基于SVG的风电场无功补偿经济运行方法研究

针对双馈风机风电场无功功率平衡和电压稳定问题,由风电场母线电压控制点的电压偏差推算出风电场的无功功率需求,基于风机自身、输电线路、箱变等在内的风电场有功损耗最小的风电机组无功分配策略。根据风机和SVG无功补偿装置的无功补偿能力,考虑风机无功出力不足时,建立了基于风机与SVG协调无功控制方案。通过仿真和试验结果验证了该方案的可行性,与传统等无功容量比例分配相比,该方案能减小风电场网损、提高发电量,实现风电场的经济运行。     

双馈风电场有功频率分层控制

风电场有功频率控制是风电场接入电网运行的关键技术。在分析双馈风力发电机组减载运行控制策略及超速法下双馈风力发电机组的减载运行调节能力的基础上,提出了提高双馈风电场的有功调节能力及接入电网后系统频率稳定性的有功频率分层控制策略。该策略根据不同风速区风电机组的减载运行调节能力差异,设计了风电场层分配策略及风电机组层控制策略,在满足有功控制要求的前提下,尽可能提高风电场对电力系统暂态频率稳定的支持。仿真结果表明,该控制策略在系统稳定运行时尽可能存储转子动能,当出现功率扰动后,能够通过快速释放转子存储的动能响应系统频率变化,从而提高了双馈风电场接入电网后的系统频率稳定性。     

基于变功率因数的分散式风电场优化运行策略

提出一种考虑负荷类型和风电机组无功极限的分散式风电场优化运行策略。建立基于静态电压特性的典型负荷通用模型;挖掘分散式风电机组无功能力,采用机端并联电容器平衡并提高双馈感应发电机无功调节能力;分析风电机组功率因数对配电网各节点电压、有功和无功网损影响规律;在此基础上,提出基于改进萤火虫算法的分散式风电场最优功率因数运行方法。基于IEEE-33节点模型进行仿真计算,结果表明:分散式风电场小范围功率因数优化调节可有效减小配电网网损,提高电压稳定性。     

基于风电机组无功裕度预测的风电场无功分层控制策略

针对风电电压波动的问题,文章基于风电机组无功裕度预测,提出了一种风电场无功分层控制策略。该策略首先以并网点电压偏差和线路有功损耗最小为目标,使用二次规划算法在线实时求解最优并网电压,进而求解风电场无功参考值;其次,采用EWT-LSSVM预测算法进行风电功率预测,并提出预测功率校正方法实时修正预测功率,精确求解风电机组的无功裕度预测值;最后,以风电机组的出口电压波动最小和预测无功裕度最大为无功分配依据,实现风电场的无功电压闭环控制。仿真结果表明,所提控制策略能够提高风电功率预测的精确性和时效性,降低了风电机组出口电压波动性,同时为风电场预留出充足的无功裕度。     

双馈风电场有功分配方式对风火打捆系统暂态稳定性的影响

针对双馈风电场和火电厂组成的风火打捆系统,研究双馈风电场内风电机组有功分配方式对风火打捆系统暂态稳定性的影响机理。基于简单系统的模型,通过理论分析,揭示火电机组减速面积与双馈风电场有功分配方式之间的关系。分析表明,在给定风电场有功调度指令后,采用更多台DFIG均摊有功指令,可增大火电机组的减速面积,从而增强风火打捆系统的暂态稳定性。最后,对简单系统和实际系统算例分析验证了该文理论研究的有效性。     

出力受限风电场群有功分配多目标优化策略

受风电发展与电网建设、负荷分布不协调等因素影响,弃风限电问题日益严峻。文章提出一种适用于因限风导致出力受限的风电场群有功分配多目标优化策略,该策略采用二次移动平均法对风电功率进行超短期预测,以风电场群实际有功出力与出力限值的差额最小以及输送线路损耗最小为目标,同时考虑风电场输出功率约束、低预测功率约束、避免机组频繁启停约束条件,基于改进遗传算法对各风电场群分配有功出力任务。以东北某实际风电场群为例,对所提出策略的可行性进行了验证。     

双馈风电场新型无功优化分配策略研究

提出一种新型的双馈风电场无功优化分配策略,以降低风电场整体损耗为目标,不仅考虑集电线路和风力机变压器的损耗,还考虑风力机内能量转换系统的损耗。同时,在进行无功优化分配时综合考虑风力机内无功分配方式对风力机能量转换系统损耗的影响,提出一种新的风力机内无功控制方式。该文优化问题由内点法求解,包括风力机无功功率极限、母线电压、相角以及潮流平衡等约束条件。通过算例对所提出的控制策略进行仿真计算和分析,结果验证了所提无功优化分配策略的有效性,并分析得出使风电场损耗最小化的无功分配原理。     

基于改进粒子群算法含双馈风电机组 配网无功优化研究

针对风电机组并网后对配电网无功补偿产生的影响,从双馈风电机组自身的有功、无功输出特性出发,基于场景概率的方法计算风力机组出力情况,以网损最小为目标函数寻求优化求解方法。利用改进粒子群算法来实现系统接入双馈风电机组后的无功优化,在Matlab 2013b软件中构造IEEE33节点模型并利用该算法求解。结果表明,双馈风电机组在参与系统无功优化时具有良好的性能,验证了该改进算法的有效性     

限风情况下风电场群有功分层协调控制策略

针对风电发展与电网建设、负荷分布不匹配产生的弃风限电问题,结合国内风电大规模、远距离集中并网的特点,提出一种适用于限风情况下的风电场群有功分配分层调控策略,包括子场层调控策略和机组层调控策略。采用加权移动平均法对风电功率进行超短期预测,基于多目标函数模型及遗传算法对子场层和机组层分配有功出力任务。以东北某实际风电场群为算例,研究表明,该调控策略能实现风电场和机组有功出力任务的优化分配,可提高电网消纳风电水平、降低线路有功损耗。     

考虑风电场无功调节能力的无功电压控制分区方法研究

分析双馈型风电机组(DFIG)风电场的P-Q容量曲线,提出同时考虑区域电气距离和区域内静态无功平衡的含风电场电力系统无功电压控制分区方法,对处理含DFIG方案,并结合New-England 39节点系统来验证方法的有效性。在无功控制分区过程中引入负荷被控空间的概念,采用先无功源节点聚类,后负荷节点归类的两阶段无功控制分区方法,有效解决了因风电有功出力影响其无功容量而带来的分区连通性和无功平衡问题。     

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.     

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.     

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.     

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.     

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。     

Biohydrogen production by Anabaena sp. PCC 7120 wild-type and mutants under different conditions: Light, nickel, propane, carbon dioxide and nitrogen

Increasing awareness of environmental problems caused by the current use of fossil fuel-based energy, has led to the search for alternatives. Hydrogen is a good alternative and the cyanobacterium Anabaena sp. PCC 7120 is naturally able to produce molecular hydrogen, photosynthetically from water and light. However, this H₂ is rapidly consumed by the uptake hydrogenase.This study evaluated the hydrogen production of Anabaena sp. PCC 7120 wild-type and mutants: hupL⁻ (deficient in the uptake hydrogenase), hoxH⁻ (deficient in the bidirectional hydrogenase) and hupL⁻/hoxH⁻ (deficient in both hydrogenases) on several experimental conditions, such as gas atmosphere (argon and propane with or without N₂ and/or CO₂ addition), light intensity (54 and 152 ??Em⁻²s⁻¹), light regime (continuous and light/dark cycles 16 h/8 h) and nickel concentrations in the culture medium.In every assay, the hupL⁻ and hupL⁻/hoxH⁻ mutants stood out over wild-type cells and the hoxH⁻ mutant. Nevertheless, the hupL⁻ mutant showed the best hydrogen production except in an argon atmosphere under 16 h light/8 h dark cycles at 54 ??Em⁻²s⁻¹ in the light period, with 1 ??M of NiCl₂ supplementation in the culture medium, and under a propane atmosphere.In all strains, higher light intensity leads to higher hydrogen production and if there is a daily 1% of CO₂ addition in the gas atmosphere, hydrogen production could increase 5.8 times, related to the great increase in heterocysts differentiation (5 times more, approximately), whereas nickel supplementation in the culture medium was not shown to increase hydrogen production. The daily incorporation of 1% of CO₂ plus 1% of N₂ did not affect positively hydrogen production rate.     

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.     

Investigation of the thermodynamic and kinetic properties of La–Fe–B system hydrogen-storage alloys

La–Fe–B hydrogen-storage alloys were prepared using a vacuum induction-quenching furnace with a rotating copper wheel. The thermodynamic and kinetic properties of the La–Fe–B hydrogen-storage alloys were investigated in this work. The P–C–I curves of the La–Fe–B alloys were measured over a H₂ pressure range of 10⁻³ MPa to 2.0 MPa at temperatures of 313, 328, 343 and 353 K. The P–C–I curves revealed that the maximum hydrogen-storage capacity of the alloys exceeded 1.23 wt% at a pressure of approximately 1.0 MPa and temperature of 313 K. The standard enthalpy of formation ΔH and standard entropy of formation ΔS for the alloys' hydrides, obtained according to the van't Hoff equation, were consistent with their application as anode materials in alkaline media. The alloys also exhibited good absorption/desorption kinetics at room temperature.     

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.