New Step-Up and Step-Down 18-Pulse Direct Asymmetric Autotransformer Rectifier Units

This paper presents two new step-up and step-down 18-pulse direct asymmetric autotransformer rectifier units for aircraft applications. The converters are designed to operate with variable frequency power supplies (400-800 Hz), while meeting tight harmonic, power factor and output voltage requirements. The main features of the proposed converters are: a minimum number of windings used to achieve the step-up and step-down voltage variation (simplifying the autotransformer structure), the lack of series-connected windings at the output of the secondary voltage terminals (reduced sensitivity to leakage inductance), and the reduced kVA rating of the autotransformers, 0.30 and 0.32 p.u. respectively. The paper includes an in-depth analysis of the ATRU autotransformers, together with a complete description of their autotransformer currents. Experimental results obtained with laboratory prototypes are used to validate the correct operation and high-performance of the proposed autotransformer rectifier units