AN1914 Freescale Semiconductor / Motorola, AN1914 Datasheet - Page 23

• Manufacturer Part Number: AN1914
• Description: 3-Phase BLDC Motor Control with Sensorless Back EMF Zero Crossing Detection Using DSP56F80x
• Manufacturer: Freescale Semiconductor / Motorola

5.4.2.2 Running - Commutation Times Calculation
T_Next[n] = T_Cmt0[n] + Per_CmtPreset[n] =
If Coef_CmtPrecomp*Per_ZCrosFlt>Max_PerCmt
Commutation time calculation is provided by algorithm bldcZCComput described in Motor
Control.pdf, chapter BLDC Motor Commutation with Zero Crossing Sensing (see [12.1]).
The following calculations are made to calculate the commutation times (T_Next[n])
during the Running Stage:
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 Stage!
then result is limited at Max_PerCmt
n-2
Zero Crossing
Detection Signal
DSP56F80x MC PWM Module in Motor Control Applications
Per_ZCros0[n] =
Per_ZCros[n-1]
T_Cmt0[n-1]
Freescale Semiconductor, Inc.
For More Information On This Product,
T_ZCros[n-1]
Zero Crossing
Detection Signal
Zero Crossing
Detection Signal
n-1
Go to: www.freescale.com
Per_Toff[n]
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
Control Technique
23