Numerical Investigation on Frequency Dependence of Hysteresis Characteristics of Conducting Ferromagnetic Materials

Abstract

The hysteresis characteristics of ferromagnetic materials have significant effects on the performance and loss of electrical devices and components. Studies have shown that the hysteresis loop changes significantly with the increase of frequency, which becomes an important factor in electrical designing and operating. In order to provide a reasonable explanation and analysis method for the variation of dynamic hysteresis loops in the wide frequency range, experimental measurements and theoretical simulations are carried out. In this paper, the change of the hysteresis loop shape caused by the increase of frequency is attributed to eddy currents in the sample, so only the static hysteresis loop is the real reflection of the material characteristics, at which frequency the eddy current effect can be ignored. In order to verify this conjecture, the static hysteresis loops and the dynamic hysteresis loops in the range of 20 Hz ~ 1000 Hz were measured for the annular sample made of 20# steel and B35A300 non-oriented silicon steel sheet. Then, based on the static hysteresis loops of their own, the finite-difference time-domain method was used to solve Maxwell equations at different frequencies to obtain the magnetic field distribution in the sample. The average magnetic induction intensity was used to get the hysteresis loops. The calculated curves are found in good agreement with the measured ones, which indicates that the loop swelling-up is due to the inaccuracy of the measurement principle, and frequency has no effect on the hysteresis characteristics of 20# steel and B35A300 non-oriented silicon steel sheet at least in the frequency range below 1 kHz.