AN1913D Freescale Semiconductor / Motorola, AN1913D Datasheet - Page 20

• 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

Control Technique
5.4.2 Running
5.4.2.1 Algorithms BLDC Motor Commutation with Zero Crossing Sensing
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The commutation process is the series of states which is assured when the Back-EMF Zero Crossing is
successfully captured. The new commutation time is calculated after Back-EMF Zero Crossing is
captured and the commutation is performed. The following processes need to be provided:
All these processes are provided by new algorithms which were designed for these type of applications
within SDK. They are described in
Diagrams aid in explaining how the commutation works. After commuting the motor phases, a time
interval (Per_Toff[n]) is set that allows the shape of the Back-EMF to be stabilized. Stabilization is
required because the electro-magnetic interference and fly-back current in antibody diode can generate
glitches that may add to the Back-EMF signal. This can cause a misinterpretation of Back-EMF Zero
Crossing. Then the new commutation time (T2[n]) is preset and performed at this time if the
Back-EMF Zero Crossing is not captured. If the Back-EMF Zero Crossing is captured before the preset
commutation time expires, then the exact calculation of the commutation time (T2*[n]) is made based
on the captured Zero Crossing time (T_ZCros[n]). The new commutation is performed at this new
time.
If (for any reason) the Back-EMF feedback is lost within one commutation period, corrective action is
taken to return regular states.
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BLDC motor commutation service
Back-EMF Zero Crossing moment capture service
Computation of commutation times
Handler for interaction between these commutation processes
BLDC control with BEMF Zero Crossing using ADC
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Figure 5-6. Alignment
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11.1.