Time-stepping finite-element analysis of brushless doubly fed machine taking iron loss and saturation into account

The stator of a brushless doubly fed machine (BDFM) is furnished with two sets of three-phase windings. These windings always have different pole numbers and are generally supplied at different frequencies. Investigation of the field distribution in a BDPM indicates that no polar symmetry can be associated to it. In addition, the motion of the field is not a simple rotation, as in a induction motor. Therefore, it is not expected that the representation of saturation by means of traditional saturation factors will yield useful results. In this paper, the authors describe a time-stepping finite-element model for the BDFM which can readily represent the effect of saturation. In addition, it is shown that iron losses can be calculated as the time-stepping solution proceeds. The model is verified using measurements made on a test machine. The use of saturation factors in conjunction with an analytical model is also investigated.