Fault-Tolerant Control of Nonlinear Systems Based on Fuzzy Neural Networks

Due to its great potential value in theory and application,fault-tolerant control strategies of nonlinear systems,especially combining with intelligent control methods,have been a focus in the academe.A fault-tolerant control method based on fuzzy neural networks was presented for nonlinear systems in this paper.The fault parameters were designed to detect the fault,adaptive updating method was introduced to estimate and track fault,and fuzzy neural networks were used to adjust the fault parameters and construct automated fault diagnosis.And the fault compensation control force,which was given by fault estimation,was used to realize adaptive fault-tolerant control.This framework leaded to a simple structure,an accurate detection,and a high robustness.The simulation results in induction motor show that it is still able to work well with high dynamic performance and control precision under the condition of motor parameters' variation fault and load torque disturbance.

Adaptive Backstepping Output Feedback Control for SISO Nonlinear System Using Fuzzy Neural Networks

In this paper, a new fuzzy-neural adaptive control approach is developed for a class of single-input and single-output （SISO） nonlinear systems with unmeasured states. Using fuzzy neural networks to approximate the unknown nonlinear functions, a fuzzy- neural adaptive observer is introduced for state estimation as well as system identification. Under the framework of the backstepping design, fuzzy-neural adaptive output feedback control is constructed recursively. It is proven that the proposed fuzzy adaptive control approach guarantees the global boundedness property for all the signals, driving the tracking error to a small neighbordhood of the origin. Simulation example is included to illustrate the effectiveness of the proposed approach.

Fault detection for nonlinear networked control systems based on fuzzy observer

Security and reliability must be focused on control sys- tems firstly, and fault detection and diagnosis （FDD） is the main theory and technology. Now, there are many positive results in FDD for linear networked control systems （LNCSs）, but nonlinear networked control systems （NNCSs） are less involved. Based on the T-S fuzzy-modeling theory, NNCSs are modeled and network random time-delays are changed into the unknown bounded uncertain part without changing its structure. Then a fuzzy state observer is designed and an observer-based fault detection approach for an NNCS is presented. The main results are given and the relative theories are proved in detail. Finally, some simulation results are given and demonstrate the proposed method is effective.

Sensor Fault Diagnosis for a Class of Time Delay Uncertain Nonlinear Systems Using Neural Network

In this paper,a sliding mode observer scheme of sensor fault diagnosis is proposed for a class of time delay nonlinear systems with input uncertainty based on neural network.The sensor fault and the system input uncertainty are assumed to be unknown but bounded.The radial basis function (RBF) neural network is used to approximate the sensor fault.Based on the output of the RBF neural network,the sliding mode observer is presented.Using the Lyapunov method,a criterion for stability is given in terms of matrix inequality.Finally,an example is given for illustrating the availability of the fault diagnosis based on the proposed sliding mode observer.

Estimation of Hammerstein nonlinear systems with noises using filtering and recursive approaches for industrial control

This paper discusses a strategy for estimating Hammerstein nonlinear systems in the presence of measurement noises for industrial control by applying filtering and recursive approaches.The proposed Hammerstein nonlinear systems are made up of a neural fuzzy network(NFN)and a linear state`-space model.The estimation of parameters for Hammerstein systems can be achieved by employing hybrid signals,which consist of step signals and random signals.First,based on the characteristic that step signals do not excite static nonlinear systems,that is,the intermediate variable of the Hammerstein system is a step signal with different amplitudes from the input,the unknown intermediate variables can be replaced by inputs,solving the problem of unmeasurable intermediate variable information.In the presence of step signals,the parameters of the state-space model are estimated using the recursive extended least squares(RELS)algorithm.Moreover,to effectively deal with the interference of measurement noises,a data filtering technique is introduced,and the filtering-based RELS is formulated for estimating the NFN by employing random signals.Finally,according to the structure of the Hammerstein system,the control system is designed by eliminating the nonlinear block so that the generated system is approximately equivalent to a linear system,and it can then be easily controlled by applying a linear controller.The effectiveness and feasibility of the developed identification and control strategy are demonstrated using two industrial simulation cases.

A Fuzzy-Neural Network Control of Nonlinear Dynamic Systems

In this paper, an adaptive dynamic control scheme based on a fuzzy neural network is presented, that presents utilizes both feed-forward and feedback controller elements. The former of the two elements comprises a neural network with both identification and control role, and the latter is a fuzzy neural algorithm, which is introduced to provide additional control enhancement. The feedforward controller provides only coarse control, whereas the feedback controller can generate on-line conditional proposition rule automatically to improve the overall control action. These properties make the design very versatile and applicable to a range of industrial applications.

An Improved SPSA Algorithm for System Identification Using Fuzzy Rules for Training Neural Networks

Simultaneous perturbation stochastic approximation （SPSA） belongs to the class of gradient-free optimization methods that extract gradient information from successive objective function evaluation. This paper describes an improved SPSA algorithm, which entails fuzzy adaptive gain sequences, gradient smoothing, and a step rejection procedure to enhance convergence and stability. The proposed fuzzy adaptive simultaneous perturbation approximation （FASPA） algorithm is particularly well suited to problems involving a large number of parameters such as those encountered in nonlinear system identification using neural networks （NNs）. Accordingly, a multilayer perceptron （MLP） network with popular training algorithms was used to predicate the system response. We found that an MLP trained by FASPSA had the desired accuracy that was comparable to results obtained by traditional system identification algorithms. Simulation results for typical nonlinear systems demonstrate that the proposed NN architecture trained with FASPSA yields improved system identification as measured by reduced time of convergence and a smaller identification error.

Decentralized Control Based on FNNSMC for Interconnected Uncertain Nonlinear Systems

针对一类具有高阶关联项的大系统提出了一种新型控制器———模糊神经网络滑模控制器，该控制器将模糊神经网络与滑模控制器有机结合，消除了一般滑模控制器中的高频颤动现象，同时不需要知道系统中的不确定性和扰动的上界．实例仿真说明了控制器不仅能得到好的控制效果。

On-Line Real Time Realization and Application of Adaptive Fuzzy Inference Neural Network

In this paper, a modeling algorithm developed by transferring the adaptive fuzzy inference neural network into an on-line real time algorithm, combining the algorithm with conventional system identification method and applying them to separate identification of nonlinear multi-variable systems is introduced and discussed.

Adaptive NN stabilization for stochastic systems with discrete and distributed time-varying delays

A new adaptive neural network（NN） output-feedback stabilization controller is investigated for a class of uncertain stochastic nonlinear strict-feedback systems with discrete and distributed time-varying delays and unknown nonlinear functions in both drift and diffusion terms.First,an extensional stability notion and the related criterion are introduced.Then,a nonlinear observer to estimate the unmeasurable states is designed,and a systematic backstepping procedure to design an adaptive NN output-feedback controller is proposed such that the closed-loop system is stable in probability.The effectiveness of the proposed control scheme is demonstrated via a numerical example.

Fuzzy logic systems are equivalent to feedforward neural networks

Fuzzy logic systems and feedforward neural networks are equivalent in essence. First, interpolation representations of fuzzy logic systems are introduced and several important conclusions are given. Then three important kinds of neural networks are defined, i.e. linear neural networks, rectangle wave neural networks and nonlinear neural networks. Then it is proved that nonlinear neural networks can be represented by rectangle wave neural networks. Based on the results mentioned above, the equivalence between fuzzy logic systems and feedforward neural networks is proved, which will be very useful for theoretical research or applications on fuzzy logic systems or neural networks by means of combining fuzzy logic systems with neural networks.

基于智能体的电力系统分布式自适应抗干扰控制

针对多机电力系统中不可避免存在非线性、不确定特性和动态干扰等问题,基于径向基神经网络(RBFNN)和非线性干扰观测器(NDO)提出一种分布式自适应抗干扰控制器,以增强多机电力系统的暂态稳定性和鲁棒性。采用RBFNN处理系统中的未知非线性问题,并基于神经网络的输出设计NDO以实现对复合扰动的在线估计;在多智能体框架下为多机电力系统提出一种分布式自适应抗干扰控制策略,实时接收通信网络测量的数据并控制储能装置动作,在外部扰动下实现各电机转速的快速同步与跟踪,并利用Lyapunov稳定性理论证明闭环系统信号的收敛性。仿真实验表明:所提策略有效可行。

基于扰动观测器的双容液位系统RBF神经网络滑模控制

针对双容液位系统存在的外部扰动、模型参数不确定等问题,设计了一种基于非线性扰动观测器(nonlinear disturbance observer,NDOB)的径向基函数神经网络滑模控制(radial basis function neural network sliding mode control,RNNSMC)方法。建立双容液位系统数学模型,采用积分型滑模面来提高系统的鲁棒性,在常规积分滑模控制的基础上,通过RBF神经网络(RBF neural network,RNN)对系统的非线性函数进行逼近,并设计非线性扰动观测器估计外部扰动,选用Lyapunov稳定性判据证明了控制策略的闭环稳定性。仿真结果表明,所提控制策略与积分滑模控制(integral sliding mode control,ISMC)方法相比,不需要精确的数学模型,且控制精度更高,抗干扰能力更强。

制冷站双目标权重自适应非线性预测控制

针对传统制冷站控制系统易产生振荡,且无法实现系统性能整体优化的问题,本文提出一种制冷站非线性预测控制策略,优化目标函数设计为满足建筑冷量需求的同时,尽可能提高系统整体能效.为解决上述两个优化目标之间的矛盾关系,本文采用模糊逻辑设计了优化目标权重自适应模块,实时求取权重因子最优解;针对非线性系统在线优化求解困难问题,本文提出了基于神经网络的非线性滚动优化算法,采用神经网络作为反馈优化控制器,并将系统优化目标函数作为在线寻优性能指标,结合Euler-Lagrange方法和随机梯度下降法对控制器权值和阈值进行在线寻优,算法计算量小,占用存储空间适中,便于采用低成本的现场控制器实现制冷站预测控制.仿真实验结果表明,本文所提出的预测控制策略与PID控制相比,在未加入优化目标函数权重自适应模块情况下,系统平均能效比提高约32.5%;进行优化目标函数权重自适应寻优后,系统平均能效提高约39.43%.

具有状态约束的机械臂切换自适应控制

为了解决具有状态约束的机械臂的控制问题,本文针对一类具有全状态约束和状态不完全可测的切换严格反馈非线性系统进行研究,通过引入状态观测器、自适应神经网络和动态表面控制技术,设计了一种基于径向基函数(RBF)神经网络的自适应输出反馈控制方法。利用Lyapunov方法和平均驻留时间理论(ADT)保证了闭环系统所有信号是半全局一致最终有界的(SGUUB),通过数值例子仿真验证了所提方法的有效性。最后将该方法应用于带电机驱动的机械臂并进行仿真实验,仿真结果表明,机械臂轨迹跟踪误差很小,有着良好的控制精度,同时也表明所提出的控制算法能够应用于实际工程模型。

一类非线性系统的神经网络自适应区间观测器设计

本文研究了一类单输入单输出非线性系统的神经网络自适应区间观测器设计问题.针对由状态和输入所描述的未知非线性函数的界不可测,现有的区间观测器方法并未有效地处理系统含有参数不确定性的未知非线性函数.首先,本文构造两个径向基函数神经网络来逼近未知非线性部分,进而分别估计系统状态的上下界;然后,选择合适的Lyapunov函数,采用网络权值校正和网络误差选择机制确保所设计的误差动态系统有界和非负性,并证明了神经网络自适应区间观测器的稳定性;最后,通过仿真实例验证了所提出的神经网络自适应区间观测器的有效性.

全状态约束切换系统的自适应神经网络控制

为了解决非线性约束切换系统的控制问题,针对一类具有非对称时变全状态约束、状态不完全可测以及未知外部干扰的切换严格反馈非线性系统进行研究,引入状态观测器、自适应神经网络和动态表面控制技术,设计了一种基于径向基函数(RBF)神经网络的自适应输出反馈控制方法.通过采用非对称时变障碍李亚普洛夫函数(barrier lyapunov function,BLF)使系统的全部状态满足非对称时变约束条件,而Lyapunov方法和平均驻留时间理论则保证了闭环系统所有信号是半全局一致最终有界.最后,在所提控制律的作用下,输出跟踪误差可以减小到任意小,2个仿真实验结果也验证了所提控制算法的有效性.

风干扰下倾转旋翼飞行器直升机模态预设性能跟踪控制

倾转旋翼机具有在复杂环境下执行任务的能力,逐渐成为新构型飞行器领域研究的热点。针对风干扰下倾转旋翼机直升机模态的建模与跟踪控制问题,提出一种基于神经网络干扰观测器与预设性能方法的跟踪控制方法。首先,对倾转旋翼机进行分体建模,并将地面风对机体的影响设定成有界外部干扰的形式,建立了风干扰下的直升机模态动力学模型。其次,为了提高直升机模态跟踪控制的鲁棒性,采用神经网络逼近系统中的未知函数,并利用干扰观测器估计机体所受扰动。再次,基于上述设计,提出一种基于预设性能函数的抗干扰跟踪控制器,并通过Lyapunov方法证明跟踪误差是有界的。最后,仿真结果表明,所提方法的位置、角度跟踪误差在2 s内就能快速收敛,并且始终位于预设的性能界内。进一步表明所提算法能够有效实现倾转旋翼机的稳定跟踪控制,并具有良好的环境适应能力与鲁棒性。

A novel compensation-based recurrent fuzzy neural network and its learning algorithm

Based on detailed study on several kinds of fuzzy neural networks, we propose a novel compensationbased recurrent fuzzy neural network （CRFNN） by adding recurrent element and compensatory element to the conventional fuzzy neural network. Then, we propose a sequential learning method for the structure identification of the CRFNN in order to confirm the fuzzy rules and their correlative parameters effectively. Furthermore, we improve the BP algorithm based on the characteristics of the proposed CRFNN to train the network. By modeling the typical nonlinear systems, we draw the conclusion that the proposed CRFNN has excellent dynamic response and strong learning ability.