31
Fundamentals of line-commuted converters
Requirements of the supply system
The line voltage must be sinusoidal, supply of a line-commuted converter via a DC voltage
source is not possible.
U
Netz
= Û * sin ( *t), Û: Peak voltage of the supply network
= 2 * * f: Angular frequency, f: Frequency of the line voltage, 1 / f = T: Period
At 50 Hz line, T = 1 / 50 = 0.02 = 20 ms
At 60 Hz line, T = 1 / 60 = 0.0167 = 16.7 ms
The rms value U
RMS
of the line voltage is measured with the voltmeter.
Û = U
RMS
* root(2) = U
RMS
* 1.41421, at 400 V
RMS
= 400 *1.41421 = 566 V
Three-phase system:
A three-phase system comprises three individual phases (U, V, W) of the same voltage and
a phase shift by 120 degrees.
Phase voltage, e.g. U
U
: The voltage of an individual phase is the line-to-neutral voltage,
single voltage measured against the neutral point of the transformer.
Phase-to-phase voltage, e.g. U
UV
: This is the voltage measured between two phases.
The phase-to-phase voltage is the phase voltage times the root (3).
e.g.: U
U
= 230 V
U
UV
= U
U
* root (3) = 230 * 1.732 = 400 V
The phase-to-phase voltage is always specified on the technical data and on the rating plate
of the SINAMICS DCM.
U
UV
U
W
Neutral point
transformer
Transformer secondary winding
Netzspannung bei 50 Hz und U
eff
= 400 V
-600,00
-400,00
-200,00
0,00
200,00
400,00
600,00
0
5
10
15
20
25
30
Zeit in [ms]
N
e
tz
s
p
a
n
n
u
n
g
i
n
[
V
]
One line period:
360 degrees electrical
= 2
U
V
W
Phases U, V, W with the line-to-
neutral voltage and the
line-to-line voltage
Line voltage at 50 Hz and V
RMS
= 400 V
Time in [ms]
L
i
n
e
V
o
l
t
a
g
e
