Performance Improvement of Grid-Integrated Doubly Fed Induction Generator under Asymmetrical and Symmetrical Faults

The doubly fed induction generator (DFIG)-based wind energy conversion system (WECS) suffers from voltage and frequency fluctuations due to the stochastic nature of wind speed as well as nonlinear loads. Moreover, the high penetration of wind energy into the power grid is a challenge for its smooth operation. Hence, symmetrical faults are most intense, inflicting the stator winding to low voltage, disturbing the low-voltage ride-through (LVRT) functionality of a DFIG. The vector control strategy with proportional–integral (PI) controllers was used to control rotor-side converter (RSC) and grid-side converter (GSC) parameters. During a symmetrical fault, however, a series grid-side converter (SGSC) with a shunt injection transformer on the stator side was used to keep the rotor current at an acceptable level in accordance with grid code requirements (GCRs). For the validation of results, the proposed scheme of PI + SGSC is compared with PI and a combination of PI with Dynamic Impedance Fault Current Limiter (DIFCL). The MATLAB simulation results demonstrate that the proposed scheme provides superior performance by providing 77.6% and 20.61% improved performance in rotor current compared to that of PI and PI + DIFCL control schemes for improving the LVRT performance of DFIG

Impact of Block Length and Temperature over Self-Assembling Behavior of Block Copolymers

Self-assembling behavior of block copolymers having water-soluble portion as one of the blocks plays key role in the properties and applications of the copolymers. Therefore, we have synthesized block copolymers of different block length and investigated their self-assembling behavior with reference to concentration and temperature using surface tension and conductance measurement techniques. The results obtained through both techniques concluded that critical micelles concentration (CMC) was decreased from 0.100 to 0.078 g/dL with the increase in length of water insoluble block and 0.100 to 0.068 g/dL for the increased temperature. ΔGmic was also decreased with the increase in temperature of the system, concluding that the micellization process was encouraged with the increase in temperature and block length. However, ΔHmic values were highest for short block length copolymer. The surface excess concentration obtained from surface tension data concluded that it was highest for short block length and vice versa and was increased with the increase in temperature of the system. However, the minimum area per molecule was largest for highest molecular weight copolymers or having longest water insoluble block and decreases with the increase in temperature

Effect of plant population densities on yield of maize.

ABSTRACT A field experiment to determine the effect of plant population densities on maize was conducted at the Agricultural Research Institute, Dera Ismail Khan, in mid July 2009. The effect of six plant population densities i.e. T 1 (40000 plants ha ). Therefore, planting density of 60000 plants ha -1 (keeping plant to plant distance of 22.70cm) is recommended for obtaining higher yield of maize

Maximum Power Tracking System Based on Power Electronic Topology for Wind Energy Conversion System Applications

Wind energy has emerged as a dominant alternative power generation source. Conventional energy resources are depleting and their increasing cost cannot be ignored. Wind energy has taken an important role in replacing fossil fuels and nuclear energy. However, optimal exploitation of wind energy systems has remained a thought-provoking problem due to the nonlinear behavior of the wind speed. Distribution generation system and isolated micro-grid (MG) are mainly used in a wind energy system in order to utilize maximum potential of wind through the maximum power tracking algorithm based on DC-DC boost power electronic converter. In this paper, authors propose a technique which is effectively workable, highly reliable, of low cost and induces less mechanical stress on the wind generator system (WGS). Experimental results of the proposed system verify that the effectiveness near optimal WGS output power increased approximately up to 50%. Thus, better exploitation of the available wind power is obtained under low wind speeds

Malignancy risk analysis in patients with inadequate fine needle aspiration cytology (FNAC) of the thyroid

Background Thyroid fine needle aspiration cytology (FNAC) is the standard diagnostic modality for thyroid nodules. However, it has limitations among which is the incidence of non-diagnostic results (Thy1). Management of cases with repeatedly non-diagnostic FNAC ranges from simple observation to surgical intervention. We aim to evaluate the incidence of malignancy in non-diagnostic FNAC, and the success rate of repeated FNAC. We also aim to evaluate risk factors for malignancy in patients with non-diagnostic FNAC. Materials and Methods Retrospective analyses of consecutive cases with thyroid non diagnostic FNAC results were included. Results Out of total 1657 thyroid FNAC done during the study period, there were 264 (15.9%) non-diagnostic FNAC on the first attempt. On repeating those, the rate of a non-diagnostic result on second FNAC was 61.8% and on third FNAC was 47.2%. The overall malignancy rate in Thy1 FNAC was 4.5% (42% papillary, 42% follicular and 8% anaplastic), and the yield of malignancy decreased considerably with successive non-diagnostic FNAC. Ultrasound guidance by an experienced head neck radiologist produced the lowest non-diagnostic rate (38%) on repetition compared to US guidance by a generalist radiologist (65%) and by non US guidance (90%). Conclusions There is a low risk of malignancy in patients with a non-diagnostic FNAC result, commensurate to the risk of any nodule. The yield of malignancy decreased considerably with successive non-diagnostic FNAC

Microwave Hydrothermal Carbonization of Rice Straw: Optimization of Process Parameters and Upgrading of Chemical, Fuel, Structural and Thermal Properties.

The process parameters of microwave-induced hydrothermal carbonization (MIHTC) play an important role on the hydrothermal chars (hydrochar) yield. The effect of reaction temperature, reaction time, particle size and biomass to water ratio was optimized for hydrochar yield by modeling using the central composite design (CCD). Further, the rice straw and hydrochar at optimum conditions have been characterized for energy, chemical, structural and thermal properties. The optimum condition for hydrochar synthesis was found to be at a 180 °C reaction temperature, a 20 min reaction time, a 1:15 weight per volume (w/v) biomass to water ratio and a 3 mm particle size, yielding 57.9% of hydrochar. The higher heating value (HHV), carbon content and fixed carbon values increased from 12.3 MJ/kg, 37.19% and 14.37% for rice straw to 17.6 MJ/kg, 48.8% and 35.4% for hydrochar. The porosity, crystallinity and thermal stability of the hydrochar were improved remarkably compared to rice straw after MIHTC. Two characteristic peaks from XRD were observed at 2? of 15° and 26°, whereas DTG peaks were observed at 50?150 °C and 300?350 °C for both the materials. Based on the results, it can be suggested that the hydrochar could be potentially used for adsorption, carbon sequestration, energy and agriculture applications

Assessment of Wind Power Potential Based on Raleigh Distribution Model: An Experimental Investigation for Coastal Zone

When compared with other renewable energy resources (RER), the wind energy share in the global energy production is increasing rapidly. Currently, the Government of Pakistan (GoP) is moving towards RER, specifically wind and solar energy. In this paper, the wind energy potential of Tando Ghulam Ali, Sindh, Pakistan is explored. For this purpose, one-year wind speed data is considered at various heights through various probability distribution functions (PDFs). Statistical comparison of Rayleigh, gamma, generalized extreme value (GEV) and lognormal PDFs have been done with two methods, namely root mean square error and (R^2) in order to select the best PDF. Results showed that the Rayleigh distribution function is the best at the above mentioned area for finding various factors like site selection and wind power cost per kWh

Seasonal Variation and Species Composition of Crustacean Zooplankton (Order : Cladocera) in

Abstract.-Qualitative and quantitative studies of crustacean zooplankton were carried out during 2001, when drought conditions prevailed. Ten species belonging to 9 genera and 4 families of order Cladocera were identified. Out of 10 species, 01 species Dunhevedia crassa is a new record from Pakistan. Enumeration of zooplankton indicated that the population of Alona rectangula and Dunhevedia crassa increased gradually during colder months (DecemberMarch). Alona rectangula peaked in February, while Dunhevedia crassa had two peaks, in December and March. Bosmina longirostris and Ceriodaphnia reticulata did not show any remarkable changes during the year. Chydorus poppei and Simocephalus exspinosus increased during warmer months. Chydorus poppei had a peak in May, while the peak of Simocephalus exspinosus was observed in July. Highest population of Macrothrix rosea was found in August, and then it decreased gradually during colder months. Population of Scapholeberis kingi remained low throughout the year, but exhibited peaks in September and March. Seasonal fluctuation of cladocerans can be correlated with the temperature and salinity of water. As the temperature and salinity decreased in colder months, the over all population of Cladocerans increased with a peak in February

Immobilization of lipase enzyme carbon nanotubes via adsorption

Lipase is an enzyme used widely in many major industries. Immobilization of enzymes will help to enhance its sustainability as enzymes are more resistance to changes in environment and can be reused. This experiment examines effects the immobilization of lipase with adsorption technique through carbon nanotubes. The paper investigates the enzyme activity and efficiency of immobilized enzyme lipase by using assay solution. It also presents the effects of pH on immobilized enzyme and the characterization of the immobilized enzyme lipase with FTIR spectrum and FESEM technique. The results showed that there are as enzyme concentration increases, the enzymatic activity increases too. However, this lowers the immobilization efficiency due to saturation of binding pores on functionalized MWCNTs. Meanwhile, the optimum pH for maximum immobilization activity of enzyme lipase is at pH 6. Based on the characterization by FTIR spectrum and FESEM, it is confirmed by the presence of functional group in FTIR spectrography. On the other side, FESEM also confirms that immobilization of enzyme has occurred

Green Plants in the Red: A Baseline Global Assessment for the IUCN Sampled Red List Index for Plants

Plants provide fundamental support systems for life on Earth and are the basis for all terrestrial ecosystems; a decline in plant diversity will be detrimental to all other groups of organisms including humans. Decline in plant diversity has been hard to quantify, due to the huge numbers of known and yet to be discovered species and the lack of an adequate baseline assessment of extinction risk against which to track changes. The biodiversity of many remote parts of the world remains poorly known, and the rate of new assessments of extinction risk for individual plant species approximates the rate at which new plant species are described. Thus the question ‘How threatened are plants?’ is still very difficult to answer accurately. While completing assessments for each species of plant remains a distant prospect, by assessing a randomly selected sample of species the Sampled Red List Index for Plants gives, for the first time, an accurate view of how threatened plants are across the world. It represents the first key phase of ongoing efforts to monitor the status of the world’s plants. More than 20% of plant species assessed are threatened with extinction, and the habitat with the most threatened species is overwhelmingly tropical rain forest, where the greatest threat to plants is anthropogenic habitat conversion, for arable and livestock agriculture, and harvesting of natural resources. Gymnosperms (e.g. conifers and cycads) are the most threatened group, while a third of plant species included in this study have yet to receive an assessment or are so poorly known that we cannot yet ascertain whether they are threatened or not. This study provides a baseline assessment from which trends in the status of plant biodiversity can be measured and periodically reassessed