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The realization of zero voltage switching (ZVS) of the bidirectional inductive power transfer (BIPT) system is critical to system stability and transmission efficiency. For the symmetrical phase shift modulation (SPSM) strategy, as system transmission power decreases, it is necessary to reduce the phase shift angle of the fundamental component of ac excitation voltages on both sides to achieve ZVS. However, it will result in a decrease in the system transmission power factor and transmission efficiency. In this article, an asymmetrical pulsewidth modulation with even harmonics (APWMEH) strategy is proposed for the BIPT system to optimize the transmission efficiency under light load conditions. First, this article analyses the relationship between ZVS and transmission efficiency of the BIPT system with SPSM. Second, the APWMEH control technique is proposed, including the analysis of the working modes of both full bridges, the condition of the ZVS realization, and the efficiency optimization of the system. Then, the control scheme of power regulation and load matching of the system are given. Finally, the comparative analysis and experimental results are performed at a BIPT experimental platform. Compared with symmetrical triple phase shift and fundamental dual phase shift, the transmission efficiency of the BIPT system with AWMEH is improved significantly under the light load conditions. [ABSTRACT FROM AUTHOR]

Bidirectional inductive power transfer (BIPT) systems for electric vehicles allow power exchange between grid and vehicle. To achieve high transfer efficiency under a wide range of transmission power, this article proposes a dual-side asymmetrical voltage-cancelation (AVC) control technique. With the proposed dual-side AVC control, the adjustment of the fundamental component amplitude of the excitation voltage, the maintenance of a large phase angle between excitation voltages as well as zero-voltage switching (ZVS) of the power switches, and the optimization of the resonant tank power transfer efficiency can be achieved simultaneously. The basic characteristics and the conditions for maximum transfer efficiency of the resonant tank are derived. The control scheme for the overall system including the control of the primary-side and secondary-side full bridges is proposed, which considers both efficiency optimization and ZVS operation of all switches. The ZVS range of the proposed dual-side AVC control technique is presented. Experiments are performed with dual-phase-shift, triple-phase-shift, and the proposed dual-side AVC control technique, which show that the BIPT system with the proposed dual-side AVC control technique achieves a higher efficiency over the others in a wide range of transmission power. [ABSTRACT FROM AUTHOR]

Steel‐concrete composite box girders offer notable advantages such as high stiffness, excellent torsional performance, and light self‐weight, making them prevalent in large‐span bridges, particularly in cable‐stayed configurations. However, a persistent challenge arises from the shear lag effect in the concrete slab within the flanges induced by shearing interactions between the webs and flanges. Limited attention has been devoted to investigating the experimental and theoretical aspects of shear lag in long‐span cable‐stayed bridges with twin box‐shaped composite girders. This research addresses this gap by designing a segmental scale twin box‐shaped composite model specimen to simulate the cable spacing of the main girder in a cable‐stayed bridge, specifically targeting the shear‐lag effect. The study successfully captures the non‐uniform distribution of cross‐sectional strain in the top concrete slab. Subsequently, analytical strain solutions for the composite girder under mid‐span concentrated load and axial load are derived using the energy variation method. The theoretical model's applicability is then calibrated against experimental results. The investigation extends to the in‐situ testing of the Chibi Yangtze River Bridge, the world's largest steel‐concrete composite girder cable‐stayed bridge, boasting a main span of up to 720 m. An established finite element (FE) analysis model for the Chibi Yangtze River Bridge simulates the transverse stress distribution under typical construction conditions of CC6. Comparative analyses between the simulated results, calculated values from elementary beam theory, and the theoretical model against field‐measured values reveal that the FE model provides a more accurate estimation of the shear lag effect in the concrete slab. Notably, the FE model effectively reflects the bridge's characteristics and serves as a baseline for subsequent studies. This comprehensive investigation contributes significantly to the understanding and analysis of shear lag phenomena in twin box composite girders of cable‐stayed bridges. The integration of experimental, analytical, and construction site validations establishes robust tools for engineering design and the construction of safe and serviceable cable‐stayed bridges. The research augments knowledge regarding shear lag behavior and underscores the necessity to appropriately consider its effects in bridge analysis and design. [ABSTRACT FROM AUTHOR]

Input current around zero-crossing point is distorted and the reduction of current ripple is limited when applying space-vector modulation (SVM) to the interleaved Vienna rectifier. In this article, a hybrid SVM method for two- channel interleaved Vienna rectifier is developed to reduce the harmonics distortion and current ripple. The topology of two-channel interleaved Vienna rectifier is introduced. The current distortion around the zero-crossing point and the ripple characteristics around the peak of the current with SVM are analyzed. Then, a zero-crossing clamped method is used to eliminate the current distortion in the sectors around the zero-crossing point. To reduce the current ripple, the phase-shifted angle of the carriers between two channels is modified in the sectors around the peak of the current. Furthermore, the realization of the proposed hybrid SVM method is presented in details. With the proposed hybrid SVM method, the current distortion is attenuated and the current ripple amplitude is reduced obviously without increasing the switching frequency. Finally, the performance of the proposed method is compared with the classical SVM methods in a two-channel interleaved Vienna rectifier prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a new cable element and a novel formation procedure of unbalanced loads for cable-stayed bridges. The proposed method couples the effects of geometric nonlinearity and concrete creep/shrinkage. An improved catenary cable element with arbitrary rigid arms is introduced to reduce the degree of freedoms in simulations. An explicit expression of tangent stiffness of the new cable element is derived. Then, an incremental stiffness equation under co-rotational coordinate system is established by introducing a recurrence equation of creep loads. Following this, a new formation method is proposed to evaluate the unbalanced loads on the current deformed equilibrium configuration. This method is illustrated and validated by two actual long span cable-stayed bridges in Yangtze River. The results indicate that the coupled algorithm can significantly enhance the computational efficiency and accuracy for the bridge analysis during construction. [ABSTRACT FROM AUTHOR]

Bidirectional inductive power transfer (BIPT) systems are of particular interest for electrical vehicles for their enabling power to exchange between grid and vehicle. In BIPT systems, it is critical to keep the voltage phasors of the primary-side and secondary-side converters synchronized to regulate the power flow. In this article, the basic operation and steady-state characteristics of the BIPT system are introduced. A phase synchronization method for BIPT systems, which does not require any communication between primary- and secondary-side controllers or complicated hardware, is proposed in this article. To assist the design of the synchronization controller, the large-signal model and small-signal model of the BIPT system are derived. Based on the derived model of the system, the controller design for the phase synchronization method is proposed, considering the coupling between the synchronization controller and the BIPT main circuit and the clock frequency deviation between the primary-side and secondary-side controllers. The parameter sensitivity of the proposed method is analyzed. The large-signal and small-signal models are verified through simulations. And the experimental verification of the phase synchronization method shows that the BIPT system with the proposed phase synchronization method has a fast transient response as well as a stable steady-state performance. [ABSTRACT FROM AUTHOR]

Three-phase three-level Vienna rectifier using powder core inductors has been widely used for power conversion. Inductor current ripple analysis of rectifier is essential for pulsewidth modulation method optimization, loss estimation, filter inductor design, etc. However, it is hard to analyze the current ripple of Vienna rectifier. Moreover, the inductance of powder core inductor varies with sinusoidal input current, which makes it even more complicated. In this article, a current ripple analysis method for three-phase Vienna rectifier considering the inductance variation of the powder core inductor is presented. The current ripple distribution of Vienna rectifier with constant inductance is studied based on the space vector approach. To determine the current ripple of Vienna rectifier with powder core inductors, an inductor voltage calculation method considering inductance variation is proposed. The compensation voltage is introduced to compensate for the effect of inductance variation on current ripple. Then, the analytical expression of the peak-to-peak current ripple with powder core inductor is derived. In addition, a design method of powder core inductor is proposed based on the analytical expression. At last, the correctness of the analytical result is verified by both simulation and experiment. [ABSTRACT FROM AUTHOR]

Compared with the conventional two-level dual-active-bridge (DAB) dc–dc converter, the three-level DAB converter could operate with lower voltage rated switching devices and provide more control degrees of freedom, which enhances the control flexibility. This paper proposes a modulation strategy with five control degrees of freedom. In the previous work with multiple control degrees, the optimization strategies for efficiency or inductor current minimization are investigated; however, these strategies all need detailed mode analysis and complex mathematical optimization tools to obtain the optimal duty cycles. In this paper, an optimization strategy for the root-mean-square value of the inductor current is proposed. This method extracts the fundamental and third-harmonic components from the high-frequency voltages on both sides and adjusts the amplitude of the bridge voltages by the vector diagram to obtain the optimal duty cycles. The inductor current can be reduced significantly at light loads with the proposed strategy, so the efficiency of the converter can be improved. Moreover, the optimization process does not need the detailed operation analysis of the converter, nor does it require the complex mathematical optimization tools. Finally, the performance of the three-level DAB and the optimization strategy are verified by the experimental results. [ABSTRACT FROM AUTHOR]

The three-level Vienna rectifier is an attractive topology for power factor correction applications. However, for practical high-frequency applications, the nonlinearity caused by snubber circuit and parasitic capacitance of Vienna rectifier's switching device will distort input current. This paper proposes a carrier-based discontinuous space-vector modulation (CB-DSVM) method with varying clamped area for Vienna rectifier in high switching frequency applications. The equivalent circuit of Vienna rectifier considering the nonlinear factors is built and the effect of pulse shaping around current zero-crossing point is investigated. The voltage errors caused by the nonlinearity of switching device will distort terminal voltage, which mainly appears at the zero-crossing time. A DSVM method with the fixed clamped area around the zero-crossing point is proposed to reduce the voltage errors and then the simplified CB-DSVM method with varying clamped area by adding a clamped factor to the judging conditions is further studied, which will reduce low-order harmonics of the CB-DSVM method. Simulations and experiments are carried out in a 600 W Vienna rectifier platform, which demonstrates the validity of the proposed method. Compared with the CB-SVM method, the proposed CB-DSVM method with varying clamped area has comparative neutral-point voltage balancing ability and better input current quality. [ABSTRACT FROM AUTHOR]

Abstract A comprehensive comparison study of the UV–visible photoresponse properties of non-aligned carbothermal ZnO nanowires (ZNWs) composited with reduced graphene oxide (RGO) and single-walled carbon nanotubes (SWCNTs) is presented. The RGO/ZNWs composites (GZWs) and SWCNTs/ZNWs composites (CZWs) have been successfully synthetized through UV-assisted photochemical reduction of GO in ZNWs suspension and ultrasonic stirring technology, respectively. The optimal contents of RGO and SWCNTs incorporated into ZNWs were determined for achieving maximum photoresponse, respectively. Experimentally, the optimal GZWs and CZWs exhibit significant enhancement in photoelectric properties than pure ZNWs. It is demonstrated that the GZWs-based photodetector has higher photoresponsivity (∼16 AW-1) than CZWs-based photodetector under low UV irradiation (<10 μWcm−2) and at 1.0 V bias, while the CZWs-based photodetector has higher on/off current ratio (8.41 × 104) and faster response time (1.99 s of rise-time and 0.39 s of decay-time) than GZWs-based one. The detail physics mechanism on the effects of RGO and SWCNTs on photoelectric characteristics of ZNWs is presented with the interface charge transfer due to the chemisorption and photo-desorption of oxygen. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Plug-in electric vehicles (PEVs) tend to be treated as a new form of the mobile energy storage system with the potentiality to promote energy management in microgrids (MGs) and smart grid. However, a conflict of interest exists regarding the optimal capacity configuration and the optimal economic dispatch of PEVs. On one hand, MGs can maximize their benefits by mobile energy transmission as much as possible. On the other hand, MGs can also minimize total cost by reducing the investment cost of PEV charging/discharging infrastructures. Both objective functions need to be considered simultaneously. This paper presents a cooperative optimization method for capacity configuration and economic dispatch of electric vehicles in MGs considering across-time-and-space energy transmission (ATSET). Considering the differences of electricity prices in different time and space, the impact of ATSET on MG economic operation is analyzed, and a two-loop optimization model is utilized to optimize capacity configuration and economic dispatch of PEVs. Improved particle swarm optimization is used to implement cooperative optimization procedure, and the effectiveness of the proposed method is validated by detailed case studies. Results show that the total costs of the MG system and PEV owners can be reduced by the proposed cooperative optimization method. [ABSTRACT FROM AUTHOR]

An intertwined single-walled carbon nanotubes (SWCNTs)/carbothermal ZnO nanowires (ZNWs) composite is synthesized using a facile ultrasonic stirring technology, which is deposited on Au-interdigitated electrodes for ultraviolet-visible (UV-Vis) photoresponse enhancement. It is found that the SWCNT attached on ZNW surface optimizes the surface-related chemical processes and provides effective carrier transport strategies, responsible for the improvement in photo-responsivity and photo-sensing speed. The UV-Vis absorption of ZNWs has been improved after compositing with the high-conductive SWCNTs, contributing to the significantly improved photo-conductance. The photodetector based on SWCNT/ZNW composites (CZWs) with an optimal SWCNT content of 0.1 wt% shows a 300% improvement in photocurrent density, a 200% improvement in responsivity, and a 400% improvement in on/off current ratio over the pure ZNWs-based device under a UV irradiation of 3.26 mW cm−2 and a bias voltage of 1.0 V. This synthetic method could be scaled up for large-scale fabrication of CZWs on substrate at low cost for practical photodetecting applications. [ABSTRACT FROM AUTHOR]

Background: Self-incompatibility (SI) is a major barrier that obstructs the breeding process in most horticultural plants including tea plants (Camellia sinensis). The aim of this study was to elucidate the molecular mechanism of SI in tea plants through a high throughput transcriptome analysis. Results: In this study, the transcriptomes of self- and cross-pollinated pistils of two tea cultivars 'Fudingdabai' and 'Yulv' were compared to elucidate the SI mechanism of tea plants. In addition, the ion components and pollen tube growth in self- and cross-pollinated pistils were investigated. Our results revealed that both cultivars had similar pollen activities and cross-pollination could promote the pollen tube growth. In tea pistils, the highest ion content was potassium (K+), followed by calcium (Ca2+), magnesium (Mg2+) and phosphorus (P5+). Ca2+ content increased after self-pollination but decreased after cross-pollination, while K+ showed reverse trend with Ca2+. A total of 990 and 3 common differentially expressed genes (DEGs) were identified in un-pollinated vs. pollinated pistils and self- vs. cross-pollinated groups after 48 h, respectively. Function annotation indicated that three genes encoding UDP-glycosyltransferase 74B1 (UGT74B1), Mitochondrial calcium uniporter protein 2 (MCU2) and G-type lectin S-receptor-like serine/threonine-protein kinase (G-type RLK) might play important roles during SI process in tea plants. Conclusion: Ca2+ and K+ are important signal for SI in tea plants, and three genes including UGT74B1, MCU2 and G-type RLK play essential roles during SI signal transduction. [ABSTRACT FROM AUTHOR]

In high-voltage output applications, the rectifier diodes in the conventional full-bridge converter have to bear the whole secondary voltage of a transformer. In this paper, a three-level rectifier structure with flying capacitors is proposed for the dc–dc converter. Compared with the conventional dc–dc converter, the converter with the proposed rectifier structure has the following advantages: low-voltage diodes could be used for high-voltage output applications; due to the secondary flying capacitors, there are no voltage spikes on the rectifier diodes even if no snubber circuits are attached; not only can the leading switches realize zero voltage switching (ZVS) as the same as the conventional converters, but also the lagging switches can realize zero current switching in discontinuous-conduction mode and ZVS in continuous-conduction mode; and the rectified voltage has no zero-state voltage, it has been raised to half of the input voltage, so the voltage fluctuation is lower than the conventional converter under the same modulation strategy, and the current ripple of the filter inductor can be reduced by half. The operation principle of the proposed rectifier structure is analyzed in details, and a prototype is fabricated to verify the features of the proposed converter. [ABSTRACT FROM PUBLISHER]

2-Dimensional (2D) wide band-gap semiconductor molybdenum disulfide (MoS2) nanosheets as an ultraviolet (UV) photo-conductive material were used in surface acoustic wave (SAW) resonators for UV light sensing. A SAW resonator based on zinc oxide (ZnO) piezoelectric film deposited on glass through radio frequency (RF) magnetron sputtering technique was prepared, in which the sub-microscale gold/chromium (Au/Cr) interdigital transducers (IDTs) and grating reflectors were fabricated onto the ZnO surfaces using the electron beam lithography and lift-off techniques to form the IDTs/ZnO/glass-based SAW resonator with a working frequency at ∼1.02 GHz. The MoS 2 nanosheets prepared by electrochemical lithiation process were coated on IDTs region to form a highly sensitive SAW UV sensor, exhibiting an interesting photoresponse behavior to UV radiation. A maximum frequency shift of ∼3.5 MHz was found under 365 nm UV radiation with power intensity of 1.466 mW/cm 2 , which is attributed to the high resonant frequency (in GHz) and high specific surface area of photo-conductive MoS 2 nanosheets. It is suggested that the adsorption and desorption of oxygen on MoS 2 nanosheets play the dominant roles in the frequency-upshift due to mass loading effect and acoustoelectric effect, meanwhile, acoustoelectric effect also creates the SAW attenuation. [ABSTRACT FROM AUTHOR]

The weak photon absorption and high recombination rate of electron-hole pairs in disordered zinc oxide nanowires (ZNWs) limit its application in UV photodetection. This limitation can be overcome by introducing graphene sheets to the ZNWs. Herein we report a high-performance photodetector based on one-dimensional (1D) wide band-gap semiconductor disordered ZNWs composited with reduced graphene oxide (RGO) for ultraviolet (UV) photoresponse enhancement. The RGO/ZNWs composites have been successfully synthetized through UV-assisted photochemical reduction of GO in ZNWs suspension. The material characterizations in morphology, Raman scattering, and Ultraviolet-visible light absorption verified the formation of graphene sheets attached in ZNWs network and the enhancement of UV absorption due to the introduction of graphene. In comparison with photodetectors based on pure ZNWs, the photodetectors based on RGO/ZNWs composite exhibit enhanced photoresponse with photocurrent density of 5.87 mA•cm-2, on/off current ratio of 3.01 x 104, and responsivity of 1.83 A•W-1 when a UV irradiation of 3.26 mW•cm-2 and 1.0 V bias were used. Theory analysis is also presented to get insight into the inherent mechanisms of separation and transportation of photo-excited carriers in RGO/ZNWs composite. [ABSTRACT FROM AUTHOR]

In high-voltage dc–dc applications, the switches in the conventional two-level dual active bridge (DAB) dc–dc converter have to bear the whole port voltage, so high voltage switches should be selected. The voltage stress of the switches in the three-level DAB converter can be reduced to half of the port voltage, so it is suitable for high-voltage applications. However, part of the switches still has to bear the entire port voltage under some operation conditions with the single phase-shifted (SPS) modulation strategy. A dual phase-shifted (DPS) modulation strategy is proposed for the converter, compared with SPS modulation strategy, it expands regulating range of transmission power and enhances control flexibility. Moreover, a control algorithm can be developed to ensure that the voltage stress of each switch is half of the port voltage. The detailed operation principle of the three-level DAB converter with DPS control is analyzed in the paper. The characteristics of each operation region and the critical conditions between different operating regions are derived. Finally, the performance of the three-level DAB converter and DPS modulation strategy are verified by the simulation and experimental results of a 125 kW prototype. [ABSTRACT FROM PUBLISHER]

This article presents a compact piezoelectric vibration energy harvester (VEH) using multiple nonlinear techniques to tuning the resonant frequency and broadening the bandwidth. The device was designed as a parallel-plate structure consisting of a suspended spring-plate with proof mass and piezoelectric transducers, a tunable stopper-plate, and supporting frames. By mechanical adjusting the vertical gap between the spring-plate and the stopper-plate (GBSS), the VEH can realize tuning of the resonant frequency and the bandwidth by multiple nonlinear effects. Experimentally, the piezoelectric VEH was assembled as a metal prototype that can be operated in three kinds of work states corresponding to the configurations of large-GBSS, small-GBSS, and over-GBSS. The sweeping-frequency measurement results show that the work frequency, bandwidth, and output-voltage of VEH depend on tuning of GBSS and excitation levels, indicating that the multiple nonlinear effects, such as Duffing-spring effect, impact effect, preload effect, and air elastic effect, have significant influence on the dynamic behaviors of VEH. The comparisons of numerical simulations with the experimental results were used to verify the validity of mathematical modeling on VEH with multiple nonlinear tuning techniques. [ABSTRACT FROM AUTHOR]

BACKGROUND The tea plant, Camellia sinensis (L.) O. Kuntz, is a perennial woody plant widely cultivated for the production of a popular non-alcoholic beverage. To rapidly identify and evaluate two different color tea varieties (yellowish and purplish), the main phenotypic traits and quality components were tested in the present study. The metabolic profiles of tea shoots and leaves were also analyzed using liquid chromatography-tandem mass spectrometry. RESULTS The yellowish variation had a higher active level with respect to metabolism of catechins, and the contents of luteolin and kaempferol 3- α- d-glucoside were much higher compared to in the other variations. However, the purplish variation had a low content of theanine and a high content of caffeine. The contents of quercetin and kaempferol 3- α- d-galactoside were highest in purplish leaves. Moreover, the yellowish variation had the highest total quality scores for green teas and black teas, whereas the purplish variation had the highest scores for oolong teas. CONCLUSION Both the yellowish variation and the purplish variation represent excellent breeding materials and are worthy of breeding as new tea cultivars. The yellowish variation is more suitable for making high-grade green teas or black teas, whereas the purplish variation is suitable for producing fine quality oolong teas. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

For the LLC series resonant converter (LLC-SRC), the resonant current inrush during the startup is a threat to the safe operation of the main switches, and frequency-decreasing startup method is usually adopted. The very high initial start-up frequency can suppress this inrush effectively, but increases the output current demand of drive ICs. In this paper, a variable duty cycle soft startup strategy based on optimal current-limiting curve is presented, which can realize the suppression of the resonant current inrush under low startup frequency. Due to the nonlinearity of the LLC-SRC, the mode transition conditions are illustrated and a generalized numerical model of the LLC-SRC is established, providing a highly accurate prediction on resonant variables and output during the startup process. Based on the numerical model, the relationship between the startup current, initial startup frequency, and the duty cycle is revealed to quantify the startup process and achieve optimal initial startup parameters. A numerical algorithm is presented to obtain the optimal current-limiting curve during the startup. Two variable duty cycle startup methods are applied to verify the effectiveness of the proposed strategy, namely the PWM startup method and the phase-shift startup method. The experimental results are presented to verify the proposed soft startup strategy. [ABSTRACT FROM PUBLISHER]

The repair of infected bone defects remains a clinical challenge. Staphylococcus aureus is a common pathogenic micro-organism associated with such infections. Gentamycin (GM) is a broad spectrum antibiotic that can kill S. aureus in a dose-dependent manner. However, the systemic administration of antibiotics may lead to drug resistance and gut dysbiosis. In this work, we constructed β-tricalcium phosphate/gelatin composite scaffolds incorporated with gentamycin-loaded chitosan microspheres (CMs(GM)-β-TCP/gelatin composite scaffolds), which helped optimize the local GM release in the infected defect areas and enhance bone regeneration. The cumulative release curves showed that both microspheres and composite scaffolds reached a sustained slow-release phase after the initial rapid release, and the latter further stabilized the initial drug release rate. The release curve of CMs(GM)-β-TCP/gelatin composite scaffolds reached a plateau after 24 h, and the cumulative release reached 41.86% during this period. Moreover, the combination of β-TCP and gelatin mimicked bone composition and were able to provide the requisite mechanical strength (0.82 ± 0.05 MPa) during the first phase of bone generation. The inner structure of the scaffold was arranged in the shape of interconnected pores, and presented a porosity level of 16%. The apertures were uniform in size, which was beneficial for cell proliferation and material transportation. Macroscopic observation and histological analysis showed that CMs(GM)-β-TCP/gelatin composite scaffolds fused with bone tissues, and new tissues were formed in defect areas without any infection. This new composite scaffold may be a promising repair material for treating infected bone defects. [ABSTRACT FROM AUTHOR]

Abstract: Power forecasting is an important factor for planning the operations of photovoltaic (PV) system. This paper presents an advanced statistical method for solar power forecasting based on artificial intelligence techniques. The method requires as input past power measurements and meteorological forecasts of solar irradiance, relative humidity and temperature at the site of the photovoltaic power system. A self-organized map (SOM) is trained to classify the local weather type of 24h ahead provided by the online meteorological services. A unique feature of the method is that following a preliminary weather type classification, the neural networks can be well trained to improve the forecast accuracy. The proposed method is suitable for operational planning of transmission system operator, i.e. forecasting horizon of 24h ahead and for PV power system operators trading in electricity markets. Application of the forecasting method on the power production of an actual PV power system shows the validity of the method. [Copyright &y& Elsevier]

This paper presents a methodology for the optimal allocation and economic analysis of energy storage system (ESS) in microgrids (MGs) on the basis of net present value (NPV). As the performance of an MG strongly depends on the allocation and arrangement of its ESS, optimal allocation methods and economic operation strategies of the ESS devices are required for the MG. To optimize the operation strategies and capacities of ESS in MGs, the financial benefit and dynamic models of ESS are discussed. And then, a matrix real-coded genetic algorithm is applied to find maximal NPV, in which each GA chromosome consists of a 2-D real number matrix representing the generation schedule of ESS and distributed generation sources. This paper is to suggest, among those available ESS, the optimal sizes and types of them and their optimal arrangement, such that the total NPV achieved during the system operational lifetime period is maximized. Finally, some computational simulation results are presented to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Neutral-point (NP) voltage fluctuation is an inherent problem in three-level inverters. Without any control measures, the NP voltage will deviate, and the dc bias and ac oscillation can be observed, which may lead to the failure of power devices and capacitors, so as to damage the system security. In this letter, a hybrid control method is proposed, which it combines zero-sequence voltage regulation with the decomposition of modulation waveform organically. This carrier-based method is simple with lower switching loss due to the unchanged switching events per switching cycle. Experiments are carried out in a 10-kVA three-level platform, which demonstrate the validity of proposed method. [ABSTRACT FROM AUTHOR]

Leaf color variations in tea plants were widely considered due to their attractive phenotypes and characteristic flavors. The molecular mechanism of color formation was extensively investigated. But few studies focused on the transformation process of leaf color change. In this study, four strains of 'Baijiguan' F1 half-sib generation with similar genetic backgrounds but different colors were used as materials, including Green (G), Yellow-Green (Y-G), Yellow (Y), and Yellow-Red (Y-R). The results of broadly targeted metabolomics showed that 47 metabolites were differentially accumulated in etiolated leaves (Y-G, Y, and Y-R) as compared with G. Among them, lipids were the main downregulated primary metabolites in etiolated leaves, which were closely linked with the thylakoid membrane and chloroplast structure. Flavones and flavonols were the dominant upregulated secondary metabolites in etiolated leaves, which might be a repair strategy for reducing the negative effects of dysfunctional chloroplasts. Further integrated analysis with the transcriptome indicated different variation mechanisms of leaf phenotype in Y-G, Y, and Y-R. The leaf color formation of Y-G and Y was largely determined by the increased content of eriodictyol-7-O-neohesperidoside and the enhanced activities of its modification process, while the color formation of Y-R depended on the increased contents of apigenin derivates and the vigorous processes of their transportation and transcription factor regulation. The key candidate genes, including UDPG, HCT, CsGSTF1, AN1/CsMYB75, and bHLH62, might play important roles in the flavonoid pathway. [ABSTRACT FROM AUTHOR]

To uncover the mechanisms that underlie the chlorina phenotype of the tea plant, this study employs morphological, biochemical, transcriptomic, and iTRAQ-based proteomic analyses to compare the green tea cultivar LJ43 and the yellow-leaf tea cultivar ZH1. ZH1 exhibited the chlorina phenotype, with significantly decreased chlorophyll content and abnormal chloroplast development compared with LJ43. ZH1 also displayed higher theanine and free amino acid content and lower carotenoid and catechin content. Microarray and iTRAQ analyses indicated that the differentially expressed genes and proteins could be mapped to the following pathways: ‘phenylpropanoid biosynthesis,’ ‘glutathione metabolism,’ ‘phenylalanine metabolism,’ ‘photosynthesis,’ and ‘flavonoid biosynthesis.’ Altered gene and protein levels in these pathways may account for the increased amino acid content and reduced chlorophyll and flavonoid content of ZH1. Altogether, this study combines transcriptomic and proteomic approaches to better understand the mechanisms responsible for the chlorina phenotype. [ABSTRACT FROM AUTHOR]

Tea ( Camellia sinensis L.) is a thermophilic evergreen woody perennial. It is poor in cold tolerance during winter. Changes occurred at metabolite level in low temperatures were poorly understood in tea plants. In this study, Metabolite profiling of tea leaves was performed to investigate the responses of tea plants to different cold conditions by using gas chromatography-mass spectrometry (GC–MS) andmultivariate analysis. A total of 105 metabolites were identified. Principal component analysis (PCA) revealed that the tea leaves in plastic greenhouse (DP) and natural condition (OA) were clearly separated by their sampling times and growth conditions. The levels of changed metabolites could be organized in four clusters by hierarchical clustering analysis (HCA). According to the pathway, raffinose, maltose, glucose and fructose derived from the hydrolysis of sucrose were all more abundant in leaves of OA than those of DP. Despite temperature fluctuation, leucine, valine, threonine, alanine were all in higher level in leaves of DP than those of OA except Nov. 16. Citric acid, fumaric acid and malic acid were in higher level under the higher temperature in DP. Shikimic acid and quinic acid presented an absolutely distinct metabolism pattern. Shikimic acid was negatively correlated with quinic acid in both treatments except Mar. 16. They were at high level on Nov. 16, and then decreased sharply in the following periods in both treatments during the experiment. The results indicated that the different low temperatures had significantly different effects on tea plants and could change their metabolic pathways in different ways. These might be helpful to understand the mechanism of cold resistance of tea plants at the metabolite level and to facilitate the future research on gene and protein expression in tea plants of DP and OA in winter. [ABSTRACT FROM AUTHOR]

Most teas, including white tea, are produced from tender shoots containing both leaf and stem. However, the effect of the stem on white tea quality remains unclear, especially during withering, an essential process. Therefore, this study investigated the withering-induced changes in the leaves and stems of Camellia sinensis cv. 'Fudingdabai' by multi-group analysis. During withering, the levels of catechin and theobromine (i.e., major flavor-related compounds) decreased slightly, mainly in the leaves. The abundance of some proteinaceous amino acids related to fresh taste increased in stems due to increased protein hydrolysis. In addition, changes in biosynthetic pathways caused a decrease in theanine (a major non-proteinaceous amino acid) and an increase in gamma-aminobutyric acid in stems. Terpenes, mainly in the stems, were partially affected by withering. Phenylacetaldehyde, a major contributor to white tea aroma, increased mainly in the stems. These findings reflect the positive contribution of the stem to white tea quality. • Catechin and theobromine decreased during withering, which mainly occurred in leaf. • Some protein hydrolysis-derived amino acid contents increased in withering stems. • Theanine synthesis decreased and GABA synthesis increased in withering stems. • Stem is vital for bud-leaf type white tea quality, because of its abundant terpenes. • Withering increased the aroma-related phenylacetaldehyde content mainly in the stem. [ABSTRACT FROM AUTHOR]

Aroma is one of the key sensory attributes of tea. Quantitative volatile measurement is essential but technically challenging. Sample extraction is the first critical step for quantification. However, volatile extraction method has not been systematically optimized. The goal of this research was to establish a quantitative volatile measurement method in tea. For this end, solvent‐assisted flavour evaporation method was used; the effects of the numbers of extraction, stirring, sample amounts, solid–liquid ratios and postharvest treatments on volatile isolation were compared. We demonstrated that stirring did not improve total volatile recovery; the number of volatiles detected was positively correlated with sample amounts and the solid–liquid ratio, excess sample amounts compromised the quantification accuracy of abundant volatiles; cryopreservation largely preserved the volatile contents and composition of fresh tea leaves. Based on these findings, volatile extraction method was optimized. The volatile compounds were qualitatively and quantitatively analysed by GC‐MS and GC‐FID, respectively; the FID relative response factor for individual volatile was calculated to calibrate individual peak area of tea volatile. By integrating these techniques, a quantitative volatile measurement method was established. As a proof of concept, the described method was applied to investigate the seasonal effects on fresh tea leaf volatile. The described method should also be applicable to other horticultural crop species. [ABSTRACT FROM AUTHOR]

• Pruning results in significant increase in shoot growth and development. • Concentration of the auxin IAA increases significantly in shoots of pruned plants. • Metabolome profiling identifies 80 differential metabolites in shoots of pruned tea. • Indole-3-acetonitrile and menaquinone are involved in auxin synthesis in pruned tea. • Genes involved in auxin synthesis are expressed in shoots of pruned plant. Pruning is a routine management practice in tea cultivation. Although pruning is speculated to contribute to shoot growth and development in tea plants, it is imperative to understand the molecular mechanism involved. In order to investigate this, tea plants were pruned at different levels. Analysis of shoot growth indices revealed significant increase in shoots number and weight in shoots of pruned tea plant. Auxin assay showed higher concentrations of indole-3-acetic acid in pruned samples. Metabolomic analysis identified 80 differential metabolites in shoots of pruned plants, of which indole-3-acetonitrile and menaquinone were the common metabolites in all levels of pruning. The metabolites are involved in auxin biosynthesis, as shown by protein-protein interaction analysis. The metabolites enriched major metabolic pathways such as tryptophan metabolism, vitamin digestion and absorption, biosynthesis of ubiquinone and other terpenoid-quinone, and biosynthesis of amino acids. Genes involved in auxin signalling and menaquinone synthesis were up-regulated in pruned plants. This study reports, for the first time in nature, the synthesis of menaquinone in plants. This study concludes that pruning enhances shoot growth and development through the modulation of indole-3-acetic acid via synthesis of indole-3-acetonitrile and menaquinone in shoots, a combined effect of tryptophan metabolism and other metabolic pathways. This study contributes to knowledge in molecular mechanism of shoot growth and development. [ABSTRACT FROM AUTHOR]

Cuticle is the major transpiration barrier that restricts non-stomatal water loss and is closely associated with plant drought tolerance. Although multiple efforts have been made, it remains controversial what factors shape up the cuticular transpiration barrier. Previously, we found that the cuticle from the tender tea leaf was mainly constituted by very-long-chain-fatty-acids and their derivatives while alicyclic compounds dominate the mature tea leaf cuticle. The presence of two contrasting cuticle within same branch offered a unique system to investigate this question. In this study, tea seedlings were subjected to water deprivation treatment, cuticle structures and wax compositions from the tender leaf and the mature leaf were extensively measured and compared. We found that cuticle wax coverage, thickness, and osmiophilicity were commonly increased from both leaves. New waxes species were specifically induced by drought; the composition of existing waxes was remodeled; the chain length distributions of alkanes, esters, glycols, and terpenoids were altered in complex manners. Drought treatment significantly reduced leaf water loss rates. Wax biosynthesis-related gene expression analysis revealed dynamic expression patterns dependent on leaf maturity and the severity of drought. These data suggested that drought stress-induced structural and compositional cuticular modifications improve cuticle water barrier property. In addition, we demonstrated that cuticle from the tender leaf and the mature leaf were modified through both common and distinct modes. [ABSTRACT FROM AUTHOR]

The efficiency of bidirectional inductive power transfer (BIPT) systems is strongly dependent on the load. Besides, the soft-switching operation of power switches is critical to high-frequency converter in the BIPT systems. In this paper, a triple-phase-shift (TPS) control strategy is proposed to achieve load matching while realizing zero voltage switching (ZVS) for all power switches within the entire power range. The load matching condition of the BIPT system with double-sided LCC compensation network is analyzed. And a dual side phase shift control is proposed to adjust power flow while realizing load matching. To realize ZVS operation, the third phase shift between primary and secondary side is introduced as an extra control variable. A time domain model of double-sided LCC compensation network is established to analyze the ZVS range. With the proposed TPS control, wide ZVS operation range of the system can be achieved while maintaining load matching. At last, a scale down prototype of 1 kW BIPT system is developed. The experimental results show good agreement with theoretical analysis, all switches realize ZVS within the entire power range and a peak efficiency of 94.83% is achieved. [ABSTRACT FROM AUTHOR]

This paper proposes a double modulation wave carrier-based pulse width modulation (CBPWM) strategy for the three-level neutral-point-clamped (NPC) inverter. This modulation strategy not only overcomes one of the main problems of the NPC inverter, which is the low-frequency voltage oscillation on the neutral point, but also reduces the common-mode voltage (CMV) generated by the inverter. Through the rigorous theoretical derivation, the unified duty cycles of each phase are derived, and the double modulation waves can be easily obtained according to different optimization objectives. However, in the previous double wave CBPWM work, the modulation strategy could not reduce the CMV, whose amplitude is still the same as that of the conventional CBPWM strategy. By rearranging the switching sequence, the vectors corresponding to the large CMV amplitude have been eliminated, and the amplitude of CMV can be reduced by half. Considering the occurrence of neutral-point voltage perturbations, a voltage controller is adopted to recover from the imbalance. Finally, the performance of the proposed modulation technique is verified by the experimental results. [ABSTRACT FROM PUBLISHER]

Tea (Camellia sinensis) germplasm affects the tea aroma quality, especially in oolong tea. However, the mechanism underlying the diversity in aroma formation induced by postharvest stresses among different tea cultivars remains unclear. In this study, correlation analyses between sensory evaluation scores and aroma compound contents of oolong teas made from 12 different cultivars was carried out. The results confirmed the contribution of three characteristic aroma compounds [i.e., indole, jasmine lactone, and (E)-nerolidol] to the oolong tea floral aroma quality. However, only the indole was positively correlated with the jasmonic acid (JA) in the simulated withering (wounding stress due to plucking) and turnover (continuous wounding stress) stages. Furthermore, the expression levels of transcription factor CsMYC2c and structural genes for the three aroma compounds were positively correlated in the simulated withering stage. Transient transcriptional activation analyses in tobacco revealed that CsMYC2c regulated the promoter activity and expression of structural genes. However, yeast one-hybrid assay showed that CsMYC2c did not directly bind to the gene promoters. The information has expanded our understanding of the causes for the variations in aromas among diverse tea cultivars in response to postharvest stress. Furthermore, it may provide the basis for breeding and selection of high-aroma tea cultivars. • Tea germplasm plays an important role in the floral aroma quality of oolong tea. • Floral aroma quality is positively correlated with characteristic aroma compounds. • Jasmonic acid causes the variation in aroma of different cultivars under withering. • CsMYC2c may regulate different expressions of synthetic genes in different cultivars. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cuticular waxes changed during leaf development and dehydration or withering treatment. • Cuticular wax loading is positively correlated to tea flavor formation. • Caffeine is a major component in tea leaf cuticular wax. • Caffeine and inositol increased during dehydration or withering treatment. Despite some studies on tea leaf cuticular wax, their component changes during dehydration and withering treatments in tea processing and suspected relation with tea flavor quality formation remain unknown. Here, we showed that tea leaf cuticular wax changed drastically in tea leaf development, dehydration, or withering treatment during tea processing, which affected tea flavor formation. Caffeine was found as a major component of leaf cuticular wax. Caffeine and inositol contents in leaf cuticular wax increased during dehydration and withering treatments. Comparisons showed that tea varieties with higher leaf cuticular wax loading produced more aroma than these with lower cuticular wax loading, supporting a positive correlation between tea leaf cuticular wax loading and degradation with white tea aroma formation. Dehydration or withering treatment of tea leaves also increased caffeine and inositol levels in leaf cuticular wax and triggered cuticular wax degradation into various molecules, that could be related to tea flavor formation. Thus, tea leaf cuticular waxes not only protect tea plants but also contribute to tea flavor formation. The study provides new insight into the dynamic changes of tea leaf cuticular waxes for tea plant protection and tea flavor quality formation in tea processing. [ABSTRACT FROM AUTHOR]

Dynamic wireless power transmission (DWPT) is considered as a solution to the problems encountered in the development of electrical vehicle (EV), such as range anxiety resulted from battery bottleneck and the difficulty of convenient charging. However, the requirement of DWPT, maintaining almost constant transmission power with constant voltage load in effective movement process, is quite different from Stationary WPT. The power fluctuation is easily brought by the coupling coils over large misalignment in movement. A general design method of primary compensation network from the perspective of DWPT is presented in this paper. Under the premise of ensuring high transmission efficiency and soft switching, a novel T-type compensation network for DWPT is proposed, which maintains a stable output characteristic over a wide misalignment, companied with an inherent current limiting ability under no-load operation. A WPT prototype with a fixed frequency operation based on the T-type compensation network is built. The output power is kept almost stable even though magnetic coupling coefficient varies twice showing the effectiveness of the design method. [ABSTRACT FROM AUTHOR]

In this paper, a reformed compensation network based on traditional LCL topology is proposed to realize robust reaction to large coupling variation that is common in dynamic wireless charging application. From the perspective of smoothing, the power characteristic against coupling factor and to achieve high efficiency simultaneously, extra reactive element is inserted into the resonant tank to provide higher degree of design freedom, forming the improved LCC type compensated inductive power transfer (IPT) system that features with distinct parameter design approach. Comparing to existing compensation topologies, the optimized LCC compensation topology shows more robust power characteristic against variation of coupling factor and, thus, minimizes the need for complex control which is usually undesired in dynamic charging scheme, thereby helping maintain effective power transfer in dynamic charging application and largely enhancing the systematic controllability. Finally, the effectiveness of the proposed method is experimentally verified. The power transfer profile is smooth against coupling factor to realize high tolerance to position as the power drop is no more than 20% within almost 200% of coupling factor variation. [ABSTRACT FROM PUBLISHER]

In this paper, an LLC resonant converter design methodology for battery charging applications is proposed aiming at achieving high efficiency. Compared with traditional resistive or constant power load applications, the battery voltage and current are nonlinear and vary with the charging profiles, making the optimal design of battery charger more difficult and complicated. Based on the characteristics of the battery charging profiles, a new time-weighted average efficiency (TWAE) index is proposed, which represents the average weight of conversion efficiency during battery charging period. Converter's losses are calculated based on the standard loss models using the current and voltage information derived from the LLC steady-state model, which is solved utilizing the numerical non-linear programming techniques. In addition, the TWAE is achieved serving as the objective function to optimize the converter parameters. To reduce the search space and speed up the search algorithm, a variable-step exhaustive search algorithm is applied considering the constraints of operation and variable range. Finally, a 3 kW prototype LLC converter, which converts 220 VAC from the grid to a wide output voltage range from 60 to 100 V is built and a TWAE of 94.74% and a peak efficiency of 95.19% are achieved, validating the effectiveness of the presented method. [ABSTRACT FROM AUTHOR]

The goal of the present study was to compare the structural and compositional differences of cuticle between tender leaf and fully-expanded leaf in Camellia sinensis, and provide metabolic base for the further characterization of wax biosynthesis in this economically important crop species. The tender second leaf and the fully-expanded fifth leaf from new twig were demonstrated to represent two different developmental stages, their cuticle thickness were measured by transmission electron microscopy. The thickness of the adaxial cuticle on the second and fifth leaf was 1.15 µm and 2.48 µm, respectively; the thickness of the abaxial cuticle on the second and fifth leaf was 0.47 µm and 1.05 µm, respectively. The thickness of the epicuticular wax layer from different leaf position or different sides of same leaf were similar. However, the intracuticular wax layer of the fifth leaf was much thicker than that of the second leaf. Total wax lipids were isolated from the second leaf and the fifth leaf, respectively. Gas chromatography-mass spectrometry analysis identified 51 wax constituents belonging to 13 chemical classes, including esters, glycols, terpenoids, fatty acids and their derivatives. Wax coverage on the second and fifth leaf was 4.76 µg/cm2 and 15.38 µg/cm2, respectively. Primary alcohols dominated in the tender second leaf. However, triterpenoids were the major components from the fully-expanded fifth leaf. The predominant carbon chains varied depending on chemical class. These data showed that the wax profiles of Camellia sinensis leaves are development stage dependent, suggesting distinct developmental dependent metabolic pathways and regulatory mechanisms. [ABSTRACT FROM AUTHOR]

Message authentication has vital significance for dynamic microgrid partition in smart grid. However, current message authentication protocols based on “public key infrastructure” are too complicated to be deployed in smart grid and lack group information management function. On the other hand, group information management protocols based on “logic key hierarchy” need to broadcast a lot of messages during microgrid partition processes, resulting in high communication costs. To address these issues, we present a novel identity-based message authentication protocol for dynamic microgrid partition called securing dynamic microgrid partition. Similar to the protocols of this field, securing dynamic microgrid partition can provide message authentication and group information management functions. However, compared to other well-known approaches, securing dynamic microgrid partition uses Bloom filter for managing group information, which can reduce the communication cost of logic key hierarchy significantly. Moreover, securing dynamic microgrid partition uses Lagrange interpolation for designing new identity-based signing and verification algorithms, which is simple to be deployed in smart grid environment and much more efficient than current identity-based protocols. Experimental results show that the proposed approach is feasible for real-world applications. [ABSTRACT FROM AUTHOR]

Renewable energy resources (RESs) with plug-in electric vehicles (PEVs) are being gradually accepted by society for their low carbon emission merits. However, reverse power from the RES will result in the grid node's voltage rise and cause protection malfunction. As large amount of PEVs plug in the grid, their overall charging power tends to be uncertain due to their complex charging behavior. At the same time, if the renewable energy is integrated into the same grid, the gird will face a great technological challenge. In this paper, a smart building energy management system (SBEMS) is proposed to mitigate negative impact of RES and PEVs to power grid and optimize the operation of the building. The proposed SBEMS is also capable with PEVs system integration, photovoltaic (PV) power forecasting, optimization algorithm implementation, and environmental evaluation criteria. Since PV's output is sensitive to the meteorology, a 1-day-ahead power forecasting model is needed and presented. The economic system of PEVs is particularly complex, because it needs optimization across multiple time steps and is strongly influenced by tariff structures. Furthermore, the optimization problem to minimize the total building operational cost including PEVs charging cost is formulated while satisfying the supply and demand balance and complicated operating constraints of every energy supply equipment and devices. The simulation results have shown that the SBEMS can effectively reduce the PEVs charging cost, building operation cost, and the environment punishment fee. It is also important for the SBEMS to be responsible for the power grid operational indices. So the trade-off between economic consideration and load factor should be made. It is verified that the SBEMS is beneficial to the PEVs owners, building operator, environment, and grid. [ABSTRACT FROM AUTHOR]