Motorola M68HC08 manual Vectors of Magnetic Fields

Freescale Semiconductor, Inc.

BLDC Motor Control

Used Control Technique

MOTOR IS RUNNING MOTOR IS STARTING

AT STEADY-STATE CONDITION

WITH REGULAR BACK-EMF FEEDBACK

Freescale Semiconductor, Inc.

STATOR MAGNETIC FIELD

ROTOR MAGNETIC FIELD (CREATED BY PM)

BORDER OF

STATOR POLE

ROTOR MOVEMENT

DURING ONE

COMMUTATIONDIRECTION OF

PHASE CURRENT

ZERO CROSSING	PHASE WINDING
EDGE INDICATOR

ALIGNMENT STATE

The rotor position is stabilized by applying PWM signals to only two motor phases

STARTING (BACK-EMF ACQUISITION)

The two fast (faster then the rotor can move) commutations are applied to create an angular difference of the stator magnetic field and rotor magnetic field.

The back-EMF feedback is tested. When the back-EMF zero crossing is recognized the time of new commutation is evaluated. Until at least two successive back-EMF zero crossings are received the exact commutation time can not be calculated. Therefore, the commutation is done in advance in order to assure that successive back-EMF zero crossing events would not be missed.

RUNNING

After several back-EMF zero crossing events the exact commutation time is calculated. The commutation process is adjusted. Motor is running with regular back-EMF feedback.

Figure 3-18. Vectors of Magnetic Fields

DRM028 — Rev 0		Designer Reference Manual
MOTOROLA	BLDC Motor Control	47
	For More Information On This Product,
	Go to: www.freescale.com