A modular AC/DC rectifier based on cascaded H-bridge rectifier

In this paper, a modular AC/DC rectifier for converting the medium voltage (MV) to the low voltage (LV) levels is presented. The proposed rectifier includes two stages: the cascaded H-bridge (CHB) converter and the isolated DC/DC converters. The CHB converter is directly connected to the MV levels and it eliminates the necessity for heavy and bulky step-down transformers, corrects the input power factor, and maintains the voltage balance across the capacitor voltages. The second stage includes the high frequency parallel-output DC/DC converters, which are connected to the primary DC buses. The second stage provides the galvanic isolation, regulates the output voltage, and attenuates the low frequency voltage ripple (2fline) generated by the first stage. The active load-current sharing technique is utilized to balance the load power among the parallel converters. The detailed analysis for modeling and control of the proposed structure is presented. The validity and performance of the proposed topology is verified by a laboratory scaled prototype.