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EN
Modular multilevel converter (MMC) is considered as a good technology for high-voltage direct current (HVDC) transmission systems. It can generate a good quality staircase output voltage waveform due to the cascaded connection of large number of identical sub-modules (SMs). Energy variations in SM capacitor lead to capacitor voltage fluctuations which affect the size and stability of MMC. Traditionally MMC arm voltages are controlled using direct modulation method. The closed loop and open loop compensated modulation methods are implemented to overcome the drawbacks created in direct modulation method. However, these methods rely on the accurate measurements or estimation of SM capacitor voltages. In this paper, capacitor energy variations in MMC based on direct modulation method under three different categories using proportional-resonant (PR) controllers are discussed as (a) pure sinusoidal arm current (b) sinusoidal arm current with addition of large 2nd harmonic (c) sinusoidal arm current with addition of 2nd +4th harmonics. Analytical and simulation results show reduction in capacitor energy variations in MMC while injecting harmonics in the arm currents using direct modulation method.
EN
The computer modeling of the solidification process in castings with local composite reinforcement (LCR) obtained as a result of in situ reactions of self-propagating high temperature synthesis (SHS) is difficult due to limited data on the thermo-physical parameters of exothermic effects and the kinetics of the synthesis reaction. In the present study, Hadfield cast steel casting was manufactured with LCR containing titanium carbide particles obtained in situ by the SHS method. Reaction kinetics of titanium carbide synthesis in the composite casting were determined on the basis of temperature measurements in the area of LCR during the process. For the estimation of the reaction, the Fourier Thermal Analysis method was used. The paper presents the results of temperature measurement and the results of the calculation of SHS reaction kinetics. It was found that the reaction time under the conditions of the analyzed casting is below 3 s.
PL
W artykule przedstawiono wyniki badań własności i mikrostruktury wytwarzanych technologią metalurgii proszków kompozytów aluminium- -grafen. Materiał badawczy stanowiły kształtki z proszku aluminium z dodatkiem 2 i 5% wag. grafenu. Porowate kształtki dwukrotnie prasowano pod pierwszym ciśnieniem wynoszącym odpowiednio 300 i 400 MPa oraz spiekano w atmosferze azotu w temperaturze 600°C przez 60 min, po czym ponownie prasowano pod ciśnieniem 300 MPa i spiekano w tych samych warunkach. Kompozyty poddano badaniom gęstości względnej, twardości, wytrzymałości na zginanie. W pracy przedstawiono także fotografie typowych obszarów mikrostruktury kompozytów oraz przełomy powstałe w wyniku trójpunktowej próby zginania.
EN
The results of investigations of properties and microstructure of aluminum - graphene composites produced by powder metallurgy technology are presented. The research material was made of aluminum powder with the addition of 2 and 5wt% graphene. The porous bodies were pressed twice under a first pressure of 300 and 400 MPa, respectively, and sintered in a nitrogen atmosphere at 600°C for 60 minutes. The composites were subjected to relative density, hardness and bending strength tests. The paper also presents photographs of typical areas of microstructure of composites and the morphology of fractures as a result from a three-point bending test.
PL
W artykule przedstawiono możliwości zastosowania wykresu Pareto-Lorenza, diagramu Ishikawy i metody 5Why do identyfikacji głównych przyczyn wad materiałowych odlewów tłoków silnikowych. Metody "leanowskie" użyto w celu ograniczenia negatywnego zjawiska o największej częstotliwości występowania, a tym samym przyczyn generowania największych kosztów związanych z reklamacjami jakościowymi odlewów dla przemysłu motoryzacyjnego. Stosując metodę "od szczegółu do ogółu" w układzie 6M-3 kategorie przyczyn wad, zaproponowano kierunki usprawniające.
EN
he paper presents the possibilities of using the Pareto-Lorenzo diagram, the Ishikawa diagram and the 5Why method to identify the main causes of material defects in engine piston castings. "Lean" methods were used to limit the negative phenomenon with the highest frequency of occurrence, thus the reasons for generating the largest costs related to quality complaints of automotive cast industry. Using the "from the detail to the general" method in the 6M-3 system, the categories of defect causes, improvement directions were proposed.
5
Content available remote Numerical study of residual thermal stresses in MMC
EN
In this paper, numerical study analysis of residual thermal stresses in aluminum matrix reinforced with silicon carbide particles with double-crack has been carried out. is studied in order to determine the thermo-mechanical behavior under the effect of different temperature gradients during cooling. For a more realistic simulation of the microstructure of these materials subjected to different loadings, a representative volume element may be used. In this paper, three different types of crack width a = 5 μm, 10 μm, 15 μm, has been carried. The thermal residual stresses are calculated by considering a wide range of cracks of different penetrations proximity to particle of 0.1, 0.2 and 0.5 μm. regarding the distribution of the stresses along the plane of the crack and in vicinity of the particle, results show that the penetration of the crack in the matrix causes an asymmetry. The inter-distance between crack and particle plays an important role regarding the generation of residual stresses. The lower the inter-distance, the higher the internal stresses of normal residual stresses of σzz.
EN
The paper presents a detailed description of one of the newest methods of vacuum saturation of reinforcing preforms in gypsum molds. As an appropriate selection of the infiltration time is a crucial problem during realization of this process, aim of the analysis shown in the paper is to present methods of selection of subatmospheric pressure application time, a sequence of lowering and increasing pressure, as well as examining influence of structure of reinforcing preforms on efficiency of this process. To realize the aim, studies on infiltration of reinforcing preforms made of a corundum sinter of various granulation of sintered particles with a model alloy were conducted. The infiltration process analysis was carried out in two stages. The first stage consisted in investigation of influence of lengthening of sucking off air from the reinforcing preforms on efficiency of this process. In the second stage, an analysis of influence of a two-staged infiltration process on saturation of the studied materials was conducted. Because the studied preforms were of similar porosity, the obtained differences of the saturation level of particular preforms have shown, that the saturation process is influenced mostly by size of pores present in the reinforcement. Because of these differences, each reinforcement type requires individual selection of time and sequence of the saturation process. For reinforcements of higher pore diameter, it is sufficient to simply increase air sucking off time to improve the saturation, while for reinforcement of smaller pore diameter, it is a better solution to apply the two-staged process of sucking off air. Application of the proposed analysis method allows not only obtaining composite castings of higher quality, but also economical optimization of the whole process.
EN
This paper investigates a control structure to enhance the DC fault ride-through capability of a full-bridge modular multilevel converter (MMC) station, while ensuring a stable controlled operation as a STATCOM during DC faults without the need for fault isolation. Taking advantage of the switching states of a full-bridge submodule, a DC current controller is proposed, which provides the DC voltage reference for the modulation when a DC fault is detected. By changing the outer controllers strategy from DC voltage or active power control to converter energy control during a fault, the decoupling of the converter operation from the DC side dynamics is realized. In this paper, the focus is on the control methodology at all times of operation and the evaluation of the STATCOM control during a fault. To this end, extensive simulations were performed on a three-terminal high voltage direct current (HVDC) grid in radial configuration and a pole-to-pole DC fault case was investigated. The results showed that the AC voltage and current were controlled within limits at all times, while the full-bridge MMC was able to provide reactive power support to the AC grid. Moreover, using the proposed control methodology, the transients at the operation transition points between STATCOM and inverter/rectifier operation were minimized and the stations were able to safely ride through the fault.
EN
The modular multilevel converter (MMC) is a well-known solution for medium and high voltage high power converter systems. This paper deals with energy balancing of MMCs. The analysis includes multi-converter systems. In order to provide clear view, the MMC control system is divided into hierarchical levels. Details of control and balancing methods are discussed for each level separately. Finally, experimental results, based on multi-converter test setup, are presented.
EN
Metal matrix composites (MMCs) are still scarcely described due to various combinations of used materials and a wide array of technologies. Applying the Failure Mode and Effect Analysis (FMEA) method to describe the quality of metal composite castings may contribute to eliminating specific (characteristic only to these materials) defects. This part of the analysis determines the criticality numbers, meaning the frequency of a given failure, detectability level and significance of a given failure to the group of specific composite casting failures. It contributes to establishing the priority number (P), which is a measure used to assess risk, a notion essential in discussing quality in a composite casting.
EN
Wear resistance of TiC-cast steel metal matrix composite has been investigated. Composites were obtained with SHSB method known as SHS synthesis during casting. It has been shown the differences in wear between composite and base cast steel. The Miller slurry machine test were used to determine wear loss of the specimens. The slurry was composed of SiC and water. The worn surface of specimens after test, were studied by SEM. Experimental observation has shown that surface of composite zone is not homogenous and consist the matrix lakes. Microscopic observations revealed the long grooves with SiC particles indented in the base alloy area, and spalling pits in the composite area. Due to the presence of TiC carbides on composite layer, specimens with TiC reinforced cast steel exhibited higher abrasion resistance. The wear of TiC reinforced cast steel mechanism was initially by wearing of soft matrix and in second stage by polishing and spalling of TiC. Summary weight loss after 16hr test was 0,14÷0,23 g for composite specimens and 0,90 g for base steel.
EN
During operation of marine pumps, one of the most common disability is tribological wear of shaft neck cooperating with the gland. In the practice, worn shafts are exchanged for new or are regenerated by chromium plating, padding or thermally sprayed of ceramic coatings, mainly Al2O3 In this article, the use of plasma sprayed Ni-5% Al-15%Al2O3 composite coatings were proposed. The surfaces of coatings by turning and burnishing treatments were shaped. Tribological properties of composite materials are dependent on the proportion and size of the reinforcing phase particles contained in a metal matrix. A reinforcement composite with very small dimensions and the amounts may result in increased wear and increase the coefficient of friction. It is therefore important to check whether the advisable of phase composition will not adversely affect the wear of the composite and the cooperating the part. The presence of a 15% volume fraction of the alumina particles on the selected tribological properties of the Ni-5% Al matrix composite coatings were evaluated. In order to assess the effect of the applied tapes of finishing on wear of MMC coatings, the tribological tests were performed on the "T05" machine with head roll- piece type. It has been found that the burnishing favours a lower wear of composite coating and the cooperating element compared to the coatings after turning treatments. At the same time observed more than ten times less wear intensity of MMC coatings in the initial time of friction, which may indicate a shorter time needed to grind of cooperating elements.
EN
The aim of this paper is the numerical analysis of the one of main part of car engine – piston sleeve. The first example is for piston sleeve made of metal matrix composite (MMC) A356R. The second improved material structure is layered. Both of them are comparison to the classical structure of piston sleeve made of Cr-Ni stainless steel. The layered material structure contains the anti-abrasion layer at the inner surface of piston sleeve, where the contact and friction is highest, FGM (functionally graded material) interface and the layer of virgin material on the outer surface made of A356R. The complex thermo-elastic model with Archard's condition as a wear law is proposed. The piston sleeve is modelling as a thin walled cylindrical axisymmetric shell. The coupled between the formulation of thermoelasticity of cylindrical axisymmetric shell and the Archard’s law with functionally changes of local hardness is proposed.
13
Content available remote Overvoltage Assessment of Point-to-Point VSC-Based HVDC Systems
PL
Artykuł przedstawia rezultaty symulacji przepięć występujących w sieci DC bazującej na wykorzystaniu VSC (voltage source converters). Układ VSC wykorzystuje technikę MMC (modular multi-level converter). Rozpatrzono też wpływ sąsziadującej z siecią DC sieci AC.
EN
The application of voltage source converters (VSCs) into medium- and high-power transmission is currently attracting increased attention. In view of this increased attention, this article provides the simulation results of the overvoltages produced by faults occurring in the DC line of a point-to-point VSC-based HVDC system as well as in a neighbouring AC line system. The VSC converters considered here use the MMC (modular multi-level converter) technique to generate the voltage waveform. For pole-to-ground faults occurring in the DC link of a symmetrical monopole system, significantly high overvoltages may arise on the sound pole. This condition is of concern, mainly during the planning stage of the VSC-HVDC project, as it may require the installation of surge arresters with a good performance and/or also additional insulation of the line. In addition, unless the faults occurring on the DC link are quickly removed, sustained overvoltages can threaten the normal operation of the surge arresters installed on the DC side of both sound and faulty poles. Faults and other events in the AC system (near the DC link) may lead to sustained overvoltages that should also be examined regarding the response of the surge arresters.
14
Content available remote Blanking-time effects in the context of modular multilevel converters
EN
Blanking-time (or blocking-time) effects in power-electronic converters have been known since long. They introduce disturbances which are not easily handled by control means. Their compensation is not straightforward, because they depend on the sign (direction) and to a much lesser degree on the magnitude of the current flowing through the switching devices. Depending on the topology of the converter and the relation between blanking time and pulse period, the influence on the output quantities is relevant. This paper analyses blanking-time effects based on measurements performed on a modular multilevel converter – where these effects also influence the harmonic content of the DC voltage considerably. A straightforward FPGA-based compensation mechanism is implemented and its mitigation effect documented.
PL
Efekty pauz (lub czasu blokowania) w przekształtnikach energoelektronicznych są znane od dawna. Wprowadzają one zaburzenia trudne do opanowania metodami sterowania. Nie są one bezpośrednio kompensowane ponieważ zależą one głównie od kierunku a w mniejszym stopniu od wartości prądu przełączników. Wpływ pauz na wielkości wyjściowe przekształtnika zależy od jego topologii oraz stosunku czasu pauzy do czasu trwania impulsów łączeniowych. Artykuł ten analizuje skutki pauz na pomiary przeprowadzone na modularnych przekształtnikach wielopoziomowych, w których wpływają one znacząco na zawartość harmonicznych i na napięcie wyjściowe. W artykule został zastosowany bezpośredni, oparty na FPGA, mechanizm kompensacji i udokumentowane zostaly jego skutki.
15
Content available remote Effect of Particulate Reinforced Aluminium Metal Matrix Composite – A Review
EN
The combined effect of reinforcements on Aluminium Metal Matrix composites with individual and multiple particulate reinforcements like Hybrid Metal matrix composites are finding increased applications in aerospace, automobile, space, underwater, and transportation applications. This is mainly due to improved mechanical and tribological properties like strength, stiffness, abrasion, impact resistance and wear resistance. In the present scenario, a lot of research activities were on pipe line. This paper guides the researchers and engineers towards proper selection of materials by their properties in the relevant field and different techniques involved in manufacturing of metal matrix composites, particularly on the liquid state metal processing technique.
Logistyka
|
2015
|
nr 3
4593--4600, CD 1
PL
Podczas eksploatacji pomp okrętowych jedną z najczęściej spotykanych niesprawności jest zużycie tribologiczne czopa wału współpracującego z dławnicą. W dotychczasowej praktyce morskiej, tak zużyte wały wymienia się na nowe lub poddaje się je regeneracji poprzez chromowanie galwaniczne, napawanie, natryskiwane cieplnie powłok ceramicznych, głównie Al2O3. W niniejszym artykule zaproponowano wykorzystanie powłok kompozytowych, MMC, Ni-5%Al-15%Al2O3, które otrzymano metodą natryskiwania plazmowego. Powierzchnię powłok kształtowano w wyniku obróbki toczeniem oraz nagniataniem. Celem oceny wpływu zastosowanej obróbki wykończeniowej na zużycie powłok MMC przeprowadzono badania tribologiczne na maszynie T05 z głowicą typu rolka-klocek. Stwierdzono, że nagniatanie sprzyja mniejszemu zużyciu powłoki kompozytowej jak i elementu współpracującego w porównaniu do powłok po obróbce toczeniem. Jednocześnie zaobserwowano ponad dziesięciokrotnie mniejszą intensywność zużycia powłok MMC w początkowym czasie tarcia, co może świadczyć o krótszym czasie potrzebnym do dotarcia współpracujących ze sobą elementów.
EN
During operation of marine pumps one of the most common disability is tribological wear of shaft neck cooperating with the gland. In the practice, worn shafts are exchanged for new or are regenerated by chromium plating, padding or thermally sprayed of ceramic coatings, mainly Al2O3 In this article, the use of plasma sprayed Ni-5% Al-15%Al2O3 composite coatings were proposed. The surfaces of coatings by turning and burnishing treatments were shaped. In order to assess the effect of the applied tapes of finishing on wear of MMC coatings, the tribological tests were performed on the "T05" machine with head roll- piece type. It has been found that the burnishing favors a lower wear of composite coating and the cooperating element compared to the coatings after turning treatments. At the same time observed more than ten times less wear intensity of MMC coatings in the initial time of friction, which may indicate a shorter time needed to grind of cooperating elements.
EN
The operation of the Modular Multilevel Converter (MMC) is the main subject of this paper. Selected operation aspects are discussed on the basis of the averaged model, with a special focus on power section parameters and control. The direct modulation method has been chosen for the control of the MMC.
EN
Application of in-situ technique allows for fabrication of composite zone in the casting with a matrix of cast steel with low carbon content. The reinforcing phase in the composite zone is titanium carbide, produced by the synthesis of substrates introduced into the mould in the form of pressed compacts. Metallographic studies were performed in order to determine of homogeneity of composite zones and characteristic features existed in transition area between the composite zone and core of the casting. The transition areas of composites zone were blurred and there were no discontinuities caused by poor bonding between the composite zone and the core of the casting. To confirm the correct run of the TiC synthesis, phase analysis was performed of the base alloy as well as composite zone. The results of this examination indicated that there were two phases in composite zone, i.e. α Fe and TiC and only α Fe was observed in base alloy. Changes of mechanical properties in the composite zone were examined, measuring its hardness HV. The average hardness values of the base alloy and composite zone were 175±4 and 696±201 HV, respectively.
PL
W odlewie z ferrytycznego staliwa o niskiej zawartosci węgla, otrzymano strefy kompozytowe. Fazą wzmacniającą strefy kompozytowej był węglik tytanu TiC, uzyskany w wyniku syntezy in situ substratów, wprowadzonych do formy w postaci wyprasek. Przeprowadzono badania metalograficzne stref kompozytowych w celu określenia jednorodności otrzymanej strefy kompozytowej oraz charakteru obszaru przejściowego: strefa kompozytowa - rdzeń odlewu. Obszar przejściowy, pomiędzy strefa kompozytowa, a rdzeniem odlewu, charakteryzował się gradientowym rozkładem TiC oraz brakiem nieciągłości. W celu potwierdzenia prawidłowego przebiegu procesu syntezy TiC, przeprowadzono analizę fazową stopu bazowego oraz otrzymanej strefy kompozytowej. Potwierdzono, że w obrębie strefy kompozytowej występują dwie fazy tj. α Fe i TiC, a stop bazowy zawiera wyłącznie α Fe. Analizowano zmiany mechaniczne w obrębie otrzymanej strefy kompozytowej, badając jej twardość HV. Średnia wartość twardości stopu bazowego oraz strefy kompozytowej wynosiła odpowiednio 175±4 i 696±201 HV.
PL
W celu otrzymania nanokompozytów zastosowano nowatorską metodę selektywnego laserowego spiekania i/lub stapiania (SLS/M). Fazą umacniającą były nanokrystaliczne proszki TiC oraz TiB2 + TiC + B4C otrzymane metodą zol-żel. Jako osnowę zastosowano komercyjny proszek stali nierdzewnej 316L. W procesach wytwarzania nanokompozytu wykorzystano urządzenie MCP HEK Realizer II. W pracy badano wpływ parametrów procesu SLM/S oraz udziału objętościowego nanokrystalicznych proszków na morfologię, mikrostrukturę oraz twardość otrzymywanych kompozytów. Kompozyty te charakteryzowano metodami TEM, SEM i XRD. Ponadto badano twardość nanokompozytowych próbek sposobem Vickersa. Stwierdzono dobrą dyspersję cząstek nc-TiC oraz Ti-B-C w osnowie stalowej, przy czym w przypadku mieszaniny proszków TiB2 + TiC + B4C zaobserwowano ich tendencję do tworzenia aglomeratów w kompozycie. W procesach SLM/S wraz ze wzrostem objętościowego udziału faz umacniających osiągnięto znaczne zwiększenie twardości nanokompozytów w porównaniu z twardością osnowy.
EN
The innovative method of the nanocomposite materials manufacturing has been developed, in which the SLM (Selective Laser Melting) technique was used. As reinforced phase nanocrystalline TiC and Ti-B-C powder, obtained in non-hydrolytical sol-gel method, have been used. As a matrix 316L stainless steel have been applied. MCP HEK Realizer II device was employed in SLM/S processes. In present work, the influence of SLM/S process parameters, and the volume fraction of nanocrystalline powders on the morphology, microstructure and hardness of the composites have been investigated. The obtained composites were characterized by TEM, SEM and XRD. In addition, the hardness of nanocomposite were examined by Vickers method. It was a good A uniform dispersion of nc-TiC and Ti-BC particles in the steel matrix was obtained, but in the case of Ti-BC nanoparticles tendency to form agglomerates in the composite was observed. In SLM/S process with increase of volume fraction of strengthening phases, a significant increase of hardness of the nanocomposites in comparison with the hardness of the matrix was achieved.
EN
As the reports in the literature regarding corrosion performance of Al/TiB2 MMC are rather contradictory, the optimization of laser surface alloying parameters for these composite coatings seems to be necessary. The characterization of the MMC was carried out by optical microscopy (OM), scanning electron microscopy (SEM/EDS) and x-ray diffraction (XRD). Partial melting of the alloying powder occurred and the chemical reactions with the a-Al in the matrix led to the formation of AlTi and AlB2 phases. Eutectics of TiB2/Al and TiB2/Ti were observed. The results of the tests indicate that TiB2 reinforcement does not give significant increase in microhardness of aluminium. The corrosion resistance of a single laser trackline MMC in a 3.65 % NaCl solution was improved, especially for the sample produced at high scan speed, with the lowest volume fraction of TiB2 particles.
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