Page - 5 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 1217 it alsoreduces the fuel consumptionas theenginestays totallyoffduring idlingperiods, forexample, traffic jams. This feature also reduces theGHGemission. Whenhigher speed isneeded, theHEV switches to the ICE.The twodrive trainscanalsoworktogether to improve theperformance.Hybrid power systemsareusedextensively to reduceor to completely remove turbo lag in turbocharged cars, like theAcuraNSX. It alsoenhancesperformancebyfilling thegapsbetweengear shifts and providingspeedboostswhenrequired. TheICEcanchargeupthebatteries,HEVscanalsoretrieve energybymeansof regenerativebraking. Therefore,HEVsareprimarily ICEdrivencars thatusean electricaldrive train to improvemileageor forperformanceenhancement. Toattain these features, HEVconfigurationsarebeingwidelyadoptedbycarmanufacturers. Figure4showstheenergyflows inabasicHEV.Whilestarting thevehicle, the ICEmayrunthemotorasagenerator toproducesome powerandstore it in thebattery. Passingneedsaboost in speed, therefore the ICEand themotor bothdrives thepower train.Duringbrakingthepower trainruns themotorasgenerator tocharge thebatterybyregenerativebraking.Whilecruising, ICEruns theboththevehicleandthemotoras generator,whichcharges thebattery. Thepowerflowisstoppedoncethevehiclestops. Figure5shows anexampleofenergymanagementsystemsusedinHEVs. Theonedemonstratedheresplitspower betweenthe ICEandtheelectricmotor (EM)byconsidering thevehiclespeed,driver’s input, stateof charge (SOC)ofbattery,andthemotorspeedtoattainmaximumfuelefficiency. (a) Direction of power flow during starting and when stopped. (b) Direction of power flow during passing, braking and cruising. Figure4.PowerflowamongthebasicbuildingblocksofanHEVduringvariousstagesofadrivecycle. Adaptedfrom[8]. 5