harmonic filters are necessary for the elimination of the harmonic waves and for the production of the reactive power at line commutated converter stations. at plants with six pulse line commutated converters, complex harmonic filters are necessary because there are odd numbered harmonics of the orders formula_1 and formula_2 produced on the ac side and even harmonics of order formula_3 on the dc side. at 12 pulse converter stations, only harmonic voltages or currents of the order formula_4 and formula_5 (on the ac side) or formula_6 (on the dc side) result. filters are tuned to the expected harmonic frequencies and consist of series combinations of capacitors and inductors.