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The hydrolysis of Mg-based alloys and their hydrides with high abundance on the earth and low cost could produce hydrogen with high theoretical capacity and the formation of by-products that have no pollution to the environment. Hence, it has been regarded as one of the most promising way for hydrogen generation. Particularly, a gravimetric capacity of 6.4 wt% and 3.4 wt% H2 could be produced from the hydrolysis of pure Mg and MgH2, respectively, even when stoichiometric water is included for calculation. The formation of passive magnesium hydroxides with dense structure, however, could immediately interrupt the hydrolysis reaction of Mg/MgH2, which leads to ultralow yield and sluggish hydrogen generation rate. Recent studies have demonstrated that the hydrolysis reaction of Mg/MgH2 could be effectively enhanced in terms of both yield and kinetics by the formation of Mg-based alloys and their hydrides. This review aims to summarize the recent progress in the hydrolysis of Mg-based alloys and their hydrides and the involved hydrolysis mechanisms.

We address the visual comparison of multiple phylogenetic trees that arises in evolutionary biology, specifically between one reference tree and a collection of dozens to hundreds of other trees. We abstract the domain questions of phylogenetic tree comparison as tasks to look for supporting or conflicting evidence for hypotheses that requires inspection of both topological structure and attribute values at different levels of detail in the tree collection. We introduce the new visual encoding idiom of aggregated dendrograms to concisely summarize the topological relationships between interactively chosen focal subtrees according to biologically meaningful criteria, and provide a layout algorithm that automatically adapts to the available screen space. We design and implement the ADView system, which represents trees at multiple levels of detail across multiple views: the entire collection, a subset of trees, an individual tree, specific subtrees of interest, and the individual branch level. We benchmark the algorithms developed for ADView, compare its information density to previous work, and demonstrate its utility for quickly gathering evidence about biological hypotheses through usage scenarios with data from recently published phylogenetic analysis and case studies of expert use with real-world data, drawn from a summative interview study.

Graph drawing readability metrics are routinely used to assess and create node-link layouts of network data. Existing readability metrics fall short in three ways. The many count-based metrics such as edge-edge or node-edge crossings simply provide integer counts, missing the opportunity to quantify the amount of overlap between items, which may vary in size, at a more fine-grained level. Current metrics focus solely on single-level topological structure, ignoring the possibility of multi-level structure such as large and thus highly salient metanodes. Most current metrics focus on the measurement of clutter in the form of crossings and overlaps, and do not take into account the trade-off between the clutter and the information sparsity of the drawing, which we refer to as sprawl. We propose an area-aware approach to clutter metrics that tracks the extent of geometric overlaps between node-node, node-edge, and edge-edge pairs in detail. It handles variable-size nodes and explicitly treats metanodes and leaf nodes uniformly. We call the combination of a sprawl metric and an area-aware clutter metric a sprawlter metric. We present an instantiation of the sprawlter metrics featuring a formal and thorough discussion of the crucial component, the penalty mapping function. We implement and validate our proposed metrics with extensive computational analysis of graph layouts, considering four layout algorithms and 56 layouts encompassing both real-world data and synthetic examples illustrating specific configurations of interest.

LCL resonance complicates the design of a current control loop and can even threaten its stability. Extensive approaches have been proposed to deal with this resonance, among which active damping (AD) schemes based on the feedback of a single filter variable have been shown to be effective and cost-efficient. This paper presents a study of such AD techniques, where a generalized approach to developing an AD controller by relating a control diagram to an equivalent circuit is proposed. Based on this approach, AD controller forms with any one of four commonly used filter variables to realize virtual resistors (VRs) in six different connections to the LCL filter are derived. Comparisons are then made between these 24 AD controller alternatives by considering the implementation complexity of the AD controller, the number of measuring sensors, and the effect of the AD controller on the power stage. Consequently, grid-side current feedback AD to realize a VR in parallel with the filter capacitor is selected as a considered alternative. Next, two issues associated with the practical implementation of the selected grid-side current feedback AD, caused by the second-order differential expression and the digital time delay, are discussed and solved. Finally, the selected AD method is analyzed in the discrete z -domain, and its effectiveness is experimentally verified.

This paper presents a novel integrated framework for simulating the charging load of an electric vehicle charging station. The framework is built based on the cellular automaton model, including five modules: vehicle generation, charging station, lane change, speed update and boundary clear. The proposed framework can effectively stimulate the system dynamics of the traffic system and charging power process in a charging station. Case studies have verified its feasibility and effectiveness.

Due to the effective frequency limitation of the small-signal model derived from the average model for buck converters, the multi-frequency small-signal model was found to solve this issue by taking another dominant sideband frequency component into consideration. Based on it, this paper proposes an enhanced multi-frequency small-signal model considering two dominant sideband frequency components, which has a better prediction of the high-frequency performance. What's more, the modeling process is simplified by replacing the describing function with frequency domain analysis. And the loop gain for close-loop design derived from the new model still maintains simplicity, which guarantees the using-friendly of this new model. In addition, an important factor which influence the accuracy of this model is also shown to guide the application. Simulation and experimental results are presented as verifications.

LCL filters have been widely applied as the interface between voltage source inverters (VSIs) and power grid. However, inherent LCL resonance complicates the design of current control or even threatens system stability. Extensive approaches have been proposed to deal with the resonance, among which the active damping (AD) methods realized by the feedback of filter state variables are proved to be effective and robust. In this paper, a comprehensive analysis of such AD by utilizing its virtual circuit property is presented. It is found that different filter state variables can be selected to achieve the effective damping functions by emulating proper virtual impedances (VIs). Meanwhile, the connection of the VI with the LCL network is not restricted by the selected state variable but mainly dependent on the applied AD controller, which, in result, enables a thorough investigation of such VI-based AD methods. Consequently, all possible forms of the AD controller to realize different connection types by utilizing different state variables are derived. The optimal selection of the AD controller together with the specific state variable is further analyzed, where the obtained results can be used to guide the design of such AD in practice. Finally, the correctness of the theoretical analyses are verified by the experimental results.

Grid-connected Voltage Source Inverters (VSIs) equipped with LCL filters are attractive in utility applications for their better power quality features, while the inherent LCL resonance may limit the current control loop bandwidth or even threaten system stability. Simple but effective single-loop current control strategies have been studied for obtaining a stable system, where either the inverter-side current or the grid-side current can be chosen as the feedback control variable. In this paper, the single-loop inverter-side current feedback (ICF) control is studied. It has already been proved that, due to the time delay effect, a stable grid-connected inverter with single-loop ICF control can be achieved only when the LCL resonance frequency is below one-sixth of the system sampling frequency (f s /6). To solve this limitation, this paper proposes an improved single-loop ICF control for widening the stable region exceed f s /6. The proposed method is implemented by directly adding a second-order lead-lag compensator cascaded with the current regulator. The added compensator aiming at compensating the time delay effect is designed based on the Pade approximation. By conducting the continuous s-domain analyses, the boundary of the widened stable region can be calculated. Moreover, parametric influences of the proposed single-loop ICF control are studied in the discrete z-domain. Finally, the effectiveness of the proposed method is validated by the experimental results.

Due to the high frequency nature and constant power load characteristics, stability issue exists widely in contemporary power electronic systems. Impedance-based criteria can be used in stability prediction. Thus, the accurate extraction of impedance becomes significantly important. For AC systems, impulse injection method has been proposed for its short measurement duration, but the accuracy needs to be improved. This paper introduces the optimization analysis of impulse injection method for impedance measurement in three-phase power electronic systems, which aims at finding the optimization impulse injection waveform in time domain to enhance the accuracy. By comparing the frequency spectrum of basic impulses, this paper proves that injecting bipolar square wave at zero-crossing point shows the best efficiency. Simulation verifies the analysis.

Grid-connected inverters equipped with LCL filters are very popular in utility applications for their better power quality features, while the LCL resonance may threaten system stability. To dampen the LCL resonance, the widely used active damping method is based on the proportional feedback of the filter capacitor current. However, it has been revealed that when the LCL resonance frequency is above one-sixth of the system sampling frequency (fs/6), the time delay existed in the digitally controlled system will generate a pair of open-loop unstable poles, which make the system become much easier to be unstable. To address this issue, this paper proposes an improved capacitor-current-feedback active damping, which is realized by inserting a second-order lead-lag compensator into the active damping loop. The added compensator aiming at removing the unstable poles is designed base on the first-order Pade approximation. By deriving the equivalent virtual circuit introduced by the proposed method, it is obtained that the region of paralleled virtual resistor being positive is extended, leading to a more robust system. After that, the modified current control loop gain is derived to compare the damping performance with that of the conventional method. Lastly, the effectiveness of the proposed active damping method is verified by the experimental results.

Cascaded DC converters are becoming widely used in DC distributed power system. When a DC converter is tightly regulated, it operates as a constant power load (CPL). In a cascaded system, instability problems usually occurs due to the negative incremental impedance characteristic caused by a CPL. In order to mitigate instability, this paper proposes a new approach by adding an additional stabilizer in parallel with the intermediate DC bus of the cascaded system. Composed of a resistor and a bi-directional Buck-Boost converter, this stabilizer is controlled to emulate a RC damper. By reducing the output impedance of source converter, impedance based stability criterion is satisfied. After applying this stabilizer, both stability and dynamic performance of the cascaded system are improved. Lastly, a simulation based on two cascaded Buck converters is presented to verify the effectiveness of the proposed stabilizer.

Grid-connected Voltage Source Inverter (VSI) with LCL filters, controlled by proportional-resonant compensator in αβ frame, is very popular in utility application for its better power quality feature, while the inherent LCL resonance characteristic limits the control loop bandwidth and threatens the system stability. The active damping is essential to dampen the LCL resonance. This paper investigates the active damping method with only grid current feedback. Compared with the most widely used capacitor current feedback active damping, this novel method avoids the use of extra sensors to detect the capacitor current, which possesses the merits of lower cost and higher reliability. By performing the equivalent control block diagram transformation, it is revealed that a virtual impedance in series or parallel with the grid-side inductor can ideally be implemented with specific active damping controllers, which also comprehensively reflects the physical circuit property of grid current feedback active damping. However, the second-order derivative terms are needed in the ideal forms of the active damping controllers which can hardly be realized in practice. To deal with this issue, a second-order transfer function is proposed to approximate the s2 term in the required frequency range for realizing the similar LCL resonance damping performance. Further, a straightforward design method to determine the parameters of the active damping controller is introduced. Finally, the effectiveness of the proposed control method and relevant design strategies are verified both in time and frequency domain.

Structural degradation of rails will unavoidably take place with time due to cyclic bending stresses, rolling contact fatigue, impact and environmental degradation. Rail infrastructure managers employ a variety of techniques and equipment to inspect rails. Still tens of rail failures are detected every year on all major rail networks. Inspection of the rail network is normally carried out at night time, when normal traffic has ceased. As the implementation of the 24-h railway moves forward to address the increasing demand for rail transport, conventional inspection processes will become more difficult to implement. Therefore, there is an obvious need to gradually replace outdated inspection methodologies with more efficient remote condition monitoring technology. The remote condition monitoring techniques employed should be able to detect and evaluate defects without causing any reduction in the optimum rail infrastructure availability. Acoustic emission is a passive remote condition monitoring technique which can be employed for the quantitative evaluation of the structural integrity of rails. Acoustic emission sensors can be easily installed on rails in order to monitor the structural degradation rate in real time. Therefore, apart from detecting defects, acoustic emission can be realistically applied to quantify damage. In this study, the authors investigated the performance of acoustic emission in detecting and quantifying damage in rail steel samples subjected to cyclic fatigue loads during experiments carried out under laboratory conditions. Herewith, the key results obtained are presented together with a detailed discussion of the approach employed in filtering noise sources during data acquisition and subsequent signal processing.