Influence of Manufacturing Tolerances and Eccentricities on the Electromotive Force in Permanent Magnet Synchronous Motors

Static and dynamic eccentricities and manufacturing tolerances are unavoidable errors in electric motors, so their diagnosis is an important issue. These deviations in dimensions and magnetizations may cause a magnetic unbalance, that is the same perturbation as eccentricity does. So, both need to be analyzed together. Therefore, in this paper their joint effect on the harmonics of the supplying phase voltage is studied, which can be really helpful in the diagnosis of these faults, and thus, a promising novel diagnosis technique can be defined. As a result of the analytical calculations, validated by finite element simulations and experimental results, the conclusion is that the deviations originated by the manufacturing tolerances produce changes in the amplitudes of already existing harmonics in the frequency spectra of the phase voltage and also create additional harmonics. Thus, it is proven that the effect of manufacturing tolerances is not negligible. In addition, some of those harmonics are also influenced by the eccentricities, and therefore, the influence of tolerances and eccentricities on the harmonics generated can be misidentified. This study proposes a new methodology to overcome this problem, based on the analytical development. The frequency harmonics of rotor tolerances are determined first considering their characteristic frequency components, and then the effect of eccentricity without the influence of tolerances is obtained normalizing the harmonics subjected to both, eccentricities and tolerances, by means of the ratio of amplitudes of two harmonics of the phase voltage. Thanks to this procedure, the effect of tolerances and eccentricities can be decoupled, and a more reliable fault identification procedure based on the electromotive force is established.