Customisable Magnetic Components Using Nanocrystalline Flake Ribbon
Power electronics plays a key role in addressing today’s energy challenges. The advancement of wide bandgap (WBG) semiconductors enables power electronic devices to operate at elevated switching frequencies, withstand higher temperatures, achieve greater power density, and deliver improved system efficiency. In accordance with the developing trend of power electronics, there is a growing demand for customising high-performance magnetic components with reduced losses, compact dimensions, lighter weight, and cost-effectiveness. Traditional methods for core customisation are cumbersome, time-consuming, and costly when producing small series of magnetic cores. Recently developed magnetic cores customised through additive manufacturing (AM) have not demonstrated desirable magnetic properties for high-power-density power electronics. In this thesis, a novel nanocrystalline flake ribbon (NFR) is proposed to customise high-performance magnetic components for power electronics in a cost-effective way without high-energy equipment. Conventional nanocrystalline alloys do offer much higher saturation flux density and lower core losses within certain frequency ranges compared to soft ferrites. However, their high-frequency performance is limited by elevated eddy current losses and uneven resin distribution within the laminations. To improve the magnetic properties of nanocrystalline materials and open new possibilities for customising magnetic components, NFR obtained from mechanically crushing the conventional nanocrystalline ribbon is introduced. The magnetic properties of NFR including the DC magnetisation curve, permeability, B-H curve and core losses are well examined. Core loss separation is performed based on Bertotti’s theory, and the classical eddy current loss and excess loss of NFR are compared to conventional nanocrystalline ribbons. To demonstrate the design of high-performance magnetic components using NFRs, this thesis first presents a sandwich-structured inductor manually made from NFR. This inductor achieves a rare combination of high current capacity and a low profile, which is challenging to achieve even with high-energy tools. The analytical models of inductance and conduction losses are developed and validated by finite element analysis (FEA) and experiments. A 5 V to 1 V, 50 A, voltage regulator (VR) is built to compare the performance of the fabricated NFR sandwich inductor to the latest commercial counterpart. Thermal performance is investigated, and stability tests under solder iron heat and reflow temperature are performed. Another demonstration involves introducing a tape-wound gapless transformer based on NFR and comparing it with two other transformers with similar specifications that use ferrite and nanocrystalline materials. The comparison is made by testing the built transformers in a 5.5 kW, 100 kHz dual active bridge (DAB) converter. Loss-separation is performed by measuring the core losses and conduction losses individually, and possible errors are analysed in detail for the loss measurement. Additionally, the transformer losses during the circuit test are measured using the high-precision power analyser, and the measurement errors are well discussed. Finally, the sum of the measured core losses and winding losses are compared with the measured transformer losses to verify the accuracy of the measurements.
Core Loss, Eddy Current Loss, Inductors, Magnetic Components, Magnetic Device Fabrication, Nanocrystalline Materials, Power Electronics, Transformers
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