IGBT Modules - Technologies, Driver and Application (Second Edition) - page 410

11B
398
power semiconductors, i.e. a bridge short circuit (e.g. switches S
1
and S
2
are closed
simultaneously) does not lead to a destructive short circuit current, as this is limited by
the DC-bus inductors L
1
and L
2
. Similarly, no dangerously high voltage appears across
the DC-bus inductors, when the current flow is interrupted to the load (e.g. switches S
1
,
S
3
and S
5
are open), because the capacitors C
1
and C
2
provide a path for the inductor
current. In addition, the Z-inverter has the advantage that there is a limitation of the
inrush current of the DC-bus capacitors by the DC-bus inductors.
shows the
basic circuit arrangement of the Z-inverter. The same type of power switches like in a
VSI or a CSI can be used. For further considerations it is assumed that the switches S
x
aremadeup of an IGBTwith a free-wheeling diode.
The basic function of the Z-inverter is derived with the following example of a single
phase DC/AC inverter and then extended to three-phase systems. The DCmay come
from a fuel cell, battery or solar panel as depicted i
Fig. 11.34
Single phaseZ-inverter with input section and output filter
TheZ-inverter has threedifferent operating states:
Active state (AS). Here, the IGBTs T
1
and T
4
or T
2
and T
3
are active (state
"on").
Zero state (ZS). Here, the IGBTs T
1
andT
3
or T
2
andT
4
areactive (state "on").
Shorted state (SS). Here, the IGBTs T
1
and T
2
or T
3
and T
4
are active (state
"on").
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