AN1914 Freescale Semiconductor / Motorola, AN1914 Datasheet - Page 24

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

Control Technique
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 =
Per_Toff[n+1] = Per_ZCrosFlt*Coef_Toff and Max_PerCmtProc minimum
Per_ZCros0 <-- Per_ZCros[n]
T_ZCros0 <-- T_ZCros[n]
T_Next*[n] = T_ZCros[n] + HlfCmt[n]
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]
Per_Toff[n+1] = Per_ZCrosFlt*Coef_Toff and Max_PerCmtProc minimum
Per_ZCros0 <-- Per_ZCros[n]
T_ZCros0 <-- T_ZCros[n]
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]
Per_ZCros0 <-- Per_ZCros[n]
T_ZCros0 <-- T_ZCros[n]
T_Cnt0 = time of the last commutation
T_Next = Time of the Next Time event (for Timer Setting)
T_zCros = Time of the last Zero Crossing
T_zCros0 = Time of the previous Zero Crossing
Per_Toff = Period of the Zero Crossing off
Per_CmtPreset = Preset Commutation Periof from commutation to next commutation if no
Zero Crossing was captured
Per_ZCros = Period between Zero Crossings (estimates required commutation period)
Per_ZCros0 = Pervious period between Zero Crossings
Per_ZCrosFlt = Estimated period of commutation filtered
Per_HlfCmt = Period from Zero Crossing to commutation (half commutation)
5.4.3 Starting (Back-EMF Acquisition)
24
The
Coef_CmtPrecompFrac, Coef_CmtPrecompLShft, Coef_HlfCmt, Coef_Toff, in structure
RunComputInit.
The Back-EMF sensing technique enables a sensorless detection of the rotor position, however the
drive must be first started without this feedback. It is caused by the fact that the amplitude of the
induced voltage is proportional to the motor speed. Hence, the Back-EMF cannot be sensed at a very
low speed and a special start-up algorithm must be performed.
•
•
•
required
If no Back-EMF zero crossing was captured during preset commutation period
(
If Back-EMF zero crossing is missed then Corrective Calculation 2. is made:
Where:
= 1/2*Per_ZCrosFlt[n]- C_CMT_ADVANCE*Per_ZCrosFlt[n]=
Per_CmtPreset
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 Stage!
Coef_Toff = 0.35 at Running Stage, Max_PerCmtProc = 100!
The best commutation was get with Advance_angle: 60Deg*1/8 = 7.5Deg
which means Coef_HlfCmt = 0.375 at Running Stage!
The best commutation was get with Advance_angle: 60Deg*1/8 = 7.5Deg
which means Coef_HlfCmt = 0.375 at Running Stage!
commutation
DSP56F80x MC PWM Module in Motor Control Applications
Freescale Semiconductor, Inc.
[n]) then Corrective Calculation 1. is made:
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timing
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is
provided
by
setting
of
commutation
constants