Design and analysis of an air-cored axial flux permanent magnet generator for small wind power application

An axial flux permanent magnet (AFPM) machine with dual rotors and single air-cored stator is studied in this paper. The machine is applied for vertical-shaft small power off-grid wind generating system. A 2-dimensional (2D) finite element analysis (FEA) method is proposed to approximately solve to the 3-dimensional (3D) magnetic field inside the AFPM machine. And a 2D analytical method is also presented to compute the air gap flux density for this dual-rotor single-air-cored-stator axial-flux surface-mounted permanent magnet machine structure. Then, a 3D FEA model is developed to validate the accuracy of these two proposed 2D methods. Finally, a prototype machine is fabricated, and experiments are carried out to test its performances and electromagnetic features. Experimental results confirm that the 2D FEA and analytical approaches are both efficient and simple with sufficient accuracy.