Developmen and Tesing of a 200 MJ/350 kw Kineic Energy Sorage Sysem for Railways Applicaions L.Garcia-Tabares 2, J. Iglesias 1,M. Lafoz 2, J.C. Marinez 1, C. Vazquez 2, C.Tobajas 1, A. Gomez-Alors 1, A. Echeandia 3, J Lucas 3,C. Zuazo 4, J.M. Carrasco 5, S. Vázquez 5. 1 ADIF. Spanish Railways Infrasrucure Manager 2 CIEMAT. Energy, Environmen and Technology Research. Spain 3 ELYTT ENERGY. Spain 4 TEKNIKER. Spain 5 GREENPOWER. Spain Absrac In 2003, he Spanish Manager for Railways Infrasrucure (ADIF) in collaboraion wih CIEMAT (formerly CEDEX, an Insiue belonging o he Public Works Minisry of Spain), launched a projec for developing a flywheel energy sorage sysem for power managemen in railways subsaions wih he aims braking energy recovery in convenional lines supplied wih 3000 V DC. A he ime of presening his paper, he firs prooype of KESS (Kineic Energy Sorage Sysem) is finished and has been esed a he CIEMAT faciliies. Prior o hese ess, wo previous and smaller prooypes have been developed and esed in he same faciliies. The sysem is based on he use of a meallic flywheel, a swiched relucance moor/generaor (SRM) and he corresponding power elecronics, including a machine side converer and a grid side converer. 200 MJ (55.6kWh) of energy can be sored in a high srengh seel flywheel, roaing over 6.000 rpm, which is magneically leviaed and guided wih convenional high speed bearings. A power of 350kW can be exchanged in he elecrical machine which is a swiched relucance, 6/4 poles, moor-generaor, working in eiher single pulse or hyseresis band, depending on is speed. The machine is driven wih a full H converer per phase, bidirecional in volage and curren hus reducing magneic losses in he roor of he SRM. Finally here is a grid side converer connecing he grid of he subsaion o a dc-link previous o he machine converer in order o supply single phase loads, conrolled using a double hyseresis-band curren sraegy. A specific and very robus digial conrol plaform has also been developed for his applicaion o manage he complee sysem. The paper will presen also he ess of he KESS uni in a real elecric subsaion specially condiioned by ADIF o perform hese ess. This subsaion is very close o Madrid-Aocha saion which is a really imporan railway juncion of Madrid commuer lines. Tess in his subsaion will show he real funcioning of he developed KESS as well as he level of reliabiliy achieved in his pioneer projec. 1. INTRODUCTION Energy consumpion in ransporaion is a serious social problem. The increase of ranspor energy consumpion is higher han in oher energy uses (in Spain, railway has increased 6 % annually since 2002). Alhough improvemen of he railway service qualiy implies a greaer energy cos, i is he ransporaion mode ha consumes less energy and ha is one of he main argumens for public auhoriies o inves in railways. Since oher ransporaion modes are improving energy efficiency railways should no neglec heir compeiive advanage and have o invesigae and innovae o keep i. Energy savings, qualiy, reliabiliy, power peaks reducion, acceleraion capaciy when saring and volage drops reducion a he caenary are some of he conceps considered in railway ransporaion research. These problems concern mainly DC railway lines (subways, commuer rains and ligh rains). Energy Sorage Sysems is one of he main soluions o improve hose applicaions and will be described in his paper. Recen sudies from ADIF have concluded ha in railway DC-lines he wase of energy due o regeneraive braking can vary beween 8 and 25% depending of he kind of raffic. This energy can no be reurned ino he grid due o he subsaion diode recifiers and i could be re-uilized by means of
energy sorage devices. Moreover he number of diary supply inerrupions could be reduced from 15 o 1 wih he same echnology. The following decision is: Wha ype of energy sorage device is more appropriae for railways? There is no an easy answer and depends on he paricular problem o be afford. Mos of he publicaions and research works during he las years are focussed on on-board soluions for rains and presen he soluion of ulracapaciors or baeries. The on-board soluion is more efficien since he energy sorage device acs direcly over he elecric machine bu a sysem off-board conneced o he DC caenary has some oher advanages such as no exra space occupied in he vehicle, no modificaions in he rain space disribuion and ha he sysem can be conneced o he caenary, solving he caenary volage problems considering whaever amoun of rains. Kineic Energy Sorage Sysems (KESS) based on flywheels is appropriae for some applicaions when very high power, no high energy, large number of cycles and shor period beween charge and discharge operaion. This echnology has hree main advanages: Firs, he high power and energy levels as well as energy/power raio o achieve he requiremens; second, he oal cos is no so linearly increasing wih he power and energy level compared o some oher echnologies like baeries or ulracapaciors; and finally he advanage of insalling he sysem in a saic locaion near he subsaion reduces he mechanical or safey problems ha flywheels or oher echnologies would inroduce when mouning on board. The Spanish Adminisraor for Railways Infrasrucure (ADIF) in collaboraion wih he Insiue for Energy, Environmen and Technology Research (CIEMAT) and oher 5 companies has promoed a projec named FERRO_SA2VE (Advanced Energy Sorage Sysems. Applicaions o Railway Transporaion), included in he frame of a bigger projec SA2VE, o insall some Kineic Energy Sorage Sysem ino a subsaion, sabilizing he elecrical nework around he railway consumpion poins by means of regulaing he DC caenary volage level and he power consumpion. Afer esing he complee sysem in laboraory providing a caenary emulaor, he sysem has been definiely insalled in a DC railway subsaion and operaed by ineracing wih real raffic. 2. TECHNOLOGY DESCRIPTION There are some commercial soluions of flywheels used for rains [Urenco, Piller, Penadyne, Beacon, ec] and many echnologies have been used in erms of ype of machine, flywheel maerials and power, energy and speed levels. The sysem developed and presened in his paper is designed o be commercially compeiive and presens several benefis: The echnology is compleely proper (machine, flywheel, power elecronics and conrol); he maerials used are convenional and he eam has previous experience in fabricaion of his ype of elecromagneic devices, vacuum, power elecronics and conrol plaforms consrucion and esing, achieving an opimal cos and ensuring he success. The sysem is composed by a meallic flywheel of 6 ons driven by a reversible swiched relucance machine used o increase and o decrease he speed and herefore he energy sored. Nominal speed is 6500 rpm and he oal ineria of he flywheel is 895 kg m 2 [13]. Figure 1 presens how he machine and he flywheel look like. Convenional ceramic bearings have been used bu since he weigh and speed level are oo high for any commercial bearings, a magneic leviaion has been disposed by means of permanen magnes pulling up he meallic flywheel. PARAMETER VALUE RPM 6600 Power 350 kw Energy 200 MJ DC Volage. 1000 V Curren/Phase 790 A Phases 3 Saor Poles 6 Roor Poles 4 Leviaion PM+Ele crica l Figure 1. Elecrical machine, he flywheel and sysem parameers.
The power elecronics equipmen is composed by he converer sage o drive he machine and he isolaed DC/DC caenary converer o connec o he railway DC caenary plus a hree-phase inverer o connec he DC-link wih he AC elecric nework. Dedicaed conrol hardware has been designed based on microprocessors and will be responsible of conrolling he power elecronics and communicaing wih he subsaion conrol. Figure 2. Power elecronics converers (machine-side, grid-side and caenary converer) and conrol plaform a he laboraory ess. Circui breaker L CLR (DC/AC) KINETIC ENERGY STORAGE CLM (DC/AC) Ω+ 400/1200-3000 V 400kVA 3000 V (b) DC/DC (a) SRM+Flywheel 12 pulses diode recifier 700-950 V Figure 3. Connecion scheme a he laboraory bu also a he subsaion. Figure 3 shows how he KESS is conneced o he DC caenary during he laboraory ess. A he Lab, he same volage condiions are reproduced by means of a double secondary power ransformer and a 12 pulses diode recifier. A DC/DC converer is conneced o he variable caenary volage ransforming he volage level ino he machine volage range (750-900V) for he operaion. An inermediae power ransformer in an AC sage is used o he adapion, ensuring he volage isolaion from caenary. Figure 4 presens he DC/DC converer opology. The machine-side converer (CLM) is used o drive he machine a he appropriae condiions depending on he load. Moreover here is a grid-side converer (CLR) o release he power ino he AC grid when no caenary access is permied in case of flywheel breaking necessiy. Rca Lca DC/DC N:1 Vca FILTRO CATENARIA DC AC FILTRO TRAFO AC DC Vou CONVERTIDOR LADO MÁQUINA Figure 4. DC/DC caenary converer opology. Figure 5 presens he connecion a he railway subsaion, subsiuing he caenary emulaor by he real caenary. The CLR converer is mainained o provide power o he AC nework. The green line indicaes he bidirecional power flux when rain is requiring or supplying power from he caenary o he KESS. The red line indicaes he power flux from caenary o AC nework.
230V AC L CLR (DC/AC) KINETIC ENERGY STORAGE 3000V RAILWAY CATENARY 3000 V DC/DC 700-950 V CLM (DC/AC) Ω+ SRM+Flywheel Figure 5. Sysem connecion a he railway subsaion. 3. INSTALLATION AT THE RAILWAY SUBSTATION The sysem has been insalled in a railway subsaion in Madrid Figure 6. Machine and Flywheel insalled in he subsaion, power elecronics converers and conrol 4. OPERATION CRITERIA FOR THE KESS UNDER RAILWAY TRAFFIC One of he main quesions relaed o he convenience of kineic energy sorage echnique is he efficiency. Several losses erms can be considered: iron losses, cupper losses and mechanical losses. Cupper losses are reduced by means of providing a very low curren densiy wire for he machine coils (less han 2 A/mm 2 is recommended). Magneizaion and demagneizaion of he elecrical machine produce some amoun of iron losses, reduced by a bidirecional curren operaion. Neverheless he mos imporan losses are he air-fricion losses of he flywheel ha implies a reducion of he oal sysem efficiency and complicaes he cooling sysem. Elecric power has been measured following equaion 1, considering he average power during a cerain number of cycles, mainaining he flywheel spinning around he fixed speed of 5000 rpm.
P losses 1 m k 1 m ( cycles ) k 1 k u i d k ; ( Equaion 1) Afer several ess a 120 kw wih differen pressures (950, 500 and 250mbar), an average power consumpion is presened in he figure 7b. Since he same power and speed is used, he inersecion wih he ordinaes axis represens elecrical power losses plus iron losses plus bearing losses. Figure 7.a presens a ypical operaion siuaion wih some cycles o recover he raed speed and a discharge cycle. The number of charge-discharge cycles and also he frequency of hese cycles is one of he imporan poins o selec his echnology insead of ohers. The higher number of charge-discharge cycles he beer efficiency is achieved for a realisic characerisic of machine fabricaion and operaion Ω P Maximum speed Recovery speed Poencia de predidas (kw) 14 12 10 8 6 4 2 0 0 100 200 300 400 500 600 700 800 900 1000 Presión de vacío (mbar) Figure 7. (a) KESS Operaion. Speed and power during charging and discharging. (b) Fricion loses wih pressure. The KESS has been proposed o work during he day, while is no exchanging any power during he nigh. During he day, i is named operaion mode. The inner pressure is conrolled around 150mbar and he machine can exchange power wih he railway caenary. The efficiency depends on he amoun of periods of power ransmission and he periods when he speed has o be mainained (an average 6kW is required o mainain he speed around 3000rpm). During nigh, i is named sorage mode. I consiss in reducing he pressure o 10mbar and mainaining during 8 hours he machine spinning wihou exchanging any power. During his ime he speed is reduced 1500rpm wihou any addiional losses and can be resared he nex day in operaion mode again. Afer esing he sysem under differen scenarios of power and exchange frequency i has been observed ha he mos imporan limiaion is he heaing due o he sysem losses (mainly Joule effec losses in he elecric machine and aerodynamic losses in he flywheel). The key elemens more sensible o he heaing are he machine coils and he bearings. Temperaure has been measured in hem deermining a maximum value of 100ºC for bearings and 120ºC for coils. Under coils emperaure limiaion, and considering he heaing and cooling response i has been concluded ha maximum power o work coninuously is 150kW. On he oher hand under bearings emperaure limiaion, he sysem can spin a 3000rpm coninuously. This way he energy able o be exchanged is 50MJ. Figure 8 presen he speed evoluion during charge, discharge and mainenance operaion. 3500 rpm Figure 8. Speed paern for he KESS during operaion 2000 rpm
5. EXPERIMENTAL RESULTS Experimenal ess connecing o he caenary have been carried ou. Neverheless, he operaion under rain demand has no been implemened ye. Several ess have o be passed wihou rain ineracion. Figure 9 presens machine curren waveform in boh moor and generaor modes by simulaing a rain braking and acceleraion. Figure 9. Machine curren during moor (lef) and generaor (righ) mode operaion. 800A curren and 3500rpm. The sysem has been also provided wih he possibiliy o supply power direcly from he caenary o he AC-line. Figure 10 includes machine currens (only wo of he hree phase currens) while a cerain AC load is supplied from he caenary (volage and curren mainaining he power facor). The conrol sraegy decides when power exchange wih he KESS and when wih he AC. Figure 10. KESS supplying power o he AC nework Figure 11 presens and energy sorage device response when a load demand is deeced from he non supply mode. 4 cycles are enough o ge raed power and a 10% of DC volage variaion is produced. Moor mode operaion Generaor mode operaion Transiion o sorage mode Transiion o supply mode Figure 11. Transiions beween KESS operaion modes
6. MAIN CONCLUSIONS This paper has presened he curren siuaion of he projec SA 2 VE joinly led by ADIF (Spanish Railways Infrasrucure Manger) and CIEMAT (Insiue for Energy, Environmen and Technology Research) wih he arge of designing, developing and esing a Kineic Energy Sorage Uni (KESS) o be used for soring he braking energy of he rains and giving back his energy o he caenary. The main resuls obained up o he dae could be summarized in he following: 1. Alhough he sysem was iniially conceived for been applied in high speed lines (HSL) o smooh he subsaion consumpion and herefore reducing he nominal power of HSL subsaions, i was finally decided o be dedicaed o sorage braking energy in commuer lines where DC subsaions don allow energy recovery o he nework. 2. The sysem composed by he flywheel, high speed bearings, leviaion sysem, elecric swiched relucance machine, power converers (machine side converer, caenary connecion converer and AC subsaion grid converer) and conrol sysem has been compleely designed and buil. 3. The whole sysem has been iniially esed in he laboraory in several seps including various incremenal power prooypes and alhough boh he iniial foreseen power and energy raes have been limied for echnological reasons, he obained resuls can be considered saisfacory. 4. The sysem, afer seing up an ADIF subsaion in Madrid commuer lines, is already insalled here and conneced o 3000DC V caenary. Firs ess have been already performed bu, as he final arge of hese ess are o check he robusness and reliabiliy; final resuls will be evaluaed afer esing he insallaion during he whole year 2011. 5. Finally, he applicaion of his Energy Sorages sysem o DC lines can save an imporan amoun of energy which is currenly dissipaed in he braking resisors. According o ADIF s analysis his energy can flucuae beween 8 and 25% of he oal consumpion, and ADIF is working no only in his direcion bu also in developing reversible subsaions which can, ogeher wih KESS, conribue o improve he Energy efficiency of he Railways sysem. REFERENCES [1] Ribeiro, P.F.; Johnson, B.K.; Crow, M.L.; Arsoy, A.; Liu,Y.; Energy Sorage Sysems for Advanced Power Applicaions. Proc. of he IEEE, Dec 2001, Vol 89, pp. 1744-1756. [2] Henschel, F.; Müller, K.; Seiner, M.; Energy Sorage on Urban Railway Vehicles. Proceedings of he UIC Energy Efficiency Conference, Paris, 2000. [3] Lafoz, M., Vázquez, C., The ACE2 Sysem: A Kineic Energy Sorage for Railway Subsaions. Procs. Elecrical Energy Sorage Applicaions and Technologies Conference (EESAT). 2007. [4] Vázquez, C.; Lafoz, M.; Ugena, D.; García-Tabarés, L.; Conrol Sysem for he Swiched Relucance Drive of a Flywheel Energy-Sorage Sysem. European Transacions on Elecrical Power. Wiley-Inerscience. 2007. [5] Miller, T.J.E.; Swiched Relucance Moors and heir Conrol. Magna Physics Publishing and Clarendon Press. Oxford 1993. [6] Krishnan, R.; Swiched Relucance Moor Drives: Modelling, Simulaion, Analysis, Design and Applicaions, CRC Press LLC, New York, 2001. [7] Raulin V., Radun A., Husain I. Modelling of Losses in Swiched Relucance Machines. IEEE Transacions on Indusry Applicaions, vol 40. Nº 6, November/December 2004. p. 1560-1569. [8] Mhombeni L.T., Pillay P. Core Losses in Moor Laminaions Exposed o High Frequency or Non-sinusoidal Exciaion. IEEE Transacions on Indusry Applicaions, vol 40. Nº5. Sepember/Ocober 2004. p. 1325-1332. [9] Paschen, F.; Uber die zum Funkenübergang in Luf, Wassersoff und Kohlensaüre bei verschiedenen Drucken erforderliche Poenialdifferen z. Ann. Phys. Chem, Ser. 37, 69-96. 1889. [10] Vukosavic, S.; Sefanovic, V.R.; SRM Inverer Topologies: A Comparaive Evaluaion. IEEE Transacions on Indusry Applicaions. Vol. 27, Nº 6, pp. 1034-1047, Nov./Dec. 1991. [11] Mir. S.; Classificaion of SRM Converer Topologies for Auomoive Applicaions. SAE Technical Paper Series 2000-01-0133. SAE 2000 World Congress. March 2000.
[12] Barnes, M.; Pollock, Ch.; Power Elecronics Converers for Swiched Relucance Drives. IEEE Transacions on Power Elecronics, Vol. 13, Nº 6, pp. 1100-1111, November 1998. [13] I.J. Iglesias. J.C. Marinez, C. Tobajas, M. Lafoz, L. García-Tabarés and C. Vazquez A Kineic Energy Sorage Sysem for Railways Applicaions. The 8h World Congress on Railway Research (WCRR 2008) Seoul, Korea, May 18h o 22h.