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Get help about sensorless FOC on MC56F84766

Question asked by changshui li on Dec 10, 2017
Latest reply on Dec 15, 2017 by changshui li

On my last project,  I used MC56F84766VLK as controller, and one quad encoder as angle/speed sample to realize PMSM motor control by using FOC algorithm:

FOC with Encoder


        (1)TMR0:quad timer0, input A/B signals from encoder as quad counter

            by one function:MCSTRUC_AngleFromEncoder() to output two angle signals as Park's & Inverse Park's angle signal(θe):

            gsM1_Drive.sSpeedPos.sAnglePosEl, gsM1_Drive.sSpeedPos.sAnglePosElUpdate

       (2) TMR1: quad timer1, input TMR0 OFLAG

            by one function:MCSTRUC_PosCalc() to get the relative position,θm: gsM1_Drive.sPosCalc.f32PosRelative

       (3) TMR2: quad timer2 and timer3, normal M/T speed calucation and low speed calucation

            by one function:MCSTRUC_SpeedClacMTMethod() to out normal speed signal,ωm:gsM1_Drive.sSpeedPos.f32Speed

            by one function:MCSTRUC_SpeedClacImproved() to out the startup speed signal:gsM1_Drive.sSpeedPos.f32SpeedImproved          


In order to get lower cost, we want to cancel the quad encoder,and consider to use back-emf observer+tracking algorithm to realize the sensorless FOC.

FOC without Encoder

By browsing our NXP resource, we found one reference(AN5014SW) may realize our task. Functions CalcObs() and Update() can out angle signal(module->data.posElEst) and speed signal(module->data.velocityElEst).


(1) How to get these signals as like encoder? or, to replace them with the sensorless Observer+Tracking :

    (a)Angle signals:gsM1_Drive.sSpeedPos.sAnglePosEl, gsM1_Drive.sSpeedPos.sAnglePosElUpdate

   (b)Relative position signal:gsM1_Drive.sPosCalc.f32PosRelative

   (c)Speed signal:gsM1_Drive.sSpeedPos.f32Speed,gsM1_Drive.sSpeedPos.f32SpeedImproved


(2) Why the angle signal(module->data.posElEst) change too much when the motor stops?

as the below figure(captured by FreeMaster):

Obs Freemaster


Wait your reply.

Thanks too much!

Lichangshui ,2017-12-11