R. Asensi

A full procedure to model high frequency transformer windings

A full procedure to model high frequency magnetic components has been developed. A finite element analysis (FEA) tool is used to compute the frequency behavior of the windings, taking into account geometry and frequency effects, like skin, proximity, interleaving, gap and end effects. The capacitive effects among the windings of the components are also taken into account. From these data, a model for the windings is developed by means of discrete components and differential equations that present the same frequency behavior as the actual component. Although the model has been developed for behavioral simulators, it can also be used in electrical simulators.<<ETX>>

A new frequency domain arc furnace model for iterative harmonic analysis

This paper presents a new frequency domain arc furnace model for iterative harmonic analysis by means of a Newton method. Powerful analytical expressions for harmonic currents and their derivatives are obtained under balanced conditions of the power system. The model offers a three-phase configuration where there is no path for homopolar currents. Moreover, it contemplates continuous and discontinuous evolution of the arc current. The solution obtained is validated by means of time domain simulations. Finally, the model was integrated in a harmonic power flow where studies have been performed in a network with more than 700 busbars and 7 actual arc furnace loads.

A new frequency domain approach for flicker evaluation of arc furnaces

In this paper, flicker magnitudes of rapidly varying loads are evaluated by means of a new frequency domain method. Analytical expressions of the instantaneous flicker sensation are obtained in terms of interharmonic voltages. The dynamic response of flicker magnitudes of such loads can be clearly described with this analysis, as well as the individual contribution of each interharmonic to the flicker sensation. The proposed method, applied to the voltages of DC and AC arc furnaces, provides very satisfactory results that have been validated with measurements performed with the standardized IEC flickermeter.

Model of the capacitive effects in magnetic components

A model for the capacitive effects in magnetic components for switch mode power supplies (SMPS) has been developed. It can be applied to multiwinding transformers. A finite element analysis (FEA) tool is used to compute the frequency behavior of the magnetic component, taking into account geometry and materials. The parameters of the model can be calculated before the magnetic component is built. An accurate capacitances modeling is expected to be crucial for common-mode EMI transmission modeling. The model takes into account winding floating voltages and the capacitance among each winding. Several model levels with different degrees of freedom are proposed. Some experimental results comparing the actual magnetic component results with the behavioural simulator results, are presented.<<ETX>>

Optimizing the winding strategy of the transformer in a flyback converter

This work presents a study of the influence of the winding strategy in the parameters of the flyback transformer. A frequency and geometry dependent model generated from FEM simulations has been employed in order to study the influence of the position of the windings on the leakage energy and AC resistance. A study of the interleaving technique in the flyback transformer has also been developed using the FEM solver. Conclusions of the advantages of the interleaving technique in the flyback transformer compared with its application in common transformers have been extracted. The influence of the leakage inductance in primary and secondary windings has been studied by means of SPICE simulations. The final goal of this paper is to obtain winding strategy design rules to minimize the leakage inductance and AC resistance in order to optimize power converter performance.

A contribution for modeling controlled and uncontrolled AC/DC converters in harmonic power flows

The main object of this paper is to present a sequential method of adjusting the operating point of power converters within the framework of harmonic power flows. To do this, a unified formulation of previous work in the frequency domain has been developed, resulting in a set of compact and powerful analytical expressions for AC and DC magnitudes. Special attention has been paid to uncontrolled rectifiers. The proposed sequential method offers a more flexible and modular framework where AC and/or DC magnitudes can be used for defining the operating point. Moreover, it provides better convergence properties for iterative harmonic analysis (IHA). Newtons method or Gausss method can be applied for IHA without special considerations. Finally, the solution obtained has been verified by means of time domain simulation and measurements.

Modeling High-Frequency Multiwinding Magnetic Components Using Finite-Element Analysis

This paper presents a magnetic component equivalent circuit as well as a methodology to extract its parameters by using a finite- element analysis tool. The model is valid for any kind of magnetic component-transformers and gapped and nongapped inductors-and takes into account frequency and geometry effects such as skin, proximity, interleaving, gap, and end effects. An additional model for capacitive effects may be coupled with the previous one to obtain a more precise result. The impedances in this model represent not only the self terms, but also all mutual terms shared between the windings. Because the simplification of concentrating impedances in one winding is not invoked, simultaneous conduction of all windings (such as forward-like converters) or in alternate conduction of the windings (such as flyback-like converters) can be accurately simulated. The parameters of these self and mutual impedances are frequency dependent, so the model represents the frequency behavior of windings in detail. This allows simulating components with nonsinusoidal currents like the ones present in switched-mode power supplies, provided there is no saturation of magnetic materials. This is not a serious limitation of the model because this kind of power supply works in linear (no-saturation) mode. When there is saturation, the core model determines the component behavior. Applying the model to several actual components has shown its usefulness and accuracy. Details concerning model parameters extraction are presented here with simulation and measurement results.

Obtaining a frequency-dependent and distributed-effects model of magnetic components from actual measurements

The behavior of the magnetic components in high frequency switched power supplies depends significantly on the working frequency because of distributed magnetic and electrical field effects. Measurement equipment such as an impedance analyzer usually offers simple equivalent models that allow characterization of the frequency behavior of some magnetic components. However, it is useful to have a procedure to generate more sophisticated models for all magnetic components, including coupled inductors and multiwinding transformers in order to characterize the frequency behavior more accurately. This paper presents a procedure to obtain the parameters of a model of magnetic components that has both frequency dependence and distributed effects. The values of the parameters of this model are obtained from actual measurements. The model is suitable for any waveforms applied to the magnetic component and can separate the working conditions of the different windings. The main drawbacks of this procedure are that it is necessary to have the magnetic component already built and to have available a measurement apparatus such as an impedance analyzer.

A method based on interharmonics for flicker propagation applied to arc furnaces

In this paper, propagation in the network of flicker produced by rapidly varying loads is analyzed by means of a new frequency domain method. By this method, the flicker level can be determined at any bus of the network when one or several loads operate simultaneously. Flicker summation effect is considered and the results obtained are compared with the summation laws proposed by IEC. The propagation algorithm has been applied to the 14-buses IEEE network and to the Spanish transmission system. The method has been validated with measurements performed with the standardized IEC flickermeter.

A unified theory of uncontrolled rectifiers, discharge lamps and arc furnaces. I. An analytical approach for normalized harmonic emission calculations

Under certain assumptions, similar models can be applied for rectifiers and devices with electric arc characteristic. The analysis considers single and three-phase uncontrolled rectifiers with continuous and discontinuous evolution of the AC current. It leads to four possible situations which fit with the harmonic behaviour of discharge lamps, arc furnaces and rectifiers with capacitive DC smoothing. A very useful set of compact and powerful analytical expressions for different magnitudes as well as for the harmonics currents are derived. It offers a direct method of selecting different operating points with their corresponding harmonic emissions. Normalized diagrams and tables of these magnitudes are depicted in a friendly way. Over these diagrams, harmonic emission limits of standard IEC 1000-3-2 and IEC 1000-3-4 are specified for Class C and Class D single-phase equipment and for three-phase equipment. Passive solutions applied to the aforementioned rectifiers to comply IEC 1000-3-2 and 1000-3-4 are obtained in a direct and normalized way.