Page - 327 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 315 Themisalignmentbetweenthecoils isdetectedusingsensorsandthevehicle’sposition is then adjustedbyappropriateautonomoussteeringuntil thedegradedpowertransfer intheDWCisrestored toanoptimumlevel. Manyvehicle trackingmethodshavebeenpreviouslyproposedwhereonepopularmethodis usingglobalpositioningsystem(GPS)sensorsand/ormagneticmarkers [18].Other trackingmethods specific forDWCapplicationsarealsoproposed in [19–21],wherea radio-frequency identification (RFID) tagandreaderwere implemented.However,onedisadvantageofmagneticmarkersorRFID tags is the rapiddecay in the strength of themagnetic fieldwith distance, as the detectormoves awayfromthemarker/tagrange. Therefore, themagneticmarkersorRFIDtagshave tobeplaced close toeachother inorder toachievehightrackingresolution,which increasesoverall construction costs. Toreduceconstructioncosts,magnetic sensinghardwarewithawiderdetectionrangehasbeen proposedas shown in [22] orusingaGaussian function-basedalgorithmtohavehigherdetection accuracy[23].However, this leads tobulkier sensorhardwarewhich isnotdesirable, especiallywhen vehiclespace isvery limitedwith theDWCsysteminstalled. Anothermethodofmagnetic tracking is theautonomouscoilalignmentsystem(ACAS),which hasbeenproposedbytheauthorsof thispaper in [24].ACASisanovelmethodof trackingavehicle’s misalignmentpositionbyonlymeasuring thevoltage in thevehicle’s loadcoil. Since thismethodonly utilizes theexistingDWCsystem, theuseofexternalmagneticorRFIDmarkers iseliminated,which leads toasignificant reduction in implementationcosts for themagnetic trackingfunctions.Onemain challengeof this approach ishowtodeterminewhether the loadcoilwasmisaligned to the left or therightsiderelative to thecenterof thesourcecoil. This isbecause thevoltagereadingsarenearly identicalonbothsides. Theproposedtwo-sensorcoilunitdesign in[24]detectedthe left/rightside positionbycalculating thedifference in thevoltage readingsof the twosensor coils. Even though theoperational feasibility of theACASwasverified, itwas only compatiblewith a specificDWC system,anditsalgorithmwasverycomplex. Ifanysignificantchangesweremadeto theDWCsystem, theaccuracyofpositiontrackingcouldbeaffected. TheACASproposedinthispaperisasignificant improvementoverthepreviousdesigndescribed in [24]. It is a single-sensor coilunit, anddetects change involtagephase to identify the left/right side position rather than the voltage difference between two sensor coils. With the newACAS design, thecomplexityof thealgorithmandhardwarecanbesignificantlyreduced,providingamore reliable system. This also allowswider application compatibilitywith otherDWCsystemswith varyingspecifications. The paper is organized as follows: an analysis of power loss due to lateral misalignment, aswell as the reasons for proposing theACAS system, are discussed in Section 2. In Section 3, themaincomponentsof theACASarediscussedanditsconcept feasibility isverifiedbysimulation. Theoperational feasibilityof theACASis furtherverifiedbyexperiments inSection4.Conclusionsare presented inSection5. 2.AnalysisofPowerLossDuetoLateralMisalignment inDynamicWirelessCharging (DWC)Systems DWCcanbeviewedasageneralWPTsystemcircuitmodel, showninFigure3,whichconsistsof asourcecoil anda loadcoil section. Theefficiencyof theWPTsystemisdefinedbytheratioof the powerdeliveredfromthesourcecoil,PS, andthe loadcoil,PL, as follows: η= PL PS (1) FromEquation(1),PS andPL canbedefinedas: PS= I1VS= ( RL+ 1jωCL+ jωLL jωM I2 ) VS (2) 327