Motorola M68HC08 - Manual (Page 47)

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