A 12-pulse diode rectifier using 3-phase bridge 6-pulse diode rectifier with 2 additional diodes and an auto-transformer

This paper presents a 12-pulse diode rectifier of capacitor input type consisting of the conventional three-phase bridge 6-pulse diode rectifier with an auxiliary circuit. Although the auxiliary circuit consists of an autotransformer with very low kVA and two auxiliary diodes with very low rating, it plays the role to increase operation pulse number to 12. As a result, harmonics of the input line currents are greatly reduced and the THD is reduced to a quarter 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