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Back-emf at start up, Bldc motor control, Freescale semiconductor, inc – Motorola M68HC08 User Manual

Page 48

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BLDC Motor Control

Designer Reference Manual

DRM028 — Rev 0

48

BLDC Motor Control

MOTOROLA

Figure 3-19

demonstrates the back-EMF during the start up. The

amplitude of the back-EMF varies 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 3-19. Back-EMF at Start Up

Figure 3-20

illustrates the sequence of the commutations during the

starting (back-EMF acquisition) state. The commutation times T2[1] and
T2[2] are calculated without any influence of back-EMF feedback. The
commutation time calculations are explained in the following section.

RUNNING

ALIGN

BACK-EMF ZERO CROSSINGS

IDEAL COMMUTATION PATTERN WHEN POSITION IS KNOWN

REAL COMMUTATION PATTERN WHEN POSITION IS ESTIMATED

PHASE BACK-EMFS

PHASE A

PHASE C

PHASE B

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STARTING (BACK-EMF ACQUISITION)

FIRST

SECOND

THIRD

FOURTH

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Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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