Offline Parameter Estimation of a 18.5 kW Doubly fed induction generator

Thesis (MEng)--Stellenbosch University, 2018.ENGLISH ABSTRACT: In the past years, technology advancements have allowed the wind energy to become one of the most economical forms of power generation in the field of renewable energies. Nowadays, wind turbines that produce electricity make use of the advance and mature technologies and generate sustainable sources of energy. In the areas where the wind is plentiful, it is a major rival to the conventional sources of energy. Many countries worldwide have vast resources of it but still, haven’t used its capacity to the fullest. The upsides of wind energy are: . Omitting the emission of greenhouse gases. . The energy supplies can be increased and diversified using wind energy. . In comparison to the other power sources, a shorter time is required for planning, design, and construction. The flexibility of such projects so that the current wind farms can host more turbines in case of higher demand for energy. . Finally, a significant saving in terms of materials, labor and investment. The extracted energy from the wind, is in the form of kinetic energy and is harnessed by the rotor blades and turned into mechanical energy. Then, this mechanical energy is transformed into the electrical energy by a wind turbine generator. The nominal power extracted from the wind varies based on the size of the rotor and the wind speed, regardless of the losses. The power ratings for wind generators varies from some hundred watts to multi-megawatt generators depending on the utilization and where they are stationed. Nowadays, a vast percentage of the larger scale wind generators employ the geared topologies, AC outputs connected to the power grid through power electronic converters, while it seems that the dynamic in the market is gradually changing towards employing the permanent magnet, gearless topologies by using the fully-rated power electronic converters. On the other hand, the small-scale turbines usually employ the direct drive generators with DC outputs and aeroelastic blades. However, the use of wind generators in a direct drive topology accompanied by the aeroelastic blades and DC outputs is rarely used and still under development. It is impossible to have the exact same power generation from the wind each year due to its variable nature. Furthermore, the wind generators can only be used in areas where a minimum speed of 4.5 m/s or higher is available. The suitable sites are chosen based on the measurements on the site and the data from a wind atlas. There are several methods for analyzing the dynamic behavior of the wind turbines. Employing the parameters of such systems is a suitable way to analysis the machine dynamic behavior and reduces complexities regarding the use of higher order models. The problem is that these parameters are subject to change in different operating conditions and need to be estimated accurately by some methods. This study concentrates on estimating the parameters of a doubly fed induction generator by employing the previously proposed Mathlab c-code and s-function codes and investigates the practical application of that method on a 18.5 kW doubly fed induction generator.AFRIKAANSE OPSOMMING: In die afgelope jaar het tegnologie vooruitgang die windenergie toegelaat om een van die mees ekonomiese vorme van kragopwekking op die gebied van hernubare energie te word. Vandag maak windturbines wat elektrisiteit produseer, gebruik van die voor- en volwasse tegnologie en volhoubare energiebronne. In die gebiede waar die wind oorvloed is, is dit 'n groot mededinger in die konvensionele energiebronne. Baie lande wêreldwyd het groot middele, maar het nog steeds nie sy vermoë tot die uiterste gebruik nie. Die opwaartse windenergie is: . Om die uitstoot van kWeekhuisgasse uit te skakel. . Die energiebronne kan verhoog en gediversifiseer word met behulp van windenergie. . In vergelyking met die ander kragbronne word 'n korter tyd benodig vir beplanning, ontwerp en konstruksie. . Die buigsaamheid van sulke projekte, sodat die huidige windplase meer turbines in die geval van hoër vraag na energie kan gasheer. . Ten slotte, 'n beduidende besparing in terme van materiale, arbeid en belegging. Die energie wat uit die wind onttrek word, is in die vorm van kinetiese energie en word deur die rotorblades aangewend en omskep in meganiese energie. Dan word hierdie meganiese energie omgeskakel na die elektriese energie deur 'n windturbine generator. Die nominale krag wat uit die wind onttrek word, hang af van die grootte van die rotor en die windspoed, ongeag die verliese. Die kraggraderings vir windopwekkers wissel van sowat honderd watt na multi-megawatt kragopwekkers, afhangende van die gebruik en waar hulle gestasioneer is. Deesdae gebruik 'n groot persentasie van die grootskaalse windopwekkers die toegepaste topologieë, AC-uitsette wat via die elektriese elektroniese omsetters aan die rooster verbind word, terwyl dit blyk dat die dinamiek in die mark geleidelik verander na die gebruik van die permanente magneet, ratlose topologieë deur die volwaardige krag elektroniese omsetters. Aan die ander kant gebruik die kleinschalige turbines gewoonlik die direkte dryfgenerators met gelykstroomuitsette en aeroelastiese lemme. Die gebruik van windgenerators in 'n direkte dryf topologie, vergesel van die aeroelastiese lemme en GS-uitsette word egter selde gebruik en steeds onder ontwikkeling. Dit is onmoontlik om elke jaar dieselfde kragopwekking uit die wind te kry as gevolg van die veranderlike aard daarvan. Verder kan die windgenerators slegs gebruik word in gebiede waar 'n minimum spoed van 4,5 m / s of hoër beskikbaar is. Die geskikte plekke word gekies op grond van die metings op die terrein en die data van 'n windatlas. Daar is verskeie metodes om die dinamiese gedrag van die windturbines te ontleed. Die gebruik van die parameters van sulke stelsels is 'n geskikte manier om die masjien dinamiese gedrag te ontleed en kompleksiteite te verminder rakende die gebruik van hoë-orde modelle. Die probleem is dat hierdie parameters onderworpe is aan verandering in verskillende bedryfsomstandighede en deur sommige metodes akkuraat beraam moet word. Hierdie studie fokus op die raming van die parameters van 'n dubbel gevoed induksie generator deur gebruik te maak van die voorheen voorgestelde Mathlab c-kode en s-funksie kodes en ondersoek die praktiese toepassing van die metode op 'n 18.5 kW dubbel gevoed induksie generator

NLRP3: Role in ischemia/reperfusion injuries

NLR family pyrin domain containing 3 (NLRP3) is expressed in immune cells, especially in dendritic cells and macrophages and acts as a constituent of the inflammasome. This protein acts as a pattern recognition receptor identifying pathogen-associated molecular patterns. In addition to recognition of pathogen-associated molecular patterns, it recognizes damage-associated molecular patterns. Triggering of NLRP3 inflammasome by molecules ATP released from injured cells results in the activation of the inflammatory cytokines IL-1β and IL-18. Abnormal activation of NLRP3 inflammasome has been demonstrated to stimulate inflammatory or metabolic diseases. Thus, NLRP3 is regarded as a proper target for decreasing activity of NLRP3 inflammasome. Recent studies have also shown abnormal activity of NLRP3 in ischemia/reperfusion (I/R) injuries. In the current review, we have focused on the role of this protein in I/R injuries in the gastrointestinal, neurovascular and cardiovascular systems

Experimental investigation of the band broadening originating from the top and bottom wall in micromachined non-porous pillar array columns

We report on the experimental investigation of the effect of the top and bottom wall plates in micromachined nonporous pillar array columns. It has been found that their presence yields an additional c-term type of band broadening that can make up a significant fraction of the total band broadening (at least if considering nonporous pillars and a nonretained tracer). Their presence also induces a clear (downward) shift of the optimal velocity. These observations are, however in excellent quantitative agreement with the theoretical expectations obtained from a computational fluid dynamics study. The presently obtained experimental results, hence, demonstrate that the employed high aspect ratio Bosch etching process can be used to fabricate micromachined pillar arrays that are sufficiently refined to achieve the theoretical performance limit

30-day morbidity and mortality of sleeve gastrectomy, Roux-en-Y gastric bypass and one anastomosis gastric bypass: a propensity score-matched analysis of the GENEVA data

Background: There is a paucity of data comparing 30-day morbidity and mortality of sleeve gastrectomy (SG), Roux-en-Y gastric bypass (RYGB), and one anastomosis gastric bypass (OAGB). This study aimed to compare the 30-day safety of SG, RYGB, and OAGB in propensity score-matched cohorts. Materials and methods: This analysis utilised data collected from the GENEVA study which was a multicentre observational cohort study of bariatric and metabolic surgery (BMS) in 185 centres across 42 countries between 01/05/2022 and 31/10/2020 during the Coronavirus Disease-2019 (COVID-19) pandemic. 30-day complications were categorised according to the Clavien–Dindo classification. Patients receiving SG, RYGB, or OAGB were propensity-matched according to baseline characteristics and 30-day complications were compared between groups. Results: In total, 6770 patients (SG 3983; OAGB 702; RYGB 2085) were included in this analysis. Prior to matching, RYGB was associated with highest 30-day complication rate (SG 5.8%; OAGB 7.5%; RYGB 8.0% (p = 0.006)). On multivariate regression modelling, Insulin-dependent type 2 diabetes mellitus and hypercholesterolaemia were associated with increased 30-day complications. Being a non-smoker was associated with reduced complication rates. When compared to SG as a reference category, RYGB, but not OAGB, was associated with an increased rate of 30-day complications. A total of 702 pairs of SG and OAGB were propensity score-matched. The complication rate in the SG group was 7.3% (n = 51) as compared to 7.5% (n = 53) in the OAGB group (p = 0.68). Similarly, 2085 pairs of SG and RYGB were propensity score-matched. The complication rate in the SG group was 6.1% (n = 127) as compared to 7.9% (n = 166) in the RYGB group (p = 0.09). And, 702 pairs of OAGB and RYGB were matched. The complication rate in both groups was the same at 7.5 % (n = 53; p = 0.07). Conclusions: This global study found no significant difference in the 30-day morbidity and mortality of SG, RYGB, and OAGB in propensity score-matched cohorts

30-Day morbidity and mortality of bariatric metabolic surgery in adolescence during the COVID-19 pandemic – The GENEVA study

Background: Metabolic and bariatric surgery (MBS) is an effective treatment for adolescents with severe obesity. Objectives: This study examined the safety of MBS in adolescents during the coronavirus disease 2019 (COVID-19) pandemic. Methods: This was a global, multicentre and observational cohort study of MBS performed between May 01, 2020, and October 10,2020, in 68 centres from 24 countries. Data collection included in-hospital and 30-day COVID-19 and surgery-specific morbidity/mortality. Results: One hundred and seventy adolescent patients (mean age: 17.75 ± 1.30 years), mostly females (n = 122, 71.8%), underwent MBS during the study period. The mean pre-operative weight and body mass index were 122.16 ± 15.92 kg and 43.7 ± 7.11 kg/m2, respectively. Although majority of patients had pre-operative testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (n = 146; 85.9%), only 42.4% (n = 72) of the patients were asked to self-isolate pre-operatively. Two patients developed symptomatic SARS-CoV-2 infection post-operatively (1.2%). The overall complication rate was 5.3% (n = 9). There was no mortality in this cohort. Conclusions: MBS in adolescents with obesity is safe during the COVID-19 pandemic when performed within the context of local precautionary procedures (such as pre-operative testing). The 30-day morbidity rates were similar to those reported pre-pandemic. These data will help facilitate the safe re-introduction of MBS services for this group of patients

An exploration study to find important factors influencing on authenticity of brand

Building an appropriate brand always makes it possible to reach better market share in competitive market. This paper presents a study to find important factors influencing the authenticity of brand. The proposed study designs a questionnaire in Likert scale consists of 21 questions, distributes it among 400 people who purchase regularly from chain stores in city of Tehran, Iran and collects 388 filled ones. Cronbach alpha is calculated as 0.712. In addition, Kaiser-Meyer-Olkin Measure of Sampling Adequacy and Approx. Chi-Square are 0.748 and 1718.212, respectively. Based on the results of our survey, we have derived five factors including brand identification, brand registration, brand position, perception image from the brand and trust to brand

Experimental investigation of the band broadening arising from short-range interchannel heterogeneities in chromatographic beds under the condition of identical external porosity

The interesting possibilities offered by micropillar array columns to investigate the relation between bed heterogeneity and band broadening in chromatographic columns are illustrated and investigated. The perfect control over the microscopic bed structure offered by the photolithographic fabrication technique could be used to produce a heterogeneous bed displaying a short-range interchannel heterogeneity and having exactly the same particle size and external porosity as the perfectly ordered bed that was used as the reference system. According to this approach, any observed difference in band broadening could be directly owed to the effect of the bed heterogeneity. Knowing that the only difference between the investigated beds was their degree of heterogeneity, the obtained plate height measurements provided a unique test to distinguish among the abilities to recognize short-range interchannel heterogeneity of the different existing plate height models. Interpreting the data with the classical van Deemter and Knox models, it was found that the increased bed heterogeneity leads not only to an increase in the A-term constant but also to a clear increase in the C-term constant

Facilitating structural elucidation of small environmental solutes in RPLC-HRMS by retention index prediction

Implementing effective environmental management strategies requires a comprehensive understanding of the chemical composition of environmental pollutants, particularly in complex mixtures. Utilizing innovative analytical techniques, such as high-resolution mass spectrometry and predictive retention index models, can provide valuable insights into the molecular structures of environmental contaminants. Liquid Chromatography-High-Resolution Mass Spectrometry is a powerful tool for the identification of isomeric structures in complex samples. However, there are some limitations that can prevent accurate isomeric structure identification, particularly in cases where the isomers have similar mass and fragmentation patterns. Liquid chromatographic retention, determined by the size, shape, and polarity of the analyte and its interactions with the stationary phase, contains valuable 3D structural information that is vastly underutilized. Therefore, a predictive retention index model is developed which is transferrable to LC-HRMS systems and can assist in the structural elucidation of unknowns. The approach is currently restricted to carbon, hydrogen, and oxygen-based molecules <500 g mol−1. The methodology facilitates the acceptance of accurate structural formulas and the exclusion of erroneous hypothetical structural representations by leveraging retention time estimations, thereby providing a permissible tolerance range for a given elemental composition and experimental retention time. This approach serves as a proof of concept for the development of a Quantitative Structure-Retention Relationship model using a generic gradient LC approach. The use of a widely used reversed-phase (U)HPLC column and a relatively large set of training (101) and test compounds (14) demonstrates the feasibility and potential applicability of this approach for predicting the retention behaviour of compounds in complex mixtures. By providing a standard operating procedure, this approach can be easily replicated and applied to various analytical challenges, further supporting its potential for broader implementation

Integrated optimization of geometrical parameters and flow variables for industrial incinerator performance improvement

Industrial incinerators play a vital role in waste disposal, yet their operations carry significant environmental and efficiency consequences. The current study aimed to optimize an industrial incinerator using a multi-objective algorithm in which the influence of geometrical parameters and flow variables were considered simultaneously. While the initial optimization reduced the waste temperature non-uniformity from 14.63 % to 5.14 % and the waste disposed temperature from 1510 to 1760.23 [K], the disadvantages of the noted approach were found to be the direct user interference as well as optimizing just one parameter per case. Therefore, the Central Composite Design (CCD) is employed to generate the necessary experiments from a statistical perspective instead of the user preference. Later, based on the obtained results from the CCD experiments, the sensitivity analysis calculated the degree of importance for each input parameter. As an instance, the location corresponding to the air injector was found to have 84 % influence on NOX generation, 61 % on the waste temperature uniformity, 90 % on the waste disposal temperature, 11 % impact on the incinerator efficiency, and 13 % COX generation. Other parameters, such as inlet fuel location and equivalence ratio, have a comparably lower impact (3–20 %) in different conditions. By further acknowledging the flow situation, the Genetic Algorithm (GA) was applied to consider the effective parameters from a multi-objective optimization perspective. Employing the input values proposed by GA, the waste disposed of temperature increased from 1760.23 to 2800 [K] while the temperature non-uniformity of waste surface reduced from 5.14 % to 3.17 %. Moreover, the efficiency was improved by 2 % compared to the initial optimization by producing lower environmental emissions by 43 % compared to the equivalent cases in the Design Of Experiment (DOE) chart