A new passive 28-step current shaper for three-phase rectification

A new passive 28-step current shaper for three-phase rectification is proposed in this paper. With a phase-shifting transformer on the ac side and six interphase transformers on the dc side, per-phase input current can be shaped into a 28-step sinusoidal waveform. The total harmonic distortion of ac input currents obtained is 6.54%, lower than one-half of that in a conventional 12-pulse converter. The transformer voltampere rating is also lowered down to one-fifth of that in a 12-pulse converter. A 2-kW experiment is performed to verify the proposed circuit.