冲击负荷接入电网的电能质量分析与治理方案研究

随着冲击性负荷的日益增多,迫切需要对大量冲击性负荷接入电网时所引发的电能质量问题进行有效的分析。结合重庆电网,提出了分析大量冲击性负荷接入系统时的电能质量评估方法并给出了综合的治理方案。首先基于电流的实测数据建立了冲击负荷的新型拟合模型,并结合ward等值理论和戴维南定理多电势转化方法搭建了重庆地区的等值电网,将冲击负荷模型接入等值电网中,以此为平台研究了多个冲击性负荷接入对重庆电网电能质量的综合影响。针对电能质量超标的情况,分析了提高冲击负荷接入的电压等级、加装滤波器或SVC等治理措施,并结合重庆电网冲击负荷实测电能质量数据提出了治理方案。在PSCAD中搭建了仿真模型,验证了分析结果的有效性和准确度,为冲击负荷接入重庆电网的综合治理提供了理论参考。     

Experimental investigation of bubble behavior in gas-solid fluidized bed

In this work, to investigate the source of pressure fluctuations, behavior of a single bubble in a two-dimensional gas–solid fluidized bed was studied. Pressure sensors located at different heights of the bed measured presure fluctuations, and simultaneously a high speed camera was used to pursue all steps from formation to eruption of bubbles. Two types of particles were applied with different sizes and densities. Experiments showed that the maximum amplitude of formation was independent of the bubble diameter. But, it depended on density of particles, velocity of injection and the distance from bed surface. When injection stopped, there was a minimum in pressure profile related to the higher dense phase voidage for a higher superficial gas velocity after injection. Also, the maximum pressure fluctuation of bubble eruptions was related to the bubble diameter, density and size of particles. It was concluded that pressure fluctuations of formation, passing and eruption of bubbles in fluidized beds are originated due to changes in dense phase voidage, bed voidage and movement of particles during bubble eruption.     

黄金企业交易风险控制管理研究

随着中国黄金市场的开放,国内黄金价格与国际黄金价格接轨,曾经在计划经济体制下的黄金企业进入一个价格瞬息万变的市场经济环境;企业经营的不确定性增强,面临的市场风险也不断增多,尤其是具有金融属性和商品属性的黄金,在全球经济背景下,其价格波动风险是黄金企业面对的首要风险。该文通过揭示黄金企业面临的金价波动风险,提出了黄金企业交易风险控制管理的建议,以促进企业的可持续经营和健康发展。     

Spatial power fluctuation correlations in urban rooftop photovoltaic systems

In this paper, we investigate the spatial dependence of variations in power output of small residential solar photovoltaic (PV) systems in a densely populated urban area (≈100km²) in and around Utrecht, the Netherlands. Research into the geo‐statistical behavior of this kind of randomly spaced collection of PV systems is complementary to other studies in the field of compact regularly spaced MW‐scale PV plants. Fluctuations in power output between PV systems are correlated up to a certain decorrelation length. Decorrelation is reached (within 1 − e⁻³≈95%) in an exponential model and the spatial scale ranges from 100 m to approx. 15 km, with a mean value 0.34(±0.2), 2.6(±0.3), and 5.0(±0.5) km for measurement time step of the time series of respectively 1, 5, and 15 min. These length scales are typical for an urban environment and is important for reduction of variability in aggregated output variability of PV systems. Furthermore, the distance‐independent variability still itself was found to be strictly linearly dependent on daily mean variability values. This is a good validation of the decorrelation of inter‐system ramp rate correlation over distances longer than the characteristic decorrelation length. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis of concentration fluctuations in gas dispersion around high-rise building for different incident wind directions

This article presents experimental results that illustrate the unsteady characteristics of gas dispersion around a complex-shaped high-rise building for different incident wind directions. A series of wind tunnel experiments were conducted using a 1:30 scale model that represented the real structures under study. The objective of this paper is to study the behaviour of concentration fluctuations through transient analysis. Tracer gas was continuously released from a point source located at different positions, and a time series of fluctuating concentrations were recorded at a large number of points using fast flame ionization detectors. The experimental data were analysed to provide a comprehensive data set including variances and associated statistical quantities. Both the unsteady characteristics of the system and their potential practical impact are presented and discussed. Under crowd living conditions, the air pollutant exhausted from one household could probably re-enter into the neighbouring households, traveling with ambient airflow. Such pollutant dispersion process is defined as air cross-contamination in this study. The results indicate that the wind-induced cross-contamination around the studied type of high-rise building should not be overlooked, and the fluctuating concentrations should be paid attention to particularly during the evaluation of a potential contamination risk. This study can help deepen our understanding of the mechanisms of air cross-contamination, and will be useful for implementing optimization strategies to improve the built environments in metropolitan cities such as Hong Kong.     

中子三轴谱仪的应用

中子三轴谱仪是最早被发明,同时也是应用最广泛的中子散射谱仪之一。它利用了单色器、样品、和分析器3个转动轴的原理,使测量时可以直观地观测倒空间和能量空间的某一个点的散射性质,因此非常适合研究固体中的各种元激发。简单介绍了三轴谱仪的基本原理,然后给出一些三轴谱仪应用的例子。在这些例子中,既包括弹性散射也包括非弹性散射,例如铜单晶中的声子谱,非常规超导体中的磁共振峰,PrO s4As12中的晶格场,以及单层锰氧化合物Pr1-xCa1+xMnO4中的漫散射。     

集散化系统的耗散结构

耗散结构理论在当代社会各诸多系统中的应用探索     

Power Control of Directly Driven Wind Generation System Based on Superconducting Magnetic Energy Storage

The increasing wind power penetration poses significant technical problems to the development of electric power systems. In this article, an integrated control strategy is proposed based on the characteristics of the directly driven permanent magnet synchronous generator wind turbine. The directly driven permanent magnet synchronous generator wind turbine is incorporated with superconducting magnetic energy storage, which can smooth the wind power fluctuations, enhance the low-voltage ride-through capability of the wind generation system, and achieve an uninterruptible power supply to local loads under isolated grid operation. According to the MATLAB/SIMULINK-based (The MathWorks, Natick, Massachusetts, USA) digital computer simulation model, the proposed control strategy is confirmed to be effective in power control of grid operation.     

2种不同结构的重力供液CO_2冷风机性能比较

对由重力驱动的3k W,R404A/CO2制冷系统(CO2作为载冷剂)的CO2冷风机进行了试验研究。设计了2种不同的CO2冷风机,一种为只有一个通道的串联冷风机,另外一种具有两通道的并联冷风机,并分析了在不同充注量下2种结构的CO2冷风机的工作性能和蒸发温度波动的原因。通过分析降温速率、库内终温以及库内温度波动可知:和大串联结构相比,两通道并联系统的最佳充注量降低为950g(36.5%),相比减小了4.5%;当系统在最佳充注量下工作时,两通道的并联系统冷风机的传热系数增加到59.5W/(m2·K),相比升高了19.5%;冷库的最低温度降低了3.2℃,同时,系统达到稳定运行,冷库的温度稳定时所需的时间更少。     

基于非线性模型的可逆式机组精确线性化控制研究

由于水泵水轮机呈现强非线性特性,以及起停频繁、工况变化剧烈等运行特点,导致以线性系统理论为基础的传统控制规律面临控制品质恶化的问题。在建立可逆式机组的仿射非线性系统模型的基础上,应用微分几何方法研究了可逆式机组在几种典型大波动工况运行时的非线性系统精确线性化控制规律,仿真试验表明该非线性控制规律可以取得优良的动态性能。研究成果将非线性控制理论应用于可逆式机组的控制,为提高我国可逆式机组的运行水平具有重要的理论与工程应用价值。