CPLD在中压变频控制器中的应用与研究

SPWM（弦脉宽调制）多电平叠加变频技术计算复杂，输出脉冲路数多，系统实时性要求高。采用单片DSP作为其控制器核心器件，不能满足控制器实时性要求；多片DSP协同工作，需要交换总线控制权而消耗核心DSP时间资源．并且也不能满足脉冲输出端口数量。DSP与CPLD两者协调工作，很好地解决了这些问题，另外该种技术方案开发周期短，生产成本低。本文正是以此为背景展开研究，详细论述CPLD功能总体设计、硬件选型设计与脉冲形成CPLD软件开发流程，并且给出了系统运行波形图。     

级联式多电平逆变器三角载波移相控制的研究

级联式多电平逆变器因其具有众多的优点,在高压变频调速领域中得到广泛应用.三角载波移相控制是级联式多电平逆变器常用的控制算法,在介绍级联式多电平逆变器的基础上,详细分析了三角载波移相控制方法的原理,在Matlab/Simulink仿真环境下对级联式多电平逆变器进行了仿真,并给出了TMS320C2812 DSP实现逆变系统的数字化控制方案,利用FPGA与DSP结合的方式实现多路SPWM脉冲对功率单元级联式逆变器进行控制.仿真和实验结果论证了FPGA与主控制器结合实时产生多路脉冲的可行性,验证了基于_二角载波水平移相级联式多电平逆变器具有优良的输出特性.     

有源箝位型三电平变频器功率器件损耗分析

针对传统中点箝位型三电平变频器运行过程中存在功率器件损耗分布不均匀问题,介绍了有源箝位型三电平拓扑的工作原理和基本调制策略,分析了有源箝位型三电平变频器的损耗特性。有源箝位型三电平拓扑使用双向功率器件取代传统中点箝位型三电平中的箝位二极管,通过选择恰当的零电压状态组合,可实现功率器件损耗均衡的目的。仿真结果表明,在各种典型工作状态下,相比于中点箝位型三电平拓扑,有源箝位型拓扑可更好地平衡功率器件内外管损耗,提升了变频器容量。     

用高速DSP在频域上实现LFM信号的实时脉冲压缩

时宽带宽(TB)积较小的线性调频(LFM)信号的脉冲压缩可用A100等器件构成的横向滤波器实现;对于TB积较大的LFM信号,在时域上对其进行脉冲压缩所需的计算量和硬件量太大。本文介绍用TMS320C6201DSP在频域上实现大TB积LFM信号的实时脉冲压缩,内容包括海明加权、循环卷积、长数据分段迭加、软件流程图和硬件框图。实验结果表明,当雷达重复周期为300Hz时,对TB积为320的LFM信号进行脉冲压缩后最大副瓣电平为-42.3分贝。     

大功率三电平防爆变频器散热分析及计算

针对大功率三电平防爆变频器工作时产生的大量损耗会导致温升,从而影响变频器性能的问题,分析了常见的电力电子器件散热方式的原理及优缺点,指出热管结合强制冷风的散热方式较适用于对煤矿井下大功率三电平防爆变频器进行散热;对采用热管散热方式的大功率防爆变频器的IGBT、二极管、快速恢复二极管等主要功率器件的损耗和温升进行了分析,得出了功率器件的温升计算公式。实验结果表明,根据功率器件温升公式计算所得结果的误差在工程允许范围内,证明该公式具有一定的可行性和准确性。     

基于F28xDSP中PWM模块的励磁调节器移相脉冲放大电路

利用F28xDSP中的PWM模块,产生双窄移相触发脉冲,再经脉冲放大电路,将DSP输出的TTL电平转换为能够驱动可控硅的电平。同时,为了进一步减少损耗和提高晶闸管导通可靠性,还讨论了通过增加HSP50415电路,再结合软件实现中频调制双窄脉冲来驱动晶闸管。     

基于DSP的异步串行通讯系统设计

利用DSP器件-TMS320C5416以及异步串行通讯器件-ST16C654实现了系统间多路数据的异步串行通讯,为系统中存在的各个分系统提供信息传输纽带.TMS320C5416的高速运算速度以及庞大的数据吞吐量为系统提供稳定的运算平台,ST16C554为系统扩展多路异步串行通讯端口,外部FLASH器件为系统程序提供存储空间,而电平转换芯片以及电源转换芯片则为系统提供外部接口需要的电平格式以及芯片工作所需要的各种电源幅值.     

基于DSP任意路PWM波的简易生成方法

脉冲宽度调制(PWM)技术在许多领域有着广泛的应用,针对多电平变换[1]多PWM信号的问题,提出了一种基于DSP核的多路PWM发生器的简易生成方法,利用格雷码[2]递推法(The recursive method)即可方便地生成任意路PWM波。文章介绍了利用美国德州仪器(TI)公司生产的TMS320F2812数字信号处理器,产生任意路带死区互补的PWM波形,实验结果表明了该设计方法的简洁性和实用性。     

基于PROFIBUS-PA总线接口的智能变频器

文章采用模块化设计并实现了一个带PROFIBUS-PA通信接口的智能变频器,介绍了该变频器的总体结构、主要部分电路原理和软件设计等。该变频器以DSP芯片(TMS320F240)作为变频部分的控制核心,并使用了专用通信接口芯片SPC4和SIM1构成PROFIBUS-PA总线中的一个智能从站,主开关器件采用功率模块PM100RSA120作为逆变器,从而可以准确判断电机的转速、位置和转动方向。     

红外无线局域网PPM接收机的DSP实现

光脉冲位置调制(PPM)通信具有光发射平均功率低峰值功率高的优点,在室内红外无线局域网得到应用。文中介绍一种建立在DSP器件(TMS320C30)上的PPM全数字接收机的结构和工作原理。     

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。     

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。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).