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 p₁ poles to p₂ poles, or from series to parallel connection of the number of turns per phase-so-called (V/Nldrf) 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.