Motorola M68HC08 - Manual (Page 48)

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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