In this paper a three-phase PFC PWM rectifier system with low effects on the mains (VIENNA Rectifier 1) which has been developed at the Technical University Vienna in 1994 is described. As compared to conventional rectifier systems the VIENNA Rectifier 1 shows significant advantages such as unity power factor, sinusoidal input current shape (fundamental ohmic mains behavior), controlled output voltage, high efficiency (typically 97%), low costs, high power density and/or low volume, high reliability, and significantly reduced conducted common-mode noise emission. Research is done on this system in companies and universities, e.g. in Europe, U.S.A., Canada, Japan, China and Australia. Furthermore, the paper presents a comparison of a two-stage converter system, which is formed by connecting the VIENNA Rectifier 1 to a DC/DC converter with high frequency isolation (e.g. for applications in uninterruptible power supply systems) and two further developements of the Technical University Vienna which feature single-stage power conversion, i.e. VIENNA Rectifier 2 and VIENNA Rectifier 3. 相似文献
System Fe2O3TiO2 in a flux environment K2O, V2O5, SiO2 was studied. Single crystals of monoclinic Fe2TiO5 and Hollandite type phase K1.45Fe1.45Ti6.55O16 have been grown and some properties of the flux were discussed. Obtained phases were characterized by X-ray diffraction and Mössbauer spectra. 相似文献
Pentatomid bugs communicate using substrate-borne vibrational signals that are transmitted along herbaceous plant stems in the form of bending waves with a regular pattern of minimal and maximal amplitude values with distance. We tested the prediction that amplitude variation is caused by resonance, by measuring amplitude profiles of different vibrational pulses transmitted along the stem of a Cyperus alternifolius plant, and comparing their patterns with calculated spatial profiles of corresponding eigenfrequencies of a model system. The measured distance between nodes of the amplitude pattern for pulses with different frequencies matches the calculated values, confirming the prediction that resonance is indeed the cause of amplitude variation in the studied system. This confirmation is supported by the resonance profile obtained by a frequency sweep, which matches theoretical predictions of the eigenfrequencies of the studied system. Signal bandwidth influences the amount of amplitude variation. The effect of both parameters on signal propagation is discussed in the context of insect vibrational communication. 相似文献
A visible‐light‐mediated oxidative iodination of electron‐rich arenes has been developed. 2.5 mol% of unsubstituted anthraquinone as photocatalyst were used in combination with elementary iodine, trifluoroacetic acid and oxygen as the terminal oxidant. The iodination proceeds upon irradiation in non‐ or weakly‐electron donating solvents (DCM, DCE and benzene) wherein a spectral window in strongly coloured iodine solutions can be observed at around 400 nm. The method provides good to excellent yields (up to 98%) and shows excellent regioselectivity and good functional group tolerance (triple bonds, ketone, ester, amide). Moreover, the photo‐iodination was also upscaled to a 5 mmol scale (1.1 g). Mechanistic investigations by intermediate trapping and competition experiments indicate a photocatalytic arene oxidation and the subsequent reaction with iodine as a likely mechanistic pathway.
Multimegawatt horizontal axis wind turbines often operate in yawed wind transients, in which the resulting periodic loads acting on blades, drive‐train, tower, and foundation adversely impact on fatigue life. Accurately predicting yawed wind turbine aerodynamics and resulting structural loads can be challenging and would require the use of computationally expensive high‐fidelity unsteady Navier‐Stokes computational fluid dynamics. The high computational cost of this approach can be significantly reduced by using a frequency‐domain framework. The paper summarizes the main features of the COSA harmonic balance Navier‐Stokes solver for the analysis of open rotor periodic flows, presents initial validation results on the basis of the analysis of the NREL Phase VI experiment, and it also provides a sample application to the analysis of a multimegawatt turbine in yawed wind. The reported analyses indicate that the harmonic balance solver determines the considered periodic flows from 30 to 50 times faster than the conventional time‐domain approach with negligible accuracy penalty to the latter. 相似文献
In the article, the low‐cycle fatigue life durability of thin‐plate auxetic cellular structures is compared with the thin‐plate specimens of standard shape. Both the re‐entrant auxetic cellular structures and the standard specimens were cut from a 2‐mm‐thick strip of aluminium alloy 7075‐T651. First, a fatigue life curve and a cyclic curve were determined for the standard specimens. A special antibuckling device was applied to prevent the bending of the specimens. The same experimental arrangement was then applied to determine the low‐cycle fatigue life of auxetic structures. In the continuation, the most appropriate method was selected to calculate the fatigue life on the basis of the measured fatigue life curves. Abaqus and SIMULIA fe‐safe software were applied for this purpose. The best predictions for the standard specimens were obtained with the Brown‐Miller method. Finally, the selected method was applied to predict the low‐cycle fatigue life of re‐entrant auxetic cellular specimens. 相似文献
Schöck Isokorb® – Serviceability under consideration of the long-term properties Cantilever components such as balconies produce thermal bridges, and therefore it is standard practice to isolate them in the connection area with the Schöck Isokorb® load-bearing thermal insulation element. Normal live loads cause deformations and vibrations to occur in the balcony slab that are further influenced by the choice of connection element. This article shows the effect of Schöck Isokorb® on the natural frequency of the balcony slab and thus also on its vibration behaviour, based on investigations at the Materials Testing and Research Institute (MPA Karlsruhe). Additionally, product-related torsion spring strength values are derived depending on materials such as stainless-steel or glass-fibre reinforcement, and the corresponding calculation formula is validated. The stiffness values determined from this can be used in serviceability checks within FE programs. This offers designers the possibility of a precise deformation calculation during structural modelling. 相似文献
The grain growth of donor-doped BaTiO3 prepared from BaTiO3 powders with different initial specific surface areas was studied. Results show that a higher initial surface area and, consequently, a smaller critical grain size at the phase boundary drastically increase the critical amount of donor dopant, causing the grain size anomaly during sintering. 相似文献
Noise is one of the most important parameters in designing a radio frequency (RF) system. Especially in ultra-high frequency (UHF) RF identification (RFID) systems noise plays and important role. This is because the noise performance of the receiver chain is defined not only by the intrinsic noise of the receiver, but also by the large self-jammer signal. This self-jammer signal on the one hand requires that the receiver is designed for high input dynamic range which increases the intrinsic noise of the receiver. On the other hand this self-jammer signal through the effects of reciprocal mixing and range correlation contributes significantly to the total noise of the receiver. To our knowledge this is the first work that deals in detail with the amplitude and phase noise in a UHF RFID system. 相似文献
Based on an analysis of basic realization possibilities, the structure of the power circuit of a new single-stage three-phase boost-type pulsewidth modulated (PWM) rectifier system (VIENNA Rectifier II) is developed. This system has continuous sinusoidal time behavior of the input currents and high-frequency isolation of the output voltage, which is controlled in a highly dynamic manner. As compared to a conventional two-stage realization, this system has substantially lower complexity and allows the realization of several isolated output circuits with minimum effort. The basic function of the new PWM rectifier system is described based on the conduction states occurring within a pulse period. Furthermore, a straightforward space- vector-oriented method for the system control is proposed which guarantees a symmetric magnetization of the transformer. Also, it makes possible a sinusoidal control of the mains phase currents in phase with the associated phase voltages. By digital simulation, the theoretical considerations are verified and the stresses on the power semiconductors of the new converter system are determined. Finally, results of an experimental analysis of a 2.5-kW laboratory prototype of the system are given, and the direct startup and the short-circuit protection of the converter are discussed. Also, the advantages and disadvantages of the new converter system are compiled in the form of an overview 相似文献
