Active series compensators

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.