GRINDING mills are responsible for more than 60% of the

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1 866 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 41, NO. 3, MAY/JUNE 2005 Technical Evaluation and Practical Experience of High-Power Grinding Mill Drives in Mining Applications José R. Rodríguez, Senior Member, IEEE, Jorge Pontt, Senior Member, IEEE, Patricio Newman, Rodrigo Musalem, Hernán Miranda, Luis Moran, Fellow, IEEE, and Gerardo Alzamora Abstract Grinding mill drives play an important role in the mining industry. Almost 60% of the electrical energy consumed by modern concentrator plants goes to grinding mill drives. Different technologies are used in grinding systems presenting special characteristics from the electrical and process points of view. This paper presents a technical evaluation and practical experience of two different technologies used in high-power grinding mill drives. The analysis is focused on the static power converter and associated control scheme required to drive the motor. Cycloconverters and load-commutated inverters are analyzed in terms of power grid interaction, motor interaction, and the required control scheme. The evaluation is supported with practical results obtained in different concentrator plant facilities. Index Terms Cycloconverters, gearless motor drives, load-commutated inverter. I. INTRODUCTION GRINDING mills are responsible for more than 60% of the electric power consumed in modern copper concentrator plants. Economic reasons have pushed modern mills to become very large in size (more than 30-ft diameter), with rated power larger than 15 MW [1] [4]. A few years ago, big semiautogenous (SAG) mills were operated at constant speed, however, it has been proved that operation with variable speed presents significant advantages in terms of productivity and efficiency [5] [7]. Most of these mills are driven by adjustable-speed drive synchronous machines, connected to cycloconverters or loadcommutated inverters (LCIs) controlling the motor speed and torque [2], [8]. In addition, the new trend is to have the ball mills Paper PID-05-01, presented at the 2003 Industry Applications Society Annual Meeting, Salt Lake City, UT, October 12 16, 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 15, 2003 and released for publication March 15, This work was supported by the Chilean National Fund of Scientific and Technological Development (Fondecyt) under Grant and by the General Direction of Research (DGIP) of the Universidad Técnica Federico Santa Maríia. J. R. Rodriguez, J. Pontt, P. Newman, and H. Miranda are with the Departamento de Electrónica, Universidad Técnica Federico Santa Maria, 110-V Valparaíso, Chile ( jrp@elo.utfsm.cl; jpo@elo.utfsm.cl; pnewman@elo.utfsm.cl; hernan.miranda@elo.utfsm.cl). R. Musalem was with the Departamento de Electrónica, Universidad Técnica Federico Santa Maria, 110-V Valparaíso, Chile. He is now with Procter & Gamble Chile, Santiago, Chile ( rodrigo.musalem@gmail.com). L. Morán is with the Department of Electrical Engineering, University of Concepción, 160-C Concepción, Chile ( lmoran@die.udec.cl). G. Alzamora is with Los Pelambres Mining Company, Salamanca, Chile. Digital Object Identifier /TIA also operating with variable speed. This fact increases the impact of large power converters on the behavior of the distribution power system of the plant [4], [9], [10]. Aspects like machines and converters control strategies, reactive power, and harmonics injected into the network are important issues to be addressed in relation to modern concentrator plants operation. This paper presents the most critical aspects to be considered in the specification, selection, and also during the operation of these high-power drives. The following sections discuss the control and supervisory requirements, interaction with the power grid, and power quality issues associated with the operation of different grinding mill equipment. II. TECHNICAL REQUIREMENTS FOR HIGH-POWER GRINDING MILL DRIVES Modern grinding mill drives used in copper, gold, and cement industries employ synchronous motors as the main driving machine. The main requirements for converter-fed synchronous motors used to move the mills are as follows: 1) starting with at least 120% rated torque without affecting the voltage profile of the distribution network; 2) operation in harsh concentrator environment with wet grinding and high altitudes, commonly higher than 2000 m (6000 ft) above sea level; 3) low-frequency output, because large diameter grinding mills must rotate at variable low speeds, in the range from 0 to 10 r/min for SAG applications; 4) high reliability and availability to keep process continuity; 5) full output frequency and voltage control with four-quadrant operation capability; 6) high quality torque control, which is achieved with vector control, also known as field-oriented control. These features can basically be fulfilled in the megawatt range with two types of power converters: cycloconverters and loadcommutated inverters. Both schemes satisfy the requirements previously described because they offer higher reliability and better efficiency at very high power. III. RECENT PROJECTS Two technologies are used in high-power mills: girth gear with double pinion and gearless motor. Fig. 1 presents the typical configuration of a mill with a girth gear and a double pinion to increase the total torque. A reducer /$ IEEE

2 RODRIGUEZ et al.: HIGH-POWER GRINDING MILL DRIVES IN MINING APPLICATIONS 867 TABLE I MILL DRIVES SELECTED IN RECENT PROJECTS Fig. 1. Typical configuration of a mill with a girth gear and double pinion. Fig. 3. Power circuit topology of a 12-pulse LCI synchronous motor drive. Fig. 2. Gearless motor drive scheme. is used between pinion and electrical motor, which is fed by a power converter. Both drives must rotate coordinately, which is a critical issue in the operation of the mill. Another solution is the use of a gearless drive, where the poles of the synchronous machine are mounted directly in the external surface of the mill, as shown in Fig. 2. This solution generates a much higher torque and provides a very smooth operation. Table I shows some mill drives selected in recent projects. A clear trend has been observed toward the use of gearless drives. The last twin motor drive with girth gear was installed in In addition, it can be observed that all new projects use cycloconverters as the preferred topology for the converter. However, several facilities still use LCIs and, for this reason, they will be considered in this paper. IV. DRIVES WITH LCIS LCIs have demonstrated themselves to be a good solution for high-power synchronous motor drives. They have been used for years showing excellent reliability, robustness and higher efficiency. Basically, the LCI is a current-source type of converter and is composed of a line-commutated rectifier, at the front stage, a current-source dc link (implemented with a reactor), and an inverter. The main characteristic of the LCI is that the inverter is implemented with thyristors, which are commutated by the synchronous motor back electromotive force (EMF). The power circuit topology of a 12-pulse LCI with a six-pulse connection at the power inverter (machine side) is shown in Fig. 3. A12 pulse connection at the machine side is also employed. In order to commutate the thyristors at the inverter stage, an induced voltage at the synchronous motor terminals is required. Using thyristors, pulsewidth modulation is not feasible in this type of converter, so the inverter output current is composed of a

3 868 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 41, NO. 3, MAY/JUNE 2005 Fig. 4. Voltage waveform at the rectifier input side of an hp LCI SAG mill drive. (a) Line-to-line bus voltage waveform ( V peak). (b) Average rms value of the associated frequency spectrum versus order of the harmonic component. quasi-square wave. The motor design has an important effect on the inverter performance since thyristors commutation depends on the motor-induced voltage. For example, if the motor has a low stator reactance, the thyristor needs less time to turn off and a lower firing angle can be used. As in a current-sourceinverter drive, the motor speed is controlled by changing the inverter output current frequency, while motor flux and torque are adjusted by controlling the amplitude of the dc-link current. DC-link current control is achieved by phase shifting the firing angle in the rectifier. One of the important characteristics of the LCI topology is that it requires a special circuit to start the motor, since at zero speed there is no back EMF in the synchronous motor and, therefore, the inverter thyristors cannot be turned off. This is also the case for operating speed lower than 10% of the rated value. For this speed range, the method of pulsing dc link is used to commutate inverter thyristors [8]. This method consists of reducing the dc-link current to zero by temporarily operating the rectifier in the inversion mode at its stability limit. During this zero-current interval, the previously conducting thyristors regain their blocking capability and the motor current can be transferred from one inverter leg to the other. Another characteristic of this topology is that at low load, the converter input power factor is poor and in large-power applications additional reactive power compensation is required. In order to assure the appropriate induced voltage at the motor terminals, which is necessary to turn off the inverter thyristors, the synchronous motor must operate in the capacitive mode, which is with leading power factor. Fig. 5. Current waveform at the rectifier input side of an hp LCI SAG mill drive. (a) Rectifier input line current (800-A peak). (b) Average rms value of the associated frequency spectrum versus order of the harmonic. TABLE II AVERAGE AND MAXIMUM THDI OF LCI INPUT CURRENT FOR SAG RATED OPERATING CONDITIONS As far as the power distribution is concerned, the LCI behaves better than cycloconverters, since the input converter is a rectifier and no interharmonics or subharmonics are present in the line current. For large power application it is common practice to use 12 or larger pulse configuration reducing the low-frequency current harmonic components injected into the system. Real current and voltage waveforms obtained from an hp LCI SAG mill drive are shown in Figs. 4 and 5. The drive is a twin motor topology and is composed of two synchronous motors rated at 9000 hp each, and driven by an LCI rated at 8000 kva each. The two LCIs are connected through coupling transformers forming a 24-pulse converter. Dominant harmonics of the input currents are the 23rd and 25th respectively. It is important to note that the SAG mill operation increases the voltage THD from 0.57% to 2.96%, and current THD from 2.82% to 3.63%. The LCI input current THD is shown in Table II. LCI drives deliver currents with a quasi-square waveform to the motor. This current contains large amounts of low-order harmonics (5th, 7th, 11th, 13th, etc). These harmonics will cause additional losses and heating in the machine. This aspect is taken

4 RODRIGUEZ et al.: HIGH-POWER GRINDING MILL DRIVES IN MINING APPLICATIONS 869 Fig. 6. Gearless motor for a high-power mill. Fig. 8. Power circuit topology of a cycloconverter-fed mill drive with two three-phase windings. Fig. 7. Power circuit topology of a cycloconverter-fed mill drive with one three-phase stator winding in the motor. into account by the drive manufacturer at an early motor design stage [11]. V. DRIVES WITH CYCLOCONVERTERS A. Power Circuit Fig. 6 represents a picture of a gearless motor used in copper concentrators. The poles of rotor winding are directly mounted on the surface of the mill. As observed in Table I, all synchronous motors used in SAG mills have a rated power larger than 10 MW. Even ball mills have a power larger than 10 MW. This is why they have an important impact on energy consumption and in power distribution system operation. Fig. 7 presents the power circuit topology of a cycloconverter-fed synchronous motor used by one major manufacturer [8]. The current in each phase is controlled by a 12-pulse cycloconverter. The 12-pulse configuration is obtained by the wye delta connection in power transformer secondaries and reduces the lowfrequency current harmonics in the load and at the input side of the converter. Fig. 9. Vector diagram of the synchronous machine. The synchronous motor has one three-phase winding in the stator. Rotor field current is controlled by a six-pulse rectifier with thyristors. Fig. 8 shows the power circuit of a synchronous motor with two three-phase stator windings. Each winding is supplied by a six-pulse cycloconverter. The resulting topology has a 12-pulse effect from the source point of view. This solution is provided by another major manufacturer. B. Drive Control Fig. 9 shows the vector machine vector diagram used to develop the field-oriented control required to adjust speed and torque. In this diagram, the meaning of the variables is:, air-gap EMF;, quadrature-axis component of current (torque-producing component); m direct-axis component of current (flux-producing component);, magnetic flux;, magnetizing current;, load angle;, flux-axis angle; and, rotor-axis angle. C. Field-Oriented Control of the Machine The principle of field orientation is used to control the machines in mill applications, to obtain a high-quality controlled

5 870 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 41, NO. 3, MAY/JUNE 2005 Fig. 11. Currents generated by the cycloconverter with large dead time. Fig. 10. Simplified block diagram of the speed and torque control for the mill with cycloconverter [8]. torque [12]. Fig. 10 shows the general block diagram of the speed control system, which includes a proportional integral (PI) controller for speed and other PI controller for flux. The speed controller delivers the reference value for the torque producing current, while the flux controller delivers the reference value of the field controlling current. The stator currents and and the voltages and are measured and used in model M1 (voltage model) to calculate the magnitude and position of the flux. Flux position is used to transform from d-q to reference frame in block 2. Block 4 transforms the two-phase currents and into three-phase reference currents, which are delivered to the current controllers of the cycloconverter. Block 6 contains the so-called current model of the machine M2, which uses the current components in field coordinates to determine the flux position with respect to the rotor axis. Later, the field position with respect to the stator axis is obtained by adding to the rotor position. The current model is useful for low operating speeds where the machine terminal voltages are too noisy to use the voltage model. Low operating speed is needed for starting and low speed positioning of the mill with 120% rated torque capability. A second flux controller is used to generate the rotor current reference value, which is fed by the controlled rectifier of block 8. Fig. 11 shows the currents generated by the cycloconverter. A large dead time is observed in the zero crossing of the stator currents to ensure a proper commutation between the two antiparallel-connected converters. A large current dead time produces a ripple in torque, as can be observed in the behavior of the torque-controlling current. Fig. 12 shows that torque ripple can be improved by reducing the dead time in the zero crossing of the motor stator currents. Fig. 12. Currents generated by the cycloconverter with reduced dead time. VI. POWER QUALITY ISSUES Power quality is a major concern in the application of mill drives, mainly due to the following reasons: 1) a failure in this equipment originates a large loss of production with significant economic losses and 2) the high power of this equipment (megawatt range) has an important impact in power distribution system operation. Two aspects in the interaction between the distribution system and the converter loads are especially relevant: power factor and current harmonics generated by the converter. It is well known that static power converters are the most important harmonic generators in electrical power systems. The power circuit of the LCI drive shown in Fig. 3 includes a 12-pulse rectifier with thyristors at the input side, to reduce input current harmonics. A reactive power compensation must be provided at the primary side of the converter, to comply with the requirements of the customers, which is typically a power factor larger than Reactive power is generated by the action of the phase shifting angle of the thyristors gating signals.

6 RODRIGUEZ et al.: HIGH-POWER GRINDING MILL DRIVES IN MINING APPLICATIONS 871 Fig. 13. Filters for the LCI drive with 12-pulse rectifier. TABLE III HARMONIC COMPONENTS IN THE INPUT CURRENTS AT THE 13.8-kV SIDE OF A 12-PULSE CYCLOCONVERTER WITH f = 50 Hz, f = 6:53 Hz Fig. 14. Input currents and frequency spectrum in a 12-pulse cycloconverter feeding a 38-ft SAG mill. Fig. 15. High-pass filter used in a SAG mill application. In addition, a 12-pulse rectifier generates harmonics of orders. Fig. 13 shows a typical power filter used in high-power LCI drives, which includes tuned filters for harmonics 11 and 13 and a high-pass filter for higher harmonics. At the fundamental frequency (50 or 60 Hz) these filters have a capacitive behavior and provide the reactive power compensation. A 12-pulse cycloconverter generates the following harmonics in the input currents [13]: where is the frequency of the harmonic and and are the input and output frequencies, respectively. Other harmonics present in the input currents are where and. These equations show that the harmonics generated by the cycloconverter depend on the mill speed. Table III shows input (1) (2) currents harmonics generated by a hp 12-pulse cycloconverter in a real installation operating with an input frequency Hz and an output frequency Hz. Fig. 14 shows the converter input current waveforms measured in a 12-pulse cycloconverter feeding a synchronous motor of 20 MW in a 38-ft SAG mill. A large amount of harmonics can be observed in this current. In addition, cycloconverters generate an important amount of reactive power, which must be compensated. The compensation is achieved by using high-pass filters instead of capacitor banks, which provide a low-impedance trajectory to a high number of high-frequency harmonics and compensate the 50-Hz reactive power. Fig. 15 shows a passive filter installation used in a large copper mine. The grinding circuit includes a variablespeed SAG mill of 12 MW with two fixed-speed ball mills with synchronous motors of 5.5 MW each. In this application, reactive power compensation requirement is fulfilled with a highpass filter of 4 Mvar tuned at the ninth harmonic. It must be noted that a complete harmonic study of the plant is a very important stage in the planning and engineering phases of the project, previous to the installation. Recent solutions for grinding plants include more gearless drives with cycloconverters. In effect, different projects now use variable-speed drives for SAG and ball mills, as shown in the

7 872 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 41, NO. 3, MAY/JUNE 2005 Fig. 16. Fig. 17. Single-line diagram of the cycloconverter drives in a copper mine. Multibranch 20-Mvar harmonic filter module. simplified single-line diagram illustrated in Fig. 16, for the solution selected in a new copper mine project, where four cycloconverter-fed gearless drives were applied. A careful study of the reactive power compensation, voltage regulation, and harmonic control had to be carried out at the early design stage. A large number of electrical system operating conditions were taken into consideration due to production system complexity and possible electrical configurations. Special procedures and software tools are needed concerning project design milestones, meeting of tradeoffs, and agreements among the parties involved. General specifications included a minimum power factor of 95% (typical) at the point of common coupling (PCC) and compliance with IEEE Std for different operating conditions. Therefore, four units of harmonic filter modules were considered (see Fig. 17) with four connection steps, each module in order to meet the stringent specifications. A control system gives the ON/OFF command for the different modules for coarse and fine voltage control of the 23-kV buses. Branch filters tuned to the second, third, and fourth harmonic order with C-Type [4] were needed to mitigate the resonances at the medium-voltage 23-kV distribution level in order to achieve low fundamental losses in the filter resistors. Branch filters of the high-pass type tuned to the 5th, 7th, and 11th harmonic orders were considered to control the characteristic harmonics injected by the four cycloconverters, including the interharmonic components. VII. EVALUATION CRITERIA Considering the experience obtained during the mill drives operation, the following criteria should be considered in the technical evaluation of different alternatives: 1) load-related aspects: smooth acceleration with 120% rated torque; capability of position control to allow for inching and creeping operation of the mill; during starting process, load could be packed, which is known as frozen charge; this is a very dangerous operating situation that can destroy the mill; for this reason, it is important that the drive provides frozen charge protection, which is achieved with an appropriate monitoring of torque and angular displacement; 2) interaction with the electrical system: good power factor, usually higher than 0.95 (with filters); reduced input current harmonics, complying with standard IEEE and other local standards; harmonics study should be done in the early engineering phase; reduced flicker generation; robustness with respect to the power system voltage regulations; robustness against blackout, a serious issue to be considered in the design of the protection scheme, to avoid the circulation of excessive currents and the generation of large transient torques; 3) other internal aspects of the drive: capability of four-quadrant operation; operation at high altitudes, for example, at 4000 m; high efficiency; refrigeration of motor and converter considering the presence of a large amount of aggressive dust, considering that concentrators present a harsh environment to the operation of electrical equipment and also considering the large losses involved in the thyristors, forced water cooling should be seriously considered; splash-proof operation with wet grinding; high availability; ease of maintenance. VIII. CONCLUSION Synchronous motors are the preferred solution for high-power mills. In last few years, a clear tendency has been observed to use gearless motors instead of twin drives, due to the high power of the mills. In addition, customers prefer cycloconverters instead of LCIs as the solution to control the power delivered to the motor. The use of high-performance control techniques, like vector control, is now mandatory in this type of application to reach smooth torque and speed control. Power quality is a main issue in the application of mill drives. In effect, the use of passive filters to compensate reactive power and control current harmonics has become standard practice. As a final conclusion, it must be mentioned that the introduction of cycloconverter-fed synchronous motors in SAG mill drives improves the quality and global performance of the grinding process.

8 RODRIGUEZ et al.: HIGH-POWER GRINDING MILL DRIVES IN MINING APPLICATIONS 873 REFERENCES [1] H. Stemmler, High-power industrial drives, Proc. IEEE, vol. 82, no. 8, pp , Aug [2] H. Akagi, Large static converters for industry and utility applications, Proc. IEEE, vol. 89, no. 6, pp , Jun [3] R. A. Errath, HP gearless ball mill drive in cement-why not!, IEEE Trans. Ind. Appl., vol. 32, no. 3, pp , May/Jun [4] R. Errath, P. Burmeister, and A. Sapin, SAG mill operation with weak network conditions, in Proc. Int. Conf. SAG Grinding, Vancouver, BC, Canada, 2001, CD-ROM. [5] S. A. Greer, Selection criteria for SAG mill drive systems, IEEE Trans. Ind. Appl., vol. 26, no. 5, pp , Sep./Oct [6] A. K. Chattopadhyay and S. P. Das, Observer-based stator-fluxoriented vector control of cycloconverter-fed synchronous motor drive, IEEE Trans. Ind. Appl., vol. 33, no. 4, pp , Jul./Aug [7] D. Bird, R. Heig, R. Harper, and A. Berges, Necott s copperton concentrator fourth lines expansion, plan performance to date and ongoing continuous improvements projects, in Proc. Int. Conf. Autogenous and Semiautogenous Grinding Technology, Vancouver, BC, Canada, Oct. 1996, pp [8] J. Trautner and A. Wick, D. C. Link converter and cyclo-converter-fed A. C. motors: The concepts and properties of large variable-speed drives, Siemens Rev. (Energy and Automation Special Issue on Large Electric Motor A.C. Variable Speed Drives), vol. 1, pp , [9] J. Regitz, Evaluation of mill drive options, IEEE Trans. Ind. Appl., vol. 32, no. 3, pp , May/Jun [10] C. Meimaris, B. Lai, and L. Cox, Remedial design of the world s largest SAG mill gearless drive, in Proc. Int. Conf. SAG Grinding, Vancouver, BC, Canada, 2001, CD-ROM. [11] R. Emery and J. Eugene, Harmonic losses in LCI-fed synchronous motors, IEEE Trans. Ind. Appl., vol. 38, no. 4, pp , Jul./Aug [12] W. Leonard, Control of Electrical Drives. Berlin, Germany: Springer, [13] L. Gyugyi and B. Pelly, Static Power Frequency Changers. New York: Wiley, Jorge Pontt (M 00 SM 04) received the Engineer and Master degrees in electrical engineering from the Universidad Técnica Federico Santa María (UTFSM), Valparaíso, Chile, in Since 1977, he has been with UTFSM, where he is currently a Professor in the Electronics Engineering Department and Director of the Laboratory for Reliability and Power Quality. He is coauthor of the software Harmonix used in harmonic studies in electrical systems. He is the coauthor of patent applications concerning innovative instrumentation systems employed in high-power converters and large grinding mill drives. He has authored more than 90 international refereed journal and conference papers. He is a Consultant to the mining industry, in particular, in the design and application of power electronics, drives, instrumentation systems, and power quality issues, with management of more than 80 consulting and R&D projects. He has had scientific stays at the Technische Hochschule Darmstadt ( ), University of Wuppertal (1990), and University of Karlsruhe ( ), all in Germany. He is currently Director of the Centre for Semiautogenous Grinding and Electrical Drives at UTFSM. Patricio Newman was born in Concepción, Chile, in He received the Electronic Engineering and Master degree in power electronics from the Universidad Técnica Federico Santa María (UTFSM), Valparaíso, Chile in Since 2002, he has been with the Power Electronics Research Group, Departamento de Electrónica, UTFSM. His main interests in power electronics are AFE rectifiers and multipulse drives. Rodrigo Musalem was born in Viña del Mar, Chile, in He received the Engineer and M.Sc. degrees in electronic engineering from the Universidad Técnica Federico Santa María (UTFSM), Valparaíso, Chile, in He recently joined Procter & Gamble Chile, Santiago, Chile. His main research interests are in automatic control and power electronics. José R. Rodríguez (M 81 SM 94) received the Engineer degree from the Universidad Técnica Federico Santa María, Valparaíso, Chile, in 1977, and the Dr.-Ing. degree from the University of Erlangen, Erlangen, Germany, in 1985, both in electrical engineering. Since 1977, he has been with the Universidad Técnica Federico Santa Maria, where he is currently a Professor and Academic Vice-Rector. During his sabbatical leave in 1996, he was responsible for the mining division of Siemens Corporation in Chile. He has several years consulting experience in the mining industry, especially in the application of large drives such as cycloconverter-fed synchronous motors for SAG mills, high-power conveyors, controlled drives for shovels, and power quality issues. His research interests are mainly in the areas of power electronics and electrical drives. In recent years, his main research interests are in multilevel inverters and new converter topologies. He has authored or coauthored more than 130 refereed journal and conference papers and contributed to one chapter in the Power Electronics Handbook (New York: Academic, 2001). Hernán Miranda was born in Valparaíso, Chile, in He received the Electronic Engineering degree in 2004 from the Universidad Técnica Federico Santa María (UTFSM), Valparaíso, Chile, where he is currently working toward the Master degree in automatic control. Since 2002, he has been with the Power Electronics Research Group, Departamento de Electrónica, UTFSM, where he is a Scientific Assistant. His main interests are in advanced motion control and adjustable-speed drives.

9 874 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 41, NO. 3, MAY/JUNE 2005 Luis Morán (M 78 SM 94 F 05) was born in Concepción, Chile. He received the degree in electrical engineering from the Universidad de Concepción, Concepción, Chile, in 1982, and the Ph.D. degree from Concordia University, Montreal, QC, Canada, in Since 1990, he has been with the Electrical Engineering Department, University of Concepción, where he is currently a Professor. He has authored more than 30 papers on active power filters and static var compensators. He has extensive consulting experience in the mining industry, especially in the application of medium-voltage ac drives, large-power cycloconverter drives for SAG mills, and power quality issues. His main areas of interests are ac drives, power quality, active power filters, FACTS, and power protection systems. Prof. Morán was the principal author of the paper that received the Outstanding Paper Award for the best paper published in the IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS during 1995 and the coauthor of the paper that received the First Paper Award given by the Static Power Converter Committee at the 2002 Annual Meeting of the IEEE Industry Applications Society. From 1997 until 2001, he was an Associate Editor of the IEEE TRANSACTIONS ON POWER ELECTRONICS. In 1998, he received the City of Concepción Medal of Honor for achievement in applied research. Gerardo Alzamora received the Ingeniero Civil Electricista degree from the Universidad Técnica Federico Santa María, Valparaíso, Chile, in In 1985, he joined Antofagasta Minerals. Since 1992, he has been responsible for the electrical portion of the mining project Los Pelambres in Chile. Since 1995, he has been the Head of the Electrical Department, Compañía Minera Los Pelambres, Salamanca, Chile. He is also currently a Consultant to CODELCO, Chile.