Hardware Design Considerations for an Efficient …

1 ApplicationReportSLVA654A June2014 RevisedJuly 2015 HardwareDesignConsiderationsfor an EfficientVacuumCleanerUsinga BLDCM otorNickObornyABSTRACTA vacuumcleaneris a devicethat usesan air pumpto createa partialvacuumto suckup dirt and dustparticlesfroma usedin homesas well as in industriesand comewitha varietyof powerlevels,smallbattery-operatedhand-he lddevices,domesticcentralvacuumcleanersa nd universalmotoris typicallyusedas a seriesDC-motorthat is speciallydesignedto operateonalternatingcurrent(AC)as well as on directcurrent(DC).Universalmotorshavehig hstartingtorque,operateat highspeed,and are also relativelyeasyto ,becauseof the wearin commutatorbrushesthis typeof motoris not preferredfor commutationthesemotorsare DCmotorsare alsoapplicableto universalmotorsbecausethis typeof motoris closerin conceptto DCmotorsthanAC (originalequipmentmanufacturers)are consideringalternativemotortypesto use of a BLDC motorforvacuumcleanerapplicationwith Motors(BLDC).. the (8 to 60-VDC PowerSupply).

2 107 CAPand (eCAN)..109 High-Resolutionand of June2014 RevisedJuly 2015 HardwareDesignConsiderationsfor an EfficientVacuumCleanerUsingaBLDCM otorSubmitDocumentationFeedbackCopyright 2014 2015, of an EfficientVacuumCleanerUsingaSLVA654A June2014 RevisedJuly 2015 BLDCM otorSubmitDocumentationFeedbackCopyright 2014 2015,TexasInstrumentsIncorporatedBLDC MotorAir FlowLow PressureHigh PressureCentrifugal motoris attachedto a centrifugalfan with the fan bladesturn,they forceair forwardtowardthe particlesare drivenforward,the densityof particles(andthereforetheair pressure)increasesin frontof the fan and decreasesbehindthe fan. The pressurelevelin the areabehindthe fan dropsbelowthe pressureleveloutsidethe vacuumcleaner(the ambientair pressure).Thiscreatessuction,whichis a partialvacuum,insidethe ambientair pushesinto thevacuumcleanerthroughthe intakeport becausethe air pressureinsidethe vacuumcleaneris lowerthanthe long as the fan is runningand the passagewaythroughthe vacuumcleanerremainsopen,thereis a constantstreamof air movingthroughthe intakeport and out of the SuctionPrincipleThe suctionmotorload considerationis or morefans are attachedto the motorshaftandare rotatedat a very high air enteringthe fan nearthe hub is forcedto spin with the fan as theair passesthroughthe fan.

3 The load to the motoris the forcerequiredto overcomethe inertiaof the air asit entersthe fan and is air flow throughthe motoris reducedby increasingthe resistanceto the air flow,the load on the motoris actuallyreducedand the speedtendsto fall. Thereforeto increasethe suctionthe currentdrawnfromthe mainsincreases,and hencethe effectof this is to increasethe suctioncreatedby the motorwhichhelpsto counteractthe effectof the resistanceto the air air flow completelycreatesthe maximumsuctionoccurswhena sealedsuctiongaugeis essence,the maximumsuctionis greaterthanthesuctionwhichis producedin the normaloperatingrangeof the wattsis an effortto rate theoutputpowerof the vacuumcleanerinsteadof the inputpowerdrawnfromthe air watt as shownin F Swhere F is the rate of air flow in ft3/m S is the vacuumin inchesof waterlift(1)3 SLVA654A June2014 RevisedJuly 2015 HardwareDesignConsiderationsfor an EfficientVacuumCleanerUsingaBLDCM otorSubmitDocumentationFeedbackCopyright 2014 2015,TexasInstrumentsIncorporatedStator with windingsRotor with Permanent MagnetsBrushlessDC Motors(BLDC) Motors(BLDC)The brushlessdirect-current(BLDC)

4 Motoris configuredlike a DC motorturnedinsideout with thepermanentmagnetson the rotorand the windingsare on the the absenceof brushesthe disadvantagesare eliminatedsuchas sparking,noiseand alsoknownas electronicallycommutatedmotors(ECMsor EC motors)and are synchronousmotorsthat arepoweredby a DC electricsourcethroughan integratedinverter,whichproducesan AC electricsignaltodrivethe motor;additionalsensorsand electronicscontrolthe is providedby backelectromotiveforce(EMF)measurementso f eitherpositionsensorsor by BLDC motoris the idealchoicefor applicationsthat requirehigh reliability,high efficiency,and BLDC motoris generallyconsideredto be a high performancemotorthat iscapableof providinglargeamountsof torqueovera vast BLDC motoris highlyreliablebecauseit doesnot haveany brushesthat wearout and ratedconditions,the life expectancyof a BLDC motoris over10 000 BLDCM otorsBLDC motorscan be constructedin the conventional(alsoknownas inrunner)configuration,the permanentmagnetsare part of the the outrunner(orexternal-rotor)

5 Configuration,the radial-relationshipbetweenthe coilsand magnetsis statorcoilsin the outrunnerconfigurationformthe centercoreof the motor,whilethe permanentmagnetsspinwithinan overhangingrotorwhichsurroundsthe this application,the showsthat the rotoris in the centerwith the permanentmagnetsand that the statorcontainsthe inrunnerconfigurationhas lowerrotorinertiaand moreefficientheatdissipationwhencompared to the mostcommonBLDC motortopologyusesastatorstructureconsist ingof a result,a standardsix-transistorinverteror six-mosfetinverteris the CrossSectionof BLDCM otor4 HardwareDesignConsiderationsfor an EfficientVacuumCleanerUsingaSLVA654A June2014 RevisedJuly 2015 BLDCM otorSubmitDocumentationFeedbackCopyright 2014 2015,TexasInstrumentsIncorporatedTorque = (4 N Blr) I= k Motors(BLDC) the BLDCM otorThe starting-currentsetupin the circuitthroughthe statorwindingssets up a magnetomotiveforce(mmf)whichis perpendicularto the mainmmfset up by the Fleming s left-handrule,a forceis experiencedby the the armatureconductorsare in the stator,areactiveforcedevelopsa torquein the torqueis morethanthe load torqueand frictionaltorque,the processof removingcurrentfromone circuitand givingit to anothercircuitis knownas the three-phaseBLDC motoroccursby the connectingthe entirebar phases(A, B, and C) togetherand namingthe connectedbar phasesa samecurrentis example,if phaseA is givenpositivecurrent,thenA will currentthenflowsthroughthe neutralnode,entersphaseB, andthenfinallypassesout throughphaseB to shownin Figure3 the positivecurrentin one phasebecomesthe negativecurrentin anotherphaseand is everycasethereare twophasesthat are contributingto positivetorqueand one phasecontributingto the torqueofeachcommutationintervalis combined,the total torqueis a contributionof two torquesfromtwo phasesthat are perfectlyflat.

6 Thereforethe torquefor the motorat everyintervaland at everyinstantis constantand a singlecurrentproducestwicethe Workingof BLDC motorThe commutationprocessis implementedusinga rotorpositionmustbe methodsare usedto find the rotorposition:sensorcontroland the use of Hall Effectarrangementat the back-endof the Effectsensorsare placed120 digitalHall sensorsdetectthe transitionfromthe northpole to the southpole of the transitionis Hall Effectsensorsincluding: The sensorsare very expensive. Sensingrequiresa magneticdisk. Additionalmechanicalpartsand wiringissuescausereliabilityproblems. Hall Effectsensorsrequirean June2014 RevisedJuly 2015 HardwareDesignConsiderationsfor an EfficientVacuumCleanerUsingaBLDCM otorSubmitDocumentationFeedbackCopyright 2014 2015,TexasInstrumentsIncorporated134265 AAAAAACCCCCCBBBBBBS tate 3 State 4 State 5 State 2 State 1 State 0 IACIABICBIBCIBAICAA ctivation Voltage (V)Back-EMF (V)P1P2P3P4P5P6 ABCABCZCZCZCZCZCZCB rushlessDC Motors(BLDC) disadvantagesof Hall Effectsensorslistedin compensatedfor by of the waysof overcomingthe disadvantagesof Hall Effectsensorsis by methodworksbecauseone coil is alwaysde-energizedaccordingto the rotorpositionis thendetectedusingthe back-EMFsignatureof that coil.

7 This signatureisthe Zerocrossingof that BLDC motoris a permanentmagnetmotorwith a trapezoidalback-EMF,as opposedto the sinusoidalback-EMFfoundin a showsthe trapezoidalwaveformsof a everycommutationstep,one phasewindingis connectedto a positivesupplyvoltage,one phasewindingis connectedto a negativesupplyvoltage,and one phaseis the floatingphaseresultsin a zerocrossingwhenthe phasevoltagecrossesthe averageofthe positivesupplyvoltageand zerocrossingsare indicatedby ZC. The zerocrossingoccursdirectlyin the middleof two a constantspeed,or a slowlyvaryingspeed,the time periodfromone commutationto zero-crossingand the time periodfromzero-crossingtothe next commutationare equalwhichis usedas basisfor the implementationof floatingphase,wherethe zerocrossingmustbe detected,changesfor ADCchannelfor eachphasewindingis neededto sensorlesscommutationmethoddoesnot workduringstartupor at very low simple-blindstart-upis tableof inter-commutationdelaysfor the first few commutationsis storedin executedwithoutattentionto the controlis thenpassedoverto EnergizingSequenceand TrapezoidalWaveforms6 HardwareDesignConsiderationsfor an EfficientVacuumCleanerUsingaSLVA654A June2014 RevisedJuly 2015 BLDCM otorSubmitDocumentationFeedbackCopyright 2014 2015, Motors(BLDC).

8 UsingZeroCrossingof the BackEMFS ignalRotor-positiondetectionoccursby usingone of the two showsthe processof 3-phaseBLDC motorhas beensplit into 12 statorpolesas showninFigure5. Phasewindingoccurssuchthat a positivecurrentcreatesa southpole at A and A will thenhavea has a northpole and thenC will havea beginwhenthe rotorpositionis rotorbeginsto movethe southpole of the rotorenterstheregionof the statorwherethe northpole sensordetectsthis movement,and beforethe rotorcan reachthe northpole (regionunderthe phaseA), phaseA is turnedoff becausethe rotorhas entereda new thenturnson. The magneticpatternon the statoris advancedby rotormustmovefurtherin orderto reachthe northpole as shownin Figure5(2). As the rotortravelstowardthe northpole,it crossesa new commutationzoneand the processcontinueson. Thereare sixstatorcommutationstatesand dependingon the rotorposition,the respectivecommutationstatecan Equation2 to calculatethe V / KE 1000(RPM)where KE = back-EMFconstant(V/kRPM)(2)The KE constantcan also be usedto determinehow fast a motorwill run with a certainvoltageappliedtoit.

9 The higherthe appliedvoltagefor a motorwith a givenbackEMFconstant(KE),the fasterthe motorwill run. Converselythe lowerthe appliedvoltagefor a motorwith a givenbackEMFconstant(KE),theslowerthe motorwill calculatethe voltagerequiredat the motor,use motor(V) = ([ L+ M] / K [R ]) + (KE w)where L= load torque(oz-in) M= frictiontorqueof motor(oz-in) K = TorqueConstant(oz-in/A) KE = backEMFconstant(V/kRPM) R = Thermalresistance( ) w = desiredmotorspeed(kRPM) Torque( ) = K Current(I)(3)7 SLVA654A June2014 RevisedJuly 2015 HardwareDesignConsiderationsfor an EfficientVacuumCleanerUsingaBLDCM otorSubmitDocumentationFeedbackCopyright 2014 2015,TexasInstrumentsIncorporatedBrushle ssDC Motors(BLDC) Equation4 to calculateefficiency. = PO/ PIwhere POis the outputpower(seeEquation5) PIis the inputpower(seeEquation6)(4)PO= where = angularvelocity(rad/s) = torque(Nm)(5)PI= ratedvoltage ratedcurrent(6)Table1 lists the specificationsof the selectedmotor(partnumberDN4261-24-053).

10 Table1. = mmNumberof phases3 Numberof poles8To find voltagerequiredat motorfor differenttorquesuse motor(V) = ([( L+ M) / K ] R ) + (KE w)where R = Lneglects M(7)Calculatethe voltageto producea torqueof 15 oz-inat = ([15 / ] ) + ( 3) = (8)Use Equation9 to find the voltageusedto producea torqueof 15 oz-inat = ([15 / ] ) + ( 4) = (9)Theseequationscan be usedto calculatea similarvoltagerequirementfor any giventorqueand curvein Figure6 is shownin Figure7 the ratedcurrentof the motoris The characteristicis an EfficientVacuumCleanerUsingaSLVA654A June2014 RevisedJuly 2015 BLDCM otorSubmitDocumentationFeedbackCopyright 2014 2015,TexasInstrumentsIncorporatedCurrent (A) (oz-in) (oz-in)Speed (kRPM) Motors(BLDC)Figure6. SpeedVersusTorqueFigure7. CurrentVersusTorqueTable2. feedbackgivesBLDC motorsLinearspeed-torquecharacteristics, betterlinearcharacteristicswhencomparedt o open-loopAC-inductionmotorsor torqueproducedat any instantinHighstartingtorquea BLDC will be twicethe torqueproducedin brushDC motorof the samerating,astwo phaseswill be on in TexasInstrumentsDRV8301motordriver, permanentmagnetin the rotorreducesefficiencyloss and increasesthe efficiencyHigherefficiencyby about10%.