The use of concentrated windings in electrical machines leads to significant rotor losses due to severe space harmonics in the airgap. Metallic retaining sleeves and sintered magnets used in high speed rotor construction have low electrical resistivities, leading to larger associated eddy currents loss. Composite materials like carbon fiber and plastic bonded magnets are investigated, due to their relative low conductivity. Analysing eddy current loss in composites can be cumbersome as they are frequently anisotropic. By observing eddy currents induced in a sample material, the material resistivity may be derived for a given direction by reverse finite element modelling. Resistivity values may be further used to calculate rotor eddy current loss.@en

Fractional pitch, concentrated winding machines are recently enjoying attention due to their suitability as basis for fault tolerant machine designs. The concentrated nature of the armature current distribution yields significant rotor eddy current loss production due to the harmonics present in the airgap, leading to significant rotor loss in high power and high speed machines. By using carbon fiber for the retaining sleeve and plastic bonded magnets for rotor magnetization, rotor eddy current loss may be reduced. Both materials require certain tradeoffs between electrical, mechanical and magnetic properties but their high electrical resistivity makes them attractive for use in high speed, fault tolerant, electrical machine design.@en

High speed electrical machines are replacing existing subsystems in aircraft. Electrical drives need to have high availability and good power density to be considered a viable replacement. To achieve high availability fault tolerance is added to the system design. Power density is increased by spatial integration of subparts. Fault tolerance extends to both machine and power electronics design. By use of low frequency modulation in a high speed, multiphase, fault tolerant drive, losses are reduced. High efficiency and power density result. The air cooled converter will be subjected to varying atmospheric conditions during flight. Low air pressure reduces cooling capacity at high altitude and requires increased air velocity to keep temperatures stable.@en