Novel 18-step diode rectifier circuit with nonisolated phase shifting transformers

A novel, economical three-phase AC/ DC interface having no controllable switching devices is proposed. The key concept is the combined use of nonisolated phase-shifting transformers and DC-side interphase reactors having tapping diodes. The resultant AC input currents take the form of 18-step waveforms having a total harmonic distortion (THD) of 10.1%, which is roughly two thirds that of 12-step waveforms.