Inversion Stage Research Articles

System design of series Z‐source inverter with feedforward and space vector pulse‐width modulation control strategy

For Z-source inverter (ZSI), the peak DC-link voltage is the actual voltage fed to the inversion stage. Controlling the peak DC-link voltage at the constant level can effectively decrease the voltage stress and simplify the design process of the inversion stage. By adopting input feedforward control, the constant peak DC-link voltage can be achieved. The feedback control of the peak output voltage is utilised to obtain the constant output without steady-stage error under load variation. Both the peak DC-link voltage and ac output is controlled to a desired level under different input and load condition. A prototype is built in the lab, and detailed design procedure of the ZSI with space vector pulse-width modulation scheme is given. Simulation and experimental results are presented to demonstrate the feasibility of the proposed control strategy and parameters design method.

Current-Fed Interleaved Phase-Modulated Single-Phase Unfolding Inverter: Analysis, Design, and Experimental Results

This paper presents a novel direct current-fed interleaved phase-modulated single-phase unfolding inverter for fuel-cell applications. Two active-clamped zero-voltage switching current-fed half-bridge isolated converters are interleaved in parallel input and series output configuration. Phase modulation is proposed to control these two converter cells, which generate a rectified sinusoidal pattern at the dc link. A simple H-bridge unfolding dc-ac inversion is used to produce single-phase sine voltage at line frequency switching using square-wave control. This not only simplifies the inversion stage in terms of modulation but also reduces the switching losses. Direct front-end current-fed based unfolding inverter is not reported in literature yet. Detailed analysis and design of the proposed direct current-fed single-phase unfolding inverter has been presented. Simulation waveforms using PSIM 9.0.4 are given to verify the presented analysis and design. Experimental results on a laboratory prototype rated at 200 W are demonstrated to support the investigation, to validate the accuracy of the proposed analysis and design, and to test the performance.

Model Based Inversion for Deriving Maps of Histological Parameters Characteristic of Cancer From Ex-Vivo Multispectral Images of the Colon

A model-based inversion method was used to obtain quantitative estimates of histological parameters from multispectral images of the colon and to examine their potential for discriminating between normal and pathological tissues. Pixel-wise estimates of the mucosal blood volume fraction, density of the scattering particles and thickness were derived using a two-stage method. In the first (forward) stage reflectance spectra corresponding to given instances of the parameter values were computed using Monte Carlo simulation of photon propagation through a multi-layered tissue. In the second (inversion) stage the parameter values were obtained via optimization using an iterated conditional modes algorithm based on Discrete Markov Random Fields. The method was validated on computer generated data contaminated with noise giving a mean normalized root mean square deviation (NRMSD) of 2.04. Validation on ex vivo images demonstrated that parametric maps show gross correspondence with histological features of mucosa characteristic of cancerous, precancerous and noncancerous colon lesions. The key signs of abnormality were shown to be the increase in the blood volume fraction and decrease in the density of scattering particles.

The Characteristics of Fault Belts Distribution in Pubei Oilfield Daqing, China

The seismic data interpretation shows that faults in Pubei Oilfield developed in the form of the lower, middle and upper fault systems, vertically corresponding to the tectonic evolution stages of Songliao Basin which are rifting, depression and inversion stages; in the plane the faults in Pubei Oilfield appear dense characteristics to be belts, especially in Fuyang oil layer, but not clear and sparse in Putaohua oil layer; faults dense belts in Fuyang oil layer from five orientations combine alternately, cutting Fuyang oil layer into the grid feature, but the faults distribution of Putaohua oil layer is related with the fault blocks division of the Pubei Oilfield. Generally, 8 fault belts separate the Pubei Oilfield into seven fault blocks.

Analysis of main controlling factors for hydrocarbon accumulation in central rift zones of the Hailar-Tamtsag Basin using a fault-caprock dual control mode

The Hailar-Tamtsag Basin is a typical rift basin where two sets of regional caprocks are developed, i.e., mudstone caprocks (containing a small amount of tuff) developed in strong rifting stage and fault-depression stage, respectively. The caprocks have a cumulative thickness of 50–120 m in general, and a single-layer thickness of 20–50 m, interbedded with sandstone about 1–2 m thick. The large set of mudstone is distributed continuously, as pure mudstone caprock. Forty-three mudstone and tuff samples were taken to perform displacement pressure test with our independently developed displacement pressure tester. Test result shows that the displacement pressure is 0.04–10.00 MPa, which is equivalent to 0.09–20.01 MPa after being corrected to the actual burial depth. As the burial depth increases, the displacement pressure rises gradually, and is 1–10 times greater than that of oil-bearing sandstone or conglomerate reservoir at the same burial depth. The difference between displacement pressure of mudstone caprock and sandstone or conglomerate reservoir increases greatly if the burial depth exceeds 1000 m. Because of the displacement pressure difference between caprock and reservoir, the maximum height of hydrocarbon column sealed by the caprock ranges from 300 m to 2000 m, much higher than the height of the trap closure at the same burial depth. No hydrocarbons will leak through such caprocks. Analysis of the reservoir GOI, homogeneous temperature, and crude maturity of both deep and shallow reservoirs in Well Wu-20 in the Wuerxun Depression shows that Damoguaihe II Member reservoir is a secondary reservoir developed during adjustment of early reservoir. It is mainly distributed in inverted structures. Faulting is one of the main factors breaking the integrity of caprocks. Three kinds of faults are often related to the migration of hydrocarbons across regional caprocks: the first type refers to the positive inverted faults breaking the early sealing conditions and making the hydrocarbons accumulated in the early period re-migration; the second type refers to the faults with shear mudstone smear structures which lose their continuity and open vertically when the fault throws exceed 5 times of the mudstone thickness; the third type refers to the normal faults developed in the structural inversion stage, which have a typical cataclastic structure and are easy to cause vertical migration of hydrocarbons. Hydrocarbon enriched horizons of the rift basins are co-controlled by “fault-caprock”. Specifically, 95% of the geological reserve is controlled by regional caprocks, and only 5% is controlled by open faults, secondary oil/gas reservoirs are developed over regional caprocks.

Effect of Tubes Length and Annealing Temperature on Energy Absorption of Aluminium Alloy Tube 6061-T6 under Inversion Collapse Mode

The purposes of this study are to investigate the effect on variation of the specimens tube length and annealing temperature on the amount of energy absorption of Aluminium tubes (AA 6061) towards inversion collapse mode. The tests were performed on the Aluminium tubes using compression test according to ASTM E8 standard procedure. In this study, a quasi-static inversion tests were conducted in order to obtain the energy absorbed during inversion stages. It was found that the energy absorbed by Aluminium tubes were increased by increasing the tube length but decreased with annealing temperature.

Grid‐tied photovoltaic system with series Z‐source inverter

This study presents a grid-tied photovoltaic (PV) system based on the series Z-source inverter. The grid-tied current control strategy, the dc-link voltage control, as well as the maximum power point tracking scheme is realised in the single-stage system. The current control strategy is performed based on dq rotating frame. Indirect dc-link control is adopted to achieve constant peak dc-link voltage and thus can simplify the controller design in inversion stage. The overall control strategy is given and analysed in detail. Simulation and experimental results demonstrate that the proposed system can be applied in PV system with a wide input voltage range, which verify the correctness and validity of the analysis.

Waveform tomography in 2.5D: Parameterization for crooked‐line acquisition geometry

AbstractA method for 2.5D viscoacoustic waveform tomography that can be applied to generate 2D models of velocity and attenuation from inversion of refraction waveforms on land seismic reflection data acquired along crooked roads is developed. It is particularly useful for typical crustal reflection surveys. First‐arrival travel time tomography is applied using a 3D method, but with constraints on the intermediate 3D velocity model; the result is the starting model for the next step. A 2.5D frequency‐domain full‐waveform inversion stage parameterizes 3D geometry in the seismic source and receiver arrays, with the assumption that the velocity and attenuation models are homogeneous in the out‐of‐plane direction. This approach results in superior results compared to a strictly 2D approach when the acquisition line is crooked, with a moderate increase in computational cost. A case study using data acquired in the Nechako Basin in south‐central British Columbia, Canada, exemplifies and validates the procedure. The velocity model derived from 2.5D waveform tomography is compared with that from a previous study in which 2D waveform tomography was applied to the same data set and with results from 3D travel time tomography. The resolution and accuracy of the velocity model from 2.5D waveform tomography are demonstrated to be greater than those from travel time or 2D waveform tomography. A model of viscoacoustic attenuation, which was not possible in the 2D case, is also generated. These models are interpreted jointly to highlight features of geological interest, such as a sedimentary basin, basement rocks, and faults, from surface to about 3 km depth.

The component miscibility evolution during polymerization of the polybutadiene containing styrene solutions

In situ graft copolymerization of polystyrene (PS) on polybutadiene (PB) during polymerization of PB solution in styrene monomer was investigated to determine the performance of grafting process, chain structure of generated copolymers, and their effectiveness as compatibilizing agents for incompatible PS-rich and PB-rich phases. The amount of copolymers and their chain structures at different stages of polymerization were determined by gel permeation chromatography (GPC) curves of the reactive blends (taken directly from the reaction) and physical blends (physically prepared based on total composition of reactive blends). It was demonstrated that copolymer formation started from the early stage of polymerization and continued up to the phase inversion stage. In addition, PS grafting on PB occurred initially via single-chain attachment and then converted to a double-chain scenario later on. Compatibilizing efficiency of the copolymers was evaluated by Huggins coefficient (k H) obtained by performing dilute solution viscometry (DSV) on samples taken at different stages of conversions. The effect of molecular weight of PB on the grafting process and the effectiveness of copolymers generated were also studied. It was found that while compatibilizing role of the copolymers produced from high molecular weight PB (HPB) increases as conversion goes further, the compatibilizing efficiency of the copolymers produced from low molecular weight PB (LPB) shows a very sharp variation in a small range of conversion. Plotting k H of physical blends against weight fraction of PB molecules in solid content of the solutions (w PB) showed negative deviation from mixture law with a W-like pattern containing two minima with a maximum in between. While a negative deviation was assumed as indication of immiscibility of the components, upward deviation at middle values of w PB was attributed to molecular segregations that reduce the interface between the incompatible PS-rich and PB-rich phases.

Cleavage, incomplete inversion, and cytoplasmic bridges in Gonium pectorale (Volvocales, Chlorophyta)

Multicellularity arose several times in evolution of eukaryotes. The volvocine algae have full range of colonial organization from unicellular to colonies, and thus these algae are well-known models for examining the evolution and mechanisms of multicellularity. Gonium pectorale is a multicellular species of Volvocales and is thought to be one of the first small colonial organisms among the volvocine algae. In these algae, a cytoplasmic bridge is one of the key traits that arose during the evolution of multicellularity. Here, we observed the inversion process and the cytoplasmic bridges in G. pectorale using time-lapse, fluorescence, and electron microscopy. The cytoplasmic bridges were located in the middle region of the cell in 2-, 4-, 8-, and 16-celled stages and in inversion stages. However, there were no cytoplasmic bridges in the mature adult stage. Cytoplasmic bridges and cortical microtubules in G. pectorale suggest that a mechanism of kinesin-microtubule machinery similar to that in other volvocine algae is responsible for inversion in this species.

Thick-skin-dominated orogens; from initial inversion to full accretion: an introduction

Abstract Fifty per cent of orogens have a thick-skin character, and have evolved from passive margin and intra-cratonic rift systems. One group of thick-skin provinces can be found at both pro- and retro-wedges of orogens associated with advancing subduction zones, that is, orogenic wedges whose advance vectors oppose the mantle flow. A second group can be found at pro-wedges of orogens associated with retreating subduction zones, that is, orogens whose advance vectors have the same direction as mantle flow. A third group is formed in intra-plate settings where mechanical strengthening is produced by internal shortening. Thick-skin province development is controlled by driving factors such as individual plate movement rates, overall convergence rates, orogen movement sense with respect to mantle flow, and pro-wedge v. retro-wedge location. These driving factors are themselves constrained by numerous internal and external factors. This introductory chapter focusses primarily on least-deformed case areas in order to understand the role of different factors in controlling the evolution of thick-skin tectonic provinces from the initial inversion stage to full accretion stage.

A Single-Stage Fuel Cell Energy System Based on a Buck--Boost Inverter with a Backup Energy Storage Unit

An energy system powered by a low-voltage fuel cell (FC) is conditioned to generate higher--voltage regulated ac voltage. The power conditioning system typically requires two power stages: a boost stage and an inversion stage. In this paper, the buck--boost inverter topology that achieves both boosting and inversion functions in a single stage is used as a building block to develop a single-phase FC-based energy system that offers high conversion efficiency, low-cost and compactness. The proposed system incorporates a backup energy storage unit to support the slow dynamics of the FC. The single-phase buck--boost inverter is voltage-mode controlled and the backup unit is current-mode controlled. The low-frequency current ripple is supplied by the backup unit that minimizes the detrimental effects of such ripple being drawn directly from the FC itself. Experimental results from a 1-kW prototype operating at 20 kHz are presented to validate the analysis and performance of the proposed system.

Geodynamic significance of the TRM segment in the East African Rift (W-Tanzania): Active tectonics and paleostress in the Ufipa plateau and Rukwa basin

The Tanganyika-Rukwa-Malawi (TRM) rift segment in western Tanzania is a key sector for understanding the opening dynamics of the East African rift system (EARS). In an oblique opening model, it is considered as a dextral transfer fault zone that accommodates the general opening of the EARS in an NW–SE direction. In an orthogonal opening model, it accommodates pure dip-slip normal faulting with extension orthogonal to the rift segments and a general E–W extension for the entire EARS. The central part of the TRM rift segment is well exposed in the Ufipa plateau and Rukwa basin, within the Paleoproterozoic Ubende belt. It is also one of the most seismically active regions of the EARS. We investigated the active tectonic architecture and paleostress evolution of the Ufipa plateau and adjacent Rukwa basin and in order to define their geodynamic role in the development of the EARS and highlight their pre-rift brittle tectonic history. The active fault architecture, fault-kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the TRM segment. Two pre-rift brittle events are evidenced. An older brittle thrusting is related to the interaction between the Bangweulu block and the Tanzanian craton during the late Pan-African (early Paleozoic). It was followed by a transpressional inversion during the early Mesozoic. This inversion stage is the best expressed in the field and caused dextral strike-slip faulting along the fault systems that now control the major rift structures. It has been erroneously interpreted as related to the late Cenozoic EARS which instead is characterized by pure normal faulting (our third and last stress stage).

Indirect Space Vector Based Modulation Techniques for High-Power Multi-Modular Matrix Converters

Combining concepts of traditional multilevel converter and matrix converter (MC), the multimodular MCs (MMMCs) have reached the medium-voltage high-power level. These topologies possess features such as elimination of dc components and are able to output high-quality multilevel waveforms. Due to the MMMC's particular topological structure, modulation strategies for the conventional converters cannot be directly adopted. This necessitates the design of specially tailored modulation schemes for them to generate sinusoidal input/output waveforms. In this paper, indirect space-vector-based modulation techniques are proposed for the MMMCs. The study begins by establishing an indirect circuit model for the three-module MMMC topology, before using space vector calculations to derive duty ratios for the model's rectification and inversion stages. As the inversion stage can be viewed as multiple sets of three-phase outputs, its switching states and duty ratios are then converted and combined with those from the rectification stage. Finally, the gating signals are produced according to two switching patterns. As demonstrated by simulation and experimental results, the presented modulation techniques can generate sinusoidal waveforms with variable frequency and magnitude, as well as adjustable angle and power factor. The superiority of the second switching pattern is also proved by the obtained results.

A Study of Pressure Gradient Characteristics of Oil-Water Dispersed Flow in Horizontal Pipe

The behavior of oil/water dispersed flow is one of the oil/water two phase flow phenomena encountered in pipeline operations commonly. Due to the different operation conditions, kinds of flow patterns (O/W and W/O) can be observed, as well as the phase inversion point. Pressure gradient characteristics of the three flows vary greatly. Pressure gradients at phase inversion point are higher than those under other conditions which pose great harm to pipeline operations. Three oil samples of different viscosities were used in this study. Mixture flowrate, oil content and mixture temperature data were obtained for oil-water tests. Data analysis shows that pressure gradients exist 3 different stages as oil content changed (O/W stage, phase inversion stage and W/O stage). Pressure gradient characteristics behave differently during the 3 stages. The viscosity of the continuous phase is the dominant factor affecting pressure gradients and droplet size and number also play a role. High mixture velocity will promote pressure gradients. Mixture velocity also affects the viscosity of the working fluid. High velocity lowers apparent viscosity and decreases pressure gradients. The increment rate of pressure gradients can slow down with the increase of mixture velocity. Mixture temperature mainly affects the viscosity of the continuous phase and creats tiny effect on the dispersed phase. High temperature lowers the viscosity of the continuous phase and decreases the pressure gradients.

Breakthrough acquisition and technologies for subsalt imaging

The recently introduced method of wide-azimuth data acquisition offers better illumination, noise attenuation, and lower frequencies to more accurately determine a velocity field for imaging. For the field data experiment to demonstrate the technologies, we used a Gulf of Mexico (GOM) wide-azimuth data set that allows us to take advantage of possible low frequencies, relatively large crossline offsets, and increased illumination. The input data was processed through true 3D azimuthal surface-related multiple elimination (SRME) with zero-phasing and debubble. Eliminating the surface-related multiples aids the velocity determination and helps uncover the subsalt sediments at the final imaging stage. After the initial velocity derivation, which was constrained to wells and geology, full-waveform inversion (FWI) was used to further update the velocity field to achieve an enhanced image. The methodology used follows the top-down approach where suprasalt sediment model is developed followed by the top of salt, salt flanks, base of salt, and finished with a limited subsalt update. To approximate the observed data by using an acoustic inversion procedure, the propagator includes effects of attenuation, anisotropy, acquisition source, and receiver depth. The geological environment is salt related, which implies that the observed data is highly elastic, even though it is input to an acoustic full waveform inversion. To use the proper constraints for the inversion, layer-stripping method is used to develop the high-resolution velocity field. The inversion stages were carefully quality controlled through gather displays to ensure the kinematics were honored. We then demonstrated the benefit of the FWI velocity field by comparing the images derived with the traditional ray-based tomographic velocity field versus the velocity field derived by FWI performing reverse time migration to produce these images. Finally, the images were compared at key well locations to evaluate the robustness of the workflow.

Morphology control of the perovskite hollow fibre membranes for oxygen separation using different bore fluids

La 0.6Sr 0.4Co 0.2Fe 0.8O 3−α (LSCF6428) perovskite hollow fibre membranes were fabricated through a phase inversion/sintering technique. The effects of the internal coagulant (bore fluid) compositions on the morphology of the resultant hollow fibres were systematically investigated. The bore fluids were specially designed to vary the solvent–nonsolvent exchange rates in the phase inversion stage by mixing different polymer solvent (1-methyl-2-pyrrolidinone–NMP) content inside the water or ethanol internal coagulant. The prepared hollow fibre membranes were characterized with scanning electron microscopy (SEM), porosity and bending strength measurements, gas-tightness examination and oxygen permeation tests at high temperatures. The results indicate that the bore fluid composition has dramatic effects on the microstructure of the resultant hollow fibre membranes. With the gradual increase of NMP concentration in the bore fluids, the membrane morphology evolution from multi-dense layers to one single dense layer has been clearly demonstrated. LSCF6482 hollow fibre membranes with one dense layer near the outside surface integrated with the highly porous structure showed the highest oxygen fluxes with a maximum value of 34.4 mmol m −2 s −1 under air/He gradient at 1000 °C. The relationships between bore fluid composition and membrane morphology change and their significant effects on oxygen permeation have been discussed extensively. This work shows the feasibility of achieving ceramic hollow fibre membranes with different architectures for various purposes in one single step simply by adjusting the bore fluid composition.

Frequency-domain elastic full waveform inversion for VTI media

SUMMARY To describe subsurface structures in anisotropic media properly, particularly in transversely isotropic media with a vertical symmetry axis (VTI), which frequently appear in sedimentary basin environments, we develop a frequency-domain elastic full waveform inversion algorithm for 2-D VTI media. The inversion algorithm is based on the cell-based finite-difference modelling method and the adjoint state of the wave equation. Because the anisotropic inversion for VTI media deals with more elastic constants than the isotropic inversion, it is more prone to obtain local minimum solutions. For this reason, we may not succeed in properly describing the elastic constants of subsurface media if we only apply the standard inversion techniques to anisotropic waveform inversion. To compensate for the ill-posedness of the anisotropic waveform inversion, we couple elastic constants C11 and C33 based on Thomsen's relationship, which is also supported by the sensitivity analysis with respect to the parameters. To enhance the inversion results, we apply the frequency-selection strategy, moving from lower to higher frequencies and we carry out the inversion process over two stages. In both stages, all of the elastic constants are simultaneously optimized, as is done in the conventional waveform inversion. However, we only accept the inversion results for C11, C33 and C44 at the first stage, which will be used as the starting models for the second stage and C13 is reinitialized as a linearly increasing model. We apply our waveform inversion algorithm to a simple 3-layered model and a part of the overthrust model. For the 3-layered model, the first inversion stage is enough to yield reasonable inversion results for all of the elastic constants. For the overthrust model, the second stage is needed to enhance the inversion results for C13.

Low shear-velocity zone in the Neapolitan-area crust between the Campi Flegrei and Vesuvio volcanic areas

Terra Nova, 22, 208–217, 2010 Abstract Some Vesuvio earthquakes recorded at OV-INGV stations in the Campi Flegrei volcanic area have been processed by FTAN (frequency–time analysis) method. The group velocities of Rayleigh-wave fundamental mode have been extracted in the period range 0.7–3 s. Regional group and phase velocity data have been considered as well at the inversion stage. Average shear wave velocity models for the uppermost 73 km of the lithosphere below the Neapolitan area, midway between Campi Flegrei and Vesuvio volcanic areas, have been obtained by the hedgehog nonlinear inversion method. The resulting structural models are characterized by the presence of the carbonate horizon at about 3 km depth. A main feature is represented by low VS velocities around 9 km depth. This low-velocity layer, already found below both Campi Flegrei and Vesuvio, can be reasonably interpreted as a magmatic reservoir of Campania active volcanoes.

Resonant technique for bidirectional flyback converter

Proposed is an improvement of the bidirectional flyback topology, proposing a resonant inversion of the output polarity voltage. The topology is applied to supply high pressure sodium lamps with a low frequency symmetrical square waveform, in order to avoid the acoustic resonance phenomenon occurrence. The resonant technique developed guarantees zero current switching commutation during the inversion stages, increasing around 15% the overall efficiency and decreasing voltage and current stresses on the switches. The proposed topology has been implemented and validated by experimental results.