交流采样中开平方算法的研究

在分析开平方迭代算法收敛速度的基础上,提出了开平方的初值选取改进算法。本算法具有算法简单,迭代次数少,精度高等特点,较好地解决了开方运算时间长问题。同时分析了求有效值（幅值）的开平方运算时间误差,并作改进。     

电量变送器中开平方算法的研究

按电工学定义实现的微机电量变送器中开平方运算耗时最长。本文首先分析了常用的牛顿迭代和快速查表两种开平方算法的缺点，对其改进，形成了两种自适应混合开方算法，大大提高了开平方运算的速度。     

基于牛顿迭代法的高精度快速开方算法

针对全波傅氏算法中的开平方运算较耗时影响微机保护瞬动性问题,提出一种选取接近定点数开方真值的牛顿迭代初值的方法,该方法利用数字信号处理器(DSP)的移位指令、256个单元的查表技术和DSP的硬件乘法器,通过1次查表和1￣2次乘法运算,就能快速确定迭代误差小于2-9的迭代初值。在TIDSP集成开发平台上,运行牛顿迭代开平方汇编程序。运算结果表明:该算法对范围在00000004.0000H￣01FFFFFF.FFFFH的定点数抽样开方运算,迭代次数均不大于3次,就达到2-16以上迭代精度,且占用内存小,非常适合带有硬件乘法器的嵌入式微处理器实现。     

微机保护开平方计算中牛顿迭代法的改进

在分析了查表法以及牛顿迭代法的基础上,对开平方计算的牛顿迭代法进行了改进。改进方法综合了查表法以及牛顿迭代法,运算过程中只需要一次牛顿迭代计算,根据精度要求定量地确定表格大小。通过实例验证了该方法具有运算速度快、精度高、占用内存小的特点,解决了长期以来开平方算法存在耗时长、精度低、存贮数据值范围难以确定的问题。     

电量变送器中一种快速高精度的开平方算法

在分析查表开平方算法和浮点数特点的基础上 ,提出一种二进制浮点数与查表法相结合的开平方算法。该算法不仅具有计算简单、运算速度快、精度高的优点 ,而且占用内存少 ,解决了长期以来开平方算法存在耗时长、精度低、存贮数据值范围难以确定的问题。对于 80C196单片机 ,若采用 12MHz晶振 ,利用本算法 ,最大耗时不超过 80 μs,平均耗时为 5 5 μs,最大误差小于 (6 .1× 10 - 3) %。     

电量变送器中一种快速高精度的开平方算法

在分析查表开平方算法和浮点数特点的基础上,提出一种二进制浮点数与查表法相结合的开平方算法.该算法不仅具有计算简单、运算速度快、精度高的优点,而且占用内存少,解决了长期以来开平方算法存在耗时长、精度低、存贮数据值范围难以确定的问题.对于80C196单片机,若采用12 MHz晶振,利用本算法,最大耗时不超过80 μs,平均耗时为55 μs,最大误差小于(6.1×10-3)%.     

三电平PWM整流器SVPWM优化算法研究

提出了一种易于DSP实现的三电平PWM整流器空间矢量脉宽调制(Space Vector Pulse Width Modulation,SVPWM)优化算法.该算法无需开平方和反正切等复杂运算,只需简单的坐标变换,将参考矢量转换到60°坐标系,然后再经过简单的算术运算即可计算出各基本矢量作用时间.仿真实验验证了SVPWM算法的正确性.     

树状网络潮流计算的新算法

介绍了一种适合树状网络潮流计算的新算法-交替迭代算法。该算法以电压和线路损耗功率交替迭代进行。文中对算法进行了收敛性分析,并证明：当树状网络存在稳态运行解时,给出的交替迭代算法是收敛的。以IEEE 33节点、RBTS68节点等系统为例,证实了该算法具有计算速度快、迭代次数少、收敛精度高、易于编程的特点。     

单芯电缆载流量迭代算法研究及试验验证

建立了基于IEC 60287电缆栽流量计算的迭代算法;用此算法计算典型电缆线路的载流量与IEC算法的结果比较,两者相近,但迭代算法的精确度和适用范围都比IEC算法要好,理论上验证了迭代算法的正确性;在国网电科院进行单芯电缆载流量试验,将电缆各层温度和层间温差的实测值与迭代计算值比较,发现两者基本吻合.迭代算法可用于精确计算结构不相同、负荷电流不均匀多回路、大环流电缆的载流量,并可用于计算电缆本体各部分的运行温度,为电缆的状态监测提供理论支持.     

电磁层析成像图像重建中的修正Landweber迭代算法

电磁层析成像技术中图像重建算法的准确与快速是其在工业现场中得以应用的关键。Landweber迭代算法是电磁层析成像图像重建中应用最广泛的迭代算法,但其需要多次迭代,收敛速度慢。该文提出一种修正的Landweber迭代图像重建算法,该算法通过在构建的电磁层析成像逆问题目标泛函中添加正则化项,并采用自适应权重系数的方法,提高了收敛速度,并且改善了重建图像的质量。利用有限元法,在Maxwell中进行电磁层析成像正问题的求解,获得了图像重建所需的灵敏度矩阵。仿真和数值实验结果表明,修正的Landweber迭代算法在收敛速度和重建图像质量两方面均优于Landweber迭代算法。     

基于Camera Link的线阵CCD外同步控制设计与实现

在纺织布匹疵点检测系统中,获取平稳清晰图像对后续布匹图像疵点的精确检测和类别正确识别至关重要。由于布匹疵点检测系统外部事件的不可预测性,如何控制线阵CCD以获取平稳清晰的图像。针对这一问题提出了一种线阵CCD相机外同步控制方法。该方法采用VHDL语言在Xilinx公司Virtex-II PRO FPGA架构上设计实现。重点介绍了相机自适应的外同步控制设计方案和实现方法,通过ModelSim仿真和布匹疵点检测系统的在线测试,验证了该方法的有效性和可行性。     

Primary and secondary frequency regulation in a longitudinal hydrothermal system by Liapunov method

The problem of primary and secondary frequency regulation of a multi-machine power system is analysed with a Liapunov function method based on a quadratic performance index. The main purpose is to determine the best set of parameters of primary and secondary regulation according to an optimisation criterion. The objective consists of achieving a settling time as short as possible which is relevant in a longitudinal system, whose structure includes long transmission lines with a reduced number of loops.     

具有特殊地形条件的长距离供水工程水锤防护

在长距离供水工程中输水管道一般按地形走势布置。针对一些地形条件特殊的供水工程,本文提出了一种空气罐与出口溢流池联合设置的水锤防护方案,并建立了出口溢流池的数学模型。在空气罐体型一定时,给出了出口溢流池截面积的理论计算公式,有效地减小了在溢流池体型初期选取过程中的盲目性和工作量。结合某长距离输水工程,对比分析了空气罐和出口溢流池联合防护与单纯的空气罐防护对水锤的影响。结果表明空气罐与出口溢流池联合防护方案在前陡后缓的长距离供水工程中能够取得良好的水锤防护效果,且溢流池的溢流水位越高,其对负压的防护效果越好。     

基于遗传算法(GA)的配网无功优化控制的两部算法

提出了基于遗传算法的两部算法,该算法经用Ｃ＋＋语言编程后,分别在１６节点和４４节点算例系统上测试,结果表明两部算法比单纯用遗传算法可以在更短的计算时间内获得更好的解。     

Numerical Investigation of a Molecular Switch Based on Conformational Change, with the Inclusion of Contacts

We discuss the possibility of implementing a switch based on a conformational change, consisting in a relative rotation of a molecule containing two benzene rings, functionalized with proper substituents. Contacts are simulated with three-atom gold clusters, which are connected to the rest of the molecule via a thiol group. Relative rotation of the two rings, induced by a transverse electric field, determines a variation of the height of the potential barrier separating them, due to the change in the amount of conjugation of the π orbitals. The action of such a barrier is evaluated by computing the shift of the electron density as a function of a longitudinal electric field.     

Performance Comparison of Circuits for Pole‐Mounted STATCOM Using SiC Devices

The recent years have seen an increasing trend in the cumulative installed capacity of distributed generators. As a result, voltage management may become difficult in existing power distribution systems in the future. A STATCOM (STAtic synchronous COMpensator) is a promising option for solving this problem because it can control reactive power rapidly and continuously. For a distribution system, STATCOM needs to be pole‐mounted to realize its low cost. However, a transformer for a STATCOM is large and heavy, and hence it is difficult to install a STATCOM on a distribution pole. We adopt a transformerless STATCOM to reduce STATCOM size and use SiC devices with low‐loss performance to obtain a more compact and efficient STATCOM. There are a large number of circuits available for a STATCOM, and there has been considerable research on performance comparisons among these circuits. However, these comparisons were drawn under different conditions, including switching frequency and level number for the circuits. In addition, these comparisons do not include the use of SiC devices. We made an equitable comparison for a 100 kVa pole‐mounted STATCOM using SiC devices. We discuss the performance and characteristics of each circuit in terms of efficiency and volume.     

Periodic steady-state solution of a synchronous generator based on a voltage-behind-reactance formulation and the Poincaré map method

A powerful blend based on a voltage-behind-reactance (VBR) model and the Poincaré map method, suitable to carry-out harmonic oriented analyses, is presented in this paper to compute the periodic steady-state solution of a synchronous generator. The VBR model, as originally conceived, is modified and instead a per-unit version, tailored to the acceleration procedure, is used. The acceleration of the convergence to the periodic steady-state is accomplished with a Newton method and the Poincaré map. A Numerical Differentiation approach allows the computation of the transition matrix involved in the acceleration procedure using a sequential perturbation of the state variables. The periodic steady-state solution of synchronous generators is reported for a set of operating conditions such as change of load, a three-phase fault and a single-phase fault. Furthermore, the harmonic analysis of a system comprising a RLC circuit with a varying degree of unbalance, fed from a synchronous generator is carried-out with the acceleration procedure. Important speedup factors up to 145 are reported for large turbine generators. The application of a Newton based acceleration procedure to a VBR synchronous machine model yields important benefits for the efficient computation of periodic steady-state solutions and it is particularly useful for test cases involving large rotary machines with an inherently large inertia.     

新型制冷剂研究及应用冰箱压缩机的设计

为了解决R12的主流替代工质R134a作为冰箱制冷剂时存在的问题,提出给R134a系统加入R600a组成混合工质R134a/R600a的方案,提供物性和热力性能比较结果,证明R134a/R600a作为冰箱制冷剂比R134a和R600a更具有优势,并提出了采用新型制冷剂的冰箱压缩机的改进方案.R134a/R600a的性能试验结果证明其与矿物油的互溶性良好,成功的解决了R134a系统由于更换润滑油而产生的一系列问题.     

靶场光雷测量数据融合定位方法研究及应用

在靶场测量中,光电经纬仪由于测量直观、可靠性好、测量精度高等特点,一直被作为外弹道跟踪测量的重要设备,但是其不具备单站定位功能且双站交会受布站等因素限制。针对这种情况,为充分利用测量数据,将部署在经纬仪附近的具有作用距离远的雷达系统与光电经纬仪建立联合定位模型。首先对雷达和经纬仪的测量数据进行时间和空间配准,然后通过单站定位方法得到目标的位置。应用结果表明,其定位精度明显优于雷达单站定位精度,该方法可以作为计算弹道坐标的一种补充。