IGBT Modules - Technologies, Driver and Application (Second Edition) - page 406

Fig. 11.29
Influence of the grounding point on the selection of the insulation class of
IGBTmodules for three-level inverters
A further implementation of a multi-level inverter is illustrated in
Here, the
output voltage of separate H-bridges will be assembled in series. The output voltage of
the separate H-bridges is made up of series connected switches. Due to the cascade
structure, this circuit design is calledCascadeCell Multi-Level (CCML) inverter.
The original motivation to design three-level inverters was to use semiconductor
switches at a DC-bus voltage above that of what can be achieved with a two-level
inverter. This was originally born out of necessity, since no high-voltage blocking
semiconductorswere availabl
. The pioneerswere applications in the fieldof traction.
Nowadays, that IGBT modules are available up to a voltage rating of 6.5kV, the focus
has shifted regarding more recent applications. There are now three-level inverters in
use where two-level inverters could be applied. Examples of applications that appear
more and more as three-level inverters are solar inverters and uninterruptible power
supplies (UPS) . If designed correctly, there are advantages in these cases over the
usual two-level solutions like...
...reduced losses
...smaller output filters
For example, before 1.7kV IGBTs were available, 1.2kV IGBTs were used for a supply voltage of 690V
in a
three-level topology.
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