Harmonic current reduction in three-phase bridge-rectifier circuits using controlled current injection

This paper describes the further development of the novel current-injection scheme devised by the authors for attenuating line current harmonics in bridge-rectifier circuits. The previous passive filters are replaced by controlled filters connected between the bridge-rectifier output and the star point of the power transformer secondary. These filters are used to inject controlled third harmonic currents into the transformer windings. Variations in bridge working conditions, due to changes in either load or bridge delay angle, lead to corresponding changes in the filter operating conditions if the harmonic attenuation is to remain optimal. The control law for the filters has been derived and the effectiveness of the new method confirmed by both simulation and laboratory tests.