3-Phase BLDC Motor Sensorless Control Using MC56F8013

System ConceptPerform alignmentAlignment timefinished?NYCalibration coeff for non-fedphase =non-fed phase voltage + 0.5All phases done?N3.3.4 Sensorless Commutation ControlYStartingFigure 3-6. CalibrationThis section describes sensorless BLDC motor commutation using the back-EMF zero crossingtechnique. To start and run the BLDC motor, the control algorithm must go through the following states:• Alignment• Starting (Back-EMF Acquisition)• RunningFigure 3-7 shows the transitions between these states. First, the rotor is aligned to a known positionwithout position feedback. When the rotor moves, a back-EMF is induced on the non-fed phase and isacquired by the ADC. As a result, the position is known and can be used to calculate the speed andprocess the commutation in the running state.3-Phase BLDC Motor Sensorless Control using MC56F8013, Rev. 032 Freescale Semiconductor