Motorola M68HC08 manual Semiconductor, Inc

Semiconductor, Inc.

Freescale Semiconductor, Inc.

BLDC Motor Control

STATOR

STATOR WINDING (IN SLOTS)

SHAFT

ROTOR

AIR GAP

PERMANENT MAGNETS

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.

Freescale

Voltage

VOLTAGE

PhasePHASEAA

Phase B

PHASE B

Phase C

PHASE C

30°

120°

120°

electricalELECTRICAL

90° 150° 210° 270° 330° angleANGLE

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

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