Optimized sequential control for electrowinning high-current phase-controlled rectifiers

This paper proposes an optimized sequential control technique for electrowinning 12-pulse high-current rectifiers. The converter comprises two series connected 6-pulse double-wye rectifiers, a step-down transformer and a tuned input filter. The 6-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. Therefore reduces the input filter´s power rating also by 62%. All this while maintaining an input power factor above 0.95. 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 rectifiers. This paper presents the design and optimization procedure of the rectifying system. Simulation results are used to evaluate the converter in a 10.5 MVA electrowinning facility, and in conjunction with results obtained with a 2.5 kVA experimental prototype are used to validate the proposed converter and control strategy