Research articles
Investigation of the magnetic flux density dispersion Bd on the gaps of the FeSiBNbCu magnetically soft nanocrystalline block core

https://doi.org/10.1016/j.jmmm.2020.166402Get rights and content

Highlights

  • Innovative technology utilizing the gaps with inserts of increased permeability.

  • Magnetic flux density dispersion phenomenon on the gaps in the multi-gap block core.

  • Multi-gap core with new inserts reduce the power losses and mass of the reactors.

Abstract

This paper focuses on the phenomenon of the magnetic flux density dispersion Bd on the gaps of the Fe73.5Cu1Nb3Si13.5B9 multi-gap nanocrystalline block core. Present state-of-the-art shows, that there is no comprehensive knowledge about the value of the magnetic flux density dispersion Bd on the gaps of nanocrystalline block core and the possibilities of its minimisation. The magnetic flux density dispersion Bd is the source of local eddy currents, which are the cause of increase of power loss and temperature in the chokes’ core. To discuss the effect of gap width and the method of its filling on the power losses in the core, the comparison between inserts of Teflon and magnetic mat composed of 70% Fe53.9Co29.1B13Nb1Si2Cu1 powder with a fraction of 20–36 µm and 30% Ultimeg epoxy resin 2004L was performed.

Introduction

Energy conversion is currently one of the most important and extensively explored issues on a global basis. At present, great emphasis is placed on research on advanced soft magnetic materials intended in particular for applications in power electronics [1]. A significant part of the electricity requires some form of transformation. The power electronic converters are used for that purpose, making it possible to change parameters of the electric currents or voltages supplied by the source so as to make them optimally suited for user loads such as electric machines, induction heaters, electricity networks, and others. (e.g. DC into AC or reversely, the change in the number of phases, frequency, voltage/current magnitude, etc.). It is worth paying attention that the majority of modern power plants based on renewable sources use power electronics [2]. These converters are used not only for processing and transmission of the main flux of energy but also for storing and improving quality of that energy. Almost always in such converters, besides active components, they incorporate also passive elements: capacitors and chokes. Chokes used in power electronics circuits, where there is a wide spectrum of voltage and current harmonics, are elements with large and difficult to limit power losses. Due to the fact, that the energy returned to the network flows through the chokes, the reduction of losses, their dimensions and mass, with demanded inductance and nominal parameters, are extremely important. Significant reduction of power losses in chokes is possible due to the use of modern, FINEMET type – soft magnetic nanocrystalline materials, which are characterized by a steep magnetization characteristic B = f(H) and low power losses in the core [3], [4], [5], [6]. The intensity of basic losses in the choke core depends on the amplitude and frequency of the harmonic currents and the maximum magnetic flux density in the core. Eddy current losses strongly depend on the thickness of the magnetic sheets and on the direction of magnetic flux density in the core. The implementation of chokes cores made of nanocrystalline FeSiBNbCu ribbons consolidated in the form of blocks, instead of the silicon steel core with 3 wt% Si, will result in a considerable reduction of power loss in the choke [7], [8]. In case of chokes with multi-gap cores for small, medium and high frequency application, the use of nanocrystalline cores will improve the technical and economic performance. In the chokes' cores the discontinuities in the form of columnar transverse air gap are applied. During choke working, the magnetic flux density dispersion Bd at the core gaps and the dispersion of magnetic fields generated by the choke winding occur and this is independent on the soft magnetic material used for core making [9], [10], [11], [12]. The intensity of the eddy currents is proportional to the value of the specific resistance and the thickness of the soft magnetic ribbon used for the choke making. If one compare the specific resistance of the nanocrystalline ribbon, which is 130 µΩ × cm with the specific resistance of Fe-Si steel with 3 wt% Si–47 µΩ × cm, it can be seen that the intensity of eddy currents in the nanocrystalline ribbon is over 2.7 times smaller than in the Fe-Si steel. Taking into account the typical thickness of the nanocrystalline ribbon (0.02 mm) and the thickness of the Fe-Si steel (0.1–0.3 mm), one can conclude that the power losses on the eddy currents in the nanocrystalline ribbon are much smaller than the power losses in the Fe-Si steel with 3 wt% Si. The use of nanocrystalline multi-gap core for choke making result in a very large reduction in eddy currents generated by dispersed magnetic fields originate from the choke winding. The intensity of these eddy currents is much smaller than the intensity of the eddy currents generated by the magnetic flux density dispersion Bd on the core gaps. Present state-of-the-art shows, that there is no comprehensive knowledge about the value of the magnetic flux density dispersion Bd on the gaps of nanocrystalline core and the possibilities of its minimization. The magnetic flux density dispersion Bd is the source of local eddy currents, which are the cause of increase of power loss in the chokes’ core. These losses can lead to hot spots inside the winding and the choke, having a negative impact on the electrical behavior and life-time.

In this paper, a developed method for measuring the magnetic flux density dispersion Bd in the Fe73.5Si13.5B9Nb3Cu1 nanocrystalline cores with four gaps is presented together with the study of the effect of gap width and the method of its filling on the power losses in the core.

Section snippets

Experimental

The consolidated nanocrystalline core with four gaps and its dimensions is shown in Fig. 1. The amorphous ribbon of Fe73.5Si13.5B9Nb3Cu1 of 35 mm width and a 20 μm thickness was used to wind the rectangular core, which was subjected to heat treatment at the temperature of 823 K/1h in Ar protective atmosphere. The second stage was a consolidation process carried out using impregnation plant for magnetic cores. After the consolidation process, by means of MAGNUTOM-500 (STRUERS) automatic high

Results and discussion

In Fig. 3 the hysteresis loop of the nanocrystalline core after the consolidation process in a state where its individual blocks were in direct contact (gap = 0 mm) is shown. The core with multi-gaps structure (see Fig. 1b) has a very low coercive field and relatively low power losses in the state of saturation magnetization for the magnetizing field of 50 Hz frequency.

The presence of a gap with suitable width in the core causes a linear dependence of the magnetic induction B = f(H). The

Conclusion

The results of this work confirmed that FeCuNbSiB-type nanocrystalline materials could be applied to the manufacturing of the block cores. These materials offer much greater possibilities for further reduction in power losses and enable lowering the dimensions and mass of the reactors, which is of great importance in many applications. Moreover, conducted investigations showed that, besides the material magnetic properties, the construction of the core is also very important. In this paper, the

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was co-financed by the National Centre for Research and Development under Smart Growth Operational Programme project number: POIR.04.01.02-00-0001/16 and TECHMATSTRATEG No. 1/347200/11/NCBR/2017.

Author statement

  • A.K.-B. devised the project, the main conceptual ideas, data analysis, proof outline, writing manuscript.

  • R.K. data analysis, writing manuscript.

  • P.Z. magnetic measurements.

  • M.H. participation in the development of technology and preparation of materials for research.

  • M.K. magnetic measurements.

  • M.Ł. the numerical calculations of inductive parts, worked on the manuscript.

  • P.Ł. the numerical calculations of inductive parts

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