Finite Element Study of Core Materials of a Planar Transformer and Comparison of its Electromagnetic Properties with a High Frequency Transformer

Abstract

In this work, an analysis of various soft magnetic materials that can be used as transformer core has been done to find the most suitable core material for a high frequency-operating planar transformer (PT). Using finite element analysis on a 2 kW, 100 kHz transformer, six soft magnetic core materials studied in this work are: cobalt-iron alloy, cold-rolled grainoriented steel, carbon steel, koolmu powder, mu-metal and ferrite. The relative permeability of ferrite material was found to be of a moderate value of about 17000, which aids in decreasing the required magnetizing current and excess core losses due to eddy current generation. Also, the saturation magnetization value of ferrite was seen to be more than 0.2 T, which is high enough to prevent immature core saturation. Thus, it was concluded that ferrite material gave the best overall properties for the studied PT, thereby justifying its wide spread use in high frequency power electronics. Then, with this ferrite core material, electromagnetic properties like magnetic flux density of core and current density of windings of a PT and a conventional high frequency transformer (HFT) were analysed. From the magnetic flux density distribution of conventional HFT, it was seen that magnetic flux due to leakage increased the peak flux of the transformer to almost three times (about 0.9 T) that of the calculated peak flux density of 0.32 T. Whereas, the flux density distribution of the PT showed that most parts of the core operated at a flux value closer to the calculated 0.32 T, thereby making it a better design with lesser leakage flux losses. Also, when current density distributions were studied, it was observed that losses due to skin effects were lesser in PT by more than 60 % when compared to HFT.