Harmonic analysis and simulation of multi-pulse rectifiers applied in electrolysis industry

Low-voltage high-current electrolysis rectifier systems are widely used in large-scale electrolysis factories. It consists of several rectifier transformers in a parallel mode with proper phase shifts. The increased pulse numbers of the rectifier system can eliminate harmonics of certain orders. In this paper, an 84-pulse rectifier system applied in aluminum electrolysis factories is designed according to the classic theory. An improved polygonal method is used to analyze the harmonic contents of the 84-pulse rectifier transformer system. Using this method it is easy to illustrate the cancellation of non-characteristic harmonic current components under the ideal condition and the appearance of residual harmonics current components when the operating condition changes. A model of the 84-pulse rectifier system based on PSCAD/EMTDC is built to verify the theoretical analysis. Comparisons of harmonic current generated by an 84-pulse and a 12-pulse rectifier are conducted as well as the harmonic current under different situations.