Motorola M68HC08 Reference Manual page 31

3.2.4.3 Effect of Mutual Inductance
DRM028 — Rev 0
MOTOROLA
Freescale Semiconductor, Inc.
0 30 60 90 120
Figure 3-6. Phase Voltage Waveform
However simple this solution looks, in reality it is more difficult, because
the sensed "branch" voltage also contains some ripples.
As shown in previous equations
inductances play an important role here. The difference of the mutual
inductances between the coils which carry the phase current, and the
coil used for back-EMF sensing, causes the PWM pulses to be
superimposed onto the detected back-EMF voltage. In fact, it is
produced by the high rate of change of phase current, transferred to the
free phase through the coupling of the mutual inductance.
Figure 3-7 shows the real measured "branch" voltage. The red curves
highlight the effect of the difference in the mutual inductances. This
difference is not constant.
BLDC Motor Control
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Brushless DC Motor Control Theory
150 180 210 240
(EQ 3-4.) through
BLDC Motor Control
270 300 330 360
uVA
uSa
- Back-EMF can be sensed
(EQ 3-6.), the mutual
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