Influence of pulse angle variations onstimulated echo acquisition mode proton nuclear magnetic resonance spectra of AB spin systems: theory and experiments with citrate

The influence of pulse angle variations in the localization sequence stimulated echo acquisition mode (STEAM) on the signal of strongly coupled AB spin systems has been examined. Experimental¹H nuclear magnetic resonance (NMR) spectra of citrate were recorded on a 1.5 T whole-body imager. Theoretically calculated spectra were generated, with good correlation to experimental results. The dependence of the signal intensity on sequence timing and pulse angles was calculated analytically. For longer sequence timings, the ratio of the signal intensity from citrate to the signal intensity from uncoupled nuclei depends strongly on the applied flip angles. The shape of spectra also changes with varying flip angles. These effects are clearly less pronounced for STEAM than for point resolved spectroscopy (PRESS). The results have to be considered for quantitative measurements of citrate in spectroscopic investigations as, e.g. of prostate neoplasms.     

高压输电线故障测距中的伪根问题及其改进方法

本文对故障电流相位修正测距算法进行了分析讨论。理论分析和数字仿真计算均表明该算法在原理上存在一定缺陷,在某些情况下可能会给出错误的测距结果。为此,本文提出了解方程算法及附加判据。利用该方法可更为可靠、准确地实现故障点定位。     

Adaptive controller design and disturbance attenuation for SISO linear systems with zero relative degree under noisy output measurements

In this paper, we present robust adaptive controller design for SISO linear systems with zero relative degree under noisy output measurements. We formulate the robust adaptive control problem as a nonlinear H^∞‐optimal control problem under imperfect state measurements, and then solve it using game theory. By using the a priori knowledge of the parameter vector, we apply a soft projection algorithm, which guarantees the robustness property of the closed‐loop system without any persistency of excitation assumption of the reference signal. Owing to our formulation in state space, we allow the true system to be uncontrollable, as long as the uncontrollable part is stable in the sense of Lyapunov, and the uncontrollable modes on the jω‐axis are uncontrollable from the exogenous disturbance input. This assumption allows the adaptive controller to asymptotically cancel out, at the output, the effect of exogenous sinusoidal disturbance inputs with unknown magnitude, phase, and frequency. These strong robustness properties are illustrated by a numerical example. Copyright © 2009 John Wiley & Sons, Ltd.     

船舶区域配电系统全智能体重构及其优化研究

为确保船舶电力系统故障发生时主电力推进动力系统不失去供电,对电力推进船舶区域配电系统的拓扑结构重构方法进行了深入研究。依托智能体理论,设计了一种环境智能感知、信念产生、目标控制、粒子群最优决策的全智能体重构方法,实施船舶区域配电系统故障的拓扑重构。重构策略以保证全船的不间断供电、负荷损失最小、继电保护效率最高等为目标。对某电力推进船舶区域配电系统电网发生三相短路工况的仿真实验表明,所设计的全智能体方法相比粒子群算法、遗传算法的电力系统重构更能保证船舶电力系统的安全运行,且具有电力系统故障时重构功率损耗更小、开关效率更高的优点;进一步提高了船舶电力系统的安全可靠性。     

燃料电池系统及其应用专辑主编述评

燃料电池因其发电效率高、环境污染小、比能量高和噪音低等优点在未来能源利用上必将占据主要的地位。燃料电池系统是一个非线性、多输入、强耦合的复杂动态系统,本专辑在总结目前研究进展的基础上,对燃料电池精确建模,参数辨识,观测器设计,水管理及系统优化等方面进行了详细的分析。     

华东电网输电线路覆冰灾害防治体系的研究

基于2008年我国大范围冰灾情况,给出华东电网500 kV输电线路的典型故障类型,针对华东电网的实际情况提出了输电线路覆冰灾害防治体系的总体框架,对框架中的结构抗冰、绝缘优化、覆/融冰机理、冰情监测等各个子模块的研究思路进行了讨论,并介绍其中部分内容的初步研究成果.     

Parameter estimation for time-delay systems based on the frequency responses and harmonic balance methods

Two parameter estimation methods for linear time-delay systems are proposed based on the frequency responses and the harmonic balance methods. One is the stochastic gradient gradient-based iterative (SG-GI) algorithm and the other is the recursive least squares gradient-based iterative (RLS-GI) algorithm. These two methods can estimate the unknown parameters and the unknown time delays simultaneously by giving sinusoidal signals with different angular frequencies. Furthermore, a comparative study reveals that the RLS-GI algorithm is more effective than the SG-GI algorithm. The effectiveness of the proposed algorithms is illustrated by a numerical example.     

基于幅频特性的复值小波构造及其在电力系统信号分析中的应用

提出了基于幅频特性的复值小波函数构造方法及其相应的复值小波变换。该方法构造的复值小波具有频率局部化性能好、提取故障信号特征分量较准确的优点。复值小波变换能准确分辨出信号中所包含的幅值信息和相位信息 ,因而 ,适用于电力系统的故障信号的检测。利用基于幅频特性的复值小波变换 ,对发电机转子部分故障信号进行了分析 ,显示了基于幅频特性的复值小波变换的电力系统故障信号分析方法 ,是一种有效的方法。     

中高压电力系统有源电力滤波器的研究现状

对中高压有源电力滤波器的应用研究现状进行了综述,详细介绍了适合应用于中高压系统的各种主电路拓扑结构,如混合滤波方案、多重化结构和多电平级联型等,对各种解决方案的优缺点进行了分析,分述了目前比较常用的各种控制方法,总结了各自的应用及优缺点。探讨了中高压有源滤波器的进一步发展方向。     

A fault segment location method for distribution networks based on spiking neural P systems and Bayesian estimation

With the increasing scale of distribution networks and the mass access of distributed generation, traditional centralized fault location methods can no longer meet the performance requirements of speed and high accuracy. Therefore, this paper proposes a fault segment location method based on spiking neural P systems and Bayesian estimation for distribution networks with distributed generation. First, the distribution network system topology is decoupled into single-branch networks. A spiking neural P system with excitatory and inhibitory synapses is then proposed to model the suspected faulty segment, and its matrix reasoning algorithm is executed to obtain a preliminary set of location results. Finally, the Bayesian estimation and contradiction principle are applied to verify and correct the initial results to obtain the fnal location results. Simulation results based on the IEEE 33-node system validate the feasibility and efectiveness of the proposed method.     

Simultaneous time‐varying actuator and sensor fault reconstruction based on PI observer for LPV systems

We consider problems of actuator and sensor fault reconstruction simultaneously for linear parameter varying systems expressed in polytopic forms. By extending the sensor fault as an auxiliary state, a polytopic unknown input proportional‐integral observer in which the actuator fault signals are assumed to be time varying is developed to estimate the system states and the actuator and sensor fault at the same time. The existence conditions of the observer are derived in terms of linear matrix inequalities that can be readily handled via some efficient tools. An example is given to demonstrate the advantages of the proposed method in comparison to the existing results. Copyright © 2014 John Wiley & Sons, Ltd.     

Design of disturbance observer based on adaptive-neural control for large-scale time-delay systems in the presence of actuator fault and unknown dead zone

This article presents an adaptive neural compensation scheme for a class of large-scale time delay nonlinear systems in the presence of unknown dead zone, external disturbances, and actuator faults. In this article, the quadratic Lyapunov–Krasovskii functionals are introduced to tackle the system delays. The unknown functions of the system are estimated by using radial basis function neural networks. Furthermore, a disturbance observer is developed to approximate the external disturbances. The proposed adaptive neural compensation control method is constructed by utilizing a backstepping technique. The boundedness of all the closed-loop signals is guaranteed via Lyapunov analysis and the tracking errors are proved to converge to a small neighborhood of the origin. Simulation results are provided to illustrate the effectiveness of the proposed control approach.