Experimental Investigation of DC-Bias Related Core Losses in a Boost Inductor

Soft magnetic components in electronic systems are often subjected to dc bias-flux conditions. These dc bias conditions result in distorted hysteresis loops, increased core losses, and have been shown to be independent of core material. The physical origin of these increased losses is not well understood and there is no simple model that can predict these losses without extensive measurements. Absence of a widely accepted model coupled with the complete lack of dc loss attributes on core manufacturers´ data sheets result in a requirement to empirically determine loss values for specific design applications. These deficiencies have motivated our efforts to investigate dc bias dependent loss phenomenon in a Fe-based Metglas core inductor operating in a dc-dc boost converter. Since dc flux levels in the core are proportional to the controllable converter load currents, this topology is ideal to study dc-related losses. Inductor core B - H hysteresis loop characterization was accomplished as a function of switching frequency, input voltage, and load current operating conditions and parameters. In this paper, the core loss results were presented as a function of the dc bias conditions, and the results showed that the core losses increased with the pre-magnetized (B_de) fields. As a result of our observations, we have proposed a modification to the conventional Steinmetz loss equation to include the effects of dc pre-magnetization flux in the core.