An Analytical Approach to Eccentricity in Axial Flux Permanent Magnet Synchronous Generators for Wind Turbines

Eccentric air-gaps occur very likely in wind generators as the turbines are subject to continued mechanical stresses. This article analyzes the effects of rotor eccentricity on axial flux permanent magnet machines' performances, such as air-gap flux density, cogging torque, and unbalanced force. In modeling axial flux machines, three-dimensional finite-element method models are required for accurate calculations. However, three-dimensional finite-element analysis is usually time consuming. In order to have a quick evaluation of the axial flux machine performance suitable for online identification, an analytical approach that utilizes quasi three-dimensional computation is developed. The proposed method allows taking into account variation of tooth skewing and different magnet shapes. The results have been validated using two-dimensional and three-dimensional finite element computations. It is shown that by using the proposed analytical approach, it is possible to assess the performance of the axial flux permanent magnet generators under eccentricity with reasonable accuracy.