Comparison of flux switching and surface mounted permanent magnet generators for high-speed applications

For embedded power generation within civil gas turbine engines, generators are anticipated to endure high rotor speeds coupled with large rotor diameters. With variable frequency permanent magnet generators finding increased roles because of the perceived higher torque density, the issue of rotor integrity becomes a critical issue. Although banding has been previously used in surface mounted PM (SPM) machines, they inevitably increase the airgap and hence reduce the torque capability of the machine. The flux-switching PM (FSPM) machine has been an intense topic of research for many years. By combining its armature and field sources in the stator, its rotor is a passive single piece, salient steel lamination, making it inherently suitable for high speed applications. This study compares both machines when optimised for high speed applications by designing the rotors of both machines for mechanical integrity and comparing the electromagnetic performance. The electromagnetic trade off in the mechanical optimisation of the FSPM machine is found to be negligible, in contrast to the ~33~ reduction of SPM flux linkage because of the increased airgap length. The performance of FSPM machine is validated on a scaled FSPM prototype.