Typically, the core loss of transformers is considered constant, regardless of the load conditions on the secondary side. However, this assumption is no longer valid for high-frequency transformers (HFTs). This article reveals that different load conditions can lead to the core loss in the HFTs deviating from the no-load case due to the variation of voltage drop on the windings' impedance and, subsequently, the magnetic field in the core, which is not commonly assessed and considered in engineering practice. To accurately estimate the core loss, the main challenge in the case of HFTs, compared to the inductors, is that the unneglectable ac winding resistance deviates depending on the load conditions, which makes the voltage across the magnetizing branch (or flux density within the core) difficult to find. The core loss variation is quantitatively evaluated in this article against various load conditions through a case study of one representative HFT. Both experimental measurements and three-dimensional finite element analysis results confirmed this phenomenon, with the physical causes of this variation discussed and investigated.

中文翻译：

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不同负载条件下高频变压器磁芯损耗的变化

通常，无论次级侧的负载条件如何，变压器的磁芯损耗都被认为是恒定的。然而，这种假设对于高频变压器 (HFT) 不再有效。本文揭示，由于绕组阻抗上的压降以及随后磁芯中的磁场的变化，不同的负载条件可能导致 HFT 中的磁芯损耗偏离空载情况，而这种情况并不常见在工程实践中进行评估和考虑。为了准确估计磁芯损耗，与电感器相比，HFT 的主要挑战是不可忽视的交流绕组电阻会根据负载条件而发生偏差，这使得磁化支路两端的电压（或磁芯内的磁通密度） ） 很难找到。本文通过一个代表性 HFT 的案例研究，针对各种负载条件定量评估了磁芯损耗变化。实验测量和三维有限元分析结果都证实了这一现象，并讨论和研究了这种变化的物理原因。