Download - 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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 2/102
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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 3/102
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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 4/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 5/102
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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 6/102
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).
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 7/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 8/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 9/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 10/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 11/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 12/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 13/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 14/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 15/102
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)
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 16/102
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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 17/102
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 18/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 19/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 20/102
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)
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 21/102
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 22/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 23/102
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 24/102
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 25/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 26/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 27/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 28/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 29/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 30/102
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)
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 31/102
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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 32/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 33/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 34/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 35/102
Hnh 3.26: in p ti trn pha A.
Hnh 3.27: in p ti trn pha B.
Hnh 3.28: in p ti trn pha C.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 36/102
Hnh 3.29: Phn tch Fourier cho in p ti trn pha A.
Hnh 3.30: Dng in ti trn A.
Hnh 3.31: Dng in ti trn 3 pha A, B, C.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 37/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 38/102
Chng 4
IU KHIN B NGHCH LU P A BC DNG
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 39/102
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 40/102
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 41/102
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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 42/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 43/102
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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 44/102
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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 45/102
Chng 5
IU KHIN B NGHCH LU P A BC DNG
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 46/102
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 47/102
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 48/102
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)
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 49/102
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;
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 59/102
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;
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 60/102
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 5.16: in p pha tm ngun trn pha A.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 61/102
Hnh 5.17: in p pha tm ngun trn pha B.
Hnh 5.18: in p pha tm ngun trn pha C.
Hnh 5.19: in p ti trn pha A.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 62/102
Hnh 5.20: in p ti trn pha B.
Hnh 5.21: in p ti trn pha C.
Hnh 5.22: Phn tch Fourier cho in p ti trn pha A.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 63/102
Hnh 5.23: Dng in ti trn pha A
Hnh 5.24: Dng in ti trn 3 pha A, B, C.
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;} }
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 67/102
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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 68/102
{ 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; } }
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 69/102
3.3.2 Kt qu m phng
Hnh 5.31: Cc thnh phn in p trn pha A.
Hnh 5.32: in p pha tm ngun trn pha A.
Hnh 5.33: in p pha tm ngun trn pha B.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 70/102
Hnh 5.34: in p pha tm ngun trn pha C.
Hnh 5.35: in p ti trn pha A.
Hnh 5.36: in p ti trn pha B.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 71/102
Hnh 5.37: in p ti trn pha C.
Hnh 5.38: Phn tch Fourier cho in p ti trn pha A.
Hnh 5.39: Dng in ti trn pha A.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 72/102
Hnh 5.40: Dng in ti trn 3 pha A, B, C.
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 86/102
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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 87/102
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:
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 88/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 89/102
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;
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 90/102
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
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 91/102
if((Earef
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 92/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 93/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 94/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 95/102
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;
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 96/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 97/102
Hnh 6.34: in p pha tm ngun trn pha A.
Hnh 6.35: in p pha tm ngun trn pha B.
Hnh 6.36: in p pha tm ngun trn pha C.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 98/102
Hnh 6.37: in p ti trn pha A.
Hnh 6.38: in p ti trn pha B.
Hnh 6.39: in p ti trn pha C.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 99/102
Hnh 6.40: Phn tch Fourier cho in p ti pha A.
Hnh 6.41: Dng in ti trn pha A.
Hnh 6.42: Dng in ti trn 3 pha.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 100/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 101/102
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.
-
Lun Vn Tt Nghip GVHD: Ts Nguyn Vn Nh
SVTH: Trn Quc Hon 102/102
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.