A coupled thermal-magnetic model for high frequency transformers. I. Model formulation and material properties

A novel model for analyzing high-frequency transformers is presented. The model is based on the simultaneous solution of the coupled, nonlinear thermal and electromagnetic equations. The modeling and assumptions used to derive the governing equations are explained. A set of integrodifferential constraints are developed to apply the proper input voltage and output impedance to the transformer windings. Next, a method of modeling the magnetic material properties as a function of temperature and magnetic flux density is given. A novel technique for modeling the complex reluctivity of the soft-ferrite core material permits a time-harmonic transformation of the electromagnetic equations. This eliminates the need to step through time while maintaining the effects of hysteresis losses. A quasi-steady formulation of the heat-conduction equation eliminates the time dependence of the thermal problem