The Critical Saturation Magnetization Properties of Nanocrystalline Alloy Under Rectangular Wave Excitation with Adjustable Duty Cycle

High-frequency transformers are subject to excitation with a changing duty cycle during operation. Due to magnetic relaxation, the duty cycle of the rectangular wave affects the magnetization time of nanocrystalline alloy for the core material, which affects whether the transformer can reach the saturation operating point. Based on the micromagnetic theory, a three-dimensional model of the nanocrystalline alloy is established, and rectangular wave excitation with different duty cycle <i>D</i> is applied to the micro-model. The influence of <i>D</i> on the magnetization process is analyzed in terms of the hysteresis loss <i>P</i>_v and magnetic moment deflection angular velocity <i>ω</i>. The results indicate that when <i>D</i> = 0.5, <i>P</i>_v is the smallest, and when <i>D</i> increases or decreases, <i>P</i>_v increases. Furthermore, <i>P</i>_v remains the same under the rectangular wave excitation that satisfies the sum of different duty cycles of 1. Regarding <i>ω</i>, the smallest value occurs at the rising edge of the excitation when <i>D</i> = 0.1, while the largest value occurs when <i>D</i> = 0.9. During the falling edge stage, <i>ω</i> is smallest when <i>D</i> = 0.9 and largest when <i>D</i> = 0.1. These results demonstrate that the duty cycle <i>D</i> influences the magnetization time of the material. Due to magnetic relaxation, changing the magnetization time determines whether the material can reach saturation magnetization. Therefore, there is a critical state, which is defined as the critical duty cycle <i>D</i>_c. The results show that for <i>D</i> < 0.5, the range of <i>D</i>_c1 is between 0.2 and 0.21, and for <i>D</i> > 0.5, the range of <i>D</i>_c2 is between 0.8 and 0.81. Increasing the amplitude of the excitation source causes a decrease in <i>D</i>_c, while increasing the frequency causes an increase in <i>D</i>_c.