并网变流器全工况阻抗模型的黑箱辨识方法

阻抗分析法因适用于并网变流器控制结构和参数均未知的黑箱系统,已成为工程中评估宽频振荡风险的重要选择。以跟网型三相两电平变流器为例,首先,使用谐波线性化方法,严格推导了计及直流侧耦合的交流侧全工况开/闭环理论阻抗模型,实现了模型参数与工作点高阶项的完全解耦。其次,依据理论模型特征,明确了黑箱辨识方法的基本原理,分析了辨识单一开/闭环阻抗模型频率响应所需的工况数量。使用辨识得到的全工况阻抗模型,实现了不同短路比条件下系统安全运行域的快速评估,并通过时域仿真验证了其准确性。此外,讨论了所提方法的合理性、普适性以及相对于深度学习方法的优越性,为阻抗分析法的实际应用提供了参考。

枇杷新品种早茂15号的选育

早茂15号是以早钟6号为母本、粤引马可为父本杂交,从F1代群体中通过单株优选而成。该品系为黄肉类型,早中熟,成熟期3月上旬至4月上旬,果实长倒卵形,果皮橙黄,易剥皮,果肉橙黄色,平均单果质量42.2 g,平均单果种子数3.3粒,果肉厚9.86 mm,可溶性固形物含量(w,后同)13.5%,维生素C含量1.51 mg·100 g^(-1),总酸含量0.53%,可食率74.4%。该品系易成花,花量大,坐果率极高,丰产性能好,甜酸适口,品质优良,适宜在广东省枇杷种植区域种植,云南、贵州等其他枇杷产区也在试种中。

宁海白×大房枇杷F_(1)杂交群体果实性状的相关性及遗传分析

【目的】探究枇杷果实重要性状的遗传倾向以及果实性状间的相关关系,以期为枇杷杂交育种的亲本选配提供参考。【方法】对宁海白与大房杂交产生的130株F_(1)杂种后代的7个果实重要性状进行调查以及相关性分析。【结果】调查的7个果实性状均呈正态分布,其中果肉厚度、果实横径、果实质量、果实纵径等4个性状表现出趋低遗传倾向;种子数、种子质量、可溶性固形物含量3个性状表现出趋高遗传倾向。相关性分析显示,果实质量与其他6个性状均呈极显著相关,而通径分析显示,果实横径、种子质量、果肉厚度、果实纵径、种子数是影响果实质量的主要因素,其中果实横径和种子质量对果实质量的影响最大,而种子数的影响最小。【结论】7个果实重要性状均为数量性状,其中果肉厚度、果实横径、果实质量、果实纵径遗传倾向趋于趋低遗传,种子数、种子质量、可溶性固形物含量为趋高遗传;果实横径和种子质量是影响果实质量的关键性状。

基于大容量电力电子功率变换的交流电弧炉柔性供配电方案

交流电弧炉作为电力系统高载能负荷的代表广泛应用于钢铁行业。针对交流电弧炉传统供配电方案在系统侧电能质量治理效果与负载侧生产效益的局限性,文中介绍了一种新型柔性供配电方案:在匹配传统方案主体结构的基础上,将多绕组移相变压器与模块化电力电子功率单元串联引入供电回路,显著提升了负载侧量测与控制精度,且改变了并联补偿治理该类负荷引发电能质量问题的固有方法。详细介绍了电源装置各部分功能,并参考传统方案工作原理设计了功率单元的控制策略。依据某100 t交流电弧炉实际参数在PSCAD/EMTDC中建立了柔性供配电方案完整仿真模型,验证了新型方案的可行性与优势。

大容量交流电弧炉柔性供配电方案控制策略

合理化供配电技术是调控大容量交流电弧炉负载能量平衡的关键。含模块化电力电子功率单元的柔性供配电方案可显著减轻交流电弧炉运行对系统电能质量的影响,通过改进其多环节控制策略可以进一步提高交流电弧炉冶炼的性能并降低对系统的频率冲击。首先,该文提出功率单元逆变级采用电流控制模式取代电压控制模式与固有电极调节配合,提升控制系统带宽;其次,设计该方案针对多种运行工况的控制策略,增加其实际应用的灵活性与面向系统的友好性;再次,改进逆变级调制策略以抑制潜在的高频共模电流风险;最后,根据实际参数仿真验证了多种控制策略的有效性,可充分发挥所提方案电力电子主导的软硬件优势。

枇杷叶片性状与单果质量的遗传规律研究

为了解枇杷(Eriobotrya japonica)叶片性状和单果质量的遗传多样性及其相关性,对‘宁海白’与‘大房’杂交组合的F1群体(123株)的7个叶片性状与单果质量进行相关分析。结果表明,叶片的长度、宽度、厚度和叶柄长度及单果质量5个性状在后代中均呈现连续性较好的正态分布,其中单果质量、叶片的长度、宽度和厚度呈趋小遗传趋势,叶柄长度呈趋中变异趋势。F_(1)杂交群体叶面形态主要以“稍皱”为主,叶片形状以“椭圆形”为主,叶基形状以“楔形”为主。单果质量与叶柄长度、叶片长度、叶片宽度、叶片厚度均表现出极显著的正相关性。因此,叶柄长度可考虑作为早期筛选大果优株的参考指标之一。

基于MMC的背靠背异步联网系统宽频带频率耦合阻抗模型及小信号稳定性分析

背靠背变流器的稳定性分析是保障电力电子化新型电力系统安全可靠运行的重要基础。该文建立详细模型,研究了基于模块化多电平变流器三相对称背靠背异步联网系统的小信号稳定性。首先提出一种系统频域稳态分析方法并使用牛顿-拉夫逊迭代快速求解多谐波变量。进而基于多谐波线性化法,建立充分计及频率耦合效应的系统交/直流阻抗模型,对比扫频结果证实其宽频带范围的精确性。最后,应用广义Nyquist判据解释小信号失稳工况,体现了包含两端变流器动态的理论模型的必要性,并讨论了交/直流互联端口判据的联系。

H桥分时复用方法及其在电力电子变压器中的应用

能源互联网中,电力电子变压器(powerelectronic converter,PET)因功率变换级数较多,体积庞大,成本高昂,且效率不佳。为此,提出了一种有助于减少PET级数的H桥分时复用方法。首先,阐明了分时复用方法的基本原理,定义了单载波周期的工作模式,分析了变压器原边的电流特征;其次,介绍了实用的谐振式开环工作模式切换方法,理论推导了电流脉冲与谐振角度的对应关系;通过样机实验验证了所提高频变压器间歇功率传输与模式切换方法;最后,基于分时复用方法构建了新型PET,并使用电力电子仿真软件PLECS真验证了基本功能。相关方法为优化PET的拓扑与控制提供了新思路。

利用PSY基因标记探讨枇杷果肉颜色的遗传倾向

【目的】研究枇杷果肉颜色的遗传倾向。【方法】以黄肉品种‘梅花霞’和‘早钟6号’及白肉品种‘白玉’为亲本,创建了9个杂交和自交后代群体,利用SRAP和RAPD分子标记技术,鉴定真杂种。利用枇杷果实特异DNA分子标记PSY基因对9个杂交和自交组合后代的果肉颜色进行早期鉴定,并对其遗传倾向进行分析。【结果】9个杂交和自交后代群体中,共鉴定出1 166株真杂种‘。梅花霞’与‘白玉’和‘梅花霞’与‘早钟6号’的正反交组合后代未出现果肉颜色性状的分离倾向,果肉颜色均鉴定为黄色;而‘早钟6号’与‘白玉’的正反交组合后代果肉黄、白色的分离比分别为1∶0.89和1∶0.87。自交组合‘梅花霞’和‘白玉’的后代无果肉颜色性状的分离,后代果肉颜色分别鉴定为黄色和白色;而‘早钟6号’自交后代黄肉与白肉分离比例为2.94∶1。【结论】枇杷果肉颜色黄色和白色可能受到一对呈显隐关系的基因控制,其中黄肉性状为显性,存在纯合和杂合的情况,其分子标记类型不同,DNA分子标记分别表现为1 031 bp(纯合)或1 031 bp和319 bp(杂合);白肉性状为隐性,DNA分子标记为319 bp。

阻抗法分析背靠背变流器稳定性的释义与推广

已有文献指出,在局部交/直流回路应用阻抗法分析多端系统稳定性是不完备的。基于一个两电平电压源型背靠背变流器,理论解释了该现象。首先,借助状态空间,完善了常用坐标系下端口/回路解析阻抗模型的一般导出方法。进而对比不同回路稳定性的频域判定结果和全系统的时域零极点信息,证实了零极点对消导致子系统对全系统模式的不完全可观,是部分判据失效的根本原因。阐明了该结论对同一变流器采用不同控制策略与不同类型变流器间的通用性。最后,由相关概念设计了一种基于阻抗交互的多端系统致稳方案。

功率复用型高频隔离FDS及其在低压配电台区的应用

目前,柔性多状态开关(FDS)多采用背靠背拓扑,需要工频变压器隔离零序回路,整体占地面积较大且效率偏低。为提升FDS在低压配电台区普及的可行性,本文提出了一种基于高频变压器隔离的功率复用型FDS。首先,介绍了变流器功率复用的基本原理,分析了时分复用方法相比频分复用方法更适合构建高频隔离FDS的原因;其次,阐明了高频隔离FDS的详细拓扑结构,设计了装置各变流器的控制策略,并使用PSCAD仿真初步验证原理;最后,设计算例验证了新型FDS在减少配电台区线损和均衡负载等方面的优势。所提装置与方法为在低压台区配电网中应用FDS提供了新选择。

三电平SPQC统一拓扑与中点电位振荡抑制策略

三电平并联型电能质量调节器(shunt power quality controller,SPQC)可集中治理三相四线制配电系统中多种由谐波电流引发的电能质量问题。三桥臂与四桥臂二极管中点箝位(neutral point clamped,NPC)拓扑作为主流方案得到了广泛应用,但缺乏不同场景下合理选择的结论。提出一种统一拓扑,可用于指导不同拓扑的参数优化,并实现补偿性能的定量比较。三电平结构固有的中点电位振荡问题严重影响装置的硬件安全与补偿效果,对不同分立拓扑分别改进脉宽调制(pulse width modulation,PWM)策略,在每个开关周期时间尺度内最大限度抑制中性点电位振荡,替代了传统控制策略的附加均压环。最后,仿真验证了理论结果与改进策略的有效性。

近悦远来风物新——党的十九大以来重庆市精神文明建设成果撷英

新年的曙光,铺满大地……春风拂,人心暖。"小区变了,街灯亮了,公交车通了,车辆乱停乱放的现象没有了……"家住九龙坡区叠彩西城的拆迁安置户夏嘉训老人喜滋滋地致信市领导,传递文明创建给自己带来的"小确幸"。"不虚此行!热情好客的重庆人直接用封桥的方式让游客拍照打卡。"在网红地千厮门大桥,中外游客发出了共同的感慨。这里是重庆,生长在这里的、抑或是来到这里的人们,正以不同的行为或告白,表达着对这方土地的喜爱……

枇杷果、叶、花相关性状QTL定位分析

以枇杷‘宁海白’ב大房’的130株F1群体为研究对象,利用已构建好的枇杷高密度遗传图谱,对枇杷17个果、叶、花相关性状进行QTL定位以及对关键QTL区间进行候选基因筛选。17个性状共获得153个QTL,其中果横径、果肉厚、种子数、种子质量、果形指数、花序宽、叶片长、叶片宽和叶基形状9个性状定位的QTL贡献率均在25%以上。特别是第4连锁群(LG4:13.500~14.276 cM和23.646~24.804 cM)、第8连锁群(LG8:0~8.851 cM)、第12连锁群(LG12:41.198~45.852 cM和65.246~66.407 cM)以及第15连锁群(LG15:92.921~95.244 cM)这6个区间有6个以上性状的QTL重合,且多个性状的QTL贡献率在35%以上。在第12连锁群(LG12:41.198~45.852cM)和第15连锁群(LG15:92.921~95.244 cM)重合区间挖掘到13个与植物生长发育、细胞分裂、细胞膨大以及植物激素调控相关的候选基因。

白肉枇杷新品种‘粤晖’

‘粤晖’以‘早钟6号’为母本,‘Ullrea’为父本杂交,从F1代群体中通过单株优选育成的白肉枇杷新品种。中熟,成熟期3月中旬—4月中旬。果实长圆形至梨形,大果,平均单果质量52.8 g;果皮黄色,较易剥皮;果肉黄白色,细腻、化渣;可溶性固形物含量11.2%,甜酸适口,品质优良;平均单果种子数3.5个,可食率71.6%。丰产性好,平均产量为9 840 kg·hm^(-2),适宜在广东和福建省枇杷产区种植。

A new alternative approach for investigating acidization dissolution front propagation in fluid-saturated carbonate rocks

The natural phenomenon associated with the chemical dissolution of dissolvable minerals of rocks can be employed to develop innovative technology in mining and oil extracting engineering. This paper presents a new alternative approach for theoretically dealing with chemical dissolution front （CDF） propagation in fluid-saturated carbonate rocks. Note that the CDF is represented by the porosity front in this study. In this new approach, the porosity, pore-fluid velocity and acid concentration are directly used as independent variables. To illustrate how to use the present new approach, an aeidization dissolution system （ADS） consisting of carbonate rocks, which belongs to one of the many general chemical dissolution systems （CDSs）, is taken as an application example. When the acid dissolution capacity （ADC） number （that is defined as the ratio of the volume of the carbonate rock dissolved by an acid to that of the acid） approaches zero, the present new approach can be used to obtain analytical solutions for the stable ADS. However, if the ADC number is a nonzero finite number, then numerical solutions can be only obtained for the ADS, especially when the ADS is in an unstable state. The related theoretical results have demonstrated that： （1） When the ADS is in a stable state and in the case of the ADC number approaching zero, the present new approach is mathematically equivalent to the previous approach, in which the porosity, pore-fluid pressure and acid concentration are used as independent variables. However, when the ADS is in an unstable state, the use of the present new approach leads to a free parameter that needs to be determined by some other ways. （2） The existence of a non-step-type dissolution front within a transient region should at least satisfy that none of the ADC number, injected acid velocity and reciprocal of the dissolution reaction rate is equal to zero in the stable ADS.

A unified theory for sharp dissolution front propagation inchemical dissolution of fluid-saturated porous rocks

This paper presents a unified theory to deal with when, why and how a sharp acidization dissolution front(ADF), which is represented by the porosity distribution curve, can take place in an acidization dissolution system composed of fluid-saturated porous rocks. The theory contains the following main points:(1) A reaction rate of infinity alone can lead to a sharp ADF of the Stefan-type in the acidization dissolution system. This sharp front is unstable when permeability in the downstream region is smaller than that in the upstream region.(2) For a finite reaction rate, when the acid dissolution capacity number approaches zero,the ADF can have a sharp profile of the Stefan-type either on a much smaller time scale or on a much larger time scale than the dissolution time scale. In the former case, the ADF may become unstable on a much larger time scale than the transport time scale, while in the latter case, it may become unstable if the growth rate of a small perturbation is greater than zero.(3) On the dissolution time scale, even if both the reaction rate is finite and the acid dissolution capacity number approaches zero, the profile of an ADF may not be sharp because it is in a transient state. In this case, not only can an ADF change its profile with time, but also its morphology can grow if the growth rate of a small perturbation is greater than zero. Due to the involvement of both the change rate and the growth rate of the ADF profile, it is necessary to conduct a transient linear stability analysis for determining whether or not a time-dependent ADF is stable in the acidization dissolution system.

Transient-state instability analysis of dissolution-timescale reactive infiltration in fluid-saturated porous rocks: Purely mathematical approach

This paper deals with how the purely mathematical approach can be used to solve transient-state instability problems of dissolution-timescale reactive infiltration(DTRI) in fluid-saturated porous rocks. Three key steps involved in such an approach are:(1) to mathematically derive an analytical solution(known as the base solution or conventional solution) for a quasi-steady state problem of the dissolution timescale, which is viewed as a frozen state of the original transient-state instability problem;(2)to mathematically deduce a group of first-order perturbation partial-differential equations(PDEs) for the quasi-steady state problem;(3) to mathematically derive an analytical solution(known as the perturbation solution or unconventional solution) for this group of first-order perturbation PDEs. Because of difficulty in mathematically solving a transient-state instability problem of DTRI in general cases, only a special case, in which some nonlinear coupling between governing PDEs of the problem can be decoupled, is considered to illustrate these three key steps in this study. The related theoretical results demonstrated that the transient chemical dissolution front can become unstable in the DTRI system of large Zh numbers when the long wavelength perturbations are applied to the system. This new finding may lay the theoretical foundation for developing innovative technique to exploit shale gas resources in the deep Earth.

An efficient time-integration method for nonlinear dynamic analysis of solids and structures

This paper presents an efficient time-integration method for obtaining reliable solutions to the second-order nonlinear dynamic problems in structural engineering. This method employs both the backward-acceleration differentiation formula and the trapezoidal rule, resulting in a self-starting, single step, second-order accurate algorithm. With the same computational effort as the trapezoidal rule, the proposed method remains stable in large deformation and long time range solutions even when the trapezoidal rule fails. Meanwhile, the proposed method has the following characteristics: (1) it is applicable to linear as well as general nonlinear analyses; (2) it does not involve additional variables (e.g. Lagrange multipliers) and artificial parameters; (3) it is a single-solver algorithm at the discrete time points with symmetric effective stiffness matrix and effective load vectors; and (4) it is easy to implement in an existing computational software. Some numerical results indicate that the proposed method is a powerful tool with some notable features for practical nonlinear dynamic analyses.

Computational simulation of wave propagation problems in infinite domains

This paper deals with the computational simulation of both scalar wave and vector wave propagation problems in infinite domains. Due to its advantages in simulating complicated geometry and complex material properties, the finite element method is used to simulate the near field of a wave propagation problem involving an infinite domain. To avoid wave reflection and refraction at the common boundary between the near field and the far field of an infinite domain, we have to use some special treatments to this boundary. For a wave radiation problem, a wave absorbing boundary can be applied to the common boundary between the near field and the far field of an infinite domain, while for a wave scattering problem, the dynamic infinite element can be used to propagate the incident wave from the near field to the far field of the infinite domain. For the sake of illustrating how these two different approaches are used to simulate the effect of the far field, a mathematical expression for a wave absorbing boundary of high-order accuracy is derived from a two-dimensional scalar wave radiation problem in an infinite domain, while the detailed mathematical formulation of the dynamic infinite element is derived from a two-dimensional vector wave scattering problem in an infinite domain. Finally, the coupled method of finite elements and dynamic infinite elements is used to investigate the effects of topographical conditions on the free field motion along the surface of a canyon.