Extraction of Ferrite Material Properties and Application to Simulation-Based Common-Mode Filter Design

The insertion impedance of common-mode chokes (CMC) is defined by the core material's permeability, permittivity and geometrical shape. The datasheet information on material properties is often insufficient, as it is function to manufacturing process, wide tolerances and defined only in a certain frequency range. A core's geometry can be optimized for a specific application by simulation, but only if the material is well known. This work demonstrates how to extract complex permeability and permittivity data by measurement, employing an impedance analyzer with commercial magnetic material test fixture or with self-built fixture and analytic formulas in order to predict the common-mode impedance for a custom core shape. Further, we present a measurement setup employing an vector network analyzer to obtain modal (common-mode and differential-mode) impedances of chokes with different core shapes and derive an equivalent circuit for transient or frequency-domain simulation. The extracted material data is also used to create a 3D electromagnetic simulation model. The different modelling and simulation approaches are compared by application to a 300 A CMC for power electronics.