11 Basic circuitsandapplicationexamples
IGBT modules are used in a variety of different applications. As diverse as these
applications may be, in general, they can be traced back to just a few basic circuits.
Generally, all basic circuits are power converters. A power converter here is a device to
convert one or more variables of a power system using power converter switches. The
mainelectrical parameters of a converter are:
Number of phases n
The operationof apower convertermay be dividedaccording t
Rectification, i.e. AC/DC converter
Conversion of direct current, i.e. DC/DC converter or chopper
Inverting, i.e. DC/AC inverter
Conversion of alternating current, i.e. AC/AC conversion
Concepts of power converters
During the operation of a converter (usually) the current flow is periodically switched
from one semiconductor switch to another semiconductor switch. This process is called
current commutation or just commutation. The commutation is the transition of current
from one branch of the converter to the following, whilst during the overlap time
(commutation period) both branches pass current.With the commutation, two cases are
distinguished: External commutation and self commutation.
Externally commutated power converters can be divided into line-commutated
converters and load-commutated converters. A line and externally commutated
converter would be, for example, if the input is connected to a three-phase AC grid and
a polarity change of the input voltage causes a change of current flow in the converter.
Since the origin of the commutation or the guiding voltage is external, it is called
external commutation. In self-commutated power converters, on the other hand, the
commutation voltage is provided by an energy storage which is part of the converter.