Harmonic current reduction of a six-pulse thyristor converter

This paper presents a line injection technique in order to reduce line current harmonics generated by AC/DC three-phase thyristor converters. The principle of this technique is to modify the current waveforms on the DC side windings of the converter transformer by injecting every harmonic components of the rectified current with an opposite phase. The proposed technique consists of an interconnection of a delta zigzag transformer between the AC and DC sides of the thyristor converter. This interconnection, in combination with conduction intervals of each thyristor, generates a circulating third harmonic current between the AC and DC sides of the converter. This technique shows a drastic minimization of the total harmonic distortion (THD ) of the input current. Derived analytical equations and Pspice simulation are verified by experimental results. The obtained results show that this technique is effective, simple and reliable in reducing the input current harmonics.