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1.
大型电力高压传输系统中,电力的运送主要采用高压供电方式,由于电压的不稳定性产生高压断续电流,需要进行整流控制提高电力系统运行的稳定性。传统方法采用电感耦合逆变控制方法,受到负载功耗的不确定因素的影响,在高压断续电流下的整流控制效果不好。提出一种基于电网功耗检测和最大功率跟踪的高压断续电流下的死区整流同步控制算法。进行了高压断续电流下的电力传输系统模型构建,然后设计电网功耗检测算法,加入死区作用逆变控制技术实现电力传输的最大功率跟踪,以高压断续电流下的电力传输系统AGC负荷为控制输入,引入自适应抗干扰项,得到前馈–反馈协调控制律,计算高压断续电流下的扰动响应,实现高压断续电流下的死区整流同步控制算法改进。采用Matlab Simulink进行仿真,实验表明,采用该算法能有效提高高压断续电流下的死区整流同步控制的性能,减小了电压波动,提高输出电压和电流的稳定性。  相似文献   

2.
针对永磁同步电机的矢量控制中励磁电流和转矩电流交叉耦合问题,采用前馈电压补偿的解耦控制策略。设计基于电流环PI调节器的差值整定电机参数模型,精确得出前馈电压补偿项,实现励磁电流和转矩电流在动态中的解耦控制,提高了电流的控制性能。仿真和实验结果验证方案的可行性。  相似文献   

3.
工业加工控制过程中,因为控制环境和控制参数非线性干扰作用的影响,导致控制死区,出现控制失稳问题发生。传统方法采用PID变结构控制算法进行工业加工的过程控制,控制性能受到环境干扰影响较大,控制死区幅度较大。提出一种改进的基于PLC和模糊扰动的加工过程防死区控制方法,基于PLC逻辑控制芯片,设计工业加工控制硬件系统,设计控制滑模面,构建控制环境和控制参数非线性干扰的微分方程,采用正态相关状态特征提取方法,基于PLC可编程逻辑模糊扰动控制,实现加工过程的扰动对数补偿防死区控制算法改进。仿真结果表明,采用该控制系统,具有较大的线性控制区间,减少过程扰动和死区幅度,提高了工业加工过程的稳定性和鲁棒性。  相似文献   

4.
提出一种采用永磁电机作风力发电机实现最大功率输出的控制系统。通过控制发电机转速,使风力机按照最大功率点跟踪方式运行。在考虑电机损耗和变频器容量的前提下,通过最优定子电流矢量控制使发电机输出最大功率。  相似文献   

5.
为达到对永磁同步电动机更好的控制性能,采用矢量控制并采用一定控制算法,分析永磁同步电动机的不同坐标的数学模型及空间矢量的原理。建立Matlab/Simulink的永磁同步电动机速度、电流双闭环仿真模型,重点分析空间矢量脉宽调制(SVPWM)基本实现方法。采用SVPWM控制永磁同步电动机响应速度快,运行稳定,并可验证其他控制算法,为系统整体设计提供理论思路及设计基础。  相似文献   

6.
以变速恒频风力发电系统为研究对象,依据发电机数学模型和交流电机矢量变换控制原理,设计了交流励磁变速恒频(VSCF)发电机定子磁链定向的矢量变换控制系统,对转子侧变换器建立外环定功率控制内环定电流控制的双闭环控制结构,实现双馈发电机定子有功P和无功Q的解耦控制,从而获得最大风能捕获的高效发电运行。  相似文献   

7.
对数字热成像的噪点信息矢量量化是实现图像去噪,提高图像识别能力的关键技术。传统方法中对数字热成像中噪点信息矢量量化算法采用LBG算法,当图像出现灰色关联度噪点时,量化算法的抗噪性能不好。提出一种基于强边缘保留和误差补偿编码的数字热成像中噪点信息矢量量化算法。用量化误差补偿法对量化的热成像进行补偿,消除当前图像块的瑕疵特征点,提高误差补偿编码处理精度。仿真表明,本算法对数字热成像噪点信息的矢量量化效果较好,去噪性能优越,进行矢量量化处理后,实现噪点去除,PSNR值较传统方法都有明显提高,提高对图像目标的识别性能,较传统方法优越。  相似文献   

8.
隋洪毅 《科技通报》2014,(4):158-160
传统的反电势转子超导永磁电机模型在对电流导数运算时需要进行偏微分计算,导致系统高频噪声扩大,产生电流畸变。利用转子磁场坐标系的高频抑制性能,提出一种改进的转子超导永磁电机模型,新模型在转子磁场坐标系中利用仿射变换方法替代传统的微分运算计算电流矢量导数,对高频噪声能有效抑制,在传统的反电势电机模型上增加一个跟踪误差补偿项,补偿电流畸变不确定性。设计出转子磁场坐标下的超导永磁电机预测控制系统模型结构。仿真实验表明,改进模型能有效对电机模型的电流畸变进行抑制,降低转矩波动,电流控制误差降低50%,电流轨迹波动呈现规则圆形,改进方法能有效地将电流畸变控制在理想范围之内。  相似文献   

9.
多通道永磁同步发电机绕组之间具有强耦合特点,以及负载时电枢反应效果非线性叠加效果难以计算的问题。本文利用Ansys MaxweⅡ软件对一款三通道永磁同步发电机进行有限元仿真研究与性能分析,针对多通道同时带负载输出功率不够和输出功率不对称等问题提出改进措施。将改进后样机的试验值与仿真值对比,误差小于2%,验证了该仿真分析方法的有效性。  相似文献   

10.
对网络漏洞进行有效检测,保障网络安全,传统方法采用攻击相位重组方法进行网络漏洞链路分析和检测,由于复杂随机阵列网络的端口的复杂性,导致漏洞检测准确性不好。提出一种基于主频分离激励分析的网络漏洞检测算法。构建了网络漏洞分布的阵列结构模型,对漏洞阵列的交换数据进行信号分析和融合处理,以此为数据依据采用主频分离激励分析方法进行漏洞检测算法改进,仿真结果表明,该算法能有效提高对网络漏洞的检测和数据跟踪性能,提高网络安全防御能力。  相似文献   

11.
Aresearch group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol--a chemical found in the skins of red grapes and in red wine--can improve the sensitivity of mice to the hormone insulin, according to a report in the October,2007 issue of Cell Metabolism. As insulin resistance is often characterized as the most critical factor contributing to the development of Type 2 diabetes, the findings“provide a potential new therapeutic approach for preventing or treating” both conditions, the researchers said.  相似文献   

12.
This study examined how students who had no prior experience with videoconferencing would react to the use of videoconferencing as an instructional medium. Students enrolled in seven different courses completed a questionnaire at the beginning of the semester and again at the end of the semester. Students at the origination and remote sites did not differ in their reactions toward videoconferencing but there was a significant difference for gender. Women reacted less favorably to videoconferencing. Compared to the beginning of the semester, students reported significantly less positive attitudes toward taking a course through videoconferencing at the end of the semester. There were no significant differences in students' attitudes toward videoconferencing across courses at the beginning of the semester but there were significant differences across the courses at the end of the semester. The results suggest the need for better preparation for both students and instructors.  相似文献   

13.
Active biological molecules and functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery, disease diagnosis and therapy, and new nanodevice construction.  相似文献   

14.
Ajoint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology and his co-workers from Norway, US and Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells, suggesting that China's projected climate warming could decrease the pest's numbers. The study was published in Proceedings of theNational Academy of Sciences on 17 September, 2007.  相似文献   

15.
CAS should stick to the principle of rendering service to, and giving impetus for, the development of China's science enterprise by making S&T innovations, said CAS President LU Yongxiang. The CAS president made the remarks in a recent talk to communicate the gist of the winter session of the Party's Leading-member Group at CAS, which was held from 7 to 11 January in Beijing.  相似文献   

16.
A computer-mediated group is a complex entity whose members exchange many types of information via multiple means of communication in pursuit of goals specific to their environment. Over time, they coordinate technical features of media with locally enacted use to achieve a viable working arrangement. To explore this complex interaction, a case study is presented of the social networks of interactions and media use among members of a class of computer-supported distance learners. Results show how group structures associated with project teams dominated who communicated with whom, about what, and via which media over the term, and how media came to occupy their own communication niches: Webboard for diffuse class-wide communication; Internet Relay Chat more to named others but still for general communication across the class; and e-mail primarily for intrateam communication. Face-to-face interaction, occurring only during a short on-campus session, appears to have had a catalytic effect on social and emotional exchanges. Results suggest the need to structure exchanges to balance class-wide sharing of ideas with subgroup interactions that facilitate project completion, and to provide media that support these two modes of interaction.  相似文献   

17.
With great care, Dr. ZHOU Zhonghe takes out a package wrapped by cotton tissue from a drawer and says: "This is the gem of our collections: the fossil of a bird that lived 125 million years ago!" Then, pointing at a tiny mound, he explains: "Look, this is the claw and that is the head. It was in the egg shell and ready to hatch ... The species fell into a family of waterside inhabitants."  相似文献   

18.
Electronic data interchange (EDI) provides means for interorganizational communication, creates network externalities, requires an advanced information technology (IT) infrastructure, and relies on standards. In the diffusion of such innovations, institutional involvement is imperative. Such institutions contain governmental agencies, national and global standardization organizations, local government, and nonprofit private organizations like industry associations. The last type of organizations we call intermediating institutions. They intermediate or coordinate ("inscribe") the activities of a group of would-be adopters. Unfortunately, little is known of how these organizations shape the EDI diffusion trajectory. In this article we examine one specific type of intermediating organizations?industry associations?and how they advanced the EDI diffusion process in the grocery sectors of Hong Kong, Denmark and Finland. We identify six institutional measures, placed into a matrix formed by the mode of involvement (influence vs. regulation) and the type of diffusion force (supply push vs. demand pull), that can be mobilized to further the EDI diffusion. Industry associations were found to be active users of all these measures to varying degrees. Their role was critical especially in knowledge building, knowledge deployment, and standard setting. Furthermore, institutional involvement varied due to policy and cultural contingencies and power dependencies.  相似文献   

19.
This essay focuses on universal service and the Internet as means to support social and political participation. The emphasis on access to telecommunications systems in conventional approaches to universal service is contrasted with access to content. A model of the information environment is described that accounts for the roles of content and conduit, both of which are necessary conditions to achieve true access. A method is outlined for employing information indicators to observe or measure the information environment.  相似文献   

20.
The increasing prospects of digital piracy has prompted the perceived need by electronic publishers to adopt technical systems of protection, and governments to reform their copyright laws. This article is a preliminary study of the management of intellectual property by electronic publishers, defined as those involved in the production of online databases, and CD-ROMs. It focuses on three main issues: (1) how electronic publishers view the increasing threat of piracy; (2) the methods of protection employed to protect intellectual property in digital format; and (3) the importance of technological protection of intellectual property in electronic publications. The analysis is based on a sample of 23 UK electronic publishers. The interviews revealed an interesting assortment of protection methods and did not show that technological protection was a preferred way. Instead, the means of protection, in addition to copyright law, comprised niche markets, pricing, trust, bad publicity, and nontechnical and technical means.  相似文献   

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