Carlos Cuellar

A High Frequency Equivalent Circuit and Parameter Extraction Procedure for Common Mode Choke in the EMI Filter

Power converters with high switching frequency generate conducted electromagnetic interference (EMI) noise. EMI filters are thus widely used to reduce these conducted noises for the compliance with electromagnetic compatibility standards. In this paper, a high-frequency (HF) equivalent circuit model for common mode (CM) chokes used in EMI filters is proposed together with its parameter extraction procedure. This procedure is based on impedance measurements and it incorporates an iterative rational function approximation fitting algorithm to extract the parameters in the model. The proposed model and procedure is applied to a planar CM choke which is used to realize an EMI filter. The simulated results of the filter show good agreement with the experimental ones. This extraction procedure is quite general and it can also be extended to identify the HF model of other passive components.

A Common-Mode Choke Using Toroid-EQ Mixed Structure

Electromagnetic interference (EMI) filters are main solutions to suppress the conducted emissions from static power converters. For some years, integration techniques for EMI filters have been widely investigated to realize more compact systems. In this letter, a common-mode (CM) choke with toroid-EQ mixed structure is presented. This structure is constituted of a toroidal CM choke embedded into an EQ core. The proposed toroid-EQ CM choke presents threefold advantages. First, it effectively increases the leakage inductance of the toroidal CM choke and hence increases the differential-mode inductance. Second, it reduces the parasitic coupling between the choke and the filter capacitors. Finally, the component can be easily fabricated with low cost. Experimental verifications have been carried out to validate the effectiveness of the proposed toroid-EQ CM choke.

Measurement method of the complex magnetic permeability of ferrites in high frequency

The passive magnetic ferrite components used in EMI filters have a complex magnetic permeability (CMP) which varies with frequency. The CMP in frequency range from 150 kHz to 30MHz is not given by manufactures. Moreover, measurement techniques require some specific size and shape of sample to measure CMP of ferrites. Common application of these passives components are EMI filters, where toroid ferrite cores need to be characterized to determine the insertion loss function. In this paper a CMP measure procedure is proposed. The leakage inductance and parasitic capacitance of an inductor are determined. Then, a rational function approximation (RTA) is applied to represent the HF equivalent impedance of CMP.

High-Frequency Behavioral Ring Core Inductor Model

The switching of the power semiconductors in static converters is the main source of electromagnetic interferences (EMI). To meet with electromagnetic compatibility standards, it is necessary to reduce the level of the conducted emissions. This reduction can be achieved by different techniques including the EMI filters whose design is mainly based on the use of ring core inductors. This element is a key point for designing efficient EMI filters, requiring then accurate inductor high-frequency (HF) models. Therefore, this paper deals with the development of an HF behavioral model of inductors, based on electrical equivalent circuit, for an implementation in circuit simulation software. The aim is to provide a robust and adjustable model under small-signal operating conditions for frequencies up to 100 MHz. The proposed model considers the frequency-dependent properties of the magnetic core material and also includes the parameterization of the electrical equivalent circuit elements with the number of winding turns and dimension of the magnetic core. Simulations results using the obtained inductor model are validated by impedance measurements with two types of magnetic materials: ferrite and nanocrystalline.

High frequency current probes for common-mode impedance measurements of power converters under operating conditions

Two current probes, based on the current injection method, are designed with appropriated high frequency magnetic material. These probes are used to measure the common-mode impedance of power converters in real-operating conditions. The characterization of this impedance is of importance for the EMI filter design. In this paper, a simple formulation of the probes transfer impedance using S-parameters is proposed. The proposed probe allows improving the accuracy of the impedance measurement in a wide frequency band up to 100 MHz. Different measurements of common-mode configurations are detailed and discussed.

Automatic identification of magnetic component equivalent circuits using impedance measurements

Impedance measurements are widely used to characterize the behavior of n-windings magnetic components. The identification process is realized manually and becomes more and more difficult as the number of equivalent circuit parameters increases. This paper deals with an automatic identification method based on Rational Function Approximation (RFA) which enables to obtain these parameter values very quickly and leads to reliable models. The effectiveness of such method is demonstrated with the characterization of a planar common mode inductor and a toroidal coupled inductor.

EMI filter design methodology taking into account the static converter impedance

The classic procedure design of EMI filters determines the insertion loss of the common mode and differential mode filters under standardized 50© at the input and output impedances. In order to choose the more adapted filter topology for a static converter, its necessary to consider the exact impedances connected to the input and output port in operating conditions. These impedances represent the LISN and the static converter which are measured with the current injection method. For simulation purpose, equivalent electrical circuit models are obtained and then applied in the filter design process.

Characterization and Modeling of Hysteresis for Magnetic Materials Used in EMI Filters of Power Converters

The magnetic material when designing EMI filter determines the inductance value and the parasitic elements that influence the insertion loss effectiveness of the filter. Moreover, the EMI filter characterization is usually realized at low power levels (low current and low voltage). When the EMI filter is subjected to higher currents through its coils, the principal characteristics of the filter (inductance variation with current and frequency) are modified. To account for these variations in the design step, it is useful to take into account the hysteresis model that represents the inductive and dissipative effects. Therefore, in this paper, an approach combining a magnetic hysteresis model together with a concept of material capacitance is proposed. The model is identified from a single turn of flat copper ribbon (STFC) experimental setup. Then, the experimental data are modeled with the proposed hysteretic and capacitive material behavior model (HCM) that is implemented in an equivalent circuit modeling approach, accounting for both the magnetic behavior law together with the “material capacitance.” The robustness of the proposed approach is evaluated by comparison and validation with the experiment results, showing good representation of the inductive and partially the dissipative effects.

High frequency model of ferrite and nanocrystalline ring core inductors

Ring core inductors are widely used as filter components for electromagnetic interferences mitigation. In order to design these filters with accuracy, a behavioral model of the inductors, based on an equivalent electrical circuit, is proposed in this paper. This model takes into account the frequency-dependent impedance of ferrite and nanocrystalline ring core inductors. The main contribution of this model is the inclusion of the capacitive effects (dielectric behavior) of the ferrite material, the skin effect in the nanocrystalline material and the parameterization of the electrical equivalent model as a function of number of winding turns. The proposed Behavioral Ring Core Inductor (BRCI) model is used in the simulations and the obtained results are validated by the measurements.

Determination of the insertion loss of EMI filters using a black-box model

Usually, the insertion loss (IL) of the EMI filter is characterized under 50Q/50Q input and output impedances even if these impedances are different in the real application. In this paper, two approaches are presented to calculate the insertion loss of the filter taking into account the arbitrary input and output impedances. First, a black-box 50Q/50Q model is obtained from S-parameters and then extended to determine the IL of the EMI filter with different impedances. And second, a direct measurement procedure interconnecting the real impedances obtained with the measurement equipment. Both approaches are compared to the real insertion loss calculated from conducted emissions with and without filter.