Input Current Step-Doubling for Autotransformer-Based 12-Pulse Rectifier Using Two Auxiliary Diodes

To significantly decrease the input line current total harmonic distortion (THD) under simple circuit configuration conditions, this article propose an input current step doubling scheme for autotransformer-based 12-pulse rectifier using two auxiliary diodes. The auxiliary diodes are installed between the two retrofitted double-tap interphase reactors, and they inject specific square wave currents to increase the output current states of the rectification bridges. This modification extends the 12-step input line current to a 24-step input line current, and the near sinusoidal input line current with THD below 5% is obtained. As the proposed scheme only requires two low current stress (3.4% Id) auxiliary diodes, it achieves high-cost performance, is easy to implement and has a simple circuit configuration. A 2.2 kW simulation and experimental prototype is built to verify the theoretical analysis.