含风—光—水—储互补电力系统的优化调度研究

随着风电和光伏发电大规模接入到电网中,其出力的随机性、间歇性和波动性对电网的安全运行带来巨大挑战。目前电网调度运行时为了确保系统的安全性,会出现大量的弃风弃光现象。但风力发电,光伏发电和水电具有自然互补的特点,利用它们的互补特性可提高电网消纳新能源的能力。提出了含风电、光伏、水电和抽水蓄能的互补发电系统,并分别以系统运行成本最低和互补系统出力波动最小为目标函数建立了两种优化调度模型。最后,算例分析验证了两种模型的合理性和可行性,并说明了互补运行可提高新能源的利用率,同时减少了风电与光伏的波动性对电网的影响。     

考虑动态频率响应的风光水互补发电短期优化调度模型

针对风光并网会降低系统惯量、削弱系统调频能力的问题,综合考虑水电机组同步惯量、风电场和光伏电站的虚拟惯量和下垂控制作用,提出含风光水的多机系统动态频率响应模型,推导系统频率变化率约束、最低点频率偏差约束和准稳态频率偏差约束。基于此,为实现清洁能源利用最大化,以弃风、弃光、弃水最小及水库调度期末蓄能最大为目标,兼顾梯级水电、风电、光伏和发电系统的多种运行约束,构建风光水互补发电系统短期优化调度模型,并使用混合整数线性规划方法进行求解。最后通过算例仿真验证所提模型的有效性和适用性。     

计及风光不确定性的新能源虚拟电厂多时间尺度优化调度

针对中国西北地区新能源消纳问题,该文聚合风力发电、光伏发电、光热电站、电储能装置组成虚拟电厂（VPP）,提出一种基于鲁棒随机优化理论的新能源虚拟电厂多时间尺度优化调度策略。首先对风力发电、光伏发电、光热电站与电储能装置进行数学描述,在此基础上建立VPP多时间尺度优化调度模型。在日前调度层中,以VPP运行效益最大为目标,依据风光日前预测出力建立日前优化调度模型;在时前调度层中,以VPP运行成本最小为目标,根据风光时前预测出力建立时前调度修正模型。同时,为了衡量风电、光伏发电出力不确定性对系统的运行影响,建立VPP随机优化调度模型。仿真结果验证该模型可提高运行效益与新能源消纳能力。     

风光水互补发电系统的优化配置

为提高风光水互补发电系统的供电可靠性,降低经济成本,研究了电源容量的优化配置。首先提出独立和并网运行调度策略,然后考虑供电可靠性和蓄水库水量平衡等约束,建立了以全寿命周期成本最小为目标的优化配置模型,采用改进遗传算法进行求解。算例探讨了供电可靠性和联络线传输容量对优化配置的影响,验证了所提方法的有效性。由仿真结果可知,独立运行时,利用风光水互补发电即可保证较高的供电可靠性;并网运行时,采用联络线的双向交互电能能力,可进一步提高系统供电可靠性,有效降低经济成本。     

基于风光互补电力入网的电力系统动态经济调度

为解决风光互补电力入网的不确定性给电网调度带来的影响,文章对其的经济调度问题进行研究。针对火电机组的排污特性引入了环境污染惩罚成本,针对风光电力输出功率的间歇波动性引入了备用容量惩罚成本,在考虑系统供需平衡与机组爬坡率等约束条件的基础上,给出了风光电力互补入网的调度策略,建立了含有风光互补电力的动态经济调度模型;应用一种改进的粒子群算法对所提模型进行求解。最后以IEEE-30节点测试系统为例进行仿真分析,仿真结果验证了所提模型的合理性及算法的有效性,同时也说明了风光互补电力入网能够平抑风电的出力波动,可以在保证系统可靠性的基础上,提高风光电力的并网率。     

龙羊峡水光互补的日优化调度研究

摘要： 提出了水光2种清洁能源互补发电模型。以水光互补在负荷高峰时段总出力最大为目标函数,综合考虑各种约束条件,构建了水光互补日间调度模型。采用模拟优化的方法求解该模型,结果表明水光互补可以明显提高调峰能力。     

并网型风光互补系统容量优化配置方法

摘要： 并网型风光互补系统利用风、光资源的互补特性,以跟踪调度曲线为输出目标。合理配置风光储的容量,既可提高互补系统跟踪调度曲线的能力,又能获得较好的经济效益。以抽水蓄能电站为储能装置,借助HOMER软件将月平均气象数据离散成小时平均数据,基于风电、光电的出力模型和互补系统的控制策略,建立了考虑风光互补性、风光资源利用率、跟踪调度曲线等约束,以工程寿命内总收益最大为目标函数的容量优化配置模型,并提出了一种变步长循环离散求解方法。算例验证了模型和算法的合理性。     

龙羊峡水电站水光互补优化调度研究

针对光伏发电大规模并网后水电站如何运行才能有效减小光电不稳定出力对电网造成的影响问题,建立了光伏发电出力预测模型及龙羊峡水光互补短期优化调度模型,采用改进的逐步优化算法对模型进行求解,设置了6种情景分析水光互补效果。结果表明,汛期或非汛期调度期内的龙羊峡水库水位在相应时段允许范围内,优化后的水光互补系统均不存在弃水仅产生少量的弃光。研究成果为光伏大规模并网后的水光互补短期优化调度方式提供了参考依据。     

基于决策树的大小水电长期协调调度模型及应用

针对西南水电富集地区大小水电抢占输电通道外送电力的问题,构建了基于决策树的大中型水电与小水电长期协调调度模型,以水电总体可消纳电量最大为目标,以确定性逐次优化方法（POA）对历史长系列水文资料进行模拟调度,在此基础上采用决策树挖掘大小水电长期协调调度规则,在应用阶段,结合CFS降雨预报信息,预报大中型水电站径流和小水电发电能力,并作为决策树输入,以获得面临时段大中型水电站的决策出力。云南省德宏地区大规模大、小水电混合分区实例应用结果表明,该模型能够有效利用具有良好调节能力的大中型水电站协调大小水电运行,提高外送通道利用率,为电力调度部门提供了一种良好的大小水电长期协调调度方法。     

考虑需求侧响应的多能互补微电网优化调度研究

随着“双碳”目标的实施，新能源渗透比例不断提高，源荷两侧的不确定性对多能互补微电网能源管理提出了新的要求。提出了一种调度优化方法，其中考虑了价格型需求侧响应，优化交流负荷曲线匹配风光出力曲线，以提高新能源的消纳率，构建了能源管理模型，模型同时考虑了电力子系统、天然气子系统与热力子系统。模型通过构建风光出力与负荷的不确定集，采用本文提出的随机-鲁棒优化方法解决多能互补微电网调度面临的新能源发电时序波动性、负荷的不确定性等问题；之后，应用线性优化强对偶定理和列和约束生成算法，将模型转化为混合整数线性规划问题，并利用商业化求解器YALMIP/GUROBI对优化模型进行求解。最后，算例从多能互补微电网优化调度结果与不确定性参数对调度结果的影响分析验证了本文优化方法的可靠性。     

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.     

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.     

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.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法，这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

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.     

Economie d'énergie en trigénération

Trigeneration is defined as the production of three useful forms of energy—heat, cold and power—from a primary source of energy such as natural gas or oil. For instance, trigeneration systems typically produce electrical power via a reciprocating engine or gas turbine and recover a large percentage of the heat energy retained in the lubricating oil, exhaust gas and coolant water systems to maximize the utilization of the primary fuel. The heat produced can be totally or partially used to fuel absorption refrigerators. Therefore, trigeneration systems enjoy an inherently high efficiency and have the potential to significantly reduce the energy-related operation costs of facilities. In this paper, we describe a model of characterization of trigeneration systems trough the condition of primary energy saving and the quality index, compared to the separate production of heat, cold and power. The study highlights the importance of the choice of the separate production reference system on the level of primary energy saving and emissions reduction.     

Mineralogical characterization of the intraseam layers of Lofoi lignite deposits in Florina basin (western Makedonia,northwest Greece)

The mineralogical composition of intraseam layers from Lofoi lignite deposits (northwest Greece) is the subject of the present study. The samples were examined by means of X-ray diffraction (XRD), thermo-gravimetric (TG/DTG) and differential thermal analysis (DTA), and Fourier transform infrared (FT-IR) spectrometry. The clay minerals prevail in most samples, with illite-muscovite being the dominant phase, and kaolinite and chlorite being the other major clay components. No smectite was found. Quartz and feldspars, dominate in two cases. The studied materials are characterized as clays to clayey sands, showing significant similarities with the intraseam layers of the adjacent Achlada lignite deposits.     

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.     

Innovative methodologies in renewable energy: A review

This paper is concerned with innovative approaches to renewable energy sources computation methodologies, which provide more refined results than the classical alternatives. Such refinements provide additional improvements especially for replacement of fossil energy usages that emit greenhouse gas (GHG) into the atmosphere leading to climate change impact. Current knowledge gap among each renewable energy source calculation is rather missing fundamentals of plausible, rational, and logical explanations for the interpretation of results. In the literature, there are rather complicated and mechanically applicable methodologies, which require input and output measurement data match with missing physical explanations. The view taken in this review paper is to concentrate on quite plausible, logical, rational, and effectively applicable innovative energy calculation methodologies with simplistic fundamentals. For this purpose, a set of renewable energy methodological approaches is revisited with their innovative structures concerning solar, wind, hydro, current, and geothermal energy resources. With the increase in the renewable energy utilizations to combat the undesirable impacts of global warming and climate change, there is a need for better models that will include physical environmental conditions and data properties in the probabilistic, statistical, stochastic, logical, and rational senses leading to refined and more reliable estimations with application examples in the text. Finally, new research directions are also recommended for more refined innovative energy system calculations.     

Decomposition of limestone in a solar reactor

The thermal decomposition of limestone has been selected as a model reaction for developing and testing an atmospheric open solar reactor. The reactor consists of a cyclone gas/particle separator which has been modified to let the concentrated solar energy enter through a windowless aperture. The reacting particles are directly exposed to the solar irradiation. Experimentation with a 60 kW reactor prototype was conducted at PSI's 90m² parabolic solar concentrator, in a continuous mode of operation. A counter-current flow heat exchanger was employed to preheat the reactants. Eighty five percent degree of calcination was obtained for cement raw material and 15% of the solar input was converted into chemical energy (enthalpy).The technical feasibility of the solar thermal decomposition of limestone was experimentally demonstrated. The use of solar energy as a source for high-temperature process heat offers the potential of reducing significantly the CO₂ emissions from lime producing plants. Such a solar thermochemical process can find application in sunny rural areas for avoiding deforestation.