Design of Coupled Inductor Using Powder Core with Concentrated Air Gap in Multiphase Operation

Powder cores demonstrate soft saturation characteristics which shows gradual decrease of inductance with increase of winding current. Concentrated air gap has been utilized to suppress soft saturation by increasing effective magnetic reluctance and modifying flux cancellation in coupled inductors. However, the saturation characteristics has not been well elaborated due to the difficulty to estimate the varied saturation levels experienced by different segments of the coupled inductor. The proposed design scheme simplifies the magnetic design and presents the least number of turns with optimized air gap length, which satisfies the target inductances. The design method features good accuracy over a wide range of winding current even with large air gap. Five prototype coupled inductors with different air gap length were built to verify the proposed design scheme. They were implemented to an interleaved boost converter to prove the precision of the proposed scheme. The experimental results also revealed that the coupled inductor with the least number of turns and an optimal air gap length presents an efficiency gain of 0.7% at 1 kW and 1.36% at 1.5 kW, respectively, compared to the case with the highest number of turns.