Switched doubly-fed machine propulsion drive

Variable speed drives (VSD) constructed with doubly-fed machines (DFM) offer interesting flexibility for power electronic drive design. They also offer opportunities for controlling interactions with an ac grid. Design options are most flexible for the VSD DFM when the machine stator can be operated from an ac or dc source, selected “on-the-fly” as appropriate. This paper presents a SCR-based transfer switch that can connect the stator of the DFM either to an ac source or a dc source “on-the-fly”. Current commutations of the SCRs and a “bumpless” transition in shaft behavior is controlled from the rotor.