A shunt hybrid active DC filter (HADF) is applied to eliminate DC transmission line current harmonics in HVDC transmission system. Since the harmonics increase transmission line losses and disturb control and monitoring equipments so HADF are used to suppress harmonics on DC transmission lines. In this paper a modified method is presented to control the shunt HADF which is not dependent on HVDC circuit parameters. HADF by injecting the compensating current to DC transmission line with the modified method suppresses the DC transmission line current harmonics significantly. Six major problems in design of modified control method have been discussed thoroughly. The principle of operation is described and the theoretical analyses are indicated to verify the control strategy. HVDC system is simulated by PSCAD/ EMTDC software. Simulation results and comparisons prove and validate the accuracy of these claims.

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