Improving power quality in mining industries with a three-level active front end

This paper deals with the power quality improvements that can be achieved in mining industries by the employment of a high power active front end. A three-level neutral-point-clamped rectifier with low harmonic distortion and high power factor is chosen alternatively to diode rectifiers. A constraint on this class of converters is its lower switching frequency that results in low order harmonics. This is often solved employing passive filters. In this paper an appropriate choice of modulator and filter topology leads to significant simplifications on the filter design and reduces both weight and cost of its elements. The Selective Harmonic Elimination is presented and though it is generally considered as a steady-state technique it was designed to work in transient conditions within a closed loop current control. The system is submitted to tests in order to assess its operational performance through simulation results. Experimental data from a prototype is also presented.