Batch Process Modelling and Optimal Control Based on Neural Network Model

This paper presents several neural network based modelling, reliable optimal control, and iterative learning control methods for batch processes. In order to overcome the lack of robustness of a single neural network, bootstrap aggregated neural networks are used to build reliable data based empirical models. Apart from improving the model generalisation capability, a bootstrap aggregated neural network can also provide model prediction confidence bounds. A reliable optimal control method by incorporating model prediction confidence bounds into the optimisation objective function is presented. A neural network based iterative learning control strategy is presented to overcome the problem due to unknown disturbances and model-plant mismatches. The proposed methods are demonstrated on a simulated batch polymerisation process.     

Batch Process Modelling and Optimal Control Based on Neural Network Models

This paper presents several neural network based modelling, reliable optimal control, and iterative learning control methods for batch processes. In order to overcome the lack of robustness of a single neural network, bootstrap aggregated neural networks are used to build reliable data based empirical models. Apart from improving the model generalisation capability, a bootstrap aggregated neural network can also provide model prediction confidence bounds. A reliable optimal control method by incorporating model prediction confidence bounds into the optimisation objective function is presented. A neural network based iterative learning control strategy is presented to overcome the problem due to unknown disturbances and model-plant mismatches. The proposed methods are demonstrated on a simulated batch polymerisation process.     

Bioreactor temperature profile controller using inverse neural network (INN) for production of ethanol

This paper presents the use of inverse neural networks (INN) for temperature control of a biochemical reactor and its effect on ethanol production. The process model is derived indicating the relationship between temperature, pH and dissolved oxygen. Using fundamental model obtained data sets; an inverse neural network has been trained using the back-propagation learning algorithm. Two types of temperature profile are used to compare the performance of the INN and conventional PID controllers. These controllers have been simulated in MATLAB for a quantitative comparison. The results obtained by the neural network based INN controller and by the PID controller are presented and compared. There is an improvement in the performance of INN controller in settling time and dead time and steady state error over the PID controller.     

Development of PARS-EX pilot plant to study control strategies

A PARtially Simulated EXothermic chemical reactor (PARS-EX) pilot plant is developed in this work to carry out and evaluate various conventional and advanced control strategies. In this reactor, the heat generated from the assumed exothermic reaction was simulated through the use of a controlled steam flow rate into the reactor. Since there is no actual reaction involved, the system is defined as a ‘partially simulated’ reactor. The temperature of the reactor was regulated by an external plate heat exchanger that both cools the process fluid and recycles it back into the reactor. A software interface was also developed to exchange real online data and implement the various control strategies. The advanced control strategies used to control the temperature of the reactor in this work are the neural network-based controllers, which overcome the hassle in periodically tuning conventional controllers. An adaptive method is also incorporated to cater for changes in the process conditions. Tests involving set point tracking and various external and internal disturbance changes were carried out to evaluate and demonstrate the robustness of the neural network-based controllers on the PARS-EX plant. For all of the realistic online cases studied, the neural network-based controllers exhibit better control results compared to the conventional controllers.     

非线性时滞系统的稳定自适应控制

针对模型不确定性的连续时间时滞系统，提出了一种新的神经网络自适应控制。系统的辨识模型是由神经网络和系统的已知信息组合构成，在此基础上，建立时滞系统的预测模型。基于神经网络预测模型的自适应控制器能够实现期望轨线的跟踪，理论上证明了闭环系统的稳定性。连续搅拌釜式反应器仿真结果表明了该控制方案的有效性。     

Experimental application of nonlinear model predictive control: temperature control of an industrial semi-batch pilot-plant reactor

This paper describes the application of nonlinear model predictive control (NMPC) to the temperature control of a semi-batch chemical reactor equipped with a multi-fluid heating/cooling system. The strategy of the nonlinear control system is based on a constrained optimisation problem, which is solved repeatedly on-line by a step-wise integration of a nonlinear dynamic model and optimisation strategy. A supervisory control routine has been developed, based on the same nonlinear dynamic model, to handle automatically the fluid changeovers. Both NMPC and supervisory control have been implemented on a PC and applied to a 16 l batch reactor pilot plant. Experiments illustrate the feasibility of such a procedure involving predictive control and supervisory control.     

Model predictive control of an industrial packed bed reactor using neural networks

This paper discusses an industrial application of a multivariable nonlinear feedforward/feedback model predictive control where the model is given by a dynamic neural network. A multi-pass packed bed reactor temperature profile is modelled via recurrent neural networks using the backpropagation through time training algorithm. This model is then used in conjunction with an optimizer to build a nonlinear model predictive controller. Results show that, compared with conventional control schemes, the neural network model based controller can achieve tighter temperature control for disturbance rejection     

基于并行自学习的神经网络内模控制及其应用研究

基于在线并行自学习的神经网络内模控制,该方法是借助于神经网络对复杂系统的辩识能力对被控对象进行正模型及逆模型的辩识,用NNM辩识对象的正模型,通过一个并行自学习系统训练的NNC辩识对象的逆模型,然后用做内模控制器去控制对象。将该种控制策略应用于火电厂热工对象中具有大迟延、大惯性和时变等特性的主汽温对象,仿真研究表明,该控制方案适应对象参数的变化并表现出良好的控制特性,具有较强的鲁棒性和自适应能力。在实际应用中具有一定的实用价值。     

Nonlinear modeling and adaptive fuzzy control of MCFC stack

To improve availability and performance of fuel cells, the operating temperature of molten carbonate fuel cells (MCFC) stack should be controlled within a specified range. However, the most existing models of MCFC are not ready to be applied in synthesis. In this paper, a radial basis function neural networks identification model of MCFC stack is developed based on the input–output sampled data. A novel adaptive fuzzy control procedure for the temperature of MCFC stack is also developed. The parameters of the fuzzy control system are regulated by back-propagation algorithm, and the rule database of the fuzzy system is also adaptively adjusted by the nearest-neighbor-clustering algorithm. Finally using the neural networks model of MCFC stack, the simulation results of the control algorithm are presented. The results show the effectiveness of the proposed modeling and design procedures for MCFC stack based on neural networks identification and the novel adaptive fuzzy control.     

Neural network synthesis for thermal processes

Neural networks are relatively new and highly attractive tools for modelling complex systems. The main feature of neural networks is their inherent plasticity which enables them to fit virtually any nonlinear function provided they have a sufficient number of parameters. Neural networks are a general class of nonlinear systems. Neural models can be used advantageously to model the dynamic behaviour of physical processes. In this paper, feedforward neural networks are used for modelling of dynamic thermal processes. The synthesis of neural networks is directly associated with the minimization of an objective function normally defined as the square of the difference between the output of the process being modelled and the output predicted by the network. Learning schemes are used for the evaluation of the connection weights of the feedforward neural network. In this paper, the dynamic modelling of several thermal processes using feedforward neural networks is presented. In one example, the identified neural model of the inverse of the plant is used as a controller.     

Multivariable predictive control of a pressurized tank using neural networks

The behavior of a multivariable predictive control scheme based on neural networks applied to a model of a nonlinear multivariable real process, consisting of a pressurized tank is investigated in this paper. The neural scheme consists of three neural networks; the first is meant for the identification of plant parameters (identifier), the second one is for the prediction of future control errors (predictor) and the third one, based on the two previous, compute the control input to be applied to the plant (controller). The weights of the neural networks are updated on-line, using standard and dynamic backpropagation. The model of the nonlinear process is driven to an operation point and it is then controlled with the proposed neural control scheme, analyzing the maximum range over the neural control works properly.     

时滞系统的神经网络辨识与控制算法

针对时滞系统、应用神经网络的非线性逼近能力,采用神经网络实现内模控制中被控对象的正模型及内模控制器,用Lyapunov稳定性定理证明神经网络控制系统的稳定性。仿真结果说明神经网络内模控制方案的优越性。     

Optimal Process Control Using Neural Networks

Infinite time optimal controllers have been designed for a dispersion type tubular reactor model by using the framework of adaptive critic optimal control design. For the reactor control problem, which is governed by two coupled nonlinear partial differential equations, an optimal controller synthesis is presented through two sets of neural networks. One set of neural networks captures the relationship between the states and the control, whereas the other set of networks captures the relationship between the states and the costates. This innovative approach embeds the solutions to the optimal control problem for a large number of initial conditions in the domain of interest. Although the main aim of this paper is to solve a process control problem, the methodology presented here can be viewed as a practical computational tool for many problems associated with nonlinear distributed parameter systems. Numerical results demonstrate the viability of the proposed method.     

Multivariable Control of a Pulsed Liquid-Liquid Extraction Column by Neural Networks

Modelling and control of chemical process systems are usual applications of artificial neural networks that have been explored so far with success. This paper deals with the potential application of neural networks to the multivariable control of a solvent extraction pilot plant. The pilot plant to be controlled is a pulsed liquid-liquid extraction column, which presents a non-linear behaviour and time-varying dynamics. Previous works have shown that the column could be maintained in its optimal behaviour by means of the control of conductivity by action on the pulse frequency. A given product specification can be obtained by the control of the product concentration in the outlet stream by acting on the solvent feed-flow rate. Owing to interactions between one variable and the other, a two input– two output control scheme has been developed and implemented. Promising experimental results have been obtained by using neural networks as an alternative tool for online control of chemical plant with dynamic changes.     

基于多层局部回归神经网络的多变量非线性系统预测控制

以罐式搅拌反应器为例,针对复杂多变量系统的强耦合性、非线性、时变性等问题,研究了多变量非线性系统的预测控制及改善控制性能的方法,采用多层局部回归神经网络离线建立预测模型,以偏差补偿和模型修正相结合的方式对预测模型进行误差补偿,以要线校正用于预测控制,通过对性能指标中的偏差项负指数加权,进一步改善预测控制性能,住址结果表明了控制算法的有效性。     

基于智能方法的真空退火炉建模与控制

真空退火炉中工件温度的精确控制是一个具有非线性和不确定性的复杂控制问题．为了实现工件温度的精确控制，以现场实际采集的数据为基础，采用小波神经网络建立对象的模型,利用自适应免疫遗传算法对小波神经网络的权值、小波基的个数和伸缩、平移因子等进行优化，提出了一种精确控制真空退火炉工件温度的优化数学模型，仿真与实验研究表明，用此方法建立的模型,其控制效果优于BP神经网络所建立模型的控制；同时，加快了网络训练速度，提高了系统的稳态精度，使系统具有较强的实时性和鲁棒性．     

热工过程时滞对象的神经网络内模控制

针对火电厂热工过程的时滞对象，提出采用基于神经网络的内模控制方法，即用神经网络对复杂系统的辨识能力来实现内模控制中被控对象的正模型及内模控制器。仿真研究表明，文中所采用的控制方案比常规PID控制表现出更好的控制品质，在实际应用中具有一定的实用价值。     

Nonlinear control structures based on embedded neural system models

This paper investigates in detail the possible application of neural networks to the modeling and adaptive control of nonlinear systems. Nonlinear neural-network-based plant modeling is first discussed, based on the approximation capabilities of the multilayer perceptron. A structure is then proposed to utilize feedforward networks within a direct model reference adaptive control strategy. The difficulties involved in training this network, embedded within the closed-loop are discussed and a novel neural-network-based sensitivity modeling approach proposed to allow for the backpropagation of errors through the plant to the neural controller. Finally, a novel nonlinear internal model control (IMC) strategy is suggested, that utilizes a nonlinear neural model of the plant to generate parameter estimates over the nonlinear operating region for an adaptive linear internal model, without the problems associated with recursive parameter identification algorithms. Unlike other neural IMC approaches the linear control law can then be readily designed. A continuous stirred tank reactor was chosen as a realistic nonlinear case study for the techniques discussed in the paper.     

A reliable multi-objective control strategy for batch processes based on bootstrap aggregated neural network models

This paper presents a reliable multi-objective optimal control method for batch processes based on bootstrap aggregated neural networks. In order to overcome the difficulty in developing detailed mechanistic models, bootstrap aggregated neural networks are used to model batch processes. Apart from being able to offer enhanced model prediction accuracy, bootstrap aggregated neural networks can also provide prediction confidence bounds indicating the reliability of the corresponding model predictions. In addition to the process operation objectives, the reliability of model prediction is incorporated in multi-objective optimisation in order to improve the reliability of the obtained optimal control policy. The standard error of the individual neural network predictions is taken as the indication of model prediction reliability. The additional objective of enhancing model prediction reliability forces the calculated optimal control policies to be within the regions where the model predictions are reliable. By such a means, the resulting control policies are reliable. The proposed method is demonstrated on a simulated fed-batch reactor and a simulated batch polymerisation process. It is shown that by incorporating model prediction reliability in the optimisation criteria, reliable control policy is obtained.