The application of high-power voltage-source converters (VSCs) to multiterminal dc networks is attracting research interest. The development of VSC-based dc networks is constrained by the lack of ...operational experience, the immaturity of appropriate protective devices, and the lack of appropriate fault analysis techniques. VSCs are vulnerable to dc-cable short-circuit and ground faults due to the high discharge current from the dc-link capacitance. However, faults occurring along the interconnecting dc cables are most likely to threaten system operation. In this paper, cable faults in VSC-based dc networks are analyzed in detail with the identification and definition of the most serious stages of the fault that need to be avoided. A fault location method is proposed because this is a prerequisite for an effective design of a fault protection scheme. It is demonstrated that it is relatively easy to evaluate the distance to a short-circuit fault using voltage reference comparison. For the more difficult challenge of locating ground faults, a method of estimating both the ground resistance and the distance to the fault is proposed by analyzing the initial stage of the fault transient. Analysis of the proposed method is provided and is based on simulation results, with a range of fault resistances, distances, and operational conditions considered.
The modeling of electric sources in the sequence domain helps understand their response during faults when they are integrated into power systems. Since the fault response of inverters is ...significantly different from that of synchronous generators, their equivalent sequence models must differ as well. While the sequence models of synchronous generators are well-known and verified, practical sequence models of inverters remain an area of research. This manuscript addresses the modeling of grid-forming inverters in the sequence domain where the focus is on three-leg three-phase inverters. To generalize the analysis, two different control strategies used with grid-forming inverters are considered. The equivalent sequence models of these inverters with both strategies are discussed in detail and numerical simulations are used to further clarify the analysis. It is observed that grid-forming inverters with different types of control strategies show a consistent behavior in the positive-sequence circuit during faults for a given voltage drop. Conversely, the negative-sequence model of grid-forming inverters is heavily influenced by the control strategy. The analysis and results are useful to develop reliable protection schemes in inverter-based grids, as understanding the characteristics of electrical elements in the sequence domain is essential for any protective function.
Three-phase three-leg inverters represent the majority of inverters that are integrated into low voltage power grids. They can develop positiveand negative-sequence components during unbalanced ...conditions including asymmetrical faults, but not zero-sequence components. This indicates that a sequence-based control strategy is required for comprehensive control of inverter currents and voltages. Positiveand negative-sequence components must be controlled separately with their own dedicated controllers in such a scheme. Given this critical need, a sequence-based control technique for grid-forming and grid-feeding inverter-interfaced distributed generators is proposed. As a necessary part of the fault ride-through capability of inverter-interfaced distributed generators, a current limiter is developed, which can limit inverter currents at a pre-defined threshold for both balanced and unbalanced faults. Whilst the current regulators work in the synchronous reference frame with simple PI controllers, the limiter works in the natural reference frame and thus treats each phase current separately, which results in current limiting at the threshold for all phases. The advantage of the proposed limiter is that it acts instantaneously such that the inverter current can be limited from the start of the disturbance. The simulation results in MATLAB/SIMULINK reveal promising performance of the proposed control strategy with the proposed current limiting.
Lipids are an important class of biomolecules with many roles within cells and tissue. As targets for study, they present several challenges. They are difficult to label, as many labels lack the ...specificity to the many different lipid species or the labels maybe larger than the lipids themselves, thus severely perturbing the natural chemical environment. Mass spectrometry provides exceptional specificity and is often used to examine lipid extracts from different samples. However, spatial information is lost during extraction. Of the different imaging mass spectrometry methods available, secondary ion mass spectrometry (SIMS) is unique in its ability to analyze very small features, with probe sizes <50 nm available. It also offers high surface sensitivity and 3D imaging capability on a subcellular scale. This article reviews the current capabilities and some remaining challenges associated with imaging the diverse lipids present in cell and tissue samples. We show how the technique has moved beyond show-and-tell, proof-of-principle analysis and is now being used to address real biological challenges. These include imaging the microenvironment of cancer tumors, probing the pathophysiology of traumatic brain injury, or tracking the lipid composition through bacterial membranes.
This paper proposes a multi-timescale volt/var optimization for the optimal dispatch of battery energy storage system in smart distribution grids. It aims to coordinate the substation on-load tap ...changer operation on slow-timescale (hourly basis) with the photovoltaic inverters and battery storage operations on fast-timescale (15 min basis). This coordination is achieved by using two-stage stochastic programming and implemented via model predictive control. The power loss and energy purchase cost are reduced while maintaining voltages within limits. The forecasting uncertainties are modeled by generating a large number of random scenarios and then subsequently reducing scenario numbers to establish a tradeoff between computational burden and accuracy of the solution. The mixed-integer second-order cone program (MISOCP) is formulated with reduced scenarios, which achieves global optimum. Simulation results demonstrate the effectiveness of proposed MISOCP model in keeping the voltages within limits under forecasting uncertainties.
The multiterminal dc wind farm is a promising topology with a voltage-source inverter (VSI) connection at the onshore grid. Voltage-source converters (VSCs) are robust to ac-side fault conditions. ...However, they are vulnerable to dc faults on the dc side of the converter. This paper analyzes dc faults, their transients, and the resulting protection issues. Overcurrent faults are analyzed in detail and provide an insight into protection system design. The radial wind farm topology with star or string connection is considered. The outcomes may be applicable for VSCs in the multi-VSC dc wind farm collection grid and VSC-based high-voltage direct current (HVDC) offshore transmission systems.
This article investigates the longitudinal end effect of the line-start permanent magnet linear synchronous motor (line-start PMLSM), where conductive ladder rungs embedded into the mover enhances ...line-start capability but induces the longitudinal end effect due to the eddy current. The longitudinal end effect is first analyzed by virtue of analytical solutions of the electromagnetic field. Then, the coefficient of longitudinal end effect is presented in a piecewise format for convenient application. An algorithm is proposed based on the simplified piecewise theory to evaluate transient responses of the line-start PMLSM. To validate the feasibility of the proposed simplified piecewise theory, cases of the line-start PMLSM are investigated, with which a prototype is manufactured and the theoretical method is proven effective and accurate by experiments. Feasible principles involving the transient characteristics are also investigated via the design cases and experiments. The major contribution of this research is a feasible and convenient method to analyze the transient responses during the line-start process.
There is emerging evidence that amyloid beta (Aβ) aggregates forming neuritic plaques lead to impairment of the lipid‐rich myelin sheath and glia. In this study, we examined focal myelin lipid ...alterations and the disruption of the myelin sheath associated with amyloid plaques in a widely used familial Alzheimer's disease (AD) mouse model; 5xFAD. This AD mouse model has Aβ42 peptide‐rich plaque deposition in the brain parenchyma. Matrix‐assisted laser desorption/ionization imaging mass spectrometry of coronal brain tissue sections revealed focal Aβ plaque‐associated depletion of multiple myelin‐associated lipid species including sulfatides, galactosylceramides, and specific plasmalogen phopshatidylethanolamines in the hippocampus, cortex, and on the edges of corpus callosum. Certain phosphatidylcholines abundant in myelin were also depleted in amyloid plaques on the edges of corpus callosum. Further, lysophosphatidylethanolamines and lysophosphatidylcholines, implicated in neuroinflammation, were found to accumulate in amyloid plaques. Double staining of the consecutive sections with fluoromyelin and amyloid‐specific antibody revealed amyloid plaque‐associated myelin sheath disruption on the edges of the corpus callosum which is specifically correlated with plaque‐associated myelin lipid loss only in this region. Further, apolipoprotein E, which is implicated in depletion of sulfatides in AD brain, is deposited in all the Aβ plaques which suggest apolipoprotein E might mediate sulfatide depletion as a consequence of an immune response to Aβ deposition. This high‐spatial resolution matrix‐assisted laser desorption/ionization imaging mass spectrometry study in combination with (immuno) fluorescence staining of 5xFAD mouse brain provides new understanding of morphological, molecular and immune signatures of Aβ plaque pathology‐associated myelin lipid loss and myelin degeneration in a brain region‐specific manner.
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We examined focal myelin lipid alterations and the disruption of the myelin sheath in amyloid plaques in 5XFAD mice. MALDI imaging mass spectrometry revealed Aβ plaque‐associated depletion of multiple myelin‐associated lipid species, prominently sulfatides. Double staining with fluoromyelin and amyloid‐specific antibody reveal amyloid plaque‐associated myelin sheath disruption on the edges of corpus callosum which is specifically correlated with plaque‐associated myelin lipid loss only in this region. Further, apolipoprotein (APOE) which is implicated with the depletion of sulfatides in the AD brain is deposited in all the Aβ plaques which suggest plaque‐associated APOE might mediate sulfatide depletion.
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