AN1913 Motorola / Freescale Semiconductor, AN1913 Datasheet - Page 25

• Manufacturer Part Number: AN1913
• Description: AN1913 3-phase BLDC Motor Control with Sensorless Back-EMF ADC Zero Crossing Detection using DSP 56F80x
• Manufacturer: Motorola / Freescale Semiconductor

Stator magnetic field
Rotor movement
during one
commutation
Border of
stator pole
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
Figure 5-9. Vectors of Magnetic Fields
Rotor magnetic
field
(created by PM)
Motor is Starting
Alignment State
The rotor position is stabilized by ap-
plying PWM signals to only two mo-
tor phases
Starting (Back-EMF Acquisitio
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