IGBT Modules - Technologies, Driver and Application (Second Edition) - page 137

125 Modulation factor
The basic aim of all modulation methods is the generation of effectively ideal output
voltages and currents for the respective application. In motor drives for example an
essentially circular field is to be generated which, as far as possible, should be free of
harmonics. For power semiconductors the modulation method chosen is relevant in so
far as themodulation factor m derived from this needs to be part of the loss calculation
for the components.
Fig. 3.9
A standardmodulationmethod for amultitude of applications is pulse widthmodulation
PWM, of which several different implementations exist. A common variant of it is, for
example, the subharmonic method also referred to as triangulation. To derive the
modulation factor m the triangulation method and the IGBT half-bridge circuit fro
s tobeused below.
Fig. 3.10
To arrive at a sinusoidal output waveform at a certain output frequency, an also
sinusoidal reference voltage u
(t) with the required frequency is compared with a
triangular voltage u
(t). The frequency of the triangular voltage equals the switching
frequency f
of the IGBTs in the application. Each time the triangular voltage u
1...,127,128,129,130,131,132,133,134,135,136 138,139,140,141,142,143,144,145,146,147,...548
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