A new technique to reduce line-current harmonics generated by a three-phase bridge rectifier

Three-phase bridge rectifiers are widely used in industry to interface DC loads to the electric utility because of their low ripple content output and high power-handling capability. The nonlinear nature of the diode type switching devices causes significant line-current harmonics resulting in increased distortion, malfunction of sensitive electronic equipment, increased losses, and contributes to inefficient use of electric energy. This paper describes a new approach to reduce those line-current harmonics generated by a three-phase diode rectifier type utility interface. The proposed approach consists of a novel interconnection of a delta-zig zag transformer between the AC and DC sides of the diode rectifier topology. This transformer connection in combination with the conduction intervals of each diode generates automatically a circulating third harmonic current between the AC and DC side of the rectifier bridge. Voltage and current analysis and simulation using the Electro-Magnetic Transients Program (EMTP) showed that the generated circulating current may drastically reduce the line current harmonics of the AC side and smooth out the DC output voltage of the rectifier