考虑磁场频率特性的变压器共模EMI宽频建模方法

Wideband Modeling Method of Transformer Common-mode EMI Considering Frequency Characteristics of Magnetic Field

变压器是隔离型变换器的关键共模噪声路径,与传导和辐射电磁干扰(electromagnetic interference,EMI)性能紧密关联。现有变压器EMI等效电路建模方法对多层交错绕组的宽频共模特性缺乏准确预测能力,文中针对该问题分析了变压器共模噪声路径对电感参数的敏感性,以及现有电路结构不适用于交错绕组的原因,提出一种改进型建模方法。通过磁场仿真提取电感频率特性参数,使模型能够反映变压器的宽频磁场特性。同时,通过改进等效电路结构,正确表示共模噪声路径和绕组电势分布。以绕线式变压器为对象,S21参数为变压器共模EMI性能的评估方法,实际测量与电路仿真结果在150kHz~100MHz具有较好一致性,表明改进型建模方法能够在宽频段准确预测、评估变压器的共模性能和谐振尖峰,扩展了现有模型的适用范围。

Transformer is the significant path of common-mode noise in isolated converters,correlating with the conducted and radiated EMI performance.The existing transformer equivalent circuit modeling methods lack accurate prediction capabilities for the wideband common-mode characteristics of multi-layer interleaved windings.Aimed at this problem,this paper analyzed the sensitivity of common-mode noise path to inductances and the reason why existing circuits are not applicable for interleaved windings.An improved method was proposed.The model can exhibit the wideband magnetic fields of transformers through extracting inductances with magnetic field simulations.Meanwhile,the model can represent the common-mode paths and the potential distributions through improving equivalent circuits.Taking wire-wound transformers as the objects and S21 parameter as the evaluation of common-mode performance,the measured and simulated results have good consistency from 150kHz to 100MHz,revealing that the improved model can accurately predict and evaluate the performance and resonances of transformers,which expands the applicability of existing models.