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 electrowinning high-current rectifiers. The converter comprises two series-connected six-pulse double-wye rectifiers, a step-down transformer, and a tuned input filter. The six-pulse rectifiers are fed from delta and polygon primary windings with different turns ratio and phase shifted by 5°. Under the proposed control scheme, one rectifier is kept at nominal output voltage, and the other one is phase controlled to control the load´s current. The proposed strategy greatly improves the rectifier´s performance, reducing its reactive power maximum demand by 62% compared to conventional rectifiers and, therefore, reduces the input filters power rating also by 62%. This is accomplished while keeping the input power factor above 0.95 throughout the whole operating range. Further, the converter´s reactive power consumption presents a low varying characteristic, allowing it to use a fixed filter, even when operating from a power system not capable of withstanding large reactive power variations. Finally, it presents a harmonic current distortion comparable to conventional 12-pulse high-current rectifiers. This paper presents the design and optimization procedure of the rectifying system. A 2.5 kVA laboratory prototype was used to validate the converter model, later employed in evaluating the converter operating in a 10.5 MVA copper electrowinning facility. The results obtained confirm the advantages of the proposed converter and its control strategy