Shielding of Leakage Flux Induced Losses in High Power, Medium Frequency Transformers

Abstract

Metal Amorphous Nanocrystalline core materials have shown great promise as the magnetic material for the isolation transformer used in high power, high frequency power converters. However, many current designs require special winding configurations that result in high parasitic capacitance. Similarly, when these designs are used in active bridge circuits where a certain minimum series inductance is required, auxiliary inductors are required. These dramatically reduce the power density and can have impacts on the efficiency. Designs that integrate the series inductance through inherently geometric approaches have resulted in catastrophic increases in losses that are not predicted by typical core magnetizing loss models and have not been viable as a result. This paper demonstrates a method of using a mix of materials to manage and direct the leakage flux through paths that are more efficient. Similarly, this approach enables deliberate tuning and design of the series inductance. This introduces a method to independently design the series inductance with the magnetizing inductance of the transformer. This will prove to enable high efficiency transformer designs with very high power density, empowering wide bandgap semiconductor-based converters to reach their full potential.