Development and experimental validation of a novel analytical model for performance prediction of SR motors under saturation

An important assumption made in the performance analysis of SRM under saturation (bulk saturation) is that the MMF spent in the iron parts is dependent only on the average flux level and not on the rotor position. The predicted static torque versus position characteristics show good agreement with experimental characteristics up to moderate values of exciting currents. For larger currents they differ by a considerable amount from the experimental results. This leads to the conjecture that the pole-body and more predominantly the pole-tip saturation (local saturation) effects may be significant. However the average torque per stroke is quite accurately determined from the consideration of bulk saturation alone being present. To evaluate the extra torque due to local saturation an analytical model is proposed and the extra torque for each rotor position is determined in this paper using a semianalytical method. This is added to the torque obtained using the analytical model proposed for bulk saturation in a previous work. It is found that this new composite model, gives a static torque characteristic which is similar in nature to the experimental torque obtained but optimistic everywhere. The discrepancy can be attributed to the nonavailability of the exact B-H data of the material used for the stator/ rotor laminations of the tested machine and noninclusion of iron losses in this model.