Environmental Engineering Reference
In-Depth Information
T1
T2
T3
T4
T5
T6
T1
A+
B+
C+
V
dc
V
ab
V
dc
V
bc
V
dc
V
ca
2/3
1/3
V
an
2/3
1/3
V
bn
2/3
1/3
V
cn
2/3
1/3
V
no
Figure 5.14 Brushless ac motor waveforms
For quasi-square waveforms, the total rms and fundamental rms are very
similar. Equation (5.4) predicts a total rms value of 0.816
U
d
and (5.8) predicts a
fundamental rms content of 0.78
U
d
. Using the same procedure for the line to
neutral voltages shown as traces 7, 8 and 9, the corresponding values are
r
U
d
2
3
U
an
¼
p
ð
5
:
9
Þ
p
p
U
d
2
U
an1
¼
where the line-neutral rms voltage given by (5.9) equates to 0.471
U
d
and its fun-
damental component,
U
an1
¼
0.45
U
d
. The relations given by (5.8) and (5.9) will be
important in later sections.
