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161.
In this paper a discrete-time adaptive sliding mode control method is newly developed and applied to the power system stabilization problem. A controllable canonical form of state space realization is constructed using the parameters identified by the on-line recursive least squares method and the system state is estimated from the input/output measurements and the simple state transformations. The identified parameters and the estimated state are then used by the discrete-time sliding mode control, which is suitable for the digital equipment. The most important advantage of the proposed power system stabilizer (PSS) is that it is able to maintain its regulating performance with a slower sampling period than that of the conventional sliding mode PSS because it is developed in a pure discrete-time domain. Another advantage of the proposed PSS is that it needs neither a mathematical model of the power system nor the full-state measurements because they are identified through on-line identifications. Several computer simulations for the linear power system are performed to verify the performance of the proposed PSS. In the computer simulations for various circumstances which are probable in a power system are considered, such as transitions of the active and reactive powers, change of parameters of the synchronous machine, line-to-ground faults and measurement noise. As a result, a new power system stabilizer which can operate in a wide range of operating conditions and can overcome various disturbances and measurement noises is proposed. 相似文献
162.
基于神经网络非线性系统辨识和控制的研究 总被引:12,自引:0,他引:12
本文提出了由静态的前馈网络和稳定的滤波器构成的非线性系统的辨识模型,在神经网络固有的逼近误差存在的情况下,从理论上讨论了神经网络应用于辨识控制过程中系统的稳定性问题,最后研究了在非线性系统的轨迹跟踪过程中增加滑动控制来偿神经网络的逼近误差,从而提高系统跟踪性能。 相似文献
163.
通过密度、可见光光谱、红外吸收光谱、Co-60辐照损伤试验及荧光光谱的测试,研究了PbO-Bi2O3-B2O3-SiO2玻璃系的光学性能与结构.密度最高可达8.464g/cm3其紫外吸收达截止波长随Pb2+及Bi3+含量升高而红移.玻璃熔化温度低达850℃.在PbO-Bi2O3-B2O3系玻璃中加人SiO2可使玻璃结构更致密.室温下该系统玻璃在360nm有一个宽的激发峰,能产生418um及438um两个弱的发射峰.该系统玻璃的结构是由[SiO4]4-、[BO3]3-、[BO4]5-、[PbO4]6-及[BiO6]9-构成.其中部分Pb2+及Bi3+以网络外体进入玻璃. 相似文献
164.
A fundamental research of structural defects induced upon post-growth processing of ZnSe/GaAs epilayers grown on (100) GaAs
was done by identifying defect-related reflections in the transmission electron diffraction (TED) patterns of ZnSe. Structural
artifacts, other than the as-grown defects, on this material system could be excluded according to our results. Four types
of abnormal reflections have been observed in addition to primary reflections. These extra reflections are sensitive to the
post-growth processing of ZnSe epilayers and may arise from various external effects, rather than epitaxy growth, such as
irradiation damage, surface oxidation, and surface contamination. By mapping these reflections at several major zone axes
using TED patterns, we found that the reciprocal lattice for a ZnSe crystal with structural defects consists of two distinct
types of extra reflections associated with irradiation damage. The first type of extra reflections is ±1/3{111} and the other
is ±1/2{111} corresponding to pure-edge and non-edge dislocation loops, respectively. For (100) oriented wafers, the ±1/3{111}
and ±1/2{111} reflections were observed only on two of the four possible 〈111〉 variants (i.e. [111]Zn and [111]Zn)and this phenomenon was attributed to the anisotropy of defect distribution. Extra reflections associated with surface oxidation
and contamination are also observed. The orientation relationships between a surface hexagonal ZnO and a cubic ZnSe film are
[0001]ZnO//[−111]ZnSe, and [01−11]ZnO//[011]ZnSe. The origin, characterization, and elimination of these induced reflections are discussed. With the knowledge about these
extra effects on structural defect formation, we have shown the real microstructure of ZnSe epilayers. 相似文献
165.
本文对激光光束通过望远系统后光束的变化进行了分析,并对6倍望远镜进行了激光损伤和破坏的实验研究,实验结果表明,激光对望远系统的损伤破坏主要是热效应所致,损伤破坏的情况与激光的能量,波长,脉冲宽度和望远系统的结构有关。 相似文献
166.
上海市吴淞工业区大气PM2.5水溶成分的元素分析及细胞毒性研究 总被引:1,自引:0,他引:1
通过ICP-MS测定了上海市吴淞地区大气PM2.5水溶成分金属元素含量,通过四唑盐(MTT)测定细胞存活率,通过超氧化歧化酶(SOD)和丙二醛(MDA)两个指标测定细胞氧化损伤,琼脂糖凝胶电泳测定细胞内DNA损伤,流式细胞仪(Flow cytometry)检测细胞凋亡和周期等实验研究了大气PM2.5水溶成分的细胞毒性.实验结果表明:PM2.5可溶成分中Zn元素含量最高,PM2.5在一定浓度范围内能导致细胞死亡,引起细胞的氧化损伤,影响DNA的复制,阻碍细胞增殖,但没有诱导细胞凋亡.PM2.5中可溶金属离子对细胞毒性表现为联合作用. 相似文献
167.
168.
Marco Dalai Author Vitae 《Automatica》2007,43(8):1418-1425
In this paper we consider the problem of constructing confidence regions for the parameters of nonlinear dynamical systems. The proposed method uses higher order statistics and extends the LSCR (leave-out sign-dominant correlation regions) algorithm for linear systems introduced in Campi and Weyer [2005, Guaranteed non-asymptotic confidence regions in system identification. Automatica 41(10), 1751-1764. Extended version available at 〈http://www.ing.unibs.it/∼campi〉]. The confidence regions contain the true parameter value with a guaranteed probability for any finite number of data points. Moreover, the confidence regions shrink around the true parameter value as the number of data points increases. The usefulness of the proposed approach is illustrated on some simple examples. 相似文献
169.
混凝土破裂过程三维数值模拟及CT验证 总被引:10,自引:1,他引:9
将混凝土简化成由骨料、水泥砂浆及其二者之间的界面层所组成的三相复合材料,建立了混凝土骨料随机分布三维模型,用界面单元多次细分技术进行有限元网格划分,基于弹性损伤本构关系采用双折线损伤演化模型描述混凝土细观各相弹性损伤退化,用弹性模量的折减程度来反映混凝土试件在加载过程中的损伤程度。对混凝土圆柱体试件进行了数值模拟计算,并从混凝土破坏过程图和荷载-位移曲线图两方面比较了数值模拟的破坏过程与CT试验结果,发现试件破坏时裂纹的萌生、扩展过程与CT观测到的过程具有相似性,说明用本文建立的三维数值模型模拟混凝土材料的损伤破坏过程是基本可行的。 相似文献
170.
Development of damage in a 2D woven C/SiC composite under mechanical loading: I. Mechanical characterization 总被引:5,自引:0,他引:5
Gérald Camus Laurent Guillaumat Stéphane Baste 《Composites Science and Technology》1996,56(12):1363-1372
An investigation has been undertaken to determine the damage mechanisms and the associated mechanical response of a 2D reinforced composite of carbon fibers in an SiC CVI-processed matrix subjected to uniaxial tensile and compressive loadings at room temperature. Under tension loading, an extended non-linear stress/strain response was evidenced and related to a multi-stage development of damage involving transverse matrix microcracking, bundle/matrix and inter-bundle debonding as well as thermal residual stress release. This tensile behavior proved to be damageable-elastic with respect to a fictitious thermalstress-free origin of the stress/strain axis lying in the compression domain. In compression, after an initial stage involving closure of the thermal microcracks present from processing, the composite displayed a linear-elastic behavior until failure. The extent of damage over the material was characterized quantitatively at the microscale by the decrease of the average transverse microcrack spacing and at the macroscale by the decrease of both the longitudinal Young's modulus and the in-plane Poisson's ratio. 相似文献