AN1913D Freescale Semiconductor / Motorola, AN1913D Datasheet - Page 25

• Manufacturer Part Number: AN1913D
• Description: 3-phase BLDC Motor Control with Sensorless Back-EMF ADC Zero Crossing Detection using DSP 56F80x
• Manufacturer: Freescale Semiconductor / Motorola

Stator magnetic field
Border of
stator pole
Rotor movement
during one
commutation
Zero Crossing
edge indicator
with regular Back-EMF feedback
Motor is Running
at steady-state condition
Phase winding
BLDC control with BEMF Zero Crossing using ADC
Direction of
Phase current
Freescale Semiconductor, Inc.
Figure 5-9. Vectors of Magnetic Fields
Rotor magnetic
field
(created by PM)
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Motor is Starting
Starting (Back-EMF Acquisitio
Alignment State
The rotor position is stabilized by ap-
plying PWM signals to only two mo-
tor phases
The two fast (faster then the rotor can
move) commutation are applied to
create an angular difference of the
stator magnetic field and rotor mag-
netic field.
The Back-EMF feedback is tested.
When the Back-EMF Zero Crossing
is recognized the time of new com-
mutation is evaluated. Until at least
two successive Back-EMF Zero
Crossings are received the exact
commutation time can not be calcu-
lated. Therefore the commutation is
done in advance in order to assure
that successive Back-EMF Zero
Crossing event would not be missed.
Running
After several Back-EMF Zero Cross-
ing events the exact commutation
time is calculated. The commutation
process is adjusted.
Motor is running with regular
Back-EMF feedback.
Control Technique
25