Mitigation of interharmonics due to large cycloconverter-fed mill drives

In the mining industry, the use of cycloconverters for driving mills with power demands of up to 20 MW has become more and more common in recent years. According to the specific, and in most cases very remote, site locations, the system is often rather weak at the plant. These conditions require substantial efforts to meet power factor requirements and especially to meet tight interharmonic limits. In this paper, experience with the connection of such cycloconverters are presented especially under consideration of interharmonics. Interharmonic currents and their dependence on speed, load and power system conditions is discussed. Possible solutions for filter banks are shown to reduce the interharmonic voltage distortion. In this context, the reactive power requirements of the drive as well as the effects of different distortion limits are discussed