Circuit Analysis of an EMI Filter for the Prediction of its Magnetic Near-Field Emissions

In this paper, a circuit analysis of the electromagnetic interference filter used in a variable-speed drive is carried out in order to predict the resonance frequencies of its magnetic near-field radiations. The parasitic elements of the filter´s components are determined by measurements and a model of the filter integrating these parasitics elements is proposed. It is used to calculate the input impedance and the transfer functions of the filter in common and differential modes. In parallel, magnetic near-field measurements were performed and the frequencies corresponding to a maximal radiation are related to the resonance frequencies of the transfer function.