Permanent-Magnet Coupled Power Inductor for Multiphase DC-DC Power Converters

Using a coupled power inductor (CPI) in a multiphase dc-dc power converter instead of using multiple single-phase power inductors (PIs) reduces the inductor size and achieves better steady state and transient performances. To further reduce the inductor size and weight used in multiphase power converters, this paper presents a two-phase CPI that utilizes a permanent magnet (PM) to achieve almost doubled saturation current with the same size or equivalently achieve significant size and weight reduction. Operation principle of the presented permanent magnet coupled power inductor (PMCI) and required PM dimensions are derived and used as a design guide. The three-dimensional physical model of the PMCI is developed by using ANSYS/Maxwell software package to "visualize" the saturation current doubling. The fabricated PMCI design, with specifications of 24 A/phase, ~4.25 μH/phase equivalent steady-state inductance, and ~2.3 μH equivalent transient inductance, is tested in a 4-8 V two-phase dc-dc boost power converter with up to 50 A input current. Results show that compared to a conventional CPI design with the same size, weight, and inductance, the fabricated PMCI almost doubles the saturation current (from 13 to 24 A/phase). Compared to another CPI with a larger size but with even a smaller saturation current (18 A/phase), the core volume of the PMCI is reduced to 51.9% and the core weight is reduced to 51.2%. In addition, the PMCI achieves ~76.3% core size and ~73.4% core weight reductions compared to two separate single-phase PIs with the same steady-state inductance and similar saturation current (~22 A) due to the dual flux cancelation effect from the coupling and PM realized by the presented PMCI structure.