A New ZCS-PWM Full-Bridge Boost Converter

The objective of this thesis is to propose, analyze, design, implement, and experimentally confirm the operation of a new Zero-Current-Switching PWM dc-dc full- bridge boost converter that does not have the drawbacks ofpreviously proposed circuits of the same type. In this thesis, the general operating principles of the converter are reviewed, and the converter’s operation is discussed in detail and analyzed mathematically. As a result of the mathematical analysis, key voltage and current equations that describes the operation of the auxiliary circuit and other converter devices have been derived. The steady state equations of each mode of operation are used as the basis of a MATLAB program that is used to generate steady-state characteristic curves that shows the effect that individual circuit parameters have on the operation of the auxiliary circuit and the boost converter. Observations as to their steady-state characteristics are made and the curves are used as part of a design procedure to select the components of the converter, especially those of the auxiliary circuit. An experimental full-bridge PWM dc-dc boost converter prototype is built based on the converter design and typical waveforms are presented. The efficiency of the proposed converter operating with the auxiliary circuit is compared to that of a standard PWM dc-dc full-bridge boost converter and the increased efficiency o f the proposed converter is confirme

Soft-Switching DC-DC Converters

Power electronics converters are implemented with switching devices that turn on and off while power is being converted from one form to another. They operate with high switching frequencies to reduce the size of the converters\u27 inductors, transformers and capacitors. Such high switching frequency operation, however, increases the amount of power that is lost due to switching losses and thus reduces power converter efficiency. Switching losses are caused by the overlap of switch voltage and switch current during a switching transition. If, however, either the voltage across or the current flowing through a switch is zero during a switching transition, then there is no overlap of switch voltage and switch current so in theory, there are no switching losses. Techniques that ensure that this happens are referred to as soft-switching techniques in the power electronics literature and there are two types: zero-voltage switching (ZVS) and zero-current switching (ZCS). For pulse-width modulated (PWM) Dc-Dc converters, both ZVS and ZCS are typically implemented with auxiliary circuits that help the main power switches operate with soft-switching. Although these auxiliary circuits do help improve the efficiency of the converters, they increase their cost. There is, therefore, motivation to try to make these auxiliary circuits as simple and as inexpensive as possible. Three new soft-switching Dc-Dc PWM converters are proposed in this thesis. For each converter, a very simple auxiliary circuit that consists of only a single active switching device and a few passive components is used to reduce the switching losses in the main power switches. The outstanding feature of each converter is the simplicity of its auxiliary circuit, which unlike most other previously proposed converters of similar type, avoids the use of multiple active auxiliary switches. In this thesis, the operation of each proposed converter is explained, analyzed, and the results of the analysis are used to develop a design procedure to select key component values. This design procedure is demonstrated with an example that was used in the implementation of an experimental prototype. The feasibility of each proposed converter is confirmed with experimental result obtained from a prototype converter

A cross-disciplinary analysis of thematic structure of dissertation abstracts

The ways by which the academic texts are investigated differ from time to time with legacies of each tradition influencing the subsequent approaches. One of the approaches that has not lost its favor ever since it was established is the Australian Systemic Functional tradition. Based on the descriptions provided by this tradition, in this study, the thematic structure (Halliday, 1994) of the gap indication move and the Introduction section (Swales, 2004) of 120 dissertation abstracts from six disciplines was investigated at two levels, i.e. choice of theme type and thematic progression. The simple topical theme was recognized as the typical theme of the rhetorical units in focus across the six disciplines. With respect to the thematic progression, the theme-reiteration and zig-zag patterns were found to be the characteristic patterns. These results indicate that the language of abstracts is remarkably factual and far from abstraction

UTJECAJ RASLOJAVANJA ČIMBENIKA OŠTEĆENJA IZAZVANIH MINIRANJEM U HOEK-BROWNOVU KRITERIJU SLOMA NA PRAĆENJE OŠTEĆENJA ETAŽA U KOPOVIMA

The process of creating a slope in a rock mass using the excavation and blasting methods consistently leads to stress release in the rock mass, resulting in a certain level of fracture and disturbance. Blast-induced vibrations can also influence the quality of the rock mass remaining after the blasting, as well as the stability and bench damage monitoring (BDM) of mines. A damage factor (D) is included in the Hoek–Brown failure criterion to compute the disturbance of a rock mass in creating a slope. Choosing the value and thickness of the blast zone for the Hoek–Brown criterion is crucial in the safety analysis and BDM of mines. However, the selection is still a crucial technical challenge in this criterion. Employing nonlinear layering, the present study divides the rock mass behind a blast hole into several layers with decreasing D values applied to each layer. The numerical simulation was conducted using the FLAC finite difference software for bench vibration assessment and damage monitoring by checking the peak particle velocity (PPV) in the bench face with different geometries. Behind the blast hole, five different layers of D were considered through which the Hoek–Brown properties of the rock mass declined nonlinearly during the execution of the model. Since the disturbance threshold of PPV was assumed to be 120 mm/s, the toe and middle parts of the small benches were in the disturbance threshold, while for the medium and high benches, only the bench toe was within the disturbance threshold.Proces stvaranja kosina u stijenskoj masi metodama iskopa i miniranja dovodi do oslobađanja naprezanja u stijenskoj masi, što rezultira određenom razinom loma i oštećenja. Vibracije izazvane miniranjem također mogu utjecati na kvalitetu minirane stijenske mase, kao i na stabilnost i praćenje oštećenja etaža (BDM) površinskoga kopa. Koeficijent poremećenosti stijenske mase (D) uključen je u Hoek-Brownov kriterij sloma za izračunavanje oštećenja stijenske mase pri izradi kosine. Odabir vrijednosti i širine zone miniranja prema Hoek-Brownovu kriteriju ključan je u analizi sigurnosti i BDM-a kopova. Međutim, odabir još uvijek predstavlja ključni tehnički izazov. Koristeći se nelinearnom slojevitošću, ova analiza dijeli stijensku masu iza minske bušotine u nekoliko slojeva sa smanjivanim vrijednostima D za pojedini sloj. Numerička simulacija provedena je korištenjem softvera FLAC za procjenu vibracija na etažama i praćenje oštećenja provjerom vršne brzine čestica (PPV) na etaži s različitim geometrijama. Iza minske bušotine razmatrano je pet različitih nizova D kroz koje su Hoek-Brownova svojstva stijenske mase nelinearno mijenjana tijekom analize modela. Budući da je granična vrijednost PPV-a pretpostavljena na 120 mm/s, vrh i središnji dijelovi malih etaža bili su na graničnoj vrijednosti oštećenja, dok je za srednje i visoke etaže samo vrh etaže bio unutar granične vrijednosti oštećenja

Fabrication of chelating diethylenetriaminated pan micro and nano fibers for heavy metal removal

In this study, commercial acrylic fibers were modified with diethylenetriamine to prepare metal chelating fibers. The effects of process parameters on the efficiency of the reaction were investigated. FTIR spectroscopy and TGA analysis were used to confirm the chemical changes made to the fibers during the reaction. The ability of the modified fibers for removal of Pb (II), Cu (II) and Ce (IV) ions from aqueous media was determined. The modified fibers showed a slight decrease in mechanical properties compared to raw ones. Furthermore, the acrylic micro fibers were electrospun to nanofibers and the ability of modified nanofibers for the adsorption of the metal ions was studied

Reversible Hydrogen Storage in Electrospun Composite Nanofibers

Composite nanofibers containing single-walled carbon nanotubes (SWNT) were prepared by using elec-trospinning technique and hydrogen adsorption/desorption isotherms were carried out by a Sieverts appa-ratus at room temperature. The SEM analysis of the nanofibers revealed that the deformation of the nano-fiber increases with increasing SWNT concentration. The diameter of neat nanofibers was below 200 nm and had smooth surface. The surface of the composite nanofibers was rough even by adding low quantity of SWNT. The hydrogen storage results showed an improvement in the adsorption capacity with increasing the SWNT content in composite nanofibers. These nanofibers were evacuated again to remove the ad-sorbed hydrogen at room temperature. Moreover, even though specific surface area and total pore volume were important factors for increasing the capacity of hydrogen adsorption. Finally, maximum adsorption capacity was 0.29 wt % in case of nanofibers with 10 wt % SWNT under 30 bar at 298 K. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3520