随机开关频率PWM（RFPWM）逆变器的研究及仿真

本文中,针对逆变器电气传动的电磁噪音及谐波造成的振动,设计了一种采用随机开关频率PWM（RFPWM）技术的逆变器。通过运用PSIM工具进行了仿真,仿真结果表明逆变器的输出谐波频谱均匀随机分布。因此,通过本文设计的RFPWM方式,可获得较小的可听噪声和机械振动。仿真的结果表明电压的谐波被扩展到宽频带区域内,从而使宽频带噪声较小,且比窄频带噪声干扰小。     

基于模糊随机PWM技术的永磁直线电机性能分析

针对恒定开关频率的变频器产生的窄带高频谐波问题,提出了一种基于模糊随机脉冲位置调制(FRPPM)的方法来降低输出电压频谱中的集中谐波簇,FRPPM方法是在较宽的频率范围内扩展原始的窄带谐波使电压频谱均匀地分散在频带上,从而降低了电机气隙磁场产生的电机震动噪声。通过MATLAB/SIMULINK对永磁直线电机控制系统进行建模仿真,并与传统切换模式进行对比分析。结果表明:变频器输出电压的集中高频谐波在开关频率处将有效降低,且使电压频谱分布更加均匀,进而改善了电机气隙磁场的波形。     

基于电网电压定向的光伏并网逆变器系统研究

针对传统的光伏并网系统逆变控制策略存在控制复杂、谐波含量多的问题,提出了一种基于电网电压定向的光伏并网逆变器直接电流控制方法,给出了以TMS320F2812为主控制器的三相光伏并网逆变器系统的硬件及软件设计。该逆变器直接电流控制方法采用过零检测电路测量电网电压的过零点时刻,得出过零点时刻的电网电压的旋转角度,从而得到逆变器输出电压的幅值和相位;采用SVPWM技术控制IPM的开断,使逆变器输出上述幅值和相位的电压,从而实现单位功率因数并网发电功能。实验结果表明,该逆变器直接电流控制方法简单,逆变器输出电流与电网电压基本保持相同的频率和相位,并网发电功率因数接近于1。     

电流型并网逆变器的模糊滞环控制

为改善滞环控制应用在并网逆变器中会出现系统开关频率不固定的问题,提出一种将模糊控制器与滞环比较器相结合的控制方法。通过对并网逆变器的建模和滞环电流控制原理的分析,可知开关频率与滞环环宽之间的关系。以电网电压及指令电流的偏微分为输入变量建立模糊控制规则,经过一定的模糊运算输出滞环环宽,从而动态地控制环宽达到稳定频率的目的。该方法能有效地降低开关频率,减小电流谐波。仿真和实验结果证明了该方法对稳定滞环开关频率是有效的,尤其是在过零点与顶点处,同时能够改善谐波特性。     

基于矢量线性组合的直接转矩控制系统仿真

针对传统直接转矩控制存在转矩脉动大和开关频率不固定的缺点,该文提出了一种采用矢量线性组合和SVPWM调制的新型直接转矩控制方法,即由空间矢量脉宽调制（SVPWM）技术产生六个基本的和六个线性组合的定子电压空间矢量,根据转矩偏差和磁链偏差优化选择定子电压空间矢量,实现对电机转矩的控制.将该控制方法应用到异步电动机调速系统,通过系统仿真实验验证,该控制方法的输出转矩脉动小、电流谐波低、开关频率固定,调速系统有着良好的动态性能和调速精度.     

非线性负载下逆变器并联系统控制策略研究

微电网并联逆变器接入非线性负载时出现的谐波电流,会引起逆变器输出电压畸变严重.以两逆变器并联运行模型为研究对象,提出一种综合控制策略.首先,在电压外环采用比例积分控制和重复控制串联控制方法的同时,考虑下垂控制所引起的基波频率偏移会进一步恶化输出电压质量,改进重复控制方法,实现在频率变化时对电压谐波的有效抑制.其次,由于SOGI可以抑制输入信号的谐波,将基于SOGI的虚拟复阻抗引入到电流反馈环,抑制谐波电流对虚拟复阻抗影响,有效改善功率均分效果和抑制逆变器间环流.最后,对所提出的综合控制策略进行仿真研究,验证所提控制策略的正确性和可行性.     

矢量变频异步电机的参数辨识技术研究

为提高矢量控制变频调速系统的静、动态性能,提出一种基于变频器自身的异步电机参数辨识新方法,采用SVPWM技术控制逆变器向异步电机施加直流或者交流信号激励,通过检测输出响应,实现对异步电机定子电阻、定子漏感、转子电阻、转子漏感及定转子励磁电感等参数进行辨识。针对输出响应信号存在噪声和谐波的特点,利用离散傅里叶变换(DFT)提取出基波电流、电压的幅值和相位等有效信息。采用基于SVPWM的死区效应时间补偿方法,避免了逆变器开关管的开关延迟、管压降及死区时间对参数辨识的影响。最后,在以TMS320F2808 DSP为控制核心的矢量变频器中采用该方法进行参数辨识实验,实验结果表明该方法的正确性。     

基于SVPWM的感应电机直接转矩控制系统的研究

针对传统的直接转矩控制转矩脉动大、开关频率不恒定等问题,提出了一种基于SVPWM技术的新型直接转矩控制系统,并利用MATLAB/SIMULINK仿真软件建立了系统模型。系统采用PI控制器调节磁链和转矩,可以得到能够准确补偿磁链和转矩的参考电压矢量。逆变器的开关状态由SVPWM控制,可以保持逆变器开关频率恒定。实验结果表明该设计是正确的,并能有效的减小磁链和转矩脉动,保持开关频率固定,改善控制系统的性能。     

降低异步电动机电磁噪声的RSVPWM变频方法

高次谐波产生的电磁噪声是当前高性能PWM逆变器存在的主要问题之一.分析PWM波的功率谱密度可知,固定的开关频率是导致电磁干扰的主要原因.针对这一点,提出了用随机改变开关频率的空间矢量调制方法（即RSVPWM法）消除电磁噪声的方案.在基于DSP的异步机变频调速系统实验平台上,进行了RSVPWM法和传统SVPWM法的对比实验,结果表明,RSVPWM法不仅保证了系统的优良调速性能,而且降低了异步电动机的电磁噪声.     

一种三相四桥臂逆变器的新型控制方案

针对在不平衡或非线性负载条件下,普通的三相三桥臂逆变器无法产生三相对称电压,基于Simulink仿真平台,提出了三相四桥臂逆变器的新型闭环控制设计方案。此方案逆变器的前三桥臂采用空间矢量脉宽调制(SVPWM),第四桥臂采用跟踪前三相电流信号的电流滞环调制(CHBM),相对于传统的四桥臂一体化的SVPWM调制,控制系统设计简单,易于分析。仿真结果表明:与普通逆变器相比,采用本文控制方案的四桥臂逆变器输出的波形更加平滑,不仅增强了系统带不平衡负载的能力,而且改善了逆变系统的效率和总谐波失真(THD)。     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

基于QTE的蒙古文显示机制研究与实现

蒙古语言是中国蒙古族使用的通用语言,由于蒙古文区别于其他文字的书写方式和其自身变形机制等特点,在很多通用的文字处理引擎中都不被支持。在嵌入式产品开发与应用领域中Linux加QTE已经成为流行方式。该文给出了一种在QTE环境上实现基于标准Unicode的蒙古文点阵显示和变形算法, 并自定义了支持蒙古文的QTE组件,扩展了QTE功能,为在Linux加QTE方式的嵌入式体系结构中处理蒙古文提供了一种解决方法。