基于V2-OCC的BUCK变换器的斜坡补偿控制研究

针对BUCK变换器的电压模式控制中,电力电子开关工作在大占空比下不稳定,易引起次谐波振荡,提出了一种基于V2-OCC的BUCK变换器斜坡补偿控制方法。增加斜坡补偿环节,在电流内环引入基于负载前馈的纹波补偿,通过匹配控制参量参数达到稳态无差调节。通过对输出电压进行补偿设计,不仅提高了系统的带载能力,同时也提高了系统的鲁棒性与稳态精确性。为验证所设计控制器的性能,在Matlab/Simulink里搭建仿真模型,并将控制效果与传统PID控制以及V2-OCC控制效果相比较,仿真结果表明引入斜坡补偿环节的控制方法具有更强的鲁棒性与带载能力。     

基于电压补偿的定直流电压及无功控制的光伏系统

在光伏并网运行中,当电网电压不平衡时会导致电压、电流等的波动,从而影响电网电能质量及系统的稳定性。结合电压补偿控制等环节,提出了一种基于电压补偿控制的定直流电压、无功控制策略,将采集到的正、负序电压经电压补偿控制环节得到电压的不平衡系数,对电网电压的不平衡度进行补偿,并引入负序电流抑制环节。在PSCAD中分别设计搭建了改进前后的仿真模型,并对光伏并网发电系统的动态变化特性进行研究。仿真结果表明,在光照强度和温度阶跃扰动下,系统能够迅速做出响应并工作于最大功率点处,电压及电流波动幅度减小,电网电能质量得到明显改善,验证了MPPT算法及改进后控制策略的准确性及有效性。     

基于全鲁棒滑模控制双馈风力发电系统空载并网控制研究

为解决PI控制在双馈风力发电机并网控制中自适应和鲁棒性差等问题,文章根据定子磁场定向矢量控制方法和全鲁棒滑模控制方法,设计了双馈风力发电机的空载并网控制策略,引入带指数函数的时变因子项,消除到达阶段;并在切换控制中引入状态误差,提高状态的收敛速度和削弱抖振。通过与PI控制进行仿真比较,结果表明,所设计的全鲁棒滑模控制策略对电网电压波动和电机参数摄动具有较强的全局鲁棒性,且响应速度快,稳态误差小,保证了定子电压的稳定性,能有效实现空载并网。     

基于双积分滑模控制的光伏电压平衡器研究

文章采用三电平Boost电压平衡器将光伏电源接入双极性直流微电网。针对变换器正、负极输出电压不平衡问题,设计了一种基于PWM技术的双积分滑模控制器对电压平衡进行控制。与传统的PI控制器相比,该方法能提高系统的动态响应速度和增强鲁棒性。仿真结果表明,相比PI控制,该方法将电压平衡器的动态调节时间缩短42%以上,电压差峰值减小33%以上。同时,系统采取的控制策略能确保电压平衡的控制对光伏最大功率点追踪的控制影响极小。     

混合微电网与配电网间的串联环节及其控制

为了提高交直流混合微电网并网运行时对配电网故障的穿越能力和电能质量,提出在配电网和交直流混合微电网之间加入串联环节,该串联环节可与微网中交直流子网间的AC/DC双向功率变换器配合提高交流子网的电能质量,同时可抑制配电网和交直流混合微电网之间的故障电流。首先介绍该串联环节的基本结构和运行模式。然后,基于在abc三相静止坐标系和dq两相同步旋转坐标系下的数学模型,设计一种配电网电压前馈、负载电压和补偿电压双反馈的电压补偿控制策略,并采用电压电流双闭环控制方法进行故障电流抑制。此外,对该串联环节的变压器进行设计。最后,通过仿真验证上述串联环节及其控制策略的有效性。     

基于无源性的直流微网虚拟惯性研究

为提高直流微网中变换器的动态性能和直流母线电压的稳定性,文中提出一种基于无源性的虚拟惯性控制策略.首先基于变换器的端口受控耗散哈密顿模型,设计出无源电流控制器,然后引入虚拟直流电机控制作为电压外环.仿真结果表明,文中所提基于无源性的虚拟惯性控制策略可较好地提高直流微网的惯性;同时相比传统的下垂控制策略,当微网系统受到扰...     

风电系统改进T型逆变器并网优化模型预测控制

将采用一种新型变换器结构用于直驱风力发电系统中,即Boost三电平变换器(简称Boost-TL变换器)和改进T型三电平逆变器级联的并网拓扑结构。改进T型三电平拓扑比传统T型三电平结构能明显减小零状态下的传导损耗。提出一种简单易行的基于空间电压矢量的开关状态预测控制优化方法,该方法加入延时补偿并且精减模型预测控制的冗长计算量。仿真和实验结果表明,在所提出的拓扑结构基础上,采用该优化算法能使系统鲁棒性增强、动态响应快、运行范围宽、稳定性提高。     

移相全桥变换器在电动汽车充电单元中的应用

分析了峰值电流控制模式下移相全桥变换器的工作原理,设计了电动汽车充电单元的串联双闭环控制器。该控制器外环主回路实时获取负载电压与输入参考电压之间的偏差,通过输入PID电压环对输出电压进行调节,其内环副回路实时计算原边控制电流与PID电压环控制输出的偏差,通过输入PID电流环对控制电流进行调节。针对当控制输入信号占空比大于50%后峰值电流变换器系统出现不稳定的问题,设计了一种斜坡补偿方法,并以PIC16F887单片机为核心,开发了一套电动汽车充电控制单元。实验结果表明,所设计的充电控制单元可以满足电动汽车的充电要求,并具有可靠性高、动态响应快、补偿网络易实现以及带宽增益较高等优点。     

基于无源性的直流微电网并联变换器控制策略

针对可再生能源聚合而形成带混合负载的直流微电网稳定性与协调性问题,提出一种将无源控制与改进非线性干扰观测器前馈补偿相结合的新型控制算法,在消除恒功率负载对直流微电网的影响的同时提高了系统鲁棒性,再利用线路阻抗补偿来改善分流精度与实现电压无偏差。该文利用Matlab/Simulink搭建并联DC-DC变换器仿真模型进行验证,通过对比传统无源控制与比例积分调节的无源控制表明,提出的控制策略抑制了恒功率负载与线路阻抗对直流微电网的影响。最后,在Opal-RT半实物实验平台验证了该策略的有效性。     

一种基于复合抗干扰的DC-DC变换器控制方法

针对光伏发电系统中DC-DC变换器由于负载和环境条件的变化等扰动引起的输出波动问题,提出一种基于模型预测控制与干扰观测器结合的复合控制策略。首先,根据光伏阵列模型,利用电流扫描法计算出最大功率点的电压值,然后运用模型预测控制方法预测系统的未来状态,再由滚动优化求出系统的最优控制变量并在线控制,得到新的开关控制策略。同时利用干扰观测器观测DC-DC变换器在运行过程中由各种不确定性所引起的内外干扰,并进行补偿。最后的仿真结果表明,文中所提的复合抗干扰方法具有更好的电压跟踪性能和鲁棒性。     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.     

Wind power for pumping: The development of the ITP windpump

Water pumping has been one of the main applications for wind power in the past and despite the spread of mains-electric pumps, more than a million windpumps remain in regular use. This paper reviews the general technical and economic requirements for pumping water using wind energy and by way of example gives an overview of the development of the new ITP wind-pump. It then considers the future prospects for this kind of technology.     

Methods of creating solar-reflective nonwhite surfaces and their application to residential roofing materials

We describe methods for creating solar-reflective nonwhite surfaces and their application to a wide variety of residential roofing materials, including metal, clay tile, concrete tile, wood, and asphalt shingle. Reflectance in the near-infrared (NIR) spectrum (0.7–2.5 μm) is maximized by coloring a topcoat with pigments that weakly absorb and (optionally) strongly backscatter NIR radiation, and by adding an NIR-reflective basecoat (e.g., one colored with titanium dioxide rutile white) if both the topcoat and the substrate weakly reflect NIR radiation. Coated steel and glazed clay-tile roofing products achieved NIR reflectances of up to 0.50 and 0.75, respectively, using only cool topcoats. Gray-cement concrete tiles achieved NIR reflectances as high as 0.60 with coatings colored by NIR-scattering pigments. Such tiles could attain NIR reflectances of up to 0.85 by overlaying a white basecoat with a topcoat colored by NIR-transparent organic pigments. Granule-surfaced asphalt shingles achieved NIR reflectances as high as 0.45 when the granules were covered with a white basecoat and a cool color topcoat.     

Thermal decay of an initially hot isothermal water body with application to thermal energy storage

The thermal decay of an initially hot isothermal water body contained in a tank was studied. Analytical solutions (including a group-theoretic solution) were obtained for the one-dimensional heat conduction equation with heat loss from the sides of the tank. The convective heat transfer coefficient was assumed not to be constant over the surface of the tank but to vary with space and time. A very good agreement was obtained between the group-theoretic solution and a numerical solution using the Crank-Nicholson finite difference scheme. The analytical results are discussed in terms of the underlying physical mechanisms.     

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.     

秸秆燃烧中温度对钾转化与释放的影响

通过对稻秆原料进行常规特性分析和EDX元素含量分析,发现钾在稻秆无机元素中占有重要地位。参考原料化学分馏法和土壤中钾的分类与测试方法,给出了对生物质原料及其燃烧产物中钾的定性与定量简易方法。通过程序控温型固定床对稻秆先进行缓慢氧化,然后以100℃为间隔从400～900℃进行成灰,并分别测试其成灰率、有效钾和全钾的份额。结合稻秆原料及其灰中钾的份额分析,进行了稻秆灰中有效钾转化与释放的计算,发现有效钾在700～800℃之间有快速的释放和形态转变。稻秆灰的XRD分析结果表明秸秆灰中钾主要以KCl、K_2SO_4形式存在,得到了钾以盐的形式进行转化与释放的机理。该文中燃烧温度对钾转化与释放的影响规律对设计秸秆电厂时的炉型选择和燃烧参数确定有一定参考价值。