The resistance R determines the width of the hysteresis loop. The larger the resistance, the wider
the hysteresis loop.
The coefficient phi_sat is roughly equal to the core flux at the deep saturation. It can be
calculated as the flux density B at the deep saturation multiplied by the core cross section area Ac.
The coefficients K1 and Kexp1 determine when the B-H curve starts to saturate (the first knee
point), and how sharp the transition of the curve is. A good guess of K1 is the ratio of the flux
density at this point versus the flux density at the deep saturation. For example, if the flux density
at this point is 0.245, and the flux density at the deep saturation is 0.35 T, the ratio will be 0.7.
The initial guess of K1 will then be 0.7.
The coefficient Kexp1 determines how sharp the transition of the curve is around this point. The
larger the value of Kexp1, the sharper the transition. A normal range of Kexp1 is from 10 for low
permeability ferrite to 200 for metglas.
The coefficients K2 and Kexp2 are associated with the second knee point in the saturation region,
and are used mainly to better fit the curve in the saturation region. A good guess of K2 is again
the ratio of the flux density at this point versus the flux density at the deep saturation. The
coefficients K2 and Kexp2 are used in rare occasions such as for ferroresonant regulators. They are
normally set as K2 > 2 and Kexp2 > 20 to keep them from affecting the B-H curve.
To illustrate the effect of the coefficients K2 and Kexp2, two B-H curves without and with the
effect of K2 and Kexp2 are shown below. The flux density on the Y-axis is normalized so that the
saturation flux density is 1.