Motorola M68HC08 Reference Manual page 26

BLDC Motor Control
Phase Magnetic
Flux Linkage
Phase Back EMF
Phase-Phase
Back EMF
Figure 3-3. BLDC Motor Back EMF and Magnetic Flux
Designer Reference Manual
26
Freescale Semiconductor, Inc.
PH. A
PH. B
PH. A
PH. B
Atop Btop Ctop
Cbot Abot Bbot
A–B
B–C
The filled areas in the tops of the phase back-EMF voltage waveforms
indicate the intervals where the particular phase power stage
commutations occur. The power switches are cyclically commutated
through the six steps; therefore, this technique is sometimes called six
step commutation control. The crossing points of the phase back-EMF
voltages represent the natural commutation points. In normal operation
the commutation is performed here. Some control techniques advance
the commutation by a defined angle in order to control the drive above
the pulse-width modulator (PWM) voltage control.
BLDC Motor Control
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PH. C
SPEED REVERSAL
PH. C
"Natural" commutation point
"NATURAL" COMMUTATION POINT
ACTING POWER SWITCH IN THE POWER STAGE
C–A
Speed reversal
DRM028 — Rev 0
MOTOROLA
Psi_A
Psi_B
Psi_C
Ui_A
Ui_B
Ui_C
Ui_AB
Ui_BC
Ui_CA