Research of the current-injection-based P-type 12-pulse ATRU

P-type 12-pulse auto-transformer rectifier unit (ATRU) is a very attractive harmonic solution in aviation situation for its lower volt-ampere rating of transformer compared with other multi-pulse methods. However, the input current THD of 12-pulse ATRU is about 15% larger than 10% THD requirement by the related standards. Current-injection method is an effective harmonic mitigation method for 12-pulse rectifiers. This paper analyzed the input current waveform based on triangle current-injection method for P-type 12-pulse ATRU. It also points that the key to get the required injection current taking use of the voltage difference across interphase reactors is to emulate a resistor. The optimum equivalent current injection resistance is derived in this paper. And a novel harmonic injection scheme based on DCM flyback converter is proposed and analyzed. Experimental results from three 4kW P-type 12-pulse ATRU testify the effectiveness of the theoretical analysis and the proposed harmonic injection method.