3-Phase BLDC Motor Sensorless Control Using MC56F8013

System ConceptMotor is Runningat steady-state conditionwith regular back-EMF feedbackStator magnetic field Rotor magneticfield (createdby permanentmagnet)Border ofstator poleMotor is StartingAlignment StateThe rotor position is stabilized by applyingPWM signals to only two motorphasesRotor movementduring onecommutationZero crossingedge indicatorDirection ofPhase currentPhase windingStarting (back-EMF Acquisition)The two fast (faster then the rotor canmove) commutation are applied tocreate an angular difference of thestator magnetic field and rotor magneticfield.The back-EMF feedback is tested.When the back-EMF zero crossing isrecognized the time of new commutationis evaluated. Until at least twosuccessive back-EMF zero crossingsare received the exact commutationtime can not be calculated. Thereforethe commutation is done in advanceto ensure that successive back-EMFzero crossing event would not bemissed.RunningAfter several back-EMF zero crossingevents the exact commutationtime is calculated. The commutationprocess is adjusted.Motor is running with regularback-EMF feedback.Figure 3-9. Vectors of Magnetic Fields3-Phase BLDC Motor Sensorless Control using MC56F8013, Rev. 036 Freescale Semiconductor