Ironless Permanent-Magnet Generators for Offshore Wind Turbines

Because nonmagnetic material is used in the stator, ironless permanent-magnet generators (iPMGs) have negligible normal force between the rotor and the stator, and there is low requirement for the strength of the supporting structures. Therefore, the generator can be light. This feature is attractive in offshore direct-drive energy conversion systems where lightweight design is preferred. The objective of this paper is to investigate systematically different concepts of iPMGs. A design strategy is developed, and codes for finite-element analysis are embedded in this design strategy to ensure the calculation accuracy. A genetic algorithm (GA) is used to find the optimal designs. The influences of machine types and diameter to the machine performances are presented and discussed. Furthermore, the laboratory test of an existing ironless axial-flux permanent-magnet generator confirms the high accuracy of the field and inductance calculations of this design strategy, and the comparison with the parametric study is conducted to demonstrate the excellent performance of the GA used.