Harmonic reduction technology at DC link in star-connected-autotransformer-based multi-pulse rectifier

In order to improve the harmonic reduction ability of the multi-pulse rectifier, this paper proposes a multi-pulse rectifier based on harmonic reduction technology at DC link. The proposed rectifier employs two diode bridges, each followed by a Boost converter. By controlling the inductor current of Boost converter, the input line current of the proposed rectifier can be approximated to sinusoidal waveform. A star-connected autotransformer is used to be phase-shift transformer and the winding of the autotransformer are interconnected, which can significantly decrease the equivalent kVA rating of the transformer and improve the power density. This paper also calculates the theoretical inductor current waveform of Boost converter when the input line current is sinusoidal, and presents the applicable current waveform. The effect of harmonic reduction method on the kVA rating of star-connected autotransformer is also analyzed. The simulated and experimental results indicate that the rectifier can restrain large harmonic contents in input current obviously and has the merits of high power density.