User Manual

Control Technique
3-Phase BLDC Motor Control with Sensorless Back-EMF, ADC, Zero Crossing, Rev. 3
24 Freescale Semiconductor
Preliminary
• 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]):
Per_ZCros[n] = T_ZCros[n] - T_ZCros[n-1] = T_ZCros[n] - T_ZCros0
Per_ZCrosFlt[n] = (1/2*Per_ZCros[n]+1/2*Per_ZCros0)
HlfCmt[n] = 1/2*Per_ZCrosFlt[n]- Advance_angle =
= 1/2*Per_ZCrosFlt[n]- C_CMT_ADVANCE*Per_ZCrosFlt[n]=
Coef_HlfCmt*Per_ZCrosFlt[n]
The best commutation was get with Advance_angle: 60Deg*1/8 = 7.5Deg
which means Coef_HlfCmt = 0.375 at Running state!
Per_Toff[n+1] = Per_ZCrosFlt*Coef_Toff and Max_PerCmtProc minimum
Coef_Toff = 0.35 at Running state, Max_PerCmtProc = 100!
Per_ZCros0 <-- Per_ZCros[n]
T_ZCros0 <-- T_ZCros[n]
T_Next*[n] = T_ZCros[n] + HlfCmt[n]
• If no Back-EMF Zero Crossing was captured during preset commutation period (Per_CmtPreset[n])
then Corrective Calculation 1. is made:
T_ZCros[n] <-- CmtT[n+1]
Per_ZCros[n] = T_ZCros[n] - T_ZCros[n-1] = T_ZCros[n] - T_ZCros0
Per_ZCrosFlt[n] = (1/2*Per_ZCros[n]+1/2*Per_ZCros0)
HlfCmt[n] = 1/2*Per_ZCrosFlt[n]-Advance_angle = Coef_HlfCmt*Per_ZCrosFlt[n]
The best commutation was get with Advance_angle: 60Deg*1/8 = 7.5Deg
which means Coef_HlfCmt = 0.375 at Running state!
Per_Toff[n+1] = Per_ZCrosFlt*Coef_Toff and Max_PerCmtProc minimum
Per_ZCros0 <-- Per_ZCros[n]
T_ZCros0 <-- T_ZCros[n]
• If Back-EMF Zero Crossing is missed then Corrective Calculation 2. is made:
T_ZCros[n] <-- CmtT[n]+Toff[n]
Per_ZCros[n] = T_ZCros[n] - T_ZCros[n-1] = T_ZCros[n] - T_ZCros0
Per_ZCrosFlt[n] = (1/2*T_ZCros[n]+1/2*T_ZCros0)
HlfCmt[n] = 1/2*Per_ZCrosFlt[n]-Advance_angle = Coef_HlfCmt*Per_ZCrosFlt[n]
The best commutation was get with Advance_angle: 60Deg*1/8 = 7.5Deg
which means Coef_HlfCmt = 0.375 at Running state!
Per_ZCros0 <-- Per_ZCros[n]
T_ZCros0 <-- T_ZCros[n]