Analysis of the Local and Global Forces Acting on the Coil Structure of a Modular Slotless Permanent Magnet Generator

This paper investigates the local and global forces acting on the coil structure of a low-speed modular permanent magnet generator for wind energy application. Two different configurations of the coil structure are studied. The first one consists of separately replaceable single-coil modules, whereas the second consists of three-phase coil-module assemblies. The purpose of the analysis is to investigate the advantages and disadvantages of each configuration in terms of vibrations and mechanical robustness. The investigations also provide the load for the mechanical analysis needed in the design of the retaining structure of the generator. The results show that there are strong fluctuations in the radial forces acting on the single-coil structure. The three-phase coil-module assembly reduces the fluctuations of the radial forces, but it results in an increase of the cogging torque, which is not suitable for the slotless design. Namely, the advantage of the slotless design is to reduce the cogging torque. The computed forces are then used in a structural mechanical simulation, the results of which are validated through strain measurements. The validation procedure is carried out on a specially built mock-up as accessing the generator on site is not possible.