Search

This study presents the commercial solar PV plant (SPVP) operation, integrated into the low voltage (LV) AC network. The SPVP has the multi‐functional operational capability. It feeds the PV array generated power to loads and the AC network, while ensuring the power quality improvement at the point of common coupling (PCC) as per the IEEE std. 519, irrespective of the load characteristic (linear/nonlinear and balanced/unbalanced). The SPVP minimises the line losses in the AC network by recouping the load reactive power requirement locally. Moreover, the SPVP operates in either maximum power extraction (MPE) mode or constant power generation (CPG) mode, depending upon the rise in PCC voltage amplitude during the peak PV array power generation and low load demand condition. The SPVP switches between the MPE and the CPG modes during the high rise in PCC voltage amplitude and regulates the PV array generated power to protect itself and the load connected at PCC. In this study, an adaptive filter technique based on maximum correntropy criterion is used for the PQI, and the perturb and observe based algorithm is used for MPE. A simulation model and reduced rating hardware prototype are developed to validate the system's performance.

Polaritons with a twist The ability to design and fabricate optical systems with tunable topological features makes them especially attractive for developing analogs of topological condensed matter systems, which by themselves tend to be fixed or limited in their tunability. Liu et al. now show that the combination of a two-dimensional material with a photonic crystal can be used to develop an analogous quantum spin Hall system. The strong coupling between the monolayer tungsten disulfide excitons with a nontrivial hexagonal photonic crystal gives rise to helical topological polaritons observed at up to 200 kelvin. The topological polaritons can be actively tuned by temperature and may further be manipulated with electric or magnetic fields, thereby providing a flexible platform with which to explore exotic topological phenomena and new phases of quantum matter. Science , this issue p. 600

The point of common coupling (PCC) voltage of the grid integrated solar photovoltaic (GSPV) system rises when the load becomes less and the SPV array generation at its peak, leads to the overvoltage at the PCC. It causes the system to shut down its operation to protect itself and the load from the overvoltage. The GSPV system also suffers from substandard power quality (PQ) due to the unbalanced or nonlinear load currents. This work addresses these issues and presents the control scheme for the GSPV-battery system. This work presents the variable power mode of operation to restrain the rise in PCC voltages below its maximum permissible limit as set by the IEEE std. 1547. The system operates either in unity power factor (UPF) mode or the constant power generation (CPG) mode or in voltage regulation (VR) mode, depending upon the battery status and PCC voltage amplitude. The system also provides shunt compensation at PCC to reduce the negative impact of the unbalanced-nonlinear load currents in the AC grid and maintains the PQ in the AC grid as per the IEEE std. 519. A simulation study is performed to demonstrate the efficacy of the presented control algorithm.

A key to successful Well, Reservoir and Facilities Management (WRFM) is to have an up-to-date opportunity funnel. In large mature fields, WRFM opportunity identification is heavily dependent on effective exploitation of measured & interpreted data. This paper presents a suite of data driven workflows, collectively called WRFM Opportunity Finder (WOF), that generates ranked list of opportunities across the WRFM opportunity spectrum.The WOF was developed for a mature waterflooded asset with over 500 active wells and over 30 years of production history. The first step included data collection and cleanup using python routines and its integration into an interactive visualization dashboard. The WOF used this data to generate ranked list of following opportunity types: (a) Bean-up/bean-down candidates (b) Watershut-off candidates (c) Add-perf candidates (d) PLT/ILT data gathering candidates, and (e) well stimulation candidates. The WOF algorithms, implemented using python, largely comprised of rule-based workflows with occasional use of machine learning in intermediate steps.In a large mature asset, field/reservoir/well reviews are typically conducted area by area or reservoir by reservoir and is therefore a slow process. It is challenging to have an updated holistic overview of opportunities across the field which can allow prioritization of optimal opportunities. Though the opportunity screening logic may be linked to clear physics-based rules, its maturation is often difficult as it requires processing and integration of large volumes of multi-disciplinary data through laborious manual review processes. The WOF addressed these issues by leveraging data processing algorithms that gathered data directly from databases and applied customized data processing routines. This led to reduction in data preparation and integration time by 90%. The WOF used workflows linked to petroleum engineering principles to arrive at ranked lists of opportunities with a potential to add 1-2% increment in oil production. The integrated visualization dashboard allowed quick and transparent validation of the identified opportunities and their ranking basis using a variety of independent checks. The results from WOF will inform a range of business delivery elements such as workover & data gathering plan, exception-based-surveillance and facilities debottlenecking plan.WOF exploits the best of both worlds - physics-based solutions and data driven techniques. It offers transparent logic which are scalable and replicable to a variety of settings and hence has an edge over pure machine learning approaches. The WOF accelerates identification of low capex/no-capex opportunities using existing data. It promotes maximization of returns on already made investments and hence lends resilience to business in the low oil price environment.

This paper presents a solar photovoltaic (SPV) array-battery energy storage-based microgrid with a two-stage converter. One is a DC-DC converter, and another one is a voltage source converter (VSC). It acts in standalone mode or grid-connected mode depends on utility grid conditions. A bidirectional DC-DC converter (BDC) is used for maintaining the DC link voltage. Maximum power point tracking (MPPT) with an incremental conductance (INC) technique is used to extract the maximum power from the SPV array. Adaptive fixed frequency third-order generalized integrator (AFFTOGI) controller is used for estimating the load fundamental and quadrature components from the distorted grid and unbalanced load. In grid-connected mode, VSC works in current control mode, and in standalone mode, it works in voltage control mode. In this paper, dynamic simulation under different operation conditions and experiments on developed laboratory prototypr are performed to evaluate the system and control algorithm performance.

The high line impedance of the low voltage AC network (LVACN), coupled with the distorted currents drawn by the nonlinear loads at the point of common coupling (PCC), creates serious power quality issues in the AC network. Furthermore, higher penetration of renewable energy sources like the solar photovoltaic (SPV) in modern LVACN escalates such power quality issues because of their fluctuating behavior. In this context, this paper presents an adaptive filtering strategy-based control for the SPV-battery energy storage (BES) system feeding nonlinear loads to improve the power quality at the PCC. The adaptive filtering scheme ensures that the distortions in the load currents are not reflected in the LVACN. Thus, the currents and voltages in LVACN remain linear. Furthermore, a power management scheme is developed to optimize the operation of the SPV-BES system. It supports the PCC voltages by limiting the supplied and drawn power from the LVACN, during peak SPV array generation or low load condition and no SPV array generation or the peak load condition, respectively. The SPV-BES system is also capable of transferring its mode of operation from a grid connected system, to a standalone system, when the supply from the LVACN is interrupted. Thus, the overall system efficiency and reliability are enhanced. Both the simulation and the experimental analyses of the SPV-BES system are presented to demonstrate the effectiveness of the power management scheme and the adaptive filtering strategy.

This work presents the design and control of PV-battery system feeding power to the AC network with diesel generator (DG) set backup at unity power factor (UPF) and the loads connected at the point of common coupling (PCC). The system improves the power factor of the AC network and the DG set to unity. Furthermore, it reduces the distortion in the currents and voltages of the AC network and DG set as par the IEEE std. 519, if any nonlinear load exists at the PCC. Moreover, it mitigates the intermittency of the PV array generation and the load demand at the PCC during the daytime operation by supplying constant power to the AC network. Hence, the variation in the PCC voltages are reduced. The PV -battery system energizes the load by operating as a standalone system if the AC grid'supply is interrupted. Furthermore, it operates as an uninterrupted power supply (UPS) if the generation of PV array reduces to zero. If the battery bank also discharges, then the DG set is connected at the PCC to energize the load. Hence, the load remains energized in all conditions. Here, the DG set operates at an optimal fuel economy zone to minimize diesel consumption and operational cost. However, it is disconnected as soon as the grid supply recovers or the battery bank charges. Therefore, diesel consumption reduces to the lowest. An extensive simulation study is performed to exhibit the performance and the seamless operation of the presented system when its working mode is sudden changes.

The commercial PV systems (PVS) lose their generation and do not exploit the clean energy generated by the PV array during the grid outage condition. This work presents the islanded operation of the PVS during the grid outage without using any energy storage. When the grid is available, the system feeds the power to the load and the grid. When the grid is not available, it feeds power to the load until the generation of the PVS remains more than the load demand. Hence, the clean energy generated by the PV array is efficiently exploited. The system also acts as an active filter and provides the shunt compensation features at the point of common coupling (PCC). Hence, it reduces the effects of the nonlinear-unbalanced loads on the AC utility and upholds the IEEE std. 519 at the PCC. The performance of the presented system is validated by the MATLAB/Simulink analysis.

Topological photonics has become an active subfield of photonics analogous to the electronic counterpart, and the bulk-edge correspondence leads to robust topologically protected interfacial states. However, a single-topological interface mode with fixed energy cannot be easily manipulated, hindering its applications in optical devices. Here, we study coupled-waveguide arrays mapped to a one-dimensional Su-Schrieffer-Heeger system with two coupled topological interfaces. This configuration greatly increases device versatility and tunability while keeping the confinement of coupled-interface modes inherited from the topological properties nearly intact. Theoretically predicted oscillations between coupled interfaces is experimentally observed. The spatial and energetic isolation of the coupled interface states from the bulk modes is experimentally observed and theoretically confirmed by calculating the degree of localization of the eigenstates, which is found to be comparable to a single-interface state. Finally, a proof-of-principle, all-optical logic circuit is fabricated based on coupled interfaces, demonstrating its potential in assembling on-chip topological optical devices.

The telecom tower depends upon the diesel generator as backup power to meet its load demand. This work presents the control of the solar PV battery system to reduce the dependability of the telecom sector on the DG set. This solar PV-battery system is used as backup power to meet the load demand when the supply from the AC utility is not available as it works in both grid connected (GC) and standalone (SA) mode. The system operates smoothly when it’s working mode is shifted from GC to SA and vice versa. It also improves the voltage profile at the point of common coupling (PCC) and utility current profile by mitigating the power quality problems caused by the nonlinear loads used in a telecom tower. An adaptive algorithm is presented to control the system in GC mode and a proportional resonant (PR) controller-based control algorithm is used in SA mode. The battery bank provides the support to the load in the SA mode when the solar PV generation is not sufficient, and it charges as soon as the utility supply reappears so that it has enough energy to supply power to the load in the SA mode. The system performance and the control algorithm have effectiveness validated through both simulation and experiment results.

One of the major problems with phase change memory (PCM) is the high current density required for the crystal–amorphous transformation via a melt-quench process. However, alternative low-energy pat...

Topological photonics provides an ideal platform for demonstrating novel band topology concepts, which are also promising for robust waveguiding, communication, and computation applications. However, many challenges such as extremely large device footprint and functionality at short wavelengths remain to be solved which are required to make practical and useful devices that can also couple to electronic excitations in many important organic and inorganic semiconductors. In this letter, we report an experimental realization of Z2 photonic topological insulators with their topological edge state energies spanning across the visible wavelength range including in the sub-500 nm regime, which requires highly optimized nanofabrication. The photonic structures are based on deformed hexagonal lattices with preserved 6-fold rotational symmetry patterned on suspended SiNx membranes. The experimentally measured energy-momentum dispersion of the topological lattices directly shows topological band inversion by the swapping of the brightness of the bulk energy bands, and also the helical edge states when the measurement is taken near the topological interface. The robust topological transport of the helical edge modes in real space is demonstrated by successfully guiding circularly polarized light beams unidirectionally through sharp kinks without significant signal loss. This work paves the way for small footprint photonic topological devices working in the short wavelength range that can also be utilized to couple to excitons for unconventional light-matter interactions at the nanoscale.

Subject area Strategy and finance. Study level/applicability MBA/MBA equivalent programme – finance specialisation. Case overview In June 2009, Mr Rakesh Vora, CEO of Alpha Power Ltd, India was facing problems while deciding the appropriate business model of the company. Without the existence of an adequate business plan, the CFO, Mr Harish Gupta, could not decide the adequate capital structure and valuation of the one million shares the company planned to issue in the market through private placement. Alpha Power Ltd is planning to start two power plants at Jatra and Chhapra. The plants are to be funded by a prudent mix of debt and equity; but, it has major issues regarding the financing arrangements. The management is undecided about how to fund these projects. Power sector in India is booming; however, the challenges faced by the company are numerous. They include possibility of a slowdown, different buying/leasing options for land, option of using better technology, decision regarding importing of superior quality, but high-cost coal and valuation of the company using various approaches, etc. Expected learning outcomes The case is intended to help future finance professionals understand the working of power plants in India and experience the decision-making process faced by managers, while making a business plan and raising funds for power projects. Supplementary materials Teaching notes.

Growth of freestanding nano- and microstructures with complex morphologies is a highly desired aspect for real applications of nanoscale materials in various technologies. Zinc oxide tetrapods (ZnO-T), which exhibit three-dimensional (3D) shapes, are of major importance from a technological applications point of view, and thus efficient techniques for growth of different varieties of tetrapod-based networks are demanded. Here, we demonstrate the versatile and single-step synthesis of ZnO-T with different arm morphologies by a simple flame transport synthesis (FTS) approach, forming a network. Morphological evolutions and structural intactness of these tetrapods have been investigated in detail by scanning electron microscopy, X-ray diffraction, and micro-Raman measurements. For a deeper understanding of the crystallinity, detailed high-resolution transmission electron microscopic studies on a typical ZnO tetrapod structure are presented. The involved growth mechanism for ZnO tetrapods with various arm morphologies is discussed with respect to variations in experimental conditions. These ZnO-T have been utilized for photocatalytic degradation and nanosensing applications. The photocatalytic activities of these ZnO-T with different arm morphologies forming networks have been investigated through the photocatalytic decolorization of a methylene blue (MB) solution under UV light illumination at ambient temperature. The results show that these ZnO-T exhibit strong photocatalytic activities against MB and its complete degradation can be achieved in very short time. In another application, a prototype of nanoelectronic sensing device has been built from these ZnO-T interconnected networks and accordingly utilized for UV detection and H-2 gas sensing. The fabricated device structures showed excellent sensing behaviors for promising practical applications. The involved sensing mechanisms with respect to UV photons and H2 gas are discussed in detail. We consider that such multifunctional nanodevices based on ZnO tetrapod interconnected networks will be of interest for various advanced applications.

Background: Hypothyroidism is a common problem that reduces the functional ability of life. Hypothyroidism is associated with altered lipid levels, which increases the cardiovascular risk. Objective: The objectives of this study were to study whether there is any correlation between serum lipid levels and hypothyroidism (subclinical and overt) in a rural population of Gujarat and to study whether there is any difference in lipid levels among menopausal and postmenopausal women. Materials and Method: A cross-sectional study was conducted at Clinical Biochemistry department, P.S. Medical College, Karamsad, which consisted 100 hypothyroid patients (subclinical and overt) and 100 similar age- and sex-matched controls. Serum total thyroxine, triiodothyronine, thyroid-stimulating hormone, free thyroxine, serum cholesterol, triglyceride, high-density lipoprotein (HDL) and low-density lipoprotein levels were examined in subclinical and euthyroid patients. Results: In patient with subclinical hypothyroidism, we found elevated serum total cholesterol (217.95) and triglyceride (148.35) levels as compared to controls (P = 0.001) but statistically insignificant HDL level (51.45; P = 0.973). In patient with overt hypothyroidism, elevated serum total cholesterol (271.92) and triglyceride (166.31) were found as compared to control (P = 0.001), but HDL level (46.57; P = 0.134) was found to be decreased. Conclusion: There is association between subclinical and overt hypothyroidism with dyslipidemia. This might be a potential risk factor for coronary artery disease.