238 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 44, NO. 1, JANUARY/FEBRUARY 2008 Multicell High-Current Rectiﬁer Eduardo P. Wiechmann, Senior Member, IEEE, Pablo Aqueveque, Student Member, IEEE, An´ ıbal S. Morales, Pablo F. Acu˜ na, and Rolando Burgos, Member, IEEE Abstract—A multicell rectiﬁer (MC) structure with N + 2 re- dundancy is presented. The topology is based on power cells im- plemented with the integrated gate commuted thyristors (IGCTs) to challenge the SCR standard industry solution for the past 35 years. This rectiﬁer is a reliable, compact, efﬁcient, nonpolluting alternative and cost-effective solution for electrolytic applications. Its structure, based on power cells, enables load shedding to en- sure power delivery even in the event of power cell failures. It injects quasi-sinusoidal input currents and provides unity power factor without the use of passive or active ﬁlters. A complete eval- uation based on IEEE standards 493-1997 and IEEE C57.18.10 for average downtime, failures rates, and efﬁciency is included. For comparison purposes, results are shown against conventional systems known for their high efﬁciency and reliability. Index Terms—Electroreﬁning, electrowinning, high-current rectiﬁers. I. INTRODUCTION T HE COPPER ELECTROWINNING (EW) and electrore- ﬁning (ER) metallurgical processes use high-current recti- ﬁers to produce electrolysis. These converters are implemented using thyristor (SCR) phase-controlled rectiﬁers that feature high efﬁciency and reliability, and as such, have become the preferred choice for the mining industry. These converters have continuously improved their performance thanks to the signiﬁ- cant advancements on thyristor technology, presenting a mini- mum conduction voltage drop of 1.3 V for EW and ER applica- tions rated 40 kA (and 300 V dc) [1]. Harmonic distortion, on the other hand, is usually addressed by paralleling 12-pulse con- verter structures. The four-star (FS) and double-bridge rectiﬁers with interphase reactors (DB) are the conﬁgurations of choice in the mining industry [2]. Both topologies present an intrinsic high reliability due to their parallel conﬁgurations and the use of thyristors. These rectiﬁers inject very low current distortion into the system throughout their operational range. Despite this low distortion injection, they consume high reactive power. For Paper PID-07-03, presented at the 2006 IEEE Industry Applications Society Annual Meeting, Tampa, FL, October 8–12, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Mining Industry Committee of the IEEE Industry Applications Society. Manuscript submitted for review October 31, 2006 and released for publication August 19, 2007. This work was supported by the Chilean Fund for Science and Technology Development (CONICYT) under Project 1060902. This work made use of the Engineering Research Center Shared Facilities supported by the National Science Foundation under NSF Award EEC-9731677 and the CPES Industry Partnership Program. E. P. Wiechmann, P. E. Aqueveque, A. Morales, and P. Acu˜ na are with the Department of Electrical Engineering, Faculty of Engineering, Uni- versity of Concepci´ on, Concepci´ on, Chile (e-mail: wiechmann@ieee.org; pablo.aqueveque@ieee.org; animorales@udec.cl; pabloacuna@udec.cl). R. Burgos is with the Center for Power Electronics Systems, Department of Electrical and Computer Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA (e-mail: rolando@vt.edu). Digital Object Identiﬁer 10.1109/TIA.2007.912728 example, a single EW rectiﬁer draws up to 4 MVAR at 32 kA. It is important to point out that an EW plant may use up to eight rectiﬁers; hence, the total reactive power consumption of a plant is a critical factor for the industrial distribution system. Moreover, EW and ER plants are usually located in remote areas being fed by relatively weak systems. The preferred so- lution for the elevated reactive power demand of SCR rectiﬁers is the use of sequentially connected tuned passive ﬁlters. These are essential for their operation since, otherwise, voltage reg- ulation and current increments would signiﬁcantly impair the power conversion efﬁciency. This solution, however, presents a number of drawbacks, namely the introduction of system res- onances, which degrade the overall system reliability, and the need for the large physical space required to install the ﬁlters (5000 ft 2 ). These factors negate this solution and open a window of opportunity for technological breakthroughs in high-current applications [3]–[6]. From the previous discussion, it may be concluded that a cost- effective solution should replace phase control, eliminating the need for reactive power compensation. The elimination of these ﬁlters would additionally simplify industrial maintenance and increase reliability, since the power system would no longer suffer from the large transients introduced by the sequential connection of the tuned-ﬁlter stages. System reliability could be further improved if N + K redundancy is somehow applied to the power converter structure. It should be borne in mind that for mining applications, any equipment failure related to the high-current rectiﬁer results in very high revenue losses, as the rectiﬁer controls the electrol- ysis itself and the production of copper. Moreover, the remote location of mining sites, in general, delays any service or major maintenance required, further aggravating the loss of produc- tion and revenues. It has been shown that these business factors, related to the rectifying system reliability, are, by far, more important than any initial investment cost on the rectiﬁers [14]. Generally, the evaluation of high-current rectiﬁers has been based on power factor and harmonic current distortion. How- ever, industrial experience shows that reliability and efﬁciency are more relevant issues. Following this trend, multicell high- current converters have emerged having the capability to be designed maximizing their reliability and availability. This type of converter architecture is compatible with N + K redundancy and eventually with hot swappability, that is the capability to replace cells for scheduled maintenance or replacement without stopping the electrolysis and the production of copper. Multicell rectiﬁers, therefore, improve availability and reduce possible downtimes with consequential economic beneﬁts. This paper proposes a multicell rectiﬁer for EW and ER applications with N + 2 redundancy based on independent but paralleled pulse width modulation (PWM) rectiﬁer cells. 0093-9994/$25.00 © 2008 IEEE