Effects of Manufacturing Imperfections in Concentrated Coil Axial Flux PM Machines: Evaluation and Tests

Due to the high torque capability, axial flux permanent magnet machines are an interesting solution for direct driven wind energy conversion systems and low speed motors. However, the structure of such machines makes them sensitive to geometrical imperfections due to manufacturing process. The present paper analyzes the effects which various types of geometrical imperfections produce in concentrated coil axial flux permanent magnet generators. In particular, a case study is presented where the mechanical stresses, the resulting axial force and the bending torques on the shaft as well as the circulation current in the winding parallel paths are calculated. The results obtained by means of an analytical approach are compared with those based on FEM simulations and are validated by some experimental results on a prototype.