光伏并网发电系统的MPPT-电压控制策略仿真

在配电网络的末端,负载的无功波动将会对电网供电电压产生较大的影响,对光伏发电系统并网处系统侧的交流电压进行控制,可以提高系统的电压水平。根据光伏并网系统的结构,采用外环为电压环、内环为并网电流环的双环控制。通过abc/dq0变换将并网电流解耦为有功分量和无功分量,引入最大功率点跟踪（maximum power point tracking,MPPT）提供的直流侧电压参考量的闭环控制调节并网电流的有功分量,引入交流侧电压参考量的闭环控制调节并网电流的无功分量,实现了具有MPPT和电压控制能力的三相光伏并网发电技术。仿真结果表明MPPT-电压控制策略既能够实现光伏并网的最大功率点跟踪,也能够控制光伏发电系统接入点的交流电压,进一步提升了光伏并网发电系统的应用前景。     

具有最大功率点跟踪功能的户用光伏充电系统的研究

从提高户用光伏系统蓄电池寿命和系统性能出发，设计出一个户用光伏充电系统。在这个充电系统中，提出了采用具有太阳能电池最大功率点跟踪(MPPT)功能和蓄电池充电电压温度补偿功能相结合的充电控制方法。实验和模拟仿真证明，系统实现了对太阳能电池的MPPT控制和对蓄电池充电的温度补偿。     

基于双曲正切函数的光伏/温差自适应MPPT控制策略研究

为了提高光伏/温差联合发电系统的效率,需要进行最大功率点跟踪（Maximum Power Point Tracking,MPPT）控制。针对传统电导增量法步长固定不变,导致跟踪速度慢和稳态误差大的缺点,提出一种恒定电压法和双曲正切型自适应变步长算法结合的MPPT控制策略。该策略利用双曲正切函数单调递增、变化速度快的特点,使步长可以根据光强等外界环境条件的变化,自适应地快速调整,同时利用恒定电压法加快追踪的响应速度。通过Matlab/Simulink软件仿真和硬件试验表明,该研究所提方法在光照强度剧烈变化时,系统能够在15 ms内快速跟踪到最大功率点,同时稳态误差低于0.3%,实现了MPPT控制在跟踪速度和稳态精度方面的同步优化。     

基于离散时间纹波控制的太阳能最大功率点跟踪算法

为了提高光伏太阳能转换率,拓展传统纹波控制技术的应用,该文提出了离散时间纹波控制算法,通过对纹波控制技术的离散化处理,将最大功率点跟踪控制问题转换为离散采样-控制问题。以太阳能板输出电压为状态量,在其处于极大值和极小值时对系统进行采样;随后采取离散时间纹波控制算法使系统快速追踪到系统的最大功率点。该文在Simulink系统中对离散时间纹波控制算法进行了仿真。仿真结果表明,在1 000和200 W/cm2,25℃的条件下,算法均可以快速准确地追踪到太阳能系统的最大功率点,追踪精度高达96%;在外部环境由1 000变为200 W/cm2时,系统能够在0.1 s内准确地追踪到新的最大功率点。     

基于DSP太阳能光伏并网系统的应用研究

光伏并网发电是太阳能光伏发电应用发展的趋势。并网逆变器是光伏并网发电系统核心部件之一,基于TM S320LF2407 DSP芯片控制的并网系统。利用DSP丰富的外围电路和强大的功能实现并网系统的所有工作、控制和相应的保护功能等。并网逆变器采用前级DC/DC的boost升压结构电路,减少了系统体积和重量;后级DC/AC逆变器采用全桥逆变电路;且具有最大功率跟踪和反孤岛效应等功能。以DSP为控制核心的光伏并网系统具有可靠性强,工作效率高,稳定性好等优点。其加快了光伏并网发电系统的应用推广。     

聚光太阳能温差发电装置性能分析与试验

为提高太阳能温差发电装置的热电转换效率,该文设计聚光太阳能温差发电装置,利用槽式抛物面反射聚光镜进行聚光,经集热体转换为热能后提高温差发电器(thermoelectric generator,TEG)热端温度,冷端采用扁平热管作为传热元件,利用水冷散热,增大TEG冷热端温差,提高装置输出功率及热电转换效率。对装置建立能量转换平衡方程,通过数值计算分析不同太阳辐射强度对热损失、光热转换效率及热电转换效率的影响。为解决多个热电模块串联在一起,无法使每个模块都工作在最大功率输出状态,从而导致整体输出功率降低的问题,采用集中-分布混合式最大功率跟踪(maximum power point tracking,MPPT),试验结果表明,经过MPPT后装置能很快达到最大功率输出点,且输出功率稳定,运行30 min输出功率增加3.2 W。搭建了装置的性能测试平台,对基于槽式抛物面反射聚光与扁平热管水冷散热的聚光太阳能温差发电装置进行试验研究,结果表明,随着冷却水流量的增加装置输出功率得到提高,当冷却水流量达到8 L/min后,输出功率趋于平缓;随着温差的增大装置的最佳匹配负载逐渐增加。装置的全天性能试验表明,试验期间装置最大输出功率为30.1 W,平均输出功率27.8 W,试验期间发出电量222.4 W·h,热电转换效率最大为5.4%,装置最大效率4.1%,该装置在远程传感器供电和微功耗供电等领域具有广阔的应用前景。     

传感器节点自主供电的环境混合能量收集系统设计

农田复杂环境及大面积监测需求对农业物联网传感器节点的供电提出了极大挑战,而环境能量收集技术则使低功耗农业物联网传感器节点的自供电及免维护成为可能。针对传统能量收集装置中收集的环境能量单一有限、装置体积大、可靠性差的问题,该文提出了一种新型混合环境能量一体化收集系统。该系统定位于环境中普遍而丰富的射频电磁波能量和振动能量,通过射频收集天线和压电陶瓷的有效结合,同时收集2种环境能量,并经整流转换成直流电能。能量收集天线使用普通FR4印刷电路板实现,工作在手机通信频段1.9 GHz(3G频段),测试的回波损耗为-20.5 d B,对电磁波能量收集的最高输出功率可达到38 mW,测得收集到的振动能量最大输出功率可达到25 mW,满足低功耗传感器节点的功率需求。该装置不仅可以有效提高系统供电的可靠性和对环境的适应能力,还大大降低了传统混合系统的尺寸,可为农业物联网快速发展中的传感器节点可靠供电问题提供参考。     

沼液微生物燃料电池的产电及有机物降解特性研究

为了使发酵沼液得到减量化、无害化处理及能源化利用,该研究构建了以玉米秸秆发酵沼液为阳极底物的双室微生物燃料电池(microbial fuel cell,MFC)。通过对比不同浓度沼液MFC产电特性、化学需氧量(chemical oxygen demand,COD)去除率及库伦效率等探究MFC对玉米秸秆沼液的降解效果及其能量回收效率。结果表明,玉米秸秆沼液MFC能够正常启动,并且能够长时间运行产生电流。当初始COD质量浓度为(3618.6±55.6)mg/L时,其最大功率密度为203.4 mW/m2,COD去除率可达63%;并随着沼液中有机物浓度降低,MFC运行稳定性下降,最大输出功率密度成线性降低。通过对原料及阳极溶液和阳极生物膜菌群结构分析可知,以玉米秸秆发酵沼液为阳极底物的MFC菌群结构合理,MFC可以利用沼液中的水解细菌分解阳极溶液中的纤维素等大分子物质,主要以Clostridia、Flavobacteria和Bacteroidia菌纲为主;同时阳极生物膜可以富集接种物中的产电细菌,分解小分子有机物产生电能,2类微生物可以互利共生,避免了沼液MFC的高浓度抑制。该研究表明,MFC可以降解较高浓度沼液废水,并产生电能,该研究可为发酵沼液的处理与利用提供参考。     

基于最大功率点与最小损耗点跟踪的光伏水泵系统效率优化

太阳能光伏电源是一种非常有潜力的再生能源,但应用成本高、投资回报率低是当前制约独立光伏水泵系统在光照充足的农村地区大面积推广的瓶颈之一。该文研究工作的核心是优化光伏水泵系统、提升效率,在不增加硬件投入的前提下,一是利用一种最大功率点跟踪（maximum power point tracking,MPPT）算法优化光伏转换效率,二是在异步电动机的损耗方面优化进而提升效率,利用一种最小损耗点跟踪（minimum loss point tracking, MLPT）算法提高水泵用异步电动机效率,并且将MPPT与MLPT耦合。通过样机试验验证了优化策略的实际运行情况,其节能效果具有一定的实际意义,从而可有效提高投资回报率。     

具有TMPPT功能的数字式光伏水泵系统的设计

设计了一种基于16位微处理器结构的简单全数字式光伏水泵系统。系统采用频率微分逼近法实现了太阳电池的真正最大功率跟踪(TMPPT)功能，运行结果证明系统运行稳定可靠，效率高于传统恒压跟踪(CVT)方式；系统具有完善的保护功能，可以实现无人值守工作。     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Effect of some fungicide seed treatments on the survival of Bradyrhizobium japonicum and on the nodulation and yield of soybean [Glycine max. (L) Merr.]

Several commercial fungicide seed treatments were evaluated for their possible effect on the survival of Bradyrhizobium japonicum on seeds and on the nodulation and yield of soybeans in a greenhouse and a field experiment. quinolate Pro (carbendazim and oxine copper), Vitavax 200FF (carboxin and thiram), and Monceren (pencycuron) had a small effect or no effect on the survival of B. japonicum and on the nodulation and yield of soybeans. They can thus be considered compatible with soybean seed inoculation. Germipro UFB (carbendazim and iprodione), Apron 35J (metalaxyl), and Tachigaren (hymexazol) decreased B. japonicum survival and the nodulation and yield of soybeans and thus cannot be considered compatible with soybean seed inoculation.     

Einfluss der düngungsmethoden auf die entwicklung von zuckerrübenkrankheiten

Während neunjähriger (1994-2002) Untersuchungen in der Versuchsanstalt Ba?cyny (Fahlerde, Fall-Gleyboden, ausgebildet aus leichtem Lehmboden) wurde der Befall mit Krankheiten an der Zuckerrübe in Abhängigkeit von der Düngungsmethode bewertet. Folgende Methoden wurden angewendet: A - Mineraldünger, B - Stalldung und Mineraldünger, C - Stroh-, Gründung und Mineraldünger, D - Kompostdünger und Biopräparate (ökologische Düngung). Auf den Objekten A, B, C wurden bei konstanter Phosphor-Kalium-Düngung die Stickstoffgaben von 0 bis 180 kg.ha^?1 differenziert. Auf dem ökologischen Objekt D ohne Mineraldünger wurden statt Stickstoff die Biopräparate P₅₀₀ und P₅₀₁ verabreicht. Der geringste Befall von Krankheiten wurde an der Zuckerrübe auf jenem Objekt festgestellt, das mit Kompost und den Biopräparaten gedüngt worden war. Im Rahmen der konventionellen Düngungsmethoden wurde allgemein die höchste Intensität der Krankheiten an der mit Stroh, Gründung und Mineraldünger gedüngten Zuckerrübe beobachtet. Ausnahmen von dieser Regel bildete das Vorkommen von echtem Mehltau und Keimlingsfäule. Auf den Objekten A, B, C nahm die Intensität der Krankheiten mit der Steigerung der Stickstoffgabe zu. Auch die auf Objekt D verabreichten Biopräparate stimulierten die Entwicklung der Krankheiten. The effect of various fertilization methods on the diseases of sugar beet was estimated on the basis of nine-year studies (1994-2002) conducted in the Experimental Production Farm in Ba?cyny on loess-based, sedimentary-gley, light-clay soil. The following fertilization methods were applied: A - mineral fertilization, B - mineral and manure fertilization, C - straw, green manure and mineral fertilization, D - ecological compost and biodynamic preparations fertilization. In the objects A, B and C fertilized with phosphorus and potassium, various doses of nitrogen ranging from 0 to 180 kg/ha^?1 were used. In the ecological object D, where mineral fertilization was not used, biodynamic preparations P₅₀₀ and P₅₀₁ were applied instead of nitrogen. The lowest ratio of the diseases of sugar beet was observed in the object fertilized with the compost and biodynamic preparations. In view of the conventional fertilization methods, generally the highest incidence of diseases was noted in the sugar beet fertilized with straw, green manure and mineral fertilizers. The exception was the occurrence of powdery mildew and the black leg. In objects A, B and C the incidence of the diseases increased with the increase in nitrogen doses. The applied biodynamical preparations in the object D stimulated the development of diseases too.     

Prospects for control of Pythium damping-off of lettuce with Trichoderma,Gliocladium and Enterobacter spp.

Summary Damping-off of lettuce (Lactuca sativa) caused by Pythium ultimum was studied in pots containing a non-sterile potting mix in the glasshouse. Fifty P. ultimum sporangia g^-1 compost reduced the plant stand to 15% and shoot dry weight to 18%, but this reduction was totally prevented by applying Trichoderma harzianum at 2×10⁵ viable propagules g^-1 potting mix. Gliocladium virens and Enterobacter cloacae also alleviated the damping-off. E. cloacae did not adversely affect the action of the fungal antagonists. The co-existence of the bacterial and fungal antagonists was revealed on the root surface and inner surface of the testa by scanning electron microscopy, indicating the compatibility of the biocontrol agents.     

细菌、真菌及植物氮营养信号研究进展

氮素吸收代谢是所有生物生命活动的核心部分,因此,各种生物对氮的吸收与同化过程都有精细的调节。这种调节依赖于生物对体内氮素状况信号及体外（生长介质中）氮素信号的感受。过去几十年中,在细菌、真菌中已经对氮素营养信号有了较好的研究,而植物中则相对缓慢,但也有了一定的认识。本文重点比较细菌、真菌及植物中氮信号系统的组成,以期为进一步认识植物中的氮信号接受与转导系统提供启示。     

Aircraft operations near concentrations of birds in Antarctica: The development of practical guidelines

Aircraft operations have the potential to disturb and to impact negatively on bird life. A gradient of increasing behavioural response is evident in birds when exposed to increasing aircraft stimulus. The most major disturbance is likely to lead to impacts on the health, breeding performance and survival of individual birds, and perhaps bird colonies. A process of revision to policies on aircraft operations contained in management plans for a number of specially protected areas in Antarctica by the United Kingdom, accompanied by consultations made within the scientific community through the Scientific Committee on Antarctic Research (SCAR) and with operational interests through the Council of Managers of National Antarctic Programmes (COMNAP) resulted in new guidelines being adopted by the Antarctic Treaty Consultative Parties in June 2004. The principal recommendations of the guidelines are that bird colonies should not be overflown below 2000 ft (∼610 m) above ground level and landings within 1/2 nautical mile (∼930 m) of bird colonies should be avoided wherever possible. These guidelines are less stringent and less specific than those that were recommended by the SCAR specialist group on birds, and represent a compromise to accommodate operational needs. While the adoption of clear and consistent guidelines for the operation of aircraft in Antarctica is welcome in that this provides practical advice that is likely to reduce incidences of close aircraft/bird encounters, there remains insufficient knowledge of the interactions between aircraft and birds in Antarctica, and the consequent impacts on individual birds and on bird populations. It is important, therefore, that the guidelines adopted are considered interim, and should be kept under scrutiny with revisions made as new and improved research results appear.     

The abundance of heterocystous blue-green algae in rice soils and inocula used for application in rice fields

Summary Algal populations were quantified (as colony-forming units [CFU] per square centimetre) in 102 samples of rice soils from the Philippines, India, Malaysia and Portugal, and in 22 samples of soil-based inocula from four countries. Heterocystous blue-green algae (BGA) were present in all samples. Nostoc was the dominant genus in most samples, followed by Anabaena and Calothrix. In soils, heterocystous BGA occurred at densities ranging from 1.0 × 10² to 8.0 × 10⁶ CFU/cm² (median 6.4 × 10⁴) and comprised, on average, 9% of the total CFU of algae. Their abundance was positively correlated with the pH and the available P content of the soils. In soil-based inocula, heterocystous BGA occurred at densities ranging from 4.6 × 10⁴ to 2.8 × 10⁷ CFU/g dw (dry weight), comprising only a moderate fraction (average 13%) of the total algae. In most soils, the density of indigenous N₂-fixing BGA was usually higher than that attained by applying recommended rates of soil-based inoculum. Whereas research on the practical utilization of BGA has been mostly directed towards inoculation with foreign strains, our results suggest that attention should also be given to agricultural practices that enhance the growth of indigenous strains already adapted to local environmental conditions.Maître de Recherches ORSTOM (France), Visiting Scientist at IRRI