AN1913 Motorola / Freescale Semiconductor, AN1913 Datasheet - Page 16

• 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

Control Technique
5.3 Back-EMF Zero Crossing sensing
5.3.1 ADC Convertor Used for Back-EMF Zero Crossing
5.3.1.1 ADC Zero Crossing Checking
16
PWM1 S
PWM2 S
PWM3 S
PWM4 S
PWM5 S
PWM6 S
Figure 5-3
arrow lines. This technique is called bipolar (hard) switching. The voltage across the two energized
coils is always ±DC-Bus voltage whenever there is a current flowing through these coils.
The Back-EMF Zero Crossing is detected by sensing the motor non-fed phase “branch“ voltage (u
Section
The Motorola DSP56F80x family offers an excellent on-chip Analog-to-Digital converter. Its unique
feature set provides an automatic detection of the signal crossing the value contained in the ADC offset
register.
Then the Back-EMF Zero Crossing can be split into two main tasks:
The Zero Crossing for position estimation is sensed using the AD convertor.
As stated, the AD convertor has individual ADC Offset Registers for each ADC channels. The value in
the Offset Register can be subtracted from the AD conversion output. The final result of the AD
I
I
I
A
•
•
B
C
ADC Zero Crossing Checking
ADC Zero Crossing Offset Setting to follow the variation of the DC-Bus voltage
3.5) and DC-bus voltage u
At
Ab
Bt
Bb
Ct
Cb
shows that the diagonal power switches are driven by the same PWM signal as shown with
Figure 5-3. BLDC Commutation with Bipolar (Hard) Switching
BLDC control with BEMF Zero Crossing using ADC
Commutation
d
utilizing the ADC. (Refer to
60
Commutation
120
Section
3).
electrical angle
vi
in