In HVDC (High Voltage Direct Current) system there are two converters one at transmitting end and other at receiving end one operating as rectifier and other as inverter , the converters produce current harmonics that interference into the DC transmission lines and the AC grid. Since the harmonics increase transmission losses, and overheating of the equip-ment, insulation failure ,the combination of passive filter and Active filter have been used to reduce the harmful effects of the harmonic currents. Active power and passive filters (APF and PF) are the traditional ways of compensating the harmonics. However, both of the filters have some problems, namely reso-nance and tuning problems in passive filters (PF), and capaci-ty, establishment cost of active filter is high so HADF (HYBRIDE ACTIVE DC FILTER) are used to suppress har-monics on DC transmission lines connected with passive filter. Removing the harmonic component of DC transmission line current is carried out by Hybrid Active DC Filter (HADF), by injecting the compensating current into the DC transmission line to suppress the DC transmission line current harmonics significantly.

Keywords HVDC Transmission Line, Active DC Filter;