Eddy-Current Loss Minimization in Conducting Sleeves of Surface PM Machine Rotors With Fractional-Slot Concentrated Armature Windings by Optimal Axial Segmentation and Copper Cladding

When a nonmagnetic high-strength metallic retaining sleeve offers advantages over a nonmetallic (e.g., carbon fiber) one, it is possible to consider the application of a high-conductivity shield "coating" on this sleeve to reduce the surface eddy-current losses due to nonsynchronous fields. One can start by using a Maxwell's equation-based analytical model to "screen" for the optimal shield thickness and then employ a "2.5D" finite-element method that accounts for periodic fields and finite rotor length, including axial segmentation and/or copper cladding. These are quantified to help design a low-loss rotor sleeve for a surface permanent-magnet machine with fractional-slot concentrated armature winding. With this type of winding, the sleeve losses can be significant due to its rich (read parasitic) asynchronous harmonic armature reaction MMF content.