Light weight design of direct-drive generator for large-scale wind turbine

A direct-drive generator for large-scale wind turbine provides higher energy density in comparison with a gear train type generator. An AFPM (Axial Flux Permanent Magnet)-type machine has been the most attractive for the direct-drive generator due to its higher torque effect per unit volume and higher power density. The electronic machine system with a very large diameter, however, has to be used due to operation at low rotational speed of main shaft. Supported structures for the electronic machine system occupy at least 80% of total weight of the direct-drive generator. The light weight design, therefore, is at issue in the industries manufacturing the AFPM-type generator for large-scaled wind turbines. In this study, a topology model of the direct-drive generator for 2.5MW wind turbine using the AFPM-type machine was proposed, which has hollow shapes of the rotor with annular disc, the stator and the main shaft mounted on coupled slew bearings. Analytic results obtained from an electro-magnetic and structural interaction analysis showed that the structural weight of the proposed model compared to conventional generator can be reduced by 30% in a condition satisfying the requirements of the structural behaviors.