Torque characteristics enhancement of ring winding axial flux permanent magnet generator for direct-drive wind turbine

Ring winding axial flux permanent magnet (PM) machine (RWAFPM) has recently been introduced, which is beneficial in terms of manufacturability and fault tolerability. This study aims to examine the use of RWAFPM for a small-scale direct-drive wind generator. The structural features of the RWAFPM make it subjected to remarkable cogging torque. Accordingly, the main efforts of this study are focused on finding a proper solution for its torque profile challenges. In this regard, extensive investigations are carried out on rotor design improvements. First, several schemes are analysed, separately, including pole skewing, pole arc ratio modifying, pole grouping and rotor disks shifting. Then an optimum combination of selected schemes is calculated by the Taguchi method and considering the mean torque value as well as the PM usage. It is demonstrated that significantly improved results could be achieved mainly through cost-effective modified fabrication. The 3D finite element models are employed throughout the study along with some experimental measurements to verify the results.