Page 270 - Power Electronic Control in Electrical Systems

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258 Power electronic equipment

Fig. 6.92 VSC based single-phase combined series/shunt connected active filter.

need to be filtered and become sinusoidal waveforms. Furthermore, in the case of a
voltage-source type converter being used, the inductor is connected at the output of
the converter as the voltage waveforms created are of a square-wave type and also
need to be filtered and become sinusoidal prior to being fed into the line.
In the case of the converter being connected in series, a transformer is used to
connect the output of the converter in series with the line. Once again both load and
mains have an inductor in series.
The unified active filter that has a series and shunt connected VSCs is shown in
Figure 6.85. The two converters share the same DC bus and the same rules to connect
them into the line are followed.
The next step is to combine the active filters with passive ones as a series and/or
parallel. These filters are discussed in the following section (Figures 6.93±6.95).

Fig. 6.93 Four-wire three-phase VSC based shunt connected active filter.