AN1913 Motorola / Freescale Semiconductor, AN1913 Datasheet - Page 45

• 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

Software Design
7.3.5 State Diagram - Process ADC Zero Crossing Checking
Commutation
Reset
Control states:
Running/Starting
preset new phase
motor
Zero Crossing
Commutated
Per_Toff after
motor Commutation
Back-EMF Zero Crossing
Zero Crossing
Detected/Missed
Disabled
Commutation
Control states:
Stop/Alignment
Zero Crossing
Back-EMF Zero
Get/Missed
Crossing Checking
Figure 7-10. State Diagram - Process ADC Zero Crossing Checking
The status of the ADC Zero Crossing checking depends on Commutation Control states. It is enabled
only during the Running and Starting Commutation Control states. When the BLDC motor is
commuted, the new Zero Crossing phase is preset. When, after motor commutation, the time interval
(Per_Toff) is passed, the Back-EMF Zero Crossing is checked. When the Back-EMF Zero Crossing is
Detected or Missed, the Commutation control process is informed that a new commutation time needs
to be computed.
This process is almost entirely provided by the BLDC Zero Crossing algorithms. The bldczcHndlr is
called with actual time from the Cmt Timer Counter. This algorithm is assigned to control requests and
set some commutation control registers. According to the request flags set by this algorithm, other
BLDC Zero Crossing algorithms are called.
This process, together with the Commutation Control Running state, are the most important software
processes for sensorless BLDC motor commutation. These process services are located in the main
loop and in the ADC Interrupt subroutine.
BLDC control with BEMF Zero Crossing using ADC
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