Auxiliary-supply-assisted phase-controlled 12-pulse rectifiers with reduced input current harmonics

Three-phase thyristor converters have been used in industries for obtaining a variable DC voltage, but they have a problem that they include large lower-order harmonics in the input currents. For high power applications a 12-pulse configuration is useful for reducing them, but it still includes the (12m±1)^th (m: integer) harmonics. In order to further reduce the harmonics, this paper proposes to insert an auxiliary voltage supply (AVS) to the DC bus of a 12-pulse phase-controlled rectifier. Theoretical analysis is presented, and a strategy to control AVS voltage is proposed. Reduction in the current harmonics is verified by simulation and experimental results. The VA rating of AVS is about 5% of the rectifier output.