一种自动布线方法：多级线探索法

本文介绍了一种在微机上实现的印制板自动布线方法──多级线探索法及其编程方法。这种方法是基于完备布线算法的概念，通过分析李氏算法和传统线探索法的不足之处而得到的。虽然它也是一种线探索法，但有较传统线探索法更强的探索能力，不需要结合李氏算法而能单独完成布线任务，是一种较理想的算法，通过实验获得了较为满意的效果。     

Developing real-time knowledge-based systems with PERFECT

PERFECT (Programming EnviRonment For Expert systems Constrained in reasoning Time) is aimed at providing the necessary engineering support in real-time knowledge-based system development. PERFECT bridges the gap between the traditional analysis and design methodologies, and the implementation tools for these systems. It does so by providing the means to construct a knowledge model and to choose a suitable inference strategy. Subsequently the properties of the knowledge model and inference strategy may be analysed. For instance, it may be checked whether the knowledge model contains sufficient knowledge to diagnose a fault in an industrial process. Moreover, it may be checked whether the inference engine is able to provide an answer to a certain problem in time. If not, the analyser of PERFECT proposes an alternative structure of the knowledge model. When the constructed knowledge model and the chosen inference strategy show the required time efficiency, the compiler of PERFECT may translate them to an actual real-time knowledge based system in COGSYS. In addition, guidelines are provided with respect to the design of the human-machine interface. The resulting system is an instrument—a source of information that can be used by the human operator during problem-solving, rather than a prosthesis—a device that solves the entire problem by itself and presents the outcome to the human operator.     

多水平外区抑制的轮廓检测

提取自然图像中的物体轮廓是机器视觉研究的重要问题,主要困难在于自然图像中的纹理性边缘严重干扰了物体轮廓的提取。研究表明视皮层方位选择性神经元的非经典感受野机制使得人类视觉系统在处理自然图像时不仅能够抑制纹理性边缘,而且能够增强物体的轮廓。基于此人们提出多种仿生轮廓检测算法,但算法中被称为抑制水平的参量在取值较高时会漏检部分轮廓,而在其取值较低时又会引入过多的纹理性边缘。针对这一问题,提出多水平外区抑制轮廓检测算法,通过整合各级单水平外区抑制的检测信息,有效抑制了纹理性边缘和降低了漏检轮廓的可能性。实验结果表明,相对于传统算法,新算法在轮廓检测性能上提高了10%左右,并具有更好的稳健性。     

模块化多电平变换器全桥型子模块优化均压控制方法

模块化多电平变换器(MMC)子模块(SM)的数量与直流侧电压成正比,当SM增加时,会导致MMC的开关损耗急剧增加,因此降低功率器件的开关频率一直是MMC的重要研究方向之一。采用最近电平逼近调制(NLM)方式,提出一种基于全桥型SM的改进均压排序法,旨在降低MMC中功率器件IGBT的开关频率,该方法实现相对简单,无需额外的控制器,且易于扩展。最后,通过在MATLAB/Simulink平台搭建了19个全桥SM的仿真模型,验证了该方法的有效性。验证了所提全桥型SM优化均压策略,可以有效避免IGBT不必要的反复投切,降低IGBT的开关损耗,同时对外部输出特性不会产生负面影响。     

采用VSG策略的MMC阻抗建模及并网稳定性分析

随着分布式能源并网的增多,局部电网逐渐呈现出弱电网特性,虚拟同步发电机（VSG）控制由于可以模拟同步发电机的特性,能够为弱电网提供惯性和阻尼支撑。本文采用谐波线性化方法对采用VSG控制策略的模块化多电平换流器(MMC)进行阻抗建模。所得到的阻抗模型在低频段主要呈容性,在高频段主要呈感性,在复杂电力系统中,可能会与电网阻抗存在谐振点。分析了VSG主要控制参数对MMC阻抗的影响,发现有功-频率下垂系数、阻尼系数和虚拟转动惯量主要影响50Hz附近的阻抗。根据阻抗稳定性判据对MMC并网系统进行稳定性分析,发现并网系统在高频段有振荡的风险。     

Multilevel microwave design optimization with automated model fidelity adjustment

A computationally efficient algorithm for electromagnetic (EM)‐simulation‐driven design optimization of microwave structures is proposed. Our technique exploits variable‐fidelity EM simulations and the multilevel design approach where an approximate optimum of the lower accuracy but faster EM model of the structure under design is used as a starting point for optimizing a more accurate model. Several enhancements of the basic multifidelity method are introduced, including an efficient algorithm of optimizing EM models that is based on local response surface approximations, as well as automated adjustment of model fidelity. Convergence of the procedure to the optimum design is ensured by defaulting to the higher fidelity model whenever the prediction given by the lower fidelity fails to improve the design. Distribution of the computational effort between the models of different fidelity allows for making larger steps in the design space at a low cost, as well as substantial reduction of the number of high‐fidelity model evaluations, because the high‐fidelity model is only referred to in the last design stage. The article provides comprehensive numerical verification of our technique. Substantial computational savings are demonstrated in comparison to the benchmark methods: over 40% on average as compared to a basic version of the multifidelity optimization approach and over 95% as compared to direct optimization of the high‐fidelity model. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:281–288, 2014.     

一种MMC型VSC-HVDC系统预充电的控制策略

模块化多电平换流器(Modular Multilevel Converter,MMC)是一种新型的电压源换流器拓扑,很适合于柔性直流输电(Voltage Source Converter Topology Applied in Voltage Source Converter-high Voltage Direct Current,VSC-HVDC)场合。在系统正常运行之前,MMC中的电容需进行预充电操作,以建立额定的电容电压和直流母线电压。首先介绍了传统启动方式存在的缺陷,为弥补这些不足,结合MMC启动时的数学模型,在详细分析换流器电容预充电动态过程的基础上,采用载波移相(Carrier Phase Shifted Modulation,CPSM)策略提出了一种适用于MMC可控阶段的新型启动方法。设计了电容电压参考值给定方式、内环电流控制以及外环电压控制,该预充电策略在限制过电流和避免过电压的同时,兼顾启动的速度和效率,提高了柔性直流输电系统启动的快速性和可靠性。由在Matlab/Simulink中所构建模型的仿真结果可以看出,所提出的控制策略正确、有效。     

双变量变频器双侧供电闭环调速系统的研究

针对异步电机定子变频在解决高压电机调速时,对输出电压的等级要求高,对调速技术要求不足,在原有仅采用控制触发增量方法的基础上加入了闭环控制。在Matlab/Simulink仿真软件中,通过在仿真模型中引入S函数,建立了定转子分段变频有级调压闭环调速系统的仿真模型,并以双变量变频器为基础设计了实验电路,编写了实验程序,从仿真和实验两个方面对定转子调速系统的性能进行分析研究。得出双变量交交变频器在绕线式异步电动机转子侧供电实现调速时具有一定的可行性。     

模块化多电平变换器功率模块的电流与损耗

为了便于对电压源变换器功率器件进行系统设计以及对其参数、冷却装置进行有效选择,需要对电流与损耗进行有效估算.通过介绍新型模块化多电平变换器（MMC）的工作模态,对其电流分布进行了详细分析,给出一种基于电流分布和元件特征曲线线性拟合的简单MMC损耗计算方法,并在此基础上分析了开关频率、功率因数等对MMC损耗的影响.仿真计算结果表明,该方法能简单有效地对不同工况下各个元件的损耗进行计算,其计算结果对功率器件及其散热装置的选择有一定的指导作用.     

模块化多电平换流器自适应故障限流控制策略

直流断路器(DCCB)的造价和体积与其开断电流大小密切相关.文中从降低DCCB的开断电流层面出发,设计了适用于半桥模块化多电平换流器(MMC)故障限流的自适应限流控制器.通过在直流故障工况下调整MMC直流电压和子模块电容电压参考值,可自动快速限制故障电流发展速度.采用数学解析的方法对自适应控制器的限流原理进行了分析.在PSCAD/EMTDC仿真环境下搭建四端柔性直流电网进行仿真验证.仿真结果表明:相比于无任何限流措施的控制方案,自适应限流控制可有效降低断路器的开断电流,明显减少避雷器吸收的能量,同时可加快故障后的系统恢复.