Harmonic cancellation of a hybrid converter

All HVDC converter stations have until now been built up of line commutated current source converters (CSCs). The CSC has the advantages of being robust and able to control the DC current especially at ground faults on the DC lines. However, one disadvantage has been the sensitivity to AC voltage disturbance and the need to supply reactive power from the AC system. Forced commutated voltage source converter (VSC) which would be less sensitive to disturbances in the AC-network and which can supply reactive power has, on the other hand, the disadvantage of being more expensive and very sensitive to disturbance on the DC side. Some studies have shown that a possible alternative solution could be to use a hybrid converter consisting of a CSC connected in series on the DC side with a VSC. It is shown in this study that the VSC can be used as an active filter to compensate the harmonics generated to the AC side from the current source converter.