Analysis of new step-up and step-down direct symmetric 18-pulse topologies for aircraft autotransformer-rectifier units

Among possible 18-pulse Autotransformer-Rectifier-Unit (ATRU) topologies, Direct Symmetric circuit (DS-ATRU) demonstrates relatively low complexity, it is insensitive to impedance mismatch and distortions of input voltage and has low common mode voltage. This paper proposes new step-up and step-down Direct Symmetric 18-pulse ATRU topologies for aircraft application. Serious study of proposed topologies was performed. The authors analyzed the kVA ratings, effects of leakage inductance on compliance with input current harmonic requirements, power sharing between diode bridges, common mode voltage and output ripple. The comparison is carried out for the full range of the input tine frequency from 400 to 800Hz. Key analyses and results obtained with Saber simulations are presented for validation of the presented work. Some experimental results are shown.