Investigation on the Selection and Design of Step-Up/Down 18-Pulse ATRUs for More Electric Aircrafts

Multi-pulse autotransformer rectifier units (ATRUs) have been widely used in aviation applications due to their rugged structure, cost-effectiveness, and high-reliability features. In this paper, up to six types of autotransformers for an 18-pulse ATRU are investigated, aiming to provide an optimal selection guideline for a proper structure. By conducting a thorough comparative study on the kilovoltampere (kVA) rating of the autotransformers and the current harmonic characteristics over a wide voltage step-up or step-down range, the asymmetric delta-polygon (DP) structure is considered as the most promising choice. Subsequently, an example 18-pulse ATRU with such structure is adopted as the front end of an alternative current (ac)/ac converter powering an onboard hydraulic pump. After analyzing the operational principle, accurate mathematical expressions among the overall voltage gain K, the total harmonic distortion (THD) of the line current, and the kVA rating of the autotransformer were carefully deduced. Before conclusions, the theoretical analyses were verified by simulations and experiments. It is shown that the THD of the input line current of the designed 10-kW ATRU is 6.74%, the rated efficiency reaches 98.5%, and the autotransformer's weight is merely 3.3 kg.