OPTIMAL ENERGY SOURCE FOR AN ENVIRONMENTALLY-FRIENDLY GO-KART

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1 Journal of Ecological Engineering Volume 17, Issue 5, Nov. 016, pages DOI: /998993/65454 Research Aricle OPTIMAL ENERGY SOURCE FOR AN ENVIRONMENTALLY-FRIENDLY GO-KART Pior Zbigniew Filip 1, Marius Osrowski 1 1 Faculy of Elecrical Engineering an Compuer Science, Lublin Universiy of Technology, Lublin, Polan, pior.filip@pollub.pl Receive: Accepe: Publishe: ABSTRACT A meho for a siing of an elecromechanical ery for elecrical go-kar was presene in he paper. The main goal of his research was o replace he inernal combusion (IC) engine by an elecric rive sysem aking ino accoun he racion properies, on he one han an he uraion of operaion on a single charge an he number of he ery life cycles on he oher. The propose meho permis an enire epreciaion of he price of he vehicle before he egraaion of he ery occurs. The resuls of he suy have been use o ajus he source for elecric gokars ha will be mass prouce. Keywors: elecrical vehicle, go-kar, opimal ery siing, racion simulaion INTRODUCTION The European Union s legislaive work aime a ighening environmenal regulaions an inroucing fire safey regulaions limi he operaion of combusion vehicles inoors, forcing proucers an users of kars o se environmenally frienly soluions. (European Commission 016). Among he soluions consiere, he mos aracive ones are kars wih elecric rive, he choice of which is affece by heir well-known operaional avanages, such as: no emissions, maximum saring orque, high ynamics, a wie range of spee conrol an quie operaion. While ajusing he elecric rive moor o he kar is no a problem, he choice of he ype an sie of is power source is a challenge for esigners. The reason for his is he irec influence of he source parameers on boh he riving ynamics an he price of he vehicle, which mus be epreciae before he egraaion of he ery occurs. Previous aemps o replace he inernal combusion (IC) engine power in mos cases i no give fully saisfacory resuls, consiering he racion properies on he one han an he uraion of operaion on a single charge an he number of he ery life cycles on he oher. There are many commercially available elecric go-kar soluions, bu mos of hem have one of he hree isavanages: worse riving ynamics han comparable IC vehicles, which is mainly ue o he excessive weigh of he elecrochemical eries applie o ensure he operaing ime of a sanar combusion kar, he ynamic comparable o he combusion version, bu no guaranee of he expece operaing ime on a single charge, saisfacory riving ynamics while ensuring he necessary operaing ime, bu he raeoff is small ery urabiliy, causing ery egraaion before is payback ime. The selecion of eries is a ifficul ask ue o he naure of he kar operaion, much ifferen from he moor car. In ypical passenger vehicles, we have o eal wih shor perios of saring an acceleraion characerie by high power eman, which are usually followe by long perios of riving a a spee wih much lower power consumpion. (Hae-Ryong Choi & Gyu-Ha Choe 010). In conras, in a ypical uy cycle of a kar we have an almos coninuous ynamic sae of alernaing perios of acceleraion an ecelera- 90

2 Journal of Ecological Engineering Vol. 17(5), 016 ion. (Heffernan e al. 010). Therefore, he ery pack use in a go-kar is expose o much higher ischarging an charging currens, an shoul have a higher curren (an hus capaciy) raing. However, i shoul be remembere ha is sie (an hus, is weigh) shoul no impair he riving ynamics an have a reasonable price for he applicaion o be use commercially. SIMPLIFIED MODEL OF A KART The key issue in he selecion of eries is o evelop a moel of he vehicle aking ino accoun is mass, fricion an racion resuling from he kin of elecric rive moor applie. For he purpose of he research, a simulaion moel was evelope in Malab wih he following simplificaions (Filip e al. 015): he vehicle has a rigi boy represene by he resulan momen of ineria reuce o he riving wheel; is movemen is on a fla an even roa; mechanical fricion orque is proporional o he vehicle mass an spee; aeroynamic rag is proporional o he square of he spee an he buing face of he vehicle; he orque of he riving wheel is ecrease by all he fricion resisance o movemen uner consieraion; he power consume by he elecrical moor is he sum of effecive power (a he riving wheel) an is mechanical an elecrical power losses; fricion mechanical losses of he moor power are proporional o is angular velociy; power losses in he elecrical circui are proporional o he square of curren (elecromagneic orque). The research was performe for he go-kar wih a BLDC moor wih a rae power oupu of 5kW, a nominal volage of 48V an he rae spee of 4000rpm, which rove he rear axle of he kar hrough a oohe ransmission bel wih a gear raio of 3. The selece powerrain was esigne o provie a riving ynamics of he vehicle wih a oal weigh up o 00kg (incluing he river) no worse han a comparable kar wih a combusion engine, which acceleraes o 50km/h in 3.5s. To assure goo ynamic parameers an high energy efficiency a vecor conrol meho was applie for he moor conrol. (Pillay & Krishnan 1989; Kolano 01). Anoher essenial elemen is he ienificaion of he loa profile uring he operaion on a single charge. For his purpose, i is necessary o analyse he riving echnique an he course of he rack. Developmen of he simulaion work on he go-kar rack is consiere helpful in eermining he nominal curren source an is elecrochemical capaciy necessary for coninuous operaion a a given ime. In a ypical uy cycle of a kar we have a perio of inense acceleraion on a sraigh line, followe by rapi braking before enering a urn an hen again alernaing perios of acceleraion an eceleraion. Therefore, a represenaion of all hose operaing saes is necessary. In he firs sage, he sraigh-line movemen of he vehicle was consiere, in which he angular velociy of he wheels was proporional o he forwar spee so i can be reae as a sysem wih one-egree of freeom. Therefore, he mass of he vehicle an is momens of ineria are replace wih he equivalen value I reuce o he riving wheel shaf erms. The movemen of he vehicle is escribe by he ifferenial equaion: T ( ) c ( ) I I wheel ( ), 1/s (1) where: is ime, ω is an angular velociy of he riving wheel, T wheel is a riving orque of he wheel, I =0.04kgm is an equivalen momen of ineria reuce o a shaf of he riving wheel erms, c=½c x ρ S r 3 Nms is an aeroynamic rag coefficien reuce o roary moion, C x = 0.5 is an aeroynamic rag coefficien of he vehicle, S = 0.7m is a buing face of he vehicle, ρ = 1.168kg/m 3 is a normal air ensiy, r=0.01m is a raius of he wheel. Someimes, afer acceleraion here is a shor ime of riving on a sraigh line sraigh wih a maximum consan angular spee of he wheel for a vehicle spee equal 50km/h. In such a case of a seay sae ( ) max cons, 1/s () he wheel riving orque compensaes only he rag T wheel ( ) c ( ), Nm (3) 91

3 Journal of Ecological Engineering Vol. 17(5), 016 Fas riving along a curvy roa means moving wih possibly he greaes spee along sraigh sreches, bu reucing he spee before going ino a sharp urn. There are some alernaives o slowing own: losing spee as a consequence of naural resisance o moion, using mechanical brakes or regeneraive braking using an elecrical moor. For ile riving wih moor urne-off he ifferenial equaion is c ( ) I ( ), 1/s (4) The ifferenial equaion for regeneraive braking can be wrien as c k ( ) I I p ( ) ( ), 1/s (5) where: k P =η is he coefficien of resisance o moion, assuming ha elecrical moor efficiency η in regeneraive an moor operaing moe are equal. When mechanical barkers are use for slowing he vehicle own, he moion can be escribe by c I ( ) ( ) TH, 1/s (6) where: T H is maximum braking orque esimae on he basis of ime neee o sop he vehicle moving wih a cerain spee. Taking ino accoun ha moor losses are lower han he value of oher vehicle losses, a simplifie moor moel was consiere for he purpose of he ery siing. Proporionaliy beween a curren of a DC source an a generae riving orque was assume. i( ) kmtmo( ), A (7) where: i represens a curren of he elecrochemical ery an k M is an exciing flux epenen coefficien of he elecrical machine. Moor mechanical losses were neglece while only elecrical losses were aken as quaraic funcion of i. Then power elivere by he ery was calculae as: P ( ) P ( ) R i ( ), W (8) inpu E where: P inpu is a useful mechanical moor power (covering mechanical rag) an R E i are elecrical power losses, in which R E represens an equivalen resisance of moor winings an ery. BATTERY SELECTION AND SIZING Esimaion of he elecrochemical source was performe for he go-kar wih he expece ime of coninuous riving on a single ery charge assume o be 1 hour. (Hunic e al. 015). In assembling he source for he applicaion in quesion, regare as mass-criical an highly power emaning. (Lowe e al. 010). LiFeMn elecrochemical cells ha have a high specific energy, specific power an a large number of life cycles were chosen. The rae volage of he ery is eermine by he nominal volage of he applie riving moor an shoul no be lower in comparison o is value. The basis for ensuring ery life is he principle ha he maximum curren rawn by he rive shoul no excee he limi value use for elecrochemical eries. A nominal ery curren was foun by comparing ery nominal energy losses an an equivalen energy losses for a operaion ime, which woul ensure keeping wihin he limi of accepable losses (prevening an overheaing) in cells a coninuous loa. R I N R i ( ), W (9) 0 where: τ is an operaion ime on a single charge, R is ery inernal resisance, I N is rae curren of he ery, i is a value of he ery curren for he insan. Thus, he rae curren was calculae as follows: I N 0 i ( ), A (10) The heoreical energy capaciy E of he source was esimae by inegraing over he ime (τ =1h) a sum of elecrical losses an power consume by elecric rive sysem P inpu require o cover he enire isance on a single charge in coninuous operaion. E 0 P R i, J inpu E (11) This value can be recalculae o he heoreical Coulombic capaciy of he ery by iviing i by is rae volage U : 9

4 Journal of Ecological Engineering Vol. 17(5), 016 E CCTeor, Ah (1) U In orer o ensure sufficien life of he eries, which is he number of life cycles allowing for he oal epreciaion of he enire vehicle, i is assume ha he ischarge shoul be no more han 80% DOD (Deph of Discharge). Furhermore, accoring o he recommenaions of he US ABC, in orer o mainain he parameers of he source consan uring he whole expece lifeime (up o ery replacemen), he acual ery capaciy was also increase by 30%. (US ABC 010; Lowe e al. 010): CC MIN.3 CC /0.8, Ah (13) 1 Teor These calculaions were performe for wo riving echniques he firs using a regeneraive braking an he secon applying only mechanical braking. In pracice, i is impossible o rive using only he mechanical- or regeneraivebraking echnique, since he final parameers of he source were average. Resuls of compuer simulaions of one acceleraion-braking cycle for he wo riving echniques were shown a Figure 1 an Figure where: a) V a vehicle spee, T wheel a wheel riving orque; b) T mo an elecromagneic orque, P mo_loss moor losses, P inpu power consume by rive sysem; c) i a ery curren, P ery power losses; ) P _ power an loss E energy elivere by he ery. Compuaions base on equaion (10) for a LiFeMn ery wih a rae volage of 48V gave a minimal value of he ery nominal curren of: I N 50A for a riving echnique wih mechanical-braking an I N 58A for a riving echnique wih regeneraive-braking. I shoul be noice, ha a value of he curren for a case of he regeneraive-braking is bigger han for he oher one because uring his operaion here is no res for he source since a charging curren generaes aiional energy losses. Consiering a mixe-braking echnique of riving, he ery curren shoul be a leas 54A. a) b) c) ) Figure 1. Simulaion resuls for one acceleraion-braking cycle of a go-kar operaion using a regeneraive-braking riving echnique. 93

5 Journal of Ecological Engineering Vol. 17(5), 016 Compuer simulaions inicae an acual minimal value of he ery Coulombic capaciy for he operaing ime of 1h on a single charge, which shoul be: CC NaMIN 111.7Ah for riving echnique wih mechanical-braking an CC NaMIN 94.74Ah for riving echnique wih regeneraive-braking. A riving applying he regeneraive braking nees smaller capaciy comparing o mechanical braking echnique because of some energy savings mae uring a charging moe. Since he mixebraking echnique is usually use in pracice, he rae value of he ery Coulombic capaciy shoul be average an no lower han 103.3Ah. The final choice of a paricular moel of an elecrochemical source shoul resul from he economic analysis an be a raeoff beween he lifecycle an he epreciaion of kar purchase price before he egraaion of he ery. CONCLUSIONS The new European regulaions concerning he inoor operaion of go-kars force heir users o replace he IC rives use in he vehicles wih ecological soluions. Among he available kars wih elecric rive few moels have he racion parameers comparable o heir IC counerpars, while proviing he life cycle necessary for epreciaion in coninuous operaion for 1 hour. The aricle proposes a selecion proceure for an elecrochemical ery in an elecric kar. The choice of a ery nominal curren is base on he equivalen losses meho. Esimaion of an acual Coulombic capaciy nees an inegraion of a consume an save (in regeneraive moe) energy uring a whole operaing ime on one charge. Since in pracice here is mixe-braking echnique of a riving, hese calculaion shoul be performe for he operaion applying a me- Figure. Simulaion resuls for one acceleraion-braking cycle of a go-kar operaion using a mechanical-braking riving echnique. 94

6 Journal of Ecological Engineering Vol. 17(5), 016 chanical an regeneraive braking, an hen final values have o be average. The proceure use for he selecion of he elecrochemical power source for an elecric kar assure opimise choice of is parameers, which resule in coninuous operaion of he kar on a single charge. A he same ime, he necessary racion ynamics of he vehicle was obaine an he assume life of he source mainaine. The resuls of he suy have been use o ajus he power source for elecric go-kars ha will be mass prouce by NABOR of Kraśnik, Polan. REFERENCES 1. European Commission, 016. Review of he EU Air Policy. hp://ec.europa.eu/environmen/air/review_air_policy.hm. Filip P.Z., Kolano K., Osrowski M Low energy consumpion conrol sraegy for elecrical vehicle, WZEE Conference, Kielce Polan (unpublishe). 3. Hae-Ryong Choi & Gyu-Ha Choe A Muliobjecive Parameric Opimiaion for Passenger- Car Seering Acuaor. IEEE Transacions on Inusrial Elecronics, 57(3), Heffernan B. & Duke R. & Zhang R. & Gaynor P. & Cusin M A go-car as an elecric vehicle for unergrauae eaching an assessmen. Universiies Power Engineering Conference (AU- PEC), 0h Ausralasian, Hunic J. & Kolano K. & Filip P. & Osrowski M Inegracja elrycnego sysemu napęowego sysemem serowania i akumulaorowym sysemem asilania w pojeźie ypu gokar, Rapor prac baawco-rowojowych na lecenie firmy NABOR, Lublin, Polan (unpublishe). 6. Kolano K. 01. Lif car oors rive sysem wih hi-efficien BLDC rive. Pregla Elroechnicny, 88(11B), Lowe M. & Tokuoka S. & Trigg T. & Gereffi G Lihium-Ion Baeries for Elecric Vehicles: THE U.S. VALUE CHAIN., 5 Ocober 010, CGGC. 8. Pillay P. & Krishnan R Moeling, Simulaion, an Analysis of Permanen-Magne Moor Drives, Par I: The Permanen Magne Synchronous Moor Drive, IEEE Transacions On Inusry Applicaions, March -April 1989, Vol. 5, No.. 9. US ABC 010. Developmen of avance high-performance eries for elecric vehicle (EV) applicaions, Unie Saes Avance Baery Consorium LLC. 95