风力发电讲座第四讲 风力发电机组的并网运行

风能是我国目前开发利用比较成熟的一种新能源,风电事业正在我国蓬勃发展。为了帮助读者了解风力发电知识,我们请长期从事风力发电研究工作的中国科学院电工研究所倪受元研究员撰写了《风力发电》讲座,以飨读者。 ——编者 风能是一种不稳定的能源,如果没有储能装置或与其他发电装置互补运行,风力发电装置本身难以提供稳定的电能输出。为了解决风力发电稳定供电的问题,目前国内外比较一致的看法是：大型风力发电机 (1000千瓦以上 )并网运行;中型风力发电机 (从几十千瓦到几百千瓦 )或者并网运行,或者与柴油发电机或其他发电装置并联互补运行;小型风力发电机 (10千瓦以下 )主要采用直流发电系统并配合蓄电池储能装置独立运行。 1 恒速恒频风力发电机的并网运行 中大型或大型风力发电机 (几百千瓦到几兆瓦 )主要是采用并网运行方式,在这种运行方式中主要解决的问题是并网控制和功率调节问题。下面根据风电系统所采用的发电机类型分别作一介绍。 1 1 同步发电机的并网运行 风力驱动的同步发电机与电网并联运行的电路如图 1所示。除风力机、增速器外,电气系统包括同步发电机、励磁调节器、断路器等,发电机通过断路器与电网相联。其运行特点是： 1 同步并网同步发电机与电网并联合闸前,为了避免电流冲击和转轴受到突然的扭矩,需要满足一定的并联条件,这些条件是：风力发电机的端电压大小等于电网的电压;风力发电机的频率等于电网的频率; 并联合闸的瞬间,风力发电机与电网的回路电势为零; 风力发电机的相序与电网的相序相同。由于风力发电机有固定的旋转方向,只要使发电机的输出端与电网各相互相对应,即可保证第 4个条件得到满足。所以在并网过程中主要应检查和满足前三个条件。     

The behavior of chromium and molybdenum in the propagation process of localized corrosion of steels

In order to clarify the effect of Cr and Mo on the propagation of localized corrosion of steels, the electrochemical behavior of pure chromium and molybdenum and of some stainless steels was studied under conditions similar to those existing inside occluded corrosion cells of steels. Oxygen-free FeCl₂ and/or CrCl₃ solutions were used for experiments. The surface films formed in these conditions were analyzed by means of AES and XPS. Cr is passive if the pH value >ca. 1.8 and Cr may retard the propagation of localized corrosion of steels in its early stage. The hydrolysis of Cr³⁺ may change the pH to even lower values. At such low pH and high Cl^? concentrations, Cr is active in the potential range of interest for localized corrosion of steels. Mo is passive under these more acidic conditions and the passivity of Mo in this potential range is attributed to the formation of a film of MoO₂ (or hydrated oxide), which is extremely thin but very protective. Mo is thus effective to retard the propagation of localized corrosion of steels in its more advanced stage.     

Thorough removal of inorganic and organic mercury from aqueous solutions by adsorption on Lemna minor powder

The adsorption ability of duckweed (Lemna minor) powders for removing inorganic and organic mercury (methyl and ethyl mercury) has been studied using cold vapour atomic absorption spectrometry. The optimal adsorption conditions were: (a) the pH value of the solution 7.0 for inorganic and ethyl mercury, 9.0 for methyl mercury, and (b) equilibrium adsorption time 10, 20, and 40 min for inorganic mercury, methyl mercury, and ethyl mercury, respectively. After adsorption by L. minor powder for 40 min, when the initial concentrations of inorganic and organic mercury were under 12.0 μg L⁻¹ and 50.0 μg L⁻¹, respectively, the residual concentrations of mercury could meet the criterion of drinking water (1.0 μg L⁻¹) and the permitted discharge limit of wastewater (10.0 μg L⁻¹) set by China and USEPA, respectively. Thorough removal of both inorganic and organic mercury from aqueous solutions was reported for the first time. The significant adsorption sites were C–O–P and phosphate groups by the surface electrostatic interactions with aqueous inorganic and organic mercury cations, and then the selective adsorption was resulted from the strong chelating interaction between amine groups and mercury on the surface of L. minor cells.     

Crystal growth and characterization of CuI single crystals by solvent evaporation technique

Cuprous iodide (CuI) crystals are grown by slow evaporation technique in three different solvents. Large CuI single crystals with dimensions of 7.5 mm × 5 mm × 3 mm are obtained in pure acetonitrile solvent at 40 °C. The as-grown crystals are analyzed by X-ray diffraction, energy-dispersive X-ray analysis, differential scanning calorimetry, current-voltage characteristic and photoluminescence spectrum. The results show that the CuI crystal has the zinc-blende structure with no secondary phase. The elemental Cu/I ratio is 1.09:1. The melting point of the crystal is 875 K and two phase transitions occur from room temperature to its melting point. The electrical conductivity of CuI platelet crystal is in the range of 1.11-2.38 Ω⁻¹ cm⁻¹. Under ultraviolet excitation, the CuI crystals exhibit three emission bands with peak positions at 426, 529 and 671 nm. The nature of the luminescence is discussed.     

The fabrication of polypyrrole–TiO2 nanorod array heterojunction with strong ultraviolet photoresponse

We prepare the heterojunction consisting of the TiO₂ nanorod array and polypyrrole (PPy) by using the photoexcited TiO₂ nanorod array to initiate polymerization. The structures of the heterojunction composites are investigated using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscopy. The dependence of the charge transfer resistances of the composite films on reaction time is shown by the electrochemical impedance. Devices are prepared from the PPy–TiO₂ composite films, which are synthesized in various reaction time, and photoresponse measured. The device exhibits strong photoresponse to ultraviolet lights, thus having potential as a photoconductive UV detector.     

Effects of different osmo‐dehydrofreezing treatments on the volatile compounds,phenolic compounds and physicochemical properties in mango (Mangifera indica L.)

The influences of different osmotic solution pretreatments (sucrose, glucose and maltose with concentration of 45%) on the volatile compounds, phenolic compounds and other physicochemical parameters in frozen mangoes were studied. Volatile and phenolic compounds were measured using SPME/GC‐MS and HPLC method, respectively. The results revealed that compared with untreated frozen mango, some volatile compounds (e.g. alcohols, aldehydes and some terpenes and esters) increased significantly and there were more compounds identified in osmo‐dehydrofrozen samples. These changes positively affected mango aroma and resulted in higher sensory scores for osmo‐dehydrofrozen samples. In addition, data on phenolic compounds showed that dehydrofrozen samples pretreated in glucose and sucrose had higher ρ‐hydroxybenzoic acid and quercetin contents, respectively, while samples pretreated in maltose showed higher ρ‐coumaric acid and sinapic acid contents compared with untreated frozen samples. The current work indicates that osmo‐dehydrofreezing can improve the retention of phenolic and aromatic compounds in frozen mango.     

流化床脱水制无水氯化镁工艺研究

水氯镁石(六水氯化镁)脱水制无水氯化镁是盐湖镁资源利用的关键环节,复盐法是水氯镁石脱水的重要方法,由复盐合成、造粒及流态化热分解等步骤组成。采用热分析技术(TG-DTG)研究了复盐热解过程。结果显示,复盐热解主要分为两个阶段:第一个阶段脱去六个结晶水;第二个阶段脱去盐酸苯胺助剂,热重结果为后续实验提供理论依据。实验首先通过均匀液滴喷射技术(振动造粒)制备得到六水氯化镁-盐酸苯胺复盐颗粒。然后在流化床中进行复盐热分解脱水、脱助剂得到无水氯化镁。通过实验探索得到水氯镁石复盐流态化热分解的最佳工艺参数:脱水氮气流量1.6 m3/h～1.8 m3/h、脱盐酸苯胺氮气流量1.0 m3/h～1.2m3/h、脱水温度300℃、脱水时间0.5 h、脱盐酸苯胺温度350℃、脱盐酸苯胺时间1 h。     

基于中间件技术的图书管理系统的设计

针对目前图书管理系统维护性和延展性差的问题,将应用服务器加入到系统的分布式结构中,给出了应用服务器、远程数据模块和本地数据模块的设计.运行结果表明,基于中间件技术的图书管理系统降低了系统的开发和维护成本,提高了系统的延展性.     

细号纯棉色织物无PVA上浆实践

研究改性淀粉浆料AS-1在细号纯棉色织物上的应用效果.分析了AS-1的浆膜性能和浆液黏附性能,测试了AS-1在不同浆液含固量下浆出纱线的性能及织造效果,并与原用PVA配方的工艺进行了对比.实践证明,AS-1不仅可以完全取代PVA用于细号纯棉色织物的上浆,还可以有效提高织机效率、降低上浆成本.