An Electromagnetic Coupling Model of Faraday Shields in High-Frequency Transformers

Le résumé fourni par la source

In high-frequency transformers, Faraday shields divert the coupling of the common-mode (CM) noise to the ground and contribute to losses in both magnetic fields and electric fields. However, the electrical model is not found in existing research, which brings challenges to the shield design. To address it, an analytical model is proposed to calculate the electrical voltage distribution, CM current, and its generated loss in the Faraday shield. With the method to couple the electric and magnetic fields, the shield is modeled as aresistance-inductance-capacitance-voltage sourcebased circuit. The voltage distribution along the shield is derived to analyze the Electromagnetic Interference (EMI). Moreover, the criteria to determine the electrical losses and to keep the shielding function are given in the possible scenarios of transformer design we foresee, where a quantitative impedance ratio and the corresponding current-shunting ratio are introduced for the shielding-function assessment. The model is applicable to shields with single and multiple turns and layers, arbitrary winding-voltage distributions, and electrical shields of magnetics. With a practical shielding criterion of$\kappa = 10$, the proposed method provides a guideline for shield-thickness design under low-loss insulation conditions.

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