3-Phase BLDC Motor Sensorless Control Using MC56F8013

System Blocks ConceptStart MotorAlignmentAlignment timeexpired?NYStarting(Back EMF Acqusition)Min. correctcommutations done?N3.3.4.1 AlignmentYRunningFigure 3-7. Commutation Control StatesBefore the motor starts, there is a short time (which depends on the motor’s electrical and mechanicaltime constant) when the rotor position is aligned to a known position by applying PWM signals to only twomotor phases (no commutation). The alignment current controller keeps the current within predefinedlimits. This state is required to create a high startup torque and to recognize the rotor position. When thepreset timeout expires, this state is finished.The alignment current controller subroutine (with PI regulator) is called to control the DC-bus current. Thesubroutine sets the correct PWM ratio for the required current. The current is sampled and the currentcontroller is calculated during every PWM cycle.The BLDC motor rotor position (with flux vectors during alignment) is shown in Figure 3-8.3-Phase BLDC Motor Sensorless Control using MC56F8013, Rev. 0Freescale Semiconductor 33