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光伏电站高比例接入电网造成电力系统结构持续性改变,导致电网可调节资源存量不断下降,抵御故障扰动的能力减弱,电网频率越限风险增加.为提高光伏电站快速频率响应能力,本文根据现有新能源调频政策,设计了光伏逆变器有功-频率下垂特性,提出了基于改进二阶广义积分锁频器的光伏逆变器快速频率响应控制策略,使光伏逆变器具备主动调频的功能.采用改进二阶广义积分锁频器快速检测系统频率,并将频率偏差直接反馈给光伏逆变器控制系统,克服了传统锁相环在电网频率突变时相位偏差大、时延等问题.仿真和实验证明了光伏逆变器快速频率响应控制的正确性与可行性. 相似文献
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西江流域由于大量兴建堤防工程导致洪水归槽,改变了原天然河道的洪水槽蓄关系,使得用于防洪规划和洪水灾害风险评估的洪水序列失去了一致性。目前洪水归槽问题研究主要集中在出槽洪水的归槽还原计算方面,对于干支流洪水与区间洪水的遭遇考虑不足,对洪水发生变异的成因及非一致性洪水的频率计算方法也缺乏系统性的研究。本文提出基于小波分析的非一致性洪水频率计算方法,并在西江梧州站作了实例验证。该方法首先利用小波分析将非一致性洪水序列分解成确定性趋势成分和随机性成分;再采用非线性函数(如幂函数、对数函数、指数函数、多项式函数等)对趋势成分进行拟合,得到非一致性洪水序列在时间域上的确定性规律;采用P-Ⅲ型频率曲线对随机性成分进行频率分布拟合,得到洪水序列在频率域上的随机性规律;采用分布合成法对确定性的预测值和随机性的设计值进行合成计算,再采用传统的一致性频率计算方法推求合成序列的频率分布,据此可以得到过去、现状、未来不同时期的洪水频率分布规律,从而可以推求变化环境下河道断面的洪水频率分布,为防洪规划和洪水灾害风险评估提供设计依据。 相似文献
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同步控制逆变电源并网预同步过程分析 总被引:1,自引:1,他引:0
在下垂特性的基础上,通过引入虚拟调速器和虚拟励磁器等概念,赋予了逆变电源频率与电压惯性保持特性,使其动态特性类似于同步发电机。研究了非理想并网合闸条件下,下垂控制同步逆变电源和虚拟同步发电机控制逆变电源并入电网的预同步动态过程。在分析逆变电源并网预同步过程中,为了突出比较两种逆变电源的动态特性,考虑电网的惯量,可以将逆变电源并入同步发电机带负荷系统。在MATLAB/Simulink仿真环境中,对无惯量和有惯量同步电源与微电网在并网动态过程中频率和电压变化进行了对比分析。研究表明,基于下垂控制的同步电源在并网预同步动态过程中,其频率和电压出现突变,变化率较大,而基于虚拟同步发电机控制的逆变电源,其频率和电压不出现突变,具有较平缓的变化幅度。 相似文献
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针对风速序列非平稳变化的特性,首先通过经验模态分解(empirical mode decomposition,EMD)将原始风速序列分解为一系列较为平稳的子序列,再使用支持向量回归(support vector regression,SVR)模型分别对每一个子序列进行预测,为了克服SVR模型盲目选取学习参数的弊端,在和声搜索优化算法中加入了进化理论中优胜劣汰的思想,提出采用进化和声搜索(evolutional harmony search,EHS)算法对每一个SVR模型进行参数寻优。实例研究表明,EHS算法全局搜索能力强,收敛速度快,提出的EHS.EMD—SVR方法能有效提高短期风速预测的准确性。 相似文献
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用于靶向热疗实验的交变磁场系统研制 总被引:2,自引:0,他引:2
本文构建了用于磁颗粒靶向热疗的实验平台并进行了磁小体加热实验.在分析实验要求的基础上,文中首先提出了高频磁场发生装置的设计方案,设计制作了 C 型磁体,搭建了频率和幅值可调的高频激励源.随后利用自制磁场测量探头对各频率点的磁场强度及其分布均匀性进行测量,对该实验平台的性能指标进行了初步评估.最后通过对含有趋磁细菌AMB-1的磁小体和磁流体进行加热实验,证明了磁小体具有较好的产热率和加热效果,为进一步的实验研究打下了基础. 相似文献
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基于物理模型开关磁阻电机定子模态和固有频率的研究 总被引:21,自引:5,他引:21
吴建华 《中国电机工程学报》2004,24(8):109-114
准确计算定子模态和固有频率是降低电机噪声和振动的基础。该文基于开关磁阻电机(SR电机)物理模型,利用3维有限元软件,全面研究了定子模态和固有频率,系统分析了绕组、端盖和安装对定子模态和固有频率的影响。研究表明,对小功率SR电机,2阶模态对噪声和振动的贡献最大。定子绕组对固有频率的影响非常严重,弹性模数远低于实心铜材,绕组不宜采用质量计入磁极或铁心的方式处理。端盖、底脚安装均导致定子固有频率明显升高。最后讨论了2维有限元模型与3维有限元模型计算结果的差异。计算结果与试验结果进行了比较验证。 相似文献
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《International Journal of Electrical Power & Energy Systems》2013,45(1):672-679
This paper presents a novel approach based on cuckoo search (CS) which is applied for optimal distributed generation (DG) allocation to improve voltage profile and reduce power loss of the distribution network. The voltage profile which is the main criterion for power quality improvement is indicated by two indices: voltage deviations from the target value which must be minimized and voltage variations from the initial network without DG which must be maximized. The CS was inspired by the obligate brood parasitism of some cuckoo species by putting their eggs in the nests of other species. Some host birds can engage direct contest with the infringing cuckoos. For example, if a host bird detects the eggs are not their own, it will either throw these alien eggs away. The CS has been compared with other evolutionary algorithms such as genetic algorithm (GA) and particle swarm optimization (PSO) and different cases have been investigated for indicating the applicability of the proposed algorithm. The results indicate the better performance of CS compared with other methods due to the fewer parameters which must be well-tuned in this method. In addition, in this method the convergence rate is not sensitive to the parameters used, so the fine adjustment is not needed for any given problems. 相似文献
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eDNA指从环境样品中提取到的一切DNA的总和。eDNA技术是通过对eDNA的鉴别来对环境中生物的种类、群落结构及生活习性等进行定性或定量分析的技术。它是一种具有经济高效、灵敏度高、对生态系统干扰低等优势的监测分析新技术。本文在叙述eDNA技术的概念、技术流程、分析方法的基础上,主要综述了该技术在入侵及珍稀濒危物种的监测、生物量估计、生物多样性的调查、水质和水污染评价及河流健康评价中的研究现状及应用,并总结了该技术相较于传统手段的优势。最后提出了eDNA技术目前为止存在的一些问题及未来的主要研究方向。 相似文献
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随着气候变化、人类活动影响的加剧,水文序列一致性条件遭到破坏。本文选择下垫面变化剧烈的西大洋水库控制流域为研究区域,采用水文变异诊断系统,分析其年最大洪峰流量序列的变化趋势及变异点,确定序列变异形式;根据非一致性水文序列频率分析方法,分别得到过去条件下、现在条件下的洪峰流量序列以及相应频率的设计值;以西大洋水库校核洪水位为极限防洪风险控制指标,采用频率分析法,分别计算出过去条件下极限防洪风险率为0.00769%,现在条件下极限风险率为0.00508%。显然,无论是过去还是现在条件下,复核后的西大洋水库的极限防洪风险率均小于现有的万年一遇校核标准(0.01%),计算结果可以为西大洋水库实行动态汛限水位控制,充分利用汛期洪水资源,提高水库的综合效益等方面提供理论指导。 相似文献
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Pedro Vicente Jover Rodríguez Anouar Belahcen Antero Arkkio Antti Laiho José A. Antonino-Daviu 《Electrical Engineering (Archiv fur Elektrotechnik)》2008,90(3):209-218
A method for determining the signatures of dynamic eccentricity in the airgap force distribution and vibration pattern of
induction machine is presented. The radial electromagnetic force distribution along the airgap, which is the main source of
vibration, is calculated and developed into a double Fourier series in space and time. Finite element simulations of faulty
and healthy machines are performed. They show that the electromagnetic force distribution is a sensible parameter to the changes
in the machine condition. The computations show the existence of low frequency and low order force distributions, which can
be used as identifiable signatures of the motor condition by measuring the corresponding low order vibration components. These
findings are supported by vibration measurements and modal testing. The low frequency components offer an alternative way
to the monitoring of slot passing frequencies, bringing new components that allow to discriminate between dynamic eccentricity
and rotor mechanical unbalance. The method also revealed a non linear relationship between loading, stress waves and vibration
during dynamic eccentricity. 相似文献
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Thomas MA Lange T Velan SS Nagarajan R Raman S Gomez A Margolis D Swart S Raylman RR Schulte RF Boesiger P 《Magma (New York, N.Y.)》2008,21(6):443-458
Objectives A major goal of this article is to summarize the current status of evaluating prostate metabolites non-invasively using spatially
resolved two-dimensional (2D) MR Spectroscopy (MRS).
Materials and Methods Due to various technical challenges, the spatially resolved versions of 2D MRS techniques are currently going through the
developmental stage. During the last decade, four different versions of 2D MRS sequences have been successfully implemented
on 3T and 1.5T MRI scanners manufactured by three different vendors. These sequences include half and maximum echo sampled
J-resolved spectroscopy (JPRESS), S-PRESS and L-COSY, which are single volume localizing sequences, and the multi-voxel based
JPRESS sequence.
Results Even though greater than 1ml voxels have been used, preliminary evaluations of 2D JPRESS, S-PRESS and L-COSY sequences have
demonstrated unambiguous detection of citrate, creatine, choline, spermine and more metabolites in human prostates. ProFIT-based
quantitation of JPRESS and L-COSY data clearly shows the superiority of 2D MRS over conventional one-dimensional (1D) MRS
and more than six metabolites have been successfully quantified. These sequences have been evaluated in a small group of prostate
pathologies and pilot investigations using these sequences show promising results in prostate pathologies.
Conclusion Implementation of the state-of-the-art 2D MRS techniques and preliminary evaluation in prostate pathologies are discussed
in this review. Even though these techniques are going through developmental and early testing phases, it is evident that
2D MRS can be easily added on to any clinical Magnetic Resonance Imaging (MRI) protocol to non-invasively record the biochemical
contents of the prostate. 相似文献
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电机的模态是分析振动的基础,由固有频率、振型和阻尼比决定。当电机工作时的激振频率与某一阶的固有频率相同或者相近时,会产生共振,导致电机剧烈振动,影响其正常运转。在对应用于航空电反推系统的双通道永磁同步电机PMSM进行三维建模之后,将三维模型送入ANSYS Workbench,在ANSYS工作平台上进行电机模态、响应谱分析与冲击响应的仿真。给出了该电机的前6阶次的固有频率和振型,以及在外加响应谱下的电机等效应力与在瞬态冲击下的电机机械结构上的应力分布。 相似文献