Ugo Reggiani

Stray capacitances of single-layer solenoid air-core inductors

This paper presents a method for predicting parasitic capacitances of solenoid HF inductors made of one layer of turns with circular cross sections, uniformly wound around a cylindrical nonconductive core. The method is based on an analytical approach to obtain the turn-to-turn and turn-to-shield capacitances of coils. The influence of the wire insulation is taken into account. An equivalent lumped parallel capacitance is derived. The method was tested by experimental measurements. The calculated and measured values were in good agreement in the considered cases. The derived expressions are useful for designing HF inductors and can also be adopted for modeling and simulation purposes.

High-frequency small-signal model of ferrite core inductors

A circuit model of ferrite core inductors is presented. The behavior of the model parameters versus frequency is considered. The total power loss in inductors consisting of the winding resistance loss and the core loss, is modeled by a frequency-dependent equivalent series resistance. The total inductance given by the sum of the main inductance and the leakage inductance is obtained as a function of frequency. In order to study the core equivalent resistance and main inductance versus frequency, the magnetic field distribution in the core is derived from Maxwells equations for a long solenoid. The complex permeability and permittivity of the ferrite core are introduced in the electromagnetic field equations. Experimental results are also given.

Model of laminated iron-core inductors for high frequencies

We propose a model with frequency-dependent lumped parameters to represent the behavior of laminated iron-core inductors that are used in switching converters, i.e., for excitation frequencies above several kilohertz. The model applies to laminated iron cores with air gaps. We show that the core parameters can be calculated by using the same analytical expressions as those valid for gapless cores if a properly defined equivalent magnetic permeability is introduced instead of the iron sheet permeability. We compare the inductor model parameters calculated as functions of frequency with those obtained by measurements for two test inductors. The behavior of the inductors showed that the effects due to the eddy currents in the laminated iron core and the turn-to-turn and turn-to-core stray capacitances become significant in different frequency ranges.

Analysis of networks with ideal switches by state equations

A new computer-oriented method for a large-signal time-domain analysis of networks containing ideal switches is presented. The method is based on a state variable approach that exploits an efficient novel algorithm developed for the systematic formulation of state equations and output equations for linear active networks. Switched networks consisting of linear elements and both externally and internally controlled switches can be investigated. Diracs delta impulses are permitted in the analysis in order to find out the correct topology after switching. A new simple and convenient method for representing Diracs delta impulses is also introduced. An example is both discussed in detail and analyzed with a computer code.

Modelling the electrical properties of concrete for shielding effectiveness prediction

Concrete is a porous, heterogeneous material whose abundant use in numerous applications demands a detailed understanding of its electrical properties. Besides experimental measurements, material theoretical models can be useful to investigate its behaviour with respect to frequency, moisture content or other factors. These models can be used in electromagnetic compatibility (EMC) to predict the shielding effectiveness of a concrete structure against external electromagnetic waves. This paper presents the development of a dispersive material model for concrete out of experimental measurement data to take account of the frequency dependence of concretes electrical properties. The model is implemented into a numerical simulator and compared with the classical transmission-line approach in shielding effectiveness calculations of simple concrete walls of different moisture content. The comparative results show good agreement in all cases; a possible relation between shielding effectiveness and the electrical properties of concrete and the limits of the proposed model are discussed.

Common- and differential-mode HF current components in AC motors supplied by voltage source inverters

In this paper, an inverter-fed ac motor drive is analyzed in order to investigate the conducted electromagnetic interferences at both the input and output sides of the inverter. HF lumped equivalent circuits for the inverter and the motor stator windings are proposed. The overall circuit model allows time- and frequency-domain analysis to be performed with standard circuit simulators. The proposed model can also predict common- and differential-mode HF current components. The equivalent circuit is verified by experimental tests carried out on a prototype of ac motor drive.

Analysis of common- and differential-mode HF current components in PWM inverter-fed AC motors

In this paper, an inverter-fed AC motor drive is analyzed in order to predict the conducted interferences at both the input and output sides of the inverter. HF lumped equivalent circuits for the inverter and the motor stator winding are proposed. The equivalent circuit allows time and frequency domain analyses to be performed with standard circuit simulators. The overall circuit model is verified by experimental tests carried out on a prototype of the AC motor drive. The proposed circuit model allows the prediction of the main common and differential mode HF current components.

Equivalent circuit of mush wound AC windings for high frequency analysis

The paper describes a lumped parameter equivalent circuit for the HF analysis of mush wound coils of AC windings. The equivalent circuit takes account of turn-to-turn and turn-to-iron stray capacitances. Dissipative phenomena due to eddy currents in the coil wires and the laminated iron core are also considered. The parameter identification is based on sinusoidal impedance measurements on a test coil. The model of a multi-coil AC stator winding can be easily derived from the proposed equivalent circuit. This model allows one to predict both common- and differential-mode conducted EMI in switching converters supplying AC motors. The simulation results obtained by PSpice are in good agreement with the experimental data.

Stray capacitances of single-layer air-core inductors for high-frequency applications

A method for predicting stray capacitances of HF inductors dependent on their geometry is presented. The analysis is performed for inductors made of one layer of turns with circular and rectangular cross-sections. The wire is uniformly wound around a cylindrical nonferromagnetic core. The method is based on an analytical approach to obtain the turn-to-turn and turn-to-shield capacitances of coils. The influence of insulating coatings of the wire is also taken into account. An overall equivalent stray capacitance is derived according to the typical HF equivalent lumped parameter circuit of inductors. The method was tested with experimental measurements and the accuracy of the results was good in most cases. The derived expressions are useful for designing of HF inductors and can be also used for simulation purposes.

Modelling shielding properties of concrete

Concrete is a porous, heterogeneous material whose abundant use in numerous applications demands a detailed understanding of its properties. Besides experimental measurements, mathematical models can be useful to investigate its behaviour with respect to frequency, moisture content or other agents. These models can be used in EMC to predict the shielding effectiveness of a concrete structure against external electromagnetic waves. This paper presents a comparison between an analytical approach that relies on measurements, and numerical simulations that make use of dispersion models. The comparative results demonstrate that the analytical approach, which is more computationally efficient than numerical solvers, can be used to predict the shielding effectiveness of concrete structures