Hybrid Core Inductors for High Saturation Capability

Abstract

Power electronics are critical for any system requiring electricity and often impact the performance of these systems. In many cases, the performance of power electronics is limited by lossy and large inductors that are constrained by the saturation of their magnetic core material. Such saturation-limited inductors are typically found in power electronics applications where the inductor sees large dc current with relatively small ac ripple, such as EMI filters or converters operating in continuous conduction mode. This thesis investigates two types of inductor designs that can achieve higher saturation capability by combining multiple materials in a single core, enabling these designs to achieve greater energy storage or lower loss than conventional single-material cores. The first design combines a permanent magnet with a soft magnetic material (e.g. ferrite) to form a PM hybrid core. This core achieves higher saturation capability by directing PM flux to oppose winding flux in the ferrite. First-order models, design processes, and other theory for the PM hybrid core are developed in this thesis, and different geometries for this core are explored. Additionally, two PM hybrid core prototypes are presented, one using a pot core geometry and one using a modified E core geometry. The PM hybrid pot core prototype achieves 70% more energy storage or 50% of the dc loss versus comparable ferrite prototypes, while the PM hybrid E core prototype achieves 30% more energy storage or a minimum of 52% of the total loss versus comparable ferrite prototypes. The second design pairs a low-frequency, high-saturation material (e.g. steel) with a low-saturation, highfrequency material (e.g. ferrite) to form a steel hybrid core. This core achieves higher saturation capability by directing most of the dc flux to the steel and all of the ac flux to the ferrite, enabling the core to leverage both materials’ advantages while avoiding their detriments. First-order models and design processes for the steel hybrid core are developed in this thesis. An example steel hybrid core design using a pot core is also presented. This design can achieve 220% more energy storage versus a comparable ferrite prototype, and it may achieve lower loss. Its performance, though, is sensitive to manufacturing and assembly imperfections. In this thesis, both the PM hybrid and steel hybrid cores are demonstrated to have great potential in achieving high saturation capability. By leveraging these hybrid cores, inductor designs can achieve greater energy storage density or lower loss and thus enable higher performance power electronics.