AN1913D Freescale Semiconductor / Motorola, AN1913D Datasheet - Page 22

• 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
5.4.2.2 Running - Commutation Times Calculation
T_Next[n] = T_Cmt0[n] + Per_CmtPreset[n] =
If Coef_CmtPrecomp*Per_ZCrosFlt>Max_PerCmt
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Commutation times calculation is provided by algorithm bldcZCComput described in
The following calculations are made to calculate the commutation times (T_Next[n])
during the Running state:
T_Cmt0[n-2]
Per_ZCros[n-2]
•
•
Service of Commutation - The commutation time (T_Next[n]) is predicted:
Service of received Back-EMF Zero Crossing - The commutation time (T_Next*[n]) is
evaluated from the captured Back-EMF Zero Crossing time (T_ZCros[n]):
Figure 5-8. BLDC Commutation Times with Zero Crossing Sensing
= T_Cmt0[n] + Coef_CmtPrecomp*Per_ZCrosFlt[n-1]
coefficient Coef_CmtPrecomp = 2 at Running state!
then result is limited at Max_PerCmt
n-2
Zero Crossing
Detection Signal
Per_ZCros0[n] =
Per_ZCros[n-1]
T_Cmt0[n-1]
BLDC control with BEMF Zero Crossing using ADC
Freescale Semiconductor, Inc.
For More Information On This Product,
T_ZCros[n-1]
Zero Crossing
Detection Signal
Zero Crossing
Detection Signal
n-1
Per_Toff[n]
Go to: www.freescale.com
Per_ZCros[n]
T_Cmt0[n]
Per_ZCros[n]
COEF_CMT_PRESET *
* Per_ZCrosFlt[n-1]
Per_HlfCmt[n]
Per_ZCros[n]
n
T_ZCros[n]
T_Next[n]
Per_HlfCmt[n]
T_Cmt0**[n+1]
Commutation is preset
T_Cmt0*[n+1]
Commuted when Back-EMF
Zero Crossing is missed
- Corrective Calculation 2.
Commuted at preset time.
No Back-EMF feedback
was received
- Corrective Calculation 1.
Back-EMF feedback
received and evaluated
Section
11.1.