Closed-Loop Sinusoidal Input-Current Shaping of 12-Pulse Autotransformer Rectifier Unit With Impressed Output Voltage

This paper presents a novel closed-loop current-control strategy for a hybrid 12-pulse rectifier that uses a two-switch boost stage for output-voltage regulation. Unlike previous attempts to mitigate input-current distortion, e.g., by modulating the rectifier output voltage with open-loop control, this new closed-loop current-control scheme directly controls the line-interphase-transformer input voltage and/or impresses sinusoidal input currents. In this paper, the control strategy is explained and the modulation functions for each (π/6)-wide mains voltage sector are derived. The hardware implementation is described, and experimental results demonstrate that the control strategy ensures a high-quality input current for ideal as well as for distorted/unbalanced mains.