平均电流控制Boost变换器的共存快慢时标不稳定现象研究

由于开关元件的存在,开关变换器的运行中蕴含着丰富的非线性现象,包括分岔、混沌等．以平均电流控制的Boost变换器为研究对象,在简化的离散时间模型基础上,运用非线性动力学对其稳定性问题进行了探讨,得出了在不同负载电阻下输入电压的稳定边界值．基于雅可比矩阵特征值的稳定性分析和仿真结果吻合得较好．文章的研究对平均电流控制的Boost变换器在环路设计、参数选择和稳定裕量估计有一定的实用价值．     

电压模式控制单级反激变换器的快时标分岔研究

以电压模式控制单级反激变换器为研究对象,在简化的离散时间模型基础上,运用非线性动力学对其稳定性问题进行了探讨,基于特征值的稳定性分析和仿真结果能够较好的吻合,并与相同运行点的直流变换器的仿真进行了比较.     

输入串联正激变换器集成变压器多绕组耦合机制及其优化

基于变压器集成的输入串联型变换器具有各串联电路自然均压、结构简单的优势。由于集成变压器各绕组间耦合参数的不同,可对变换器自然均压效果产生一定影响。以输入串联型正激变换器作为研究对象,针对集成变压器多绕组耦合参数对变换器输入均压效果的影响机制进行分析,总结出能提升输入均压效果的正激式集成变压器多绕组耦合参数优化方法。在理论分析的基础上,利用Saber建立输入串联变压器集成正激变换器模型,对分析内容进行仿真研究,仿真结果验证了理论分析的正确性及优化方法的可行性。     

三端口直流变换器的光储实验平台设计

针对光储实验平台硬件封闭、占地空间大的问题,开发了一套基于项目驱动、模块化的三端口直流变换器实验平台。首先构建基于三端口直流变换器的实验平台,其次设计光伏、储能及负载的功率变换拓扑,然后建立变换器控制系统并研究控制策略;设计主电路电感、电容参数及系统电路,进行控制系统软件设计;最后完成软硬件实验平台测试与分析。实验结果表明,三端口直流变换器负载电压调整率小于2%,系统效率高于94%,光伏侧实现最大功率点跟踪(MPPT),蓄电池实现稳定充放电功能。     

基于数字移相的高频链光伏供电系统设计

随着分布式光伏发电和光伏建筑一体化的发展,光伏直流供电系统将得到广泛的使用。在大功率光伏直流供电系统中,通过采用移相全桥变换器实现光伏能量的控制,用于实现最大功率点跟踪或者稳压。本文主要以光伏直流供电系统为研究对象,对光电互补并联供电系统中的全桥电路进行了最大功率点跟踪和稳压设计,采用DSP进行数字移相控制,重点对补偿网络进行了数字化设计,并进行了供电系统的软硬件设计。样机实验结果表明,采用数字移相的高频链光伏供电系统可以实现光伏阵列的最大功率点跟踪或者直流负载稳压。     

多电平变换器中性点电压平衡控制的拓展型教学案例设计

多电平变换器是电力电子领域的重要研究方向。针对多电平变换器中性点电压平衡控制,设计了实验教学案例。由于涉及功率开关器件、拓扑结构、电路分析、变换器建模、调制与控制等知识,多电平变换器的学习要求学生具有一定的背景知识。对于广泛应用的中性点钳位型变换器,直流侧电容器的电压平衡控制是保障系统安全稳定运行的关键技术之一。基于嵌套式中点可控型五电平变换器,对其中性点电压平衡问题展开讨论。通过循序渐进的课程设置,让学生从原理到实践了解并掌握相关知识;鼓励学生进一步在拓扑结构、调制算法和控制策略等方面提出自己的优化思想和创新思路。     

伽马能谱仪中开关功率变换器非线性动力学行为

为提高伽马能谱仪中开关功率变换器的工作稳定性,研究了开关功率变换器非线性行为的分析方法,其中包括数值仿真、理论分析和电路实验研究方法。以电压控制模式的Buck变换器为例,分析该变换器的工作过程,建立相应的数学模型,对该模型进行数值仿真,观察到该变换器的非线性行为。从理论上分析该现象的本质原因,通过电路实验来验证。最后,证明这3种方法对研究开关功率变换器非线性行为的可行性和准确性,为伽马能谱仪中开关功率变换器的设计提供理论指导。     

非隔离型高升压直流变换器拓扑推演及平台设计

高升压、高效率、高功率密度的DC-DC变换器是可再生能源系统的重要组成部分。耦合电感因其良好的调压特性和高功率密度等特点广泛应用于高升压直流变换器拓扑的构造。基于耦合电感的高升压boost变换器种类非常多,为了帮助学生更好地理解这些变换器,并掌握它们的拓扑规律,该文采用“倍压单元-变换器拓扑-演化规律”思路,总结了一系列非隔离型高升压直流变换器的演变规律。以Y源结构的耦合电感高升压boost变换器为例,进行了模态分析和电压增益推导。为了验证该高升压直流变换器的稳态性质和动态性质,搭建了实验平台,并验证了该变换器的可行性和稳定性,旨在帮助学生加强对电力电子中高升压直流变换器的直观认识和理解,并提升归纳总结能力。     

直流电动机转速控制实验系统研制

研制了直流电动机脉宽调制转速控制实验系统.该系统由数字控制器,脉宽调制波形显示电路、全桥变换器、直流电动机和光电编码器.为了实现直流电动机实时智能控制,利用模糊控制技术,设计了复合模糊控制器.实验证明该系统可以实现直流电动机实时智能控制功能,具有良好的启动特性和加速特性,并且系统的稳定性和控制的精确性能够满足系统设计的要求.实验系统可以使教学演示更加直观,学生能方便地观察到脉冲宽度的变化,使学生对控制系统和脉宽调制有更深的理解,从而有利于增加学生对电动机控制系统的感性认识.     

改进重复控制的负载模拟变换器仿真实验

为了使控制理论课程的教学效果更加理想,提出将控制理论的教学与负载模拟变换器仿真实验相结合的教学方法。探讨解决传统PI控制稳定性差、无法实现对指令电流的无静差跟踪等问题,提出了改进重复控制的方案。给出了改进重复控制器的设计步骤以及具体参数。在Simulink仿真平台上建立了负载模拟变换器的系统仿真模型,对阻感性负载、阻容性负载以及突变负载进行了模拟与分析。结果表明:采用改进重复控制的负载模拟变换器,可以实现对指令电流的无静差跟踪,并且谐波畸变率低,可以更好地模拟负载。     

卡思卡特城堡

It is worthy of noting that, whilst Crookston Castle witnessed the earlier and happier portion of Mary's variegated life,     

不同的吃喝玩乐

一、吃和喝吃苹果 eat an apple, 吃药 take medicine,吃糖 have some sweets,吃饭 have one's meals,吃馆子 dine out,吃惊 be surprised/     

漏洞百出的教育

Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help?     

只要努力,不要后悔

There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love.     

浅谈移民问题

Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject.     

Sister Carrie, an Adherent of Desires

Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities.     

Improvement of one-cycle controller by use of proportional integral differential controller

1.IntroductionOne-cyclecontrolmethod,whichwasproposedaboutonedecadeago[1],hasbecomeanattractivemethodinspecialfieldssuchaspowerfactorcorrection[2-6],switchingamplifiers[7,8],etc.Themainideaofthiscontrollerisbasedonintegrationofdiodevoltageinone-cycleandforcesittobeexactlyequaltothereferencevalue.Themainadvantageofthiscontrollerisitsrealtimeabilitytorejectthevariationofinputvoltage[1].Despitethisgreatability,ithasnogoodperformancesinrejectingofloaddisturbanceandfollowingreferencecommands.Espec…     

库克斯顿城堡

城堡, 是欧洲典型的建筑之一, 每个城堡都有一个美丽的传说或是一段历史。从本期开始, 我们将推出“城堡之旅”, 带各位读者去浏览、观赏欧洲各地的城堡, 开始一段文化与历史的旅途!     

The Reader Response Approach to Teaching of English Literature

During interview with English majors, it was found that a majority of students expressed disappointment with their experience of English literature classes. Students' dislike of learning English literature appears to be the major problem of teaching English literature in China. Reader response approach is a good way to solve this problem. In this paper, I explain the rationale behind the reader response approach, such as its origin, definition, features, assumptions, and strategies. Then I illustrate how reader response approach works as a teaching strategy by presenting several teaching models. At last I evaluate its usefuiness for teachers and present the advantages of reader response approach in Chinese context.