Computation of Core Losses in Electrical Machines Using Improved Models for Laminated Steel

Two new models for specific power losses in cold rolled motor lamination steel are described together with procedures for coefficient identification from standard multi-frequency Epstein or single sheet tests. The eddy current and hysteresis loss coefficients of the improved models are dependent of induction (flux density) and/or frequency and the errors are substantially lower than those of conventional models over a very wide range of sinusoidal excitation, from 20Hz to 2kHz and 0.05T up to 2T. The model that considers the coefficients to be variable, with the exception of the hysteresis loss power coefficient that has a constant value of 2, is superior in terms of applicability and physical interpretation. Also included are a comparative study of the material models on three samples of typical steel, mathematical formulations for the extension from the frequency to the time domain and examples of validation from electrical machines studies.