Page - 22 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 1217 Thebatterypacksused inEVsaremadeofnumerousbatterycells (Figure26). TheTeslaModelS, for example, has7104Li-Ioncells in the85kWhpack. All these cells aredesired tohave the same SOCatall times tohavethesamedegradationrateandsamecapacityover the lifetime,preventing prematureendof life (EOL) [46].Apowerelectroniccontroldevice, calledacellvoltageequalizer, can achievethis featbytakingactivemeasures toequalize theSOCandvoltageofeachcell. Theequalizers canbeofdifferent typesaccordingto theirconstructionandworkingprinciple. Resistiveequalizers keepall thecellsat thesamevoltage levelbyburninguptheextrapoweratcellswithhighervoltages. Capacitiveequalizers,ontheotherhand, transfersenergyfromthehigherenergycells to the lower energyonesbyswitchingcapacitors. Inductivecapacitors canbeofdifferent configurations: basic, Cuk, andsingleofmultiple transformerbased; butall of themtransfer energy fromhigherenergy cells to theoneswith lowerenergybyusing inductors [46–52]. All these configurationshave their ownmeritsanddemerits,whichareshowninTable8; theschematicsareshowninFigures27and28. Table9showscomparisonsbetweentheequalizer types. Figure26. Battery cell arrangement inabatterypack. Cooling tubesareused todissipate theheat generated in thebatterycells. (a) (b) Figure27.Equalizerconfigurations: (a)Resistiveequalizer, extrapower fromanycell isburnedupin theresistance; (b)Capacitiveequalizer, excessenergy is transferredto lowerenergycellsbyswitching ofcapacitors. 22