Stability Improvement of AC System by Controllability of the HVDC

Transcription

1 Vol:9, No:3, 5 Stbility Improvement of AC Sytem by Controllbility of the HVDC Omid Borzjni, Alirez Rjbi, Mojtb Seedimoghdm, Khodkht Ipour Interntionl Science Index, Electricl nd Computer Engineering Vol:9, No:3, 5 wet.org/publiction/7 Abtrct High Voltge Direct Current (HVDC) power trnmiion i employed to move lrge mount of electric power. There re everl poibilitie to enhnce the trnient tbility in power ytem. One dequte option i by uing the high controllbility of the HVDC if HVDC i vilble in the ytem. Thi pper preent control technique for HVDC to enhnce the trnient tbility. The trtegy control the power through the HVDC to help mke the ytem more trnient tble during diturbnce. Lo of ynchronim i prevented by quickly producing ufficient decelerting energy to counterct ccelerting energy gined during. In thi tudy, the power flow in the HVDC link i modulted with the ddition of n uxiliry ignl to the current reference of the rectifier firing ngle controller. Thi modultion control ignl i derived from peed devition ignl of the genertor utilizing PD controller; the utiliztion of PD controller i uitble becue it h the property of ft repone. The effectivene of the propoed controller i demontrted with SMIB tet ytem. T Keyword HVDC, SMIB, Stbility, Power Sytem. I. INTRODUCTION HE power trnfer cpbility of long AC trnmiion line i generlly limited by lrge ignl tbility. The development of effective wy to utilize trnmiion ytem cloe to it therml limit h ttrcted much ttention recently []. The centrl purpoe of conventionl HVDC trnmiion i to trnfer pecific mount of electric power in one node to nother nd to offer the ft controllbility of rel power trnfer. If the HVDC link i operted in prllel with crucil AC line the lod-flow of the AC line could be controlled directly. The HVDC link cn therefore be employed for improving trnient tbility [], [3]. HVDC link, under trditionl control, don't provide ynchronizing or dmping effect in rection to diturbnce on AC ide. However, the cpcity of n HVDC connect to rpidly modulte the power flow, in repone to mnge ignl, h been utilized for ome time to enhnce the dynmic tbility of AC-DC ytem [4]. For n AC DC ytem, [5] hve dicued the effect of DC modultion on the dynmic tbility of (i) one mchine, infinite bu nd (ii) two mchine, infinite bu configurtion. Luc nd Peiri [4] hve utilized prllel-mll power DC link to improve the AC ytem mll-ignl tbility. However, the power ytem tbilizer (PSS) hve been widely utilized to improve dmping of thee ocilltion, through modultion of the genertor excittion. Erikon et l. [] hve tudied the impct of conventionl HVDC link on the trnient tbility in nine-bu benchmrk power ytem. Rhmn nd Khn [] hve tudied ingle mchine infinite bu connected by double circuit AC line, converted for imultneou AC DC power trnmiion; it i bi-polr DC power trnmiion through double circuit AC trnmiion line. Thi pper preent concept of improving the trnient tbility of power ytem by modulting the power trnfer in HVDC. A SMIB ytem connected vi prllel AC nd DC power trnmiion h been tudied. In thi tudy, the power flow in the HVDC link i modulted by the ddition of n uxiliry ignl to the current reference of the rectifier firing ngle controller to enhnce the trnient tbility. The trtegy i dependnt on ft blncing of the ccelerting energy. The driving mechnicl power hould be blnced by the electric power to keep the ytem in ynchronim. Thi i completed by controlling the power through the HVDC. II. MODEL EXPLANATION A. HVDC Link The HVDC conidered in thi pper (Fig. ) i of conventionl type bed on the CIGRE benchmrk ytem [6] [8]. The rectifier nd the inverter re -pule converter uing two 6-pule thyritor bridge connected in erie. The trnformer tp chnger re not imulted nd fixed tp re umed. Rective power required by the converter i provided by et of cpcitor bnk plu th, 3th nd high p filter on ech ide. A erie rector i lo included between the two HVDC ttion to mke the DC current mooth. The control ued re primrily thoe of the CIGRE Benchmrk model [8] [] modified to uit the necery power. Omid Borzjni, Alirez Rjbi, Mojtb Seedimoghdm, Khodkht Ipour re with the Deprtment of Electricl Engineering, Dhtetn Brnch, Ilmic Azd Univerity, Dhtetn, Irn (e-mil: Borzjni_omid@yhoo.com). Fig. The HVDC ytem digrm Interntionl Scholrly nd Scientific Reerch & Innovtion 9(3) 5 37 cholr.wet.org/37-689/7

2 Vol:9, No:3, 5 Interntionl Science Index, Electricl nd Computer Engineering Vol:9, No:3, 5 wet.org/publiction/7 Preliminry qulittive nlyi ugget tht commonly ued technique in HVDC/AC ytem my be dopted for the purpoe of the deign of protective cheme, filter nd intrumenttion network. In ce of ymmetricl fult in the trnmiion ytem, gte ignl to ll the SCR re blocked nd the byp vlve re ctivted or force retrdtion method i pplied (i.e. forcing the rectifier into inverion) to protect rectifier nd inverter bridge [], []. At the inverter the commuttion filure prevention control will detect AC fult nd reduce the mximum dely ngle limit in order to decree the rik of commuttion filure. By controlling the firing ngle for the rectifier α AOr, the power through the HVDC i controlled. The current controller i hown in Fig.. The limited current I ref-lim reference i generted uing the Voltge Dependent Current Limit (VDCL) unit. Thee unit provide current reference vlue during tedy nd trnient tte condition repectively. In order to mintin the opertion of the AC ytem, VDCL limit the current in the DC line, if the DC voltge decree, e.g. due to n AC ytem diturbnce. When norml opertion h returned nd the DC voltge recovered, current return to it tedy-tte level I ref ( p.u.). B. Tet Power Sytem Fig. The current controller A ingle mchine ytem connected to infinite bu through prllel AC nd DC link i conidered nd i hown in Fig. 3. The genertor i equipped with n excittion ytem (IEEE- Type I). Power ytem tbilizer (PSS) hve been utilized to improve dmping of ocilltion, through modultion of the genertor excittion. The mechnicl power upplied by turbine i conidered invrint for the durtion of trnient imultion run. HVDC link i ued to demontrte the enhncement of tbility by utilizing the controllbility of the HVDC line. Fig. 3 Prllel AC-DC ytem The power cn go either through the AC line or through the HVDC. The totl power trnfer P totl i 95 MW; the nominl vlue of the AC ytem re 5 kv nd 5 Hz. The AC trnmiion line i 35 km long nd nominl rting i MW (P c ). The HVDC i operting t 5 kv DC (V ) nd i trnferring 75 MW (P ) of totl power in tedy-tte. Fig. 4 how the power through the HVDC (P ), the AC line (P c ) nd totl power trnfer (P totl ) in tedy tte condition. Power (W) x P Pc Ptotl Fig. 4 P totl, P c nd P power trnfer in tedy tte condition. III. TRANSIENT STABILITY OF POWER SYSTEMS The firt electric power ytem w ytem built by Edion in 88. The ubequent power ytem tht were contructed in the lte 9 th century were ll ytem. However depite the initil populrity of ytem by the turn of the th century c ytem trted to outnumber them. The c ytem were thought to be uperior c mchine were cheper thn their counterprt nd more importntly c voltge re eily trnformble from one level to other uing trnformer. The erly tbility problem of c ytem were experienced in 9 when inufficient dmping cued pontneou ocilltion or hunting. Thee problem were olved uing genertor dmper winding nd the ue of turbinetype prime mover [] [4]. The tbility of ytem refer to the bility of ytem to return bck to it tedy tte when ubjected to diturbnce. A mentioned before, power i generted by ynchronou genertor tht operte in ynchronim with the ret of the ytem. A genertor i ynchronized with bu when both of them hve me frequency, voltge nd phe equence. We cn thu define the power ytem tbility the bility of the power ytem to return to tedy tte without loing ynchronim. Uully power ytem tbility i ctegorized into tedy tte, trnient nd dynmic tbility. Stedy tte tbility tudie re retricted to mll nd grdul chnge in the ytem operting condition. In thi we biclly concentrte on retricting the bu voltge cloe to their nominl vlue. We lo enure tht phe ngle between two bue re not too lrge nd check for the overloding of the power equipment nd trnmiion line. Thee check re uully done uing power flow tudie [3] [6]. Trnient tbility involve the tudy of the power ytem following mjor diturbnce. Following lrge diturbnce the ynchronou lterntor the mchine power (lod) ngle chnge due to udden ccelertion of the rotor hft. The objective of the trnient tbility tudy i to certin whether the lod ngle return to tedy vlue following the clernce of the diturbnce. The bility of power ytem to Interntionl Scholrly nd Scientific Reerch & Innovtion 9(3) 5 37 cholr.wet.org/37-689/7

3 Vol:9, No:3, 5 mintin tbility under continuou mll diturbnce i invetigted under the nme of dynmic tbility (lo known mll-ignl tbility). Thee mll diturbnce occur due rndom fluctution in lod nd genertion level. In n interconnected power ytem, thee rndom vrition cn led cttrophic filure thi my force the rotor ngle to incree tedily. In thi chpter we hll dicu the trnient tbility pect of power ytem [7] [8]. A. Power-Angle Reltionhip In thi ection we hll conider thi reltion for lumped prmeter lole trnmiion line. Conider the inglemchine-infinite-bu (SMIB) ytem hown in Fig. 5. P in Pmx 8 mx (6) Interntionl Science Index, Electricl nd Computer Engineering Vol:9, No:3, 5 wet.org/publiction/7 Fig. 5 An SMIB ytem In thi figure, the rectnce X include the rectnce of the trnmiion line nd the ynchronou rectnce or the trnient rectnce of the genertor. The ending end voltge i then the internl emf of the genertor. Let the ending nd receiving end voltge be given by V S V V We then hve I S, R V V V jx V co V jv in jx + The ending end rel power nd rective power re then given by V co V jv in PS + jqs VS IS V ( co + j in ) jx Thi i implified to ( V VV ) VV in + j co PS + jqs X Since the line i lo le, the rel power diptched from the ending end i equl to the rel power received t the receiving end. We cn therefore write P VV X in in e PS PR Pmx where P mx V V /X i the mximum power tht cn be trnmitted over the trnmiion line. The power-ngle curve i hown in Fig. 6. From thi figure we cn ee tht for given power P. There re two poible vlue of the ngle nd mx. The ngle re given by () () (3) (4) (5) B. Swing Eqution Fig. 6 A typicl power-ngle curve Let u conider three-phe ynchronou lterntor tht i driven by prime mover. The eqution of motion of the mchine rotor i given by [] [] d J Tm Te T θ where J i the totl moment of inerti of the rotor m in kgm ; T m i the mechnicl torque upplied by the prime mover in N-m; T e i the electricl torque output of the lterntor in N-m; θ i the ngulr poition of the rotor in rd. Neglecting the loe, the difference between the mechnicl nd electricl torque give the net ccelerting torque T. In the tedy tte, the electricl torque i equl to the mechnicl torque, nd hence the ccelerting power will be zero. During thi period the rotor will move t ynchronou peed ω in rd/. The ngulr poition θ i meured with ttionry reference frme. To repreent it with repect to the ynchronouly rotting frme, we define θ ω t + where i the ngulr poition in rd with repect to the ynchronouly rotting reference frme. Tking the time derivtive of the bove eqution we get dθ d ω + Defining the ngulr peed of the rotor dθ ω r (7) (8) (9) () Interntionl Scholrly nd Scientific Reerch & Innovtion 9(3) cholr.wet.org/37-689/7

4 Vol:9, No:3, 5 Interntionl Science Index, Electricl nd Computer Engineering Vol:9, No:3, 5 wet.org/publiction/7 We cn write (9) d ω r ω () We cn therefore conclude tht the rotor ngulr peed i equl to the ynchronou peed only when d/ i equl to zero. We cn therefore term d/ the error in peed. Tking derivtive of (9), we cn then rewrite (7) d J Tm Te T Multiplying both ide of (3) by ω m we get d J ωr Pm P () (3) where P m, P e nd P repectively re the mechnicl, electricl nd ccelerting power in MW. We now define normlized inerti contnt H Jω S Stored kinetic energyt ynchronoupeed in meg-joule Genertor MVA rting rted Subtituting (4) in () we get S d H ωr Pm P ω rted (4) (5) In tedy tte, the mchine ngulr peed i equl to the ynchronou peed nd hence we cn replce ω r in the bove eqution by ω. Note tht in (5) P m, P e nd P re given in MW. Therefore dividing them by the genertor MVA rting S rted we cn get thee quntitie in per unit. Hence dividing both ide of (5) by S rted we get per unit H d Pm P ω (6) Eqution (6) decribe the behviour of the rotor dynmic nd hence i known the wing eqution. The ngle i the ngle of the internl emf of the genertor nd it dictte the mount of power tht cn be trnferred. Thi ngle i therefore clled the lod ngle. C. Equl Are Criterion The rel power trnmitted over lole line i given by (5). Now conider the itution in which the ynchronou mchine i operting in tedy tte delivering power P e equl to P m when there i fult occur in the ytem. Opening up of the circuit breker in the fulted ection ubequently cler the fult. The circuit breker tke bout 5/6 cycle to open nd the ubequent pot-fult trnient lt for nother few cycle. The input power, on the other hnd, i upplied by prime mover tht i uully driven by tem turbine. The time contnt of the turbine m ytem i of the order of few econd, while the electricl ytem time contnt i in milliecond. Therefore, for ll prcticl purpoe, the mechnicl power i remin contnt during thi period when the electricl trnient occur. The trnient tbility tudy therefore concentrte on the bility of the power ytem to recover from the fult nd deliver the contnt power P m with poible new lod ngle [] []. Conider the power ngle curve hown in Fig. 7. Suppoe the ytem of Fig. 5 i operting in the tedy tte delivering power of P m t n ngle of when due to mlfunction of the line, circuit breker open reducing the rel power trnferred to zero. Since P m remin contnt, the ccelerting power P become equl to P m. The difference in the power give rie to the rte of chnge of tored kinetic energy in the rotor me. Thu the rotor will ccelerte under the contnt influence of non-zero ccelerting power nd hence the lod ngle will incree. Now uppoe the circuit breker re-cloe t n ngle c. The power will then revert bck to the norml operting curve. At tht point, the electricl power will be more thn the mechnicl power nd the ccelerting power will be negtive. Thi will cue the mchine decelerte. However, due to the inerti of the rotor me, the lod ngle will till keep on increing. The incree in thi ngle my eventully top nd the rotor my trt decelerting, otherwie the ytem will loe ynchronim [8] [9]. Note tht d d d d Fig. 7 Power-ngle curve for equl re criterion. Hence multiplying both ide of (6) by rerrnging we get H ω d d d ( Pm ) (7) d nd (8) Multiplying both ide of the bove eqution by nd then integrting between two rbitrry ngle nd c we get Interntionl Scholrly nd Scientific Reerch & Innovtion 9(3) cholr.wet.org/37-689/7

5 Vol:9, No:3, 5 c H d ω c ( Pm ) d (9) To obtin decription for the criticl clering time, let u conider the period during which the fult occur. We then hve P e. We cn therefore write from Now uppoe the genertor i t ret t. We then hve d/. Once fult occur, the mchine trt ccelerting. Once the fult i clered, the mchine keep on ccelerting before it reche it pek t c, t which point we gin hve d/. Thu the re of ccelerting i given from (9) d ω P H m (3) Integrting the bove eqution with the initil ccelertion being zero we get c m e d A ( P P ) () t d ω ω Pm Pm t H H (4) Interntionl Science Index, Electricl nd Computer Engineering Vol:9, No:3, 5 wet.org/publiction/7 In imilr wy, we cn define the re of decelertion. In Fig. 7, the re of ccelertion i given by A while the re of decelertion i given by A. Thi i given by [] m A ( P P ) d e m c () Now conider the ce when the line i recloed t c uch tht the re of ccelertion i lrger thn the re of decelertion, i.e., A > A. The genertor lod ngle will then cro the point m, beyond which the electricl power will be le thn the mechnicl power forcing the ccelerting power to be poitive. The genertor will therefore trt ccelerting before i low down completely nd will eventully become untble. If, on the other hnd, A < A, i.e., the decelerting re i lrger thn the ccelerting re, the mchine will decelerte completely before ccelerting gin. The rotor inerti will force the ubequent ccelertion nd decelertion re to be mller thn the firt one nd the mchine will eventully ttin the tedy tte. If the two re re equl, i.e., A A, then the ccelerting re i equl to decelerting re nd thi i define the boundry of the tbility limit. The clering ngle c for thi mode i clled the criticl clering ngle nd i denoted by cr. We then get from Fig. 7 by ubtituting c cr cr m ( Pm ) d ( Pe Pm ) cr d () We cn clculte the criticl clering ngle from the bove eqution. Since the criticl clering ngle depend on the equlity of the re, thi i clled the equl re criterion. Now frequently ked quetion i wht doe the criticl clering ngle men? Since we re intereted in finding out the mximum time tht the circuit breker my tke for opening, we hould be more concerned bout the criticl clering time rther thn clering ngle. Furthermore, notice tht the clering ngle i independent of the generlized inerti contnt H. Hence we cn comment tht the criticl clering ngle in thi ce i true for ny genertor tht h d-xi trnient rectnce of. per unit. The criticl clering time, however, i dependent on H nd will vry thi prmeter vrie. Further integrtion will led to t ω ω Pm t Pm t + H 4H (5) Replcing by cr nd t by t cr in the bove eqution, we get the criticl clering time 4H ω P cr cr m t ( ) (6) To illutrte the repone of the lod ngle, the wing eqution i imulted in MATLAB. The wing eqution of (6) i then expreed d ωr H d ω ωr ( P P ) m e (7) where ω r i the devition for the rotor peed from the ynchronou peed ω. It i to be noted tht the wing eqution of (7) doe not contin ny dmping. Uully dmping term, tht i proportionl to the mchine peed ω r, i dded with the ccelerting power. Without the dmping the lod ngle will exhibit utined ocilltion even when the ytem remin tble when the fult clered within the criticl clering time. Fig. 8 depict the repone of the lod ngle for two different vlue of lod ngle. It i umed tht the fult occur t.5 when the ytem i operting in the tedy tte delivering.9 per unit power. The lod ngle during thi time i contnt t The lod ngle remin tble, lbeit the utined ocilltion when the clering time t cl i.53. The clering ngle during thi time i The ytem however become untble when the clering time.53 nd the lod ngle incree ymptoticlly. The clering time in thi ce i Thi i clled the lo of ynchronim. It i to be noted tht uch incree in the lod ngle i not permiible nd the protection device will iolte the genertor from the ytem. Interntionl Scholrly nd Scientific Reerch & Innovtion 9(3) cholr.wet.org/37-689/7

6 Vol:9, No:3, 5 Fig. Equl re criteri for DC control Interntionl Science Index, Electricl nd Computer Engineering Vol:9, No:3, 5 wet.org/publiction/7 Fig. 8 Stble nd untble ytem repone function of clering time IV. CONTROL TECHNIQUE Trnient tbility in power ytem refer to the bility of power ytem to mintin connected genertor in ynchronim fter the ytem h been ubjected to mjor diturbnce uch trnmiion ytem fult. The trnient tbility control trtegy developed in the pper i bed on ft blncing of the ccelerting energy [9],[ ]. The driving mechnicl power mut be blnced by the electricl power to keep the ytem in ynchronim. Thi i performed by controlling the power through the HVDC. The equl re criteri for tbility tudy my be dopted to e the trnient tbility limit of the ytem. Fig. 9 how tht the ytem become untble for high vlue of pre-fult power P totl ( P m ), which i equl to the mechnicl power input. If the fult clering time t i not very ft then the correponding ngle become lrger thn the criticl clering ngle nd the ytem become untble. Fig. 9 Equl re criteri: P c tedy tte AC power by AC ytem, P tedy tte DC power by the DC ytem; P totl totl power trnfer; tedy tte power ngle; power ngle t the time of clering the fult by opening CB (B nd B); A c ccelerting energy gined due to decrement of AC power (P c ) cued by the fult; A ccelerting energy gined due to decrement of DC power (P ) cued by the fult; A retrding energy of the genertor. HVDC link, under trditionl control, do not provide ynchronizing or dmping effect in repone to diturbnce on AC ide. However, the controllbility of n HVDC link i inherently ft nd thi cn be ued to modulte the power flow fter the fult clernce for producing ufficient decelerting energy to improve the trnient tbility. When 3-phe fult occur in the AC trnmiion line, both P c nd P become zero. The fult i clered fter t econd by tripping B nd B, o Pc remin to be zero even when the fult i clered. But P i llowed to flow through the line. Referring Fig., t the intnt of clering fult t rpid control of the converter ytem incree the DC power flow to P / : / P P + P m (8) where B i increment of DC power required to give ufficient retrding energy to genertor (A c + A kinetic energy gined by the rotor during ccelertion) When rpid control to incree DC power i not dopted, B. The ccelertion re (A c + A ) become lrger thn decelertion (A) nd the genertor my tep-out. A counter meure to improve the trnient tbility nd olve the firt wing tbility, the DC power i increed by n mount: B P ( A c + A ) A P / P (9) (3) The criterion given in () i implemented by dding I control ignl to the limited current reference (I ref-lim ) of the rectifier current regultor. The control ignl ( I ) i derived from peed devition ignl ( ω) of the genertor uing PD controller hown in Fig.. Fig. Current controller nd uxiliry ignl Interntionl Scholrly nd Scientific Reerch & Innovtion 9(3) cholr.wet.org/37-689/7

7 Vol:9, No:3, 5 Interntionl Science Index, Electricl nd Computer Engineering Vol:9, No:3, 5 wet.org/publiction/7 V. SIMULATION RESULTS The imultion tudy i crried out for the following ce. At time t three-phe to ground fult occur t the AC trnmiion line cloe to bu A hown in Fig. 3. After period of m, trip ignl re given imultneouly to circuit breker B nd B t both end of fulty line to cler the fult. Therefter, circuit breker re recloed fter dely of 4 m from the intnt of clering fult. So the totl fult clering time become 5 m in tht ce. Time, t Three phe to ground fult occur ner bu A Time, t. Diconnection of AC line Time, t.5 Reconnection of AC line Fig. how the trnient repone for thi fult condition. Comprion of reult between both ce with DC power modultion (curve ) nd without DC power modultion (curve ) for the imilr nture nd durtion of fult indicte: It cn be oberved through imultion tudie tht, AC DC ytem without DC power modultion become untble in the firt wing. However, with DC power modultion the ytem remin tble fter firt wing. Fig. () give the vrition of genertor peed. A cn be een in the figure, the ytem fll out of ynchronim when the HVDC i trnferring contnt mount of power, i.e. no uxiliry power control. When the control trtegy i pplied, the firt wing i controlled in uch wy tht the ytem remin tble. Fig. (c) how the genertor terminl voltge. The voltge drop during the fult but recover quickly fter the diconnection of the fulted line. The rel power ocilltion ubide much fter when the control trtegy i pplied. It cn be oberved tht, there re no opertionl problem due to the modultion of the DC power (through the modultion of the rectifier firing ngle) to improve the tbility of the ytem. VI. CONCLUSION Thi pper preent control technique for HVDC to enhnce the trnient tbility in power ytem. The trtegy control the power through the HVDC to help mke the ytem more trnient tble during diturbnce. The propoed control trtegy include the PD controller; the utiliztion of PD controller i uitble becue it h the property of ft repone. During the trnient period fter the fult clernce, AC power flow i temporrily witched off nd the DC power flow i modulted to produce retrding torque to bring bck the genertor to it norml peed. It' h been demontrted tht the power flow in the HVDC link i modulted by the ddition of n uxiliry ignl to the current reference of the rectifier firing ngle controller to enhnce the trnient tbility in power ytem. The PD controller work well nd dmp the firt wing ocilltion trnient o the ytem remin tble. Therefore, the control of HVDC h the potentil for future ppliction to power ytem. Speed (pu) Power (pu) Power (W) PhDiff (deg) 3 - (b) x 9 (d) P Pc Ptotl (f) () Voltge (pu) Speed (pu) Power (W).5.5 DC Voltge (pu)...99 Fult Dic of c Line Reco of c Line t t Accelerting energy Decelerting energy tr (c) x 9 (e) P - Pc Ptotl (g) Fig. () Genertor peed (b) Genertor ctive power output (c) Genertor terminl voltge (d) AC (P c ), DC (P ) nd totl (P totl ) power trnfer (e) AC (P c ), DC (P ) nd totl (P totl ) power trnfer (f) Trnmiion ngle (P hdiff ) between two end (g) DC Voltge Genertor: APPENDIX Sn MVA, Vn 3.8 kv, f 5 Hz, Xd.35 pu, Xd.96 pu, Xd.5 pu, Xq.474 pu, Xl.8 pu, Tdo., Tdo.53, Tqo., R.8544 pu, H 3.7, Xq.43 pu, Excittion Sytem: K, T., Ke, Te, K f., T f.. Power Sytem Stbilizer: T w, T.6, T, T3, T 4, V _mx.5 pu, V _min -.5 pu, K PSS.5. Genertor Trnformer: MVA, 3.8 kv/5 kv Converter Trnformer: Rectifier Trnformer, 5/.4* kv, MVA; Inverter Trnformer,.4*/5 kv, MVA. Converter: V d nom 5 kv, I d nom 5 A, P nom 75 MW. Rectifier: α min 5, α mx 45. Inverter: α min, α mx 5 Interntionl Scholrly nd Scientific Reerch & Innovtion 9(3) cholr.wet.org/37-689/7

8 Vol:9, No:3, 5 Interntionl Science Index, Electricl nd Computer Engineering Vol:9, No:3, 5 wet.org/publiction/7 REFERENCES [] H. Rhmn, Upgrdtion of Exiting EHVAC Line by Compoite AC- DC Trnmiion, Interntionl Conference on Communiction, Computer nd Power (ICCCP'9), MUSCAT, Februry 5-8, 9. [] H.R. Erikon, V. Knzkin, L. Soder, On the ement of the impct of conventionl HVDC on tet power ytem, IEEE, Sympoium, Bulk Power Sytem Dynmic nd Control, Augut 9 4, 7, Chrleton, SC, USA. [3] K. P. Bu, Stbility Enhncement of Power Sytem by Controlling HVDC Power Flow through the Sme AC Trnmiion Line, IEEE, Sympoium on Indutril Electronic nd Appliction, Mlyi, 9. [4] J. Rohn Luc, H. Jhn C. Peiri, Increing the power trnfer cpbility of n c trnmiion line uing prllel mll power link, Trnction of the IEE Sri Lnk, vol 3, No, Apr. [5] J.W. Klein, P.C. Krne, L.A. Fernnde, Invetigtion of DC modultion in prllel AC/DC power ytem, IEEE Winter Meeting, A7835-4, 978. [6] U. Vni, R. Ro, Dmping effect of Supplementry Control Signl for Enhncement of Trnient Stbility in AC-DC Power Sytem, Interntionl Journl of Engineering Science nd Technology, Vol. (7),, [7] V. K. Sood, HVDC nd FACTS Controller Appliction of Sttic Converter in Power Sytem, Kluwer Acdemic Publiher, 4. [8] N. Wton, Jo Arrillg, Power Sytem Electromgnetic Trnient Simultion, IET London, United Kingdom, 7. [9] N.G. Hingorni, L.K. Gyugyi, Undertnding FACTS Concept nd Technology of Flexible A.C. Trnmiion Sytem, IEEE Pre,. [] L.K. Gyugyi, Unified power flow concept for flexible A.C. trnmiion ytem, in: IEE Proceeding, July 99. [] T. Vijy Muni, T. Vinodith nd D. Kumr Swmy, Improvement of Power Sytem Stbility by Simultneou AC-DC Power Trnmiion, Interntionl Journl of Scientific & Engineering Reerch, Volume, Iue 4, April-. [] P. Kundur, power ytem tbility nd control, Mcgrw Hill edition, New Delhi 993, th reprint. [3] T. C. Cihlr, J. H. Wer, D. N. Ewrt, nd L. K. Kirchmyer, Electric Utility Sytem Security, Proc. Americn Power Conference, vol. 3, 8. [4] L. H. Fink nd K. Crlen, Operting Under Stre nd Strin, IEEE Spectrum, vol. 5, pp , Mrch 6. [5] J. Zborzky, K. W. Whng, nd K. V. Prd, Monitoring, Evlution nd Control of Power Sytem Emergencie, Proc -- Sytem Engineering for Power Conference, Engineering Foundtion Report CONF-7994-P, Dvo, Switzerlnd, Oct 9. [6] R. P. Schulz nd W. W. Price, Clifiction nd Identifiction of Power Sytem Emergencie, IEEE Trn. Power Apprtu nd Sytem, vol. PAS-3, pp ,. [7] R. P. Schulz, L. S. VnSlyck, nd S. H. Horowitz, Potentil Appliction of Ft Phor Meurement of Utility Sytem, IEEE PICA Conference Proceeding, pp , My. [8] J. F. Huer, D. J. Trudnowki, G. J. Roger, W. A. Mittelt, W. H. Litzenberger, nd J. M. Johnon, Keeping n Eye on Power Sytem Dynmic, IEEE Computer Appliction in Power, pp. 5-54, October. [9] B. Frdneh, S. Zelingher, A. P. S. Meliopoulo, G. Cokkinide, nd J. Ingleon, Multifunctionl Synchronized Meurement Network, IEEE Computer Appliction in Power, pp. 6-3, Jnury 998. Interntionl Scholrly nd Scientific Reerch & Innovtion 9(3) cholr.wet.org/37-689/7