Eddy current behaviour in saturating laminations with impressed flux waveforms

In the course of a study of iron loss in switched reluctance motors, the authors sought to explain the measured variation in the shapes of the B/H loops and in the loss in laminated steels, when excited with sinusoidal and triangular impressed flux waveforms over a wide range of magnitudes and frequencies. Measured B/H characteristics are first presented showing how the loops vary with both frequency and saturation. The surprising shapes of these loops are briefly explained qualitatively using the simple model, including eddy current behaviour interacting with saturation. A more detailed model is then developed, based on dividing laminations into a sufficient number of layers to allow for both skin effect and the variation of saturation across the lamination. Finally the new model is used to show the effects of eddy currents and saturation on the flux distribution within a lamination and hence on the overall B/H characteristic.