hows different switching states of one part of the Vienna rectifier, in
dependenceof themains voltage and the IGBT switch.
Each part bridge can provide three voltages
, 0 and
relative to the
centre point N, i.e. the circuit has a three-level nature. Accordingly, this explains the
alternative name for theVienna rectifier: Three-Level PWM rectifier.
11.3 DC/DC converter
The transformation of a given DC voltage into a DC voltage of different magnitude
and/or polarity is done with DC/DC converters or DC choppers. Over the years, a
number of different topologies have been established in the market. Each of them has
benefits related to the specific application. Despite the variety of topologies, these can
usually be reduced to just a few, which arepresented hereafter.
The applications of DC controllers cover a range of several decades of power.
Especially in the lower power region MOSFETs have established themselves as active
switches. Here, the employment of IGBTs is rather unusual, since the desired switching
frequencies cover the range of some 10kHz towell above 100kHz.Whereas inmedium-
power applications and then up to several megawatts, the IGBT is used as a switch.
The basic functions of the circuit do not change, however.
hows a typical circuit of a buck converter. Here the input voltage is
transformed toanoutput voltage of the same polarity, but reducedmagnitude.
The active switch is the transistor T
, which periodically switches the input voltage U
via the inductance L
to the load R. The ratio of time t
in which the transistor is
switchedon, in relation to the total time periodT is known as duty cycleD. Therefore: