基于点估计法和随机潮流约束的电网及风电场相关特性研究

针对传统电网多目标规划方法的规划过程中随机变量分布不均,导致精度低、误差大、成本高等问题,以点估计法和随机潮流约束为基础,研究了风电场相关特性,提出相关电网规划方法,通过多项式正态变换技术,对电网内部的不确定因素,即非正态相关变量进行处理,结合最小二乘拟合法计算正态变换项数,引用点估计法确定电网中随机变量的边缘分布和相关性,进行建模,统计分布概率,简化建模模型,通过分析总体样本均值和样本方差均值,确定出量化相关性对电网规划的影响,经过变换得到采样点,进行潮流计算,获得电网输出目标矩阵,实现电网多目标规划,完成风电场相关特性研究。对IEEE-RTS节点进行算例分析,结果表明,基于点估计法和随机潮流约束的电网多目标规划方法具有很强的分析能力,当风电场相关系数达到0.8时,采样值出现极大值和极小值的概率极大增加,规划最大误差小于1.5%,提高了规划效果。     

UPFC在江苏电网中的应用与控制效果

摘要： 晋北—南京和锡盟—泰州特高压直流工程落点苏北电网后,将会对江苏电网潮流分布带来不小的影响,因此,有必要对这2个直流投产后周边500 kV电网进行潮流优化控制研究。首先在PSS/E仿真程序中建立统一潮流控制器（unified power flow controller, UPFC）的机电暂态仿真模型;然后针对江苏电网2020年规划运行方式下,晋北—南京直流和锡盟—泰州直流相关断面线路N-1和N-2典型故障,研究断面线路潮流转移与过载情况;最后在江都—大港和泰州—凤城500 kV线路上安装UPFC,对存在线路潮流过载的故障,通过UPFC控制断面线路潮流转移,并计算所需的UPFC容量。     

分布式发电所有权对配电网规划的影响

分布式发电（DG）在配电扩容中的作用越来越显著,而传统的电网规划未考虑DG带来的潜在效益,这阻碍了配电网辅助服务的开展。在考虑DG并网的潜在效益基础上,基于多年多期最优潮流法建立了两种所有权情况下电网公司对DG选址定容的优化模型,通过分析既有电网下新增DG的最优并网容量,研究了DG所有权对配电网规划的影响。实例应用结果表明,电网公司有DG所有权的情况下DG的渗透率更高,电网公司对DG的管理更具有主动性和高效性。     

一种电力市场下考虑安全约束的OPF算法

提出了一种以综合目标为优化方向的最优潮流算法,对电力市场环境下的发电成本、输电成本及无功服务成本进行了综合建模,获得电力市场环境下更好的电网潮流优化效果;算法还考虑了静态安全约束,使用线性化建模技术构建约束方程,最终使用内点法求解;对测试电网模型的仿真结果说明了方法的有效性与实用性。     

一种基于深度强化学习的电网潮流特征提取方法

为了解决现有特征提取方法存在特征辨识度低的问题,基于深度强化学习设计电网潮流特征提取方法,为了提升潮流特征的辨识度,利用点估计法计算电网潮流,以此为基础,通过模拟退火算法生成电网潮流图,并灰度处理电网潮流图,以灰度处理后的电网潮流图为依据,利用深度强化学习方法提取电网潮流特征,实现了电网潮流特征的提取。实验结果表明：与现有的电网潮流特征提取方法相比,文中电网潮流特征提取方法极大地提升了特征辨识度,证明了基于深度强化学习的电网潮流特征提取方法具备更好的特征提取性能。     

跨区域全时空基于深度学习的分布式潮流态势预估方法

基于人工智能中的深度学习方法,文章提出了分布式经济调度及其潮流态势预估方法。在传统集中式经济调度方法的基础上,给出了分布式经济调度模型及其求解方法;在该模型中,建立了负荷分布关联的特性及其模型;使用深度学习方法对负荷分布关联模型及分布式经济调度潮流进行学习训练,预估未来电网潮流运行态势。以实际电网对所提方法进行验证,结果显示具有较高的准确度。     

华东电网统计型潮流评价指标的分析与应用

潮流监视与控制作为电网调度运行部门的重要工作,是保证电网安全稳定的重要举措。针对传统"单维度"、"限额型"潮流监控指标的不足,在充分挖掘电网历史数据潜在价值的基础上,提出了基于统计分析的潮流评价指标PFI,根据PFI指标绘制潮流分布曲线,为电网输电断面潮流分析、潮流预控及中长期电网统计分析提供辅助手段,实现电网潮流监控指标向"多维度"、"统计型"指标的转变。PFI指标为电网调度运行人员及时发现电网潜在威胁,保障电网安全、经济、优质运行,提供了技术支撑,是华东电网建设多指标自趋优智能电网的重要组成,已成为安全校核、潮流实时监控之外的又一种重要的潮流分析手段。     

黄金峡泵站、电站接入电力系统规划及主变压器调压方式的选择

辐射状的开式电网潮流计算是单一供电网络规划中的一个基本内容,较之回路闭合的闭式电网来说,潮流计算要简单。一般工程中常从输电线路始端、终端的功率、电压4个参数中选取其中2个参数求出其余参数。根据黄金峡电站、泵站的不同运行方式,初步确定的导线截面,对不同工况下系统网络各节点的功率、电压进行了的计算,确定了黄金峡泵站及电站主变压器的调压方式。     

华东电网统计型潮流分析指标的研究与应用

潮流监视与控制作为电网调度运行部门的重要工作,是保证电网安全稳定的重要举措。针对传统"单维度"、"限额型"潮流监控指标的不足,通过充分挖掘电网历史数据潜在价值,提出了基于统计分析的潮流评价指标(PFI),并根据PFI指标绘制潮流分布曲线,为电网输电断面潮流分析、潮流预控及中长期电网统计分析提供辅助手段,实现了电网潮流控制指标向"多维度"、"统计型"指标的转变。PFI指标为电网调度运行人员及时发现电网潜在威胁、保障电网安全、经济、优质运行提供重要手段,是华东电网建设多指标自趋优智能电网的重要组成,具有很高的工程应用价值。     

最小费用法在福建电网电源扩展优化规划中的应用

本文结合MIPPS电源规划综合软件的使用体会，探讨了电源扩展优化规划中的最小费用法原理及其在福建电网中的应用     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.