Sequential connection and phase control of a high-current rectifier optimized for copper electrowinning applications

This paper proposes an optimized sequential control technique for copper el ectrowinning high-current rectifiers, The converter comprises two series-co nnected six-pulse double-wye rectifiers, a step-down transformer, and a tun ed input filter. The six-pulse rectifiers are fed from delta and polygon pr imary windings with different turns ratio and phase shifted by 5 degrees. U nder the proposed control scheme, one rectifier is kept at nominal output v oltage, and the other one is phase controlled to control the load's current . The proposed strategy greatly improves the rectifier's performance, reduc ing its reactive power maximum demand by 62% compared to conventional recti fiers and, therefore, reduces the input filters power rating also by 62%, T his is accomplished while keeping the input power factor above 0.95 through out the whole operating range. Further, the converter's reactive power cons umption presents a low varying characteristic, allowing it to use a fixed t ilter, even when operating from a power system not capable of withstanding large reactive power variations, Finally, it presents a harmonic current di stortion comparable to conventional 12-pulse high- current rectifiers, This paper presents the design and optimization procedure of the rectifying sys tem. A 2.5-kVA laboratory prototype was used to validate the converter mode l, later employed in evaluating the converter operating in a 10.5-MVA coppe r electrowinning facility. The results obtained confirm the advantages of t he proposed converter and its control strategy.