Brushless doubly fed machines

We describe a brushless doubly fed machine (BDFM) comprising a stator having first and second sets of poles with p1, p2 respective numbers of pole pairs, and a rotor having (p1 + p2) sets of electrically conducting loops. Each loop comprises a pair of conducting elements extending longitudinally along a direction of rotation of said rotor. Each said set of electrically conducting loops comprises at least first and second loops electrically connected in series with one another and at least one third loop configured to form a parallel load on said stator. An area encompassed by said third loop is less than an area encompassed by either of said first and second loops. Embodiments of this rotor design efficiently couple to two stator magnetic fields and suppress a space harmonic field