This paper investigates the design and analysis of a robust nonlinear controller for voltage source converters (VSCs) connected to weak AC grids. Feedback linearization method is used to develop the ...control inputs that regulate the active power and output voltage of the grid-connected converter. The frequency-domain model of an LCL filter in <inline-formula><tex-math notation="LaTeX">dq</tex-math></inline-formula>-frame is used to develop the nonlinear control blocks for small-signal stability analysis. Impact of phase-locked loop (PLL) is added to the control block through feedforward loops. It is shown that unlike vector controlled converters, the proposed controller is not negatively affected by the PLL gains and a broader range of operation is achieved. In addition, the designed controller is robust against sudden active power commands from 0 to 1 p.u., and is capable of fault ride through when AC grid is very weak. The robustness of the proposed controller is evaluated using eigenvalue analysis of the linearized closed-loop model and time-domain simulations of a grid-connected VSC in various cases.
Fiber elongation is the key determinant of fiber quality and output in cotton (Gossypium hirsutum). Although expression profiling and functional genomics provide some data, the mechanism of fiber ...development is still not well understood. Here, a gene encoding a calcium sensor, GhCaM7, was isolated based on its high expression level relative to other GhCaMs in fiber cells at the fast elongation stage. The level of expression of GhCaM7 in the wild‐type and the fuzzless/lintless mutant correspond to the presence and absence, respectively, of fiber initials. Overexpressing GhCaM7 promotes early fiber elongation, whereas GhCaM7 suppression by RNAi delays fiber initiation and inhibits fiber elongation. Reactive oxygen species (ROS) play important roles in early fiber development. ROS induced by exogenous hydrogen peroxide (H₂O₂) and Ca²⁺ starvation promotes early fiber elongation. GhCaM7 overexpression fiber cells show increased ROS concentrations compared with the wild‐type, while GhCaM7 RNAi fiber cells have reduced concentrations. Furthermore, we show that H₂O₂ enhances Ca²⁺ influx into the fiber and feedback‐regulates the expression of GhCaM7. We conclude that GhCaM7, Ca²⁺ and ROS are three important regulators involved in early fiber elongation. GhCaM7 might modulate ROS production and act as a molecular link between Ca²⁺ and ROS signal pathways in early fiber development.
As the most important natural raw material for textile industry, cotton fibres are an excellent model for studying single-cell development. Although expression profiling and functional genomics have ...provided some data, the mechanism of fibre development is still not well known. A class I TCP transcription factor (designated GbTCP), encoding 344 amino acids, was isolated from the normalized cDNA library of sea-island cotton fibre (from –2 to 25 days post anthesis). GbTCP was preferentially expressed in the elongating cotton fibre from 5 to 15 days post anthesis. Some expression was also observed in stems, apical buds, and petals. RNAi silencing of GbTCP produced shorter fibre, a reduced lint percentage, and a lower fibre quality than the wild-type plants. Overexpression of GbTCP enhanced root hair initiation and elongation in Arabidopsis and regulated branching. Solexa sequencing and Affymetrix GeneChip analysis indicated that GbTCP positively regulates the level of jasmonic acid (JA) and, as a result, activates downstream genes (reactive oxygen species, calcium signalling, ethylene biosynthesis and response, and several NAC and WRKY transcription factors) necessary for elongation of fibres and root hairs. JA content analysis in cotton also confirmed that GbTCP has a profound effect on JA biosynthesis. In vitro ovule culture showed that an appropriate concentration of JA promoted fibre elongation. The results suggest that GbTCP is an important transcription factor for fibre and root hair development by regulating JA biosynthesis and response and other pathways, including reactive oxygen species, calcium channel and ethylene signalling.
•A laboratory box considering double tubes in two-layered subsurface was introduced.•Effects of ground stratification were investigated numerically and experimentally.•Numerical models with layered ...and equivalent thermal properties were compared.•Double-tube interference is significant in high thermal diffusivity material.
Based on a laboratory apparatus, this paper investigates the transient heat transfer performance of ground heat exchangers (GHEs) in a layered ground experimentally and numerically. The 6.25 m × 1.5 m × 1 m experimental box was filled with sand and clay, consisting of two U-tubes and precisely positioned thermocouples. Predictions from numerical models with layered and equivalent thermal properties were compared and validated with experimental data from a 24 h heat injection experiment. Numerical models with layered and equivalent thermal properties gave similar water temperatures while different thermal exchange and ground temperature distributions along the depths of tubes. Compared to the homogeneous numerical model, both the measurements and layered model can well elaborate the effect of ground stratification, where an obvious temperature decline can be observed in the interface from sand to clay, the slope of which doubled during the last 12 h heat injection period. Application of the material with a large thermal diffusivity such as sand results in lower water and ground temperatures, as well as a more significant interference effect of multi-tubes. Therefore, the well-controlled laboratory apparatus is validated to provide reliable and detailed data, and can be used for further investigations on thermal performances of the layered subsurface.
The ratoon rice planting area is gradually expanding, but there has been relatively little research on ratoon rice grains contaminated with Cd.
In this study, five ratoon rice varieties were selected ...and divided into three groups according to early-maturity (growth duration: 100-110 days), mid-maturity (growth duration: 110-120 days) and late-maturity (growth duration: 120-130 days) varieties. Field experiments were done to study the differences in Cd accumulation among ratoon rice varieties with different growth duration.
The results showed that the Cd accumulation and concentration of grains spikelet at each growth stage in the main crop were in the order of late-maturity > mid-maturity > early-maturity varieties. However, the trends in Cd concentration and accumulation in grains spikelet during the ratoon crop were the opposite. Analysis found that as the growth duration of the variety extended, the accumulated temperature and daily average temperature in the main crop increased, which significantly increased the translocation factors of Cd from root, stem, and leaf to grains spikelet, and increased the daily average Cd accumulation rate in grains spikelet. The daily average temperature in the ratoon crop increased as the growth duration shortened. The early-maturity variety had higher Cd accumulation in stubble, which promoted the translocation of Cd from the root, stem, and leaf of the plant to the grains spikelet.
Therefore, appropriately shortening the growth duration of the main crop and extending the growth duration of the ratoon crop are important ways to reduce Cd accumulation in ratoon rice in areas with mild Cd pollution.
Pulsed power loads (PPLs) consume a huge amount of energy within a short time. An energy storage system (ESS) is usually installed in a shipboard power system (SPS) for PPL accommodation. Online ...accommodation strategies, where the PPL is connected to the SPS through the ESS all the time, have great advantages in reducing the hardware cost and increasing the PPL deployment frequency. But there is a lack of online accommodation solutions to deal with the operational requirements. This article presents a barrier-Lyapunov-function-based optimal control solution for online PPL accommodation in dc SPSs. By introducing the state-constrained technique, the operational constraints on the supply current for PPL accommodation and the bus voltage are all respected. Three control objectives, including safe and fast ESS charging, high-quality regulation of the dc bus voltage, and generation cost dynamic minimization, are realized simultaneously. The stability and optimality of the control solution are guaranteed rigorously via the Lyapunov synthesis. Simulations based on a switch-level SPS model demonstrate the effectiveness of the proposed control solution.
Various types of porous media materials inherently contain pore structures of different scales, ranging from nanoscale to millimeter scale. Due to the limitations of the existing imaging technology, ...it is challenging and intractable for any single method to obtain and characterize the multiscale pore structure features of porous media accurately and comprehensively. To address the issue, according to the inherent logical correspondence and mutual conversion relationship between different‐scale image pixels, we propose an improved universal fusion algorithm for constructing three‐dimensional (3D) multiscale porous media. We successfully applied this algorithm to the construction of multiscale pore structure model of carbonate rock, sandstone and coal, and subsequently made quantitative extractions and characterizations of their pore structure characteristics. In addition, the finite element method (FEM) was used to calculate their absolute permeability. The results show that the improved fusion algorithm can effectively solve the problem of pore bias of the existing algorithm, which reduces the porosity of the multiscale model to a certain extent, while maintaining good pore interconnectivity. Besides, the multiscale model obtained by the improved fusion algorithm has a wider pore size distribution interval than that of the existing algorithm, and the absolute permeability of the former, computed using the FEM, is closer to the laboratory‐measured value than that of the latter.
Key Points
We propose an improved universal fusion algorithm to improve the accuracy of the reconstruction of three‐dimensional (3D) multiscale porous media
The pore structure characteristics of multiscale models are significantly increased and improved compared with that of single‐scale models
The improved universal fusion algorithm promises to be applicable for the multi‐scale model reconstruction of various types of porous media
This paper introduces four co-simulation platforms for testing deep reinforcement learning (DRL)-based control solutions in power systems. The first one is to connect the off-the-shelf Matlab DRL ...toolbox with the developed Matlab Simulink power system models (platform 1). The second is to utilize the Python-C interface to integrate the algorithm design in Python and the model development in Matlab, wherein the developed model is first generated to C-code and then compiled into a shared library (platform 2). The third and fourth platforms are based on the real-time simulator, whereas these two employ two different communication protocols, i.e., TCP/IP (platform 3) and EtherCAT (platform 4). The Opal-RT real-time simulators utilized by platforms 3 and 4 ensure that both platforms can run the models in a real-time manner. Specifically, platform 4 possesses capabilities for conducting real-time DRL training and control owing to the real-time feature of both communication and simulation. The detailed procedures regarding implementing these different DRL co-simulation platforms are provided in this paper, with the pros and cons of each one commented on, which can help researchers speed up the preliminary design of DRL-based control solutions for dynamic power systems. Note to Practitioners -This article is motivated by the emerging deep reinforcement learning-based control solutions for dynamic power systems. There is an urgent need for co-simulation platforms that enable a high-fidelity and real-time simulation of power systems and a thorough evaluation of various DRL control algorithms. Since most existing DRL testing tools are developed using Python with simplification adapted to large time-scales or specific functionalities, limiting their applicability in small-time-scale online control. The model with higher granularity is necessary for small-time-scale online control problems for power system applications that involve fast dynamics. The developed platforms allow for direct integration of the dynamic Matlab Simulink power system model and run complex dynamic models in a real-time manner via the Opal-RT simulator. A classic optimal generation control problem for a test power system is studied in this paper to validate the effectiveness of the developed online and real-time DRL platforms. For other power system applications, one only needs to follow the procedures provided in this paper to customize the corresponding dynamic models or environments. The comprehensive real-time and online tests of different DRL control algorithms can be accomplished on the developed platforms with slight effort.
In isolated ac microgrids, multiple controllable distributed energy resources (DERs) may simultaneously participate in load frequency control (LFC). To improve system frequency dynamics and reduce ...the frequency deviation for such a multiple-DER microgrid,this paper presents a novel LFC method based on an optimal reset control (ORC) scheme. The proposed ORC comprises a baseline linear controller and resetting elements, i.e., the integrator outputs, determined by a linear quadratic regulation problem. The overshoot in frequency regulation induced by integral control is reduced, and the settling time is shortened. Besides, the simple structure facilitates its real-time application, making ORC a simple yet effective solution for the LFC of microgrids. By coordinating the reset controllers of all controllable DERs, the ORC further improves the overall frequency control performance. The asymptotic stability of the closed-loop system is theoretically proved. Finally, the effectiveness of the presented LFC method is validated by switch-level simulation studies.
Background Aging is a dynamic and heterogeneous process that may better be captured by trajectories of aging biomarkers. Biological age has been advocated as a better biomarker of aging than ...chronological age, and plant-based dietary patterns have been found to be linked to aging. However, the associations of biological age trajectories with mortality and plant-based dietary patterns remained unclear. Methods Using group-based trajectory modeling approach, we identified distinctive aging trajectory groups among 12,784 participants based on a recently developed biological aging measure acquired at four-time points within an 8-year period. We then examined associations between aging trajectories and quintiles of plant-based dietary patterns assessed by overall plant-based diet index (PDI), healthful PDI (hPDI), and unhealthful PDI (uPDI) among 10,191 participants who had complete data on dietary intake, using multivariable multinomial logistics regression adjusting for sociodemographic and lifestyles factors. Cox proportional hazards regression models were applied to investigate the association between aging trajectories and all-cause mortality. Results We identified three latent classes of accelerated aging trajectories: slow aging, medium-degree, and high-degree accelerated aging trajectories. Participants who had higher PDI or hPDI had lower odds of being in medium-degree (OR = 0.75, 95% CI: 0.65, 0.86 for PDI; OR = 0.73, 95% CI: 0.62, 0.85 for hPDI) or high-degree (OR = 0.63, 95% CI: 0.46, 0.86 for PDI; OR = 0.62, 95% CI: 0.44, 0.88 for hPDI) accelerated aging trajectories. Participants in the highest quintile of uPDI were more likely to be in medium-degree (OR = 1.72, 95% CI: 1.48, 1.99) or high-degree (OR = 1.70, 95% CI: 1.21, 2.38) accelerated aging trajectories. With a mean follow-up time of 8.40 years and 803 (6.28%) participants died by the end of follow-up, we found that participants in medium-degree (HR = 1.56, 95% CI: 1.29, 1.89) or high-degree (HR = 3.72, 95% CI: 2.73, 5.08) accelerated aging trajectory groups had higher risks of death than those in the slow aging trajectory. Conclusions We identified three distinctive aging trajectories in a large Asian cohort and found that adopting a plant-based dietary pattern, especially when rich in healthful plant foods, was associated with substantially lowered pace of aging. Keywords: Aging trajectory, All-cause mortality, Plant-based diet index, Diet quality, Cohort
PDF
