Personal Computer - Word Processor User Manual

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°

Frees

cale Semiconductor,

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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