BLDC Motor Control
Designer Reference Manual
DRM028 — Rev 0
38
BLDC Motor Control
MOTOROLA
Figure 3-13. The Zero Crossing Detection
3.3 Used Control Technique
3.3.1 Sensorless Commutation Control
This section concentrates on sensorless BLDC motor commutation with
back-EMF zero crossing technique.
In order to start and run the BLDC motor, the control algorithm has to go
through the following states:
•
Alignment
•
Starting (Back-EMF Acquisition)
•
Running
Figure 3-14
shows the transitions between the states. First the rotor is
aligned to a known position; then the rotation is started without the
position feedback. When the rotor moves, back-EMF is acquired so the
Phase Selection
MUX Command
Phase Comparator
Output
(Zero crossing edge)
Reference Level
"Branch" Voltage
(Interval of phase
Back-EMF zero
crossing detection)
Commutation
Signal
Zero Crossing
Signal
90°
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