Motorola M68HC08 Reference Manual page 48

BLDC Motor Control
PHASE BACK-EMFS
BACK-EMF ZERO CROSSINGS
IDEAL COMMUTATION PATTERN WHEN POSITION IS KNOWN
B
TOP
C
BOT
REAL COMMUTATION PATTERN WHEN POSITION IS ESTIMATED
B
TOP
C
BOT
FIRST
ALIGN
Designer Reference Manual
48
Freescale Semiconductor, Inc.
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.
PHASE C
C
TOP
A
BOT
C
TOP
A
BOT
SECOND THIRD
STARTING (BACK-EMF ACQUISITION)
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.
BLDC Motor Control
For More Information On This Product,
Go to: www.freescale.com
PHASE A
PHASE B
A
TOP
B C
BOT BOT
A
TOP
B C
BOT BOT
.................
FOURTH
B C
TOP
TOP
A
BOT
B C
TOP TOP
A
BOT
RUNNING
DRM028 — Rev 0
MOTOROLA