Motorola M68HC08 Reference Manual page 47

MOTOR IS RUNNING
AT STEADY-STATE CONDITION
WITH REGULAR BACK-EMF FEEDBACK
STATOR MAGNETIC FIELD
BORDER OF
STATOR POLE
ROTOR MOVEMENT
DURING ONE
COMMUTATION
ZERO CROSSING
EDGE INDICATOR
DRM028 — Rev 0
MOTOROLA
Freescale Semiconductor, Inc.
ROTOR MAGNETIC
FIELD (CREATED BY PM)
DIRECTION OF
PHASE CURRENT
PHASE WINDING
Figure 3-18. Vectors of Magnetic Fields
BLDC Motor Control
For More Information On This Product,
Go to: www.freescale.com
MOTOR IS STARTING
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
back-EMF feedback.
BLDC Motor Control
Used Control Technique
is running with regular
Designer Reference Manual
47