Active series
compensators
ü Advances in power electronic technologies and new topologies for
these devices have resulted in new options for providing voltage sag ride
through support to critical loads. One of the important new options is a device
that can boost the voltage by injecting a voltage in series with the remaining
voltage during a voltage sag condition.
ü These are referred to as active series compensation devices. They are available in size ranges from
small single-phase devices (1 to 5 KVA) to very large devices that can be
applied on the medium-voltage systems (2 MVA and larger).
ü Figure shows an example of a small single-phase compensator that
can be used to provide ride-through support for single-phase loads.
ü A one-line diagram illustrating the power electronics that are
used to achieve the compensation is shown in Fig. When a disturbance to the
input voltage is detected, a fast switch opens and the power is supplied
through the series-connected electronics.
ü This circuit adds or subtracts a voltage signal to the input
voltage so that the output voltage remains within a specified tolerance during
the disturbance. The switch is very fast so that the disturbance seen by the
load is less than a quarter cycle in duration. This is fast enough to avoid
problems with almost all sensitive loads. The circuit can provide voltage
boosting of about 50 percent, which is sufficient for almost all voltage sag
conditions.
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