Axial Unbalanced Magnetic Force in a Permanent Magnet Motor Due to a Skewed Magnet and Rotor Eccentricities

We investigate the effect of a skewed permanent magnet (PM) with overhang on the axial unbalanced magnetic force (UMF) of a PM motor, especially in the presence of static and dynamic eccentricities of a rotor. We derive the mathematical equations of the axial UMF acting on PM motor due to the skewed PM with overhang and rotor eccentricities. We develop a 3-D finite-element model of the PM motor, not only to verify the frequency components of the proposed equations but also to determine the amplitude of the axial UMF. Further, we develop an experimental setup to measure the axial UMF caused by a skewed PM with overhang and rotor eccentricities. We confirm that the skewed PM with overhang generates an axial UMF with the harmonic of the least common multiple of pole and slot numbers. In addition, the static and dynamic eccentricities with the interaction of the skewed PM and overhang generate the axial UMF with the pole harmonics and slot harmonics, respectively.