Novel 20 MW downhill conveyor system using three-level converters

This Paper presents a very new drive system used to transport ore from the mine down to the concentrator plant in the copper mine Los Pelambres. Eight 2,500 kW motors are driven by three-level inverters with GTOs. A three-level Active Front End (AFE) is used at the input side of each inverter. A GTO chopper is used to provide controlled electrical braking in case of line loss. The paper presents the requirements and alternatives for the drive system and the control strategies for the converters and the belt. A novel application of the selective harmonic elimination method is used to reduce the input current harmonics. Special attention is dedicated to the interaction with the electrical network. The most relevant features of the system are: i) fuseless operation; ii) adjustable power factor; iii) reduced input current harmonics; iv) smooth transition between motoring and regenerating modes and 15 MW of regenerated power with more than six months of successful operation.