基于改进LSSVM的城市轨道交通供电故障诊断方法

小样本条件下供电系统故障快速诊断是保证城市轨道交通安全稳定运行的保证.文中提出了一种基于量子粒子群优化最小二乘支持向量机(LSSVM)的供电系统故障诊断方法.该方法首先基于主成分分析提取能够表征系统运行状态的特征参数,并降低数据维数.然后利用LSSVM构建小样本故障诊断模型,通过量子粒子群算法对LSSVM模型参数进行优...     

用微机实现威布尔分布参数的双线性回归最小二乘估计

威布尔分布是可靠性分析中常用的一种分布,本文针对威布尔分布参数估计中传统的图估计法的弊端,阐述了用微机数值估计方法取代图估计法的可行性、必要性及其重要意义,根据双线性回归原理在微机上用Ｍａｔｌａｂ实现了威布尔分布参数的最小二乘估计。     

基于weibull模型的风机变桨器短期可靠性分析

作为变桨系统的核心,变桨驱动器的高可靠性是风力发电机安全、高效、可靠运行的重要保证。针对变桨器运行环境的复杂性、故障数据难以完整收集等特点,提出了一种基于威布尔分布模型的短期可靠性分析方法。该方法对变桨驱动器模型进行适当简化,以二参数威布尔分布模型建立元件的可靠度模型,以最小二乘法估计模型未知参数。去除变工况因素(如环境温度骤然升高、风速过大)对采集样本的影响,得到元件因耗损失效的寿命分布曲线及可靠度,并以内蒙某风场实际统计数据为例验证了方法的有效性。所得结论不仅可以使风场操作人员更有效的认知元件设备的寿命分布特征及当前所处的可靠度水平,从而作出合理的维修决策,降低维修成本;还可以为元件设备的研发、设计、生产人员提供辅助的理论支撑。     

基于LSM的LED寿命的计算与分析

准确地对LED寿命进行估计是十分必要的。通过加速寿命的试验就可以得到产品性能指标和可靠性指标的估计,从而了解产品的质量。其方法则是应用威布尔分布描述红外LED的寿命,采用最小二乘法,估计出威布尔参数,对各应力下的数据拟合直线,实现寿命图,并完成试验数据的统计和分析,算出其平均寿命和可靠寿命。     

威布尔分布下VFD恒定应力加速寿命试验与统计分析

为了精确地估计真空荧光显示器(VFD)的可靠性寿命,节省试验测试时间,通过建立加速寿命试验模型开展了4组恒定应力加速寿命试验,采用威布尔函数描述VFD寿命分布,利用最小二乘法(LSM)估计威布尔参数,完成了试验数据的统计分析,并自行开发了寿命预测软件,确定了加速寿命方程,实现了VFD的寿命估计。数值结果表明,试验设计方案是正确可行的,VFD的寿命服从威布尔分布,其加速模型符合线性阿伦尼斯方程,每个加速应力水平下VFD的失效机理不变,精确计算出的VFD寿命对其生产厂商和技术人员具有重要的指导意义。     

小时间尺度网络流量混沌性分析及趋势预测

小时间尺度的网络流量的混沌性被噪声掩盖难以预测,本文通过局部投影降噪得到可预测的混沌性流量趋势.针对网络流量存在的时变性和长周期性,提出一种最优样本子集在线模糊最小二乘支持向量机(Least Squares Support Vector Machine,LSSVM)预测方法:以与预测样本时间上以及欧式距离最近的样本点构...     

真空荧光显示屏恒定及步进应力加速寿命试验的研究

为了解决在较短的时间内预测真空荧光显示屏（VFD）寿命的问题,降低寿命预测成本,通过加大灯丝温度进行了恒定和步进应力相组合的加速寿命试验,研究制定了其加速寿命试验的设计方案。应用威布尔分布函数描述其寿命分布,利用最小二乘法完成了试验数据的统计和分析,并开发了寿命预测软件。研究结果表明．试验设计方案是正确可行的,VFD的寿命服从威布尔分布,其加速模型符合阿伦尼斯方程,加速参数的精确计算确保以后在很短的时间内便可估算出VFD在正常应力下的寿命。     

基于BRM的白光OLED恒定与步进应力加速寿命试验研究

为了获得白光OLED的寿命信息,通过加大电流应力开展了二组恒定和一组步进应力相组合的加速寿命试验。采用威布尔函数描述白光OLED的寿命分布,利用双线性回归法(BRM)估计出威布尔参数,确定了加速寿命方程,对白光OLED寿命是否符合威布尔分布进行了Kolmogorov-Smirnov检验,并利用自行开发的寿命预测软件计算出平均寿命和中位寿命。数值结果表明,恒定步进应力加速寿命试验方案是切实可行的,白光OLED的寿命服从威布尔分布,寿命应力关系满足线性Arrhenius方程,精确计算的加速参数可实现在短时间内OLED寿命的预测。     

Weibull分布下基于MLE的红外发光二极管寿命预测

为了对红外发光二极管(LED)恒定及步进应力加速寿命试验的数据进行统计分析,应用Weibull分布函数描述了其寿命分布,利用极大似然法(MLE)及其迭代流程图估计出形状参数和尺度参数,通过最小二乘法确定了红外LED加速寿命方程,对红外LED寿命是否符合威布尔分布进行了Kolmogorov-Smirnov检验,并利用自行开发的寿命预测软件计算出平均寿命和中位寿命。数值结果表明,红外LED的寿命服从Weibull分布,加速寿命方程符合逆幂定律,所估计出的红外LED的寿命对生产厂商和用户有很强的指导意义。     

一种基于最小二乘的K-分布参数估计方法

提出了一种基于最小二乘的K-分布参数估计方法,并利用仿真对该方法进行了验证。这种方法利用变量替换将杂波矩量和分布参数之间的关系转换为线性函数,然后通过最小二乘方法求解线性超定方程组获得K-分布参数的估计,这样能够避免常规矩量法在处理实际杂波数据时由于数据长度和噪声所导致的错误估计的发生,利用最小二乘法提高了估计精度。     

Estimating effective dielectric thickness for capacitors with extrinsic defects by a statistical method

Simulated capacitor breakdown voltage data are fit to a mixture of two Weibull distributions using the method of maximum likelihood. The dielectric thickness of extrinsic capacitors is estimated as a part of a mixture distribution, allowing simultaneous prediction of failure times using both intrinsic and extrinsic failures. Confidence intervals on the reliability parameters and the 10 year FIT rate at 5 V are successfully estimated using the delta method. The same approach is applied to a real data set with similar results.     

Effect of size and plasma treatment and the application of Weibull distribution on the breakdown of PECVD SiNx MIM capacitors

The dielectric breakdown field is one of the important concerns for device reliability. The breakdown of dielectric is originated at a fatal flaw that grows to cause failure and can be explained by the weakest-link theory. In this study, metal-insulator-metal (MIM) capacitors with plasma enhanced chemical vapor deposited (PECVD) SiN_x are prepared. Ammonia (NH₃) plasmas are applied after the deposition of the dielectric SiN_x. The Weibull distribution function, which is based on the weakest-link theory, is employed to analyze the effect of the electrode area as well as the plasma treatment on the breakdown of the MIM capacitors. The time dependent dielectric breakdown testing indicates a decrease in both the leakage current and the lifetime of the MIM capacitors treated with plasma. Possible dielectric degradation mechanisms are explored.     

Robustness of the exponential sequential probability ratio test (SPRT) when Weibull distributed failures are transformed using a “known” shape parameter

Assumptions accompanying exponential failure models are often not met in the life-testing of many products. Several authors have suggested sequential life testing techniques that transform Weibull failure times to an exponential density using the “known” Weibull shape parameter. In practice, this parameter is never known and must be estimated. This paper demonstrates that procedures based on this transformation are extremely sensitive to mis-specification of the shape parameter. Furthermore, it is doubtful that the shape parameter may be estimated with enough precision to successfully implement these procedures. Using a Weibull sequential test without the transformation yields better results; however, sensitivity analysis to shape parameter mis-specification is recommended before any specific test is implemented.     

Accelerated Life Test Planning With Independent Weibull Competing Risks With Known Shape Parameter

This article presents methodology for accelerated life test (ALT) planning when there are two or more failure modes, or competing risks which are dependent on one accelerating factor. It is assumed that the failure modes have respective latent (unobservable) failure times, and the minimum of these times corresponds to the product lifetime. The latent failure times are assumed to be s-independently distributed Weibull with known, common shape parameter. Expressions for the Fisher information matrix, and test plan criteria are presented. The methodology is applied to the ALT of Class-H insulation for motorettes, where temperature is the accelerating factor. Two-level, and 4:2:1 allocation test plans based on determinants, and on estimating quantiles or hazard functions, are presented. Sensitivity of optimal test plans to the specified Weibull shape parameter is also studied     

固态介质薄膜的电击穿场强

对于微电子和光电子元器件及其集成电路来讲,固态介质薄膜是一类重要的基础材料。它们的电击穿场强是一个特殊的特性参数。本文从理论上论述了这类薄膜的电击穿场强,并概述了现在所用的测试方法和多位研究者得出的测试结果。此外, 文中还分类提出了这类薄膜内的弱点类型。     

Reliability of Liquid Crystal Display

This paper reports the reliability of twisted nematic liquid-crystal display for basic applications such as watches and calculators. We have studied significant stress factors such as voltage, temperature and humidity, and their corresponding failure modes. The main failure mode is LCD misalignment; many different modes appear corresponding to different stress conditions as well as material and process for the LCD. We have analyzed the accelerated test results by Weibull distribution, elucidated accelerating factors, and estimated life time. The life is inversely proportional to 1.78-2.45 power of applied voltage, depending upon misalignment modes. The distribution of life is well expressed by Weibull distribution with shape parameter between 2.5-3.0, and proportional to the square of coefficient of variation of life. We conclude that the acceleration factors could be determined and 99.9% of tested displays will live more than 10 years. The knowledge on reliability of LCD can be now applied to new fields of LCD, such as industrial use, home appliance, and automotive instruments.     

Estimation of threshold stress in accelerated life-testing

The author presents a method that uses accelerated life-test data to estimate the mean life at the service stress and the threshold stress below which a failure is unlikely to occur. The relation between stress and mean-life at that stress is assumed to follow an inverse power law that includes a threshold stress. The failure times at a given stress are assumed to follow a Weibull distribution in which the shape parameter varies with the stress. This model extends the well-known Weibull inverse power law model. If only the mean life but not a specific percentile point at a service stress is sought, the maximum likelihood method is useful for parameter estimation. This is a tradeoff in the parametric approach. For adoption of an appropriate probability model, the likelihood ratio test as well as the Akaike Information Criterion are used. Type I right censored data are considered. Extensions of the method are discussed     

基于威布尔分布的某半导体器件贮存寿命分布规律初探

对有机电致发光二极管（Organic Light-Emitting Diode,OLED）微型显示器件进行90℃、80℃、70℃的高温贮存试验,获得产品的失效数据。基于威布尔分布模型,采用最小二乘法进行参数估计,对失效数据分析,获得OLED微型显示器件失效分布函数。应用经典可靠性理论,计算产品在90℃、80℃、70℃的特征寿命、可靠寿命及平均故障间隔时间（Mean Time Between Failure,MTBF）。采用Arrhenius模型,依据90℃、80℃、70℃的贮存特征寿命,获得常温下产品的贮存特征寿命。分析结果表明,该方法合理、简便、有效,数据结果可以进一步应用到推导产品常温贮存寿命。     

威布尔分布无故障数据的可靠性评估

对于威布尔分布无故障数据可靠性评估方法中形状参数已知和未知的两种方法,通过一个例子进行对比分析,指出当形状参数毫无所知时,所得到的基本可靠度置信下限估计最为保守。通过相似产品的信息和工程经验对形状参数作出一个较为精确的估计是可行的。     

Estimation of Weibull Parameters With Competing-Mode Censoring

Existing results are reviewed for the maximum likelihood (ML) estimation of the parameters of a 2-parameter Weibull life distribution for the case where the data are censored by failures due to an arbitrary number of independent 2-parameter Weibull failure modes. For the case where all distributions have a common but unknown shape parameter the joint ML estimators are derived for i) a general percentile of the j-th distribution, ii) the common shape parameter, and iii) the proportion of failures due to failure mode j. Exact interval estimates of the common shape parameter are constructable in terms of the ML estimates obtained by using i) the data without regard to failure mode, and ii) existing tables of the percentage points of a certain pivotal function. Exact interval estimates for a general percentile of failure-mode-j distribution are calculable when the failure proportion due to failure-mode-j is known; otherwise a joint s-confidence region for the percentile and failure proportion is calculable. It is shown that sudden death endurance test results can be analyzed as a special case of competing-mode censoring. Tabular values for the construction of interval estimates for the 10-th percentile of the failure-mode-j distribution are given for 17 combinations of sample size (from 5 to 30) and number of failures.