High frequency modeling for transformer Common Mode noise coupling path based on multiconductor transmission line theory

Transformer is an important common mode (CM) noise coupling path in isolated power converters. But the EMI behavior of transformer is difficult to predict because of the complicated high frequency parasitics. This paper proposes a transformer Common-mode (CM) noise coupling path modeling approach based on multiconductor transmission line (MTL) theory. The MTL model can include the complicated magnetic and electrical couplings among the windings, the distribution of parasitic parameters, and the high frequency losses caused by skin and proximity effects. Physical structure oriented model is established in Maxwell 2D to extract the high frequency parasitic parameters of the transformer based on finite element method (FEM). With the MTL model the CM noise caused by the converter can be well predicted in the whole conducted EMI frequency range from 150 kHz to 30 MHz, which is validated by measured results with EMI receiver.