Effects of active rectifiers on power quality in supply systems in mineral mining industry

Abstract

Mass use of variable-frequency induction-motor drives in the mineral mining industry results in deterioration of power in supply systems of mines: wattless power consumption grows and sinusoidal waveform of supply voltage is distorted by higher harmonics generated by semiconductor current converters. Until recently the main solution to the problem of power deterioration in mine supply systems using electric drives with semi-conductor converters was the use of LC-type filters. At present a promising way of improving the power quality in mines using variable-frequency induction-motor drives is inclusion of a frequency converter in the active rectifier. On the other hand, neglect of the power supply system properties, the active rectifier specifications, and their interference and interaction can result in emergency situations in mining practices. The analysis of the influence exerted by the power supply system and the active rectifier filter on the transient and steady-state processes enables recommendations on synthesizing the automatic control systems for the rectifier. With these recommendations fulfilled, it is possible to eliminate various-nature fluctuations and, consequently, power quality deterioration. For the active rectifier, the author puts forward some variants of setting its automatic control system with regard to the power supply system parameters and the active rectifier filter presence. The recommendations are given to select the setting variants for the current controllers of the active rectifier so that to eliminate current resonances in the power supply and to have the standard quality power.