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340 Transient studies of FACTS and Custom Power equipment

Fig. 8.58 DVR controller implemented in PSCAD/EMTDC.

The simulations carried out showed that the DVR provides excellent voltage
regulation capabilities. It must be observed that its capacity for power compensation
and voltage regulation depends mainly on two factors: the rating of the DC storage
device and the characteristics of the coupling transformer. These two factors deter-
mine the maximum value of series compensation that the DVR can provide.
In similar way as with the D-STATCOM, the coupling transformer plays a very
important role in the behaviour and performance of the DVR. Thus, it is necessary to
select the transformer properly. In order to avoid saturation under every condition,
the coupling transformer must be sized to handle at least twice the normal steady-
state flux requirement at maximum rms injection voltage, without saturation. Nor-
mally a high reactance is necessary to filter out the harmonic distortion introduced by
the PWM action of the inverter. However, a high reactance of the coupling trans-
former will slow down the response of the DVR and fast transients will be difficult to
identify and correct.