Interntionl Journl of omputer Theory nd Engineering, Vol. 2, No. 3, June, 2 793-82 Genetilly Tuned STTOM for Voltge ontrol nd Retive Power ompenstion Nveen Goel, R.N. Ptel, Memer, IEEE, Sji T. hko strt In this pper Stti Synhronous ompenstor (STTOM) is used for voltge stility nd the ompenstion of retive power. The STTOM ontins n Insulted Gte ipolr Trnsistor (IGT) sed voltge soure onverter for voltge ontrol nd retive power ompenstion. The STTOM is used to ontrol the retive power with the voltge soure onverter in omintion with D voltge soure. The vlues of the D link pitor nd ttery soure were optimized using the Geneti lgorithm tehnique nd the simultions results for the sme were oserved under the indutive s well s pitive lod onditions. The omprison of voltge ompenstion for vrious onditions show tht the performne of STTOM tuned with G ws the est nd losest to the nominl vlue of voltge. The simultion is done in MTL for STTOM nd Voltge Soure onverter (VS). Index Terms Geneti lgorithm, Optimiztion, Retive power ompenstion, STTOM, Voltge soure onverter. I. INTRODUTION The genertion of ulk power t remote lotions neessittes the use of trnsmission lines to onnet genertion sites to lod enters. Furthermore, in order to enhne system reliility multiple lines tht onnet lod enters to severl soures, interlink neighoring utilities nd uild the needed levels of redundny. This phenomenon hs grdully led to the evolution of omplex interonneted eletril trnsmission networks. These networks now exist in ll ontinents. n eletril power trnsmission network omprises mostly 3-phse lterntingurrent () trnsmission lines operting t different trnsmission voltges (generlly t 23 kv nd higher). With inresing requirement of power-trnsmission pity nd for longer trnsmission distnes, the trnsmission voltge ontinues to inrese nd hene the trnsmission losses re redued. In omplex interonneted trnsmission network, the soure to lod power flow hs multiple trnsmission pths. For system Mnusript reeived July 2, 29. This work ws supported in prt y ITE, New Delhi (INDI) through the reer wrd for Young Tehers sheme to Dr. R. N. Ptel (ITE File No. - 5/FD//7/27-8). Nveen Goel is with the dept. of Eletril Engineering, SSET, hili (.G.), Indi, e-mil: ngoel_8@rediffmil.om R. N. Ptel is with the dept. of Eletril Engineering, SSET, hili (.G.), Indi, (orresponding uthor: e-mil: rmnptel@gmil.om, Phone: +9-9827494379) Sji T. hko is with the dept. of Eletril Engineering, SSET, hili (.G.), Indi, e-mil: hkosji68@gmil.om 345 omprising multiple soures nd numerous lods, lodflow study must e performed to determine the levels of tive nd retive power flows on ll lines, impedne nd the terminls voltges. The line loding nnot e ontrolled, hene for inresing the reliility of trnsmission network s power supply the line impedne n e modified y using series nd/or shunt iruit elements. flexile trnsmission system (FTS) is used for generting or soring retive power. Stti synhronous ompenstor (STTOM) is FTS ontroller operted s shunt onneted stti VR ompenstor sed on voltge soure or urrent soure onverter whose pitive or indutive output urrent n e ontrolled independent of the system voltge. lot of work hs een omplished in the field of retive power ompenstion. The STTOM hs speil hrteristi tht it does not depend on the system voltge []-[4] nd yet ompenstes for ny devition in system voltge. The STTOM is omposed of voltge soure inverter with d pitor, oupling trnsformer, nd signl genertor nd ontrol iruit [5], [6]. Due to its verstile nture nd speedy response, STTOM finds wide pplition in the field, oth s retive power ompensting devie nd hrmoni sorer [7], [8]. There hs een lot of reserh in the reent pst in order to improve the hrteristi nd response time of STTOM. The pplition of rtifiil intelligene tehniques is reltively newer ddition in the field [9]-[]. non-liner fuzzy logi ontroller is used to overome the prolems generted y different unertinties tht exist in power systems. Different input vriles re used to design the ontroller. Prmeters of the proposed ontrollers re djusted y mens of Neurl Network tehniques to improve the performne of the system. rtifiil Neurl Network (NN) is lso introdued in the oordintion of ontrollers, whih sustitute for the tp hnging mehnism [2]. NN is utilized s lssifier with n integer vlue s the output, whih is tp position [3]. Modern Power Systems re lrge, omplex, widely distriuted nd highly non liner systems. Power Systems opertion onditions nd topologies re time vrying nd the disturnes re unforeseele. These unertinties mke it very diffiult to effetively del with power system stility prolems through onventionl ontroller tht is sed on linerized system model. Therefore, fuzzy logi ontrol hs een emerging in reent yers s omplement to the onventionl pproh. The fuzzy logi ontroller is
Interntionl Journl of omputer Theory nd Engineering, Vol. 2, No. 3, June, 2 793-82 designed y. jmi nd S.H. Hoiseini for STTOM to enhne the trnsient stility in power systems [4]. In onventionl sheme, STTOM is ontrolled y PI nd PID ontrollers. The Geneti lgorithm (G) finds its pplition in otining the est vlues for PI nd PID ontroller gins. With G, we n otin preise solution with good omputtion effiieny. This method hs roust stility nd effiieny to solve the tuning prolem of PI nd PID ontroller prmeters more esily nd quikly thn ny other method. The use of G for the lultion of optimum prmeters in the design of PI nd PID ontroller n ring out optimum dynmi response, in very short time [5]-[2]. II. RETIVE POWER OMPENSTING DEVIES Synhronous ondensers, Stti VR ompenstors (suh s TR, TS, TSR, F, nd Hrmoni filter), STTOM, series pitors nd retors, shunt pitors nd shunt retors re some of the retive power ompensting devies. VS re often preferred over urrent soured onverters for FTS pplitions. Sine the diret urrent in VS flows in either diretion, the onverter vlves hve to e idiretionl [8]. The d voltge is unidiretionl; the turn off devies need not hve reverse voltge pility, suh turns off devies re known s symmetri turn off devies. Thus VS vlve is mde up of n symmetri turn off devie suh s GTO with prllel diode onneted in reverse. Some turn off devies, suh s the IGTs et., my hve prllel reverse diode uilt in s prt of omplete integrted devie suitle for voltge soured onverters. For high power onverters, provision of seprte diodes is dvntgeous. silly VS genertes voltge from d voltge []. It is often referred to s inverter, even though it hs the pility to trnsfer power in either diretion. VS n ontrol the mgnitude, the phse ngle & the frequeny of the output voltge. V i + - urrent onn onn2 onn3 onn4 VS Id + v - Volt. i + - I V I 2 Liner Trnsformer 24 V V Mg_V_I I P_Q tive & Retive Fig. : Simultion model of single phse VS with supply & D onstnt voltge soure I Id (In mp.) 4 2-4 -6 - -3-4 -5-6 I Sope.5..5.2.25 time (): urrent through system urrent t d Side III. SIMULTION OF THE VS The VS is modeled in MTL s shown in Fig.. The urrent nd voltge wveforms re shown in Figs. 2 nd 3.VS re often preferred over urrent Soure onverters (S) for FTS pplitions. Sine the diret urrent in VS flow in either diretion, the onverter vlves hve to e idiretionl nd s the d voltge does not reverse, the turnoff devies need not hve reverse voltge pility. The VS my e lssified s 6, 2, 24 nd 48 pulse onverters. ording to the type of onverter there re different trnsformer onnetions. V(In Volts) -7 8 6 4 2-4 -6.2.4.6.8..2.4.6 tim e (In Se.) (): urrent of pitor in VS V -8 -.5..5.2.25 time( In se.) (): Voltge of System in VS Fig 2: Simultion results of single phse VS with supply nd D onstnt voltge soure 346
Interntionl Journl of omputer Theory nd Engineering, Vol. 2, No. 3, June, 2 793-82 Thyristor Voltge & urrent of VS Vt nd It( In volt. & mp.) 8 6 4 2 voltge urrent.2.4.6.8..2.4 Time( In se.) Fig. 3: Simultion result of single phse VS IV. WORKING PRINIPLE OF STTOM Stti Synhronous ompenstor (STTOM) is primry shunt devie of the FTS fmily, whih uses power eletronis to ontrol power flow nd improve trnsient stility on power grids. The STTOM regultes voltge t its terminls y ontrolling the mount of retive power injeted into or sored from the power system. The vrition of retive power is performed y mens of voltge soure onvertor (VS) onneted on the seondry side of oupling trnsformer. The VS uses fored ommuted power eletronis devies (TO s or IGT s) to synthesize the voltge from d voltge soure. The operting priniple of STTOM is explined in Fig. 4. It n e seen tht if Es> Et then urrent Iq flows from the ounter to system through retne nd onverter genertes pitive retive power for system. On the other hnd, if Es< Et then urrent Iq flows from system to the onverter nd onverter sors indutive retive power from system. Finlly, if Es= Et then there is no exhnge of retive power. For omputtion purposes, we ssume tht the tive nd retive power is trnsferred etween two soures V nd V2. V represents the system voltge to e ontrolled nd V2 is the voltge generted y the VS. In stedy stte opertion, the voltge V2 generted y the VS is in phse with V ( =, ngle of V w.r.t. V2) so tht only the retive power is flowing from V to V2; i.e. STTOM is oserving retive power. In ontrry, if V2 is higher thn V, retive power is flowing from V to V2 i.e. STTOM is generting the retive power. The mount of retive power is given y: V.( V V 2) Q = x pitor onneted on the D side of the VS ts s d voltge soure. In order to ompenste for trnsformer nd VS ses nd to keep the pitor hrges, the following two VS tehnologies n e used: 347 Fig. 4: STTOM working onept VS using GTO sed squre wve inverters nd speil interonnetion trnsformers typilly with three level inverters re used to uild 48 step voltge wve form. VS using IGT sed PWM inverters use PWM tehnique to synthesize sinusoidl wveform from d voltge soure with typil hopping frequeny of few kilo-hertz. V. GENETI LGORITHM S OPTIMIZTION TOOL The si purpose of Geneti lgorithm is Optimiztion. It is very useful for gret vriety of tsks. In ll optimiztion prolems, there is prolem of mximizing nd minimizing n ojetive funtions f(x) for given spe x of ritrry dimension. rute fore whih would onsist in exmining every possile x in order to determine the element for whih f(x) is optiml is lerly infesile. G gives heuristi wy of serhing the input spe for optiml x, tht pproximtes rute fore without enumerting ll the elements nd therefore ypss performne issues speifi to exhustive serh []. n elementry unit of G is lled hromosome, whih rries the informtion out the set of prmeters representing prtiulr instne of disriminted funtion. The pproprite two hromosomes re omined to form new one using single point rossover. rndom point in the hromosome is piked. ll the informtion from prent is opied from the strt up to the rossover point, then ll the informtion from prent is opied from the ross over point to the end of the hromosome. The new hromosome thus gets the hed of one prent hromosome omined with the til of the other. Muttions re ruil prt of the lgorithm s they llow retion of rdilly new solutions. olony is olletion of hromosomes, whih evolve s the lgorithm progresses. It is reted y providing two rndom hromosomes nd is then propgted through epohs. olony size is kept ound to speed up the lgorithm onvergene. Eh hromosome hs numer of genes equl to the numer of prmeters used in the ojetive funtion. Thus, gene is inry representtion
Interntionl Journl of omputer Theory nd Engineering, Vol. 2, No. 3, June, 2 793-82 of the vlue of the prmeters. It is sequene of its ( nd ) nd its length (whih is pre-determined) reflets the preision of prmeter vlues. fitness funtion of hromosome is mesure of its performne nd it is quntity tht the lgorithm is trying to mximize/minimize. The proess of optimiztion y G is shown in rief in Fig. 5. VI. RESULTS ND DISUSSIONS Fig. 6 shows the test system implemented in MTL to rry out simultions for the STTOM. The system hs 23 KV trnsmission system with MV feeding into the primry of three winding trnsformer. vrying lod is onneted to the KV seondry side of trnsformer. two level STTOM is onneted to the KV tertiry winding of the trnsformer. 3.3 miro Frd pitor provides the STTOM energy storge pilities. Strt Inputs: Popultion size, Mx no. of genertions, rossover, Muttion nd Reprodution proilities Gen = Rndomly generte initil popultion Find the sore of eh individul in the urrent popultion hek for onvergene? Stop Fig. 5. Optimiztion proess with G The iruit rekers ( s) re provided on the different points s shown in Fig. 6, in order to onnet nd disonnet the different lods suh s lod, lod, lod D nd STTOM t different times. In order to show the effetiveness of this ontroller in providing ontinuous voltge regultion nd retive power, simultions were rried out with nd without STTOM onneted to the system. set of simultions were rried out on the test system for time period of.9 se.. Simultion Results without STTOM The STTOM is disonneted from the system using iruit reker 4. t. se., n RL lod is onneted through. From the simultion results s shown in Fig.7, it is oserved tht there is dip in the system voltge level nd it drops from its nominl vlue of. pu to.7 pu nd t.2 se. further drop in voltge is seen due to ddition of nother RL lod through 2. pitor nk lod is onneted to the system t.6 se through 3 nd it is oserved tht there is swell in system voltge level. The voltge rises to.2 pu from its nominl vlue. The retive power vrition is shown in Fig. 8. It is thus onluded tht due to ddition of Rl lod t. nd.2 se., there is sorption of retive power nd is shown y the negtive Q in the test results s shown in Fig. 8, wheres t.6 se. due to ddition of pitive lod, there is genertion of retive power. The ddition of pitive lod mkes the nture of overll lod onneted to the system pitive in nture nd it is seen from the figure tht Q is positive for this period. Is Gen = Mx genertions Stop Selet prents sed on their sores Produe hildren y pplition of geneti opertors Gen = Gen + Reple the urrent popultion with hildren to form next genertion 348
- Interntionl Journl of omputer Theory nd Engineering, Vol. 2, No. 3, June, 2 793-82 RMS3 signlrms T T V I f(u) Fn PQ V()pu Vref. Vref.. s (s+5) Zero-Pole P Out s Integrtor V()pu Unit Dely delt mod. voltge O/p Puls z Sturtion Susystem urrent ontroller R Y 74 KV R6 R7 R8 2 2 2 3 3 3 23// KV MV t3=.6 V I V-I om t2=.2 P & Q t= RL RL RL2 Lod RL5 RL4 RL3 t4= Q Lod STTOM G G2 G3 G4 G5 G6 + Lod D 6 om om 2 om 4 3 4 5 reker p ttery reker Fig. 6. ontrol nd test system implemented in MTL to rry out the STTOM simultion.4 V without Sttom.4 V with sttom.2.2 V (In Vo lts).8.6.4 V (In Volts).8.6.4.2.2..2.3.4.5.6.7.8.9 Time (se.) Fig. 7: Voltge without ompenstion..2.3.4.5.6.7.8.9 Time (se.) Fig. 9: Voltge with STTOM ompenstion 2 x 8 Retive Power without Sttom x 8 Retive Power with sttom Retive Power ( VR).5.5 -.5 Retive Power (VR).5 -.5 - -.5 -..2.3.4.5.6.7.8.9 Time (Se.) Fig. 8: Retive power without ompenstion.5..2.3.4.5.6.7.8.9 Time (se.) Fig. : Retive power with STTOM. Simultion Results with STTOM nd without Prmeter Optimiztion The simultion is now rried out with STTOM onneted through 4. The simultion results for system 349
Interntionl Journl of omputer Theory nd Engineering, Vol. 2, No. 3, June, 2 793-82 voltge level nd retive power ompenstion re shown in Figs. 9 nd. It is ler from Fig. 9 tht the severity of voltge drop s oserved due to ddition of RL lod t. se nd t.2 se hs een susequently redued. The voltge dip whih ws to the extent of 4% hs lmost ome down to to 5%. Similrly, t.6 se. due to introdution of pitive lod, the voltge swell, whih ws oserved in Fig. 7 without STTOM hs een overome. It is seen tht the system voltge level is now mintined in etween.9 to.95 pu. s for oservtion of Fig., it is inherent tht with the introdution of STTOM, the retive power sorption (i.e. negtive Q), whih ws oserved from. to.6 se. due to RL lod, hs een ompensted. The STTOM devie fulfills the retive power requirement of lod during the ove mention period whih ws previously drwn from the soure nd vie vers from.6 se. onwrds on onnetion of pitive lod.. Simultion Results with STTOM nd with G The simultions re now rried out with STTOM onneted nd prmeter optimiztion of STTOM nd voltge soure onverter. The G tool is used for fine tuning of the system prmeters. The vlues of the D link pitne nd ttery soure were optimized using the tehniques nd the simultions results for the sme s for system voltge profile nd retive power ompenstion re shown in Figs. nd 2 respetively. It is very ler from Fig. tht the system voltge level is mintined onstnt t. pu during the stedy stte ondition even when there is ddition of indutive s well s pitive lod. The omprison of voltge ompenstion for ll three onditions hs een shown in Fig. 3. The performne of STTOM tuned with G, ws the est nd losest to the nominl vlue of voltge i.e. pu. The optimiztion ws done with the fitness funtion s the totl integrl error, s elow: T J = V V ref. dt Where, Vref = Nominl vlue of voltge (i.e. pu) V = The tul voltge (in pu), nd T = Totl period for whih ompenstion is desired Fig. 4 shows the optimized prmeter vlues with G. The totl numer of itertions seleted ws. The optimized vlues of pitor nd ttery soure were found to e 5e-3 Frd nd 6e3 Volts respetively. The first prmeter vlue is not evident from Fig. 4 due to uneven sling of the grph for the two prmeters. The other prmeters used in simultion re given in ppendix. With the ever inresing requirement of qulity supply for sensitive lods, the pplition of STTOM is expeted to inrese nd use of geneti lgorithm s n optimiztion tool n improve its performne signifintly. V (In Volts) Retive Power (VR) V (In Volt).4.2.8.6.4.2..2.3.4.5.6.7.8.9 Time (se.) -.5 -.5 Fig. : rms voltge with STTOM nd G.5 x 8 - Retive Power with sttom & G.5..2.3.4.5.6.7.8.9 Time (se.).2..5 Fig. 2: Retive power with STTOM & G.4.2.8.6.4 Fitness.5vlue with Sttom & G.2 with Sttom without Sttom.2.4.6.8 Time(se) Fig. 3: ompenstion of voltge profiles est:.28747 Men:.849 2 3 4 5 6 7 8 9 Genertion 2 x 4 urrent est individul.5.5 urrent est Individul 2 Numer of vriles (2) est fitness Men fitness Fig. 4: Optimized prmeter vlues with G 35
Interntionl Journl of omputer Theory nd Engineering, Vol. 2, No. 3, June, 2 793-82 VII. ONLUSIONS STTOM model hs een developed with ll the neessry omponents nd ontrollers in order to demonstrte its effetiveness in mintining simple nd fst voltge regultion t ny point in the trnsmission line. The vlues of the D link pitor nd ttery soure were optimized using the Geneti lgorithm nd the simultions results were ompred with tht of the system without ompenstion nd with STTOM, under oth optimized nd un-optimized onditions. The omprison of voltge ompenstion for indutive s well s pitive lod onditions show tht the performne of STTOM tuned with G ws the est nd losest to the nominl vlue of voltge of per unit. PPENDIX Line Prmeters: Supply System = 32KV, Trnsformer: MV, Primry Voltge = 32 KV, Seondry Voltge = KV, Tertiry Voltge = KV STTOM speifitions: pitor = 5e-3F, ttery=6e3 Volt Lods: Lods : R=.5 Ω, L=.59 H Lods : R=2. Ω, L=.926 H Lods D: = 3µF [2] Gwng Won Kim nd Kwng Y. Lee, oordintion ontrol of ULT trnsformer nd STTOM sed on n rtifiil neurl network, IEEE Trnstion on Power System, vol. 2, No. 2, My- 25, pp. 58-586. [3]. Ksztenny, E. Rosolowshi, J. lzykowshi, M.M. Sh nd. Hillstrom, Fuzzy logi ontroller for on-lod trnsformer tp hnger, IEEE Trns. Power Sys. vol. 3, No., Jn. 998, pp. 64-7. [4] jmi nd S.H. Hosseini, pplition of fuzzy ontroller for trnsient stility enhnement of trnsmission system y STTOM, SIE-ISE Interntionl Joint onferene 26, Ot. 8, exo, usn, Kore, pp. 659-663, 26. [5] R. N. Ptel, pplition of rtifiil Intelligene for Tuning the Prmeters of n G, Interntionl Journl of Mthemtil, Physil nd Engineering Sienes, World demy of Siene, Engineering nd Tehnology (WSET), Vol., No., 27, pp. 34-39. [6] P.Ro, M.L. row, Z.Young, STTOM ontrol for power system voltge ontrol pplition, IEEE Trns. Power Delivery, No. 5, 2, pp. 3-37. [7] P.S. Sensrm, K.R. Pdiyr, V. Rmnryn, nlysis nd performne evlution of distriution STTOM for ompensting voltge flutution, IEEE Trns. Power Delivery, vol. 6, 2, pp. 25964. [8] S. Pnd, R. N. Ptel, N. P. Pdhy, Power System Stility Improvement y TS ontroller Employing Multi-Ojetive Geneti lgorithm pproh, Interntionl Journl of Intelligent Tehnology, vol., No. 4, 26, pp. 26673. [9] P.W.D.S. Lehn, Modeling nlysis nd ontrol of urrent soure inverter sed STTOM, IEEE Trns. Power Delivery, No.7, 22, pp. 24853. [2] H. hen, R. Zhou, Y. Wng, nlysis of voltge stility enhnement y roust non liner STTOM ontrol, Proeedings of IEEE PES Summer Meeting, vol. 3, 2, pp. 924-929. REFERENES [] N.G. Hingorni nd Gygyi, Understnding FTS, IEEE Press, 2. [2].K. Lee, Joseph S.K. Leung, S.Y. Ron Hui nd Henry Shu-Hung hung, iruit level omprison of STTOM tehnologies, IEEE Trns. Power Eletronis, vol. 8, July 23, pp.84-92. [3].J. Htziduniu nd F.E. hlkidkis, trnsformer less high pulse stti synhronous ompenstor sed on the 3 level GTO inverter, IEEE Trns. Power delivery, vol. 3, July 998, pp. 883-888. [4] young-kuk Lee nd Mehrdd Ehsnt, simplified funtionl simultion model for three phse voltge soure inverter using swithing funtion onept, IEEE Trns. Industril Eletronis, vol. 48, pril 2, pp. 39-32. [5] S. Pnd nd R. N. Ptel, Improving Power System Trnsient Stility with n Off entre Lotion Of Shunt FTS Devies, Journl of Eletril Engineering, vol. 57, No. 6, 26, pp. 365-368. [6] S. Pnd nd R. N. Ptel, Optiml Lotion of Shunt FTS ontrollers for Trnsient Stility Improvement Employing Geneti lgorithm, Eletri Power omponents nd Systems, vol. 35, No. 2, Fe. 27, pp. 893. [7]. Shuder, M. Gernhrdt, E. Stey, T. Lemk, L. Gyugyi, T.W. ese nd.edris, Development of ± MVR stti ondenser for voltge ontrol of trnsmission systems, IEEE Trns. Power Delivery, vol.6, July 995, pp. 486-49. [8]. Shuder, E. Stey, M. Lund, L. Gyugyi, L. Kovlsky,. Keri,. Mehrn, nd. Edris, EP UPF Projet: instlltion, ommissioning nd opertion of the ± 6 MV STTOM (Phse I), IEEE Trns. Power Delivery, vol.3, Ot. 998, pp. 53-535. [9] R. N. Ptel, S. K. Sinh, nd R. Prsd, Design of Roust ontroller for G with omined Intelligene Tehniques, Interntionl Journl of Eletril Power nd Energy Systems Engineering, vol., No. 2, Spring 28, pp. 95-. [] S. Pnd, N. P. Pdhy, R. N. Ptel, pplition of Geneti lgorithm for FTS-sed ontroller Design, Interntionl Journl of omputer, Informtion, nd Systems Siene, nd Engineering, vol., No., 27, pp. 4-47. [] Jyh-Shing Roger Jng, NFIS: dptive network sed fuzzy inferene system, IEEE Trnstion on Power System, MN, ND YERNETIS, vol. 23, No.3, My/June-993. 35