AN1914 Freescale Semiconductor / Motorola, AN1914 Datasheet - Page 28

• 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
5.4.3.1 Starting - Commutation Times Calculation
coefficient Coef_CmtPrecomp = 2 at Starting Stage!
coefficient Coef_HlfCmt = 0.125 with advanced angle Advance_angle: 60Deg*3/8 = 22.5Deg
Coef_Toff = 0.5 at Running Stage, Max_PerCmtProc = 100!
28
Figure 5-11. Calculation of the Commutation Times during the Starting (Back-EMF
.
The calculations made during Starting (Back-EMF Acquisition) Stage can be seen in Motor
Control.pdf, chapter BLDC Motor Commutation with Zero Crossing Sensing (see
Even the sub-states of the commutation process of Starting (Back-EMF Acquisition) state remain the
same as during Running state, the required commutation timing depends on MCS state (Starting Stage,
Running
Coef_CmtPrecompFrac, Coef_CmtPrecompLShft, Coef_HlfCmt, Coef_Toff, in structure
StartComputInit (differs from RunComputInit). So the commutation times calculation is same as
described in
T_Cmt0
T_ZCros[0]
Per_CmtStart
[1]
n=1
T_Cmt0
Stage).
T2[1]
at Starting Stage!
Section
[2]
DSP56F80x MC PWM Module in Motor Control Applications
Zero Crossing
Detection Signal
Zero Crossing
Detection Signal
Zero Crossing
Detection Signal
2*
Per_Toff[n]
5.4.2.2, but the following computation coefficients are different:
It
Per_CmtStart
n=2
Freescale Semiconductor, Inc.
For More Information On This Product,
is
provided
T_Cmt0
T2[2]
Go to: www.freescale.com
[3]
Acquisition) Stage
COEF_CMT_PRESET *
* Per_ZCrosFlt[n-1]
by
Per_HlfCmt[n]
n=3
T_ZCros[n]
different
Per_HlfCmt[n]
T2**[n]
T2[n]
Commutation is preset
setting
Commuted at preset time.
No Back-EMF feedback was
received - Corrective Calculation 1.
T2*[n]
Commuted when Back-EMF
Zero Crossing is missed
- Corrective Calculation 2.
Commuted when correct
Back-EMF feedback
received and evaluated.
of
commutation
Section
constants
12.2).