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Ultrasonic wave propagation in epoxy materials is modeled to understand NDE procedures and also to provide reliable input to more complex models of guided wave propagation in layered structures. The models are extended to simulate wave propagation in materials with mechanical properties varying in the spatial dimension and it is achieved by using electric circuit transmission line analogs to the viscoelastic mechanical system.

The current distribution in a stripline is calculated by using a partial inductance formulation to produce a circuit model that is evaluated with the SPICE program. The program also simulates the signals produced in a recently invented magnetic current probe. Measurements using the current probe have been made over a wide range of frequencies and compared to the calculations. Agreement is achieved within the measurement accuracy. This technique can be used directly to find current distributions with pulse excitations. Index Terms--Circuit models, current distribution, magnetic probes.

The requirements for driving gallium nitride (GaN) heterostructure field-effect transistors (HFETs) and the design of a resonant drive circuit for GaN power HFET switches are discussed in this paper. The use of wideband III-nitride (such as GaN) devices today is limited to telecom and low-power applications. The current lack of high-frequency high-power drivers prevents their application in power converters. The proposed circuit is based upon resonant switching transition techniques, by means of an LC tag, to recover part of the power back into the voltage source in order to reduce the power loss. This circuit also uses level shifters to generate the zero and negative gate-source voltages required to turn the GaN HFET on and off, and it is highly tolerant to input-signal timing variances. The circuit reduces the overall power consumed in the driver and thus reduces the power loss. This is particularly important for high-frequency driver operation to take full advantage, in terms of efficiency, of the superior switching speed of GaN devices. In this paper, the topology of the low-power-loss high-speed drive circuit is introduced. Some simulation results and preliminary experimental measurements are discussed. Index Terms--Gallium nitride (GaN) heterostructure field-effect transistors (HFETs), high speed, resonant drive circuit.

A high-resistance (R) connection in an induction-motor electrical circuit results in localized overheating and supply-voltage unbalance, which leads to a decreased efficiency and reliability and an increased fire hazard in the electrical distribution system and motor. Therefore, it is important to monitor and correct high-R connections for a reliable, efficient, and safe operation of the industrial facility. This paper focuses on the development of an online technique for detecting poor connections based on monitoring the asymmetry in the voltage and current measurement. The development of the technique begins with the derivation of the dynamic model of an induction motor with high-R connections. Based on the analysis of the model, two approaches for detecting poor contacts using the negative-sequence current and zero-sequence voltage are proposed. In addition to detecting the existence of faults, the location and severity of the fault can also be determined using the proposed method. An experimental study on a 10-hp induction machine under simulated and realistic high-R conditions shows that the proposed techniques provide a simple low-cost solution for reliably detecting poor contact problems at an early stage. It is also shown that the severity and location of the high-R contact fault can be assessed with high accuracy. Index Terms--AC electric machines, condition monitoring, diagnostics, electrical distribution system, high-resistance (R) connection, induction machine, symmetrical components.

This technical note presents a modified test for positive-realness of scalar real-rational functions which avoids the need to test residue conditions. Necessary and sufficient conditions for the positive-realness of some classes of low-order real-rational functions are given by making use of the modified test. Index Terms--Electric circuits, mechanical networks, network synthesis, passivity.

This paper presents a model of the typical dielectric barrier plasma discharge at atmospheric pressure, structured as an equivalent electric circuit whose elements are identified with, and deducted from, the main influential variables of the process, namely, the applied gas, the geometry of the reactor, the breakdown parameters, as well as the power supply associated to the dielectric barrier discharge cell. Considering a parallel-plate reactor and a high-voltage sinusoidal power supply, an electrical comprehensive Simulink/MATLAB model has been developed in order to reveal the interaction between these two elements. The main components of this discharge model are as follows: 1) a double dielectric capacitance; 2) a voltage-controlled current source; and 3) a gas capacitance associated to the ionized gas. A sinusoidal voltage of up to 15 kV peak to peak at frequencies of 12.5 and 47 kHz has been applied to the discharge electrodes. The electrical model is based on the power law proposed by Roth, which defines the V-I behavior during the discharge startup. A series of simulations has been carried out in order to estimate the total current and voltage consumed during each discharge and to identify those parameters which are not measurable during the process. Finally, both the experimental and simulated voltage and current results in helium, argon, and nitrogen, as well as their Q-V graphics, are shown, and a comparison between them is discussed. Index Terms--Dielectric barrier discharge (DBD), voltage-controlled current source, voltage source inverter (VSI).

This paper investigates the influence of supply, circuit and magnetic material parameters on the occurring of fundamental-mode ferroresonance in a series inductance--capacitance--resistance (LCR) circuit with a nonlinear inductor. The analysis is developed using a modeling approach, validated by experiments, which accurately describes the magnetic behavior (dynamic hysteresis and eddy currents) of the saturable inductance. The conditions leading to subharmonic ferroresonance are also investigated. Index Terms--Ferroresonance, finite-element method, hysteresis, skin effect.

In this paper, a versatile method for modeling coupled magnetic field and circuit problems is presented. The field problem is solved by applying the finite element (FE) method. The nonlinear circuit equations are solved by applying the Newton--Raphson method. The finite element model and the circuit are solved separately, which in turn gives the possibility of considering different time constants for each domain. The idea is to extract values of the slowly varying lumped parameters describing the finite element model in the circuit equations at a rate related with the time constant of the finite element system, and to use them to iterate the circuit equations between two updates with a time step adapted to the significantly smaller time constant of the electric system. Contrary to the widely used numerically strong coupled methods, this paper introduces a different approach by applying an energy-based parameter identification. Index Terms--Electric circuit, electromagnetic coupling, energy methods, finite element (FE) methods.

The dielectric properties of Ni-coated BaTi[O.sub.3]- polymethyl methacrylate (PMMA) composite were examined. Results suggest the realization of K values of about 100 with temperature-stable X7E characteristics.

By using some properties of driving-point functions and adopting an iterative circuit synthesis approach, the location, extent, and type of change introduced in a model winding could be identified, based on terminal measurements. In this study, a model winding was used. From knowledge of its measured short-circuit and open-circuit natural frequencies, and pertinent winding data, an equivalent circuit was synthesized (called reference circuit). Next, changes were introduced at different locations in the model winding and its natural frequencies were measured. Corresponding to every new set of measured natural frequencies, a new circuit was synthesized (with topology remaining unchanged). A comparison of these circuits with the reference circuit revealed that a mapping could be established between changes introduced in the model winding and those predicted by the synthesized circuits. Many case studies are presented by considering continuous-disc and interleaved winding representations. Reasonably good results were obtained. Thus, localization of changes, based on terminal measurements, is shown to be a possibility. So, it is believed that these findings could be of some assistance in addressing the ultimate task of locating mechanical deformations in actual transformer windings. Index Terms--Circuit synthesis, driving-point functions, open-circuit and short-circuit natural frequencies, winding deformation and localization.

Various limitation experiments with coated conductors in function of the temperature based on a processing route with a stainless steel shunt and a gold shunt are explained. The temperature sensors used are found to show great time response and sensitivity.

A normal dc resonant charger was transformed into a command-mode charger by connecting a spark gap at its output terminal, prior to the load circuit. This charging spark gap was triggered by a transformer connected in series, pulsed by a fast spark gap circuit. Noise suppression schemes were implemented throughout the command charger, in particular around the charging spark gap to order prevent misfiring. The ringing noise and spikes from the capacitor discharge and those of the stray capacitance of coaxial cable were strongly suppressed by a simple LCR circuit so that these would not induce self-breakdown in the charging spark gap. This triggered spark gap command charger was tested to 2 kHz and < 10 kV with a resistive load. A transversely excited atmospheric C[O.sub.2] laser was operated up to 300 Hz and (10-15) kV that was limited only by the flow rate of the laser gas mixture. Index Terms--Command charging, noise suppression, spark gap, transversely excited atmospheric (TEA) C[O.sub.2] laser, transverse air flow.

Blind source separation (BSS) aims at recovering statistically independent source signals from their linear mixtures without knowing the mixing coefficients. Besides independent component analysis, nonlinear principal component analysis (NPCA) is shown to be another useful tool for solving this problem, but it requires that the measured data be prewhitened. By taking into account the autocorrelation matrix of the measured data, we present in this paper a modified NPCA criterion, and develop a least-mean-square (LMS) algorithm and a recursive least-squares algorithm. They can perform the online BSS using directly the unwhitened observations. Since a natural gradient learning is applied and the prewhitening process is removed, the proposed algorithms work more efficiently than the existing NPCA algorithms, as verified by computer simulations on man-made sources as well as practical speech signals. Index Terms--Blind source separation (BSS), independent component analysis, natural gradient, nonlinear principal component analysis (NPCA), recursive least-squares, whitening.

A new converter topology for a three-phase multi-pulse rectifier circuit is described. This converter draws almost sinusoidal currents from the ac system with very low harmonic content and typically less than 3% total harmonic distortion. The topology uses only passive components and has a lower component count than other rectifier circuits with similar performance. Two six-pulse rectifier bridges are connected in series, fed by a series connection of transformers, to form a 12-pulse system. An additional low power harmonic injection circuit enhances the performance of the circuit to obtain low harmonic current pollution levels that are comparable with those achieved from a 24-pulse rectifier. The circuit operation is explained and experimental results are presented. Index Terms--Autotransformers, rectifier bridges, sinusoidal currents, three-phase multipulse rectifier circuit.

This paper presents a novel method of power-factor correction (PFC) using a high-frequency resonant energy tank for the dc-link inverter. The proposed approach has advantages over conventional PFC techniques in terms of a lower current stress and lower switching losses. The developed PFC circuit is implemented on a series-load resonant inverter for illustrative purposes. The experimental results validate the theoretical analyses. The PFC circuit can achieve a power factor of almost one with a very low harmonic distortion. Index Terms--Energy tank, inverter, power-factor correction (PFC), resonant.

The asymmetrical half-bridge (AHB) topology discussed in this paper is one of the complementary driven pulse-width modulated converter topologies, which presents an inherent zero-voltage switching (ZVS) capability. In the previous work, the ideal operation of the converter and the ZVS realization process have been analyzed. However, the influence of the circuit parasitics on the output voltage drop and the design constraints of the circuit parameters to ensure the ZVS operation have not been investigated. The minimum load needed to ensure the ZVS operation is also not readily available. This paper presents a detailed and practical design for a 1-MHz AHB converter. A revised voltage transfer ratio of the converter is derived considering the influence of circuit parasitics and the ZVS transition. Two circuit parameters responsible for maintaining the ZVS operation are the transformer leakage inductance and the interlock delay time between the gate signals of two switches. A design method of the two parameters is proposed, which can ensure the ZVS transition. The possible ZVS range of the load variation is also investigated. A 50-W AHB converter with 1-MHz switching frequency was constructed, and a maximum efficiency of 91% was achieved. Index Terms--Asymmetrical half-bridge (AHB) topology, pulse-width modulated (PWM), zero-voltage switching (ZVS).

The ability of monitoring the chip temperatures of power semiconductor modules at all times under various realistic working conditions is the basis for investigating the limits of the maximum permissible load. A novel transient thermal model for the fast calculation of temperature fields and hot spot temperature evolution presented recently is extended to include time-dependent boundary conditions for variations of ambient temperature and surface heat flows. For this a Green's function representation of the temperature field is used. Also, general initial temperature conditions are included. The method is exemplified by application to a dc/ac converter module for automotive hybrid drives. The thermal model, which can be represented by a thermal equivalent circuit, then is combined with an electrical PSpice-metal-oxide semiconductor field-effect transistor (MOSFET) model to allow for the fully self-consistent electrothermal circuit simulation of 42-V/14-V dc/dc-converter modules. 670 converter periods with altogether 8000 MOSFET switching cycles in the six-chip module can be simulated within 1-h computing time on a Pentium PC. Various simulation results are presented, which demonstrate the feasibility of the simulation method and allow for the optimization of converter losses. Short circuit modes of converter operation are investigated with a high temperature increase also revealing the thermal interaction between different chips. Index Terms--DC- and ac-converter for automotive, electrothermal simulation, multichip modules, PSpice metal-oxide semiconductor field-effect transistor (MOSFET) model, thermal equivalent circuit, time-dependent boundary conditions.

A new steady-state approach for determining the optimal shunt active power filter (APF) reference compensation current injections to control harmonic currents generated by the nonlinear load and for reactive power compensation under ideal or nonideal supply voltages are presented in the paper. Conventionally, the compensation currents injected by the shunt APF are determined to eliminate harmonic currents of the load. However, when considering different APF performance indices such as minimizing source current distortion and maximizing compensated load power factor, the issues related to sizing the APF to meet IEEE-519 harmonic current limits and other constraints such as current imbalance limits and minimum load power factor requirement are rarely investigated. In the paper, a new theory of APF control in the a-b-c lreference frame is proposed to determine the APF current injections to meet different constraints with an optimal APF size, where the filter control strategy is formulated as a nonlinear programming problem and is solved to find the optimal current injections. Results obtained by simulations with Matlab/Simulink show that the proposed approach is more flexible and effective than the conventional approaches on compensating reactive power and harmonic currents of the load. Index Terms--Active power filter, IEEE-519, nonlinear programming, reference compensation current, reference-frame transformation.

This paper describes analysis results of a combined operation of the unified power quality conditioner with the distributed generation. The proposed system consists of a series inverter, a shunt inverter, and a distributed generator connected in the dc link through rectifier. The proposed system can compensate voltage sag and swell, voltage interruption, harmonics, and reactive power in both interconnected mode and islanding mode. The performance of proposed system was analyzed using simulations with power system computer aided design/electromagnetic transients dc analysis program, and experimental results with the hardware prototype. The proposed system can improve the power quality at the point of installation on power distribution systems or industrial power systems. Index Terms--Distributed generation (DG), power system computer-aided design/electromagnetic transients dc analysis program (PSCAD/EMTDC), unified power-quality conditioner (UPQC).

This paper describes the use of modal analysis in electromagnetic transient studies of ac networks having long transmission lines. Modal analysis provides structural information on the system and nicely complements the results from conventional time and frequency response simulations. Results of energization studies on a small test system, having a long transmission line, are included. The simulations obtained from modal analysis were compared with those produced by a conventional electromagnetic transients program, showing good agreement. The modal analysis methodology may lead to more efficient computation in parametric studies, as shown in the paper. Index Terms--AC networks, electromagnetic transients, linear analysis, modal analysis, s-domain, transmission lines.