一种风电场经VSC-HVDC并网的VSG变参数负荷频率控制策略

风电的大规模并网导致系统等效惯量下降、不确定性增加,给电力系统的负荷频率控制(loadfrequency control,LFC)带来新的挑战。考虑到柔性直流输电系统(voltage source converter based high voltage DC,VSC-HVDC)具有的潜在调频能力,对此展开研究,针对风电场经VSC-HVDC并网的情形提出了一种虚拟同步发电机(virtual synchronous generator,VSG)变参数负荷频率控制策略。首先,在风电场经VSC-HVDC并网的LFC模型及拓扑结构分析基础上,为了提高VSC-HVDC的可控性,对换流器的控制环节进行了VSG控制方法的设计;然后,对VSG控制参数与频率变化的关联性进行分析,并基于分数阶梯度下降法(fractional-order gradient descent method,FOGDM),利用频率的分数阶导数提取频率深层变化特征,以优化VSG控制参数;在此基础上,考虑到系统的不确定性,设计触发机制对VSG变参数优化模式进行调整,以降低VSG参数的变换频次,提高系统频率控制的针对性。仿真结果表明:所提控制方法能有效改善电网负荷频率控制效果,具有良好的适应性。

基于动态相量的LCC-HVDC输电系统等值技术评述

立足于逆变侧换流站受端交流母线看向送端的基于电网换相换流器的高压直流输电(high-voltagedirectcurrent basedlinecommutedconverter,LCC-HVDC)系统的单端等值,对于优化设计继电保护、安稳控制和直流控保具有重要意义。为了同时获取计算的高精确性和实时性,动态相量模型以牺牲较低的仿真精度换取计算速度的提升,是实现LCC-HVDC输电线路双端等值的重要方式,但是用于LCCHVDC输电系统单端等值还存在难以平衡等值精度和计算速度的问题。针对该问题,该文分析了基于动态相量的LCCHVDC输电系统等值的应用价值、需求及难点,分别从等值计算模型中的提前触发角计算、换相重叠角计算、换相失败的判别及其对开关函数的影响和信号调制等4个因素评述现有研究现状及存在的问题,并提出了后续的研究建议。

人LIGHT和HSV-TK-EGFP基因共转染的MSCs抗肿瘤免疫的体内研究

目的研究与单纯疱疹病毒的糖蛋白D竞争结合单纯疱疹病毒进入介导物(herpes virus entry mediator,HVEM)的淋巴毒素类似物(homologous to lymphotoxins,exhibits inducible expression,and competes with HSV glycoprotein D for HVEM,a receptor expressed by T lymphocytes,LIGHT)基因和单纯疱疹病毒胸苷激酶(herpes simplex virus thymidine kinase,HSV-TK)基因共转染的骨髓间充质干细胞(mesenchymal stem cells,MSCs)在体内的抗肿瘤免疫功能。方法将pIRES2-LIGHT基因和HSV-TK-EGFP基因共转染小鼠骨髓间充质干细胞(MSCs/LT组),以转染空载体和转染HSV-TK-EGFP基因的骨髓间充质干细胞作对照。流式细胞仪检测LIGHT分子和HSV-TK-EGFP分子在稳定转染的骨髓间充质干细胞上的表达。体内迁移实验观察MSCs/LT在小鼠体内迁移情况。观察更昔洛韦注射前后MSCs/LT对荷瘤小鼠体内肿瘤的治疗作用。ELISA法检测小鼠肿瘤组织中IFN-γ,IL-2和IL-10的水平。结果流式细胞仪检测发现,MSCs/LT能稳定高表达LIGHT分子。MSCs/LT有特异地向肿瘤组织趋化的特性。MSCs/LT和MSCs/T有较好的抑制肿瘤生长的能力,但在更昔洛韦诱导后,MSCs/LT的抗肿瘤效应下降甚至消失。同时,MSCs/LT可促使T细胞进入肿瘤组织,并促进T细胞分泌IL-2、IFN-γ,抑制IL-10分泌(P<0.05)。结论共转染人LIGHT和HSV-TK-EGFP基因的骨髓间充质干细胞能稳定高表达LIGHT分子,能特异性地向荷瘤小鼠体内肿瘤组织趋化并抑制肿瘤的生长,这种体内抗肿瘤功能可能与促进T淋巴细胞IL-2、IFN-γ等细胞因子的分泌,改善局部免疫抑制环境有关。

提高系统暂态稳定性的VSC-HVDC有功无功联合附加控制策略

依据基于电压源型换流器的高压直流输电(VSC-HVDC)对系统暂态稳定性的影响机理,提出一种提高系统暂态稳定性的VSC-HVDC有功无功联合附加控制策略。从VSC-HVDC功率特性与系统等值功角的关系出发,建立含VSC-HVDC有功无功附加量的交直流混联系统暂态稳定分析数学模型。针对数学模型的非线性,采用精确反馈线性化进行坐标变换,并采用滑模控制利用反映系统暂态特征的等值功角变化速度与加速度设计切换面,结合设计的有功无功配合方式,确定了VSC-HVDC有功无功附加量随系统暂态特征量实时调节的控制律,其参数设计与计算过程简便。仿真结果表明所提控制策略充分利用了换流站的功率调节能力,有效降低了系统等值功角首摆幅度,加快系统恢复稳定。

基于模块化思想的LCC-HVDC改进小信号建模及交互稳定性分析

随着电网换相型高压直流输电(line commutated converter based high voltage direct current, LCC-HVDC)技术的广泛应用,交直流混联电力系统的交互稳定性问题日益突出。首先基于状态空间平均法建立了考虑非线性换相重叠动态过程的LCC换流器传递函数模型。为适应愈加复杂的直流输电系统建模,提出利用模块化思想分别建立LCC-HVDC各子系统小信号模型,并推导了能反映交直流系统和换流器之间电气耦合特性的接口矩阵实现子系统连接,从而模块化建立精确且易于扩展的计及控制链路延时和锁相环输出相位波动的双端LCC-HVDC系统改进小信号模型。最后分析了控制系统参数和控制链路延时对系统小干扰稳定性的影响以及失稳模态的主导因素,揭示了双端LCC-HVDC系统交直流混合谐振机理及送受端交互影响具体过程。研究结果可以为系统参数设计、谐振抑制措施提供理论基础。

经LCC-HVDC输电送出系统单端混合等值计算

现有电网换相换流器型高压直流输电(line commutated converter based HVDC,LCC-HVDC)输电系统动态等值计算依赖于送受端电压同步实时量测,无法实现经LCC-HVDC输电送出系统的单端暂态等值计算。论文基于直流系统动态相量等值计算框架,提出仅基于逆变侧单端交流电压信息的经LCC-HVDC直流输电送出系统的等值计算方案,论证整流侧准稳态模型+逆变侧动态相量模型的混合等值计算框架的可行性,解决换相失败准确判别等关键问题,仿真对比分析了多场景故障,证明所提出的计算框架在送端交流系统信息缺失的情况下,能实现受端交流线路故障暂态大扰动下经LCC-HVDC输电送出系统响应的准确实时计算。

用于DR-HVDC系统连接的海上风电场电网形成控制方法

基于二极管整流器的高压直流DR-HVDC(diode-rectifer-based high voltage direct current)输电系统是一种很有前景的海上风电低成本接入方案,它可将风能从偏远的海上风电场输送到陆上电力系统。然而随着海上DR-HVDC系统的不断增多,可能会导致风机WT(wind turbine)的变流器控制难度增大,系统稳定性变差。基于此,提出了一种适用于DR-HVDC连接海上WT变流器的新型电网形成控制方法。该方法采用2个正序控制回路来调节WTs的输出有功功率,并维持海上交流电网的频率和电压,其中第一个控制器可将每台WT的有功功率误差调节为电压角偏差,从而造成系统频率偏差;第二个控制器通过调整WT的交流电压幅值以抵消频率偏差。变流器内部电流控制回路用于限制故障电流,并消除系统中的高频谐振。最后,通过故障穿越、WT功率变化、无功扰动和WTs停机4个方面的电磁暂态仿真,验证了所提控制方法的有效性和优越性。

雷公藤多苷片对IgA肾病大鼠LIGHT-HVEM/LTβR通路的影响

目的 基于炎症相关通路探讨雷公藤多苷片对IgA肾病大鼠肾脏的作用机制。方法 雄性SPF级SD大鼠,随机分为空白组、造模组。造模组采用联合“牛血清白蛋白+四氯化碳+脂多糖”建立IgA肾病大鼠模型。造模成功的大鼠随机分为模型组、泼尼松组、雷公藤多苷片组,于第13周开始治疗组灌胃给药,给药4周后留取大鼠24 h尿液、血液、肾组织并检测尿红细胞数、24 h-UTP、BUN、Scr;ELISA检测血清IL-1β、TNF-α水平;HE染色观察各组大鼠肾组织病理学变化;Western blot及RT-PCR检测大鼠肾组织LIGHT、HVEM、LTβR蛋白及其mRNA的表达。结果 雷公藤多苷片明显降低IgA肾病大鼠尿红细胞数、24 h-UTP、BUN、Scr水平,改善肾组织病理,降低血清炎症因子IL-1β、TNF-α水平,降低肾组织中LIGHT、HVEM、LTβR蛋白及其mRNA表达水平。结论 雷公藤多苷片可能通过下调LIGHT-HVEM/LTβR信号通路,抑制免疫反应,减少炎症因子释放,从而减轻炎症反应,降低尿红细胞及尿蛋白,改善肾脏病理损伤,保护肾功能。

不同模型对MMC-HVDC系统大信号稳定性分析准确性影响的对比研究

模块化多电平换流器高压直流输电(MMC-HVDC)系统运行中不可避免地遭受大信号扰动,可能导致不稳定现象的发生。基于混合势理论(MPT)对比分析了MMC-HVDC系统3种不同模型下的大信号稳定性。首先,建立了MMC-HVDC系统的全阶模型、降阶模型和等效恒功率负载(CPL)模型,并从理论层面对比分析了三者之间的差异性。利用MPT分别推导了基于3种模型的MMC-HVDC系统大信号稳定性判据,对比研究了3种不同模型对大信号稳定性分析结果的影响,并做出了系统在电网电压暂降大扰动下的稳定运行边界。最后,通过Matlab/Simulink时域仿真验证了理论分析的正确性。

基于改进GWO-LightGBM的磨煤机故障预警方法研究

为提高燃煤电厂磨煤机运维效率、降低运维成本,对磨煤机故障预警进行了研究。创新性地提出一种基于改进灰狼优化(GWO)算法的轻量级梯度提升机(LightGBM)故障预警方法。通过建立LightGBM轴承温度预测模型获取磨煤机轴承温度阈值,并引入改进GWO算法优化模型超参数,以提高算法效率和性能。试验结果表明,改进GWO-LightGBM算法相比支持向量机(SVM)等传统算法具有更高的精度和更优的泛化能力。通过实际故障案例证明,该方法能够提前2 h对磨煤机进行早期故障预警。该方法对燃煤电厂磨煤机安全运维具有指导意义。

基于CEEMDAN-VMD-TCN-lightGBM模型的水质预测研究

针对目前水质预测模型中因为数据本身的复杂性、在信号处理过程中存在的噪声干扰以及分解深度不够导致单一分解难以全面捕捉信号非线性特征的问题,提出了一种基于二次分解的水质预测模型。该模型采用完全自适应噪声集合经验模态分解(CEEMDAN)对原始数据进行分解,再利用变分模态分解(VMD)对熵值最高的模态分量进行二次分解,最终将处理后的时间序列输入到TCN-lightGBM多特征预测模型中。同时,采用麻雀算法(SSA)对预测模型进行优化。以山东省玉符河水质为例,本模型的均方根误差(RMSE)是0.1053,平均绝对误差(MAE)是0.0815,决定系数(R2)是0.9471,与GRU、LSTM、LightGBM、TCN等当下较为流行的模型的预测指标进行比较。结果显示,在R2上本模型提升了53.04%、70.41%、66.07%、65.20%等,在RMSE上减少了62.76%、65.50%、64.93%、64.80%等,在MAE上降低了62.76%、66.24%、63.80%、65.24%等。由此可知,基于CEEMDAN-VMD-TCN-lightGBM的模型具有更好的预测性能、泛化能力和捕捉信号非线性特征的能力。

直驱风电场经MMC-HVDC并网送端系统稳定性分析及振荡抑制

基于模块化多电平换流器MMC(modular multilevel converter)的高压直流输电HVDC(high voltage direct current transmission)因具有无源网络支撑等优势而被广泛应用于大容量新能源外送消纳。受电力电子设备交互作用等因素影响,送端系统易发生振荡失稳现象。首先,建立了直驱风电场经MMC-HVDC并网送端系统的小扰动线性化模型,分析了风场有功输出对系统稳定性的影响。然后,建立了MMC及风机并网变流器交流侧dq阻抗模型,从阻抗角度揭示了送端系统振荡失稳机理。进一步,提出了基于MMC交流电压控制外环q轴附加阻尼的振荡抑制策略,可满足系统满功率范围内的运行稳定性要求。最后,基于全比例模型的仿真结果验证了所提振荡抑制策略的有效性。

Public health importance of light intensity physical activity

1.Light intensity physical activity(PA)benefits health PA guidelines worldwide recommend that adults accumulate 150 min of moderate intensity or 75 min of vigorous intensity PA(moderate-to-vigorous PA(MVPA))weekly to achieve health benefits.1-3 Absent from these guidelines are recommendations for light intensity PA(LPA,e.g.,walking at a leisurely pace of 3 km/h or less,equivalent to 1.5-2.9 metabolic equivalents).

Effects of thinning on the understory light environment of different stands and the photosynthetic performance and growth of the reforestation species Phoebe bournei

Light levels determine regeneration in stands and a key concern is how to regulate the light environment of different stand types to the requirements of the understory.In this study,we selected three stands typical in south China(a Cryptomeria japonica plantation,a Quercus acutissima plantation,and a mixed stand of both)and three thinning intensities to determine the best understory light environ-ment for 3-year-old Phoebe bournei seedlings.The canopy structure,understory light environment,and photosynthe-sis and growth indicators were assessed following thin-ning.Thinning improved canopy structure and understory light availability of each stand;species composition was the reason for differences in the understory light environ-ment.Under the same thinning intensity,the mixed stand had the greatest light radiation and most balanced spectral composition.P.bournei photosynthesis and growth were closely related to the light environment;all three stands required heavy thinning to create an effective and sustained understory light environment.In a suitable understory light environment,the efficiency of light interception,absorption,and use by seedlings was enhanced,resulting in a higher carbon assimilation the main limiting factor was stomatal conductance.As a shade-avoidance signal,red/far-red radia-tion is a critical factor driving changes in photosynthesis and growth of P.bournei seedlings,and a reduction increased light absorption and use capacity and height:diameter ratios.The growth advantage transformed from diameter to height,enabling seedlings to access more light.Our findings suggest that the regeneration of shade-tolerant species such as P.bournei could be enhanced if a targeted approach to thinning based on stand type was adopted.

Model prediction of inactivation of Aeromonas salmonicida grown on poultry in situ by intense pulsed light

The aim of this study was to evaluate the factors influencing the inactivation effect of intense pulsed light(IPL)on Aeromonas salmonicida grown on chicken meat and skin,and to further develop prediction models of inactivation.In this work,chicken meat and skin inoculated with meat-borne A.salmonicida isolates were subjected to IPL treatments under different conditions.The results showed that IPL had obvious bactericidal effect in the chicken skin and thickness groups when the treatment voltage and time were 7 V combined with 5 s.In addition,the lethality curves of A.salmonicida were fitted under IPL conditions of 3.5-7.5 V.The comparison of statistical parameters revealed that the Weibull model could best fit the mortality curves and could accurately predict the mortality dynamic of A.salmonicida grown on chicken skin.And further a secondary model between the scale factor b and the treatment voltage in Weibull model was established using linear equations,which determined that the secondary model could accurately predict the inactivation of A.salmonicida.This study provides a theoretical basis for future prediction models of Aeromonas,and also provides new ideas for sterilization approaches of meat-borne Aeromonas.

基于LightGBM的智能可穿戴设备用户行为预测

智能可穿戴设备产生的大量数据是人类宝贵的数字资源。使用开放数据集和主流数据分析工具,如可进行快速模型开发的PyCaret模块,有助于人们进行数据挖掘工作,且不被细节所困扰。作为Kaggle竞赛爱好者的常用工具,LightGBM分类器对用户行为的预测表现优异,对此文中的研究结果也得到验证。

新能源基地经LCC-HVDC送出系统振荡机理分析与抑制策略(三):振荡抑制策略

针对新能源基地经电网换相换流器型高压直流(line commutated converter-based high voltage direct current,LCC-HVDC)送出系统次/超同步振荡问题,现有研究主要通过新能源侧阻抗重塑设计实现振荡抑制,考虑到实际系统并网台数多、机型繁杂、故障穿越性能等因素制约,其设计裕度受到限制。该文通过LCC-HVDC阻抗重塑实现系统次/超同步振荡抑制。首先,提出送端换流站定触发角控制、受端换流站定直流电流控制的LCC-HVDC阻抗重塑控制策略,建立计及阻抗重塑的LCC-HVDC阻抗解析模型,并验证阻抗模型的准确性。然后,对比分析重塑前后阻抗特性变化,阐述阻抗重塑控制策略的作用机理,消除原有送端换流站直流电流环与功率电路重叠效应所产生的负阻尼。进一步,基于LCC-HVDC阻抗重塑,优化新能源并网点系统阻抗特性,提升直驱风机(permanent magnet synchronous generator,PMSG)、双馈风机(doubly-fed induction generator,DFIG)以及光伏(photovoltaic,PV)不同类型新能源基地经LCC-HVDC送出系统稳定裕度,消除系统次/超同步振荡风险。最后,不同类型新能源基地经LCC-HVDC送出系统仿真结果验证了该文提出的基于LCC-HVDC阻抗重塑振荡抑制策略的有效性。

CAEFusion: A New Convolutional Autoencoder-Based Infrared and Visible Light Image Fusion Algorithm

To address the issues of incomplete information,blurred details,loss of details,and insufficient contrast in infrared and visible image fusion,an image fusion algorithm based on a convolutional autoencoder is proposed.The region attention module is meant to extract the background feature map based on the distinct properties of the background feature map and the detail feature map.A multi-scale convolution attention module is suggested to enhance the communication of feature information.At the same time,the feature transformation module is introduced to learn more robust feature representations,aiming to preserve the integrity of image information.This study uses three available datasets from TNO,FLIR,and NIR to perform thorough quantitative and qualitative trials with five additional algorithms.The methods are assessed based on four indicators:information entropy(EN),standard deviation(SD),spatial frequency(SF),and average gradient(AG).Object detection experiments were done on the M3FD dataset to further verify the algorithm’s performance in comparison with five other algorithms.The algorithm’s accuracy was evaluated using the mean average precision at a threshold of 0.5(mAP@0.5)index.Comprehensive experimental findings show that CAEFusion performs well in subjective visual and objective evaluation criteria and has promising potential in downstream object detection tasks.

受端近区光伏电站对LCC-HVDC系统稳定性影响分析

中国湖北等地已形成高比例新能源和直流共同馈入的新型受端电力系统,光伏电站馈入直流受端换流站近区时,电力电子设备次同步振荡特性及子系统间交互作用有待分析。采用特征值分析法,对大规模光伏电站馈入对直流系统稳定性影响展开研究。首先,建立了大规模光伏电站直流受端并网系统小信号分析模型,从模态角度证实光伏电站馈入对直流系统稳定性存在较大影响。进一步,通过主导模态观察各子系统间的交互作用特性,以减小系统次同步振荡风险为目标,整定光伏控制参数可行域。最后,定义子系统参与度,衡量运行参数对系统间次同步交互作用的影响,得出受端电网强度较小、光照强度较大时,光伏电站与直流系统间交互作用更强的结论,同时在设计光伏电站并网时应选取阻抗比小的导线,减小光伏并网线路距离。研究结论可为光伏并网设计提供理论依据。

Generation of structured light beams with polarization variation along arbitrary spatial trajectories using tri-layer metasurfaces

Conventionally,the spatially structured light beams produced by metasurfaces primarily highlight the polarization modulation of the beams propagating along the optical axis or the beams'spatial transmission trajectory.In particular,along the optical axis,the polarization state is either constant or varies continuously in each output plane.Here,we develop innovative spatially structured light beams with continually changing polarization along any arbitrary spatial transmission trajectories.With tri-layer metallic metasurfaces,the geometric characteristics of each layer structure can be adjusted to modulate the phase and polarization state of the incident terahertz(THz)wave.The beam will converge to the predefined trajectory along several paths to generate a Bessel-like beam with longitudinal polarization changes.We demonstrate the versatility of the approach by designing two THz-band structured light beams with varying polarization states along the spatial helical transmission trajectory.Continuous linear polarization changes and linear polarization to right circular polarization(RCP)and back to linear polarization changes are realized respectively.The experimental results are basically consistent with the simulated results.Our proposal for arbitrary trajectory structured light beams with longitudinally varying polarization offers a practical method for continuously regulating the characteristics of spatial structured light beams with non-axial transmission.This technique has potential uses in optical encryption,particle manipulation,and biomedical imaging.