The Yokeless Dual Rotor Electrically Excited Synchronous Machine

This paper presents an innovative concept for the electrically excited synchronous machine (EESM), which combines the advantages of conventional EESMs with those of yokeless dual rotor machines. The proposed yokeless dual rotor electrically excited synchronous machine (YDR-EESM) achieves high torque density through a large effective air gap area and the absence of a stator yoke, but in contrast to the popular yokeless and segmented armature (YASA) machine it is expected to offer greater mechanical stiffness due to its rotor design and simplified manufacturing due to the radial flux path. In addition, the YDR-EESM avoids the use of permanent magnets (PMs), which enables greater efficiency in the field weakening range and allows a wide constant power speed range by controlling the excitation current. The YDR-EESM is analyzed using finite element analysis (FEA) and compared to a conventional EESM in terms of power and torque density. Finally, the mechanical structure and possible cooling concepts of the machine are discussed.