Specifications

Space Vector PWM
6-62
Figure 6–25. Basic Space Vectors and Switching Patterns
U
120
(010) U
60
(011)
U
140
(100) U
300
(101)
U
0
(001)
CCW direction
(SVRDIR=0)
CW direction
(SVRDIR=1)
U
out
T
1
T
2
U
380
(110)
The binary representations of two adjacent basic vectors are different in only
one bit. That is, only one of the upper transistors switches when the switching
pattern switches from U
x
to U
x+60
or from U
x+60
to U
x
. Also, the zero vectors
O
000
and O
111
apply no voltage to the motor.
Approximation of Motor Voltage with Basic Space Vectors
The projected motor voltage vector U
out
, at any given time, falls in one of the
six sectors. Thus, for any PWM period, it can be approximated by the vector
sum of two vector components lying on the two adjacent basic vectors:
U
out
= T
1
U
x
+ T
2
U
x+60
+ T
0
(O
000
or O
111
)
where T
0
is given by T
p
–T
1
–T
2
and T
p
is the PWM carrier period. The third term
on the right side of the equation above doesn’t affect the vector sum U
out
. The
generation of U
out
is beyond the scope of this context. For more details on
space vector PWM and motor control theory, see The Field Orientation Princi-
ple in Control of Induction Motors by Andrzej M. Trzynadlowski.
The above approximation means that the upper transistors must have the on
and off pattern corresponding to U
x
and U
x+60
for the time duration of T
1
and
T
2
, respectively, in order to apply voltage U
out
to the motor. The inclusion of
zero basic vectors helps to balance the turn on and off periods of the transis-
tors, and thus their power dissipation.
6.7.2 Space Vector PWM Waveform Generation with Event Manager
The EV module has built-in hardware to greatly simplify the generation of sym-
metric space vector PWM waveforms. Software is used to generate space
vector PWM outputs.