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3 used control technique, Used control technique, The zero crossing detection – Motorola M68HC08 User Manual

Page 38

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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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