AN1914 Freescale Semiconductor / Motorola, AN1914 Datasheet - Page 27

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

Figure 5-10
according to the rotor speed. During the Starting (Back-EMF Acquisition) state the commutation is
done in advance. In the Running state the commutation is done at the right moments.
Figure 5-11
Stage. The commutation times T2[1] and T2[2] are calculated without any influence of Back-EMF
feedback.
Phase Back-EMFs
Back-EMF Zero Crossings
Ideal Commutation Pattern when position is known
Real Commutation Pattern when position is estimated
Align
C
C
B
B
BOT
BOT
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TOP
1’
st
illustrates the sequence of the commutations during the Starting (Back-EMF Acquisition)
demonstrates the Back-EMF during the start-up. The amplitude of the Back-EMF varies
DSP56F80x MC PWM Module in Motor Control Applications
2’
nd
A
C
A
Freescale Semiconductor, Inc.
Starting (Back-EMF Acquisition)
TOP
BOT
BOT
For More Information On This Product,
Figure 5-10. Back-EMF at Start-Up
Go to: www.freescale.com
C
TOP
Phase C
3’
rd
B
4’
BOT
Phase B
rd
B
BOT
Phase A
A
.................
TOP
A
TOP
C
C
BOT
BOT
Running
B
B
Control Technique
TOP
TOP
A
A
BOT
BOT
C
C
TOP
TOP
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