InstaSPIN(tm) BLDC Lab - TI.com

1 ApplicationReportSPRABN7 November2011 instaspin MCU(DRV8312-C2-KIT) (theDRV8302-HC-C2-KITorDRV8301-HC-C2-KIT canalsobeused)witha PiccoloF28035controlCARD subsystemtorunthesensorlessInstaSPIN bldc technique. (.out) , ,RSTB, andRSTC mustbein ,MOB, :Whatdoyouthinkwillhappenif youconnectthemotorwiresin a differentorder?(a)Thebrushesin themotorwilloverheatandcouldcausea fire.(b)Thecurrentin thewireswillreversethepolarityoftheanti- protonsin themagneticfield,causinganantimatterexpl osion.(c)Nothingwillhappenexceptthemotor mayspinin theoppositedirection.(d)Youcouldpotentia llydamagetheDRV8312,resultingin yourimmediateterminationfromTI.

2 (e)Thisis a trickquestionbecausetheconnectoris keyed,prohibitingthemotorwiresfrombeingc onnectedin anyotherwaythanwhatis ,controlCARD, November2011 instaspin BLDCLabSubmitDocumentationFeedbackCopyri ght 2011,TexasInstrumentsIncorporatedUsingth eInstaSPIN BLDCLabSPRABN7 November2011 SubmitDocumentationFeedbackCopyright 2011, SetupandProgrammingTheincludedcontrolCAR D comeswiththeswitch(SW3)settoholdtheXDS10 0v1emulatorin JTAG reset(switchis up(OFF)) ,allowJTAG accessbysettingSW3down(ON). (CCS4). NewTargetConfiguration(seeFigure3). (forexample, ). :TMS320F28035andclickSave(seeFigure4). November2011 instaspin BLDCLabSubmitDocumentationFeedbackCopyri ght 2011,TexasInstrumentsIncorporatedUsingth eInstaSPIN ,rightclickonyournewTargetandclick"Launc hSelectedConfiguration"in thecontextmenu(seeFigure5).

3 "Target->ConnectTarget"(seeFigure6). ,clickthemenuitem"Target-> ". "Browse"buttonandfindthefile" "fromUSBS tickorC:\ti\controlSUITE\development_kit s\DRV8312-C2-KIT_v1XX\~ "Open"andthen"OK".Theflashis BLDCLabSPRABN7 November2011 SubmitDocumentationFeedbackCopyright 2011, "TerminateAll"(seeFigure7) :\ti\controlSUITE\development_kits\DRV83 12-C2-KIT_v1XX\~ youseethemessageshownin Figure8, click"Yes". "Connected"in thelowerlefthandcorner(seeFigure9). AlsoverifythattheFaultStatus,DCBus, fullquickstartguidefortheInstaSPINBLDCGU I canbefoundinC:\ti\controlSUITE\developme nt_kits\DRV8312-C2-KIT_v1XX\~ November2011 instaspin BLDCLabSubmitDocumentationFeedbackCopyri ght 2011,TexasInstrumentsIncorporatedUsingth eInstaSPIN ,click"EnableMotor"(seeFigure10).

4 :DutyCycle= !YoujustdidInstaSPIN! ,butInstaSPINBLDC andtheGUIalloweasiertuninginformationtob egatheredforthemotorin "StartContinuousRead"ontheuppergraphs(se eFigure11). BLDCLabSPRABN7 November2011 SubmitDocumentationFeedbackCopyright 2011, (seeFigure12):TopGraph:Displaystheper-un it(PU) :Displaystheper-unit(PU)PhaseA :Displaystheper-unit(PU)PhaseA , thecommutationis happeningtoolateascanbeseenbytheovershoo twheretheredarrowis pointingin November2011 instaspin BLDCLabSubmitDocumentationFeedbackCopyri ght 2011,TexasInstrumentsIncorporatedUsingth eInstaSPIN "FluxThreshold"toa smallervalue( )untilthecommutationhappensattheinflecti onpointofthevoltagewaveform(seeFigure14) .

5 Feelingfortuningis , ,torqueresponsealsoimprovesbyloweringthe fluxthreshold(canyouguesswhy?)..It turnsoutthata bldc motorworksverymuchlikea ,youwanttoadvancethesparktimingbecauseit takesa finiteamountoftimetoignitethefuelvaporin theengineisrunningathighRPM,bythetimethe fuelhasignitedandtheforceoftheexplosioni s feltonthepiston, takesa finiteamountoftimetocommutatea bldc motor(getthecurrentextinguishedin onecoilandbuiltupin themotoris runningathighRPM,bythetimethecommutation takesplace, justlikeadvancingthesparktimingin BLDCLabSPRABN7 November2011 SubmitDocumentationFeedbackCopyright 2011.)

6 CascadeSpeedControlWithInstaSPINBLDCW iththeControlModestillsetto"DutyCycle", nocontrolloopregulatingthespeed, ,enableeither"Velocity"modeor"Cascade" "Cascade"onthe"Settings" "Main"tabagainandverifythattheControlkno bis startsupsmoothlyandrampstoa theMotorSpeedRPMwindow(seeFigure16). ,themotoreventually9 SPRABN7 November2011 instaspin BLDCLabSubmitDocumentationFeedbackCopyri ght 2011,TexasInstrumentsIncorporatedUsingth eInstaSPIN becauseoftheintegratorsthathavebeenenabl edin a negativefeedbackcontrolsystemcannottoler ateanysteadystateerrorandwilldriveit tozero(thatis,thecommandedvalueandthecon trolledvaluewillbeequal).

7 However,theresponseofthesystemis ratherspongy,isn t it?Inotherwords,thisis nota "stiff" , "Settings" :1 msRampStartSpeed:50 RPMRampEndSpeed:500 RPMKp(current) (current):20 StartupCurrent(PU) (velocity) (velocity):60 VelocityLoopLimit(PU) :8 polesBaseElectricalFrequency(Hz):200 ControlMode:CascadeIf setcorrectly, t changedtheControlknobonthe"Main"tab,it shouldstillbesettoa not,changeit ,enablethemotor,andverifythatit startsupsmoothlyandachievesa BLDCLabSPRABN7 November2011 SubmitDocumentationFeedbackCopyright 2011, BLDCS olutionAgain, muchstifferin termsofmaintainingthecommandedspeed, thehighergainsettingsresultin muchbettertrackingperformance,thenwhydid n t wespecifythemasthedefaultvaluestobeginwi th?

8 Toanswerthisquestion,let s ,slowlydecrementthecommandedspeedonenumb erata , :Sowhywouldthesystembestableathigherspee ds,butunstableatlowerspeeds?(Thisisa trickyone).Thinkaboutit fora :It hassomethingtodowithhowthevelocityfeedba cksignalis :Inordertomeasurevelocityin a sensorlesssystem, spinningathighspeed,therearemanycommutat ionintervalspersecond,whichmeansthatthev elocityfeedbackvalueis ,whenthemotoris spinningatlowspeed,thecommutationrateis low,whichmeanstheupdaterateforthevelocit yvalueis ,thevelocityfeedbackvaluebecomes"stale"w henit isnotupdatedfora ,thereis a phaselagbetweenthetruevelocityandthemeas uredvelocitywhenthevelocityvalueis ,andwhenit is allgone, (forexample,fans,blowers,andcompressors) ,thisis notaproblem,becauseit doesn t (forexample,washerdrumagitation)

9 ,lowspeedoperationis a requirement,whichsuggeststhata differentcontrolschemeis "EnableMotor",closetheGUI, November2011 instaspin BLDCLabSubmitDocumentationFeedbackCopyri ght 2011, s revieweachofthepanelsin :TheEnableMotorcheckboxis usedtostartorstopthemotorControlModedrop downboxallowstheselectionoffourdifferent controlmodes: DutyCycle:Themotoris commutatedusingthesensorlessalgorithmbut is drivenin anopen-loopdutycyclemode. Current:Themotoris commutatedusingthesensorlessalgorithmwhi lethecurrent(torque)isregulatedusinga highspeedin thismode. Velocity:Themotoris commutatedusingthesensorlessalgorithmwhi lethemotorspeedis regulatedusinga a PWMdutycycle.

10 Cascade:Themotoris commutatedusingthesensorlessalgorithmwhi lethemotorspeedis regulatedusinga a motorcurrentcommandthatis regulatedbya usedtoadjustthemotor s separatefunctionforeachcontrolmode: DutyCycle:TheknobadjuststhePWMdutycyclet othemotor. Current:Theknobadjuststheper-unit(PU)com mandedcurrentthroughthemotor. Velocity:Theknobadjuststheper-unit(PU)mo torcommandedspeed. Cascade:Theknobadjuststheper-unit(PU) TopGraph:Displaystheper-unit(PU)integrat edmotorflux. SecondGraph:Displaystheper-unit(PU)Phase A BEMF waveform. ThirdGraph:Displaystheper-unit(PU)PhaseA currentwaveform. FourthGraph:Displaysthemotorspeedin ;theMotorSpeedgraphis BLDCLabSPRABN7 November2011 SubmitDocumentationFeedbackCopyright 2011, (seeFigure18).