Adjustable speed drive and variable speed generation systems with reduced power converter requirements

This paper describes the physical configuration of the brushless doubly-fed machine (BDFM) and its potential as an alternative low cost adjustable speed drive. Particular interest in this type of machine is now being shown because of its flexibility as a variable speed generator. Applications which have been demonstrated in the laboratory and for which patents have been issued include a synchronous industrial motor drive that will revert to an induction motor in the event of converter failure, a controllable power factor correction device (synchronous condenser), a generator for wind turbines and low-head hydroelectric power, and a generator for automobiles. These two latter applications are covered in detail. The diversity of the potential applications and the unusual configuration of the BDFM has necessitated the development of several analytical approaches which are now being developed into design tools.