Partial Saturation in Permanent Magnet Inductors

Permanent magnets (PMs) can be used to increase the saturation current of DC flux-biased magnetics, e.g., DC inductors and flyback transformers, which significantly reduces the component size and weight. To achieve these reductions without PM demagnetization, certain magnetic geometries have been proposed in which the PM is placed outside of the winding flux path. These geometries can experience the problem of partial saturation. Partial saturation limits the improvement in saturation current and results in a derated differential inductance at currents above the saturation current. Partial saturation is then followed by complete saturation at higher currents. In this paper, the cause of partial saturation is analyzed. Hardware testing and 3D finite element analysis simulation results up to 150 A are shown for a permanent magnet inductor made from a C-shape nanocrystalline core with NdFeB N42 block magnets. Furthermore, a parameter sensitivity study to partial saturation is discussed. Finally, design guidelines are given to increase saturation current and minimize partial saturation for permanent magnet inductors.