【作者】 章国升；

【导师】 杨凌；

【作者基本信息】 兰州大学 ， 通信与信息系统， 2010， 硕士

【摘要】 非线性动态系统的辨识一直是控制领域研究的难点和热点。传统的前馈神经网络在处理非线性动态系统辨识中存在很多缺陷。而递归神经网络能够利用自身内部的状态反馈来描述系统的非线性特性,更适用于非线性系统的辨识。递归神经网络有很多不同的结构,本文介绍了5种常用的递归网络：Hopfield、Jordan、Elman、DRNN、ESN网络。并将Elman、DRNN、ESN网络模型用于实际非线性系统的辨识。对学习算法的研究一直是神经网络研究的核心。而递归神经网络常用的学习算法有BPTT、RTRL算法,它们都是基于梯度下降法的,因此避免不了误差梯度带来的诸多缺陷。因此本文在研究了3种常用智能优化算法的基础上,提出了2种改进的优化算法,对3个基准函数的优化比较了5种优化算法的性能,找到了性能最好的优化算法—IACA(Improved Ant Colony Algorithm),并将此算法用于优化神经网络的结构和参数。本文以兰州石化某厂乙烯、丙烯精馏塔动态化工系统为辨识对象,首先通过实验研究了Elman、DRNN网络用于非线性系统辨识的优势及不足,针对传统递归网络训练算法的缺陷,将IACA用于网络结构和参数的设计,获得了较好的辨识性能；此外,文章比较细致地研究了新型递归神经网络——ESN用于乙烯、丙烯精馏塔的辨识问题,主要研究了ESN网络的3个重要参数(储备池规模N、谱半径γ、连接密度(?))对网络辨识性能的影响,并针对常规ESN网络学习算法易导致病态解的问题,将IACA用于优化ESN网络的输出权值,获得了相对最佳的辨识结果。本文通过大量的仿真实验结果表明,递归神经网络相比于前馈网络更适合于非线性动态化工系统的辨识,将IACA算法引入到神经网络的结构及参数的设计中,有效地改善了网络的学习效率,提高了网络的训练速度,较好地克服了传统梯度下降法的局部极小问题以及ESN网络的病态解问题。基于对乙烯、丙烯精馏塔的辨识研究,本文最后提出了基于IACA算法的ESN网络辨识模型的精馏塔产品质量实时预测方案。文章最后对全文的工作进行了总结,并提出了一些今后研究工作的方向和重点。更多还原

【Abstract】 The identification of nonlinear dynamic system is always the difficulty and the focus in the fields of control research.There are many defects of Traditional feedforward neural networks in dealing with nonlinear dynamic system identification.And the recurrent neural network can use its own internal system of state-feedback to reflect the non-linear characteristics,so it is more suitable for nonlinear system identification.There are many different types of recurrent neural networks, and this paper has only described five common recurrent neural networks:Hopfield networks, Jordan network, Elman network, DRNN network and ESN network.In this paper,Elman, DRNN, ESN network models have used in the actual nonlinear system identification.The research of learning algorithm has always been the core of the neural network research.The learning algorithm of the recurrent neural network commonly use BPTT algorithm, RTRL algorithm, which are based on gradient descent.Therefore the commonly algorithms can not prevent many defects to the error gradient.After the study of three kinds of intelligent optimization algorithm,this paper has proposed two kinds of improved optimization algorithms and has compared the optimization results of three benchmark functions to find the best performance algorithm in the five kinds of optimization algorithms.The IACA algorithm has the best performance,and the algorithm has used to optimize the neural network structure and parameters.Taking the factory in Lanzhou,the dynamic chemical system petrochemical ethylene, propylene distillation column for the identification objects,First,It is advantages and disadvantages of the experimental study of the Elman,DRNN network for nonlinear system identification.There are many shortcomings of the traditional recurrent network training algorithm.So it has a better recognition performance for using the IACA algorithm to design the network structure and parameters.In addition,this paper has detailed studied a new type of recurrent neural networks which is ESN network,and has used it for the identification problem of ethylene, propylene distillation.Also this paper has studied the three important parameters (reserve pool size N, the spectral radiusγ,connection density (?)) of ESN network on the Network Identification properties.It is easily lead to pathological problems of ESN network regular learning algorithm,so this paper has used the IACA algorithm for optimizing the output weights of ESN network, and it has obtained the relative best results of identification.Through a large number of simulation experiments,the results show that recurrent neural networks are more suitable for nonlinear system identification than feedforward neural networks.Using the IACA algorithm to design the network structure and parameters,it can Effectively improve the network efficiency,improve the training speed of network,also it can solve the local minimum problem of traditional gradient descent and pathological problem of ESN Network.Finally,the distillation product quality real-time prediction program,which used the ESN network based on IACA algorithm,has proposed for the study identification of ethylene, propylene distillation.In the final of this paper,it summarizes the work of this article and proposes some future research directions and priorities.更多还原