Structural mass reduction by integrating active material in direct drive generator design

Permanent magnet synchronous generator technology is known for its low power to mass ratio. Its heavy structural design results from the need to ensure a small air-gap at a large diameter between stator and rotor parts. Numerous options for lowering structural mass are considered. In this paper, an overall mass reduction strategy which entails the integration of the magnetically active parts with the support structure are presented. Two three megawatt generator designs, one with a single bearing and the other with double bearing lay-up, are considered. These models comprise three-dimensional elements, isotropic and orthotropic materials, linear static extreme hub loads, and magnetic stresses. Shape and size optimisations are applied in calculation of structural mass saving incurred from structural integration and the altering of rotor and stator yoke thicknesses. The results show that total generator mass reduction is possible through the integration of the active material.