Hierarchical control of dc microgrids with constant power loads

This dissertation proposes general methodologies for designing hierarchical control schemes for dc microgrids loaded by constant power loads (CPLs). CPLs form a major proportion of the system loads in many microgrids. Without proper control, CPLs present destabilizing effect at the dc microgrid. In addition to stable operation of microgrid, proper current sharing among paralleled sources is essential. The proposed hierarchical control strategy consists of two control levels. The lower level consists of droop-based primary controllers which enables current-sharing among paralleled sources and also damps limit cycle oscillations due to CPLs. The higher level consists of secondary controller which compensates for voltage deviations due to primary controller. This higher level is implemented either as autonomous controllers or as a centralized controller. In the case of autonomous secondary controllers, they operate alongside of primary controllers in each of the paralleled converters. In the case of centralized secondary controller, a remote secondary controller uses a high speed communication link to communicate to local controllers. Interfacing sources with different characteristics and voltage ranges necessitates the use of complex converter topologies. As an initial step towards implementing hierarchical control scheme for such microgrids with CPLs, a linear controller is proposed for dc microgrids with standalone SEPIC, Cuk and Zeta converters. During the first stage of the two stage controller, limit cycle oscillations are damped by inserting a virtual resistance in series with the converter input inductor. During the second stage, an integral controller is added to the first stage to compensate for voltage deviations. For microgrids containing different converter topologies, stability of equilibrium points is examined and stability conditions are derived and explained. Experiments performed on a prototype microgrid are used to verify the proposed control laws. Expanding study on stability of microgrids, the maximum real power load in a dc microgrid bus is traced geometrically. The generalized circle diagram approach used in a conventional power system is modified for this purpose. The different types of buses present in a dc microgrid are described and the locus of operating points is obtained. The proposed method is verified by simulations on an example dc microgrid.Electrical and Computer Engineerin

What causes the word gap? Financial concerns may systematically suppress child-directed speech

Parents with fewer educational and economic resources (low socioeconomic-status, SES) tend to speak less to their children, with consequences for children’s later life outcomes. Despite this well-established and highly popularized link, surprisingly little research addresses why the SES “word gap” exists. Moreover, existing research focuses on individual-level explanations with little attention to structural constraints with which parents must contend. In two pre-registered studies, we test whether experiencing financial scarcity itself can suppress caregivers’ speech to their children. Study 1 suggests that caregivers who are prompted to reflect on scarcity—particularly those who reflect on financial scarcity—speak to their 3-year-olds less than a control group in a subsequent play session. Study 2 finds that caregivers speak less to their children at the end of the month—when they are more likely to be experiencing financial hardship—than the rest of the month. Thus, above and beyond the individual characteristics of parents, structural constraints may affect how much parents speak to their children

Effect of salt on survival and P-solubilization potential of phosphate solubilizing microorganisms from salt affected soils

AbstractA total of 23 phosphate solubilizing bacteria (PSB) and 35 phosphate solubilizing fungi (PSF) were isolated from 19 samples of salt affected soils. The ability of 12 selected PSB and PSF to grow and solubilize tricalcium phosphate in the presence of different concentrations of NaCl was examined. Among 12 PSB, Aerococcus sp. strain PSBCRG1-1 recorded the highest (12.15) log viable cell count at 0.4M NaCl concentration after 7days after incubation (DAI) and the lowest log cell count (1.39) was recorded by Pseudomonas aeruginosa strain PSBI3-1 at 2.0M NaCl concentration after 24h of incubation. Highest mycelial dry weight irrespective of NaCl concentrations was recorded by the Aspergillus terreus strain PSFCRG2-1 (0.567g). The percent Pi release, in general, was found to increase with increase in NaCl concentration up to 0.8M for bacterial solubilization and declined thereafter. At 15 DAI, strain Aerococcus sp. strain PSBCRG1-1 irrespective of NaCl concentrations showed the maximum P-solubilization (12.12%) which was significantly superior over all other isolates. The amount of Pi released in general among PSF was found to decrease with increase in NaCl concentration at all the incubation periods. Aspergillus sp. strain PSFNRH-2 (20.81%) recorded the maximum Pi release irrespective of the NaCl concentrations and was significantly superior over all other PSF at 7 DAI

Reactive power optimization in distribution systems considering load levels for economic benefit maximization

Introduction. The need for electrical energy has been increased sharply due to hasty growth in industrials, social and economic improvements. From the previous studies, it has been agreed that almost 13 % of the total power generated is wasted as heat loss at distribution level. It has been extensively recognized that the node voltage profile along the distribution system can be enhanced under steady state power transfer controlled by proper reactive power compensation. Capacitors have been acknowledged as reactive power compensating device in distribution systems to achieve technical and economical benefits. Novelty of this work is the application of Archimedes optimization algorithm for reactive power optimization in distribution systems so as to obtain an improved solution and also a real 94-bus Portuguese network and modified 12-bus network has been taken and validated for three different load levels which are totally new. Purpose of the proposed work is to maximize the economic benefit by reducing the power loss and capacitor purchase cost at three different load conditions subject to satisfaction of equality and inequality constraints. Methods. The economic benefit has been validated using Archimedes optimization algorithm for three load levels considering three distribution systems. Results. The computational outcomes indicated the competence of the proposed methodology in comparison with the previously published works in power loss minimization, bus voltage enhancement and more economical benefit and proved that the proposed methodology performs well compared to other methods in the literature.Вступ. Потреба в електроенергії різко зросла через стрімке зростання промисловості, соціальних та економічних поліпшень. З попередніх досліджень було встановлено, що майже 13 % усієї електроенергії, що виробляється, витрачається марно у вигляді втрат тепла на рівні розподілу. Загальновизнано, що профіль напруги вузла вздовж розподільчої системи може бути поліпшений при передачі потужності в режимі, що встановився, керованої відповідною компенсацією реактивної потужності. Конденсатори були визнані як пристрої компенсації реактивної потужності в розподільчих системах для досягнення технічних та економічних переваг. Новизна цієї роботи полягає у застосуванні алгоритму оптимізації Архімеда для оптимізації реактивної потужності в розподільчих системах з метою отримання покращеного рішення, а також було взято та перевірено реальну португальську мережу з 94 шинами та модифіковану мережу з 12 шинами для трьох різних рівнів навантаження. які абсолютно нові. Мета запропонованої роботи полягає в тому, щоб максимізувати економічний ефект за рахунок зниження втрат потужності та вартості купівлі конденсатора за трьох різних режимів навантаження за умови дотримання обмежень рівності та нерівності. Методи. Економічний ефект було підтверджено з використанням алгоритму оптимізації Архімеда для трьох рівнів навантаження з урахуванням трьох систем розподілу. Результати розрахунків показали компетентність запропонованої методології порівняно з раніше опублікованими роботами в галузі мінімізації втрат потужності, підвищення напруги на шині та більшої економічної вигоди, а також довели, що запропонована методологія добре працює порівняно з іншими методами в літературі

Cognitive Based Attention Deficit Hyperactivity Disorder Detection with Ability Assessment Using Auto Encoder Based Hidden Markov Model

Attention deficit hyperactivity disorder (ADHD) is a frequent Neuro-generative mental disorder. It can persist in adulthood and be expressed as a cognitive complaint. Behavioural analysis of ADHD consumes more time. This is a multi-informant complex procedure due to the overlaps in symptomatology which is the cause for delay in diagnosis and treatment. Dur to these behavioural consequences and various causes, no single test is utilized till now for diagnosing this disorder. Hence, a diagnosing model of ADHD based on Continuous Ability Assessment Test (CAAT) can enhance and balance behavioural assessment. The objective behind this study is to use a deep learning based model with CAAT for predicting ADHD. The proposed Auto Encoder Based Hidden Markov Model (AE-HMM) produces low-dimensional features of brain structures, and a novel Pearson Correlation Coefficient (PCC) is employed for normalizing these features in order to minimize batch effects over populations and datasets. This goal is consistently achieved and thus the proposed model outperforms few standard approaches which are considered like CogniLearn and 3-D Convolutional Neural Networks (3DCNN). It is found that the proposed AE-HMM method achieves 93.68% of accuracy, 90.66% of sensitivity, 87.72% of specificity, 87.78% of F1-score and 74.22% of kappa score

Blood cancer care in a resource limited setting during the Covid-19 outbreak; a single center experience from Sri Lanka

BackgroundThe Covid-19 pandemic has caused significant morbidity and mortality among patients with cancer. Most countries employed measures to prevent spread of Covid-19 infection which include shielding, quarantine, lockdown, travel restrictions, physical distancing and the use of personal protective equipment. This study was carried out to assess the change in patient attendance and the efficacy of newly implemented strategies to mitigate the impact of Covid-19 on services at the Lanka Hospital Blood Cancer Centre (LHBCC) in Colombo, Sri Lanka.MethodologyTelephone consultation, infection control, personal protective measures and emergency admission policy were implemented with the aim of having a Covid-19 free ward and to prevent cross-infections. This descriptive cross-sectional study was conducted with 1399 patient episodes (in-patient care or day-case review). We analysed patients treated as in-patient as well as day-case basis between 01st April 2020 and 31st December 2020.ResultsThere were 977 day-case based episodes and 422 in-patient based episodes. There was a 14% drop in episode numbers compared to same period in 2019. There was no cross infection and no patients with Covid-19 related symptoms or positive test results entered the LHBCC during the study period.ConclusionServices in blood cancer care were maintained to prevent late stage presentation and adverse outcome. Measures implemented to prevent Covid-19 were effective to allow continuation of treatment. This study highlights the importance of implementing strict protocols, clinical screening, use of appropriate personal protective equipment in delivering blood cancer care during the Covid-19 pandemic. This is the only documented study relating to outcome and successful applicability of measures to prevent spread of Covid-19 infection and maintaining services among blood cancer patients in Sri Lanka

Response and Survival Estimates of Patients With Plasma Cell Myeloma in a Resource-Constrained Setting Using Protocols From High-Income Countries:A Single-Center Experience From Sri Lanka

There is a significant disparity in global cancer care and outcome between countries. Progress in the treatment of symptomatic plasma cell myeloma (PCM) in high-income countries is not seen in low- and middle-income countries. MATERIALS AND METHODS: This is was a retrospective cohort study of all patients diagnosed with PCM between May 1, 2013, and September 30, 2021, at the first hemato-oncology center in Sri Lanka. We aimed to provide data on clinicopathologic characteristics, response, and survival estimates. RESULTS: A total of 79 patients with PCM received first-line therapy during the study period. The median age was 64 years, and approximately one third (33%) of patients were older than 70 years. There were 42 (53%) males and 37 females. Hypercalcemia, renal impairment, anemia, and bone disease were detected in 36.7%, 38%, 72.1%, and 81%, respectively. Thirty-nine, 34, and six patients received a combination of cyclophosphamide, thalidomide, and dexamethasone; bortezomib, thalidomide, and dexamethasone; and other treatments, respectively. The overall response rate (≥ partial response) was approximately 97% for both cyclophosphamide, thalidomide, and dexamethasone and bortezomib, thalidomide, and dexamethasone. Twenty-three (29%) of these patients died during the study period, but only 14 (18%) died due to PCM or associated sepsis. After a median follow-up of 40.6 months (range, 35.2-59.07 months), the median overall survival was 84.2 months (95% CI, 60.87 to not available). The 5-year estimated overall survival was 65%. CONCLUSION: To our knowledge, this is the only well-characterized study on long-term survival of patients with PCM in Sri Lanka. We have shown that it is possible to successfully apply Western treatment and supportive care protocols to the local population. These published data will help to benchmark and improve the treatment and develop blood cancer care in the local setting