Structural optimization of a permanent-magnet direct-drive generator considering eccentric electromagnetic force

Permanent-magnet direct-drive generators (PMDDGs) running at low speed need large electromagnetic force to generate the necessary torque. This type of electromagnetic force is one of the sources for rotor mechanical stress. In actual operation, mechanical stress will be worsened by the rotor imbalance. In this paper, a joint optimization of electromagnetic and stress field analysis is developed for a PMDDG. The mechanical stress and deformation caused by rotor weight, eccentricity, and terminal fault conditions are optimized in transient structural analyses. The proposed method and model are employed to study electromagnetic forces acting on the rotor core of a 7 MW wind turbine generator.