一种简单实用维修电源

该电源是由黑白机电源电路改制而成,元件参数见图1所示。调整管应加大散热片。图中的交流130V是由隔离调压器来的。     

一种简单实用的SPWM控制器

在交流调速领域,PWM变频技术是目前中小功率交流电机的主要发展方向。对于一般PWM脉冲波形的生成,可以分别采用软件和硬件方式。采用微处理器控制的PWM逆变系统,在PWM脉冲波形生产方面具有很大的灵活性,控制算法也多种多样,这对于一些高性能要求的交流调速系统,以及PWM理论研究是很有意义的。对于采用硬件实现PWM脉宽调制,国外已制成大规模专用集成芯片,国内在这方面的工作还甚少,过去也都是采用     

一种简单实用的电动机保护电路

三相异步电动机结构简单,成本低,运行维护方便,力学性能能满足大多数生产机械的要求。因此,在工农业生产中广泛应用。 异步电动机的故障一般有:过负荷、堵转、断相、轴承磨损、通风不良和绝缘老化等。异步电动     

一种简单实用的电动自行车控制系统

对无刷直流电动机采用定子反电动势检测,使电动自行车控制系统设计简单,成本低,转换效率较高,其驱动方式采用轮毂式直接驱动,驱动电机采用外转子永磁无刷直流电机,控制系统采用模拟器件和逻辑器件产生６路驱动波形,功率转换采用ＭＯＳＦＥＴ管,转速采用反电势检测。     

A new approach to routing of two-layer printed circuit board

This paper presents a new method for routing two-layer printed circuit boards with fixed geometry, i.e. alternate columns of pins and vias. Circuit components are mounted on top of the board, and conductor wires are to be laid on the board such that circuit connections can be properly made. The proposed approach gives 100 per cent routability. The method consists of three steps, namely: partitioning of multi-pin nets into 2-pin subnets, via assignment, and routing on the two layers. In comparison with the traditional unidirectional routing, the method offers more flexibility and it requires usually about half as many vias. A computer program based on the presented algorithms was written. Its implementation is presented along with testing examples.     

水库调洪过程中特征变量对初始扰动的非线性响应研究

本文对水库调洪系统的非线性响应特性进行分析,旨在探索水库防洪调度过程中的内在随机性问题,为进一步分析水库调洪过程的不确定性及风险问题奠定基础。研究采用系统动力学和模拟方法,分析在不同类型调洪规则下水库调洪数学模型特征变量所具有的非线性动力学特征。结果表明:在调洪规则的畅泄段,调洪过程中系统对施加的初始微小扰动不敏感,水库调洪系统具有稳定的吸引点;而在控泄段分段式的调洪规则下,初始的微小扰动则可能被放大,表现为后续状态变量的较大差异。确定性调洪数学模型在微小初值扰动下的这一非线性响应行为,关系到水库防洪风险和效益问题,值得深入研究和讨论。     

一种基于蚁群系统的配电系统母线槽布线算法

配电系统母线槽的布线问题是一个典型的NP完全的组合最优化问题，随着问题规模的增大，求解时间按指数规模增长。本文提出一种新的基于蚁群系统的布线算法，通过模拟蚁群寻找从蚁巢到食物最短路径的过程来求解最优布线路径。试验结果表明：该算法能够在整个解空间求解布线问题，时间复杂度相对较低，易于和约束条件结合，且有很好的鲁棒性。     

一种简单实用的传动控制方式

介绍了一种SIEMENSS7-300PLC与三菱FR -A500变频器通过PROFIBUS网络连接的控制技术 ,该技术发挥了两产品的优势 ,提高了系统的可靠性、自动化程度及性价比 ,增强了其竞争优势。     

A practical approach to arc flash hazard analysis and reduction

Recent efforts to quantify the dangers associated with potential arc flash hazards rely on overcurrent protection to remove a given fault condition. The effectiveness of various devices is determined by a clearing time related to the maximum available fault current for each system location. As industrial and commercial facilities begin to embrace arc flash labeling procedures and begin to recognize arc flash prevention as a part of a complete safety program, the current method of calculation will allow them to quantify the incident energy (cal/cm/sup 2/) associated with a maximum three-phase fault condition. Most faults produce current magnitudes less than the three-phase maximum. This paper will consider fault current magnitudes less than that of the maximum three-phase condition, and discuss the resulting calculations for incident energy across the range of current magnitudes. Under these additional scenarios, the performance of various overcurrent protection devices will be demonstrated. Associated considerations for design, modeling, and maintenance will be presented.     

洪水预报不确定性分析及其在水库调度决策中的应用研究

洪水预报是汛期水库调度决策的重要支持,其不确定性将直接影响到水库调度运行.传统的模型参数优选方法未考虑不确定性,得到的最优参数在一些场次洪水预报中精度不高,难以满足汛期水库调度要求,需要研究洪水过程预报的不确定性辅助水库调度决策.本文基于常用的水文预报模型和水文不确定性GLUE分析方法,对洪水预报的不确定性进行分析,并将其引入水库调度决策中,建立了应用不确定性分析进行水库调度的决策模型.结果表明,考虑洪水预报不确定性,将能在期望意义上提高洪水预报水平,更好地为水库调度提供决策支持,发挥水库综合效益.     

A practical approach to EMC education at the undergraduate level

In view of the importance of electromagnetic compatibility (EMC), universities worldwide are paying more attention to training electronic engineers with good EMC design knowledge. As part of the EMC training, a practical printed circuit board (PCB) layout project has been offered as an elective to the undergraduates in the authors' universities. The project requires the students to design the PCB layout of a standard digital circuit twice, the first time with no EMC consideration at all, and the second time with careful EMC consideration. The significant difference in the levels of radiated emissions of the two layouts allows the students to appreciate the importance of EMC design at an early stage of product development.     

A simple approach to voltage stability assessment in radialnetworks

Analytical approach to voltage collapse proximity determination is proposed for radial networks. Under corresponding assumptions, a radial network with arbitrary bus loads is transformed into a two bus equivalent. The voltage phasors at the generator bus and at the last load bus of the radial network are transformed to form the voltage phasors of the two bus equivalent. The latter are further used for assessment of voltage collapse proximity. Exact stability limit relations for a two bus system derived from Jacobian matrix can be exploited. Moreover, an analytical expression is derived for calculation of active and reactive power reserve margins for a radial network equivalent. The proposed procedure has been tested for practical examples of radial networks with inductive and capacitive loads     

A simple approach to analysis of faulted power systems

In this paper the common approach for analysis of symmetrical faults and the linear circuit theory are used to analyse the unbalanced disturbances in a power network. The positive, negative and zero sequence impedance data of the faulted power system are fed separately to the program developed for analysis of symmetrical (three-phase) faults and the node voltages corresponding to each sequence impedance data are obtained. These sequence node voltages are then corrected to yield the correct sequence node voltages by multiplying them by the actual ‘impedance ratios’ obtained from the orientation of the sequence network for the particular type of fault considered. Numerical examples are presented to support the developed theory.     

一种新型实用的便携式充电箱

详细介绍了一种新型实用的便携式充电箱。该充电箱充电电池只数多 ,可充电池种类多 ,一机多用 ,自动化程度高 ,具有结构新颖、通用性好、实用性强等特点