in p DC to c.

Trong lun vn ny chn cch b tr sng mang nh H6.17a, v theo cch b tr

sng mang ny s t c s cn bng cng sut gia 2 b nghch lu cu mt pha

( trnh by trong chng 3 phn 2.2.2).

Tng t nh trng hp ngun DC cn bng, vi cch phn b ca cc ngun

DC nh H6.17a th s gp kh khn trong vic xc nh cc bc in p H(x), L(x) v



cc mc in p VH(x), VL(x) khi thc hin phng php iu ch vector khng gian

dng sng mang trong vng iu ch c Vref < 0. Do , ta thc hin php bin i

tng ng sau:

Hnh 6.18: Bin i tng ng cc mc in p.

Khi trong mch nghch lu ta xem nh tn ti 1 im trung tnh O c in th

bng 0 (zero), quan h vi trung tnh O nh sau:

VOO = Va1 + Va2 (6.15)

V in p iu ch cng thay i tng ng:

Vxref,O = Vxref,O + VOO = Vxref,O + (Va1 + Va2) (6.16)

Cu trc mch nghch lu sau khi thc hin php bin i ny c th minh ha

nh sau:



Hnh 6.19: Minh ha mch nghch lu sau khi bin i.

thun tin cho qu trnh tnh ton trong m phng, cc mc in p DC s

c chuyn thnh cc mc tn hiu in p DC theo php tham chiu:

vx1 = Vx1 / Vdx ;

vx2 = Vx2 / Vdx ; (6.17)

Vi Vdx = (Vx1 + Vx2) / 2 ; x = A,B,C.

Tm li, ng dng phng php iu ch vector khng gian dng sng mang

vo b nghch lu dng cascade ta phi thc hin cc bc bin i sau:

Hnh 6.20: Biu din cc php bin i trong gii thut ca b nghch lu cacscade.



T y ta thy phn b cc mc in p DC ca b nghch lu cascade hon ton

ging vi cch phn b ngun DC ca b nghch lu dng NPC. Do ta hon ton c

th p dng gii thut ca phng php iu ch vector khng gian dng sng mang

trong trng hp ngun DC khng cn bng nh trnh by trong phn trn cho b

nghch lu a bc dng cascade.

3. M phng iu khin b nghch lu cascade vi ngun DC khng cn bng

3.1 Chng trnh trong khi DLL

Ta xy dng khi DLL phc v cho m phng b nghch lu cascade i vi

ngun khng cn bng nh sau:

Ng vo ln lt l Va1, Va2, Vb1, Vb2, Vc1, Vc2, va12, vb12, vc12 tng ng vi in[0], in[1], in[2], in[3], in[4], in[5], in[6], in[7], in[8].

Ng ra ln lt l vap, varef, vbp, vbref, vcp, vcref, vomax, vomin, vop, voadd tng ng vi out[0], out[1], out[2], out[3], out[4], out[5],

out[6], out[7], out[8], out[9].

Chng trnh trong khi DLL: // KCB_MedCM_DPWM.h #pragma once using namespace System; namespace KCB_MedCM_DPWM { #include __declspec(dllexport) void math (double t,double delt,double *in, double *out) { double Va1,Va2,Vb1,Vb2,Vc1,Vc2; double a,b,c,Max,Min,e; double vomax,vomin,vop,vap,vbp,vcp; double Eha,Ehb,Ehc,Earef,Ebref,Ecref; double Vda,va1,va2; double Vdb,vb1,vb2; double Vdc,vc1,vc2; double EminH,EminL,voadd; double vaf,vbf,vcf,varef,vbref,vcref; e = 0.1; // Bien e khong c gia tri trong thuat toan va

Va1 = in[0]+ e; // khong anh huong den ket qua, no chi la Va2 = in[1]+ e; // mot sai so de mo phong duoc trong Psim Vb1 = in[2]+ e; // ta co the chon gia tri bat ki Vb2 = in[3]+ e; Vc1 = in[4]+ e; Vc2 = in[5]+ e;



a = in[6]; b = in[7]; c = in[8]; // Tinh gia tri Primitive Phase to Pole Voltage Vxp if(a>b) { if(a>c) { Max = a; if(b>c) { Min = c;} else { Min = b;} } else { Max = c; Min = b;} } else { if(b>c) { Max = b; if(a>c) { Min = c;} else { Min = a;} } else { Max = c; Min = a;} } vomax = 4-Max; vomin = -Min; // Tinh Medium Common Mode vop = (vomax + vomin)/2; vap = a + vop; vbp = b + vop; vcp = c + vop; // Tinh cac muc dien ap trung binh Vda = (Va1 + Va2)/2; va1 = Va1/Vda; va2 = Va2/Vda; Vdb = (Vb1 + Vb2)/2; vb1 = Vb1/Vdb; vb2 = Vb2/Vdb; Vdc = (Vc1 + Vc2)/2; vc1 = Vc1/Vdc; vc2 = Vc2/Vdc; // Tinh Eha, Earef if(vap



if((Earef



Ti RL u dng sao (Y) c R = 5 , L = 0.02H. 3.2.2 Kt qu m phng

Hnh 6.21: Cc ngun in p DC khng cn bng.

Hnh 6.22: Cc thnh phn tn hiu in p iu ch.

Hnh 6.23: in p pha tm ngun pha A.



Hnh 6.24: in p pha tm ngun pha B.

Hnh 6.25: in p pha tm ngun pha C.

Hnh 6.26: in p ti pha A.



Hnh 6.27: in p ti pha B.

Hnh 6.28: in p ti pha C.

Hnh 6.29: Phn tch Fourier cho in p ti pha A.



Hnh 6.30: Dng in ti pha A.

Hnh 6.31: Dng in ti trn 3 pha.

3.3 M phng trong trng hp ngun khng cn bng c ly t b chnh lu cu 3 pha diode

3.3.1 Cc thng s m phng Ch m phng l Medium common mode DPWM. Thng s m phng:

Cc ngun DC c ly thng qua b chnh lu cu diode 3 pha, cc t in C = 1F, vi cc in p nhp vo ngun sin 3 pha ln lt l

Vsina1[linelinerms] = 155V, Vsina2 = 145V, Vsinb1 = 160V,

Vsinb2 = 140V, Vsinc1 = 135V, Vsinc2 = 165V.

Sng iu khin c tn s 50Hz, sng mang dng PD tn s 2000 Hz; Ch s iu ch m = 0.8;



Ti RL u dng sao (Y) c R = 5 , L = 0.02H. 3.3.2 Kt qu m phng

Hnh 6.32: Cc ngun DC khng cn bng.

Hnh 6.33: Cc thnh phn tn hiu in p iu ch trn pha A.



Hnh 6.40: Phn tch Fourier cho in p ti pha A.


Hnh 6.42: Dng in ti trn 3 pha.



4. Nhn xt

Dng in p ti trong trng hp ngun khng cn bng r rng l c cht lng

km hn so vi trng hp ngun DC cn bng mc d c hiu chnh. Qua phn

tch Fourier ta thy thnh phn sng hi bc bc cao vn cn tn ti trong dng sng

ca in p ti.

Dng in ti trn 3 pha trong trng thi xc lp c th xem l cn bng.

Vic iu khin b nghch lu p trong trng hp ngun khng cn bng c th

kt hp vi cc ch common mode khc nhau ging nh trong trng hp ngun

cn bng.



Kt lun

Lun vn c bn thc hin c vic nghin cu k thut PWM cho b nghch

lu a bc ghp tng. i vi tng phng php iu ch trnh by c l thuyt

c bn, thc hin m phng trong Psim, phn tch v nh gi kt qu t c. c

bit i vi phng php iu ch vector khng gian dng sng mang a ra c

gii thut tng ng cho b nghch lu cascade c th thc hin m phng. Trong

trng hp iu khin vi ngun khng cn bng hiu chnh c p ng dng

in v in p v dng cn bng.

Tuy nhin, do qu thi gian hn ch nn lun vn cha thc hin m phng c

cho b nghch lu cascade dng 7 bc (hoc cao hn na), cha m phng c vic

iu khin vi ti c tnh thc t nh ng c khng ng b...

Hng pht trin ca ti c th l nghin cu m rng phm vi iu khin

tuyn tnh in p ng ra, thc hin m phng cho b nghch lu vi s bc cao hn,

hay iu khin vng kn trong trng hp ti l ng c c hi tip t c cht

lng in p v dng in cao hn.



Ti liu tham kho

[1] Nguyn Vn Nh, Gio trnh in t cng sut 1, Nh xut bn i hc Quc gia

Thnh ph H Ch Minh, 2002.

[2] Nguyn Vn Nh & Hong Hee Lee, Analysis of Carrier Based PWM Methods

Based on Optimization of Voltage Errors.

[3] Nguyn Vn Nh & Hong Hee Lee, Theoretical Analysis of Carrier Algorithms

For Multilevel Inverters with Unbalanced DC Voltages.

[4] Nguyn Vn Nh & Hong Hee Lee, Optimized Discontinuous PWM Algorithm

with Variable Load Power Factor for Multilevel Inverters.

[5] Nguyn Quang Tin, K thut PWM, Lun vn tt nghip i hc, Trng i

hc Bch Khoa Tp HCM, 2006.

[6] Nguyn B Mch, Nghin cu k thut iu ch PWM cho b nghch lu a bc

vi ngun p DC khng cn bng, Lun vn Thc s, Trng i hc S Phm K

Thut Tp HCM, 2006.

[7] Phm Xun H, So snh cc k thut iu ch gin on cho b nghch lu p a

bc, Lun vn Thc s, 2006.

bao cao lvtn tranquoc hoan0

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