改进无差拍控制在单相并网逆变器中的应用

为解决在单相并网逆变器中应用无差拍控制时,由于采样及处理器计算的延时而导致系统不稳定的问题,提出了一种基于CMAC神经网络的无差拍控制策略。控制策略通过MPPT算法跟踪光伏电池的最大输出功率,然后将最大功率减去电路中功率损失后除以电网电压的有效值平方得到逆变器参考电流的系数k,再根据CMAC神经网络预测出下一时刻的电网电压和参考电流,最后计算出下一时刻的开关周期的占空比对逆变器进行控制。此方法实现了对采样及处理器计算的延时的补偿,可提高了系统的稳定性,使并网逆变器的输出电流快速、准确地跟踪电网电压,降低逆变器输出电流中的总谐波歧变。通过对该策略进行了仿真和试验,结果表明该控制策略有效性和可行性。     

三相H桥级联逆变器的错时采样单周期控制策略

针对三相H桥级联逆变器提出一种单周期控制策略,推导了各逆变单元开关的占空比计算公式,指出可通过控制开关的占空比使每个开关周期中开关变量的平均值等于或正比于控制参考量;为了增加级联逆变器输出电压的电平数,提出将错时采样技术应用于级联逆变器单周期控制策略的方案,即将各逆变单元的采样时间依次错开。仿真结果验证了错时采样单周期控制策略用于三相H桥级联逆变器的可行性,且该控制策略可使逆变器的输出电压具有较小的谐波含量,且响应快速,鲁棒性强。     

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。     

改进电流型三相并网逆变器控制建模和仿真

研究改善传统三相并网逆变系统并网功率不易控制的问题,针对电网稳定控制供电,为了提高并网动特性,提出了一种基于正弦波脉宽调制与电流控制相结合的新型控制方案.对三相逆变器的输出参数应用PARK变换,并采取双电流环PI加前馈控制策略,实现了对电流的有功分量与无功分量对并网逆变器系统输出性能的控制.在Simulink环境下建立了系统的仿真模型,仿真结果表明,改进型的电流控制方法可以有效控制并网系统的有功与无功功率,谐波畸变小,是一种有较强应用价值的三相逆变器控制方案,为设计提供了科学依据.     

带谐波补偿的T型三电平并网逆变器控制研究

为了提高光伏逆变器并网电流质量,鉴于有源滤波器的控制算法,提出了一种新型的带谐波补偿的T型三电平并网逆变器控制策略。首先,采用锁相环分析电网电压矢量相位角,并根据光伏阵列输出的功率计算光伏并网逆变器的基波输出电流。然后,通过自校正滤波器技术提取网侧负载谐波电流。最后,根据基波输出电流与负载谐波电流确定T型三电平光伏并网逆变器的开关导通序列。为验证该控制策略,搭建了基于Matlab/Simulink的仿真模型。仿真试验结果表明:该控制策略可有效改善网侧谐波电流,提高并网电流质量,在不增加设备的前提下实现光伏并网与有源滤波双重功能。该研究对于T型三电平逆变器在光伏并网及电能质量治理领域的推广应用具有重要价值。     

基于单周控制的单相并网逆变算法

提出一种基于单周控制的小型风力发电机组逆变并网算法.该方法结合PI调节和单周控制,在半周期内把逆变器等效为BUCK电路进行分析,使单相全桥逆变器工作在并网状态.基于该算法的单相并网逆变器在半周期内有一对开关管保持关断状态,与传统的双极性调制方式比较,能降低开关损耗,也可避免因加入死区时间带来的波形失真.Simulink仿真结果表明:在风机输出功率变化以及电网电压幅值受到扰动的情况下,基于单周控制的单相并网逆变器的输出电流能有效、快速地跟踪参考电流,并能与电网电压的频率、相位保持一致,从而使小型风力发电机组达到对电网输入能量的要求.实现该方法的硬件电路较为简单,宜作进一步研究应用.     

不对称故障下两级式光伏逆变器的LVRT策略

为提升基于Boost电路的两级式光伏逆变器的并网运行稳定性,研究了不对称故障下光伏逆变器的运行特性,提出了以Boost调节直流母线电压配合负序电压前馈的电流控制策略,来实现低电压穿越(Low Voltage Ride Through,LVRT)。首先,分析了两级式光伏逆变器的常规Boost电压控制模式和电流控制策略。在电网故障时通过引入基于故障前光伏阵列最大功率点电压前馈的母线电压控制外环改变Boost电压控制模式,以稳定直流母线电压和防止逆变器过流。接着,为在不对称故障期间控制并网电流三相对称,提出了基于电网负序电压前馈的电流控制策略;结合根据电压跌落深度直接给定参考值的方式调节输出电流,为电网提供无功功率支撑;为实现前述电流控制,设计了基于二阶广义积分器(Second Order Generalized Integrator,SOGI)的正负序分离锁相模块。最后,利用PSCAD/EMTDC仿真软件搭建100 kW光伏逆变器模型进行控制策略验证,结果表明该策略在单相电压跌落至0.2 p.u时仍能快速有效地抑制直流母线电压升高,使光伏逆变器安全地实现低电压穿越。     

基于改进型重复PI控制的三相并网逆变器

针对三相大功率并网逆变器在开关频率较低情况下采用传统重复PI控制策略所存在的控制精度问题,提出了一种降低其输出并网电流THD的改进型重复PI控制策略。该策略基于线性插值理论计算出重复控制相位补偿中的分数拍提前,从而实现了电网全周期范围内的任意相位补偿,克服了整数拍相位补偿精度不高的问题,改善了并网电流的波形质量,同时对降低LCL型滤波器的体积和成本也起到了良好的作用。基于所提出的控制策略,利用MATLAB/Simulink仿真平台对系统进行了建模仿真。仿真结果表明了所提控制策略的正确性和可行性。     

电流预测无差拍在三相并网逆变器中研究

针对传统的无差拍控制器在控制上的延时,同时为进一步解决静态误差、抗干扰等问题,提出了一种预测电流无差拍功率解耦控制结合SVPWM调制的策略。新的无差拍控制器在电流内环控制上可以很好地解决三相电压型逆变器在并网运行时锁相问题。在PSIM软件下对三相并网逆变器进行建模,利用无差拍方法对输出电流跟踪与dq坐标系下电网电压定向对功率解耦,从而控制逆变器的输出功率。仿真和实验结果证实此方法在逆变器并网锁相时具有良好的效果。     

高速低载频比传感信号下的逆变器有源阻尼自适应控制

逆变器工作在高频运行和控制载波比低的情况下,存在谐振尖峰抑制,提出了高速低载频比传感信号下的逆变器有源阻尼自适应控制技术。在高速低载频比传感信号下,构建逆变器数学模型。输出电流到电容电压与定子电流之间的传递函数,将逆变器的有源阻尼等效成一个控制电压环。调整有源阻尼自适应控制回路的参数,制定逆变器有源阻尼自适应控制策略。实验结果表明：文中技术的稳定裕度由2.46 dB下降至1.18 dB,可以保证逆变器的稳定运行;在不同采样频率下,可以控制逆变器输出与电网电压相同相位和频率的并网电流,其中在采样频率为5.9f时,输出并网电流和电压均表现为正弦状态,波动范围分别为[35 A,58 A]和[185 V,225 V],具有较好的控制效果。     

煤矿井下安全监控分站的设计及其仿真实现

为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值.     

View-based model-driven architecture for enhancing maintainability of data access services

In modern service-oriented architectures, database access is done by a special type of services, the so-called data access services (DAS). Though, particularly in data-intensive applications, using and developing DAS are very common today, the link between the DAS and their implementation, e.g. a layer of data access objects (DAOs) encapsulating the database queries, still is not sufficiently elaborated, yet. As a result, as the number of DAS grows, finding the desired DAS for reuse and/or associated documentation can become an impossible task. In this paper we focus on bridging this gap between the DAS and their implementation by presenting a view-based, model-driven data access architecture (VMDA) managing models of the DAS, DAOs and database queries in a queryable manner. Our models support tailored views of different stakeholders and are scalable with all types of DAS implementations. In this paper we show that our view-based and model driven architecture approach can enhance software development productivity and maintainability by improving DAS documentation. Moreover, our VMDA opens a wide range of applications such as evaluating DAS usage for DAS performance optimization. Furthermore, we provide tool support and illustrate the applicability of our VMDA in a large-scale case study. Finally, we quantitatively prove that our approach performs with acceptable response times.     

A pragmatic multi-method investigation of discrepant technological events: Coping,attributions, and ‘accidental’ learning

Discrepant technological events or situations that entail a problem, a misunderstanding or a difficulty with the Information Technology (IT) being employed, are common in the workplace, and can lead to frustration and avoidance behaviors. Little is known, however, about how individuals cope with these events. This paper examines these events by using a multi-method pragmatic approach informed by coping theory. The results of two studies – a critical incident study and an experiment – serve to build and test, respectively, a theoretical model that posits that individuals use a variety of strategies when dealing with these events: they experience negative emotions, make external attributions, and adopt engagement coping strategies directed at solving the event, eventually switching to a disengagement coping strategy when they feel they have no control over the situation. Furthermore, users’ efforts may result in ‘accidental’ learning as they try to overcome the discrepant IT events through engagement coping. The paper ends with a discussion of the results in light of existing literature, future opportunities for research, and implications for practice.     

The Distributed Time-Triggered Simulation Scheme: Core Principles and Supporting Execution Engine

Distributed real-time simulation is a young technology field but its practice is under increasing demands. In recent years the author and his collaborators have been establishing a new approach called the distributed time-triggered simulation (DTS) scheme which is conceptually simple and easy to use but widely applicable. The concept was initiated in the course of developing a new-generation object-oriented real-time programming scheme called the time-triggered message-triggered object (TMO) programming scheme. Some fundamental issues inherent in distributed real-time simulation that were learned during recent experimental studies are discussed along with some approaches for resolving the issues. An execution engine developed to support both the TMOs engaged in control computation and the TMOs engaged in DTS is also discussed along with its possible extensions that will enable significantly larger-scale DTSs.     

Software-Konfigurationsmanagement in großen Softwareprojekten

Zusammenfassung Mit zunehmender Größe der Softwaresysteme verschärfen sich die für die Software-Herstellung typischen Probleme: Beherrschen großer Objektmengen, Erhalten der Systemkonsistenz, Kontrolle der ständigen Änderungseinflüsse und Gewährleisten einer langen Lebensdauer. Die Disziplin Konfigurationsmanagement bildet den methodischen Ansatz, diese Probleme besser zu beherrschen. Software-Konfigurationsmanagement faßt die Herstellung von Softwaresystemen als eine Abfolge von kontrollierten Änderungen an gesicherten Zwischen- und Endergebnissen auf. Dargestellt werden die Objekte und Funktionen des Software-Konfigurationsmanagements sowie die hierfür in großen Software-Projekten benötigten Methoden, Instanzen und Hilfsmittel.     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and     

Editorial:Brain-machine interface(BMI) and cyborg intelligence

正Brain-machine interfaces(BMIs)aim at building a direct communication pathway between the brain and an external device,and represent an area of research where significant progress has been made during the past decade.Based on BMIs,mind information can be read out by neural signals to control     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate     

SCIENCE CHINA Information Sciences SUBJECT INDEX TO VOLUME 57(2014)

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Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate