A Nonlinear Behavioral Ferrite-Core Inductance Model Able to Reproduce Thermal Transients in Switch-Mode Power Supplies

More compact Switch-Mode Power Supplies (SMPSs) satisfying typical design specifications can be obtained by exploiting ferrite core inductors working in partial saturation. In this case, the inductance is no longer a constant parameter, since it exhibits a sharp drop as the inductor current increases. A behavioral model was recently proposed, which provides the inductance at steady state as a function of easy-to-measure quantities. Here, a generalization of this model is presented, in order to capture the inductance behavior also during thermal transients. The model fitting to experimental measurements relies on an iterative optimization procedure grounding on accurate SMPS simulations based on shooting analysis. The model validation exploits the envelope analysis method, particularly suitable for slow-fast systems. The obtained fitting results show a good agreement with experimental data both in transient conditions (after sudden variation of the SMPS operating condition) and at steady state. Finally, by partially re-identifying the model based on data measured when the inductor is cooled with a fan, we still obtain a good matching between model and experimental data.