Power Dense Inductors Based Upon Co-Based Nanocrystalline Alloys

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There exist needs for advanced inductors that are (1) power dense, (2) highly efficient, and (3) high temperature stable for a range of power electronics applications which include on-board converters and off-board charging systems for electric vehicles. Nanocrystalline soft magnetic alloys are of great interest for medium frequency and medium to high power applications due to their large saturation flux density relative to ferrites, as well as their improved losses and reduced magnetostriction relative to amorphous alloys. However, state-of-art commercial Fe-based nanocrystalline alloys display inherently large permeabilities and consequently they require gapping for high power inductor applications and suffer from inherent limitations of mechanical brittleness and relatively poor temperature stability (rated at 150C).Recent advances in Co-based nanocrystalline alloys have enabled a new class of highly scalable inductors which overcome the limitations of existing Fe-based nanocrystalline alloys through in-line tension anneal processing to enable a new level of control for large-scale inductor designs not previously possible without the requirement for core gapping. Local permeability control (i.e. permeability engineering) is made possible through real-time controls of applied tension and controlled thermal processing during the in-line processing step, of particular interest for reduced peak temperature rise and highly power dense inductor designs by engineering the distribution of magnetic flux throughout the core. Advanced thermal processing techniques can also be applied during the in-line processing stage to tailor the characteristic spatial length-scale and distribution of the spatially varied permeability profile, and after the in-line processing to tailor domain structure and optimize losses. Temperature stability of magnetic properties are also far superior to traditional Fe-based alloys, with current experiments showing the potential for stability of structure and magnetic properties as high as 400C and even approaching 500C.The presentation will address the latest advances in Co-based nanocrystalline strain annealed gapless inductors for power dense inductor applications. Topics to be addressed will include:1) Phase identity and magnetic property variation as a function of chemistry in Co-based nanocrystalline alloys;2) The latest in tension annealing at scale and spatially tuned permeability engineering methods;3) Demonstrations of engineered permeabilities as well as optimized domain structures for taliored magnetic properties;4) Development of tailored multi-objective optimization tools specifically for permeability engineered gapless core inductors;5) Application of advanced lmulti-objective optimization tools for inductor design and benchmarking in both electric vehicle and medium voltage power electronics applications;The presentation will conclude with recent experimental results as well as emerging ideas and future perspectives for highly optimized thermal processing methods and techniques, including spatial optimization of the crystallization process and consequently the magnetic properties through spatially tailored rapid thermal processing with electromagnetic field-assisted methods and techniques.