Stability analysis of networked control systems with time-varying sampling periods

In this paper, we present an interval model of networked control systems with time-varying sampling periods and time-varying network-induced delays and discuss the problem of stability of networked control systems using Lyapunov stability theory. A sufficient stability condition is obtained by solving a set of linear matrix inequalities. In the end, the illustrative example demonstrates the correctness and effectiveness of the proposed approach.

H_∞ Controller Design for Networked Control Systems via Active-varying Sampling Period Method

这份报纸学习由使用一个活跃变化的采样时期方法与两导致网络的时间延期和包退学学生为联网的控制系统(NCS ) 设计 H 控制器的问题，在采样时期在一个有限集合切换的地方。一个新奇线性基于评价的方法被建议补偿包退学学生，和 H 控制器设计被使用多客观的优化方法论也介绍。模拟结果说明活跃变化的采样时期方法和线性基于评价的包退学学生赔偿的有效性。

NOISE AMPLIFICATION ANALYSIS AND COMPARISON OF TWO PERIODIC NONUNIFORM SAMPLING RECONSTRUCTION METHODS USED IN DPCA SAR

General Sampling Expansion Reconstruction Method (GSERM) and Digital Spectrum Reconstruction Method (DSRM), which prove effective to reconstruct azimuth signal of Displaced Phase Center Apertures (DPCA) Synthetic Aperture Radar (SAR) system from its Periodic Non-Uniform Sampling (PNUS) data sequences, would amplify the noise and sidelobe clutter simultaneously in the reconstruction. This paper formulates the relation of the system transfer matrixes of the above two methods, gives the properties, such as periodicity, symmetry, and time-shift property, of their Noise and Sidelobe Clutter Amplification Factor (NSCAF), and discovers that DSRM is more sensitive than GSERM in the white noise environment. In addition, criteria based on initial sampling point analysis for the robust PRF selection are suggested. Computer simulation results support these con-clusions.

Guaranteed cost control of networked control systems under limited communication capacity and variable sampling

The problem of guaranteed cost control for the networked control systems(NCSs) with time-varying delays, time-varying sampling intervals and signals quantization was investigated, wherein the physical plant was continuous-time one, and the control input was discrete-time one. By using an input delay approach and a sector bound method, the network induced delays, quantization parameter and sampling intervals were presented in one framework in the case of the state and the control input by quantized in a logarithmic form. A novel Lyapunov function with discontinuity, which took full advantages of the NCS characteristic information, was exploited. In addition, it was shown that Lyapunov function decreased at the jump instants. Furthermore, the Leibniz-Newton formula and free-weighting matrix methods were used to obtain the guaranteed cost controller design conditions which were dependent on the NCS characteristic information. A numerical example was used to illustrate the effectiveness of the proposed methods.

Life prediction and test period optimization research based on small sample reliability test of hydraulic pumps

Hydraulic pumps belong to reliable long-life hydraulic components. The reliability evaluation includes characters such as long test period,high cost,and high power loss and so on. Based on the principle of energy-saving and power recovery,a small sample hydraulic pump reliability test rig is built,and the service life of hydraulic pump is predicted,and then the sampling period of reliability test is optimized. On the basis of considering the performance degradation mechanism of hydraulic pump,the feature information of degradation distribution of hydraulic pump volumetric efficiency during the test is collected,so an optimal degradation path model of feature information is selected from the aspect of fitting accuracy,and pseudo life data are obtained. Then a small sample reliability test of period constrained optimization search strategy for hydraulic pump is constructed to solve the optimization problem of the test sampling period and tightening end threshold,and it is verified that the accuracy of the minimum sampling period by the non-parametric hypothes is tested. Simulation result shows it could possess instructional significance and referenced value for hydraulic pump reliability life evaluation and the test's research and design.

A Method to Reconstruct Nth-Order Periodically Nonuniform Sampled Signals

It is well known that nonuniform sampling is usually needed in special signals processing. In this paper, a general method to reconstruct Nth-order periodically nonuniform sampled signals is presented which is also developed to digital domain, and the designs of the digital filters and the synthesis system are given. This paper extends the studies of Kohlenberg, whose work concentrate on the periodically nonuniform sampling of second order, as well as the studies of A.J.Coulson, J.L.Brown, whose work deal with the problems of two-band signals’ Nth-order sampling and reconstruction.

Digital Spectral Representation of Nonuniformly Sampled Periodic Signals

This paper presents a digital spectrum analysis technique developed for nonuniformly sampled periodic signals and a closed-form digital spectral representation of nonuniformly sampled periodic signals,and discusses some important properties of digital spectra.

Global Exponential Stability of Almost Periodic Solution of Cellular Neural Networks with Time-Varying Delays

In this paper, global exponential stability of almost periodic solution of cellular neural networks with time-varing delays （CNNVDs） is considered. By using the methods of the topological degree theory and generalized Halanay inequality, a few new applicable criteria are established for the existence and global exponential stability of almost periodic solution. Some previous results are improved and extended in this letter and one example is given to illustrate the effectiveness of the new results.

Performance of Optical Sampling Based on SHG in CPPLN Waveguide

Sampling efficiency and bandwidth of the optical sampling system based on second harmonic generation （SHG） in chirped periodically poled LiNbO3 （CPPLN） are numerically researched. A broad sampling bandwidth can be obtained by adjusting chirp coefficient and waveguide length of CPPLN, and sampling efficiency can be improved by using higher pump power, increasing waveguide length and choosing appropriate chirp coefficient. Results show that both sampling bandwidth and efficiency in CPPLN waveguides are controllable and that CPPLN waveguides are more suitable for multiwavelength optical sampling systems.

Weighted Pseudo Almost Periodic Solutions for a Class of Hematopoiesis Model with Time-Varying Delay

In this paper, firstly, a notion of a class of generalized weighted pseudo al- most periodic function is introduced, then we investigate some basic and essential properties of the space that consists of these functions. Finally, we study the exis- tence of weighted pseudo almost periodic solutions to hematopoiesis model with time- varying delay.

Analysis of the Mode of the Periodically Time-varying Vibration Systems

By Liapunov reducibility theorem, the periodically time-varying vibration system can be transformed to a linear time-invariant system. Based on the dynamic characteristics of the linear time-invariant system, the mode of the periodically time-varying vibration system has been discussed. The paper defines the mode and analyzes its characteristics. It can be found that the mode of the periodically time-varying system is periodically time-varing but has such characteristics as orthogonality. Finally, a method is given to solve the mode. By solving the eigenvalues and the eigenvectors of the state transition matrix in one period, the periodically time-varying mode can be obtained.

入侵意图分析下的软件定义网络DDoS攻击检测方法

为在数据样本回溯期内解决因本地信息熵值增大而造成的服务攻击问题,维护软件定义网络的运行安全性,提出入侵意图分析下的软件定义网络分布式拒绝服务(DDoS)攻击检测方法。按照软件定义网络场景重构原则,确定因果网转换标准,实现对识别参数的更新处理,完成攻击性行为的入侵意图分析,再定义DDoS数据集,根据攻击行为的时空特性,求解模型参数的取值范围,完成入侵意图分析下软件定义网络DDoS攻击检测方法的设计。实验结果表明,在该算法控制下数据样本回溯期为10 min,低于传统算法,能够较好维护软件定义网络的运行安全性。

五相感应电机变采样周期模型预测控制策略

针对无调制模块的模型预测控制器MPC(model predictive controller)存在的谐波含量高问题,提出1种新型基于模型的变采样周期MPC策略,并将其应用于五相感应电机驱动系统。分析了MPC对时间固定离散化所带来的问题,而引入调制或调制替代来解决此问题将使控制系统复杂度增加,故遵循更简单、自然的思路,基于追击算法来改变采样间隔,结合MPC确定最优控制动作和实施时间,实现变采样周期MPC方案。利用五相感应电机驱动系统开展实验,实验结果验证了新型变采样周期MPC优良的参考跟踪和电流谐波性能。

塔里木河“四源”洪水演变规律及成因分析

基于1981—2020年塔里木河流域“四源”5个水文站的日径流数据及格网温度、降水和雪深等数据,采用最大值及POT采样法,分析洪水发生量级、频率和峰现时间等特征,同时采用相关性分析揭示不同洪水指标与影响因素之间的关系并识别关键影响因子。结果表明:(1)1981—2020年塔里木河“四源”各站点洪峰流量大小依次为:卡群>协和拉>同古孜洛克>沙里桂兰克>大山口,年及季节尺度洪峰流量普遍呈增加趋势,冬季洪峰发生时间均呈提前状态,其中沙里桂兰克年均提前最多为2.61 d,卡群站提前仅0.67 d。(2)研究时段内塔里木河流域共有2个洪水高发期,为1994—2002年和2006—2011年,流域内大量级洪水集中发生在1990年之后。(3)洪水发生前不同时间内最小温度、降水和雪深以增加趋势为主;而最大温度以减少趋势为主。春季洪水指标与最大3 d降水的相关性最高,而秋季洪水指标与最大7 d降水的相关性最高。相比于单日降水,多日降水与洪水指标的相关性更高。在雪深相关因子中,最大15 d雪深与各站点的春季洪水指标相关性最高。研究结果对区域水资源管理以及洪水灾害预测提供理论依据。

结合虚拟样本生成的油菜花期集成学习预测模型

针对统计和线性回归模型难以完全揭示花期影响因子与花期之间的复杂非线性关系及油菜花期样本稀少的问题,提出了一种结合虚拟样本生成的集成学习算法来实现油菜花期的预测。该研究利用浙江省衢州市龙游县1999—2023年油菜盛花期与1998—2023年气象数据,通过基于高斯混合模型的虚拟样本生成(GMM-based virtual sample generation,GMM-VSG)算法与三次样条插值法(cubic spline interpolation)分别对原始样本进行扩充,采用8种机器学习算法建模并基于贝叶斯优化器进行超参数优化,最后通过Stacking集成学习方法,对8种算法进行不同的组合,建立了油菜花期预测模型。研究结果表明:相较于原始数据集,通过三次样条插值法与高斯混合模型生成的两个扩展数据集在各种机器学习算法中的性能显著提升,其中通过三次样条插值法生成的数据集表现最为优异。通过Stacking思想能提升模型的精度,其中以核岭回归(kernel ridge regression,KRR)、支持向量回归(support vector regression,SVR)、极端梯度提升树(extreme gradient boosting,XGBoost)这3种算法作为基模型,线性回归作为元模型的SRX_L模型表现最优,其平均绝对误差、均方根误差和决定系数,分别为0.1056 d、0.1227 d和0.9997。该研究结果可为油菜花期的准确预测提供有效方法。

平均降采样多周期微分均值的旋转部件故障特征增强方法

为解决编码器的瞬时角速度(Instantaneous Angular Speed,IAS)信号中旋转部件故障特征微弱的难题,本文提出一种平均降采样多周期微分均值(Average Down⁃Sampling Multi⁃period Differential Means,ADSMPDM)的故障特征增强方法。基于IAS信号的估计特性,开展了IAS信号的平均降采样研究,验证了平均降采样具有抑制随机噪声的特性;基于平均降采样抑制随机噪声特性、降低计算成本和减小存储空间的优势,结合多周期微分均值的累积特性,提出一种ADSMPDM算法对原始IAS信号中的旋转部件故障分量进行增强处理;通过阶次谱分析揭示故障特征。采用仿真数据和实验数据进行验证分析,并与快速谱峭度、可调整多点优化最小熵反卷积、离散随机分离和谱幅值调制算法进行对比,验证了ADSMPDM算法增强旋转部件故障特征的有效性和优势。

考虑传输时滞的电力负荷频率采样控制系统稳定性分析

研究了一类考虑传输时滞的电力负荷频率采样控制系统相关稳定性问题。首先,采用PI型的LFC系统方案,并建立考虑采样和传输时滞的LFC闭环系统模型;其次,根据建立的模型,采用基于双边闭环泛函判据计算系统的时滞稳定裕度,研究系统采样周期与时滞稳定裕度之间的关系,并通过单区域LFC系统对结果进行仿真验证。计算结果表明,与现有文献结果相比,在相同的系统参数条件下,使用提出方法得到的结果保守性降低,且采样周期越大,系统时滞稳定裕度越小,而一定大小的时滞可以增大系统采样周期上界;仿真结果进一步验证了所提出方法的有效性和优势。

交交变频调速系统中变周期均值采样的研究应用

针对交交变频调速系统中电压、电流纹波含量较大且纹波周期时变,无法直接反馈于调速控制系统的问题,提出一种变周期均值采样算法。首先,该算法以实时交交变频功率器件触发脉冲的间隔时间作为均值周期,对电压、电流实际值进行均值计算。其次,根据电压、电流实时频率及均值周期计算该均值周期所带来的相位滞后角度。最后,按照相位滞后角度进行滞后补偿及插补运算,得到更理想的电压、电流反馈值,用于调速控制系统。相较于一般的均值采样,该算法更适合交交变频纹波周期时变的情况,并能消除采样滞后,提升调速系统控制性能及稳定性。

不同采样周期下BDS GNSS精密单点定位验潮精度分析

利用海上移动平台搭载GNSS接收机采集观测数据,开展全球卫星导航系统(Global Navigation Satellite System,GNSS)精密单点定位(precise point positioning,PPP)采样周期对验潮精度影响的研究。以30 s、60 s、90 s和120 s为周期抽取成四个数据集,用Trip软件进行动态处理,获取每个测量历元坐标,比较各采样周期下两台接收机潮位测量结果,以标准差作为精度评价指标。研究结果表明,采样周期越短,PPP验潮精度越高,当采样周期缩短至60 s后,变化不再明显;采样周期从120 s逐级递减至90 s、60 s和30 s,精度分别提升63.0%、60.4%和10.0%。另外,对比了BDS GPS GLONASS三系统组合和GPS GLONASS双系统组合GNSS PPP在验潮精度上的差异,结果显示,在30 s、60 s、90 s、120 s采样周期下,三系统较双系统PPP在验潮精度上分别提升了88.9%、90.4%、78.7%和44.7%。

甘精胰岛素注射液质量状况评价与研究

目的评价甘精胰岛素注射液的质量现状及存在问题,对现行质量标准的科学性及合理性进行评估,为其安全评价及安全监管提供参考。方法对甘精胰岛素注射液进行国家评价性抽检,采用法定标准方法对抽检样品的有关物质及含量测定项目进行检验,并对不同企业的样品进行了稳定性研究及样品使用期有关物质增长情况研究,采用LC-MS方法对含量较高的有关物质进行了结构确认,根据研究结果对企业标准及《中华人民共和国药典》(2020年版)各论中有关物质的限度规定进行了科学性及合理性评估。结果按照法定标准检验,48批次的甘精胰岛素注射液样品有关物质及含量测定结果均合格,合格率100%。稳定性研究发现,部分企业样品有关物质的数量及含量结果偏高;样品使用期有关物质增长情况研究发现,部分企业样品中最大有关物质的含量有超出企业质量标准限度规定的风险。结论甘精胰岛素注射液总体质量较好。建议企业考察产品在货架期及使用期(尤其是近效期产品)的有关物质的增长情况,并参考《中华人民共和国药典》(2020年版)甘精胰岛素注射液各论,科学合理地制定标准限度规定。