Analysis of voltage tolerance of AC adjustable-speed drives forthree-phase balanced and unbalanced sags

摘要

Adjustable-speed drives are the type of equipment most sensitiveto voltage sags. This paper analyses the behavior of three-phase ACadjustable-speed drives during balanced and unbalanced sags. Emphasis isplaced on the DC bus voltage and on the drop in speed, both assumingthat the drive will not trip. By using a previously-introducedclassification of three-phase unbalanced sags, voltage tolerance curvesare obtained for AC adjustable-speed drives. The conclusion from theanalysis is that voltage sags due to three-phase faults are a seriousproblem for adjustable-speed drives. However, single-phase andphase-to-phase faults, causing the majority of voltage sags, can betolerated by adding a relatively small amount of DC buscapacitance