Permanent Magnet Hybrid Core Inductors for High Saturation Capability

Abstract

Inductor designs with large dc current relative to ac ripple are often constrained by saturation, which limits their size, loss, and current-carrying capability. Typical saturation-limited designs, though, further handicap their performance by substantially underutilizing their core material's flux carrying capabilities. Instead of operating the core across its full flux swing range from reverse saturation to forward saturation, these designs only use half the range. To use the full range, we propose a permanent magnet (PM) hybrid core in which a PM provides a dc flux offset in the core, boosting its effective saturation capability. In the proposed core, the PM is placed outside of the main winding flux path to reduce losses and risk for PM demagnetization. In this work, we derive first-order theory for analyzing and designing the PM hybrid core. We then provide some example PM hybrid core implementations. Finally, we demonstrate a working proof-of-concept prototype using off-the-shelf parts that outperforms two comparable ferrite inductor designs. This PM hybrid core prototype achieves half the dc resistance of a ferrite inductor with the same energy storage, and it achieves 70% more energy storage than a ferrite inductor with the same dc resistance. The prototype's improved performance thus demonstrates the potential advantages of the PM hybrid core.

Keywords

• Inductors
• magnetics
• permanent magnets
• saturation flux density