Analysis and Experimental Evaluation of Symmetric and Asymmetric 18-Pulse Autotransformer Rectifier Topologies

This paper presents the analysis and experimental evaluation of symmetric and asymmetric 18-pulse autotransformer rectifiers. Specifically, three symmetric topologies having the capability to feed from dual ac voltage networks-rated at 0.5 and 1 p.u., and three asymmetric topologies of minimum number of windings and kVA rating were considered. The evaluation assayed the voltage regulation, input power factor, input current THD, dc common-mode voltage, and power conversion efficiency, all obtained while operating at 400 and 800 Hz for both types of topologies, and additionally from 0.5 and 1 p.u. ac voltages for the symmetric topologies. The results obtained using 2 kW scaled-down prototypes show that the best symmetric topology is the one optimized to operate from 1 p.u. voltages, and the best asymmetric ones the topologies based on polygon autotransformers.