Short-circuit Conditions Research Articles

Packaging of semiconductor thermoelectric energy generators with in-plane thermocouples and isolation cavities

With the advent of semiconductor foundry services, thermoelectric energy generator (TEG) by CMOS/BiCMOS process has been preferable for production yield, cost effectiveness, and device scalability. The thermocouples in semiconductor TEG often have thermal isolation cavity to reduce heat loss. Both die- and wafer-packaging are proposed in this work to seal the cavity, prevent moisture/dirt from contamination, and avoid short circuit condition in the thermocouples for TEG applications in wearable devices. For a TEG design by 3P6M (3 polysilicon layers and 6 metal layers) BiCMOS process, the die-level packaging by aluminum film of thickness 50 μm over the TEG is shown to be effective, though there is about 23 % temperature gradient loss by the packaging. The voltage factor is 18.22 V/cm2K, about 77 % of that before packaging. For a TEG design by 1P6M CMOS process, the wafer-level packaging by bonding two identical TEG device wafers is shown to have about 22 % loss in temperature gradient. Yet the TEG performance is increased significantly on the same footprint because of doubling area density, and hence doubling both the power factor and voltage factor. The power factor and voltage factor is 0.164 μW/cm2 K2 and 24.32 V/cm2K, respectively, on the TEG in series circuit after packaging.

Surfactant-Encapsulated Polyoxometalate Complex as a Cathode Interlayer for Nonfullerene Polymer Solar Cells

Surfactant-Encapsulated Polyoxometalate Complex as a Cathode Interlayer for Nonfullerene Polymer Solar Cells

Comparative Investigation of Fullerene PC71BM and Non-fullerene ITIC-Th Acceptors Blended With P3HT or PBDB-T Donor Polymers for PV Applications

Fundamentally, organic solar cells (OSCs) with a bulk-heterojunction active layer are made of at least two electronically dissimilar molecules, in which photoabsorption in one (donor) generates Frenkel excitons. The formation of free charge carriers emerge after exciton dissociation at the donor:acceptor interface. In the past decade, most of the progress in enhanced device performance has been steered by the rapid development of novel donor and acceptor materials and on device engineering. Among these donor materials, regioregular poly(3-hexylthiophene) (P3HT) produced better performance despite the mismatch of its absorption coefficient with the solar emission spectrum. Comparatively the donor PBDB-T exhibits an outstanding absorption coefficient with a deeper-lying highest occupied molecular orbital (HOMO) level. Previously most of the efficient acceptors were based on fullerene molecules characterized by limited photoabsorption and stability. In contrast, the recently developed non-fullerene OSCs have a tunable absorption spectrum and exhibit improved stability. In this work, we explore the fundamental sources of the differences in the device performance for different blend compositions made of fullerene derivative (PC71BM) and non-fullerene (ITIC-Th) when paired with the polymer donors P3HT and PBDB-T. The characteristic changes of the optical properties of these blends and their roles in device performance are also investigated. We also studied charge generation where PBDB-T:PC71BM showed the highest maximum exciton generation rate (Gmax) of 3.22 × 1028 s–1 while P3HT: ITIC-Th gave the lowest (0.96 × 1028 s–1). Also noted, PC71BM based counterparts gave better charge transfer capabilities as seen from the lower PL quenching and higher charge carrier dissociation plus collection probability P(E,T) derived from a plot of Jph/Jsat ratio under short-circuit conditions against the effective voltages.

Design of All-Fused-Ring Electron Acceptors with High Thermal, Chemical, and Photochemical Stability for Organic Photovoltaics

High-performance donor–acceptor electron acceptors containing 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (INCN)-type terminals are labile toward photooxidation and basic conditions, and ...

An Intelligent Dual-Mode Control Strategy for Extending MPPT Operation Interval of DFIG

An intelligent dual-mode control strategy is proposed to extend the MPPT operation range of doubly-fed induction generator (DFIG) and improve the power generation efficiency under low wind speed in this article. By adjusting the strategy of the machine-side converter (MSC) and the necessary switchover, DFIG can automatically operate in two modes depending on the wind speed: the traditional DFIG mode and the DFIG stator short circuit (SSC) mode. In addition, aiming at the characteristics of short time, large impact, and long impact of mode switching process, this article focuses on the flexible mode switching control methods rarely mentioned in other studies, especially the specific process of bidirectional mode switching, MSC control strategy, and the selection of generator load. Finally, the hardware-in-the-loop (HIL) simulation results based on RT-lab show that the control strategy proposed in this article takes the advantages of the low cost of DFIG and the wide speed range of full-power generator (FPG), and achieves fast and flexible switching between the two modes.

Design of Vibration Frequency Method with Fine-Tuned Factor for Fault Detection of Three Phase Induction Motor

This research article focuses on industrial applications to demonstrate the characterization of current and vibration analysis to diagnose the induction motor drive problems. Generally, the induction motor faults are detected by monitoring the current and proposed fine-tuned vibration frequency method. The stator short circuit fault, broken rotor bar fault, air gap eccentricity, and bearing fault are the common faults that occur in an induction motor. The detection process of the proposed method is based on sidebands around the supply frequency in the stator current signal and vibration. Moreover, it is very challenging to diagnose the problem that occur due to the complex electromagnetic and mechanical characteristics of an induction motor with vibration measures. The design of an accurate model to measure vibration and stator current is analyzed in this research article. The proposed method is showing how efficiently the root cause of the problem can be diagnosed by using the combination of current and vibration monitoring method. The proposed model is developed for induction motor and its circuit environment in MATLAB is verified to perform an accurate detection and diagnosis of motor fault parameters. All stator faults are turned to turn fault; further, the rotor-broken bar and eccentricity are structured in each test. The output response (torque and stator current) is simulated by using a modified winding procedure (MWP) approach by tuning the winding geometrical parameter. The proposed model in MATLAB Simulink environment is highly symmetrical, which can easily detect the signal component in fault frequencies that occur due to a slight variation and improper motor installation. Finally, this research article compares the other existing methods with proposed method.

Performing Analysis of Current Transformer in Short Circuit and Open Circuit Conditions By ANSYS@Maxwell

Calculation of the design parameters of current transformers (CTs) is very complex due to their magnetic and thermal properties, complexity of their structure, different ferromagnetic properties of the materials and the nonlinearity of the B-H curve of the core material. The secondary output of these transformers is used for both measurement and protection circuits. Therefore, AT's accuracy must be very good and precise. In this study, the transformer is modeled as 2D using the Finite Element Method (FEM). ANSYS@Maxwell program, which realizes a solution based on finite element method, has been used in magnetic and thermal analysis of the current transformer. Analyzes of the transformer were carried out in 2D under open and short circuit conditions. From the results obtained from the analysis, the scattered electromagnetic flux distribution occurred in the core of the current transformer, which caused the secondary current of the CT to be erroneous. Therefore, it has been observed that unwanted operating conditions occur in the protection circuits..

Single Input Single Output Two Level Isolated Dc-Dc Converter With Secondary Side Phase Shifting For Solar Applications

The isolated dc–dc converters with primary-side phase shifting (PPS) provides severely narrow soft-switching range for main devices in the primary side leg of full bridge converter. The leakage inductance of the high frequency transformer should be large enough for providing the energy needed for soft switching operations and also the idling power loss due to circulating current in the converter legs under large phase-shift angle, which makes reduction of conversion efficiency and complicated in designing the parameters of transformer. Furthermore, the turn-off diode commutations in the output-side rectifier are performed by hard-switching mode. To overcome all these drawbacks, a secondary side phase shifting (SPS) technique has been developed for two-level isolated DC-DC converter. This scheme provides wider soft switching range and reduced power loss due to elimination of circulating current in the primary side of high frequency transformer. In addition, SPS control also provide no reverse recovery current in diodes and hence no power losses in the secondary rectifier circuit. The control switches operate under soft switching even under rated load and short circuit conditions.

A Novel Fault Diagnosis Technique of Interturn Short-Circuit Fault for SRM in Current Chopper Mode

The interturn short-circuit fault of stator winding is a common failure mode in switched reluctance motors (SRMs), which can severely harm the operation of the motor. In this article, a novel method for diagnosing the interturn short-circuit fault in the current chopping mode is proposed, which is suitable for online monitoring and protection of SRMs. The proposed method achieves a fast response and high sensitivity and can mitigate the interference of load conditions on detection reliability. Moreover, this method is based on phase currents, which does not require additional sensor or detection circuits. Meanwhile, the effects of interturn fault location in the stator winding on the motor flux and motor parameters are analyzed in detail through finite-element analysis, which is helpful to establish a reliable diagnostics technique for various fault conditions. Experimentations based on an 8/6 four-phase SRM with special windings designed to simulate interturn short circuit conditions are conducted, and the results have verified the effectiveness of the proposed method.

Lead-free tin perovskite solar cells

Summary The development of efficient and stable lead-free perovskite solar cells (PSCs) is crucial for addressing the concern of environmental pollution from the toxic element lead. In recent years, tin PSCs have emerged as a promising candidate for high-performance, eco-friendly photovoltaic technology with a high certified power conversion efficiency (PCE) of more than 11%, indicating a great potential for future applications. Here, we review the recent efficiency progress of tin PSCs based on the equivalent circuit model of solar cells. We then discuss approaches toward efficiency improvement from the device viewpoint, such as optimizing the band gap, increasing the light-harvesting efficiency and carrier diffusion length, surface passivation, and regulating the interface energy-level alignment. Finally, we point out the possibility of reaching 20% PCE for tin PSCs and issues regarding enlarging the cell size and realizing scalable production in the future. We expect that these perspectives will be helpful for accelerating the commercialization of tin PSCs.

Short circuit detection and driving control with no blanking time for high voltage high power insulated gate bipolar transistors

Insulated gate bipolar transistors (IGBT) short-circuit (SC) protection is one of the most important protection methods for IGBT converter equipment. The fast detection and protection response time could reduce the permanent damage of devices, and extend their use life cycle. At present, the collector emitter voltage vce desaturation method is widely used in the commercial IGBT drive circuit, which has blanking time of fault detection and protection. In this paper, an improved adaptive vce SC detection and protection is proposed to realize the blanking time adjustment under different SC conditions. By the determination of the di/dt characteristics of the current variation on the parasitic inductance between the power emitter and the Kelvin emitter of IGBT modules, the execution time of the two detection methods can be set. According to the switch process and the SC type, the corresponding logic processing will be carried out to realize the fast detection of different SC conditions. The circuit scheme without blanking time detection and protection is designed, and the circuit is modelled and simulated by Pspice. The IGBT driving circuit SC test without blanking time detection and soft turn-off protection has been carried out. Simulation and test results can verify the feasibility of the proposed circuit.

Discriminative common vector in sufficient data Case: A fault detection and classification application on photovoltaic arrays

In this study, the derivation of the Discriminative Common Vector (DCV) approach which is first introduced for a face recognition task in the insufficient data case, for the sufficient data case is obtained and it is applied for a photovoltaic (PV) panel fault detection and classification. Two experimental studies are performed including two different fault configurations. In the first experimental study, as the faulty conditions open-circuit, short-circuit, and partial shading conditions are taken and healthy condition is taken as reference. Thus, a four-class fault detection and classification scheme is constructed. In the second experimental study, the serial resistance degradation fault is considered. This fault detection and classification scheme includes four classes that are healthy and three different serial resistance degradation. The data used in the experimental studies are formed to be 1x3 dimensional vectors which include the current, voltage, and power values obtained from the simulations in the PSIM program. In all two experimental studies for each class, a discriminative common vector (DCV) which represents the common properties of that class, thus, having a high discriminative ability is obtained. As a contribution to the literature, the derivation of DCVA which has high discrimination ability for sufficient data case, and usage of it for PV panels fault detection and classification is proposed for the first time in this study. The proposed method's performance is evaluated with the performance of PCA method that is recently used for the fault detection and classification problem in PV panel systems in the literature. In the first experimental study, the proposed method's performance (99%) is obtained significantly higher than the performance of the PCA method (95%). And in the second experimental study, while PCA can only detect the faulty condition but cannot classify the serial resistance degradation, the proposed method can both detect and classify with 99% accuracy the PV panel serial resistance degradation.

New Method of Detection, Identification, and Elimination of Photovoltaic System Faults in Real Time Based on the Adaptive Neuro-Fuzzy System

This article proposes an adaptive neuro-fuzzy system (ANFIS)-based method to detect, identify, and eliminate defects/faults in a photovoltaic (PV) system. The control is conducted using two tests. The first test measures the difference between the power estimated by the ANFIS and the real power of the generator. This test detects defects and isolates the affected branch using controlled switching devices to prevent shutting down the entire power supply by disconnecting the inverter. The second test measures the consistency between the real current and voltage of the generator and the short-circuit current and open-circuit voltage estimated by the ANFIS, to identify open-circuit and short-circuit conditions. Each system has its own dedicated irradiation and ambient temperature sensors whose positions differ to avoid the influence of faults overlap. The method was studied through simulation using MATLAB Simulink and experimentally validated via panels of different power ratings and technological makeup that are more than five years old, utilizing a DS1104 dSPACE controller board. The technique overcomes the limitations of existing methods that are based on comparisons between the estimated and measured variables as the discrepancy between real and simulated behavior; system change because of environment, topology, or age; and the need for frequent intelligent system updates as it does not rely on real data for learning. Additionally, this method includes an aging analysis, and it can be used to control most typical PV installations via a gain factor—the ratio of the new value to the learn value.

Accurate modeling and simulation of solar photovoltaic panels with simulink-MATLAB

A unique procedure to model and simulate a 36-cell-50 W solar panel using analytical methods has been developed. The generalized expression of solar cell equivalent circuit was validated and implemented, making no influential assumptions, under Simulink/MATLAB R2020a environment. The approach is based on extracting all the needed parameters by exploiting the available parameters from the data sheets of commercial PV panels and by estimating the slopes at both short-circuit and open-circuit conditions of the current–voltage characteristic, usually provided by most solar panels manufacturers under standard test conditions (STC). The effects of solar irradiance and temperature were both considered in the modeling. A system of coupled nonlinear simultaneous equations for diode saturation current, diode ideality factor, and series and shunt resistances has been solved. To accurately model the PV module used in our simulation and analysis, the needed temperature- dependent parameters have been extracted for the first time. At STC irradiance of 1000 W/m2, the modeled I-V curve was found identical to the experimental one which is provided by the solar panel manufacturer. The maximum power output of the PV module increases from 8.75 W to 50 W when irradiance varies from 200 W/m2 to 1000 W/m2 at STC temperature. At temperatures higher than STC and for the same solar irradiance, the power output of the PV module came down about 14.5% only when the operating temperature reached a value of 65 °C. However, as temperature is below STC, the power output went up of about 7.4% beyond the maximum power of the rated PV panel. The calculated power temperature coefficient was about −0.39%/ oC which is quite close to the one provided by the solar panel manufacturer.

Initial Results of an Extensive, Long-Term Study of the Forecasting of Voltage Sags

This paper presents the preliminary results of our research activity aimed at forecasting the number of voltage sags in distribution networks. The final goal of the research is to develop proper algorithms that the network operators could use to forecast how many voltage sags will occur at a given site. The availability of four years of measurements at Italian Medium Voltage (MV) networks allowed the statistical analyses of the sample voltage sags without performing model-based simulations of the electric systems in short-circuit conditions. The challenge we faced was to overcome the barrier of the extremely long measurement times that are considered mandatory to obtain a forecast with adequate confidence. The method we have presented uses the random variable time to next event to characterize the statistics of the voltage sags instead of the variable number of sags, which usually is expressed on an annual basis. The choice of this variable allows the use of a large data set, even if only a few years of measurements are available. The statistical characterization of the measured voltage sags by the variable time to next event requires preliminary data-conditioning steps, since the voltage sags that are measured can be divided in two main categories, i.e., rare voltage sags and clusters of voltage sags. Only the rare voltage sags meet the conditions of a Poisson process, and they can be used to forecast the performance that can be expected in the future. However, the clusters do not have the characteristics of memoryless events because they are sequential, time-dependent phenomena the occurrences of which are due to exogenic factors, such as rain, lightning strikes, wind, and other adverse weather conditions. In this paper, we show that filtering the clusters out from all the measured sags is crucial for making successful forecast. In addition, we show that a filter, equal for all of the nodes of the system, represents the origin of the most important critical aspects in the successive steps of the forecasting method. In the paper, we also provide a means of tracking the main problems that are encountered. The initial results encouraged the future development of new efficient techniques of filtering on a site-by-site basis to eliminate the clusters.

Optimal coordination of overcurrent relays with constraining communication links using DE–GA algorithm

Dynamic changes in the network can occur due to short-circuit conditions, the maloperation of the relays, development, operation, and repairs on any part of the power system. Also, most of the new protective schemes are based on a communication channel, which cannot be guaranteed in practice. In other words, the communication channels are operating with high load and therefore become more vulnerable when the power grid is in contingent conditions. Thus, relying on the communication channel for decision making may not be the optimal solution for protective relays, although it might be beneficial to have information exchange. In this article, a novel protective logic is proposed based on phasor measurement units (PMUs) data for optimal coordination of overcurrent relays. PMUs measure the positive sequence voltage at two substations separated by hundreds of miles which are synchronized precisely with the aid of a GPS satellite system. The precise time-tags are attached with samples, and this information is exchanged over communication channels and collected by control centers and/or substations. By extracting the relevant information from these measurements, phasor information can be obtained at any node where PMUs are installed in the power grid. This can be used to do more accurate state estimation, control, and protection. In these relays, besides current and voltage, phasor information has become an important measurement in decision making. The proposed method is tested on the IEEE 8-bus and 14-bus standard network.

量子阱带间跃迁探测器基础研究（特邀）

Recently, the anomalous carrier transport in the quantum wells with the PN junction structures has been found experimentally, and the corresponding physical mechanism and the carrier transport model have been proposed. It is observed that the open circuit voltage or short-circuit current can be measured in the resonant excitation mode. Comparing the photoluminescence (PL) spectra of the two kinds of external circuits, it is found that the PL intensity decreased significantly under the short circuit condition. This suggests that the photogenerated carriers under the short circuit condition are not confined in the quantum well, but escaping from the junction region. However, this phenomenon of photocarriers escaping from the quantum wells is not found in the NN-type quantum well structure. Therefore, the effect of thermal excitation or tunneling is excluded to drive the carrier escaping from the quantum well. Based on this, the corresponding physical mechanism and carrier transport model are proposed. It is concluded that photogenerated carriers can escape from the quantum well directly under the built-in electric field of PN junction, and the radiative recombination luminescence occurs after the carrier escape process.

Application of combined gas chromatography and dielectric spectroscopy in SF6 gas insulated high voltage converter transformer bushing insulation performance

High voltage converter transformer bushing is widely used in the outlet part of high-end converter transformer, and its operation safety and stability directly determine the operation effect of converter transformer. The bushing of SF6 gas insulated high voltage converter transformer is a typical multi-media insulation structure. The air end of the bushing includes SF6 gas insulation medium, and the bushing tail is in contact with transformer oil. The bushing body is generally epoxy impregnated paper composite insulation structure. For the complex insulation system, the running state of converter transformer bushing should be monitored in real time. For gas phase insulation, gas chromatography is generally used to dynamically analyze the composition of SF6 gas; for epoxy impregnated paper solid insulation, dielectric spectrum technology is generally used to analyze its wide frequency domain dielectric characteristics. Therefore, the combination of gas chromatography and dielectric spectroscopy technology can effectively characterize the insulation performance of SF6 gas insulated high-voltage converter bushing. In view of this, this paper first gives the basic theory of frequency domain dielectric spectroscopy technology and gas chromatography technology, and further analyzes the current carrying and heating conditions of the central conductor of high-voltage converter bushing under overload and short-circuit conditions. The dielectric spectrum characteristics of the converter bushing core under different temperature conditions are obtained by experiment, and the Cole-Cole model is used for fitting analysis. The decomposition characteristics of SF6 insulation gas in epoxy resin composite insulator under overload and short-circuit conditions are analyzed experimentally, and the variation curve of SF6 characteristic decomposition gas with time is obtained. Combined with the above relationship between gas chromatography and dielectric spectrum, an operational evaluation strategy for the performance of SF6 gas insulated high voltage converter bushing is proposed. In this paper, for the first time, the internal insulation performance of high-voltage converter bushing is comprehensively evaluated by gas chromatography and dielectric spectrum analysis technology for the first time, which has certain theoretical and practical application value for the operation, maintenance and overhaul of converter bushing.

On the Solution of Equilibrium Points of Power Systems With Penetration of Power Electronics Considering Converter Limitation

Increasing penetration of power electronics is changing the understanding of modern power systems. In particular, current saturation of converters leads to multiple equilibrium points for both normal and short-circuit conditions. This paper aims to identify equilibrium points in power systems with penetration of power electronics. First, a steady-state model of power systems considering the power electronics operation is presented. Then, a general methodology is developed to obtain equilibrium points including all possible combinations of converter current saturation states. A system of equations is defined for each combination and is solved considering the possibility to have single or multiple solutions. This methodology is suitable for steady-state analysis in normal operation and during short-circuit scenarios. Test systems with Voltage Source Converters are used to validate the presented methodology.

Analysis of vibration forces of magnetic origin acting on tank walls of power transformer

The aim of this paper is to present the impact of the leakage flux on magnetic shunts and tank walls of power transformers from vibrational point of view. The experimental studies of the large power transformers show that tank vibrations and the resulting acoustic emission at load condition are significantly higher than at no-load condition. The paper presents 3D finite elements model in electromagnetic domain used for the analysis of magnetic forces applied to shunts at rated short circuit state which are the origin of tank vibration. The main finding of the work is that forces equivalent to the magnetostriction deformation of the shunt interior are comparable with magnetic forces resulting from the stray field and applied to the shunts’ surface.