Active Harmonic Reduction for 12-Pulse Diode Bridge Rectifier at DC Side With Two-Stage Auxiliary Circuit

A 12-pulse diode bridge rectifier is often used in high-power rectification. However, the total harmonic distortion (THD) of input line current in 12-pulse rectifier does not meet the IEEE-519 standard. In order to reduce the harmonics to an acceptable level, we use a two-stage auxiliary circuit at dc side of the 12-pulse rectifier to eliminate harmonics actively. The effect of the auxiliary circuit´s parameter on the system performance is analyzed first, which indicates the necessity of applying two-stage auxiliary circuit. The front-stage auxiliary circuit plays a role in producing circulating current to cancel harmonics, and the back stage adjusts the output voltage of the front stage and feeds the power absorbed by the front stage to load in accordance with load current and input voltage of 12-pulse rectifier. Besides the good performance in harmonic elimination, the proposed auxiliary circuit has low kilovolt ampere rating.