Reduction Of Short Circuit Current Research Articles

Charge transport in quantum dot organic solar cells with Si quantum dots sandwiched between poly(3-hexylthiophene) (P3HT) absorber and bathocuproine (BCP) transport layers

We have modeled a multilayer quantum dot organic solar cell that explores the current-voltage characteristic of the solar cell whose characteristics can be tuned by varying the fabrication parameters of the quantum dots (QDs). The modeled device consists of a hole transport layer (HTL) which doubles up as photon absorbing layer, several quantum dot layers, and an electron transport layer (ETL). The conduction of charge carriers in HTL and ETL has been modeled by the drift-diffusion transport mechanism. The conduction and recombination in the quantum dot layers are described by a system of coupled rate equations incorporating tunneling and bimolecular recombination. Analysis of QD-solar cells shows improved device performance compared to the similar bilayer and trilayer device structures without QDs. Keeping other design parameters constant, solar cell characteristics can be controlled by the quantum dot layers. Bimolecular recombination coefficient of quantum dots is a prime factor which controls the open circuit voltage (VOC) without any significant reduction in short circuit current (JSC).

Short‐circuit current reduction techniques of the doubly‐fed induction generator based wind turbines for fault ride through enhancement

Grid voltage disturbances result in high magnitudes of rotor currents and DC-link voltage of the doubly-fed induction generator based wind turbines (DFIG-WTs), which may lead under severe fault conditions into deactivation of the machine side converter (MSC) and violation of the fault ride through (FRT) requirements of the grid codes. In this essence, several solutions were proposed, which vary between installing extra hardware components and control modification. However, the extra costs as well as the control limitations degrade the feasibility of the proposed solutions. In this study, new techniques are proposed to enhance the FRT through peak short-circuit current reduction of the DFIG-WT. The new techniques are developed based on the open-loop and close-loop dynamic response of the DFIG. The new techniques utilise the available MSC voltage, in order not to violate the voltage limits, to increase the rate of change of the DFIG internal transient voltage and to increase the magnitude of the transient impedance. Additionally, the mean variance mapping optimisation is used to optimally tune the gains in the second two techniques. The new techniques were implemented in a manufacturer-based simulation model, and the simulation results show their effectiveness, where the maximum peak current reduction achieved was 23.6%.

A read disturbance free differential read SRAM cell for low power and reliable cache in embedded processor

Energy consumption and data stability are vital requirement of cache in embedded processor. SRAM is a natural choice for cache memory owing to their speed and energy efficiency. Noise insertion to the SRAM cell during read is a serious problem which reduces its stability. A read disturbance free differential SRAM cell consisting of seven transistors is proposed here which increases cell stability along with maintaining the most desirable differential read technique for faster read. The read SNM of the proposed cell is 154%, 31% and 58% large than that of the conventional 6T-SRAM cell and 2 other 7T-SRAM cells [5,6] compared here. Various factors such as short circuit current reduction, use of single write access transistor, partial bit line swing etc. reduces the overall energy consumption of the proposed cell by 41% compared to 6T-SRAM cell. The proposed cell is also compared with an eight transistor based read disturbance free SRAM cell. The cell delay of the proposed cell is around 55% lesser than that of the 8T-SRAM cell. Besides CMOS the performance achievement of the proposed 7T-SRAM cell is also validated at miniaturized dimension of 20nm using FinFET based predictive technology model library.

Current Starving the SRAM Cell: A Strategy to Improve Cell Stability and Power

In SRAM cell design, the energy consumption and cell stability are the major performance indices which need to be improved. Several techniques reported earlier attempt to improve either of the stability or the energy consumption. In this paper, a scheme is proposed which uses current starving on conventional SRAM cell to improve cell stability and also to reduce energy consumption. Unlike separating the read and write port of the SRAM cell in most of the techniques proposed earlier, this technique results more ideal voltage transfer characteristic of the cross-coupled inverter leading to larger noise margin. It also reduces the dynamic energy consumption through short circuit current reduction during state transition. The proposed technique is compared with NC-SRAM [3], IWLVC-SRAM [18], 10T-SRAM [16] and a conventional 6T-SRAM cell. The read and retention stability of the current starving SRAM (CS-SRAM) cell increases by 31 and 41%, respectively, with respect to the 6T-RAM cell. These two SNMs are also significantly higher than the other compared cells. The proposed technique consumes 22% lesser energy in comparison with the 6T-SRAM. The energy consumption is also reduced in comparison with the other compared cells. The compared cells are designed both in CMOS process and in FinFET technology (20 nm PTM library). The performance enhancement of the proposed cell maintains same trend in both technologies.

GA-based multi-objective optimization for distributed generations planning with DLMs in distribution power systems

In the present scenario of all over world, the planning of distributed generations (DGs) in distribution power systems are very important issues from power system performances viewpoints. The broad categories of different types of DGs on the basis of their power delivering characteristics are considered T1, T2, T3 and T4 with different load models (DLMs) for the analysis in this paper. This paper presents the impact assessment of optimally placed different types of DGs (such as T1, T2, T3 and T4) with DLMs by employing genetic algorithm (GA) in the distribution power systems (DPSs) form total minimum real power loss of the system viewpoint. Different DPS performance parameters such as minimization of real power loss, minimization of reactive power loss, improvement of voltage profile, reduction of the short circuit current or MVA line capacity and reduction of the environmental green house gases like carbon dioxide (CO2), sulphur dioxide (SO2), nitrogen oxide (NOx) and particulate matters in emergency e.g. under fault, sudden change in field excitation of alternators or load increase in the distribution power system are considered. The contribution of the present work is to investigate the comparisons of different DGs with DLMs by excercizing GA in the distribution systems form minimum total real power loss of the system viewpoint. The effectiveness of the proposed methodology is tested on IEEE-37 bus distribution test system. The different types of DGs (such as T1, T2, T3 and T4) with DLMs have shown different behaviours for power system performance indices such as PLI, QLI, VDI, SCCI and EIRI viewpoints. The sequence of overall power system performance indices such as PLI, QLI, VDI, SCCI and EIRI are as follows: T2>T1>T4>T3. This paper presents that the overall performance of T2 type DG is better as compared to T1, T3 and T4 types DGs in the distribution system form minimum real power loss of the system viewpoint.

Photodegradation of Metal Oxide Interlayers in Polymer Solar Cells

The effect of 1 sun illumination for 24 h on encapsulated inverted organic photovoltaic devices is studied through a series of electrical and optical characterizations for donor/acceptor polymer solar cells based on poly(dithienogermole‐alt‐thienopyrrolodione)/[6,6]‐phenyl C71 butyric acid methyl ester blends. Power conversion efficiency is significantly reduced after light exposure due to a 45% drop in the device fill factor and a 40% drop in both the open circuit voltage and short circuit current. The decrease in open circuit voltage is attributed to a reduction in the built‐in field in the device due to photodegradation of the ZnO interlayer. The reduction in fill factor and short circuit current is shown to be due to the formation of an extraction barrier for hole collection as a result of photodegradation of the MoOx interlayer. Using a 400 nm long pass filter to block the UV light, device stability is significantly enhanced, resulting in a decrease in power conversion efficiency of less than 5% under the same operation conditions.

Radiation‐Hard and Ultralightweight Polycrystalline Cadmium Telluride Thin‐Film Solar Cells for Space Applications

AbstractAchieving high‐specific‐power and radiation hardness of solar cells is of great importance to perform tasks and achieve duration in space. Therefore, we investigated the proton irradiation resistance of ultralightweight CdS/CdTe thin film solar cells having high specific power values. High‐energy proton beams (15 MeV) with doses ranging from 1×1012 to 1×1015 cm−2 were used, equivalent to more than 2000 years in low Earth orbit. Although 70 % decrease in cell conversion efficiency was observed after proton irradiation with dose of 1×1015 cm−2, it still maintained the photovoltaic performance. The specific power of the fabricated cell decreased from 358 W kg−1 to 109 W kg−1 after proton irradiation (dose=1×1015 cm−2), which is still comparable to specific powers of other types of solar cells. Our work indicated that reduction of short circuit current is a major factor of deterioration of the cell performance under the high energy proton irradiation. This work revealed that our lightweight CdS/CdTe solar cells have significant potential for the use in space applications: reduction of launch cost by achieving high specific power and assurance of durability over prolonged space missions.

An improved energy efficient SRAM cell for access over a wide frequency range

Leakage current contribution to the power consumption cannot be ignored in the sub-100nm technology. Drastic reduction of channel length of the modern highly scaled device enhances the leakage current significantly. Two novel 8T-SRAM cells low-leakage-current SRAM cell (LLC-SRAM cell) and low-leakage-current high-threshold-voltage SRAM cell (LLC-HVT SRAM cell) are proposed to offer high energy efficiency. The cell performances are compared with 8T NC-SRAM cell and 6T-SRAM cell. The proposed cells significantly reduce the overall power consumption. The cell array simulations are performed in spectre with a general purpose 45nm technology library. The short-circuit current reduction during state transition helps to decrease the dynamic power consumption. In standby mode the cell operates at a voltage lower than the supply which brings down the leakage current and hence leakage power. Besides the energy prospective the stability, speed and writ-ability analysis are also performed in this work.

A numerical study on the influence of interface recombination on performance of carbon nanotube/GaAs solar cells

Carbon nanotubes (CNT) have unique electronic properties and remarkable optical properties. Despite of on layer thickness of CNTs, it has able to absorb photons from visible to far infrared and terahertz. These unique properties lets to create heterojunction devices by semiconductor/CNTs or metal/CNTs junctions e.g. photodiodes, sensor and heterojunction solar cell. The CNTs can play the role of a heterojunction component for charge separation as a high conductive network for charge transport and as a transparent electrode for light illumination and charge collection. The main objective of the present article is to establish a relation between interface recombination and the characteristics parameters of the heterojunction solar cell based on armchair single walled carbon nanotube as absorber and GaAs as window. It is shown that by increasing the interface recombination open circuit voltage decreases dramatically. Depletion current, J–V characteristic and ideality factor variation in terms of interface recombination has been calculated. Interface recombination at the SWCNT/GaAs interface of the cell leads to a considerable drop of the cell voltage and to a lesser extent to the associated reduction in the cell short circuit current.

Multi objective optimal allocation of fault current limiters in power system

Transmission systems, connection of distributed generation to the grid are increased due to increase in power demands. This fact causes the increase in short circuit level of power networks. The occurrence of fault in such networks leads to large short circuit currents throughout the system, which may exceed the rating of existing circuit breakers and can damage system equipment. There are some approaches to reduce this fault current such as power network reinforcement and utilization of fault current limiter (FCLs) in power systems. Power system reinforcement is too difficult if not impractical. Therefore, the utilization of FCLs can provide an effective way to suppress fault currents. The effectiveness of FCL depends on the number of FCLs and their installation location. In this paper, a novel approach is presented to determine the optimal number and location of FCLs to improve the power network reliability and fault current reduction based on different conflicting objective functions. IEEE 39 BUS system and IEEE 57 BUS system are considered to evaluate the effectiveness and feasibility of the proposed method. The objective functions considered for the optimal allocation are reliability of power system, economic impact and short circuit current reduction. Unlike what has been previously done in literature, in this paper Pareto based optimization algorithms, namely non-dominated sorting algorithm, multiobjective particle swarm optimization and multiobjective evolutionary algorithm based on decomposition, are utilized to deal with this problem. The use of these methods made it possible to obtain the Pareto optimal front in which these objective functions are optimized simultaneously.

Genetic algorithm optimized impact assessment of optimally placed DGs and FACTS controller with different load models from minimum total real power loss viewpoint

This paper presents the impact assessment of optimally placed different distributed generations (DGs) with different load models (DLMs) (such as DG-1, DG-2, DG-3 and DG-4) and flexible alternating current transmission system (FACTS) controller like static VAR compensator (SVC) by employing genetic algorithm (GA) in a distribution power systems (DPSs) from minimum total real power loss viewpoint. Different DPS performance indices such as minimization of real power loss, minimization of the reactive power loss, improvement of the voltage profile, reduction of the short circuit current or MVA line capacity and reduction of the environmental greenhouse gases like carbon dioxide (CO2), sulphur dioxide (SO2), nitrogen oxide (NOx) and particulate matters in an emergency e.g. under fault, sudden change in field excitation of alternators or load increase in DPSs are considered. A comparison among different DGs with DLMs (such as DG-1, DG-2, DG-3 and DG-4) and FACTS controller like SVC is presented in this paper by employing GA. The effectiveness of the proposed methodology is tested on IEEE 37-bus distribution test system (38-node system). This paper clarifies the fact that, among the four types of DGs considered, DG-2 and DG-4 types of DGs at different operating power factors and FACTS controller like SVC offer better DPS performance indices when power factors varies from 0.80 to 0.99 leading and lagging, respectively. It is revealed that DG-2 type DG and SVC gives better DPS performance indices as compared to DG-1, DG-3 and DG-4 types DGs with DLMs and SVC. It is observed that DG-2 with SVC is more reliable and efficient as compared to the rest types of DG like DG-1, DG-3and DG-4 with SVC.

A novel evaluation method of societal benefits of ultra high voltage power grid optimizing power energy allocation

Although Ultra High Voltage (UHV) power grid requires heavy investment, it can also produce vast social economic benefits by optimizing power energy allocation. Owing to the existing controversy over the economy of the UHV power grid, it is necessary for policymakers to propose a scientific method used to comprehensively analyze huge costs and benefits caused by the UHV power grid. In this paper, Life Cycle Cost (LCC) is introduced to analyze cost dimensions of the UHV power grid and shadow price theory is used to evaluate huge potential social benefits brought by UHV power grid. Based on these shadow prices, social benefits of UHV power grid are put forward from aspects of saving installation benefit, saving coal-fired benefit, power loss reduction benefit, short-circuit current reduction benefit, sustainable development benefit, and social resource distribution optimization benefit. Some evaluation indexes for social benefits based on input-output analysis table of the LCC mode are calculated to be comparable with those of the traditional cost mode. A certain UHV power grid of China is applied to verify the effectiveness and feasibility of the proposed evaluation method.

Thickness-modulated InGaAs/GaAsP superlattice solar cells on vicinal substrates

InGaAs/GaAsP superlattice (SL) is a promising narrow-gap material for III–V multi-junction solar cells on Ge. In metal-organic vapor phase epitaxy (MOVPE) of SL on vicinal substrates, the component layers tend to be undulated due to step bunching occurring at high temperature. In this paper, the effects of growth temperature and thickness modulation of the SL-region on the photovoltaic performance were investigated. Lowering the growth temperature successfully enabled epitaxy of an extremely uniform SL, from which a clear step-like absorption spectrum including sharp exciton peaks was obtained due to layer-by-layer deposition of the individual layers. Larger layer undulation at higher temperature led to poorer in-plane coverage of the InGaAs region, resulting in the reduction of both light absorption and short circuit current. The open circuit voltage, on the other hand, was higher for the cells grown at higher temperature owing to suppressed dark current as a result of reduced crystal defects. Moreover, the lateral thickness variation of the GaAsP barriers in the undulated SL allowed efficient tunnel transport through the thinner part of the barrier, and improved the carrier collection and the fill factor. By optimizing the growth temperature for SL on vicinal substrates, an N-on-P cell including 100-period SL with a bandgap of 1.21 eV achieved 1.11 times higher efficiency than a GaAs reference cell with 36% current enhancement as middle cell performance.

DEGRADATION OF THREE–JUNCTION AMORPHOUS SI : H BASED SOLAR CELLS

The operating experience of hydrogenated amorphous silicon (a−Si : H) based solar cells has shown that besides their low efficiency this type of photovoltaics degrade much faster compared to single crystal based solar cells. As far as the processes deter- mining the degradation of amorphous materials based solar cells are not well studied, and the degradation of similar cells without light exposure has also been reported, we conducted an experiment to compare the temporal change characteristics of main solar cell parameters in darkness and under natural light. The demonstration of short circuit current reduction in darkness aged solar cells should be considered as one of the most interesting results of the work. Moreover we have shown that the change of this parameter is on average the same for the illuminated cells, while for some cells short circuit current reduction is substantially higher. This is indicative of the fact that the observed effect is not related to the Staebler—Wronski effect.

Machine design and control strategy for wide-speed-range PMSG systems

Purpose – The purpose of this paper is to focus on the machine design and control strategy of the permanent magnet synchronous generator (PMSG) system, especially utilized in variable speed applications, in order to stabilize the output voltage on the dc link over a wide speed range. Design/methodology/approach – Different ac/dc power converter topologies are comparatively studied, each with an accordingly designed PMSG, so as to investigate the influence of the armature winding inductance as well as the relationship between the PMSG and power converter topologies. Findings – Pulse width modulation (PWM) rectifier is preferable for the said application due to its good performance and controllability. Moreover, by employing the PWM rectifier, relatively large inductance of the PMSG is considered for both short-circuit current reduction and field regulation. Originality/value – Field-regulating control is realized with a space vector PWM (SVPWM) rectifier, which can weaken the PMSG magnetic field during high-speed operation, while even properly enhance the field at low speed, ensuring a small change of the PMSG output voltage and a stable dc voltage.

High Speed Level Converters With Short Circuit Current Reduction

The level converter is used as interface between low voltages to high voltage boundary. The efficient level converter has less power consumption and less delay are the design considerations of the level shifter. In this paper two new CMOS level converters are presented with high driving capability with low propagation delay. The proposed level converters are simulated using Cadence software with 0.18 µm CMOS technology. The simulation result shows that the proposed circuits have less propagation delay than the existing ones. The circuits are simulated for different load capacitor values and different voltages. The proposed level converters operate for different input pulse signal amplitude values are +0.8 V, +1 V, +1.2 V and V DDH values of +1.8 V and +3.3 V .

Reliability evaluation of power systems with high short-circuit current reduction

Similar to other cities worldwide, the increasing amounts of short-circuit current in Bangkok (Thailand) and the vicinity areas are becoming higher than the interrupting capacity (IC) of circuit breakers. To cope with the problem, the Electricity Generating Authority of Thailand (EGAT) has come up with the solutions of network reconfiguration, e.g. bus splitting and transmission line disconnecting. These solutions help reduce effectively the amounts of short-circuit currents by increasing the equivalent system impedance. However, bus splitting and transmission line disconnecting tend to decrease the system reliability. One of the alternative approaches, the installation of high-voltage direct current (HVDC) can help reduce the amounts of short-circuit currents, while the system reliability is maintained. Therefore, this paper mainly presents the reliability evaluation method of the systems with HVDC installation, which requires AC/DC power flow calculation. To avoid system constraint violation, generation redispatch, load shedding, and DC power flow control are executed. The Monte Carlo simulation is used to repeatedly evaluate the system reliability until convergence. The proposed method is tested in (i) the IEEE Reliability Test System 79 (RTS79) to confirm the correctness of reliability evaluation and (ii) the system of EGAT Bangkok including its vicinity areas to show the readiness for real implementation. Comparison of reliability indices among all solutions of short-circuit current reduction is presented and discussed. The results show that the proposed method is effective and the HVDC installation can increase the system reliability, depending on its installation location and capacity. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Influence on functional parameters of intestinal tract induced by short-term exposure to fumonisins contaminated corn chyme samples

The gut is a possible target toward mycotoxin fumonisins (FBs) exposure. The study aims to investigate the effects induced by FBs contaminated-corn chyme samples on functional parameters of human and rat intestine by using Ussing chamber. Fumonisins-contaminated corn and processed corn samples were undergone to in vitro digestion process and then added to luminal side. A reduction (about 90%) of short circuit current (Isc μA/cm2) during exposure of human colon tissues to fumonisins-free corn chyme samples was observed, probably related to increased chyme osmolality. This hyperosmotic stress could drain water towards the luminal compartment, modifying Na+ and Cl− transports. The presence of FBs in corn chyme samples, independently to their concentration, did not affect significantly the Isc, probably related to their interference towards epithelial Na+ transport, as assessed by using a specific inhibitor (Amiloride). The rat colon tract represents a more accessible model to study FBs toxicity showing a similar functional response to human. In the rat small intestine a significant reduction (about 15%) of Isc parameter during exposure to uncontaminated or FBs contaminated corn chyme samples was observed; therefore such model was not suitable to assess the FBs toxicity, probably because the prevalent glucose and amino acids electrogenic absorption overwhelmed the FBs influence on ionic transport.

Photodegradation in Encapsulated Silole‐Based Polymer: PCBM Solar Cells Investigated using Transient Absorption Spectroscopy and Charge Extraction Measurements

AbstractLight induced degradation has been observed in the performance of organic solar cells in the absence of oxygen and a detailed analysis of the effect of this photodegradation on optical and electrical features has been accomplished. This photodegradation study has been performed on encapsulated photovoltaic blend devices comprised of the silole‐based donor–acceptor polymer KP115 blended with [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM). Photodegradation induces an almost 20% decrease in power conversion efficiency, primarily as a result of a reduction in short circuit current, JSC. The initial burn‐in phase of the photodegradation has been examined using a combination of transient absorption spectroscopy and charge extraction measurements, including photo‐CELIV (charge extraction by linearly increasing voltage) and time‐resolved charge extraction using a nanosecond switch. These measurements reveal a bimodal KP115 polaron population, comprised of both delocalised and localised/trapped charge carriers. The photodegradation results are consistent with an alteration of this bimodal KP115 polaron population, with the polarons becoming trapped in a broader, deeper density of localised states. Under laser illumination and at open circuit conditions, this enhanced trapping after light soaking inhibits charges from undergoing bimolecular recombination, leading to higher extracted charge densities at long times. At the lower charge densities operating at short circuit conditions and under continuous white light illumination, where bimolecular recombination is much less significant, the JSC decreases after light soaking due to a reduction in the efficiency of trapped charge carrier extraction.

Thermal endurance study of polymers used in low concentration photovoltaic modules

Thermal endurance studies were performed on the major polymeric components used in a Low concentration photovoltaic (LCPV) module using a thermal gravimetric analysis (TGA) method. Activation energy of the various polymers was obtained, and lifetimes were predicted based on the assumption of 5% weight loss for 30 years. Oven aging was used to verify the TGA thermal endurance prediction. Reasonable agreement between TGA prediction and oven baking results were reached, with the exception of ethylene-vinyl acetate (EVA) encapsulant that demonstrated a second-order reaction inconsistent with TGA assumptions. As a result, a more LCPV-relevant way to characterize the degradation of EVA was developed and demonstrated a linear relationship between PV device short-circuit current degradation and yellowness index. For the purpose of this EVA degradation analysis, a 20% reduction in PV device short circuit current was selected as the failure criteria.