290 IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, VOL. 54, NO. 2, APRIL2012 Circuit Analysis of an EMI Filter for the Prediction of its Magnetic Near-Field Emissions C´ ecile Labarre, Member, IEEE, and Franc ¸ois Costa, Member, IEEE Abstract—In this paper, a circuit analysis of the electromag- netic 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 compo- nents are determined by measurements and a model of the filter integrating these parasitics elements is proposed. It is used to cal- culate 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. Index Terms—Electromagnetic interference (EMI) filter, mag- netic near-field emission. I. INTRODUCTION A LTOUGH near-field scanning is not referred to in stan- dards, except for ICs emissions, it constitutes conve- nient tool for characterizing complex radiating systems and for analysing root cause of electromagnetic interference (EMI) [1], [2], [3]. From near-field scannings, equivalent models can be de- duced for representing electromagnetic emissions [4]–[6]. From magnetic near-field scanning measurements over an industrial device, an adjustable-speed drive (ASD), there have been iden- tified three main radiating sources: the internal switching mode power supply (SMPS), the power inverter, and the EMI filter [7]. Since the EMI filter is situated at the ASD input, it collects all conducted perturbations of the system as presented in Fig. 1 [8]. The main part is dissipated inside the filter; however, a small amount is radiated in magnetic near field by the wounded com- ponent (common mode (CM) inductor) and by the connections linking the components of the filter. The consequences of this effect are damageable for sensitive functions of the system like sensors, other filters, or low-level electronics and they also con- tribute to far-field emissions. Therefore, analyzing this behavior is proposed in order to present some solutions to reduce it. A process to correlate the magnetic near-field spectrum and the electric working of each source separately has been de- veloped. It consists in establishing an equivalent circuit model Manuscript received April 15, 2010; revised January 16, 2011 and May 30, 2011; accepted June 1, 2011. Date of publication July 22, 2011; date of current version April 18, 2012. C. Labarre is with the URIA, Ecole des Mines of Douai, Douai 59500, France (e-mail: cecile.labarre@mines-douai.fr). F. Costa is with the Institut Universitaire de Formation des Maˆ ıtres de Cr´ eteil, University Paris Est Creteil, France, Cr´ eteil 94010, France (e-mail: francois.costa@satie.ens-cachan.fr). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TEMC.2011.2159563 Fig. 1. EMI filter positioning regarding SMPS and inverter sources. including parasitic elements and determining the resonance fre- quencies by impedance analysis. It has been implemented for both sources (SMPS and power inverter). As far as the filter is concerned, the process has to be adapted and this is the purpose of this paper: on one hand, the filter is at the same time a radi- ating source and a victim of two other sources, and on the other hand, contrarily to the other sources of magnetic near field of the ASD, the filter is designed to operate in common and dif- ferential modes (CM–DM), which contribute both to magnetic near-field emissions. In the second section, the studied EMI filter is described and the measurement setups are presented. In the third section, a two-port electrical model of the filter for each propagation mode is introduced. Actually, for economic reasons the filter is designed indistinctly for a three-phased or a single-phased ASD but there is a need to establish a single-phased model. Thanks to this model, the input impedance and the transfer functions of the filter are calculated. This section is also dedicated to the determination of the parasitic elements of each component of the filter necessary for the modeling of the complete filter in CM–DM. In the last section, magnetic near-field scannings are presented and the complete electrical model is used to relate the magnetic near-field radiation resonances to the resonance frequencies of the transfer function. II. EMI FILTER DESCRIPTION The EMI filter inserted in an ASD is a π-shaped EMI filter (see Fig. 1) and it is constituted of six DM capacitors C x and three CM capacitors C y . L CM is the nanocrystalline CM inductor. All components are routed on a four layers printed circuit board (PCB), one of the layer is a ground plane. To reduce the parasitic inductances of connections, the conductors are large, as it can be seen in Fig. 2. 0018-9375/$26.00 © 2011 IEEE