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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.

IGBThalf-bridge

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.

Pulsewidthmodulation

To arrive at a sinusoidal output waveform at a certain output frequency, an also

sinusoidal reference voltage u

ref

(t) with the required frequency is compared with a

triangular voltage u

tri

(t). The frequency of the triangular voltage equals the switching

frequency f

SW

of the IGBTs in the application. Each time the triangular voltage u

tri

(t)

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