Complex Permeability Measurements in a Nanocrystalline Toroidal Core

In the design of power electronic converters, the choice of the suitable magnetic alloys and the measurement of the variations of their magnetic properties versus the temperature are fundamental issues. A theoretical model based on Neel theory and that takes into account wall displacement and coherent rotation was elaborated to derive the expression of the complex permeability versus the frequency. The static and the dynamic behavior are considered. The dependence of temperature is implicit in this model, i.e. the parameters involved in the expression of the complex permeability may depend on the temperature. An impedance analyzer has been used to measure the open circuit and short circuit complex impedances of a toroidal core versus the frequency at several temperatures ranging from 20°C to 180°C. The complex permeability of the material is then deduced. Finally, the theoretical model is used to identify the domain susceptibility and the anisotropy energy of the materials. The effect of temperature on these parameters is analyzed. The result obtained are valuable for the design of a power electronic converters from the magnetic and thermal viewpoints. The results prove the need for the combination of heat transfer and magnetic mechanisms at the design.