Influence of parasitic inductances on transient current sharing in parallel connected synchronous rectifiers and Schottky-barrier diodes

The transient current sharing in parallel connected Schottky-barrier diodes and MOSFET synchronous rectifiers is analysed. It is shown that, because of parasitic inductances the desired reduction of dead-time conducting losses and reverse-recovery peak current is limited, when discrete devices are used. The total amount of conducting losses in the free-wheeling circuit can increase. A reduction of switching losses in half-bridge configurations is possible because of secondary effects.     

A commutation strategy for IGBT-based CSI-fed parallel resonant circuit for induction heating application

A brief study on a commutation strategy for a current source inverter (CSI)-fed parallel resonant circuit, using switches formed by IGBTs with series diodes, is presented in this paper. The dynamic behaviour of the inverter and different strategies for its reliable operation are discussed here considering parasitic inductance and overlap time between CSI switching devices. The dynamic behaviour of the switches decides the upper frequency limit for the application. IGBTs with the series diodes behave as uni-directional current switches with bi-directional voltage blocking capability. This feature should be taken into account to decide on an appropriate switching strategy for this converter configuration.     

Multiscale Computations of Parameters of Power Transformer Windings at High Frequencies. Part I: Small-Scale Level

We propose a hierarchical multiscale approach to modeling of high-frequency phenomena in power transformers. The method is based on considering high-frequency effects on two spatial levels. Part I of the paper focuses on a small-scale level where eddy-current as well as geometrical and proximity effects in conductors of transformer windings are examined. It develops a computer model that accounts for anisotropic frequency-dependent diamagnetic properties of transformer windings, which are represented as composite media with periodic structure. Calculations of effective characteristics of the laminated transformer core take into account anisotropic magnetic properties of steel sheets. The frequency-dependent parameters of transformer elements thus obtained will be further used in Part II for computing effective inductances and resistances of windings and integral losses on a large-scale level, i.e., for the whole transformer.     

Multi‐Nonvolatile State Resistive Switching Arising from Ferroelectricity and Oxygen Vacancy Migration

Resistive switching phenomena form the basis of competing memory technologies. Among them, resistive switching, originating from oxygen vacancy migration (OVM), and ferroelectric switching offer two promising approaches. OVM in oxide films/heterostructures can exhibit high/low resistive state via conducting filament forming/deforming, while the resistive switching of ferroelectric tunnel junctions (FTJs) arises from barrier height or width variation while ferroelectric polarization reverses between asymmetric electrodes. Here the authors demonstrate a coexistence of OVM and ferroelectric induced resistive switching in a BaTiO₃ FTJ by comparing BaTiO₃ with SrTiO₃ based tunnel junctions. This coexistence results in two distinguishable loops with multi‐nonvolatile resistive states. The primary loop originates from the ferroelectric switching. The second loop emerges at a voltage close to the SrTiO₃ switching voltage, showing OVM being its origin. BaTiO₃ based devices with controlled oxygen vacancies enable us to combine the benefits of both OVM and ferroelectric tunneling to produce multistate nonvolatile memory devices.     

Numeral-source,high-resolution,staircase multi-level inverter with low number of conducting switches

Abstract

A high-resolution, staircase-output multi-level inverter is proposed in this paper. The topology can provide high number of levels with low number of sources and conducting switches. A 1-2-7 source version of the proposed topology can generate 21 levels with 3 DC sources, 11 total bidirectional switches, and 3 conducting switches plus 3 conducting diodes. The topology can also be expanded horizontally to achieve higher resolution; a 1-2-7-14-source version of this new topology can generate 49 levels with 4 DC sources, 15 total bidirectional switches, and 3 conducting switches plus 3 conducting diodes. Providing modularity also leads to easy maintenance in the proposed topology. The feasibility of the inverter is investigated through experimental results. In comparison with other inverters, the proposed inverter can function with 25% fewer conducting switches while providing the same resolution. A stand-alone application under renewables with low output voltage is the goal application.     

Determination of winding inductances in ferrite type permanent magnet electric machinery by finite elements

A key design factor in ferrite type permanent magnet machines is the accurate knowledge of the values of machine winding inductances during the design stage. In the present paper, a method which is based on perturbation of the energy stored in the magnetic field, and on numerical models of simulation of such permanent magnets is used in calculating machine inductances. The effect of change in the values of these winding inductances with magnet position throughout the cycle of operation of such machines is given. These inductances also include the apparent and incremental values, whose definition is directly related to the choice of apparent or incremental reluctivities in the energy perturbation process. Results of application of this method to the calculation of inductances in a 15 hp 6-pole ferrite type electronically operated permanent magnet machine are given. These calculated values of inductances are in good agreement with the measured values.     

Method for angular alignment of birefringent fibers in fiber-opticpressure/strain measurement

A simple method for angular alignment of principal birefringence axes of a highly birefringent (HB) polarization-maintaining (PM) optical fiber is presented. The method is based on longitudinal strain-induced cross-coupling phenomena which occur in HB fibers and it can be straightforwardly applied to construct a fiber-optic pressure or strain sensor independent of disturbing thermal effects. The method is also particularly suitable for splicing birefringent fiber pigtails to laser diodes in all-fiber configuration for a fiber-optic pressure (strain) sensor     

Semiconductor devices suitable for use in cryogenic environments

The low temperature behaviour of semiconductor diodes, Zener diodes, varactor diodes, tunnel diodes, of bipolar transistors, and of field effect transistors is investigated. It is discussed which semiconductor materials and devices are best suited for use at 4.2 K. A great number of currently available diodes and transistors have been tested. The ones working satisfactory at 4.2 K are listed and their performance in cryogenic environments is described.     

On the statistical aspects of threshold switching in thin polymer films

Threshold switching was observed under voltage pulse excitation in thin (2000– 8200 Å) polymer films. For a given applied voltage V (greater than the threshold) the sequence of switching events stops after a given time; new switchings are possible if the applied voltage is increased. Data on the statistical distribution of the number of events in a given switching sequence versus applied voltage amplitude suggest the existence of two independent gaussian phenomena. We assume these to be related to weak spots and to true bulk phenomena of the films during switching.     

All-optical flip-flops based on DFB laser diodes and DFB-arrays

We present numerical and experimental results on a number of different all-optical flip-flops which are based on DFB laser diodes or DFB-arrays. All these flip-flop concepts show potential for fast switching with low switching energy and high extinction ratio. They are moreover very robust in the sense that the switching pulses (and the injected CW beam in some cases) can be of arbitrary wavelength and that the bistability characteristics can be tuned by simple variation of the current injected into the devices. Two different designs for all-optical flip-flop operation will be discussed in detail. The first one is a DFB or DBR laser diode coupled to a semiconductor optical amplifier, in which the bidirectional coupling between laser and amplifier causes the bistability. The second concept is based on bistable behaviour in a single AR-coated DFB laser, with low coupling coefficient and in which a CW signal is injected. These all-optical flip-flops can easily be extended to optically switchable multistate devices with any number of stable states. Such multistate devices are briefly discussed at the end.     

A simple method for the evaluation of microwave mixer diodes

A simple method is described for the evaluation of the various microwave mixer diodes which can be used in 9-GHz electron paramagnetic resonance (EPR) spectrometers using magnetic field modulation below 1 kHz. The advantage of this method over other methods is that it is optimized for EPR applications and determines the optimum operating conditions for each microwave diode. This method utilizes a microwave bridge with a reference arm with an attenuator to control the microwave bias power level, and a signal arm where the signal is attenuated, phase shifted, and modulated at the typical magnetic field modulation frequencies. The microwave power from the two arms is recombined and demodulated by the microwave diode. The output of the microwave diode is then recorded with various video loads, microwave bias power, and modulation frequencies. Measurements are performed to determine the effect of the preamplifier that followed the microwave diode on the signal-to-noise ratio (SNR). The recorded spectra are used to determine the SNR, the noise floor, and the 1/f corner frequency. Comparison of these factors for the different types of microwave diodes shows that some Schottky-barrier diodes have noise figures at 1 kHz that are as low as those for tunnel diodes     

High-voltage GaAs diodes with subnanosecond gate voltage recovery

High-voltage GaAs switching diodes with subnanosecond characteristic times of reverse current decay on switching from forward to reverse bias were studied. The diode structures studied had impurity concentration profiles in the base region close to those of the charge-storage diodes and operated in the regimes corresponding to those employed in silicon-based high-voltage fast-recovery drift diodes. The application prospects of the proposed GaAs diodes are demonstrated, for example, in the devices generating pulses with a front width of several hundred picoseconds, a current of several hundred amperes, and a voltage of a several kiloelectronvolts at a frequency of up to several hundred kilohertz.     

Commutations dans des couches très minces de composés amorphes obtenus par condensation de tellure sur aluminium

We have investigated the current-voltage characteristics of MSM structures which were prepared by the deposition of tellurium on aluminium. We obtained switching effects and, after a limited number of cycles, a memory effect in the high conductivity state. The properties of the threshold voltage, defined when switching occurs, have been studied as functions of several parameters. The existence of a very thin film of amorphous semiconductor which forms along the Al-Te contact is used to discuss the switching and memory effects. We suggest that the observed phenomena can be explained in terms of a “forming process” encountered in structures using thicker amorphous films and containing chalcogenides.     

Instability/collapse of polymeric materials and their structures in stimulus-induced shape/surface morphology switching

With the current development in 3-D printing and origami-inspired technologies, stimulus-induced shape/surface morphology switching becomes a novel approach to produce complex 2-D/3-D mechanisms/structures. This paper briefly discusses major instability/collapse phenomena in the shape change/memory effect based such switching in polymeric materials and their structures, from the beginning of fabrication and programming to the final step of shape/surface morphology switching. As shown here, stimulus-induced shape/surface morphology switching is essentially a mixture of mechanism and structure, so that on the one hand it shares many common features as in conventional mechanisms and structures, while on the other hand it has some unique characteristics; instability may happen during programming as well, and instability may be utilized as a powerful self-assembly technique for surface morphology switching. In most cases, traditional theories of mechanics may be applied directly in analysis/design to either avoid instability/collapse or purposely induce these phenomena for our intended purpose.     

Microwave switches based on 4H-SiC <Emphasis Type="Italic">p-i-n</Emphasis> diodes

Problems pertaining to the modeling and development of a microwave modulator based on 4H-SiC p-i-n diodes are considered. The results of theoretical and experimental investigations of the microwave characteristics of 4H-SiC p-i-n diodes and the parameters of a microstrip modulator for a 1–10 GHz range based on these diodes are reported for the first time. In the diode switching schemes studied, the transmission losses amount to 0.8–8 dB and the decoupling is within −15 to −18 dB. The experimental characteristics of modulators are determined primarily by the parameters of diodes and agree well with the results of model calculations.     

Modelling and analysis of an open-loop induction motor drive incorporating the effect of inverter dead-time

The objective of this paper is to study the influence of inverter dead-time on steady as well as dynamic operation of an open-loop induction motor drive fed from a voltage source inverter (VSI). Towards this goal, this paper presents a systematic derivation of a dynamic model for an inverter-fed induction motor, incorporating the effect of inverter dead-time, in the synchronously revolving dq reference frame. Simulation results based on this dynamic model bring out the impact of inverter dead-time on both the transient response and steady-state operation of the motor drive. For the purpose of steady-state analysis, the dynamic model of the motor drive is used to derive a steady-state model, which is found to be non-linear. The steady-state model shows that the impact of dead-time can be seen as an additional resistance in the stator circuit, whose value depends on the stator current. Towards precise evaluation of this dead-time equivalent resistance, an analytical expression is proposed for the same in terms of inverter dead-time, switching frequency, modulation index and load impedance. The notion of dead-time equivalent resistance is shown to simplify the solution of the non-linear steady-state model. The analytically evaluated steady-state solutions are validated through numerical simulations and experiments.     

A metric for characterizing the bistability of molecular quantum-dot cellular automata

Much of molecular electronics involves trying to use molecules as (a)?wires, (b)?diodes or (c)?field-effect transistors. In each case the criterion for determining good performance is well known: for wires it is conductance, for diodes it is conductance asymmetry, while for transistors it is high transconductance. Candidate molecules can be screened in terms of these criteria by calculating molecular conductivity in forward and reverse directions, and in the presence of a gating field. Hence so much theoretical work has focused on understanding molecular conductance. In contrast a molecule used as a quantum-dot cellular automata (QCA) cell conducts no current at all. The keys to QCA functionality are (a)?charge localization, (b)?bistable charge switching within the cell and (c)?electric field coupling between one molecular cell and its neighbor. The combination of these effects can be examined using the cell-cell response function which relates the polarization of one cell to the induced polarization of a neighboring cell. The response function can be obtained by calculating the molecular electronic structure with ab initio quantum chemistry techniques. We present an analysis of molecular QCA performance that can be applied to any candidate molecule. From the full quantum chemistry, all-electron ab initio calculations we extract parameters for a reduced-state model which reproduces the cell-cell response function very well. Techniques from electron transfer theory are used to derive analytical models of the response function and can be employed on molecules too large for full ab initio treatment. A metric is derived which characterizes molecular QCA performance the way transconductance characterizes transistor performance. This metric can be assessed from absorption measurements of the electron transfer band or quantum chemistry calculations of appropriate sophistication.     

Analysis of characteristics of silicon metal/insulator/semiconductor tunnel diodes with d.c.-plasma-grown oxide

In this work the I–V and C-V characteristics of silicon metal/insulator/semiconductor (MIS) tunnel diodes with d.c.-plasma-grown oxide are analysed in order to investigate further some basic relationships between the oxide properties and the plasma anodization conditions. It is shown that once such relationships are established, the device-grade ultrathin (2–5 nm) oxide can be grown on silicon by use of the plasma anodization technique. The MIS tunnel diodes formed in this way exhibit properties comparable with those containing thermally grown oxide.     

Injection ionization mechanism of current instability during switching off an integrated field controlled thyristor

The process of switching off an integrated field-controlled thyristor chip operating in a circuit with inductive load has been experimentally and theoretically analyzed. It was established by independent measurements of the anode and cathode emitter currents that the electron injection in all unit cells of the structure cannot be instantaneously interrupted under real conditions due to the shunting of the controlled emitters through the external circuit; the maximum current that can be switched off in this mode was also determined. A numerical simulation has revealed instability of the current distribution over the operation region, which facilitates its emergency localization, and has shown an urgent need to reduce stray inductances and resistances in the chips and shunting circuit when designing high-voltage integrated thyristors and related power modules.     

Study on the new control scheme of class-E inverter for IH-jar application with clamped voltage characteristics using pulse frequency modulation

A new control scheme of Class-E inverter for induction heating jar applications with clamped voltage characteristics using pulse frequency modulation (PFM) is introduced. To reduce the voltage stress of a switch, the proposed PFM control scheme does not need any auxiliary circuit. It can decrease the voltage stress of a switch through the modulation of switching frequency. The Class-E inverter using the proposed control scheme has the advantages of not only the same output power when it is compared with an active clamped class-E (ACCE) inverter, but also zero-voltage-switching, which are characteristics of conventional Class-E and ACCE inverter. The control principles of the proposed method are explained in detail and its validity is verified through experimental results