A harmonic reducing scheme for 3-phase bridge 6-pulse diode rectifier

This paper presents a 12-pulse diode rectifier of the capacitor input type. This diode rectifier consists of the conventional three-phase bridge six-pulse diode rectifier and an auxiliary circuit. Although the auxiliary circuit consists of only an autotransformer with very low kVA and two auxiliary diodes with very low rating, it plays the roll to increase operating pulse number from original 6 to 12. As a result, harmonics of the input line currents are greatly reduced and the THD is improved to theoretically a quoter of the conventional 6-pulse rectifier. Since the new rectifier does not consist of a self-turn-off device nor a controller, the proposed scheme results in a compact, reliable and efficient solution to obtain uncontrolled DC-voltage from the utility without harmonic pollution. In this paper, the unique arrangement and particular operation of the auxiliary circuit are introduced. Then, experimental results are shown to confirm the validity of the theory