Motorola M68HC08 Reference Manual page 24

BLDC Motor Control
Designer Reference Manual
24
Freescale Semiconductor, Inc.
Figure 3-1. BLDC Motor Cross Section
The motor can have more than just one pole-pair per phase. This defines
the ratio between the electrical revolution and the mechanical revolution.
The BLDC motor shown has three pole-pairs per phase, which represent
three electrical revolutions per one mechanical revolution.
Voltage
VOLTAGE
Phase A
PHASE A
Phase B
PHASE B
Phase C
PHASE C
30°
30°
Figure 3-2. 3-Phase Voltage System
The easy to create rectangular shape of applied voltage ensures the
simplicity of control and drive. But, the rotor position must be known at
certain angles in order to align the applied voltage with the back-EMF
(voltage induced due to movement of the PM). The alignment between
BLDC Motor Control
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120°
120°
90° 150° 210°
90° 150° 210°
STATOR
STATOR WINDING
(IN SLOTS)
SHAFT
ROTOR
AIR GAP
PERMANENT MAGNETS
electrical
ELECTRICAL
270° 330°
270° 330°
angle
ANGLE
DRM028 — Rev 0
MOTOROLA