Current Issue : January - March Volume : 2018 Issue Number : 1 Articles : 5 Articles
In recent years the aerospace industry has made a growing effort to develop a quieter and\nmore environmentally friendly aircraft. In particular, several research activities have been focused on\ninnovative solutions aimed at the design/optimization of an on-board electric system fully compatible\nwith this new approach. A first important step in the evolution towards an All Electric Aircraft (AEA)\nis the replacement of the hydraulic actuators with fully electric ones. The transition process is not easy\nto carry out, since weight, size and reliability represent highly critical issues for aircraft applications.\nIn this context, the significant improvements in semiconductor technologies can be exploited as\na critical means to overcome the constraints mentioned. Indeed, this work proposes a Silicon Carbide\n(SiC) based Power Factor Correction (PFC) converter, whose design and control have been tailored in\norder to properly supply a wide range of on-board Electro-Mechanical Actuators (EMA). In particular,\nwhile the adopted circuit topology allows for power factor correction and bi-directional power\nflow, the SiC technology, thanks to the higher efficiency with respect to other semiconductor-based\ntechnologies, leads to a significant reduction in the overall system weight/volume. Furthermore,\nto meet the strict requirements in terms of dynamic and steady state performance imposed by\nthe application, a novel adaptive regulator is conceived. A reduced-scale laboratory prototype of\nthe SiC-based converter (3 kVA) is realized in order to verify the effectiveness of the proposed design\nand control approach....
Multilevel modulation strategy is an important factor affecting the output performance of\nmultilevel converters. In this paper, the relationship between phase-shifted pulse width modulation\n(PWM) and phase disposition PWM is analyzed, and then an improved hybrid modulation strategy is\nproposed for cascaded H-bridge. In addition, the implementation method of multilevel discontinuous\nmodulation for an improved modulation strategy is described. The new modulation strategy is\noptimized to increase the DC link voltage utilization and further improvement in output harmonics\nby the injection of a common voltage into the reference. Simulation and experiment verify the\neffectiveness of the proposed modulation strategy....
Aimed to clarify the correlation characteristics between the internal partial discharge (PD)\nin negative direct current (DC) gas insulated system (GIS) and gas pressure initiated by two typical\ndefects (i.e., free-metal particles and metal protrusion), this study on PD decomposition of sulfur\nhexafluoride (SF6) was investigated under different pressures on the basis of constructing a SF6\ndecomposition experimental platform with DC PD. Free-metal particles and metal protrusion in a GIS\nwere simulated using a spherical-bowl electrode and a needle-plate electrode, respectively. Trends\nand differences in the performance of SF6 decomposition components SOF2, SO2F2, CO2, and SO2\nat different pressures were compared and analyzed by experiments under different defects. Based\non gas microscopic ionization theory, the relationship between the decomposition component and\ngas pressure was deduced and verified. The concentrations of different decomposition components\nwere found to vary with the change in gas pressure under different defects, whereas the characteristic\nratios of decomposition components versus gas pressure showed a similar trend....
A DC micro plasma jet for local micro deposition of a:C-H film in the ambient vacuum\nof scanning electron microscope (SEM) chamber is proposed. Acetylene (C2H2) gas was locally fed\ninto the chamber through an orifice shaped gas nozzle (OGN) at 6.6 sccm in flow rate by applying\n80 kPa-inlet pressure with an additional direct pumping system equipped on the SEM chamber.\nAs a cathode, a cut of n-type silicon (Si) wafer was placed right in front of the OGN at 200 �¼m gap\ndistance. By applying a positive DC voltage to the OGN, C2H2 plasma was generated locally between\nthe electrodes. During discharge, the voltage increased and the current decreased due to deposition\nof insulating film on the Si wafer with resulting in automatic termination of discharge at the constant\nsource voltage. A symmetric mountain-shaped a:C-H film of 5 �¼m height was deposited at the center\nby operation for 15 s. Films were deposited with variation of gas flow rate, gap distance, voltage\nand current, and deposition time. The films were directly observed by SEM and analyzed by surface\nprofiler and by Raman spectroscopy....
This paper describes the design of a high-efficiency energy harvesting circuit with an\nintegrated antenna. The circuit is composed of series resonance and boost rectifier circuits for\nconverting radio frequency power into boosted direct current (DC) voltage. The measured output DC\nvoltage is 5.67 V for an input of 100 mV at 900 MHz. Antenna input impedance matching is optimized\nfor greater efficiency and miniaturization. The measured efficiency of this antenna-integrated energy\nharvester is 60% for âË?â??4.85 dBm input power and a load resistance equal to 20 kÃ?© at 905 MHz....
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