Characterization of MnZn ferrite materials and finite element method for MnZn ferrite core loss calculations

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Virginia Tech

This work presents the method of calculating the core loss in ferrite cores by using a linear and sinusoidal finite element solver based on the material property data (the complex permeability, the dielectric constant, and the AC conductivity) measured in the laboratory. Due to the lack of published material data and fundamental test procedures, this work also demonstrates the measurement techniques of material data which are necessary for the finite element analysis (FEA) of the ferrite core loss.

First, a linear mathematical model of the ferrite core loss is formulated to characterize the hysteresis loss and the eddy current loss. The magnetic properties (the real and the imaginary components of the complex permeability) and the electric properties (the dielectric constant and the conductivity) are required.

Second, the experimental procedures of those four properties are first presented. Toroids with 1.1 OD/ID ratios are selected as samples to obtain the magnetic properties. It is illustrated that the hysteresis loss should be measured at the frequency of interest, instead of DC, due to its frequency-dependence. The electric property data of ferrites are collected by using a disk sample which forms a capacitor. The conductivity tested is frequency-dependent due to the combination of the dielectric loss and the DC conduction loss.

Finally, core loss simulations for the sample toroid, an EE core, and an RMIO core are performed and compared with the measurements. The flux and loss distributions are demonstrated in the last two cores. The hot spots are identified from the field plots.

measurement techniques