Analysis of Critical-Speed Increase of Induction Machines via Winding Reconfiguration With Solid-State Switches

Commonly used speed-control concepts permit speed ranges up to two–three times the base speed via voltage to frequency ($V$/$f$ ), that is, field-weakening control. This paper teaches the extension of the speed-control range up to nine times the base speed through online reconfiguration of the motor windings via electronic switches. The switchover of the windings, either from a winding with $p_{1}$ poles to $p_{2}$ poles, or from series to parallel connection of the number of turns per phase—so-called ($V$/ $N$·$f$) control—lasts less than a 60-Hz cycle. Such fast switchover causes small transients only, and therefore, this concept is applicable to most variable-speed drives.