Abstract: In power systems with a large percentage of nonlinear loads, there is usually an imbalance among the three-phase input voltages. This article carries out a detailed analysis of the impact that the unbalanced input condition has upon the output voltage and input current of a 12-pulse auto transformer rectifier units (ATRU). In order to counter the effect of input unbalance, the article adopts a harmonics blocking reactor (HBR) to suppress current harmonics. It compares several implementation solutions of the HBR, and finally decides on the optimal one. Furthermore, a 2 kW laboratory prototype is developed, and the experimental results show that under the condition of input imbalance the use of HBR leads to a dramatic improvement in performance.

Key words: aero power, harmonic, auto transformer rectifier unit, input voltage imbalance, harmonic blocking reactor