With the active DC-filter, ABB can fulfil the toughest HVDC interference level requirements with a minimum of equipment.
Demands on the HVDC converter stations regarding permitted interference levels from DC lines have become increasingly stringent in recent years. ABB has therefore developed an active DC filter that enables efficient filtering using a small-size filter. The active DC-filter is now installed in a number of HVDC projects.
Operating principles
The principle of the active DC filter is to inject a current generated by a power amplifier into the DC circuit cancelling the DC side harmonics coming from the HVDC converter. The amplifier is controlled by a high speed digital signal processor controller.
Circuit diagram of active DC filter
These measurements were taken in a prototype active DC filter that was installed in 1991 in the Konti-Skan 2 HVDC transmission.
Harmonic current content on the DC line
Active DC-filter in the Swedish station in the Baltic Cable HVDC inter-connection. The high voltage DC-filter capacitor can be seen in the right. The small house to the left contains the DC-filter control, the amplifiers and associated equipment.