Harmonic reduction for 12-pulse four star thyristor rectifier with active auxiliary circuit

12-pulse four star thyristor rectifiers are widely used in electro-chemical industries, but large lower-order harmonics are included in the input currents. In order to reduce the harmonics to an acceptable level, a dc-side compensation strategy to reduce the harmonic of input line current in 12-pulse four star thyristor rectifier is proposed. According to the proposed strategy, a new active auxiliary circuit is added to the dc side of the 12-pulse thyristor rectifier and injects a specific triangular current. The specific triangular current shapes the distorted input line current as sine wave approximately. The active auxiliary circuit consists of a single transformer, a single PWM rectifier and a buck converter. Analysis of the proposed scheme is examined and simulation results are shown.