Auxiliary Supply-Assisted 12-Pulse Phase-Controlled Rectifiers With Reduced Input Current Harmonics

Three-phase thyristor rectifiers have been used in industries for obtaining a variable dc voltage, but they have a problem of including large lower-order harmonics in the input currents. For high-power applications, a 12-pulse configuration is useful for reducing the harmonics, but it still includes the (12 m plusmn1)th (m: integer) harmonics. In order to further reduce the harmonics, this paper proposes to insert an auxiliary supply producing a square wave voltage to the dc bus of a 12-pulse phase-controlled rectifier. Theoretical investigation to reduce harmonics is presented, and a strategy to control the auxiliary supply voltage based on pulse-width-modulation is proposed. Reduction in the current harmonics is verified by simulation and experimental results. The volt-ampere (VA) rating of the auxiliary supply is about 5% of the rectifier output.