【作者】 李晴；

【导师】 何怡刚；

【作者基本信息】 湖南大学 ， 电气工程， 2013， 博士

【摘要】 模拟电路故障诊断理论和方法的研究是目前研究的热门课题。现代电子技术正在日新月异的高速发展，电路规模和结构日趋模块化和功能化，给模拟电路故障诊断提出了新的更具挑战性的要求。从本质上来看，模拟电路的故障诊断问题，属于一种模式识别问题。当前，模拟电路故障诊断研究中的两大问题是如何提取信号特征和如何建立诊断机的问题。小波理论的出现和发展，机器学习算法的日益成熟，使得利用小波对故障信号进行预处理，再利用机器学习算法来进行故障诊断成为有效和值得研究的解决方法，为模拟电路的故障诊断提供了新的有效途径。神经网络和支持向量机均为机器学习领域非常流行的方法。神经网络的优化原理是基于经验风险最小化，缺点是易陷入局部最优，但在处理大样本情况时性能很好；而支持向量机有严格的理论和数学基础，基于结构风险最小化原则,泛化能力优于前者，且算法具有全局最优性,但目前主要是一种针对小样本统计的理论算法。因此本文在对遗传免疫算法、蚁群算法、小波分析、神经网络和支持向量机进行研究的基础上，深入探讨了模拟电路故障诊断神经网络方法和向量机方法存在的问题，提出一些新的融合算法用于对故障诊断分类器进行优化。而利用小波分析作为神经网络的预处理手段，进行信号的前置处理也是目前研究的热点，可以更好的提取故障信号的特征向量。适用合适的特征向量输入分类器进行故障诊断，可以提高诊断速度并得到更高的诊断正确率。基于此，本文也提出一种新的故障特征小波提取方法，并在实例中将得到的故障特征值输入神经网络完成故障诊断。本文最后还介绍了基于模拟电路故障诊断神经网络理论而研发的自动测试与诊断系统装备的相关技术方案，完成了模拟电路故障诊断神经网络方法从理论到实践的完整过程。本文的主要内容和创新点主要体现在以下几个方面：1．对模拟电路故障诊断的神经网络方法进行了研究。在分析和阐述了神经网络各种学习规则及用算法原理的基础上，着重介绍了BP网络和RBF网络，以及使用神经网络进行模拟电路故障诊断的方法，并详细分析和比较了两者各自的优缺点和适用的场合。2.对小波神经网络的模拟电路故障诊断方法进行了研究，并提出新的故障特征提取方法。小波的突出优点，是有良好的时频局部性，因此，可将小波作为故障诊断信号的预处理器，先利用小波变换来对电路测试节点的电压信号进行消噪和分解。本文针对分解后的小波系数，提出一种提取故障特征的方法，即小波系数各分量均方根法。具体操作方法是对消噪和分解后的信号进行小波变换，分别计算其小波系数各分量的均方根，然后再进行主元分析与归一化处理，将得到的数据作为故障特征，对神经网络进行训练，再用训练后的神经网络来进行故障分类，完成故障诊断过程。本文通过诊断实例对此方法进行了详细阐述，并通过诊断结果验证了方法的有效性和实用性。3.提出一种新的模拟电路故障诊断的优化神经网络方法。本文针对RBF网络核函数参数难以选择的缺点，提出一种新的优化算法——免疫蚁群算法，并将其用于RBF网络参数的寻优过程。接下来将通过优化得到的RBF网络用于模拟电路故障诊断，通过实例给出详细的训练算法。该方法在对免疫算法、蚁群算法进行深入研究的基础上，提出使用注入免疫因子的蚁群来实现对RBF网络核函数参数的寻优，新算法引入免疫算法的“抗体浓度”概念，使算法既具有全局搜索的能力，又提高了收敛性能，在充分搜索寻优空间的同时，提高算法的运行时间。本文对免疫蚁群算法和传统算法进行了比较，并通过诊断实例将免疫蚁群算法用于优化RBF神经网络。实例证明,同遗传神经网络进行比较，这种新的免疫蚁群RBF网络有较少的计算工作量，可以在更快的收敛速度下得到更高的诊断正确率。4.研究了支持向量机（Support Vector Machine,SVM）用做分类器的一般方法和过程，并提出了一种基于改进蚁群算法对向量机核函数进行优化的算法。支持向量机有扎实的理论基础，和传统的神经网络相比，算法的效率和精度都比较高。但SVM目前在处理海量数据和多分类问题时还存在一些困难，尤其是目前尚无成熟完善的理论来指导选择对分类器性能起关键作用的参数。基于此，本章提出了利用改进蚁群算法进行SVM核函数参数的寻优，利用蚁群算法的良好优化性能，减少SVM的训练量，再用SVM形成故障分类器，达到对故障进行快速诊断的目的。本章最后给出了将优化后的SVM应用于模拟电路故障诊断的仿真实例，并与使用传统双线性搜索法得到参数的SVM故障诊断进行了比较，证明了此方法的有效性、合理性和性能优势。5.描述基于DSP控制的自动测试与诊断系统(Automatic Test and DiagnosisSystem, ATS)的技术方案。在模拟电路故障诊断理论与方法的指导下，本文介绍了系统的测试原理，硬件结构和软件实现，给出了基于DSP控制的主板模块、激励源模块、数字测试模块、PCB模块的基本原理以及硬软件实现方案。更多还原

【Abstract】 Analog circuits fault diagnosis theory and method is currently a hot researchtopic. The rapid development of modern electronic technology and modular design ofcircuit size and structure proposed a more challenging requirement for analog circuitfault diagnosis. Basically, the problem of analog circuits fault diagnosis is a patternrecognition problem. The two major problems in this study are how to extract thesignal characteristics and how to create a diagnostic machine.The appearance and development of wavelet theory and machine learningalgorithms made the study move into a new level. Currently, it’s becoming a verypopular method to use wavelet analysis to pre-process the test signals and usemachine learning algorithm to do diagnosis. This solution provides a new andeffective way to solve the problem of analog circuit fault diagnosis.Neural network (NN) and support vector machine (SVM) both are effective andpopular methods in machine learning algorithm. The optimization principal of neuralnetwork is based on Empirical Risk Minimization (ERM). NN has a good performancein dealing with large sample case, but its disadvantage is easy to fall into localoptimum. The optimization principal of SVM is based on Structural RiskMinimization（SRM）,which made SVM has a strict mathematical theory basis. Also,SVM has global optimality and better generalization than NN. But at present, SVM ismainly a theoretically algorithm focus on small sample situation.Therefore, based on research about genetic algorithm, immune algorithm, antcolony system, wavelet analysis, NN and SVM, difficulties of NN-based analog faultdiagnosis approach and SVM-based analog fault diagnosis approach are discussed inthis dissertation. Next, some new optimization algorithms of NN and new waveletmethod of analog fault diagnosis are presented. At the last, a technical solutions ofrelevant automatic test and diagnosis system (ATDS) based on DSP，NN and expertsystem is introduced.The main contents and achievements of the paper are as follows:1. Neural-network-based fault diagnosis of analog circuits is proposed. Based onresearch and analysis of NN learning principle and application, back propagation (BP)neural network and radial basis function (RBF) neural network are introduced indetail. Described the application of the two networks in fault diagnosis, and compared the advantages and disadvantages of the two. Also, the applicable condition isdiscussed in detail in this paper.2. A new fault features extraction methods is proposed based on research aboutwavelet theory. The outstanding advantage of wavelet is good time-frequencylocalization. Therefore, we can use wavelet as a preprocessor to do de-noising anddecomposition of test node voltages of analog circuits. Then use the components ofwavelet coefficients to extract fault features. In this paper, a new method based on theroot mean square(RMS) value of the components of wavelet coefficients is proposed.After principal component analysis (PCA) and normalization, the RMS value is usedas the inputs of neural network to identify fault classes. The detailed steps are listedthrough diagnosis examples, and correctness of the methods is also verified.3. A new optimized neural network based fault diagnosis method of analogcircuits is proposed. Aimed to resolved the problem of hard to choose parameters forRBF neural network(RBFNN), a new method based on immune algorithm and antcolony system(ACS-IP) is presented. This method based on the research of immunealgorithm, ant colony system and genetic algorithm, which bring the concept ofimmune factor into ant colony. ACS-IP introduced ‘Antibody concentration’ toimprove global optimization and convergence of RBFNN. This method cansignificantly shorten the running time, at the same time, it can enlarge optimizationsearching space. The specific steps and application results of the new method andtraditional method are discussed in a comparing way in detail in this paper. Andsuperiority of ACS-IP is proved by the comparison. It has less computational work,faster convergence speed and higher diagnostic accuracy.4. A new optimization algorithm is proposed to select Support Vector Machine(SVM) parameters for analog circuit fault diagnosis. The theory and algorithm ofSVM, especially the application in fault diagnosis, is researched in this paper. Withsolid theoretical foundation, SVM has better performance than NN. But SVM hasdefects on dealing with mass data and multi-classification problems. Particularly,there is no developed method to choose parameter of SVM. An improved ant colonysystem is proposed to solve this problem. To get better performance with betterparameters, SVM can be designed as classifiers for fault diagnosis with less trainingand shorter running time. The effectiveness and superiority the proposed method isfurther verified by examples.5. Described the technical solution of Automatic Test and Diagnosis System (ATS). With the theoretical guide of neural network method to do analog circuit faultdiagnosis, the experimental device of DSP-based ATDS is built. This paper introducedthe basic design principles, hardware structure and software realization. The designrules and solution of communication between DSP and PC, DSP-based mainboard,excitement module, analog&digital testing module and printed circuit board (PCB)testing module are all presented in this paper.更多还原