Characterization of power losses in soft magnetic materials

The power density of electric machines may be increased by designing for operation at higher rotation speeds and temperatures. Such operation increases the mechanical stresses, frequency, and temperature attained in the soft magnetic materials. Increased power losses in the magnetic material can be quantified empirically by controlled hysteresis experiments allowing improved simulation of machine operation. Standard hysteresis experiments operate at ac excitation, room temperature, and no applied mechanical stress. This is the extent of variables considered by some electromagnetic simulation programs. The involved research community is currently developing semi-empirical models that account for additional power losses due to rotation, pulse waveform modulation, compressive stress, and residual forming stresses and/or machining damage. Concurrently, models also account for reduced power losses due to tensile stress and increased temperature. This paper discusses a model for each environmental variable using the performance of Hiperco/sup /spl reg//50HS (a cobalt-iron-vanadium steel) as an example.