Power sharing and control strategy for provisionally coupled microgrid clusters through an isolated power exchange network

The two common mechanisms of load-shedding and renewable curtailment can prevent provisional overloading and excessive generation and the subsequent unacceptable voltage and frequency deviation in standalone microgrids (MGs), which makes MGs less resilient and reliable. However, instead of enabling load-shedding or renewable curtailment, such overloading or over-generation problems can be alleviated more efficiently and cost-effectively by provisionally interconnecting the neighboring MGs to exchange power amongst themselves. In such a scheme, the interconnected MGs can supply their local demand, as well as a portion of the demand of the adjacent MGs. In order to implement this strategy, a three-phase ac link can be used as the power exchange network, while each MG is coupled to the link through a back-to-back power electronics converter, in order to maintain the autonomy of each MG if they are eachoperated under different standards. This paper proposes a suitable decentralized power management strategy without a communication link between the MGs to achieve power-sharing amongst them and alleviate unacceptable voltage and frequency deviation along with the required control technique for the power electronic converters, which can be implemented at the primary level based on the measurement of the local parameters only. To this end, one of the converters should always regulate the dc link voltage while the other converter should operate in droop control mode when the MG is healthy and in constant PQ mode when overloaded or over-generating. Suitable status detection and mode transition algorithms and controllers were also developed and are proposed in this paper. The performance of the proposed power exchange and control mechanisms were evaluated and verified via PSIM®-based numerical simulation studies. The stability and sensitivity of the proposed power exchange topology are also analyzed against several critical design and operational parameters

Dispersion Study of a Broadband Terahertz Focusing Reflecting Metasurface for 6G Wireless Communication

In 6G wireless communications, functional terahertz reflecting metasurfaces are expected to play increasingly important roles such as beamforming and beamsteering. This paper demonstrates the design of a functional and efficient beamforming metasurface in the burgeoning D-band (0.11-0.17~THz). In addition to achieving broadband operation (0.135-0.165~THz), this design is polarization-maintaining, diffraction limited, simple in design, exhibits 64.1\% broadband efficiency (1.9 dB insertion loss) and 20\% fractional bandwidth. Despite being formed by an array of highly dispersive resonators, the metasurface exhibits very low temporal dispersion, which avoids pulse reshaping and its consequent limitations on achievable data rate. The design and performance of the focusing reflector are presented followed by a group delay and group delay dispersion analysis revealing that a 2.83\% temporal broadening of the pulse is observed at the focus

Dynamic frequency and overload management in autonomous coupled microgrids for self-healing and resiliency improvement

Autonomous microgrids (MGs) are being installed in large remote areas to supply power where access to the utility grid is unavailable or infeasible. The power generation of such standalone MGs is largely dominated by renewable based energy sources where overloading or power deficiencies can be common due to the high intermittency and uncertainty in both load and power generation. Load-shedding is the most common mechanism to alleviate these problems to prevent system instability. To minimize load-shedding, most MGs are equipped with local battery energy storage (BES) systems to provide additional support. Furthermore, in the event of severe overloading or when BES capacity is insufficient to alleviate the overload, neighboring MGs can be provisionally coupled to provide mutual support to each other which is a more effective, economic and reliable approach. Such a coupling is preferred to be via power electronic converters to enhance the autonomy of the MGs. This paper proposes a two-stage, coordinated power sharing strategy among BESs and coupled MGs for overload management in autonomous MGs, through dynamic frequency control. Both local BES and the neighboring MGs can work in conjunction or individually to supply the required overload power demand. For this, BES’ state of charge should be above a minimum level and extra power generation capacity needs to be available in the neighboring MGs. A predefined framework with appropriate constraints and conditions, under which the power exchange will take place, are defined and formulated. The proposed mechanism is a decentralized approach, operating based on local frequency and state of charge measurements, and without any data communication amongst the MGs. The dynamic performance of such a network, is evaluated through extensive simulation studies in PSIM Ⓡ and verifies that the proposed strategy can successfully alleviate the overloading situation in the MGs through proper frequency regulation

Studies on genetic variability and interrelationship in bottle gourd [Lagenaria siceraria (Mol.) Standl]

The genetic parameters were studied to elucidate the genetic variability, correlation and path co-efficient analysis in thirty-nine genotypes of bottle gourd [Lagenaria siceraria (Mol.) Standl] in randomized complete block design with three replications. Observations were recorded for eleven quantitative characters viz., days to first male flower open, days to first female flower open, node number of first female flower, braches plant-1, days to harvest, number of fruits plant-1, fruit weight, fruit length, fruit girth, 100 seed weight and yield ton ha-1. The analysis of variance showed highly significant differences for all the characters studied indicating considerable variability among the genotypes. The highest GCV (35.57%) and PCV (35.62%) were observed for fruit length. The differences between GCV and PCV were high for fruit number plant-1 and days to first male flower open indicating environmental influences. High heritability associates with high estimates of genetic advance in percent of mean were noted for length of fruit, yield, girth of fruit and number of fruits plant-1. It indicated presence of additive gene effect and selection for these traits would be effective. Yield were positively and significantly correlated with fruit weight, 100 seed weight, branch plant-1 and number of fruits plant-1 .Negative associations of yield were noted with days to first male and female flower open, days to harvest and length of fruit. Path analysis revealed that fruits plant-1 (0.93) and weight of fruit (0.467) had very high positive effect on fruit yield ton ha-1 .Int. J. Agril. Res. Innov. & Tech. 8 (1): 14-17, June, 201

Linkage between Corporate Governance and Financial Performance in an Emerging Economy

The objective of this study is to explore the Linkage between Corporate Governance and Financial Performance in an Emerging Economy in the banking sector of Bangladesh. The data have been taken from primary sources. Data were collected from 22 listed banks on the Dhaka Stock Exchange (DSE). This data were analyzed by using different statistical tools like structural equation model (SEM) with the help of SmartPLS-3 software. It is found that some important factors like enablers that improve corporate governance, obstacles that affect corporate governance those are the influential factors to build performance of selected bank. This study further supports the argument that when bank implement good corporate governance principles, it experiences improved financial performance. This study, with its emphasis on developing a corporate governance model, makes a significant contribution to the body of knowledge on corporate governance in emerging economies like Bangladesh

Occurrence, diversity and morphology of poroid wood decay by Ganoderma spp. from tropical moist deciduous forest region of Bangladesh

There are many hot spots in tropical moist deciduous forest region where wood decay fungi grow naturally. An investigation was carried  out  to  collect, identify  and  preserve wood decay Ganoderma spp. on the basis of morphological characteristics  from Pabna,  Dhaka and  Rajshahi under tropical  moist deciduous  forest  region in Bangladesh during  June  to September  2016 and July to October  2017. This study was conducted to  record the  morphological  variability,  distribution,  habitat  and diversity of  the Ganoderma  population. A  total  of  40 Ganoderma  samples  were  collected  and identified to nine species  under  Ganodermataceae family.  The samples were collected from the sites by walking through the area following standard method. The field data and laboratory analytical data was recorded during sample collection and in the laboratory, respectively.The highest density of occurrence (23%) was recorded for Ganoderma lucidum and Ganoderma oregonense followed by Ganoderma applanatum (20%), Ganoderma praelongum (19%), Ganoderma lesklokorka (18.5%), Ganoderma pfeifferi (17%), Ganoderma boninense (15%), Ganoderma lipsiense (13%) and Ganoderma tsugae (11%). The highest frequency of occurrence (10%) was recorded for Ganoderma applanatum and Ganoderma oregonense followed by Ganoderma lucidum (9%), Ganoderma pfeifferi (8%), Ganoderma boninense (8%), Ganoderma praelongum (7%), Ganoderma lesklokorka (7%),Ganoderma tsugae (6%) and  Ganoderma lipsiense (5%). During survey, Koroi (Albizia procera), Aurjun (Terminalia arjuna), Sisso plant (Dalbergia sissoo), Neem (Azadirachta indica), Golden shower (Acacia auriculiformis) and Rain tree (Albizia lebbeck) were found as hosts of Ganoderma spp. The specimens were preserved in the SAU Herbarium of Macro Fungi (SHMF) and might be useful in mushroom breeding and development program for medicine and food industry sector in future

Effect of various electron and hole transport layers on the performance of CsPbI3-based perovskite solar cells: A numerical investigation in DFT, SCAPS-1D, and wxAMPS frameworks

CsPbI3 has recently received tremendous attention as a possible absorber of perovskite solar cells (PSCs). However, CsPbI3-based PSCs have yet to achieve the high performance of the hybrid PSCs. In this work, we performed a density functional theory (DFT) study using the Cambridge Serial Total Energy Package (CASTEP) code for the cubic CsPbI3 absorber to compare and evaluate its structural, electronic, and optical properties. The calculated electronic band gap (Eg) using the GGA-PBE approach of CASTEP was 1.483 eV for this CsPbI3 absorber. Moreover, the computed density of states (DOS) exhibited the dominant contribution from the Pb-5d orbital, and most charge also accumulated for the Pb atom as seen from the electronic charge density map. Fermi surface calculation showed multiband character, and optical properties were computed to investigate the optical response of CsPbI3. Furthermore, we used IGZO, SnO2, WS2, CeO2, PCBM, TiO2, ZnO, and C60 as the electron transport layers (ETLs), and Cu2O, CuSCN, CuSbS2, Spiro-MeOTAD, V2O5, CBTS, CFTS, P3HT, PEDOT: PSS, NiO, CuO, and CuI as the hole transport layers (HTLs) to identify the best HTL/CsPbI3/ETL combinations using the SCAPS-1D solar cell simulation software. Among 96 device structures, the best-optimized device structure, ITO/TiO2/CsPbI3/CBTS/Au was identified, which exhibited an efficiency of 17.9%. The effect of absorber and ETL thickness, series resistance, shunt resistance, and operating temperature was also evaluated for the six best devices along with their corresponding generation rate, recombination rate, capacitance-voltage, current density-voltage, and quantum efficiency characteristics. The obtained results from SCAPS-1D were also compared with wxAMPS simulation software.Comment: 34 pages, 12 figures, Supporting Information (3 figures

Geometric distortion measurement for shape coding: a contemporary review

Geometric distortion measurement and the associated metrics involved are integral to the rate-distortion (RD) shape coding framework, with importantly the efficacy of the metrics being strongly influenced by the underlying measurement strategy. This has been the catalyst for many different techniques with this paper presenting a comprehensive review of geometric distortion measurement, the diverse metrics applied and their impact on shape coding. The respective performance of these measuring strategies is analysed from both a RD and complexity perspective, with a recent distortion measurement technique based on arc-length-parameterisation being comparatively evaluated. Some contemporary research challenges are also investigated, including schemes to effectively quantify shape deformation

Spectral Line-by-Line Pulse Shaping of an On-Chip Microresonator Frequency Comb

We report, for the first time to the best of our knowledge, spectral phase characterization and line-by-line pulse shaping of an optical frequency comb generated by nonlinear wave mixing in a microring resonator. Through programmable pulse shaping the comb is compressed into a train of near-transform-limited pulses of \approx 300 fs duration (intensity full width half maximum) at 595 GHz repetition rate. An additional, simple example of optical arbitrary waveform generation is presented. The ability to characterize and then stably compress the frequency comb provides new data on the stability of the spectral phase and suggests that random relative frequency shifts due to uncorrelated variations of frequency dependent phase are at or below the 100 microHertz level.Comment: 18 pages, 4 figure