Unbalanced magnetic pull in permanent magnet machines

The paper studies the unbalanced magnetic force due to rotor eccentricity in permanent magnet machines. An analytical technique is presented for predicting the magnetic field distribution in a non-uniform airgap and the resulting unbalanced magnetic pull caused by eccentricities. The method is based on a simple modification of a 2D analytical technique for the prediction of airgap magnetic field distribution in surface-mounted permanent magnet machines with no eccentricity. Predictions from the analytical model are compared to 2D/3D finite element analysis. A test set-up is designed and built and measurement results are presented to validate both the analytical and finite element results.