Current Issue : October - December Volume : 2013 Issue Number : 4 Articles : 5 Articles
Eliminating the specific harmonics especially low-order harmonics of the output voltage of 9-level inverter using SHE-PWM\r\ncontrol scheme is investigated.Harmonic minimization is the intricate optimization problems because the nonlinear transcendental\r\nequations have multiple local optima. Increasing the degrees of freedom in the suggested method means that the number of\r\nswitching angles increases. The suggested method is able to eliminate high number of undesired harmonics. As the number of\r\nswitching angles increases, using either traditional iterative techniques or resultant theory method gets useless. In this paper to\r\novercome this problem the imperialist competitive algorithm (ICA) is used. Also a DC-DC converter is used to enhance the SHE\r\nperformance in the range for which the conventional SHE methods do not have any solution. Experimental and simulation results\r\nof a 9-level inverter show that the proposed method effectively minimizes a large number of particular harmonics so the total\r\nharmonics distortion of output voltage will be lower....
Ceramics have been used as bearing and cutting tool components,which are subjected to contact loading during their operation.The\r\npresence of surface cracks on these components decreases their contact strength.Thus, the reliability of ceramic components can be\r\nincreased by improving their contact strength through crack healing. In the present study, the effects of crack healing on the contact\r\nstrength of a silicon carbide-(SiC-) reinforced silicon nitride (Si3N4) composite subjected to various machining processes were\r\ninvestigated. The contact strength of this composite was evaluated using a sphere indentation test in which acoustic emission was\r\nused.The results showed that the contact strength of the composite improved when it was subjected to crack healing in combination\r\nwith rapping; this was true even when the composite had cracks due to a heavy machining process....
Solar energy is becoming an alternative for the limited fossil fuel resources. One of the simplest and most direct applications of\r\nthis energy is the conversion of solar radiation into heat, which can be used inWater Heating Systems. Ogun State in Nigeria was\r\nused as a case study.The solar radiation for the state was explored with an annual average of 4.775kWh/m2 recorded.The designed\r\nsystem comprised storage tanks and the collector unit which comprises wooden casing, copper tube, and aluminium foil. Test\r\nresults for the unlagged and lagged storage tanks for water temperature at various angles of inclination (2.500Ã?°ââ?¬â??20.000Ã?°) were on\r\nthe average 27.800Ã?°C and 28.300Ã?°C, respectively, for the inlet temperature and 60.100Ã?°C and 63.000Ã?°C for the outlet temperature,\r\nrespectively.The efficiency of the SolarWaterHeating System was 72.500%and the power saved 2.798kW.The cost of the unit is put\r\nat 1121,400 ($145) as at August 2012. The unit developed can be applied for the purpose of reducing the cost of energy, dealing with\r\nenvironmental challenges, and improving the use of energy, hence serving as a climate mitigation process as this can be extended\r\nfor water heating for domestic and other industrial purposes....
Structural ceramics are superior to metallic materials in terms of their high-temperature strengths and critical heat proof temperatures.\r\nHowever, compared to metallic materials, ceramics exhibit lower fracture toughness, so they are more sensitive to flaws\r\nsuch as pores and cracks. The shortness considerably decreases the component reliability. To overcome the shortness, in this study,\r\nspecial attention is paid to structural ceramics with self-crack-healing ability.There are several advantages for using a material with\r\nself-crack-healing ability. (1) After an efficient machine operation, the materials are able to self-heal the cracks introduced by the\r\nmachining. (2)Thematerials are able to self-heal the cracks introduced during service and recover the strength completely at healing\r\ntemperature. However, ways of organizing the available knowledge to increase the through-life reliability of ceramics components\r\nhave not been extensively studied. The authors propose a new concept and the corresponding flowchart. This new concept is a\r\npromising technique for increasing the through-life reliability of ceramics components with excellent self-crack-healing ability....
This paper considers the potential of replacing step-down power transformers of the entire power grid as well as part of their\r\ntransmission line branches with wireless power transfer (WPT) technology components. Exploiting the state-of-the-art evolutions\r\nin the fields of WPT technology, coupled resonators in domino arrangementsââ?¬â?domino coupled resonator (DCR) configurationsââ?¬â?\r\nare proposed as suitable technological substitute for step-down power transformers and are investigated in terms of performance\r\nmetrics such as power transfer efficiency (PTE) and transformation ratio (TR). The contribution of this paper is fivefold. First, an\r\nanalytical theoretical analysis appropriate to the study of practicalDCRconfigurations is demonstrated. In order to support theDCR\r\nconfiguration replacement venture, a detailed set of assumptions regarding efficient mid- and long-range high-power WPTs as well\r\nas related technical issues is first presented. The validity of the theoretical analysis is verified through experimental measurements.\r\nSecond, applying the proposed theoretical analysis, a wealth of system parameters that mainly influences the PTE and TR of DCR\r\nconfigurations is identified. Their quantitative effect as well as corresponding DCR configuration adjustments are first presented.\r\nThird, an approximate method, denoted as approximate chain scattering matrix (CSM) method, is first introduced. Based on the\r\nscattering matrix theory formalism, the approximate CSM method is suitable for mid- and long-range DCR configurations when\r\nthe theoretical analysis becomes computationally slow. The numerical results of approximate CSM method are compared with the\r\nrespective ones of theoretical analysis validating the extent and the accuracy of approximate CSM method. Fourth, the potential\r\nof power transformer replacement with practical DCR configurations is thoroughly investigated in terms of their TRs. A plethora\r\nof high-voltage/medium-voltage (HV/MV), MV/low-voltage (MV/LV), and HV/LV power transformers used across the world is\r\ninvestigated verifying their replacement potential with practical DCR configurations in all the cases examined. Fifth, based on a\r\ndetailed collection of dimensions concerning power transformers and transmission line branches, it is first verified that practical\r\nDCR configurations cannot only substitute all step-down power transformers of the todayââ?¬â?¢s power grid but also replace entire\r\ntransmission line branches too. Finally, it is obvious that there is a long journey ahead for WPT technology and its ultramodern\r\nDCR configurations to be affordably, widely, reliably, sustainably, and safely adopted in the human society. During these first steps of\r\nWPT development for power transmission and distribution, theoretical analyses and visions are necessary. The last cable problem,\r\nthat is, the seamless power delivery as easily as information is now transmitted through the air, is one of the major technological\r\nchallenges of the 21st century, and, thus, WPT technology will certainly play key role....
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