Closed-form analysis of adjustable-speed drive performance under input-voltage unbalance and sag conditions

  • Lee K
  • Jahns T
  • Berkopec W
 et al. 
  • 11


    Mendeley users who have this article in their library.
  • 50


    Citations of this article.


Voltage unbalance or sag conditions generated by the line excitation can cause the input rectifier stage of an adjustable-speed drive (ASD) to enter single-phase rectifier operation. This degradation of the input power quality can have a significant negative impact on the induction-machine performance characteristics. This paper provides an approximate closed-form analysis of the impact of line-voltage sags and unbalance on the induction-machine phase voltages, currents, and torque pulsations for a general-purpose ASD consisting of a three-phase diode bridge rectifier, a dc link, and a pulsewidth modulation (PWM) inverter delivering constant volts-per-hertz excitation. Attention is focused on the impact of the dominant second harmonic of the line frequency, which appears in the dc link voltage during the sag/unbalance conditions, neglecting the impact of the other higher order harmonics. In addition to the closed-form analytical results that assume constant rotor speed, both simulation and experimental results are presented, which confirm the key analytical results, including the dominance of the second harmonic in the resulting torque pulsations. The analytical results can be used as a valuable design tool to rapidly evaluate the approximate impact of unbalance/sag conditions on ASD machine performance.

Author-supplied keywords

  • Adjustable-speed drives (ASDs)
  • Input-voltage sag and unbalance
  • Power quality
  • Torque pulsation

Get free article suggestions today

Mendeley saves you time finding and organizing research

Sign up here
Already have an account ?Sign in

Find this document


  • Kevin Lee

  • Thomas M. Jahns

  • William E. Berkopec

  • Thomas A. Lipo

Cite this document

Choose a citation style from the tabs below

Save time finding and organizing research with Mendeley

Sign up for free