Motorola M68HC08 - Manual (Page 28)

BLDC Motor Control
Designer Reference Manual DRM028 — Rev 0
28 BLDC Motor Control MOTOROLA
Figure 3-5. Power Stage — Motor Topology
The second goal of the model is to find how the motor characteristics
depend on the switching angle. The switching angle is the angular
difference between a real switching event and an ideal one (at the point
where the phase-to-phase back-EMF crosses zero).
The motor-drive model consists of a normal 3-phase power stage plus a
brushless dc motor. Power for the system is provided by a voltage
source (U
d
). Six semiconductor switches (S
A/B/C t/b
), controlled
elsewhere, allow the rectangular voltage waveforms (see Figure 3-2 ) to
be applied. The semiconductor switches and diodes are simulated as
ideal devices. The natural voltage level of the whole model is put at one
half of the dc-bus voltage. This simplifies the mathematical expressions.
B
C A
backEMF b
backEMF c
backEMF a
Rb
Ra Rc
Lb
Lc
u
u
u u
u
u
u
La
u u
u /2
d =
+
-
u /2
d =
+
-
u
AB
I
Sa
I
d0
S
At
S
Bt
S
Ct
S
Ab
S
Bb
S
Cb
I
Sb
I
Sc
u
BC
u
CA
u
Sb
u
Sc
u
Sa
u
0
u
VC
u
VB
u
VA
O
F
re
e
sc
a
le
S
e
m
ic
o
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u
c
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Freescale Semiconductor, Inc.
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