Alberto Reatti

Comparison of various methods for calculating the AC resistance of inductors

The paper reviews several expressions for high-frequency winding resistance of inductors proposed by several authors and compares the theoretical predictions calculated from these expressions with experimental results. It identifies the expressions that yield the most accurate prediction of the winding high-frequency resistance. The comparison shows that the method proposed by Dowell (1966) accurately predicts the AC resistance if the winding contains less than three layers. The methods proposed by several other authors accurately predict the high-frequency resistance only in certain frequency ranges. In addition, these expressions yield inaccurate results for the inductor quality factor. One expression, however, accurately predicts both the high-frequency winding resistance and the quality factor of inductors over a wide frequency range from the DC to the first resonant frequency. The paper concludes with a simple and accurate circuit model describing the frequency behavior of inductors.

Low-cost high power-density electronic ballast for automotive HID lamp

A low-cost high-efficiency high power-density electronic ballast for 35 W automotive high intensity discharge (HID) is presented along with the results of theoretical computations and experimental tests. The ballast circuits is based on a 100 kHz resonant inverter, a half-wave rectifier and a 400 Hz operated square-wave inverter. The converter operates at zero turn on losses, nearly zero turn off losses, and at a reduced electromagnetic interference level. The ballast circuit is designed to prevent inappropriate operations due to the acoustic resonances. The lamp voltage waveform has limited dv/dt and no DC component contributing to a long operating life of the lamp. A breadboard of the electronic ballast was designed and experimentally tested on a 35 W lamp, for a DC input voltage ranging from 9 V to 16 V. The electronic ballast performs all the features required to turn-on, warm-up and drive at the steady state a 35 W HID lamp and operates at a maximum steady state efficiency /spl eta/=84%,.

Small-signal model of PWM converters for discontinuous conduction mode and its application for boost converter

A small-signal circuit model for pulsewidth-modulated DC-DC converters operated in discontinuous conduction mode is presented. The model is composed of controlled current sources, an independent voltage source and resistances. The principle of energy conservation approach is used to take into account parasitic resistances of the transistor and diode and the diode threshold voltage. The proposed model is suitable for small-signal, frequency-domain representation of the converters. This model is used to derive the expressions for a boost converter control-to-output transfer function, input-to-output voltage transfer function, input impedance and the output impedance. Bode plots are also given for these transfer functions. The predicted and experimental results were in excellent agreement.

Modelling iron-powder inductors at high frequencies

A high-frequency model of iron-powder core inductors is studied. The skin and proximity effects that cause the winding parasitic resistance to increase with the operating frequency are considered. The inductor self-resonance due to the parasitic capacitances is also taken into account. The frequency response of the inductor model is compared to that of an experimentally tested iron-powder core inductor. The first self-resonant frequency is determined from the plot of the measured reactance and allows for the calculation of the parasitic capacitance. Equations for the inductor parasitic resistance are derived in a closed form. Expressions giving the AC resistance as a function of the operating frequency are given. These expressions allow for an accurate prediction of the inductor power loss over a wide frequency range. The measured and calculated values of the inductor impedance magnitude end phase, the real and imaginary parts of the inductor impedance, the inductance, and the inductor quality factor are plotted versus frequency and compared. Theoretical results were in good agreement with those experimentally measured. Therefore, it is demonstrated that the discussed equivalent circuit has a frequency response matching that of the real inductor. Moreover, the circuit model is simple, it allows for an immediate understanding of iron-powder core inductor behavior and can be easily used in computer simulations of electronic circuits.<<ETX>>

MODELLING WINDING LOSSES IN HIGH-FREQUENCY POWER INDUCTORS

A high-frequency model of iron-powder-core inductors is studied. The skin and proximity effects that cause the winding parasitic resistance to increase with the operating frequency are considered. The inductor self-resonance due to the parasitic capacitances is taken into account as well. The frequency response of the inductor model is compared to that of an experimentally tested iron-powder-core inductor. Expressions giving the ac resistance as a function of the operating frequency are given. These expressions allow for an accurate prediction of the inductor power loss over a wide frequency range. The measured and calculated values of the inductor impedance magnitude and phase, the real and imaginary parts of the inductor impedance, the inductance, and the inductor quality factor are plotted versus frequency and compared. Theoretical results were in good agreement with those experimentally measured. A design procedure for solid wire winding inductors based on the results of the inductor modelling is also given in the paper.

SAPWIN-a symbolic simulator as a support in electrical engineering education

Gaining an insight into circuit properties in electrical engineering classes can be achieved by using computer based tools. A computer program which combines symbolic and numerical simulation capabilities is of great help, because such a program provides students with automatic analysis tools. This paper presents the program SAPWIN, which has been developed to perform an automatic symbolic and numerical analysis of linear circuits. The paper presents program features, their development lines and fundamental aspects. Also, the educational purposes which are contained in the use of the program itself are presented.

Neural network based model of a PV array for the optimum performance of PV system

This paper presents an application of Artificial Neural Network (ANN) for modeling a photovoltaic (PV) module. A feedforward neural network consisting of two hidden layers containing 6 and 12 neurons (first Linear and second logsig transfer function) has been used in the designed network, and a set of measured data, (acquired through a data acquisition system realized on purpose) and Levenberg-Marquard backpropagation optimization function has been used for the training. Efficiency of the realized Neural Network model is evaluated by comparing the predicted values with a set of experimental data different from those used in training the ANN. The results of this work are useful to estimate the site productivity and to proceed to a correct design and optimization of the entire PV system.

High-frequency models of ferrite core inductors

A model of ferrite core inductors is presented. The skin and proximity effects which increase the ac resistance of the inductor winding are considered. The core losses are studied. Power losses of the inductor are modeled by means of a frequency dependent series resistance. Parasitic capacitances which affect the inductor high-frequency operation are also considered. The model is applicable to cores with and without an air gap. Calculated and measured inductor parameters such as equivalent series inductance (ESL), reactance, equivalent series resistance (ESR), impedance magnitude and phase, and quality factor are plotted as functions of the operating frequency and compared. Calculated results were in good agreement with the measured ones up to the inductor self-resonant frequency. As a consequence, the discussed model is suitable to represent the frequency response of ferrite core inductors and can be effectively used for designing inductors.<<ETX>>

Class E full-wave low dv/dt rectifier

An analysis and experimental verification for a Class E full-wave current-driven low dv/dt rectifier are given. Basic parameters of the circuit are derived using the time-domain analysis and Fourier series techniques. The rectifier diodes turn on and off at low dv/dt, yielding low switching noise and low switching losses. Diode parasitic capacitances do not adversely affect the circuit operation. The absolute value of di/dt is limited at diode turn-off, significantly reducing the reverse recovery current. The rectifier input voltage waveform differs only slightly from an ideal sinusoid, resulting in a low total harmonic distortion. The circuit has theoretically zero-ripple voltage and, therefore, zero loss in the equivalent series resistance (ESR) of the filter capacitor. The Class E full-wave topology has lower diode conduction loss than the Class E half-wave rectifier. The efficiency is almost constant over the load range from 10% to 100% of the full load. The rectifier offers high-power density and high-frequency rectification and is suitable for low-voltage and high-current applications, as shown by experimental results given for a 75-W rectifier which was operated at 1 MHz with an output of 5 V and 15 A. The theoretical and experimental results were in good agreement. >

Open loop small-signal control-to-output transfer function of PWM buck converter for CCM: modeling and measurements

A practical procedure for measuring the control-to-output transfer function of a PWM buck converter operated in continuous current mode (CCM) is given. It is shown that a simple, low cost measurement setting can be used. The results of the presented procedure shows that the frequency behavior of a PWM buck converter depends on the filter capacitor equivalent series resistance (ESR). It is also shown that models of a PWM buck converter presented in previous works yields an accurate result only if the capacitor ESR variation with the operating frequency is taken into account. The result of this work can be used in designing an appropriate feedback loop of the converters.