Improved voltage control strategy for photovoltaic grid-connected system based on double-layer coordination control

An improved automatic voltage coordination control strategy(AVCCS) based on automatic voltage control(AVC) and battery energy storage control(BESC) is proposed for photovoltaic grid-connected system(PVGS) to mitigate the voltage fluctuations caused by environmental disturbances.Only AVC is used when small environmental disturbances happen,while BESC is incorporated with AVC to restrain the voltage fluctuations when large disturbances happen.An adjustable parameter determining the allowed amplitudes of voltage fluctuations is introduced to realize the above switching process.A benchmark low voltage distribution system including PVGS is established by using the commercial software DIg SILENT.Simulation results show that the voltage under AVCCS satisfies the IEEE Standard 1547,and the installed battery capacity is also reduced.Meanwhile,the battery’s service life is extended by avoiding frequent charges/discharges in the control process.     

评价学生成绩的一种方法

将模糊控制理论的加权平均决策法,应用到学生成绩综合评定中,得出每一个学生的决策量,决策量更科学合理地反映出学生的学习成绩。     

企业创业导向与组织绩效关系的元分析

企业创业导向与组织绩效关系的研究是目前公司创业领域中最受关注的议题,而不同研究发现创业导向对组织绩效的作用并不一致。本文通过检索学术数据库之重要期刊中从1983年到2009年(也包括一篇2010年的)关于企业创业导向与组织绩效关系的研究文献,在对符合要求的30篇文献的基础上,对二者之间的关系进行了元分析,结果表明二者之间存在显著的关系,同时探索了可能调节二者之间关系的变量,并提出未来研究的方向。     

C语言指针教学思路

指针是C语言的重要数据类型,也是C语言的精华所在。正确而灵活地运用指针,可以编制出简练紧凑、功能强而执行效率高的程序。本文将从以下几方面介绍在教学中如何让学生走出指针学习的误区。。     

知识存取：内涵、特征及其量素

论述图书馆的本质特征是知识存取。知识存取具有系统性、动态性、增值性特征。知识存量是知识增长的静态表征,是系统在特定时点的知识储备水平,反映知识的组织状况和供应能力;知识取量是知识的动态表征,是系统在特定时段的知识流动总量,反映知识的扩散速度和水平;知识质量是知识内在质的规定性,是系统知识现实与潜在价值的总和,反映知识的直接效用和耐用程度;知识变量是知识在存取中的变化值,是系统知识的变化总量,反映知识在存取中转化的程度。知识存取,正是要努力地实现客观知识朝着理想的增函数曲线方向变化。     

Anticipatory postural adjustments during cutting manoeuvres in football and their consequences for knee injury risk

Abstract

Anticipatory postural adjustments (APAs), i.e. preparatory positioning of the head, the trunk and the foot, are essential to initiate cutting manoeuvres during football games. The aim of the present study was to determine how APA strategies during cutting manoeuvres are influenced by a reduction of the time available to prepare the movement.

Thirteen football players performed different cutting tasks, with directions of cutting either known prior to the task or indicated by a light signal occurring 850, 600 or 500 ms before ground contact.

With less time available to prepare the cutting manoeuvre, the head was less orientated towards the cutting direction (P = 0.033) and the trunk was even more rotated in the opposite direction (P = 0.002), while the foot placement was not significantly influenced. Moreover, the induced higher lateral trunk flexion correlated with the increased knee abduction moment (r = 0.41; P = 0.009).

Increasing lateral trunk flexion is the main strategy used to successfully perform a cutting manoeuvre when less time is available to prepare the movement. However, higher lateral trunk flexion was associated with an increased knee abduction moment and therefore an increased knee injury risk. Reducing lateral trunk flexion during cutting manoeuvres should be part of training programs seeking the optimisation of APAs.     

一种不确定性机器人的变结构控制

考虑机器人的不确定项,首先利用反馈控制技术,把基于拉格朗日方程的多关节机器人动力学模型转化成一线性状态方程.然后基于此状态方程,运用变结构控制思想,并结合李雅普诺夫函数设计出一种新的机器人鲁棒控制器,这种控制器能够保证机器人机械臂的跟踪误差渐近收敛到零点.无论是理论推导还是实验仿真都说明了所设计的控制器有着很好的鲁棒性和有效性.     

转化思想在复变函数解题中的应用

从复变函数中的复函数的极限、复函数的积分两个方面入手,阐述了转化思想在复变函数解题中的重要应用.     

一类函数方程的振动准则

主要研究了高阶非线性变系数时滞函数方程的解的振动性。采用反证法和迭代法,得到该方程解振动的若干个充分条件,并且还以实例对结果进行了说明和验证。     

模糊随机变量的收敛性

主要研究了模糊随机变量的收敛性，总结出了几乎一致收敛和依均值收敛的概念，并讨论了各收敛的数学性质和收敛之间的关系．