Motorola M68HC08 Reference Manual page 32

BLDC Motor Control
NOTE:
CAUTION:
Designer Reference Manual
32
Freescale Semiconductor, Inc.
0 V
Figure 3-7. Mutual Inductance Effect
Due to the construction of the BLDC motor, both mutual inductances
vary. They are equal at the position that corresponds to the back-EMF
zero crossing detection.
The branch waveform detail is shown in
Figure 3-8 shows the disturbed "branch" voltage. The superimposed
ripples clearly match the width of the PWM pulses, and thus prove the
conclusions from the theoretical analysis.
The effect of the mutual inductance corresponds well in observations
carried out on the five different BLDC motors. These observations were
made during the development of the sensorless technique.
The BLDC motor with stator windings distributed in the slots has
technically higher mutual inductances than other types. Therefore, this
effect is more significant. On the other hand the BLDC motor with
windings wounded on separate poles, shows minor presence of the
effect of mutual inductance.
However noticeable this effect, it does not degrade the back-EMF zero
crossing detection because it is cancelled at the zero crossing point.
Simple additional filtering helps to reduce ripples further.
BLDC Motor Control
For More Information On This Product,
Go to: www.freescale.com
Figure 3-8. Channel 1 in
DRM028 — Rev 0
MOTOROLA