Used Control Technique - Motorola M68HC08 Reference Manual

BLDC Motor Control

3.3 Used Control Technique

3.3.1 Sensorless Commutation Control
Designer Reference Manual
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Phase Selection
MUX Command
Phase Comparator
Output
(Zero crossing edge)
"Branch" Voltage
(Interval of phase
Back-EMF zero
crossing detection)
Reference Level
Commutation
Signal
Zero Crossing
Signal
Figure 3-13. The Zero Crossing Detection
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
BLDC Motor Control
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90°
DRM028 — Rev 0
MOTOROLA