Sliding mode approach for control and observation of a three phase AC-DC pulse-width modulation rectifier

Introduction. For AC-DC conversion systems, the electrical systems typically use thyristor or diode bridge rectifiers, which have relatively poor performance. Nowadays, three-phase pulse-width modulation rectifiers are widely applied in various applications for their well-known intrinsic benefits, such as adjustable DC link voltage, unity power factor, bidirectional power flow and very low total harmonic distortion. Purpose. The objective of this work is to achieve better stability and dynamic performance using sliding mode strategy for control and observation. Methods. For that purpose, first a sliding mode controller is introduced on the DC-link side to ensure a fast and accurate response of the output load voltage. Then, the sliding mode approach is employed to control the quadrature and direct components of power to maintain the input power factor at unity. Finally, this approach is used to design two observers for grid voltage estimation and online variation of load resistance. To overcome the problem associated with the use of the classical low-pass filter, an adaptive compensation algorithm is used to compensate the attenuation of the amplitude and phase delay of the observed grid voltages. This algorithm is based on the use of the two low-pass filters in cascade and ensures the minimization of chattering. Results. Comparative studies have been carried out between sliding mode control method for controlling the three-phase AC-DC pulse-width modulation rectifier and other conventional techniques. The validation by simulation and the tests carried out gave very satisfactory results and proved the effectiveness and feasibility of the sliding mode for both control and observation of three phase pulse-width modulation rectifier.Вступ. Для AC-DC систем перетворення електричні системи зазвичай використовують тиристорні або діодні мостові випрямлячі, які мають відносно погані характеристики. В даний час трифазні випрямлячі з широтно-імпульсною модуляцією широко застосовуються з різними цілями завдяки їх добре відомим внутрішнім перевагам, таким як регульована напруга у ланці постійного струму, одиничний коефіцієнт потужності, двонаправлений потік потужності та дуже низькі загальні гармонічні спотворення. Метою даної роботи є досягнення кращої стабільності та динамічних характеристик з використанням стратегії ковзного режиму для контролю та спостереження. Методи. З цією метою спочатку на стороні ланки постійного струму вводиться регулятор режиму ковзання, щоб забезпечити швидку і точну реакцію на вихідну напругу навантаження. Потім використовується метод ковзного режиму для управління квадратурною та прямою складовими потужності, щоб підтримувати вхідний коефіцієнт потужності рівним одиниці. Нарешті цей підхід використовується для розробки двох спостерігачів для оцінки напруги мережі та зміни опору навантаження в режимі онлайн. Для подолання проблеми, пов'язаної з використанням класичного низькочастотного фільтру, використовується алгоритм адаптивної компенсації, що компенсує загасання амплітуди і фазової затримки напруг мережі, що спостерігаються. Цей алгоритм заснований на використанні двох низькочастотних фільтрів у каскаді та забезпечує мінімізацію брязкоту. Результати. Були проведені порівняльні дослідження між методом керування ковзним режимом для керування трифазним випрямлячем AC-DC з широтно-імпульсною модуляцією та іншими традиційними методами. Перевірка за допомогою моделювання та проведені випробування дали дуже задовільні результати та довели ефективність та здійсненність ковзного режиму як для управління, так і для спостереження за трифазним випрямлячем з широтно-імпульсною модуляцією

Influence of granular activated carbon media properties on natural organic matter and disinfection by-product precursor removal from drinking water

Operational and financial constraints challenge effective removal of natural organic matter (NOM), and specifically disinfection by-product (DBP) precursors, at remote and/or small sites. Granular activated carbon (GAC) is a widely used treatment option for such locations, due to its relatively low maintenance and process operational simplicity. However, its efficacy is highly dependent on the media capacity for the organic matter, which in turn depends on the media characteristics. The influence of GAC media properties on NOM/DBP precursor removal has been studied using a range of established and emerging media using both batch adsorption tests and rapid small-scale column tests. DBP formation propensity (DBPFP) was measured with reference to trihalomethanes (THMs) and haloacetic acids (HAAs). All GAC media showed no selectivity for specific removal of precursors of regulated DBPs; DBP formation was a simple function of residual dissolved organic carbon (DOC) levels. UV254 was found to be a good surrogate measurement of DBPFP for an untreated water source having a high DOC. Due to the much-reduced concentration of DBP precursors, the correlation was significantly poorer for the coagulation/flocculation-pretreateed water source. Breakthrough curves generated from the microcolumn trials revealed DOC removal and consequent DBP reduction to correlate reasonably well with the prevalence pores in the 5–10 nm range. A 3–6 fold increase in capacity was recorded for a 0.005–0.045 cm3/g change in 5–10 nm-sized pore volume density. No corresponding correlation was evident with other media pore size ranges

Electrochemical evaluation of dsDNA—Liposomes interactions

The aim of the present work was to evaluate the interaction between double-stranded DNA (dsDNA) and liposomes by voltammetric methods. The experimental results were analyzed considering the initial studies regarding the oxidation mechanism of dsDNA purine bases by cyclic and differential pulse voltammetry at the glassy carbon electrode (GCE). The interaction between dsDNA and 1,2-Dimyristoyl-sn-glycero-3-phosphocholine (DMPC) was studied in a suspension containing both dsDNA and DMPC liposomes, prepared in pH = 7.0, 0.1 M phosphate buffer and using different incubation time periods. The formation of dsDNA-liposome complex was put in evidence by the decrease of the dsDNA oxidation peaks, dependent upon the incubation time. This behavior was explained considering the electroactive centers of dsDNA, guanosine monophosphate and adenosine monophosphate residues, part of them hidden inside the dsDNA-liposome complex structure and thus being unable to reach the GC electrode and preventing their oxidation. The electrochemical results are relevant for a better physicochemical characterisation of the dsDNA and dsDNA-liposome complex, which can be important for the development of gene therapy vectors

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

Sliding mode approach for control and observation of a three phase AC-DC pulse-width modulation rectifier

Introduction. For AC-DC conversion systems, the electrical systems typically use thyristor or diode bridge rectifiers, which have relatively poor performance. Nowadays, three-phase pulse-width modulation rectifiers are widely applied in various applications for their well-known intrinsic benefits, such as adjustable DC link voltage, unity power factor, bidirectional power flow and very low total harmonic distortion. Purpose. The objective of this work is to achieve better stability and dynamic performance using sliding mode strategy for control and observation. Methods. For that purpose, first a sliding mode controller is introduced on the DC-link side to ensure a fast and accurate response of the output load voltage. Then, the sliding mode approach is employed to control the quadrature and direct components of power to maintain the input power factor at unity. Finally, this approach is used to design two observers for grid voltage estimation and online variation of load resistance. To overcome the problem associated with the use of the classical low-pass filter, an adaptive compensation algorithm is used to compensate the attenuation of the amplitude and phase delay of the observed grid voltages. This algorithm is based on the use of the two low-pass filters in cascade and ensures the minimization of chattering. Results. Comparative studies have been carried out between sliding mode control method for controlling the three-phase AC-DC pulse-width modulation rectifier and other conventional techniques. The validation by simulation and the tests carried out gave very satisfactory results and proved the effectiveness and feasibility of the sliding mode for both control and observation of three phase pulse-width modulation rectifier

Is survival enough for quality of life in Sagliker Syndrome-uglifying human face appearances in chronic kidney disease?

PubMedID: 18446747Background: It is known that secondary hyperparathyroidism (SH) and particularly skeletal changes is a severe condition in chronic kidney disease (CKD). Sagliker syndrome (SS) is a very prominent feature in CKD including uglifying human face appearances, short stature, extremely severe maxillary and mandibulary changes, soft tissues in the mouth, teeth-dental abnormalities, finger tip changes and severe psychological problems. Methods: In the last 8 years we have confronted 36 extremely incredible SS cases in CKD by performing an international study in Turkey, India, Malaysia, Romania and Egypt. Results: In addition to the uglifying human face appearance, we found extremely severe X-ray and tomographical, pantomographical, histo-pathological changes in the head and whole body. Finally, we compared previous face pictures with recent ones. Just a few years earlier they had been pretty and good-looking young boys and girls. By investigating their history, we understood they had not received proper therapy and were in the late-irreversible period. Conclusion: SS is a serious and severe complication of CKD. Late and unproper treatment leads to abnormalities throughout skeleton particularly in the skull and face. Changes particularly in children and teens become irreversible-disastrous for appearance and psychological health. Appropriate treatment must begin as early as possible in specialized centers. It is possible that SS patients may survive long-term with dialysis, but with all those particular changes could anyone claim this type of life would continue in an acceptable way without extending their height, correcting all the changes in the skull and face, remodeling new faces and most particularly convincing the patients to deal with all those tragy-dramatic psychological problems? © Società Italiana di Nefrologia