Variable-speed drives (VSDs) combined with doubly-fed machines (DFMs) offer interesting flexibility forpower electronic drive design. These also provide opportunities for controlling interactions with an ac grid. Design options are most versatile for the VSD DFM when the machine stator can be operated from an ac or a dc source, selected as appropriate. This paper presents a silicon-controlled rectifier (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 are both controlled from the rotor. Experimental results demonstrate wide-speed-range and four-quadrant operation of the drive achieved with a rotor converter rating that is one third of the DFM power rating.