3 IREP Syposiu-ulk Syste Dynis nd ontrol -IX (IREP), ugust 5-3, 3, Rethynon, Greee ttery Energy Storge sed Virtul Synhronous Genertor. Vssilkis, V. Krpnos P. Kotspopoulos, N. Htzirgyriou IEEE ener Ntionl Tehnil University of thens. e-il: vkrpnos@gil.o e-il: vssil@il.ntu.gr, kots@power.ee.ntu.gr, nh@power.ee.ntu.gr strt The purpose of this pper is to investigte the intertion of the Virtul Synhronous Genertor () units with the grid. Within this sope, test-senrios of different power systes with inresing penetrtion levels, re siulted nd evluted. The ility of ttery storge syste to provide priry frequeny regultion, s prt of virtul synhronous genertor, is lso exined wheres severl ontrol strtegies re used to properly nge the ttery storge syste ording to the tehnil speifitions of the ENTSO-E. Introdution Nowdys interest in generting eletriity using reltively sll sle deentrlized genertors is inresing. These sll power genertors re onneted inly t distriution level influening the tehnil spets of the distriution grid []. The trditionl power syste is hrterized y reltively sll nuer of lrge entrlized power plnts, sed on synhronous genertors, in order to oplish the power lne etween energy prodution nd energy dend. Up to now, the short-ter dyni stility of the power syste hs een inly sed on the intrinsi rotor inerti of synhronous genertors (SG). s the lssi vertil power syste trnsfors into ore horizontl power syste with greter penetrtion of inverter oupled generting filities, this nturlly provided inerti will grdully e redued. The frequeny of power syste with low inerti will hnge rpidly for rupt vritions in genertion or lod. In this se, dditionl frequeny response nillry servies ust e provided to ensure tht frequeny liits re not exeeded []. The provision of Virtul rottionl inerti in order to reinfore the stility of the power syste, hs een introdued to the grid-onneted syste s proising solution. The ide of operting n inverter to ii synhronous genertor hs een gining populrity in the reent yers. Severl tehniques hve een proposed towrds this diretion. The Virtul Synhronous Mhine (VISM) perfors rel tie lultions of eletrogneti synhronous hine properties [3]. The voltges t the point of oon oupling with the grid re esured to lulte the phse urrents of the VISM. These urrents re used s referene for urrent-ontrolled inverter. nother siilr onept is tht of synhonverter, where the phse urrent is esured nd the output voltge is rel tie lulted so tht it is equl to the k EMF tht synhronous genertor would produe under the se onditions on the grid [4]. The Virtul Synhronous Genertor () odels the rottionl inerti of synhronous hine without onsidering other synhronous hine properties [5]. ttery KiM Model SO Exhnged With the tteries ESSS ontrol lgorith P so Interfe P vsg ontrol Exhnged With the Grid Grid Voltge Fig.. The priniple of ttery Energy Storge sed Virtul Synhronous Genertor. The generl onept of unit is presented in Fig.. ttery Energy Storge Syste (ESS) exhnges power with the grid ording to ESS nd ontrol lgoriths. The outline of the ttery sed odel used in this study is given in the following setion. The perforne is fterwrd studied, through vrious test-senrios when the penetrtion level inreses. The lst prt investigtes the ility of the ttery sed to provide priry frequeny regultion. Rel frequeny dt re used to test nd opre the perforne of severl ttery ngeent strtegies. Model Ipleenttion High level ontrol The in ojetive of the ontrol of is to eulte the two inherent fetures of synhronous genertor tht re identified to e ruil in the stle nd relile opertion of power syste. These fetures re the rottionl inerti due to the rotting sses nd the speed-droop hrteristis of synhronous genertor for lod shring. The differentil eqution tht desries the rotor elertion 978--4799-99-9/3/ $3. 3 IEEE
of synhronous hine given the inerti onstnt J is: f ref P SO P P e = d( /Jω ) where, P is the ehnil power of the genertor nd P e is the eletril power of the genertor, while ω is the ngulr veloity of the rotor. () f S - df Δ f K d K p - N S P The rte of hnge of speed of the rotor is dependent on the oent of inerti of the rotting ss. The kineti energy tht is stored during the stedy opertion of the genertor is very enefiil t n ilne of torques. This kineti energy will e sored y the syste to itigte the speed devitions fro the synhronous speed [6]. y sustituting P P e with P V SG in eq. () n expression for the eultion of rottionl inerti is given y eq. () P V SG = K d dω In power genertion, rotor speed regultion is hieved with the use of governor. Hene, to intin onstnt frequeny under norl operting onditions, n uxiliry ontrol is required whih responds to slow frequeny devitions. For this reson droop prt is dded to eq. () s follows: () P V SG = K d dω K p(ω ω ref ) (3) ording to eq. (3), exhnges power with the grid in se the frequeny devites fro the noinl vlue nd/or rte of hnge of frequeny is deteted. The K d oeffiient is onstnt tht defines the ount of tive power interhnged with the network when the xiu speified rte of hnge of frequeny ( Hz /s) ours. The K p is the droop oeffiient nd defines the power tht needs to e sored or injeted into the syste due to the devition of frequeny fro the referene vlue [7]. The ontrol lw of eq. (3) is depited in Fig. in lok digr for. The ontroller ontins derivtive ter tht y produe rupt referene signl leding the syste over its opertion liits. Therefore, it is good prtie to filter the frequeny in order to lulte the tive power referene of the. Low level ontrol The purpose of the low level ontrol is to lulte the output urrent. Fig. 3 shows the ost iportnt prts of the three phse ontrol unit. The first lok perfors the trnsfortion of the -phse voltges t the point of oon oupling to the synhronous referene. The preter Fig.. lok digr of the high level ontrol of the. θ is extrted y Phse Loked Loop (PLL) lok nd defines the referene fre of the trnsfortion. The seond lok, whih refers to the high level ontrol, lultes the tive nd retive power tht should e produed y the, tking s input the frequeny of the syste nd the phse voltge t the dq referene fre. Within the sope of this work only the tive power is tken into onsidertion setting the retive power equl to zero (K V = in Fig. 3). The phse voltge long with the tive power, re pssed to the urrent referene lultion lok whih deterines the instntneous urrent referenes. sin(θ) sin (θ V d V [ π 3 ) sin(θ π 3 ) q os(θ) os(θ π 3 V ]= ) os (θ π V 3 ) V V ] Fig. 3. ontrol. 3 [ V V V Low level ontrol ulultions [ I d I q ] ][ V d,v q V d V q P Q urrent referene lultion = /3 V d V q [ V d V q V q V d ][ P Q] PLL High level ontrol P =K p ( f f ref )K d df Q =K V ( V d V q V ref ) I d I q I I [ I I ]=[ sin (θ) os(θ) sin(θ π 3 ) os (θ π 3 ) sin(θ ][ π 3 ) os(θ π 3 ) onfigurtion of unit onsisting of High nd Low level The odel of the s power iruit, onsists of three phse ontrolled urrent soure. s long s no swithing devies re inluded, the verge odel of the is sed on the energy onservtion priniple, whih ens tht the instntneous power on the side ust e the se with the D side (ssuing idel onversion). The D urrent n e therefore oputed s: P D = P I D = v i v i v i V D (4) ttery odeling The ttery energy storge syste is ipleented ording to the Kineti ttery Model (KiM) [8]. This odel is divided into two prts s shown in Fig. 4: f df I I I I d I q I ]
3 The pity odel, whih estites the stte of hrge (SO) of tteries. The voltge odel, tht lultes the terinl voltge of the tteries. SG R E jx E Lrge re KiM pity Model Lod Profile Vrile Lod Lod [ q k ( ) k ] [ q q ] = [ k ( ) q ] [ ] I k T q x q x( I)= e KT (kt e kt ) q I Exhnged Interfe Exhnged Fig. 5. One re syste oprising SG nd onneted to the grid. x 4 Voltge Model V =E I R E=E X X /( D X ) Terinl Voltge Lod [W] Fig. 4. The priniple of Kineti ttery Model. 3 4 5 6 7 8 9 () The pity odel is le to ddress oth the reovery nd the rte pity effet of the ttery. The first one refers to the effet where n ount of hrge eoes ville to the ttery when no hrge urrent is presented, while the seond one refers to the effet where less hrge n e drwn fro ttery when the dishrge urrent is inresed. The voltge odel of the seond lok onsiders the ttery s voltge soure in series with resistne tht is ssued to e onstnt. The terinl voltge depends oth on the stte of hrge s well s on the ount of the urrent drwn fro the ttery. Opertion nd Results The ojetive of this setion is to prove tht the is ple to derese the size of frequeny devitions tht re used y lod vritions in different networks. In order to evlute the ontriution of the in the overll stility of the syste, its stedy stte opertion is distured y hnging the tul totl lod of the syste. The disturnes re evluted in respet to the penetrtion level of the. The penetrtion level n e lulted s funtion of the noinl tive power genertion over the totl lod dend [9]. %V SG penetrtionlevel = PV SG PLod % (5) Prllel opertion of nd SG in lrge network The test network oprises of generting sttion, nd vrile lod tht re onneted to the grid through trnsission line. lod hnges its vlue ording to siple lod profile, using disturnes to the frequeny of the syste. The siultion network is shown in Fig. 5. The power onsuption on onstnt lod is 9 kw while the Frequeny [pu] tive [kw].4 %..9998.9996 4 3 4 5 6 7 8 9 () 3 4 5 6 7 8 9 () Fig. 6. Frequeny nd tive power of the syste during lod vritions. ) Lod profile, ) Frequeny respone, ) tive power response. lod devition does not exeed % of the noinl power of the generting sttion ( kv). The penetrtion of the inreses grdully. In this wy three su-senrios re exined, with penetrtion levels of %, %, nd 3%, respetively. Grph () Fig. 6 illustrtes the frequeny response of the power syste due to the lod hnges while the penetrtion level of the inreses. The tive power produed nd sored y the for eh level of penetrtion is depited in Grph () of Fig. 6. Siultion of the in two re syste In this senrio, the syste of Fig. 7 onsists of two generting sttions delivering power through two typil H.V. trnsission lines. The syste oprises of onstnt nd vrile lods nd unit. The penetrtion level of the is rted t % while the power onsuption on onstnt lod is 3 MW. The genertion sttions hve noinl power of 55 MV nd MV respetively. The vrile lod follows the lod profile of Fig. 8(). Fig. 8(), illustrtes the siultion results for the two odes of opertion, with % penetrtion of the nd without the, the oprison of whih kes disernile the effet of the unit on the xiu frequeny devition. % 3% % 3%
4 3-MHINE 9-US SYSTEM PUL M. NDERSON P.38 Givernor Mhine MV 8kV 36 rp RE, jx E, Vf Mhine MV 3.8kV 36 rp V series pitors (kv) -K- I_Fult () VkV Multieter Freq V (pu) wt 8MW Z-Z Freq V_5 reker Multieter Two re syste oprising two SG s nd. Grid 9MW 3MVr [I_] 75MW 5MVr I_ () Vrile Lod Lod Vf_ Z-Z Z-Z 3 V_5 (pu) V_5 Fig. 7. Z -Z SG Z -Z 6 MV-6 Hz 8 kv-5 kv Givernor RE, jx E, Vf_ Vf 6 MV-6 Hz 3.8 kv-5 kv SG MW 35MVr Lod Goto Sin_os 6 MV-6 Hz 6.5 kv-5 kv 3-phse PLL ontinuous Mhine 3 5 MV 6.5kV 36 rp Givernor Z-Z Vf_ Vf Lod [MW] 4 Fig. 9. 3.6 ()...3.4.6.5. No %..45 Frequeny [pu] Frequent [Hz] Frequeny [pu] Siulink odel of the 3-hine 9-us syste. No 5%.3.3.5.999.9985.998.997.997 ()...3.4.5.6 Fig. 8. Frequeny response for two odes of opertion: with % penetrtion of nd without for the two re syste..5..5..5.3.35.4.45.5 Fig.. Grid frequeny vrition for two odes of opertion: with 5% penetrtion of nd without for the 9-us siultion syste. Opertion of in three re syste The siultion syste is onstituted y the lssil nine us dyni power syste tht inludes three generting sttions nd three lods []. This syste is lrge enough to e nontrivil nd thus perits the illustrtion of ore relisti results. The oplete lok digr of the syste, is presented in Fig. 9. The ojetive of the siultion is to otin the response of the frequeny fter the trnsient is introdued. lod of % of the totl power is onneted, inititing the disturne. The totl tive lod of the syste is 345 MW while the penetrtion level of the virtul synhronous genertor is rted t 5 %. The dyni response of the frequeny of the power syste for the two odes of opertion, is shown in Fig.. ttery ngeent strtegies the tehnil speifition of ENTSO-E []. The priry ontrol is t the opertionl reliility of the power syste of the synhronous re nd stilizes the syste frequeny t sttionry vlue fter disturne. In se of n inident with lrge frequeny drop, the tivtion of priry ontrol reserve (tivted within seonds lsting less thn 5 in) is followed up y seondry ontrol reserve (tivted within inutes) whih is supported nd followed up y the tertiry ontrol reserve. UTE-wide tivted Priry ontrol Reserve tivted Seondry ontrol Reserve Shedule tivted Tertiry ontrol Reserve Diretly tivted Tertiry ontrol Reserve Tie Frequeny ontrol ording to ENTSO-E Fig.. Priniple frequeny devition nd susequent tivtion of reserves []. requireent for the opertion of the power syste is the lne etween power supply nd power dend t ny tie. Even under norl onditions, the dend of the syste is sujeted to ontinuous hnges. Therefore, severl levels of ontrols re perfored to intin the syste frequeny t its noinl vlue. Fig., deonstrtes the three types of ontrol perfored in different suessive steps ording to The ENTSO-E rules speify tht the noinl frequeny should e 5 Hz nd define frequeny zone of ± Hz within whih the frequeny vritions re onsidered non ritil. The xiu of ± Hz fro noinl frequeny is indited s perissile devition where the full priry ontrol hs to e tivted.
5 ttery sed for frequeny regultion In this setion the effet of operting the for priry frequeny regultion on the ttery energy storge syste is investigted. The ngeent of tteries iposes seletive restritions on the opertion of, e.g. when the ttery is fully hrged no ore tive power n e sored. Severl ttery ngeent strtegies hve een ssessed ording to the iniu ttery pity required for the oplishent of frequeny regultion []. The urrent frework uses rel frequeny dt for the tie period st to 8th of July tht were provided y the Greek independent power trnsission opertor (DMIE). For siultion resons we hoose hypothetil priry reserve ontrt of P n = MW whih sttes tht the syste is le to produe this power for t lest 5 in in ordne to ENTSO-E. onsequently, the iniu eptle energy of the storge syste would e: E reserve = P n h/4. The in funtion of the frequeny ontrol is to openste the frequeny devitions fro the grid. The size nd the rte of hnge of the devition deterine how uh power should e exhnged with the network. When the frequeny is hnged to vlues tht exeed the non ritil window, the ontrol should ret y soring or injeting power ording to eq. (3). onlusively, the priry reserve power P n should e provided when the xiu llowed frequeny devition of ± Hz ours or when the xiu speified rte of hnge of frequeny (.4 Hz /s) is relized. ontrol strtegies onstnt hrge-dishrge strtegy: Sine the ontrols re designed to work idiretionlly, the noinl stte of hrge should e in the iddle of the upper nd lower opertionl oundries of the storge syste. If we deterine the xiu depth of dishrge up to 4 % of the totl pity of the storge, then the referene stte of hrge is SO ref = 8 %. ontrol strtegy, is onsidered where the tteries re hrging t non-ritil periods ( f < Hz) nd seprte lgorith is tking to onsidertion the stte of hrge of the storge. The ojetive is - longside with priry frequeny regultion - to intin the ttery stte of hrge t the referene level, hrging or dishrging respetively, when the SO is less or greter thn the speified vlue SO ref. sll portion % to 5 % of P no is used for hrgerehrge power. The ontrol lgorith n e forulted in the following eqution: K P V SG = p (f f ref ) K d df, K so sgn(so SO ref ) f Hz f < Hz (6) where sgn is the sign funtion nd K so denotes the hrgedishrge power when the syste is out of the ritil window. Fig., illustrtes the depth of dishrge of the storge s funtion of tie for different odes of opertion with hrge-dishrge power of %, 3 %, nd 5 % of P n. The iniu energy tht needs to e reserved in the ESS for the opertion of frequeny regultion, during the siultion period, is losely relted to the ount of hrge-dishrge power. The lower the rehrge rte, the greter the depth of dishrge of the ESS nd therefore, the lrger ount of iniu energy is required to e reserved. Proportionl hrge-dishrge strtegy: This ontrol strtegy pplies the notion of nlog ontrol in the stte of hrge of the tteries. In the previous ontrol strtegy the hrging-dishrging power reined onstnt t predeterined power level, regrdless the proxiity of the ttery SO to the SO ref. In proportionl ontrol, ny devition fro the speified vlue (SO ref in our se) is onsidered s n error nd, therefore the lrger the error, the greter the power tht restores the syste to its referene ondition. The ojetive now is to regulte the ttery SO when the syste is inside the non-ritil window with vrile hrgedishrge power, whih depends on how fr fro the SO ref the syste is [3]... The opertion rule of the lgorith n e forulted in reltion to eq. (6) in the following wy: Depth of Dishrge.3.4.5.6.7 3 4 5 Tie (points) Fig.. Depth of dishrge of the storge s funtion of tie for the onstnt rehrge ontrol with hrge-dishrge power of %, 3 %, nd 5 % of noinl power P n. % 3 % 5 % x 5 K p (f f ref ) K d df P V SG =, f Hz K so (SO SO ref ), f < Hz SO x where, SO x = SO ref SO in =.. The onstnt frtion Kso / SO x is lulted in suh wy tht portion of hrge-dishrge power (.P n to.5p n ) is tivted when the hnge in the stte of hrge rehes (7)
6 the opertionl oundries of the storge syste. Therefore, the hrge-dishrge power is portion of the norlized oeffiient K so y the rtio (SO SO ref )/ SO x. The grph in Fig. 3 show the depth of dishrge of the storge s funtion of tie for different odes of opertion with K SO of %, 3 %, nd 5 % of P n.. only in few instnes throughout the siulted tie period when the ESS is in ritil stte. onlusions This pper provides vlidtion of the opertion of the in severl test-networks. Siultions show tht y inresing the level of penetrtion of the, the frequeny devition indued y the lod vritions is iproved. Depth of Dishrge..3.4.5.6.7 3 4 5 Tie (points) Fig. 3. Depth of dishrge of the storge s funtion of tie for different odes of opertion with K SO of %, 3 %, nd 5 % of P n. Fig. 4, ples together the xiu depth of dishrge nd the xiu hrge-dishrge power tht ourred s funtion of the K so for the foreentioned ontrol strtegies. Pririly, it illustrtes the effet of inresing the rte of hrge-dishrge power on the xiu depth of dishrge of the syste. The higher the oeffiient K so is, nd therefore the rte of hrge-dishrge power, the lower the xiu depth of dishrge of the storge, until threshold where further inrese kes no rel hnge. sll K so vlue of out 4 % 5% of P n is shown to e the upper liit for the syste for oth ttery ngeent strtegies, while sller vlue sees to e suffiient to intin the ttery SO. Fro the xiu depth of dishrge point of view, the onstnt nd proportionl ontrol lgoriths re oprle. Mxiu Depthof Dishrge.8.6.4 onstnd ontrol fitting urve Proportionl ontrol fitting urve...3.4.5.6.7 oeffiient Kso Fig. 4. Mxiu depth of dishrge nd xiu hrge-dishrge power s funtion of the K so. Moreover, Fig. 4 shows the xiu hrge-dishrge power ourred during siultion s funtion of the K so. The proportionl ontrol hrges the storge syste with greter xiu power, given tht this xiu power tkes ple only when the syste exeeds the opertionl oundries of the storge syste (i.e. SO < SO in ). This hppens % 3 % 5 % x 5 8 7 6 5 4 3 Mxiu hrge Dishrge power [% of Pn] oprison of severl ontrol strtegies of ttery storge syste with virtul inerti support for the frequeny regultion is lso provided. The siultion senrios onsidered herein uses rel frequeny dt for tie period of week. ethod is dopted to evlute the ttery ngeent strtegies ording to the iniu required ttery pity needed for the oplishent of frequeny regultion. The results show good perforne of oth onstnt nd proportionl hrge-dishrge strtegies. The ipt of different rehrge powers to the overll opertion is investigted showing tht rehrge power s sll s 3 % of P n is dequte for the intenne of the ESS. Referenes [] M. Donnelly, J. Dgle, D. Trudnowski, nd G. Rogers, Ipts of the distriuted utility on trnsission syste stility, IEEE Trnstions on Systes, vol., no., pp. 74 746, My 996. [] K. Vissher nd S. De Hn, Virtul synhronous hines ( S) for frequeny stilistion in future grids with signifint shre of deentrlized genertion, in SrtGrids for Distriution, 8. IET- IRED. IRED Seinr, Jun. 8. [3] H.-P. ek nd R. Hesse, Virtul synhronous hine, in Interntionl onferene on Eletril Qulity nd Utilistion, 7. [4] G. W. Qing-hng Zhong, Synhronverters: Inverters tht ii synhronous genertors, Industril Eletronis, IEEE Trnstions on, vol. 58, no. 4, pp. 59 67,. [5] T. V. Vn, K. Vissher, J. Diz, V. Krpnos,. Woyte, M. lu, J. ozelie, T. Loix, nd D. Federeniu, Virtul synhronous genertor: n eleent of future grids, in Innovtive Srt Grid Tehnologies onferene Europe (ISGT Europe), IEEE PES. IEEE, Ot.. [6] J. Mhowski, J. ilek, nd D. J. uy, Syste Dynis: Stility nd ontrol, nd ed., De. 8. [7] V. Krpnos, S. de Hn, nd K. Zwetsloot, Rel tie siultion of power syste with hrdwre in the loop, in IEON - 37th nnul onferene on IEEE Industril Eletronis Soiety. IEEE, Nov., pp. 3748 3754. [8] J. F. Mnwell nd J. G. MGown, Led id ttery storge odel for hyrid energy systes, Solr Energy, vol. 5, no. 5, pp. 399 45, My 993. [9] V. Vn Thong, E. Vndenrnde, J. Soens, D. Vn Doelen, J. Driesen, nd R. elns, Influenes of lrge penetrtion of distriuted genertion on n- sfety opertion, in Engineering Soiety Generl Meeting, 4. IEEE, Jun. 4, pp. 77 8. [] P. M. nderson nd.. Foud, syste ontrol nd stility. Wiley, Ot. 3. [] Opertionl hndook: Lod-frequeny ontrol nd perforne, ENTSO-E, Teh. Rep..5. [Online]. ville: https://www.entsoe.eu/ filedin/user_uplod/_lirry/pulitions/e/oh/poliy_finl.pdf []. Oudlov, D. hrtouni, nd. Ohler, Optiizing ttery energy storge syste for priry frequeny ontrol, Systes, IEEE Trnstions on, vol., no. 3, pp. 59 66, 7. [3] Krpnos, V., Yun, Z., de Hn, S. W. H., nd Vissher, K., ontrol lgorith for the oordintion of ultiple virtul synhronous genertor units, in Proeedings of the IEEE teh onferene, June 9-3, Trondhei, Norwy,.