THD Mitigation in Line Currents of 6-Pulse Diode Bridge Rectifier Using the Delta-Wye Transformer as a Triplen Harmonic Filter

The uncontrolled three-phase bridge rectifier has the least line current distortion among six-pulse rectifiers; however, its total harmonic distortion (THD) of 31.08% is unacceptable as per the contemporary power quality standards. This paper seeks to address the issue by elimination of triplen harmonics in the line currents by providing a deltawye transformer at the ac interface i.e. between the three-phase supply and the diode bridge rectifier. The triplen harmonics circulate in the delta loop of the primary winding but are not manifested in the line currents thus reducing their THD values. The efficacy of the technique is proved by simulations considering the bridge rectifier with and without the delta-wye transformer of vector group Dy1. Experimental results with the Dy1 transformer and without it are presented. Keywords— diode bridge rectifier, improved power quality, total harmonic distortion, triplen harmonics.