AN1913D Freescale Semiconductor / Motorola, AN1913D Datasheet - Page 27

• 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

5.4.3.1 Starting - Commutation Times Calculation
coefficient Coef_CmtPrecomp = 2 at Starting state!
coefficient Coef_HlfCmt = 0.125 with advanced angle Advance_angle: 60Deg*3/8 = 22.5Deg
The following figure illustrates the sequence of the commutations during the Starting (Back-EMF
Acquisition) state.
Figure 5-11. Calculation of the Commutation Times during the Starting (Back-EMF
As can be seen in
influence of Back-EMF feedback
The calculations made during Starting (Back-EMF Acquisition) state can be seen in
Even the commutation process sub-states of the Starting (Back-EMF Acquisition) state remain the
same as during the Running state. The required commutation timing depends on the MCS state
(Starting state, Running state). It is provided by different settings of the commutation constants
Coef_CmtPrecompFrac, Coef_CmtPrecompLShft, Coef_HlfCmt, Coef_Toff, in structure
StartComputInit (differs from RunComputInit). The commutation times calculation is the same as
described in Section 5.4.2.2; however, the following computation coefficients are different:
Coef_Toff = 0.5 at Running state, Max_PerCmtProc = 100!
T_Cmt0
T_ZCros[0]
Per_CmtStart
[1]
n=1
T_Cmt0
T2[1]
at Starting state!
[2]
Zero Crossing
Detection Signal
Zero Crossing
Detection Signal
Zero Crossing
Detection Signal
2*
Figure 5-11
Per_Toff[n]
Per_CmtStart
BLDC control with BEMF Zero Crossing using ADC
n=2
Freescale Semiconductor, Inc.
For More Information On This Product,
T_Cmt0
the commutation times T2[1] and T2[2] are calculated without any
T2[2]
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[3]
Acquisition) State
COEF_CMT_PRESET *
* Per_ZCrosFlt[n-1]
Per_HlfCmt[n]
n=3
T_ZCros[n]
Per_HlfCmt[n]
T2**[n]
T2[n]
Commutation is preset
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.
Control Technique
Section
11.1.
27