Motorola M68HC08 manual Used Control Technique, Sensorless Commutation Control

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

BLDC Motor Control

Phase Selection

MUX Command

Phase Comparator

Output

(Zero crossing edge)

"Branch" Voltage (Interval of phase Back-EMF zero crossing detection)

Reference Level

Commutation
Signal	90°

Zero Crossing

Signal

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 3-14shows 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

Designer Reference Manual		DRM028 — Rev 0
38	BLDC Motor Control	MOTOROLA
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