Short-circuit Conditions Research Articles

Исследование механизмов изменения степени униполярности при термической обработке сильно легированных кристаллов LiNbO-=SUB=-3-=/SUB=-:ZnO

Phenomenological mechanisms of an increase in unipolarity degree at thermal treatment under short circuit conditions of strongly doped crystals are researched by comparison with thermal behavior of nominally pure LiNbO3 crystals of congruent composition. It has been shown that an increase in unipolarity degree, and correspondingly vanishing of domain structure in strongly doped LiNbO3:ZnО crystals starts by thermal decomposition of charged polar clusters. These clusters stabilize domain walls. The decomposition is accompanied by sharp jump-like injection of additional charge carriers (Li+ cations). Due to this, conductivity of LiNbO3:ZnО crystals is one order of magnitude higher at temperature above 800K than in nominally pure LiNbO3 crystals of congruent composition. The injection leads to decomposition of domain structure in LiNbO3:ZnО crystals in spite of LiNbO3 crystals of congruent composition.

Уравнения магнитоэлектрического вентильного двигателя при витковых замыканиях обмотки статора

The article considers the differential equations of a switched permanent magnet motor in which a short-circuit fault occurred in one or more turns in one of parallel stator winding branches. Owing to the occurred asymmetry of the phase quantities, symmetrical line-to-line voltages at the stator winding terminals are assumed. It is shown that turn-to-turn short-circuit faults give rise to non-sinusoidal and imbalanced phase currents and voltages at the nominal load torque on the shaft, and it should be noted that initially, a growth of the frequency and ratios of currents in the phases with an increase in the number of short-circuited turns are observed, after which the phase currents tend to decrease (with a continuing growth in the current through the short-circuited loop), and the rotor stalling occurs. The growth of motor rotation frequency and decrease of its overloading capacity take place due to a growth in the demagnetizing effect of armature reaction caused by the current through the short-circuited stator winding turns.

Application of Duality-Based Equivalent Circuits for Modeling Multilimb Transformers Using Alternative Input Parameters

The principle of duality is applied for electromagnetic transient (EMT) modeling of industry scale (i.e. 50, 390 MVA) multilimb transformers. While saturation, hysteresis, deep-saturation, and remanent flux are accounted for, the need for transformer internal design information such as core dimension or material is eliminated. This is achieved by formulating the equivalent circuits with an alternative set of parameters that are either provided by the manufacturer or can be determined using conventional techniques. Open-circuit tests confirm that the models produce accurate excitation currents at different saturation levels when compared with measurement results. Furthermore, the models facilitate correct short-circuit condition with support for arbitrary number of windings. Upon validating the models, inrush current is simulated and the worst-case scenario is determined due to potential remanent flux values. The findings agree with an established EMT simulation model as well as manufacturer analytical approximations. Simulated hysteresis loops are also investigated.

Determination of Equivalent Circuit Parameters of a Solid Rotor Asynchronous Electric Machine

The article deal with the determining the equivalent circuit parameters of a solid rotor asynchronous electric machine. To solve the problem, we determined the structure and parameters of a mathematical model using known geometric relationships and parameters of used materials. The least square method is used to determine the equivalent circuit parameters of an unlaminated-rotor asynchronous electric machine. The magnetic field distribution is calculated when the stator winding is supplying with a sinusoidal current and under short-circuit conditions. The imaginary part of the stator phase inductance versus stator current frequency when the rotor is fixed is calculated using the field theory. This dependence is approximated. The system of algebraic equations determining the approximation parameters is non-linear. The Levenberg-Marquardt method provides solution convergence of the equation system when using two or more loops on the rotor. The selection of the initial approximation largely determines the convergence of the solution made by the iterative method. The preliminary studies showed that the use of simplified scheme of the substitution of an asynchronous electric machine with one contour on the rotor is suitable as an initial approximation of parameters. The numerical solution of the equations determined the approximation parameters. The equivalent circuit parameters of high-speed electric generator with solid asynchronous rotor was made as an example of using of the approach under consideration. We need to use three loops on the rotor in the mathematical model of the asynchronous electric machine to take into account the effect of current displacement in solid rotor.

Structure and properties of the hybrid and topological transformer models

Three topological transformer models for low-frequency transient simulations are considered in increasing order of their topology. It is first shown that the well-known hybrid model is not a strictly topological one, but despite this, it can be used in many applications. The next is the simplified model, which is a strict electric equivalent of the popular magnetic model, and the last is a detailed electric model, which takes into account thicknesses of transformer windings. This model improvement allows one to reproduce experimentally observed behaviors of the magnetic fluxes in the legs and yokes under short circuit conditions.

Charge photogeneration and recombination in single-material organic solar cells and photodetectors based on conjugated star-shaped donor-acceptor oligomers

Abstract Single-material organic solar cells (SMOSC) are attracted by their simple structure and ease of fabrication so that they are virtually free from a number of drawbacks of heterojunction organic solar cells. However, the performance of SMOSC is still low, first of all because of poor understanding of losses on the way of energy conversion from light to electricity. In this work, we present solution-processed SMOSC based on star-shaped π-conjugated donor-acceptor oligomers with triphenylamine donor (N-Ph3) and alkyl- or phenyl dicyanovinyl acceptor (DCV-R) of general formulae N(Ph-nT-DCV-R)3, where nT stands for n-oligothiophene, and study charge photogeneration and recombination in them. SMOSC demonstrate small energy losses resulting in high open-circuit voltage of 1.08–1.19 V and the power conversion efficiency up to 1.22% under illumination intensity of 0.45 sun (1.13% under one sun) with the maximum external quantum efficiency up to 24% for N(Ph-2T-DCV-Ethyl)3, which are among the highest for SMOSC based on conjugated donor-acceptor small molecules or oligomers. It was found that monomolecular recombination dominates at the short-circuit condition and the maximum power point, but at the open-circuit condition the photoinduced charges recombine nearly bimolecularly. The bottleneck in the SMOSC performance was shown to be the field-assisted charge generation perfectly described by the Onsager model in the limit of weak electric fields. The results obtained suggest that intermolecular charge delocalization in conjugated donor-acceptor molecules would be beneficial for further progress in SMOSC.

Impedance Determination for High Voltage Air-Core Reactor Over Wide Frequency Range Based on Impulse Injection Technique

To analyze interference induced by transient overvoltage, this article proposes an impulse injection technique for determining the impedance of a high-voltage air-core reactor over a wide frequency range. By injecting nanosecond pulses into reactor in open-circuit, short-circuit and loading conditions, the linear characteristics of air-core reactor can be revealed up to several MHz. Then the equivalent two-port impedance including stray parameters can be derived from the measured current waveforms. Using vector fitting and impedance synthesis, the equivalent circuit is obtained and can be further applied in transient simulation. As an example, a 110 kV reactor is studied in this paper and its equivalent circuit is deduced in the frequency range of [2.5 kHz, 10 MHz]. The accuracy of the model is validated based on the measurements of a loading experiment.

Design of a New Relieving-DC-Saturation Hybrid Reluctance Machine for Fault-Tolerant In-Wheel Direct Drive

This article aims to propose a new hybrid reluctance machine equipped with relieving-dc-saturation (RDCS) ability for electric vehicle in-wheel drive. The proposed machine uses integrated ac and dc current excitation to eliminate extra dc field coils for the efficient torque generation. Besides, considering the inherent dc saturation in stator core caused by dc current excitation, slot PMs are artificially introduced to provide RDCS effect and thus boost torque density. Moreover, with a modular magnetic field configuration, the proposed topology exhibits excellent fault-tolerant potential at both open-circuit and short-circuit condition, making it suitable for safety-critical in-wheel vehicle propulsion. In this article, the machine configuration and operation principle are introduced, with emphasis on its RDCS effect and corresponding design consideration. Further, performance of this new topology is evaluated by both finite element analysis and prototype experiments. It is revealed that, with this RDCS ability, torque density of the proposed machine can be enhanced by about 25% under relatively high current density.

Impact of Repetitive Short-Circuit Tests on the Normal Operation of SiC MOSFETs Considering Case Temperature Influence

This article presents the impact of repetitive short-circuit (SC) tests on the normal operation of a commercial silicon carbide (SiC) MOSFET and the influence of different case temperatures on the SC degradation process. To ensure repeatable SC test conditions, the maximum SC withstanding time is studied at three different case temperatures and the critical energy is identified. To investigate the effect of SC stress on the normal operation, the static and dynamic characteristics are periodically measured along with the repetitive SC activity. The turn-on switching loss increases gradually with the increasing number of repetitive SC tests. This is associated with the increase in the gate leakage current during the SC tests, which shows a reduction in the ON-state gate voltage because of the gate oxide degradation. Then, since the case temperature of the device is subject to the operating condition in the application, the degradation process of repetitive SC tests with respect to different case temperatures is investigated, and the relationship between the number of repetitions to failure and the initial case temperature is established. Finally, the case temperature influence is explained by a 1-D transient thermal model based on the SC condition.

Photoelectrochromic devices with cobalt redox electrolytes

In this work, the use of cobalt redox electrolytes in partly covered photoelectrochromic devices is investigated experimentally for the first time. The fabricated devices consist of a conductive glass photoanode coated with an electrochromic WO3 film of optical quality, including a mesoporous TiO2 layer (sensitized by the MK2 organic dye) that covers 20% of the device area. The liquid electrolyte is composed of 0.22 M Co(II)(bpy)3(PF6)2, 0.5 M LiClO4 and 0.5 M 4-tert-butylpyridine. A platinized conductive glass cathode completes the cell set-up. The fabricated devices are almost transparent in the bleached state with a Tlum value above 50%. They exhibit coloration speeds in the order of minutes, with a maximum contrast ratio of 2.9:1 after 21 min of illumination at 1000 W m−2 under open circuit conditions (OC), and high reversibility to fully bleached state in short circuit conditions. They provide a maximum measured power conversion efficiency of 0.28% due to limitations imposed by conflicting requirements of the photovoltaic and electrochromic elements, which is nonetheless sufficient to drive the coloration process. Since only the reduced specie Co2+ is present, initial illumination under OC for 3 min at 1000 W m−2 is necessary, prior to measurements, to oxidize Co2+ to Co3+ through the dye regeneration process in the electrolyte. The higher recombination losses of the Co2+/3+ redox shuttle compared to I−/I3−, which lead to a considerable reduction in coloration depth 20 days post fabrication due to loss of photoelectrons at the WO3/electrolyte interface, are suppressed by the use of a 35 nm thick ZnS barrier deposited on top of WO3. Remarkably, it results in a stabilized contrast ratio of 1.5:1, 23 days post fabrication. In addition, the color coordinates of the present devices resemble those of typical electrochromics: they exhibit blue coloration, as a result of the lack of the absorbing iodine in the electrolyte that produces a green tint.

Real Time Short Circuit Fault Analysis of a Sub-Station by Soft Computing

Most of the faults on the power system lead to a short–circuit condition. As our power system runs at uncertain constraints so it is impossible to maintain uninterrupted power supply due to random occurrence of faults. Now a day, Power Industries depend on reliability constraints but due to faults they are impossible to maintain because our system operates in grid networks. Any malfunctioning lines are capable to make other lines malfunction. So, to maintain one grid in one nation it is mandatory to analyse each and every faults in power system lines whether it may be symmetrical or unsymmetrical. So in this paper we are trying highlight analysis of power system faults and its responses. In a feeder or distribution line the main aim is to supply power uninterruptedly by maintaining its systems’ security and stability. So we are analyse a short circuit condition in a distribution network by ETAP software and give an idea of importance of short circuit analysis in power system. Because short circuit analysis will give us a clear idea of short circuit current in every buses which help us design and development of protection equipment in substation. ETAP (Electrical Transient Analysis and Program) is well known software to analyse a short circuit and transient fault. It is not possible for analysis of short circuit fault in high voltage live (transmission/distribution) lines so we can easily analyse short circuit by ETAP software where we can test, design and analyse a high voltage line by soft computing methods and find out easily its parametric values. For that reason we chose ETAP software for short circuit analysis. The analysis of this paper is based on real live system (132/33/11kv) of Kalyani Substation of West Bengal. All the data used for these analyses are collected from 132/33/11kv substation under the W.B.S.E.T.C.L.

Output power density enhancement of triboelectric nanogenerators via ferroelectric polymer composite interfacial layers

To date, several attempts have been made to improve the performance of triboelectric nanogenerators (TENGs). Although notable advancements have been made in the output power density, it is still relatively low and further improvement in the output power density has been limited by air breakdown issue. In this work, we proposed preferable composite structures and an electrical activation method to maximize the output performance of TENGs by adopting ferroelectric composite interfacial layer. Specifically, by doping Nylon 11 with Poly (methyl methacrylate) - PMMA, we intensified the positive triboelectricity of Nylon 11 and simultaneously improved its physical durability. The negative triboelectricity of PVDF-TrFE was also enhanced by compositing with ZrO2 nanoparticles (NPs). Triboelectricity of both polymer composites was further boosted by polarizing them in favorable direction. Therefore, high frictional surface charge density of 220 μC/m2 was achieved in short-circuit condition, effectively promoting charge outputs. Consequently, the open circuit voltage and short circuit current density of ~500 V and ~500 μA cm−2 were achieved, respectively, exhibiting a remarkable output power density of ~42 mW cm−2.

Grid-Synchronization Stability Analysis for Multi DFIGs Connected in Parallel to Weak AC Grids

Recent works have shown that phase-locked loop (PLL) synchronized wind turbines (WTs) suffer stability issues when integrated into weak grids. However, most of the current studies are limited to a single machine case, the interactions among the WTs are usually overlooked. This paper studies the stability of multiple doubly-fed induction generators (DFIGs) that are connected in parallel to a weak AC grid. A state space model of a two-DFIG system is firstly presented. Subsequently, eigenvalue sensitivity analysis shows that instability can occur at low short-circuit ratio (SCR) or heavy loading conditions. Meanwhile, participation factor analysis implies that the unstable mode is primarily induced by the interactions between the PLLs of the two WTs. Further, to make out how the PLLs interact to cause instability, a reduced-order model is proposed for analysis simplicity, and an explanation in terms of transfer function residue is given for illustration. Detailed model-based time domain simulations are conducted to validate the analyses’ results.

On-Board Short-Circuit Detection of Li-ion Batteries Undergoing Fixed Charging Profile as in Smartphone Applications

In this paper, an effective and robust algorithm is developed for on-board detection of battery anomaly caused by short circuit (SC). The proposed algorithm uses the battery-terminal voltage and current information measured using battery-management system during standard uses. The proposed method is purely a noninvasive, software-based solution and does not need any additional hardware. It extracts a set of designed features from the recorded data and stores their statistics as normal operating behavior for the initial five charge–discharge cycles. After the initial characterization of the battery, the likelihood of the features of being normal are evaluated for the subsequent cycles. If a feature is likely to be healthy, then the statistics for that feature get updated with the current value. However, if the feature is not likely to be healthy, then the battery is considered to be faulty with respect to that particular feature. If more than $\text{50}\%$ of the features identify the battery as faulty, then the overall battery status is classified as faulty. A mobile application is developed to log the smartphone's battery data during charging and discharging for testing. The faulty data are generated by connecting SC resistances of various values to the battery terminals, which emulates the SC condition in the battery. The data logged in the smartphones are transferred to a PC for analysis using the proposed algorithm. $\text{100}\%$ detection accuracy is achieved for SC resistance values less than $\text{200}\,\Omega$ .

Measuring Competing Recombination Losses in a Significantly Reduced Langevin System by Steady-State Photoinduced Absorption and Photocurrent Spectroscopy

Understanding and disentangling photophysical properties of long-lived photoexcitations in bulk heterojunction (BHJ) solar cells, which contribute mostly to photocurrent, provide essential guidelines to their improvement. However, to construct improved physical models, their rational design relies on reliable measurement techniques for charge recombination. Here, we combine photocurrent and photoinduced absorption spectroscopy (PCPIA) to directly probe the free carrier concentration and investigate loss mechanisms of long-lived excitations in nearly 10% efficient PPDT2FBT/PC70BM BHJ solar cells under steady-state operational conditions. From the PCPIA data obtained under open-circuit and short-circuit conditions, the absorption cross section and the concentration of photoexcitations are obtained. This material system exhibits an exceptionally low bimolecular recombination rate, about 300 times smaller than the diffusion-controlled electron and hole encounter rate. Furthermore, we observe that the fill factor is limited by losses originating from long-lived photoexcitations undergoing dispersive bimolecular recombination.

Investigation on the Short-Circuit Oscillation of Cascode GaN HEMTs

This article presents the study on the self-sustained oscillation of cascode gallium nitride (GaN) high-electron-mobility transistors (HEMTs), which occurs under the short-circuit (SC) condition. Based on the SC test, it is found that the self-sustained oscillation can be excited in the SC event of cascode GaN HEMTs. Moreover, the gate resistance $R_{G}$ does not have a significant damping effect on the self-sustained SC oscillation. The SPICE simulation is performed to study the oscillation waveforms of the internal depletion-mode HEMT (DHEMT) and low-voltage (LV) mosfet . This article reveals two positive feedback loops, which excite the SC oscillation. One loop is related to the positive feedback process of the DHEMT itself. Another loop is induced by the interaction between the DHEMT and LV mosfet . The two positive feedback loops are interrelated and can reinforce each other. As a result, a very strong driving force is generated to excite the self-sustained oscillation. During the oscillatory transient, the parasitic elements of the device's package play a critical role in exciting the positive feedback process. By analyzing the influence of the parasitic elements on the positive feedback process, the necessary methods are proposed to suppress the SC oscillation. The SPICE simulation validates the effectiveness of the proposed methods.

Electrical-Field-Driven Tunable Spectral Responses in a Broadband-Absorbing Perovskite Photodiode.

Controllably manipulating the spectral response of broadband-absorbing semiconductors is crucial for developing wavelength-selective optoelectronic devices. In this article, we report for the first time, the bias-dependent spectral responses for a metal-halide perovskite photodiode. Tunable external quantum efficiencies in the short- and long-wavelength regimes, and the full spectral range (ca. 300-800 nm) are observed when the device is operated under short-circuit, and forward and reverse bias conditions, respectively. This observation is understood by the interplay of wavelength-dependent penetration depth and barrier formation within the photodiode device stack. The general applicability of this concept is confirmed by a systematic study on a series of mixed-halide perovskite devices. These results suggest that the proposed concept allows as a promising platform and should inspire further exploration of multispectral responsive optoelectronic devices.

High-Temperature Characterization of a 1.2-kV SiC MOSFET Using Dynamic Short-Circuit Measurement Technique

Threshold voltage and channel mobility of a 1.2-kV planar-channel SiC MOSFET at high junction temperature ( $T_{j}$ ) up to 700 °C have been extracted and analyzed for the first time, by virtue of a specially designed short-circuit (SC) measurement technique we developed. Under the SC condition, $T_{j}$ of the SiC MOSFET can rise significantly within a few microseconds, which can be extracted based on the SC waveforms and thermal calculations. The planar-channel SiC MOSFET investigated in this work can maintain normally-off operation at an elevated $T_{j}$ up to 700 °C. Furthermore, the underlying mechanisms of the temperature dependence of the threshold voltage and channel mobility are also analyzed. The threshold voltage of the SiC MOSFET exhibits a different temperature dependence over a wide range (120–700 °C) compared with that of Si counterparts, which is attributed to interface traps’ response. The channel mobility shows a non-monotonic temperature dependence, due to divergent scattering mechanisms.

Elucidating the Impact of Charge Selective Contact in Halide Perovskite through Impedance Spectroscopy

AbstractThe electron and hole selective contact (SC) plays a pivotal role in the performance of perovskite solar cells. In order to separate the interfacial phenomenon from bulk, the influence of charge SC is elucidated, by means of impedance spectroscopy. The specific role played by TiO2 and Spiro‐OMeTAD as electron and hole SC in perovskite solar cells is investigated at short circuit condition at different temperatures. The methylammonium lead triiodide (MAPbI3) and mixed perovskite of formamidinium lead iodide and methylammonium lead bromide namely; (FAPbI3)0.85(MAPbBr3)0.15 are probed and parameters such as charge carrier mobility, recombination resistance, time constant, and charge carrier kinetics in perovskite layer and at the interface of perovskite/SC are elucidated. Charge carrier mobility in mixed perovskite is found to be nearly two order of magnitude higher as compared to MAPbI3. Moreover, the carrier mobility in devices with only electron SC is found to be higher as compared only hole SC. The charge accumulation at TiO2/perovskite/Spiro‐OMeTAD interfaces is studied via frequency dependent capacitance, revealing higher charge accumulation at perovskite/Spiro‐OMeTAD than at TiO2/perovskite interface. By performing varying temperature frequency dependent capacitance measurements the distribution of density of state within the bandgap of the perovskites, the emission rate of electrons from the trap states and traps activation energy is determined.

Electrical Modeling of Dye-Sensitized Solar Cells for Improving the Overall Photoelectric Conversion Efficiency

An electrical model of dye-sensitized solar cell (DSSC) is derived on continuity and transport equations for all the four charged species i.e. electrons, iodide ions (I-), triiodide ions (I3-) and cations. The device model comprises of a pseudo-homogeneous active layer, where solar photovoltaic effect including both diffusion of electrons in nanoporous TiO2 layer as well as ions in electrolyte occur, and a bulk electrolyte layer, where only ions diffuse take place. The distribution of the electrons, iodide and tri-iodide ions as function of the pseudo-homogeneous active layer thickness of the DSSC under both the open-circuit and short-circuit operation conditions were performed. Parametric studies were conducted to analyze (J–V) characteristic of the DSSC with three different sets of porosity and also for different sets of TiO2 layer thicknesses.