High-Speed Sensorless-FOC Reference Design for Drone ESCs

1 Copyright 2016, Texas Instruments IncorporatedElectronic speed controllerDRV8305 CSD18540Q5 BFlight controller interfacePower supplyLMR16006 Duty cycleserial interface2- to 6-cell LiPO3 PWM HS3 PWM LS3 phase current sense3 phase voltage senseHost processor ESCTMS320F2806xFx FAST Observerx InstaSPIN-FOCx PWMx ADCx Interface 3 31 DC link voltage sense1 TIDUCF1 December2016 SubmitDocumentationFeedbackCopyright 2016,TexasInstrumentsIncorporatedHigh-Sp eedSensorless-FOCR eferenceDesignfor DroneESCsTI DesignsHigh-SpeedSensorless-FOCR eferenceDesignfor DroneESCsOverviewESCmodulesare importantsubsystemsfor non-militarydronesand usersdemandingmoreefficientmodelsthat providelongerflighttimesand higherdynamicbehaviorwith smootherand TI Designimplementsan electronicspeedcontroller(ESC)commonlyus edfor unmannedaerialvehicles(UAV)or speedcontrolisdonesensorless,and the motorhas beentestedup toa (12 kRPMwith a 6-polepair motor)

2 , high -speedsensorless-FOCreferencedesignf or droneESCsprovidesbest-in-classFOCalgorit hmimplementationto achievelongerflighttime,betterdynamicper formanceand higherintegration,resultingsmallerboards ize and s FAST softwareobserverleveragingInstaSPIN-Moti on C2000 LaunchPad and DRV8305 BoosterPack .ResourcesTIDA-00916 DesignFolderDRV8305 ProductFolderTMS320F28069 FProductFolderDRV8305N3-PhaseMotorDriveB oosterPackToolFolderC2000 PiccoloF28069 MMCUL aunchPadToolFolderTIDA-00643 DesignFolderASKOur E2E ExpertsFeatures InstaSPIN-FOC SensorlessFOCA chievesHighestDynamicPerformance,Testedu p to12,000 RPMWithThreeLiPoCells HighDynamicPerformance.

3 1 to 10 kRPM(ElectricalFrequency100 Hz to 1 kHz)Speedin< s to ProvideHighPerformanceYawand PitchMovement FastSpeedReversalCapabilityfor Roll Movement LongerFlightTimeDue to ImprovedEfficiencyofFOCOverBlockCommutat ion HigherPWMS witchingFrequency,Testedup to 60kHz to ReduceCurrentand TorqueRippleWithLow-Inductance, high -Spee dMotorsand to AvoidInterferenceWithUltrasonicSensors FlexiblePowerStageSupportsTwo to Six LiPoCells FastTime-to-MarketDue to InstaSPIN-FOC sAutomaticMotorParameterIdentification:A uto-TuningSensorlessFOCS olution MotorTemperatureEstimationFromWindingRes istanceChangesto ProtectMotorFromDamageDuringTemporaryOve rloadConditionsApplications Dronesand UAVs high -SpeedMotors Battery-OperatedPowerToolsFlight ControllerBrain of the flying system; accepts the commands from remote; interfaces with sensors systems and controls ESCs, camera commands, gimbal, stability, and so on.

4 Assist in image transmission Battery PackSingle or typically multi-cell LiPO or Li-Ion batteries for example 3S LiPOElectronic speed Controller (ESC)Typically four or more, brushed DC or brushless DC motor, speed control for thrust and direction change Sensor systems Multiple sensors (Ultrasonic, LiDar, IR, Accelero, Gyro) for collision detection, landing assist, stability, all interfaced to main controller; GPS for navigation PayloadApplication dependent addition to the Drone flight ; for example, gimbal with camera for photo or videography, thermal camera for agriculture crop analysis, package holder and package for delivery, and so December2016 SubmitDocumentationFeedbackCopyright 2016,TexasInstrumentsIncorporatedHigh-Sp eedSensorless-FOCR eferenceDesignfor DroneESCsAn IMPORTANTNOTICEat the end of this TI referencedesignaddressesauthorizeduse, intellectualpropertymattersand otherimportantdisclaimersand a Drone ,the followingmoduledefinitionsare typicallyusedto the differentsubsystemsneededto buildthe full is shownin Modulesfor DroneFlightSystemThis TI designguidefocuseson the electronicspeedcontroller(ESC)

5 DronesThe ESCdefinesthe dynamicmovementperformanceand the flighttime of the themovementpatternsthat the dronehas to be able to do are: Precisemovementpatterns:traveling,hoveri ng Quickmovementpatterns:360 turnsin x,y,zdirections,max speedhorizontal,max speedverticalTo providethesefeatures,a goodESCis neededto controlthe generatedlift at all speedsof the way the stabilizationalgorithmsbasedon the positionsensormodulecan compensatethevibrationand externalforcesaffectingthe fasterthe motor s speedcan be changed,the fewerspeedchangesthe stabilizationalgorithmhas to perform;this leadsto usingless energythanrunningthedroneat a highlyvaryingspeed,whichwouldbe the casewith an ESCof less detailsfromthe previoussectionsis importantto knowwhatsystemperformanceof the droneis systemspecification,the performanceof the ESCcan be of droneis beingbuilt,compromisescan be madeto the performanceof the low-enddrone,typicallya brushedDC motoror a three-phasetrapezoidalback-EMFcontrolled motoris usedbecausethey are cheapand with openloop is true for bothangleand A HPWM A LPWM B HPWM B LPWM C HPWM C LPHASE December2016 SubmitDocumentationFeedbackCopyright 2016.

6 TexasInstrumentsIncorporatedHigh-SpeedSe nsorless-FOCR eferenceDesignfor DroneESCsFor a mid-rangedrone,typicallya three-phasetrapezoidalback-EMFmotoris differencefrombeforeis now that this motorwouldrun with a closedloop angleestimation,and maybea simplecurrentcontrolalgorithm,but typicallyit wouldbe openloop low-performancecontrolleris used,thus high -enddrones,usuallythree-phasesinusoi dalback-EMFmotorsare somecases,also atrapezoidalback-EMFmotorsare used,leadingto currentlya trendof transitioningfromtrapezoidalto sinusoidalcontrol,and with this movesensorlesscontrolbecomesmoreimportan tas an anglesensorwouldmakethe solutionnot ,a secondissuehereis the high speedrequiredfromthe of causegeneratessomeeffortfor peoplewantingto buildan ESCto developa sensorlessalgorithmthat will give goodenoughangleaccuracyto controlthe this TI Design ,the focusis on an ESCusinga choice,considerthefollowing.

7 Measurethe magneticfield angleof the rotorwithina 1- to 5-degreeminimumaccuracyto ensuremaximumtorqueusingFOCalgorithm,or Estimatethe rotormagneticanglebasedon the motor s phasevoltagesand phasecurrents(sensorlessalgorithm)Figure 2 showstypicalPWMhigh-sideand low-sidepatternsfor threephasesand the correspondingidealfilteredphasevoltagesa fterremovingthe PWMcarrierwhenrunningthe motorwith Generationof IdealPWM-to-SinusoidalPhaseVoltagesDue to the smallchangeof angle,the torquerippleof the systemis kept to a minimumcomparedto controlalgorithmhas beenchosen,the next step is to decideif thecontrolshouldbe openor an open-loopcontrol,the synchronousmotor(BLDCor BLAC)

8 Is blindlydrivenwith a controlsignalandit is assumedthat it followsthe 2016, Texas Instruments IncorporatedElectronic speed controllerGate driverFETsFlight controller interfacePower supplyDuty cycleserial interface2- to 6-cell LiPO3 PWM HS3 PWM LS3 phase current sense3 phase voltage senseHost processor ESCx PWMx ADCx Interfacex sensorless control algorithm 3 31 DC link voltage December2016 SubmitDocumentationFeedbackCopyright 2016,TexasInstrumentsIncorporatedHigh-Sp eedSensorless-FOCR eferenceDesignfor DroneESCsOne issueis the assumptionthat the motorfollowsthe controlsignalmay be ensurethatthe motorperformscorrectly,morecurrentthanwh atis ideallyneededis put on the windingsto ,this is the mainreasonwhy systemefficiencyin an open-loopcontrolis reducedwhencomparedto a closed-loopcontrol,the motorcontrolhas the abilityto test if the motormovesas not, thecontrolloop automaticallycompensatesby eitherreducingor increasingthe closed-loopcontrolor a sensorlessalgorithm,the current-and voltagesignalshaveto bemeasured,so they can be usedas sinusoidalcontrol,measureup to the voltagemeasurements,choosebetweenmeasuri ngonly the DC link voltageor the three-phasevoltagesand the DC link showsmeasurementconfigurationsfor moredetailon controlalgorithms.

9 See the motorcontrolcompendium[9]. (ESC)The motorsof the dronehaveto run on a speedthat dependson the weightof the droneand the size ofthe propellersto generatethe neededlift for the droneto fly. Lookingat typicalthree-phasebrushlessmotorsbuilt for drones,the followingpropertiesare common: Low inductance Low resistance Two to eightpole pairs 1000-Hzor higherelectricalfrequencyThe motoris built to be optimizedto use with LiPobatterieswith two to six cells,meaninga DC to Thesevoltagesare usedto designthe maximumspeedfor the typicalissuehereis runningthe motorcloseto VBUSat maximumspeed,as hereboththe FOCalgorithmand the sensorlessalgorithmhaveto be goodenoughto supportthis ESCusedin this reportis built to workfor a three-phasebrushlessmotorusinga the ESCmoduleis shownin BlockDiagramfor December2016 SubmitDocumentationFeedbackCopyright 2016.

10 TexasInstrumentsIncorporatedHigh-SpeedSe nsorless-FOCR eferenceDesignfor SystemSpecificationsFor this TI Design ,a three-phasehalf-bridgepowerstageis requiredwith the aforementionedsensingcapabilitiesto generatethe feedbacksignalsfor the powerstagehas to run froma LiPobatterywith betweentwo to six cells,meaninga to the low time constantof the motorand frequencydependentsensors,the PWMfrequencyis high ;typicalcurrentdesignsuse PWMfrequenciesof around45 to 60 kHz with a tendencyto increaseit ,a way to communicatewith the flightcontrolleris required,whichcan be doneusingduty cycleor Key to 45 V supportingLiPobatterytwo to six cellsor morePWMfrequencyfor motorphases45 kHz or higherAngledetectionSensorlessangleestim ationusingInstaSPIN-FASTfor full speedrangeSensorlessangleaccuracyFor high efficiency.