High-Frequency Loss Modeling of Amorphous and Nanocrystalline Cores With Different Air Gaps

In general, an air gap plays an important function in the magnetic core. It will enhance the stability of the inductance value of a reactor, increase the power density of the inductor, and optimize the properties of a high-frequency transformer. Hence, it is of great significance to study the influence of the air gap on the properties of magnetic cores. Based on a novel designed tester, the dynamic magnetic properties of the C-type amorphous (AMCC025) core and nanocrystalline (F3CC0125) core with different lengths of the air gaps are measured and analyzed when the cores are excited at different frequencies. In addition, the modified Steinmetz empirical formula which takes the fringing magnetic flux near the air gap into account is proposed. The calculated magnetic properties obtained from the modified formula show great agreement with the measured results. The average prediction error of the modified model is confined in 10%. Both the calculated and experimental results indicate that the influence of the fringing magnetic flux could be ignored when the length of the air gap is less than 5% length of the equivalent magnetic circuit. In particular, the frequency-dependent losses decrease to a minimum value and then increase with the increase in flux density accordingly. The modified loss model and results would be beneficial to the design of high-frequency inductors and transformer cores.