DC traction power substation using eighteen-pulse rectifier transformer system

<span lang="EN-US">Twelve-pulse rectification system had been widely integrated in today’s DC traction power sub-station (DC-TPSS). This configuration had successfully mitigated low order harmonic distortion. As some research findings had confirmed that the dc voltage and current ripple factors may further minimize by increasing the number of rectification pulses to 18, 24, or 36. This paper had presented a simulation study to investigate the prospect of implementing an eighteen-pulse rectification system in a DC-TPSS. The theory of phase-shifting transformer used to produce an 18-pulse rectifier is presented with simulation verification. Simulation result shows that 3.69% of grid current distortion index is recorded without installing any filters. In addition, the dc voltage and current ripple may also be further reduced for about 30% compared to a conventional twelve-pulse rectification system.</span>

Influence of Different Rotations of Organic Formamidinium Molecule on Electronic and Optical Properties of FAPbBr3 Perovskite

Hybrid organic–inorganic halide perovskites (HOIPs) have recently represented a material breakthrough for optoelectronic applications. Obviously, studying the interactions between the central organic cation and the Pb-X inorganic octahedral could provide a better understanding of HOIPs. In this work, we used a first-principles theoretical study to investigate the effect of different orientations of central formamidinium cation (FA+) on the electronic and optical properties of FAPbBr3 hybrid perovskite. In order to do this, the band structure (with and without spin–orbit coupling (SOC)), density of states (DOS), partial density of states (PDOS), electron density, distortion index, bond angle variance, dielectric function, and absorption spectra were computed. The findings revealed that a change in the orientation of FA+ caused some disorders in the distribution of interactions, resulting in the formation of some specific energy levels in the structure. The interactions between the inorganic and organic parts in different directions create a distortion index in the bonds of the inorganic octahedral, thus leading to a change in the volume of PbBr6. This is the main reason for the variations observed in the electronic and optical properties of FAPbBr3. The obtained results can be helpful in solar-cell applications.

The Effect of Structural Phase Transitions on Electronic and Optical Properties of CsPbI3 Pure Inorganic Perovskites

Hybrid inorganic perovskites (HIPs) have been developed in recent years as new high-efficiency semiconductors with a wide range of uses in various optoelectronic applications such as solar cells and light-emitting diodes (LEDs). In this work, we used a first-principles theoretical study to investigate the effects of phase transition on the electronic and optical properties of CsPbI3 pure inorganic perovskites. The results showed that at temperatures over 300 °C, the structure of CsPbI3 exhibits a cube phase (pm3m) with no tilt of PbI6 octahedra (distortion index = 0 and bond angle variance = 0). As the temperature decreases (approximately to room temperature), the PbI6 octahedra is tilted, and the distortion index and bond angle variance increase. Around room temperature, the CsPbI3 structure enters an orthorhombic phase with two tilts PbI6 octahedra. It was found that changing the halogens in all structures reduces the volume of PbI6 octahedra. The tilted PbI6 octahedra causes the distribution of interactions to vary drastically, which leads to a change in band gap energy. This is the main reason for the red and blue shifts in the absorption spectrum of CsPbI3. In general, it can be said that the origin of all changes in the structural, electronic, and optical properties of HIPs is the changes in the volume, orientation, and distortion index of PbI6 octahedra.

Capacitors placement in distribution systems with nonlinear load by using the variables’ inclusion and interchange algorithm

This work presents a substantial improvement of the variables’ inclusion and interchange algorithm (VIIA) for capacitors placement that considers circuits with harmonic distortion. Several load states are considered, and fixed and switched capacitors are employed in optimization. All the pertinent constraints of voltage magnitude, total harmonic distortion, individual harmonic distortion, and of overstress of capacitors are implemented. The here defined global harmonic-distortion index states the distance to the feasibility or the unfeasibility of a solution with respect the harmonic distortion constraints. The inclusion in the sequential quadratic programming sub-problem of an inequality linear constraint on this global harmonic-distortion index, allows the determining of solutions that comply with the harmonic distortion related constraints. A comparison of the solutions of various examples obtained by the presented method with the best solutions obtained by the Matlab’s genetic algorithm shows the effectiveness of this method.

Analysis of Hue Circle Perception of Congenital Red-green Congenital Color Deficiencies Based on Color Vision Model

To investigate individual property of internal color representation of congenital red-green color-deficient observers (CDOs) and color-normal observers (CNOs) precisely, difference scaling experiment using pairs of primary colors was carried out for protans, deutans, and normal trichromats, and the results were analyzed using multi-dimensional Scaling (MDS). MDS configuration of CNOs showed circular shape similar to hue circle, whereas that of CNO showed large individual differences from circular to U- shape. Distortion index, DI, is proposed to express the shape variation of MDS configuration. All color chips were plotted in the color vision space, (L, r/g, y/b), and the MDS using a non-linear conversion from the distance in the color vision space to perceptual difference scaling was successful to obtain U-shape configuration that reflects internal color representation of CDOs.

Performance of a Low Speed Axial Fan Under Distortion: An Experimental Investigation

In the pursuit of reducing the fuel burn, future aircraft configurations will feature several types of improved propulsion systems, e.g. embedded engines with boundary layer ingestion, high-bypass ratio engines with short intakes, etc. Depending on the design and phase of flight, the engine fan will encounter inflow distortion of varying strength, and fan performance will be adversely affected. Therefore, investigation of the flow phenomena causing performance losses in fan and distortion interaction is important. This experimental study shows the effect of varying distortion index on four aspects of fan performance: distortion topology, upstream redistribution, performance curve, and flow unsteadiness. A low speed fan is tested under 60° circumferential distortion of varying strength, generated using distortion screens. The flow field in the upstream redistribution region is measured using PIV (planar and stereo). The fan performance is obtained using total pressure measurements. The noise spectra measured by a microphone are used to quantify the unsteadiness in the flow field. The distortion index (DC60) varies linearly with the grid porosity at constant wall thickness and aspect ratio of the grid cells. However, the distortion topology is significantly different as a stream-wise vortex pair appears in distorted flow at higher DC60. The vortices are stronger at higher DC60, but their order of magnitude is much lower than the circulation corresponding to fan itself. The spinner, distortion index and topology significantly affect the upstream redistribution mechanism. The vortex pair redistributes the flow which results in lower asymmetry in the symmetry plane. With increasing distortion, the performance is reduced and the unsteadiness is increased.

Aerodynamic and Stealth Characteristics Analysis for a New Type of S-Shaped Inlet With Inner Bulge

Searching for the optimal solution of the comprehensive performance of the aerodynamic and stealth characteristics of the aircraft inlet has become the trend of the development of the aircraft inlet due to the rapid development of radar detection technology. The aircraft inlet is a vital source of scattering due to its own cavity structure characteristic. Accordingly, reducing the electromagnetic stealth characteristic value of the stealth aircraft inlet can be served as the main way to reduce the RCS value of the whole airplane. Accordingly, a new type of stealth aircraft inlet that incorporates the design of the inner bulge is designed in this paper, which significantly reduces the value of radar-cross section (RCS) of the inlet by transforming the three-dimensional shape of the inlet. The design of this kind of inlet is based on the parametric rapid reconstruction geometry method that produces a geometry profile of the inlet through controlling a limited number of characteristic parameters. At the same time, the profile coordinates of the inner bulge is decided by means of three parameters, including the area of inner bulge, the circumferential distance and the radial offset. This paper calculates the aerodynamic characteristics of the seven S-shaped inlets, including six S-shaped inlets incorporated the inner bulges with different parameters, and an ordinary S-shaped inlet without the inner bulge as a control model. Total pressure recovery and distortion index are used as the indicators for judging the flow characteristics of these inlets to evaluate the effects on the aerodynamic characteristics of the stealth inlet after incorporating the inner bulge, which plays an important role in further evaluating the influence of the working environment of the compressor after the inlet. These S-shaped inlets with inner bulges on them resulting a decrease on total pressure recovery by 0.69% to 1.14%, at the same time, the total pressure distortion index at the exit of inlet is increased by 14.77% to 26.85%. Overall, the aerodynamic performance of the inlet with the design of the inner bulge can’t be seen a large decline. What’s more, this paper also compares the electromagnetic properties of the S-shaped inlet models with the inner bulge with the inlet without the inner bulge, using the algorithm of iterative physical optics (IPO) to evaluate the stealth characteristics of the models. This method is a kind of high-frequency approximation method for analyzing the scattering characteristics of the cavity scattering, with the high calculation accuracy as well as the high calculation efficiency. At the same time, the calculation takes up less memory, this is simply because that the mesh is coarser in calculation when using the IPO algorithm. The resulting inlet design achieving a dramatic improvement in stealth performance that the value of RCS is reduced by up to 97% after incorporating the design of inner bulge. In general, the stealth characteristics of optimized stealth aircraft inlet has greatly improved.