Optimal Air Gap Length Design in Powder Core Inductors

The main requirements of magnetic components for power electronics applications are high power density and low power losses, driven by the need for more compact and more efficient power converters. Metal powder materials are a common choice for high-power and high-frequency inductors subject to a large magnetic field bias, since they feature high saturation flux density and low magnetic permeability (i.e., a "distributed" air gap), allowing for the adoption of un-gapped cores. Despite this, under high values of magnetomotive force (i.e., deep core magnetic saturation), the insertion of a concentrated air gap can lead to higher core inductance factor values with respect to an un-gapped configuration. In this context, this article proposes a straightforward procedure to maximize the inductance factor of metal powder magnetic cores by identifying the optimal air gap length for a specified design operating point. In particular, the procedure completely relies on information available in the core manufacturer's datasheet and does not require experimental characterization of the core itself, dramatically simplifying the inductor design procedure. The proposed methodology is theoretically described and then experimentally validated on an XFlux 60 core from Magnetics.