基于改进混合粒子群优化的特定谐波消除脉宽调制策略

针对传统迭代法求解特定谐波消除脉宽调制策略(SHEPWM)开关角方程组需要合适的初值和难收敛的问题,提出一种改进的混合粒子群优化(HPSO)算法对其进行求解.该算法对粒子群(PSO)算法的权重系数和学习因子进行了改进,并且提出了一种温度系数线性递减的模拟退火(SA)算法与粒子群算法结合,有效弥补了传统粒子群(CPSO)算法求解开关角收敛速度慢和精度低的缺点.仿真分析表明,该算法消除了对初值的依赖,提升了算法寻优的能力,从而提高了求解速度与精度,并且通过实验验证了该算法的可行性.     

大功率电力电子装置的混合实时仿真

为实现大功率电力电子装置特性的全面物理测试,将装置的动态过程划分为装置级电磁暂态过程、器件级开关暂态过程和热动态过程,并对这3个动态过程进行实时交互计算.基于分段插值拟合方法实现了开关暂态实时化功能模型,并在此基础上实现混合实时数字仿真平台.通过一台±50 Mvar静止无功发生器装置的仿真应用实例,说明所提出的混合实时数字仿真方法可以事先对电力电子装置的控制和保护系统进行全面有效的物理测试验证.     

基于电压源变频器的异步电机定子电阻辨识方法研究

获得准确的电机参数是实现异步电机矢量控制、直接转矩控制、逆解耦控制等高性能控制策略的关键,尤其定子电阻误差对定子磁链观测精度有直接的影响.本文分析了传统基于变频器的异步电机定子电阻参数辨识存在问题,并提出了一种既可以消除电力开关器件通态压降影响又解决高频谐波干扰问题的定子电阻辨识方法.设计了跟踪-微分器从高频干扰电流信号中提取直流电流.搭建了仿真测试平台,测试了多组实验数据,构造数据矩阵,并采用最小二乘法估计待辨识的定子电阻,仿真结果验证了该方法具有很强的抗干扰能力及高的辨识精度.     

三相四线制系统3D-SVPWM调制策略优化设计

在深入分析传统三维空间矢量脉宽调制(3D-SVPWM)算法的基础上,证明传统调制算法在运算过程中是可以简化的,并由此对传统调制算法进行改进,提出优化的3DSVPWM调制算法.采用所提出的优化3D-SVPWM调制算法,可以在保证系统效果和性能的前提下对传统调制算法进行大幅简化,有效降低调制算法的复杂度和计算量,提高调制算法的稳定性和实时性,减轻系统的软件负荷,为系统控制算法的改良和升级提供更多的可操作空间.通过在三相四线制电容中分式有源电力滤波器中的仿真和实验,验证了所提出算法的可行性与优越性.     

仿奥米亚棕蝇的小型短波天线阵测向算法

根据奥米亚棕蝇(Ormia ochracea)的耦合听觉系统放大两耳信号相位差的机制,提出将奥米亚棕蝇耦合听觉系统运用于小型天线阵列的测向中.通过调整天线的导向矢量,放大包含来波信号到达角信息的不同通道接收信号间的相位差,再利用多重信号分类(MUSIC)算法进行测向.利用垂直放置的二元单极子交叉环阵列进行仿真实验,结果表明:利用奥米亚棕蝇耦合系统的MUSIC算法估角具有更高的估角精度,10 dB信噪比条件下估角均方根误差相对传统MUSIC算法估角降低了 2°,估角精度提升了约55％,验证了该方法应用于小型天线阵列测向的可行性.     

基于改进RRT的无人机电力杆塔巡检路径规划

为了达到无人机在电力输电线路环境中能够进行有效的路径规划以及轨迹跟踪的目的,立足于RRT(Rapidly Exploring Random Trees)算法,提出一种在电力输电线路中适用于无人机的路径规划算法．该算法在融合无人机的动力学特性,及RRT扩展的随机性的基础上,通过设计最大航向角以及路径高度的约束,使得规划的路径在高度方向上向目标点渐进逼近,并能克服传统RRT在狭窄空间规划失败的问题.算法在ROS(Robot Operating System)-Gazebo环境中进行了仿真试验,验证了该算法在电力输电线路环境下的实用性.     

晶闸管和IGBT混合的三相电机两相变频控制策略

现有三相交直交变频电路中大多使用IGBT作为电力电子器件,为了进一步降低低压大容量变频器设备成本,减少IGBT的使用,提出了一种晶闸管和IGBT混合的三相电机两相变频电路结构及四开关八电压矢量直接转矩控制策略.首先分析了利用IGBT辅助晶闸管关断的三相电机两相变频电路结构,并分析了不同开关状态下的瞬时电路工作原理,给出三相四开关拓扑下的八电压矢量生成方法;其次提出四开关八矢量异步电机直接转矩控制策略,并给出扇区划分、电压矢量选择和电压矢量伏秒生成原理;最后通过仿真实验验证所提策略的正确性和可行性.仿真结果验证了上述电路结构和控制方法的有效性.     

应用整数小波变换的LZ77电力数据压缩算法

针对电力系统采样数据量大,传输、存储困难等问题,根据采样数据特点,整数小波变换理论以及LZ系列压缩算法,提出应用整数小波变换的LZ77电力数据压缩算法.该算法针对电力系统数据周期性的特点,选择合适的小波基,依据其多分辨率分析特性,将电力数据信号变换到小波域,使信号分解为低频分量和高频分量.对具有重要价值的低频信息使用LZ77压缩算法进行无损压缩,对高频分量进行阈值量化处理.通过仿真测试,获得了10.76%的压缩比和2.078%的重构误差,证实该算法是一种有效的实时数据压缩方法.     

开关磁阻电动机转矩算法研究

针对开关磁阻电动机在传统控制方式下转矩出现严重波动的问题,提出了控制开关磁阻电动机的直接转矩算法,通过查询开关表选取合适的电压矢量来控制磁链大小和方向,把转矩作为直接控制量。首先,从直接转矩算法理论出发,基于Matlab/Simulink平台分别设计了直接转矩控制和电流斩波控制下的系统仿真模型;其次,在开关磁阻电动机模型和电动机负载一致的情况下,将直接转矩算法仿真结果与电流斩波算法比较;最后,通过硬件实验平台验证直接转矩算法的可行性。该研究表明,直接转矩控制下转矩脉动可以得到良好的抑制,拓宽了开关磁阻电动机的应用领域。     

一种基于状态机的毛刺信号滤波方法

提出并实践了一种状态机的实时滤波方法,并成功应用于某军用车辆速度检测. 该方法以CPLD(FPGA)作为硬件,在高频时钟驱动下检测信号中瞬态脉冲宽度,滤除宽度短的脉冲,输出宽脉冲,从而实现脉冲干扰滤波功能. 阐述了该方法的原理和状态机实现方法,分析了该方法的滤波特性,并通过仿真计算其在方波毛刺信号上的应用,论证了该方法的可行性以及滤波宽度变化对该方法精度的影响.      

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that