基于PSModel的海上风电场全电磁暂态建模与仿真

开发有效的风机电磁暂态模型是进行海上风电并网研究的基础。根据不同生产厂家所提供的直驱风机模型,提出了一种基于厂家黑盒模型的直驱风机电磁暂态建模方法。利用厂家所提供的模型测试数据解析风机的故障响应特性,推导了不同厂家在电压故障下有功和无功功率响应表达式,包括故障期间的穿越控制过程及不同过程间的暂态切换策略。提出了加权平均压降的风电场等值方法,采用自主研发的全电磁暂态仿真软件(power system model,PSModel)对我国广东某海上风电场进行全电磁暂态建模。根据稳态潮流及暂态特性结果验证了模型可通过系统测试,且有效实现了海上风电场的全电磁暂态建模,从而为该风场接入大电网后的安全稳定分析提供了研究基础。

A new analysis of fractional fish farm model associated with Mittag-Leffler-type kernel

In this paper,we analyze the dynamical behavior of fish farm model related to Atangana-Baleanu derivative of arbitrary order.The rnodel is constituted with the group of non-linear differential equations having nutrients,fish and mussel.We have included discrete kind gestational delay of fish.The solution of fish farm model is determined by employing homotopy analysis transforms method(HATM).Existence of and uniqueness of solution are studied through Picard-Lindelof approach.The influence of order of new non-integer order derivative on nutrients,fish and mussel is discussed.The complete study reveals that the outer food supplies manage the behavior of the model.Moreover,to show the outcomes of the study,some numerical results are demonstrated through graphs.

Climate Change Impacts and Adaptation in Rainfed Farming Systems: A Modeling Framework for Scaling-Out Climate Smart Agriculture in Sub-Saharan Africa

Improving agricultural water productivity, under rainfed or irrigated conditions, holds significant scope for addressing climate change vulnerability. It also offers adaptation capacity needs as well as water and food security in the southern African region. In this study, evidence for climate change impacts and adaptation strategies in rainfed agricultural systems is explored through modeling predictions of crop yield, soil moisture and excess water for potential harvesting. The study specifically presents the results of climate change impacts under rainfed conditions for maize, sorghum and sunflower using soil-water-crop model simulations, integrated based on daily inputs of rainfall and evapotranspiration disaggregated from GCM scenarios. The research targets a vast farming region dominated by heavy clay soils where rainfed agriculture is a dominant practice. The potential for improving soil water productivity and improved water harvesting have been explored as ways of climate change mitigation and adaptation measures. This can be utilized to explore and design appropriate conservation agriculture and adaptation practices in similar agro-ecological environments, and create opportunities for outscaling for much wider areas. The results of this study can suggest the need for possible policy refinements towards reducing vulnerability and adaptation to climate change in rainfed farming systems.

Model Farm Services Center Approach: An Implication to Boost Farmer’s Yield

The instant study was conducted to estimate the Model Farm Services Center’s (MFSC) contribution in yield improvement of major crops/vegetables in district Dera Ismail Khan, Khyber Pakhtunkhwa, Pakistan, during the year 2014-15. Based on Sekaran sampling technique 306 respondents were selected and were personally interviewed through well prepared and pre-tested interview schedule. To find out the actual performance of yield improvement by Model Farm Services Center along with other repressors, step by step analysis was performed. The results of Wilcoxon Sign Rank Test showed significant improvement in yield of sugarcane, wheat, maize, rice and tomato by Model Farm Services Center. Pearson’s correlation coefficient showed highly significant positive relation of sugarcane and wheat yield difference before and after Model Farm Services Center registration with MFSC. Ordinary Least Square Multiple-Regression Model indicates that MFSC registration duration and landholding significantly define the variation in dependent variables at 1% and 5% level of significance respectively for sugarcane yield. Whereas solely Model Farm Services Center registration duration profoundly highly significantly (P ≤ 0.01) explains the variation in dependent variables in wheat yield.

海上风电场经交流海缆并网谐波谐振放大分析

采用交流海缆接入电网的海上风电场在电缆线路分布电容的作用下,可能出现陆上风电场不常见的谐波谐振与谐波放大现象,严重威胁到海上风电场安全可靠运行。为研究海上风电场谐波谐振机理与谐波放大影响因素,首先,建立了海上风电场输电系统与集电系统两部分的状态空间模型,并给出谐波放大倍数、谐波含量等指标的计算方法;其次,通过特征值和参与因子揭示了谐波谐振机理及关键影响因素;然后,通过根轨迹法研究了电网短路容量、高压电缆参数和风电机组并网台数对谐振模态的影响;最后,在Matlab/Simulink仿真平台搭建江苏某海上风电场.验证理论分析的有效性。

A Study on the Operating Model of Internet + QQ Farm

The'Internet+QQ farm'creative agriculture presented in this paper is the innovation based on the currently booming reality QQ farm,aimed at reducing cost,improving efficiency and optimizing human and material resource elements.It can make Internet provide technical support for intelligence-based life,leisure,entertainment,with good prospects for development.

The Evolution of Organic Carbon in Chinese Mollisol Under Different Farming Systems: Validation and Prediction by Using Century Model

Soil organic carbon （SOC） is an important indicator of soil degradation process. In this study, the long-term SOC evolution in Chinese mollisol farmland was simulated and predicted by validating, analyzing, processing and assorting concerning data, based on clarifying parameters of Century model need, combined with best use of recorded data of field management, observed data of long-term experiments, climate, soil, and biology, and achieved results from Hailun Agro-Ecological Experimental Station, Chinese Academy of Sciences. The results were showed as follows： Before reclamation, SOC content was around 58.00 g kg^-1, SOC content dropped quickly in early years, and then decreased slowly after reclamation. SOC content was around 34.00 g kg^-1 with a yearly average rate of 8.91‰ decrease before long-term experiments was established. After a long-term experiment, SOC would change under different farming systems. Shift farming system changed as follows： By 20-year model simulation, SOC content decreased from 34.03 to 30.19 g kg^-1, with a yearly average rate of 5.97‰; by 100-year model simulation, SOC content decreased to 24.31 g kg^-1, with a yearly average rate of 3.36‰. Organic farming system changed as follows： By 20-year model simulation, SOC content decreased slowly from 34.03 to 33.39 g kg^-1, with a yearly average rate of 0.95‰, 5‰ less than that of shift farming system; by 100-year model simulation, SOC content decreased to 32.21 g kg^-1, with a yearly average rate of 0.55‰. ＂Petroleum＂ farming system changed as follows： By 20-year model simulation, SOC content decreased from 34.03 to 32.88 g kg^-1, with a yearly average rate of 1.72‰, much more than that of organic farming system; by 100-year model simulation, SOC content decreased to 30.89 g kg^-1, with a yearly average rate of 0.96‰. Combined ＂petroleum＂-organic farming system changed as follows： By 20-year model simulation, SOC content was increased slightly; by 100-year model simulation, SOC content increased from 34.03 to 34.41g kg^-1, with a yearly average rate of 0.11‰. The above results provided an optimal way for maintaining SOC in Chinese mollisol farmland： To increase, as much as possible within agro-ecosystem, soil organic matter returns such as crop stubble, crop litter, crop straw or stalk, and manure, besides applying chemical nitrogen and phosphorous, which increased system productivity and maintained SOC content as well. Also, the results provided a valuable methodology both for a study of CO2 sequestration capacity and for a target fertility determination in Chinese mollisol.

Spatial Analysis and Modelling of Wind Farm Site Suitability in Nasarawa State, North-Central Nigeria

There has been an increasing global and local interest in developing renewable, clean, and cheap energy towards achieving Goal number 7 of the Sustainable Development Goals (SDG). However, decisions involving suitable and sustainable locations for renewable energy projects remain an important task. This study employed Geographic Information System (GIS) and Multi-Criteria Decision Analysis (MCDA) to spatially analyze and model wind farm site suitability in Nasarawa State. The aim is to integrate the environmental, social, and economic aspects of decision-making for identifying sustainable wind farm sites. The study distinguished between two sets of decision criteria: decision constraints and decision factors. The former defined the exclusion zones while the latter were standardized based on fuzzy logic to depict varying degrees of suitability across the State. The MCDA applied the weighted linear combination method, with relative weights generated through pairwise comparisons of the analytic hierarchy process to analyze three policy scenarios: equal weights, environmental/social priority, and economic priority scenario. A combination of resulting composite maps from the constraints and the factors gave the final suitability maps. The resulting suitability index (SI) for the respective policy scenario describes the degrees of suitability: Ideal locations were denoted by one (1) and the not suitable locations by zero (0), with values in-between depicting varying degrees of wind farm site suitability. Based on the SI, priority locations indicating areas with good prospects, in addition to the most suitable parcels of land, were identified and delineated. The composite decision constraint revealed that wind farm projects would not be viable in more than half (57.58%) of the State. Wind speed was the major constraint and accounted for the exclusion of 46.25%, with a mean fuzzy membership value of 0.2008 indicating low suitability across the State. Also, the average acceptable wind farm location for the three-policy scenario was 33.33% of the entire study area. Lafia, Obi, Keana, Awe, Nasarawa-Eggon, Wamba and Kokona LGAs were the identified priority Local Government Areas (LGAs). However, only Lafia, Obi, and Nasarawa-Eggon were consistent with changes in the policy objectives. All the priority LGAs have one or more of the most suitable parcels within their administrative boundaries except for Wamba. Despite the severe limitations of wind speed, substantial parts of Nasarawa State still provide great development potentials for wind energy. The “most suitable” locations in Lafia, Nasarawa-Eggon, and Obi LGAs should have first consideration for the development of wind energy in the State.

新农科背景下“BOPPPS+在线资源”模式在耕作学中的改革与实践

随着国家实施乡村振兴战略,加快推进农业转型升级和农业现代化的建设,对高等农业院校农业人才培养和教育教学提出更高的要求。为有效提高农学专业课程的教学效果,培养适合社会需求的素质高、技能精、实践强、有担当且敢于迎接挑战并坚持创新的新农科人才。该文以农学专业核心课程耕作学教学为对象,设计并实践“BOPPPS+在线资源”的混合式教学模式,该模式将学科文化和学科发展与思政教育结合、理论知识与生产实践结合、线下与线上教育资源结合。该模式能够优化创新学习策略,构建新农科背景下课上“活跃”课下“忙碌”的混合式教学新模式,有效提高耕作学的教学质量,为培养高素质应用型新农科人才提供重要的参考依据。

基于等效粗糙度模型的风电场尾流数值模拟方法

随着风电场规模的扩大和密度的增加,风电场整场的尾流效应也日益显著且备受关注。准确评估风电场尾流效应对于风电场的建设和开发具有重要的意义,但目前仍缺乏同时兼顾计算精度和效率的尾流计算方法。本文基于OpenFOAM平台中的雷诺时均方法,实现了风电场等效粗糙度模型和雷诺平均方法的嵌套。结果表明,该方法相较于工程中常用的Jensen尾流模型和尾流叠加模型,计算精度得到了大幅的提高,且因为其对于风电场建模简单,所需计算资源较少,是用在大型风电场的一种工程应用价值较高的下游尾流计算方法。

AIC-Based Selection of Growth Models: The Case of Piglets from Organic Farming

The selection and comparison of different growth models for describing weight gain of piglets raised in organic farming is investigated by using the Akaike’s Information Criterion (AIC). In total, 49,699 data points of 5188 piglets recorded between 2007 and 2013 were considered. From the day of birth, up to 40 days (i.e. until weaning) the model of von Bertalanffy was favored by the AIC. This model is with 60.32% more likely to truly reflect reality than any other of the analyzed models. Up to 105 days, the two-linear model was favored by the AIC (probability 99.75%). The intersection point of the two-linear model was calculated by 53.8 days, which fitted well to the actual change in the food situations.

劳动投入水平、要素禀赋与农户行为可分性检验——基于南方稻农地块层次数据的验证

生产和消费行为交织在一起是农户的重要特征。农户的生产和消费行为是否可分成为众多农户行为模型的基本假设前提,直接影响农户行为分析的结论和政策建议的合理性。通过构建农户模型,从农户农业生产劳动投入水平与家庭人地禀赋关系的视角切入,分析不同要素市场条件下农户行为可分和不可分特征。在此基础上,利用2015、2019年对中国南方稻农地块层次调研的混合截面数据对农户行为可分性进行实证检验。结果表明,当前中国南方稻农行为呈现出可分性特征,在处理了内生性、替换核心解释变量、替换被解释变量,结果依然稳健。进一步分析表明,劳动力市场越完善,农户行为可分性特征越明显;随着时间的推移,农户行为由不可分性向可分性发生转变。与前期关于农户行为可分性检验从劳动力配置视角切入不同,从劳动力投入强度和要素禀赋之间的关系来验证农户可分性,并利用一手调研的地块层面数据进行验证,为基于要素市场识别农户行为可分与不可分的具体情境研究提供了新的视角和经验证据。

考虑迟延的风电场模型预测尾流优化控制

降低风电场出力波动性有利于促进电网友好运行,而尾流优化控制是降低整场出力波动的重要措施。现有尾流优化控制大都基于稳态模型,却忽略尾流动态迟延特性。但尾流迟延在风速不确定性基础上会进一步增加风电场出力的波动性。为此,该文基于稳态尾流模型辅以迟延计算,构建风电场准稳态尾流模型以同时兼顾尾流干涉作用与动态迟延特性。在此基础上,提出一种考虑迟延的模型预测平稳控制方法(predictive control considering delay,MPC-D),以指令跟踪与功率波动最小为目标协调各机组出力。最后,在WFSim上构建含33台机组的风电场仿真模型,并基于此分析尾流迟延对风电机组以及整场运行性能影响。结果表明,所建准稳态尾流模型能同时模拟尾流速度损失、机组功率迟延和整场功率阶梯变化等特性。并且由MPC-D所得整场出力较基于稳态模型的控制方法平均相对误差、均方根误差以及滑动均方根误差均得到改善,同时能防止机组桨距角频繁动作。

基于单机等值与主成分分析法的海上风电场等值建模研究

在借鉴海上风电场实际项目经验的基础上,重点分析了海上风电场集电线路的等效方式以及海上风电场的等值建模。综合目前风电场动态等值中单机等值与多机等值的优缺点,以实际风电场作为参考,提出了单机等值法和多机等值法相结合的双层等效方法。按风机的馈线分布对风电场进行一次单机等值,再以主成分分析法对一次等值后的机组提取主导变量,作为二次多机等值的分群指标并进行机组分群,保证风电场等值的精确度。该等值建模对海上风电场进行二次等效建模,通过仿真验证,将等效后的仿真模型与实际详细模型做对比,验证了该等效方法的可行性。

坑沟式“稻+鱼”综合种养模式的示范推广及存在问题分析——以广西三江侗族自治县为例

旨在促进稻鱼产业绿色高质高效发展,助推乡村产业振兴。对广西三江侗族自治县坑沟式“稻+鱼”综合种养模式示范推广及其存在的问题进行实地调查和分析研究。全县示范推广“稻+鱼”综合种养模式达5507 hm2,稻鱼总产值达2.9亿元,实现贫困人口年人均增收1000元以上。除“稻+鳖”“稻+鳅”综合种养模式水产品的净产值明显高于稻谷之外,坑沟式“优质稻+再生稻+鱼”“稻+螺”“稻+虾”综合种养模式水产品的净产值与稻谷相当。然而,在示范推广过程中,存在用工不足、产品附加值低、产业链稳定性差等问题。推广应用“稻+鱼”综合种养模式,可实现稻田纯收益翻番。加强培训指导、市场监管、技术创新、标准化生产和品牌打造等,是突破当地稻鱼产业高质量、可持续发展瓶颈的良策。

电力系统风力发电建模与仿真研究综述

对于大规模风电并网的电力系统安全稳定分析,构建合适准确的风电场模型至关重要。首先,梳理了现有风电机组的模型结构以及风电场的动态等值,阐述了风力发电系统的参数辨识方法。其次,介绍了电力系统中风力发电系统常用的时域仿真分析技术,主要综述了电磁暂态仿真、机电暂态仿真、中长期动态仿真、机电-电磁暂态混合仿真和数模混合仿真技术。然后,简述了风力发电系统建模与仿真的新进展。最后,分析了电力系统中风力发电系统的建模及其仿真技术面临的挑战与瓶颈,并结合新型电力系统的需求,对其建模与仿真技术进行了展望。

家庭农场创业资源整合驱动因素与作用机理研究——基于扎根理论和SEM模型的融合方法

我国现有家庭农场尚处于起步阶段,因受自身弱质性、创业资源匮乏、创业环境复杂性等因素制约而面临着巨大挑战。文章基于相关文献将家庭农场创业资源整合过程界定为识别、获取、配置和运用,使用扎根理论方法分析30个家庭农场资源整合案例,形成创业资源、内在需求、整合意愿、农场主个性特征、创业环境和家庭农场创业资源整合6个维度理论构想,建立驱动因素模型。依据分析结果,借鉴相关测量量表开发创业资源整合驱动因素量表,验证量表信效度并利用结构方程模型对建构的理论模型进行实证检验。结果表明,创业资源和整合意愿直接驱动家庭农场进行创业资源整合,内在需求经由整合意愿驱动家庭农场进行创业资源整合,农场主个性特征和创业环境在内在需求与整合意愿关系中起调节作用。通过拓宽创业资源整合的研究外延,丰富家庭农场创业问题的理论与方法体系,为家庭农场破解资源约束困境提供了新思路。

抚养负担、非农就业与宅基地流转意愿

宅基地流转是盘活乡村资产,增加农民财产性收入,实现乡村振兴的重要举措。本文利用CRSS数据库262份拥有闲置宅基地的农户样本数据,在理论分析的基础上,运用二元Probit模型,实证分析抚养负担,非农就业对宅基地流转意愿的影响。结果表明:抚养负担对宅基地流转意愿存在显著抑制作用,非农就业在抚养负担与宅基流转意愿中具有显著的中介作用;从抚养负担结构来看,抚幼负担对宅基地流转意愿的影响要强于老龄化负担。因此,应进一步完善农村社会保障体系,非农就业培训体系,加大农户本地非农就业的扶持力度,缓解抚养负担对宅基地流转的抑制作用。

风电场站等值模型综合评价体系

为实现多类风电场站等值模型综合评价,搭建全拓扑详细模型作为基准模型,通过集电网络等值与风电机组聚合分别得到单机等值模型、馈线等值模型2个评价对象。提出基于改进层次分析的等值模型综合评价体系,包含多工况的时空层面评价指标。针对所提评价指标,在PSCAD/EMTDC环境中对3个模型展开仿真测试,给出2个等值模型的综合评价结果:在对仿真速度要求不高时,馈线等值模型评价综合值更高,具备多种问题分析能力,普适性更好。所提综合评价体系从仿真层面出发,实现了对风电场站等值模型包括稳态运行点、小干扰、暂态运行条件、集电网络空间体征、仿真速度多项指标的全方位评价。

海上风电桩基础打桩过程中桩周土强度弱化模型试验研究

在海上风电桩基础的打桩过程中,桩周土体强度会产生明显的弱化现象,为明确桩周土体强度弱化影响因素以及弱化规律,开展模型试验模拟打桩过程,研究在不同锤击能量下,不同桩体尺寸情况下,桩身侧摩阻力随着贯入深度的变化规律,建立描述土体强度弱化规律的弱化公式,并通过打桩软件对多个海上风电桩基础工程中大直径及超大直径钢管桩的打桩实测数据进行打桩分析。研究结果表明:在打桩过程中,桩周土体强度的弱化同时受到桩体质量以及锤击能量的影响,桩基质量和锤击能量越大,土体强度弱化程度越高。在打桩的可打入分析中,采用该文所建立的弱化公式可模拟出不同尺寸桩体沉桩时土体强度的折减规律。