Environmental Engineering Reference
In-Depth Information
Fig. 4.8
Voltage waveforms
in six-step operation
The fundamental r.m.s. value of the three-phase, line-to-line output voltage is:
U
ab
=
√
6
π
U
d
= 0
,
78
·
U
d
(4.7)
Note that in this configuration the output frequency is adjustable by controlling
U
d
, but the output voltage amplitude is not. The currents results from the interaction
of the output voltage with the a.c. side system which may be an induction machine.
4.3.3.2 Voltage-Source PWM Inverter
Figure 4.9 shows a three-phase, two-level converter, with semiconductor elements
as in Fig. 4.7, and an ohmic-inductive load at the a.c. output. Output frequency and
fundamental voltage can be controlled in switch-mode operation.
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