Analysis of new 18-pulse direct symmetric autotransformer rectifiers with dual AC-voltage feeding capability

Ever increasing power quality requirements have impelled the development and usage of new front end AC-to-DC converters. Multi-pulse direct symmetric autotransformer rectifiers (DSAR) have arisen as a most advantageous passive solution, featuring high reliability and simplicity of operation, minimum kVA ratings, solid multi-pulse operation insensitive to impedance path mismatch or voltage distortion, reduced common-mode voltage, and reduced size and weight-hence the interest for transport applications. This paper proposes three new DSAR topologies with the capability to operate from 0.5 pu and 1 pu voltage sources while generating 1 pu output DC voltage, thus significantly enhancing their operational flexibility. The paper presents a complete evaluation using simulated (Synopsys Saber) and experimental results in order to fully assess the thermo-electromagnetic capabilities of these new topologies, focusing on losses and efficiency, size and weight, and the overall power quality of these converters. Specifically, it analyzes efficiency, input current distortion, common-mode voltage and DC voltage ripple, all of this while operating from ideal and low power quality AC voltage networks rated at 0.5 pu and 1 pu. From these results specific design guidelines and criteria for selection are derived and presented.