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This paper presents a high-performance torque and flux control strategy for high-power induction motor drives. The control method uses the torque error to control the load angle, obtaining the appropriate flux vector trajectory from which the voltage vector is directly derived based on direct torque control principles. The voltage vector is then generated by an asymmetric cascaded multilevel inverter without need of modulation and filter. Due to the high output quality of the inverter, the torque response presents nearly no ripple. In addition, switching losses are greatly reduced since 80% of the power is delivered by the high-power cell of the asymmetric inverter, which commutates at fundamental frequency. Simulation and experimental results for 81-level inverter are presented. [ABSTRACT FROM AUTHOR]

Grinding mill drives play an important role in the mining industry. Almost 60% of the electrical energy consumed by modem 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. [ABSTRACT FROM AUTHOR]

High-power pulsewidth-modulated inverters for medium-voltage applications operate at switching frequencies below 1 kHz to keep the dynamic losses of the power devices at a permitted level. Also, the sampling rate of the digital signal processing system is then low, which introduces considerable signal delays. These have adverse effects on the dynamics of the current control system and introduce undesired cross coupling between the current components id and iq. To overcome this problem, complex state variables are used to derive more accurate models of the machine and the inverter. From these, a novel current controller structure employing single-complex zeros is synthesized. Experimental results demonstrate that high dynamic performance and zero cross coupling is achieved even at very low switching frequency. [ABSTRACT FROM AUTHOR]

Electric Wining haul trucks are one of the most challenging applications of power electronics in automotive systems. This paper presents some advances in very-high-power trucks used in copper mines. The special operational and environmental requirement for this application are highlighted It is established that the use of inverter-fed three-phase induction motors with vector control is the preferred Solution to reach the required high starting torque and good dynamic performance required by these vehicles. Packaging is a key issue and special attention is dedicated to the forced-air cooling system, because the air has a high dust level including conductive and corrosive materials. The truck's high-performance electric retarding system is described along with a novel use of trolley lines in a diesel boost mode as a way to increase the power and speed of the truck and reduce fuel consumption. Advanced features like remote monitoring, the use of global Positioning systems and Internet diagnostic and troubleshooting are also discussed. The paper clearly shows that modem electric haul trucks are highly sophisticated systems that make full use of advances in modem technologies to increase safety and Productivity levels. [ABSTRACT FROM AUTHOR]