Patent ID: 8228693

Claim:
A DC filter for use in a voltage source converter based HVDC transmission system comprising a first and a second pole line, said filter comprising: a first connection point connected to the first pole line, a second connection point connected to the second pole line, a third connection point connected to ground, two LC filters serially connected between the first and the second connection point, and an inductor provided between ground and a junction between the two LC filters, wherein values of the LC filters and the inductor are chosen so that Ω pm 2 =1÷( L 3× C 3) and Ω gm 2 =1÷([2 ×L 4 +L 3 ]×C 3), wherein Ω pm are pole mode harmonic frequencies and Ω gm are ground mode harmonic frequencies to be filtered in rad/s.