VSC-HVDC 1.1 VSC-HVDC l g? VSC-HVDC ( Voltage source converter High voltage direct current) l cng ngh truyn ti in mt chiu s dng cch bin i ngun p p so vi cng ngh truyn ti in mt chiu truyn thng l bin i ngun dng CSC HVDC Vi vic tip tc phat trin ph ti va kh khn trong vic xy dng RoWs ( tuyn hanh lang) cho ng dy mi. Cc ng dy hin ti t ti gii hn truyn tai,nu co s c s khin cht lng in b suy gim v gy tc ng ti n nh h thng. Do , cn thit phi thit lp h thng hin ti tng kh nng truyn ti in trn c s ca tn ti RoWs ( hnh lang an ton li in) cua ng dy cu. S dng cng ngh VSC-HVDC l 1 phn trong gii php cho cc vn pha trnVSC-HVDC l dng truyn ti DC ( mt chiu)cng ngh mi. Cc van c s dng l cac van IGBT v b iu ch PWM to ra cc dng sng mong mun, Vi iu ch PWM c th to ra bt k cc dng sng no, mi gc pha, mi ln ca thnh phn tn s c bn v cho php kh nng iu chnh rng.1.2 Thnh phn VSC-HVDC Cu hnh ca mt VSC_ HVDC . Bao gm b lc xoay chiu ( AC Filter) , my bin p ( transformer) , b bin i ( Converter) , cun cm pha ( Phase reactor) , T mt chiu ( DC Capacitor) v cp mt chiu ( DC cable ).

Hinh 2.5: S cu hinh cua b loc

B bin i B bin i l cc VSCs lm vic trn van bn dn cng sut IGBT, v c vn va l chnh la hoc nghch lu. Hai b bin i c th c s dng mt trong hai kt ni (lng v lng) hoc truyn ti qua cp mt chiu DC.My bin pBnh thng, b bin i kt ni vi li xoay chiu thng qua my bin p. V mt trong nhng chc nng quan trng l l bin di in p ca li xoay chiu ti in p thch hp cho b bin i Cun cm phaCun cm pha c s dng iu khin dng cng sut tc dung v cng sut phn khng bi iu chnh dng in trn cuc cm . Cc cuc cm cn c th nh l mt b lc xoay chiu gim cc thnh phn sng hi ca dng in xoay chiu xyra khi vn hnh VSCsB lc xoay chiu in p xoay chiu c cc thnh phn sng hi, do bt tt ca van IGBT. Cc sng hi c phat vao li xoay chiu phai bi gii han nhm ngn nga cac sai hng trn thit b ca li xoay chiu hoc l nhng tc ng ln cc thit b truyn thng , radio. Cc b lc cao c thit lp gim thiu thit hi do cc sng hi. Vi b bin i VSC khng cn thit phi b bt c cng sut phn khng no v sng hi trn li xoay chiu lin quan trc tip qua tn s PWM. Do , Tng cc b lc trn b bin i c gim xung so vi cng nghchuyn mch ng bin iT mt chiuTrn li 1 chiu s c hait xp chng cng kch thc. Kch thc ca t da trn yu cu ip p mt chiu, Mc tiu ca t l cung cp nng lngtrung gian gi c cn bng cng sut trong qu trnh qu v gim in p gn sng trn li mt chiu.Cp DCCp c s dng trong VSC-HVDC l dng cap mi pht trin , cch in c lm t p Polyme . Cp Polymeric c la chn cho cc hu ht cc truyn ti HVDC bi v bn chc ,tnh cht co dn ti trng nh

Cc cp DC thng gim thiu c cc tch ng ngn mch ca yu t t nhin nh bo, cy Mt trong nhng c trng quan trng ca truyn ti VSC l cch ly s c ng dy bng my ct hai u ng dy nhm cho php gii thot c nng lng phn khng v tr v vi dng cng sut bnh thng tc rt chmKhng c gii hn chiu di trong cp DC m khng cc trm chuyn tip, Bnh thng, Cc cp c tc ng mi trng nh hn so vi ng dy trn khng. Trng in t hu ht b loi b vi cc h thng lng cc v khng to ra cc dng trn dy trung tnh, Hn na, vng i ca mt cp cch in DC tt hn so vi cp xoay chiu Truyn ti VSC cho php ch cn mt cc DC v cho php cc cp khng cn phi thit k o cc, . Vi c tnh cho php s cc cp cch in Polymeric , thay vo cc cp cc in giy v du truyn thng, Cc vt liu poly c th chu c lc cao v bn cao ro thch hp trong cc cp truyn ti xuyn bin cc vng nc su, l l do m cc dng cp ny c th dng bc st, trong khi vi xoay chiu th trnh cc vt liu t, Trong khi HVDC th cp in ch c th t t 84-150kV nhng cp VSC l 300kVTrong cc cp cch in Polymernic gm 3 phn vi din n b mt v cch in b mt, Vi thit k mnh m, thch hp truyn ti ngmi vi cc cp p HVDC c thit k ng ti mi cc vi vic chng li dng ngc chiu c th lc gim c in trng

1.3 B BIN I Nh cc b bin i bao gm cc thnh phn bin i 3 pha 2 cp 6 cu hoc 3 pha 3 cp 12 xung . c biu din trong hnh 2.6.

Cu hnh cu hai cp l cu hnh n gin nht, chungc th xy dng c cu VSC chuyn i mch lc ba pha, c c cho mnh nhiu ng dng truyn ti cng sut . Nh trong hnh 2.6 b bin i 2 cp bao gm 6 van.C kh nng to ra in p t +0.5 ti -0.5. B bin i ba cp bao gm 4 van trong 1 nhnh( cnh tay) Chng c th to ra c ba cp in p cui l -0.5 ,0, 0,5. Trong chng yu cu 2 hoc 3 cu c kt ni vi nhau c th t c mc cng sut cao nu cn thit v mi van c th l cc nhm cc thit b ni tip cng cc diot song song ngc. S lng thit b c quyt nh bi t l cng sut ca cu v dung lng cng sut trn cc b ng m

Trong cng ngh nhng nm sau 2010 pht tin b bin i a cp MMC (modular muti converter) b bin i a cp c kh nng cn du tt hn so vi cc b bin i khc1.4 B lc ACTrn thc t cc dng v in p trn b chnh lu v b nghch lu l cc sng khng sin, bi v qua trinh ng m cc van.Cc dng khng sin gm thnh phn tn s c bn v sng hi bc cao. Cc b lc th ng trn VSC-HVDC lc cc sng hi bc cap. Do , cc dng sin v in p c ththu c t cun th cp. Hn na, b cng sut phn khng c th c thc hin bng b loc cao p B PWM c dng sng ra bao gm cc sng hi MfcNf1, Trong fcl sng mang, f1 l tn s c bn ca li, M v N l cac s nguyn, Tng M + Nl cc s l. Thm vo th thnh phn tn s c bn , c di tn in p ra bao gm tn s sng mang ca PWM v bi s ca sng mang .Nh c lm r bng 2.1, Tng cc in p sng hi c th tnh ton bi cu trc tam gic PWM vi t l ca bin iu tn s , do c nh ngha nh sau:

La chn ph thuc vo mc cn bng gia tn tht trn bt tt v tn tht sng hi, Cc gi tr cao lm tng tn tht bt tt nhng gim tn tht sng hi

M 1 2 3

Bc sng h 39f178f1 117f1

39f1+2fc78f1+1fc117f1+2fc

39f1+4fc78f1+3fc117f1+4fc

39f1+6fc78f1+5fc117f1+6fc

T bng 2.1, thnh phn sng hi co th cho bit. Cc c tn s gi tr thp nht ca sng hi, do vi vic s dng PWM, cc b lc th ng c la chn lc cc sng hi bc cao, Bnh thng b loc cp hai va cp ba th ng c biu din trong hnh 2.7 c ng dng trong cu hnh HVDC.

Khi thit k cc b lc, h s Q c la chon t c tnh vt yu cu ca dai tn s. Cc gi tr ca h s Q nm gia 0,5 v 5.

1.5 Thit k cua t in p mt chiu B bin i c th c iu chnh cc dng sng vo sin nht.Cc in p danh nh c th t xp x. B bin i 2 cp c kh nng to ra cp in p tDo , cc in p DC c iu chinh gp 1634 ln so vi gi tr hiu dng in p xoay chiu Thit k cc t mt chiu l mt phn quan trng trong thit k HVDC, Bi v qua trinh bt tt cua PWM trong VSC-HVDC , dng in chy v pha mt chiu c cc thnh phn ca song hai, dn ti kt qua la in ap gn sng trn li mt chiu . ln cua cac gn song phu thuc vao kich c tu va tn s bt tt.

Do o, Cac tu c nho co th c s dung, chung la cac kt qua ly thuyt trong phan hi cua b bin i nhanh. Cc t c th d tr nng lng theo yu cu cua iu khin dong cng sut. Cac tu mt chiu co c tinh la hng s thi gian, c xac inh ti s nng lng d tr trn in ap mt chiu va gia tri cng sut biu khin cua b bin i SN:

Hng s thi gian la phng trinh thi gian nap in p t 0cho n gi tr in p . Nu b bin i c cung cap vi gia tri cng sut tc dung c inh ti Sn. Thi hng s thi gianco th c la chon vi gia tri nho nht e thoa man gn song va qua ap trong qua trn li DC. Chung co quan h v thi gian cho phep iu cng sut tc dung va cng sut phn khng

2. Phng php iu khin cua VSC HVDC 2.1 Gii thiu Vi HVDC truyn thng cng sut phn khng khng th iu chinh c lp vi cng sut tc dung . Vi VSC-HVDC c khnng iu chinh goc t do iu khin cng ngh VSC-HVDC co th iu khin cng sut tc dung va cng sut phn khng c lp. Cng sut phn khng co th iu khin tach bit vi mi yu cu in ap xoay chiu thng thng. Cng sut tc dng co th c iu chinh thong qua in ap mt chiu v tiu chnh di tn s a dang tai pha li xoay chiu , Nghia la cng sut tc dung , cng sut phn khng , in p xoay chiu , in p mt chiu va tn s co th iu chinh khi s dung VSC-HVDC .Trong qu kh, vi cc cu hnh a cp , a xung vi cc van bt tt ti tn tn s c bn, bin ca in p xoay chiu s l ph thuc trc tip vo t l t in p t in mt chiu. Cng sut c th i t pha xoay chiu vo mt chiu hoc ngc li, V do bin ca lch pha gia in p h thng xoay chiu v b bin i. Khi cng sut i cung cp cho cc t in th in p cng tng v cng sut c ly ra t t in th in p suy gim, Mt nhc im ca s dng cp in mt chiu iu khin in p xoay chiu l thi gian np in diHin ny cc cu hnh HVDC-VSC khng hiu hiu qu ch vn hnh na, Thay vo , chng c thit k gi in p danh nh mt chiu v iu khin in p b bin i xoay chiu bng vic s dng cng ngh PWM, Trong b bin i VSC-PWM, in p xoay chiu c coi l bin l modul tn hiu , n c xc nh bng t s ca bin in p yu cu so vi in p xoay chiu ti a c th iu khin c trn t mt chiu . Khi ch s modul gn t c mc in p ca b bin , th in p b bin i ln hn in p xoay chiu v cng sut phn khng truyn ti ti in p xoay chiu, Khi ch s thp ( in p b bin i nh hn in p h thng),ngc li b bin i hp th cng sut phn , S cho 2 phng thc iu iu chnh ch s, iu khin trc tip ( Direct control) v iu khin vecto ( Vector control)Trong , iu khin trc tip ( Direct control) ch s modul ( ) hay gc pha c iu chnh thng s trc tip

iu khin vecto (Vector control), ngt lin kt iu chnh cc ch s modul ra khi gc pha, Iu khin dng hng n chin lc bo v vc van khi qu ti, nhng dng ng c tc phn hi kh chm.

Chng ta s cng xem xt k c tnh ca phng phpiu khin nhanh vector c hoan thin bi cac tinh cht iu khin phu cung cp cac gia tri tham chiu cho iu khin vecto, Do o, b iu khin vector se la vong lp trong va b iu khin phu se co cac vong lp ngoai. B iu khin ngoai gm co b iu khin in p mt chiu ,b iu khin in p xoay chiu, B iu khin cng sut tc dung , b iu khin cng sut phn khng va b iu khin tn s. Cho vi du nh hinh3.1 , mi bn cua ng dn co th lachon b iu khin in p mt chiu hoc b iu khin cng sut phn khng . Mi iu khin u cho ra cac gia tri tham chiu cho b iu khin vector .Chng ta cng xem tng qut s ca iu khin ca HVDC-VSC;

Tt nhin cac b iu khin se co thi gian hoat ng khac nhau.S la chon b iu khin thch hpda trn cac ng dung va cac c tinh u th cua n trong tng thiim. VSC-HVDC co th iu khin c tn s va in p xoay chiu , nu cac tai thu ng . VSC-HVDC co th iu khin in ap va cng sut phn khng nu cac tai la mt li xoay chiu. Tuy nhin, V cng sut tc dngi vo pha mt chiu phai co s cn bng. B iu khin in ap mt chiu phim bo cn bng cng sut tc dung . cng sut tc dung i ra t pha mt chiu c tinh toan bng cng sut tc dung vao trong mt chiu tr i tn tht trn li DC, Vi moi khac bit dn ti kt qua thay i nhanhgi trin ap. Cac b bin i co th iu chinh moi gia tri cng sut tc dng trong khoang gii han cua h thng.

2.2iu khin Vectoriu khin Vector da trn quan h c bn ca dng trong hnh 3.2 v c th thit lp trong h ta dp

Trong hnh 3.3 l tn s hi p,gia in p ca b bin i trn nt ca b lc in p v gia in p b bin i s vi dng ca my bin p c v lc b v . Chng ta c th thy phan hi tai tn s thp nhm hng ti c v khng c Rd v Ld, ng nghab lc t c xem xt nh l 1 t l tng.i,e Rd v Ld c lc b. Chng ta c th xem xt nh sau:

B iu khin vector da trn mi quan h c bn trong mch in v c th hin trong h ta dq vi trc q ta theo in p tham chiu nhm tch knh iu khin cng sut phn khng v cng sut tc dngH phng trnh cho trm chuyn i VSC c tnh ton trn l :

Ba phng trnh trn th hin mi quan h gia in p ng ra VSC v thnh phn dng in, l c s xy dng mch vng iu khin dng in nhm xc nh gi tr tham chiu cho b PWM iu khin pht xung p ng yu cu ca h thng2.2.1 iu khin dng trong2.2.2 iu khin vector song cng2.2.3 iu khin Vector vi T lc LCL2.2.4 Gii hanDo VSC-HVDC khng c b kh nng qu ti nh l mt my pht ng b, c cc dng qu ln do s nhiu lon gy trn cc van, Do , cc dng gii hn bt buc thit lp trn trn h thng iu khin.Hn na, do bin in p ti a ca VSC b gii hn bi kh nng in p VSC. Cc qu trnh in p tham chiu ly t cc iu khin vector phai xp x gii hnCc dng gii hn c so snh vi ln dng tnh ton t dng cng sut tc dng v dng cng sut phn khng, Khi dng gii hn b vt mc, c cng sut tc dng v cng sut phn khng u b gii hn.La chn t mt trong hai gai tri gii hn ph thuc vo hin trng loi. V d, nu b bin i c kt ni vi mt mng li mnh . Gi tr dng cng sut tc dng s c chn, Khi gi tr dng vt gii hn .chng s c nhiu cng sut tc dng hn. Cc cng sut tc dng c tnh ton xp x theo .Nu b bin i vi mt li yu hoc cung cp cho li cng nghip,n s u tin chn dng cng sut phn khng nhm gi in p cho h thng khi dng in vt mc gii hn. Dung lng con lai l cho cng sut tc dng pht. V phng trnh thu c l

Khi dng c thit lp tham chiu phn khng ti a. Nh c yu cu duy tri iu khin chnh xc v gim tn s sng hi, Bin in p ra ti a ca VSC b gii hn trong lc gic . Bin ca l phng trnh .

2.3 B iu khin ngoiB iu khin ngoi bao gm b iu khin in p mt chiu, b iu khin in p xoay chiu, iu khin cng sut tc dng,iu khin cng sut phn khng v iu khin tn s.2.3.1 B iu khin in p 1 chiuNh c xy dng trong hnh 2.8 v cng sut tc dng v cng sut phn khng nm trong vi gi tr cng sut Prec truyn ti c bin din ci cc cng thc sau:

Vi iDC l dng trn DC ca b bin i tim im vn hnh h thng, in p-dp l gia tri hng ti l in p, Do in p l 0 v l in p t l. Yu cu v mt h thng n nh, cc iu khin ngoai phai chm hn so vi iu khin vector .Ti cc thi im ca iukhin in p 1 chiu, dng c xut l gi tr tham chiu. Sau xut, cng sut tc dng v phn khng c din ta nh sau:

Lc b tn tht trn b bin i v cuc cm, phng trnh ca cng sut truyn ti trn AC v DC ca trng bin i t (3.45) v (3.46)

Nu cc im khng cn bng gia AC v DC dn n s thay i in p qu trn dung lng ca ng dy 1 chiu, c cho nh sau

Vi iload l dng ra t h thng DC, nh trnh by 2.8. Bi c ng bng phng php Euler v xut ca iDC v iload l hng trong qu trnh bin i gi tr in p DC, ta c phng trinhsau:

T (3.48) ti (3.50) ta c:

T (3.51) phng trinh iu khin cua gia tri dong tham chiu thu c la :

Vi

H s iu chinh h s khuch ai nhm am bao n inh.2.3.2 B diu khin cng sut tc dng L phng php iu khin cng sut tc dng trong iu khin vng lp m.Gi tr dong cng sut phn khng c xem xt thu c (3.46):

Vi Pf* c l cng sut tc dng mong mun , Nu iu khin chnh xc ca cng sut tc dng l cn thit , bao gm ca phn hi vong v vng lp m c s dung:

Vi va la cac ti s va h s tich phn cua iu khin cng sut tac dung.

2.3.2 iu khin cng sut phn khngTng t nh iu khin cng sut tc dng ta thu c:

Ti Qf l gi tr tham chiu cng sut phn khng, hay nh mt cch iu khin khc bao gm phn hi vng lp v vng lp m

Vi va l cc ty l khuch i v tch phn khuch i ca iu khin cng sut phn khng.2.3.4 B iu khin in p in p di trn cm khng Rv+jLvtrong hnh 3.8 xp x nh sau:

Khi cun cm XvRv , do in p ri ch ph thuc duy nht vo cng sut phn khng Qf . Theo (3.47) in p xp xi co th c iu chnh bi iu khin thanh phn d cua dong2.3.5 B iu khin Tn sTrong cc tiu mc ny chng ta s xem xt 4 loi iu khin tn s khc nhauiu khin tn s 1 c xem xt nh l b iu khin tn s c inh. C tn s c inh fvsc* cung cp tn s danh inh cho in p ra VSC. B iu khin vector dual, chng c th cung cp trc tip cc gi tr ip p tham chiu, B iu khin tn s c th s dng cung cp tn s cho h thng m khng cn ngun ca iu khin tn sB iu khin tn s 2B iu khin tn s 2 cung l b iu khin tn s c inh .Tn s c inh fvsc* cung cp in p VSC. Cc tn s c inhthu c t qu trnh ng trn dy DC, Nh chng ta a bit, Nng lng trong t c biu din nh sau.

Tn tht ca bt tt ca c 2 b c lc b. Qu trnh ng trn cc t s l s khc bit gia cng sut vao trong h thng DC Prec v cng sut ra h thng DC Pinv, cho l:

Theo c tinh ca tn s cng sut tc dng trong cc h thng li lin kt , gi tr tn s c inh tham chiu cho b iu khin tn s 2 c th cho t cc phng trnh sau:

Ti UDC* l cc gi tr tham chiu, kfCII l h s khuch i v fo l gi tr tn s danh nh. B iu khin tn s 2 do l mt dng ty l.B iu khin tn s 3Nh cc thnh phn c bn ca b iu khin tn s 3 da trn c s c tinh cua tn s cng sut tc dng ca cc h thng lin kt. Cc tch phn tng phn c trong b iu khin tn s 3 trnh cch im khng n inh, i,e v b iu khin PI. Gia tri vo ca b iu khin tn s 3 t pha ng vng .2.4 Cng ngh PWM VSCPulse With Modulation (PWM) hay cn c gi l b bm xung chng c kh nng iu ch cc xung c rng ty vi cc tn hiu vo l bng cc tn hiu analogQu trnh hot ng ca PWM s so snh vi cc tn hiu tn s c bn hoc cc tn hiu sng mang nh to ra cc xung kch cho vic iu ch sng ca b bin i VSC, Qu trnh so snh to ra cc xung c rng khc bitMc ch c bn ca cng ngh ca l gim sng hi, gim tn tht v tng c mc in p. Cng ngh PWM c kh nng iu khin a dng, trong s l tnh sin PWM, vecto PWM, ti u PWM. Trong tnh sin PWM c kh nng lc gim c sng hi l thng dng nht,Trong cng ngh PWM khi lm vic trn m phng DigSILENT cho tnh sin PWM khi n so snh vi cc sng sin ca tn s c bn vi tn hiu sng mang to ra xung kch vo b bin i,Tc l s c hai sng c s dng tham gia iu khin cng mt pha ca b bin i, Tn s ca sng mang quyt nh tn s bt tt ca b bin i

3. Cc c trng c bn trong vn hnh VSC3.1 Qu trnh bin i tn hiu trong b bin iVn hanh h thng VSC-HVDC c c gii thch bng in ap u cui nh la mt ngun ap c kt ni vi li xoay chiu thng qua h thng cun cam ni tip. Trong cc phn trc chng ta i tm hiu cc vn v cc l thuyt iu khin ca h thng VSC-HVDC v trong cc mc sau chng ta s tp chung vo cc qu trnh ng m van bin i tn hiu trong h thng HVDC-VSC v t kt lun c kh nng truyn ti ca cng ngh mi ny,Nh chng ta bit kh nng ng m hon ho ca cc van cch ly IGBT v GTO , tuy nhin nu mt van c m ra th cc van khc s phi ng ngay lp tc iu c kh nng to ra cc dng ngn mch trong cc t d tr. Qu trnh chuyn tip trng thi ng m ca van khi kt ni vi pha, th dng xoay chiu s c np vo mt trong hai bn dng hoc bn m ca t mt chiu , Kt qu to ra dng sng in p gm hai cp +Vdc/2 v Vdc/2. V thng c gi l b bin i hai cp

Hin nay trong thc t cc nguyn l bin i c da trn b bin i a cp d cc t v diodes nhm tng cp bin i v dt c cc cp in p khc nhau, nhm t c cht lng sng tt nht.

B bin i ba cp s c 4 van mt cnh ca b bin i , Nguyn l ng m l trong mt thi im s c hai van m , V d V1 &V2 ; V2 &V3. Hai van V1&V2 s m vi in p im cui xoay chiu ( c gi l v tr P ) . V2 v V3 s m im gia (MP) thng qua Diode gi. V3 v V4 m ra ti im N .Kt qu ca qu trnh chuyn in p bao gm ba cp in p

3.2 Kh nng truyn ti cng sutTrong hinh 2.8 chung ta thy gian cua b bin i kt ni qua li xoay chiu. Cc ngun xoay chiu va iu khin ngun ap c ni qua h thng cun cam. Cac b bin i c thit lp nh la mt iu khin ngun ap tai li AC va iu khin ngun dong tai li DC, Cac ngun dong co th c tinh toan da trn cn bng cng sut tai hai phia xoay chiu va mt chiu ca b bin i. iu khin ngun ap c thc hin bi b iu khin h thng cua b bin i , gm cc thnh phn bin , pha va tn s chng c iu khin c lp. Va c din ta bng cng thc sau :

Tai o M la chi s c inh nghia la ti s l gia tri ca inh song bin i so vi gia tri inh cua song mang.in ap mt chiu . la tn s, la goc pha cua in ap ra, Cac chi s co th iu chinh bng b iu khin VSC. Nh kt qua trn, ip ap ri trn cac cun cam co kha nng iu chinh rng cng sut tc dung va cng sut phn khng . Gitr ca tn s c bncho iu khin VSC nh la mt chinh lu va nhn cng sut phn khng cua li xoay chiu. Trong trng hp ip ap ra VSC co bin nho va gc pha bi tr. Cng sut tc dung gia li xoay chiu va b bin i co th iu chinh

bi goc pha(), gia in ap tn s c ban c to ra bi VSC va in trn cun th cp cua MBA. Cng sut tc dung c tinh toan theo vic lc bo tn tht cua cuc cam

Cng sut phan khang c quyt inh bi bin cua va c tinh toan theo cng thc :

Trong VSC-HVDC cng sut tc dung trn li xoay chiu c din t bng phng trinh cng sut tc dung truyn tai t li xoay chiu ti pha mt chiu khi n inh . Nu mt trong hai b bin i iu khin truyn tai cng sut tc dung truyn n b bin i cn li siu khin in ap mt chiu . Cng sut phn khng san xut va tiu thu co th iu khin din ap AC cua h thng. Trong hinh 2.9 cua VSC-HVDC trong lc P-Q co 2 in ap khac nhau va khi o ,, Thay vao o, VSC-HVDC co th vn hanh bt ky im nao trong hinh tron trn. Tuy nhin , ban kinh VSC-HVDC c biu din t l cng sut b bin i MVA chung la phng trinh tinh toan cua dong ti a va ip ap xoay chiu do dung lng MVA suy giam khi in ap suy giam.

Trong hinh 2.10 cng sut tc dung va cng sut phn khng qua li va truyn tai VSC la mt ng tron. T hinh 2.10 chung ta thu c la giao cua ng kha dung VSC va ng tron cua li biu din im lam vic cua cac cp in ap. Hn na trong hinh 2.10 con trinh din chuyn i cng sut tc dung va cng sut phn khng khi co s sup ap. Chung ta thu c suy giam cng sut tc dung khi in ap suy giam.

Hnh 3. ng biu kin trong vn hnh HVDC-VSC

3.3 ng dng VSC-HVDC kt ni 2 liKh nng iu chinh in cao cho phep VSC-HVDC co cac c tinh u im ln. Chung co cac la chon khac nhau lam vic, Chng nay se tp chung vao vn hanh cua VSC-HVDC hoan chinh tai im n inh. Khi cac tai thay i va nhiu loan trn li cung cp, Hn th na , do iu khin cua truyn tai HVDC trn b bin i ngun ap s dung PWM chung cn thit cho cac m phong cua h thng VSC-HVDC vi cac bc nho, Vic giam tc cac bc m phong lam tng thi gian yu cu hp l ca hu dingj cua cac m phong, Do o, vi ng lng nhng cac m phong cua ch n gian cua VSC-HVDC bi anh gia trong cac nhiu loan trn li cung cp .Trong ch y u thi b bin i bao gm 3 pha, 2 cp va 6 xung cu, B bin i van cu c biu din bi cac khoa ly tng. Ca tiinr tht va tn tht bt tt c lc bo va cac cuc cam cua pha ca mba c nghi gn nht, Trong cac b lc gian cac tt bt cua cac van bi lc bo, va c anh du tai hnh 2.5 va 2.8 , Chi co iu khac bit gia b hoan chinh va b gian lc la kt ni gia 2 bn AC vf DCCac ap ng cua VSC-HVDC , s dung b hoan chinh , trong cac nhiu loan nh s c, va thay i cng sut se c tim hiu . trong chng nay , cac t khoa c lam ro bi cac ai lng c ban, Cac m phong se c biu din c chng nghim b lc bo va b hoan chinh