Suboptimal control of nonlinear systems

The Modified LJ search method used by Nair[1] to find suboptimal controllers for linear systems is extended to the case of nonlinear systems. To illustrate the method, three numerical examples are discussed.     

An exact penalty function algorithm for solving general constrained parameter optimization problems

An exact penalty function type of algorithm is proposed to solve a general class of constrained parameter optimization problems. The proposed algorithm has the property that any solution obtained by it will always satisfy the problem constraints, and that it will obtain a solution to the constrained problem, within a given specified tolerance, by solving a single unconstrained problem, i.e. it is not necessary to solve a sequence of unconstrained optimization problems. The algorithm applies a modification of Rosenbrock's (Rosenbrock, 1960) polynomial boundary penalty function, and a negative exponential penalty function with moving parameters, to modify the objective function in the neighborhood of the constrained region; a robust unconstrained algorithm (Davison and Wong, 1975) is then used to solve the resulting unconstrained optimization problem. Some standard test functions are included to show the performance of the algorithhm. Application of the algorithm is then made to solve some computer-aided design problems occurring in the area of control system synthesis.     

Discrete event simulation of a proton therapy facility: A case study

Proton therapy is a type of particle therapy which utilizes a beam of protons to irradiate diseased tissue. The main difference with respect to conventional radiotherapy (X-rays, γ-rays) is the capability to target tumors with extreme precision, which makes it possible to treat deep-seated tumors and tumors affecting noble tissues as brain, eyes, etc. However, proton therapy needs high-energy cyclotrons and this requires sophisticated control-supervision schema to guarantee, further than the prescribed performance, the safety of the patients and of the operators. In this paper we present the modeling and simulation of the irradiation process of the PROSCAN facility at the Paul Scherrer Institut. This is a challenging task because of the complexity of the operation scenario, which consists of deterministic and stochastic processes resulting from the coordination-interaction among diverse entities such as distributed automatic control systems, safety protection systems, and human operators.     

Optimal control of primary coolant temperature in a nuclear plant

Optimal control theory is applied to the design of a temperature controller for the primary coolant in a nuclear power plant. The optimal control law is obtained via orthogonal transformations applied to an augmented system consisting of models of the plant and measurable disturbances and a reference model to follow. Divergent oscillations caused by velocity limits of the actuator are suppressed by a new anti-reset windup device. Performances and robustness of this control system are examined and shown to be superior to that of other existing or proposed controllers.     

Application of modern control concepts on a kraft paper machine

This is a case study from the DAPP project, the main goals of which were to furnish improved knowledge about computer control to the Norwegian paper industry, to install a computer system including some recently developed software systems, and finally to test some modern approaches in control theory to the automatic feedback regulation on sub-processes of a Kraft paper machine. In this paper, two such processes will be presented in some detail: Least Square Quadratic (L.S.Q.) Optimal control theory applied to the control of a pressurized headbox, and to the control of thick stock consistency control. The systems have been running in the mill almost continuously since 1972. Four years of experience proves that these systems were successful implementations of modern control theory.     

全局优化视角下的有色冶金过程建模与控制

为提高生产效率、降低能源消耗、减少环境污染,需要对有色冶金过程进行建模,在系统模型的基础上,通过控制与优化技术,使过程系统运行在最优工况.本文以几个典型有色冶金过程为背景,阐述有色冶金过程建模、控制与优化三者之间的内在关联;从科学研究层次的角度上指出建模、控制与优化分属于不同层次的问题,且从方法论的角度指出建模、控制分两步进行:选择模型结构和估计模型参数、选择控制器结构和整定控制器参数,有色冶金过程系统模型、控制器的结构和参数确定问题均可以看成是非凸优化问题;探讨了全局优化视角下,建模、控制问题转化为优化问题以及在求解优化问题过程中存在的难点,提出解决这些难点的一些可行方案.     

混杂系统的研究进展

混杂系统理论和应用是近年来的一个研究热点．在介绍混杂系统概念的基础上，对混杂系统研究中的常用模型进行分类比较，并对混杂系统的性质分析和混杂控制设计中的主要内容和主要研究方法进行总结，最后对今后的研究方向做了总体展望。     

A software modeling approach for the design and analysis of cooperative optimization systems

Optimization problems are ubiquitous in our daily lives and one way to cope with them is using cooperative optimization systems that allow to obtain good enough, fast enough, and cheap enough solutions. From a practical point of view, the design and the analysis of such systems are complex tasks. In this work, an integrated system (DACOS) for helping in the design and analysis of cooperative, centralized optimization systems is presented. Also, the methodology used for the creation of DACOS (mainly, the use of software modeling) is described in detail. This may also be useful for researchers who want to build up their own system for their particular needs. DACOS has been developed using the Eclipse developing framework, which, among other advantages, is also able to automatically generate source code. Finally, a practical case of use is presented: the application of DACOS to the configuration and analysis of a cooperative strategy on a location problem. Copyright © 2010 John Wiley & Sons, Ltd.     

烧结法配料过程计算机控制系统

针对烧结法配料过程的工艺特点及技术要求,提出了实现综合生产指标优化的配料过程计算机控制系统,讨论了由过程控制、过程管理二层结构组成的计算机控制系统的结构、功能及优化控制策略,基于人工智能方法实现了过程控制。该系统成功应用于某氧化铝厂烧结法配料生产过程,磨机产能和生料浆一次配料合格率得到了大幅度提高,实现了配料过程的优化控制、优化运行、优化管理,取得了显著的应用成效。     

Practical-optimal control of a drum boiler power plant

Multivariable control of power plants has been studied by many researchers and also a number of practical applications have been presented in the last few years with the aim of improving the load following capabilities of thermal units. This paper summarizes the main results of an experimental application of optimal control to a drum boiler power plant at the Italian national electricity board. Referring to a previous work for the process model building, first a model reduction is performed with the main purpose of getting a simplified control structure. Then, an optimal regulator including feedforward and integral control is synthesized and some practical drawbacks of the synthesis are discussed with referrence to traditional control schemes leading to a reformulation of the optimal regulator which, while conserving optimality, exhibits a number of practical advantages and improved robustness against typical plant parameter variations. Since the motivation of the control structure reformulation is mostly derived from experimental results, field trials are reported where the performances of a well tuned coordinated control, of the classical optimal regulator and of the reformulated optimal control structure are compared. Perspectives of future industrial applications are briefly discussed in the conclusions.     

Computer aided design of multivariable nonlinear control systems using frequency domain techniques

The application of frequency domain methods to the study of a class of multivariable nonlinear feedback systems is considered within the context of a comprehensive interactive graphics design procedure and a new computational method is outlined for the determination of limit cycle operation which emphasises the effects of off diagonal system elements. It is shown how compensation can be applied using classical graphical design methods to avoid critical regions in the frequency domain. Two examples of use are given.     

A simulation optimization approach in production planning of failure prone manufacturing systems

In this paper, the implementation of a new method to control the production rate of manufacturing systems, based on the combination of stochastic optimal control theory, discrete event simulation, experimental design and response surface methodology is outlined. The system under study consists of several parallel machines, multiple-product manufacturing system. Machines are subject to failures and repairs and their capacity process is assumed to be a finite state Markov chain throughout the analytical control model. The problem is to choose the production rates so as to minimize the expected discounted cost of inventory/backlog over an infinite horizon. We first show that, for constant demand rates and exponential failure and repair times distributions of the machines, the hedging point policy is optimal. The structure of the hedging point policy is then parameterized by factors representing the thresholds of involved products. With such a policy, simulation experiments are combined to experimental design and response surface methodology to estimate the optimal control policy. We obtain that the hedging point policy is also applicable to a wide variety of complex problems including non-exponential failure and repair times distributions and random demand rates. Analytical solutions may not be easily obtained for such complex situations.     

Asymptotic methods in the optimal control of distributed systems

A short review of the various problems which arise in connection with the use of asymptotic methods in the optimal control of distributed systems is presented. We consider the cases when the asymptotic analysis comes from the state equation, or from the cost function, or both and also when the state equation is defined in perturbed domains.     

Computer systems simulation in education: Description of an experience

Computer Simulation will play an important role in future changes in Education. Here we will review how the Spanish National Project for Computers in Education, called Atenea, looks at Modelling and Simulation and how the first training courses for teachers, recommended by this project, are being carried out. We will give particular attention to the applications of the Simulation in the classroom using System Dynamics techniques. A real case study, developed by the pupils of a Simulation course for teachers, is outlined showing numerical and graphics results. Afterwards, SDSE—System Dynamics Simulator for Education—is superficially described: it is a microcomputer based system which has been developed by the authors to assist the process of building and simulating System Dynamics models in educative environments.Finally, some pedagogical applications, alternatives of use and major problems of the Simulation in educational environments are presented.     

A computer-enabled solution procedure for food wholesalers’ distribution decision in cities with a circular transportation infrastructure

This paper addresses the food distribution decision from a wholesaler's perspective, as the wholesalers are often faced with thorny issues such as when, where, how to deliver products at the lowest costs to best satisfy the retailers’ changing needs. This research relies on a distribution problem encountered at Northern Grocery Company in Beijing as an example to develop a two-stage solution procedure and subsequent computer-enabled programs for identifying efficient vehicle routing alternatives. The solution process, which integrates heuristic search algorithms and an integer programming model, can be applied to a wide range of distribution problems with specified route durations and a circular transportation network structure as exemplified by City of Beijing.     

A control engineering review of fuzzy systems

Many complex industrial processes cannot be satisfactorily controlled using the results of modern control theory, mainly because their precise structure is unknown. However, this is often balanced by a considerable amount of ‘engineering feel’ for the process which is difficult to quantify and utilise. Fuzzy set theory is a relatively new concept which allows this qualitativeness to be expressed rigorously and in this paper its usefulness for control is assessed. The state of the art is reviewed and reveals a surprising number of practical successes.     

Control of linear systems with multiparameter singular perturbations

The singular perturbation theory is extended to systems with several small parameters which can change the system order. Difficulties arising in testing the boundary layer stability in multiparameter linear problems are discussed. The theory is applied to linear quadratic optimal control and Nash game problems.     

冷连轧计算机控制仿真系统结构与功能

在对某钢厂冷连轧机计算机控制系统的仿真过程中,力度参数的预计算是仿真系统的核心内容。该文通过对原设定值预计算系统的消化研究,总结出了原系统设定计算模块的基本结构及基本功能,依此对仿真系统进行了设计,就信息系统计算中存在的几个问题提出了解决方法,并讨论了仿真结果。     

A simplified fuzzy multivariable structure in a manufacturing environment

Applications of fuzzy control to industrial processes are mainly of multivariable structure. Using the traditional Zadeh principle would require a multidimensional relation to be developed representing a fuzzy model of the system. Such a multidimensional relation would result in memory overload to most industrial computers. Moreover, it would result in a highly complex compositional rule of inference to achieve the final output(s) of the system. This paper proposes a new simplified technique that avoids such complexity as well as memory overload for multivariable structure. Section 2 describes the proposed simplified multivariable technique to avoid memory overload. Section 3 demonstrates these techniques in the form of a robotic welding example where the objective is to control the speed of a robotic arm following an irregular path of weld. The speed value is dependent on the cavity size and determined by the cavity width and cavity depth as inputs. Section 4 describes an experimental application of the technique applied to an industrial process in the manufacture of force transducers termed as the cornering process. This application is composed of a two-inputs-two-outputs system.     

Large scale control problems in electric power systems

The main large-scale control problems in electric power system operation, from optimal allocation of generation and transmission resources to network state estimation, frequency and exchange power control, system stability and dynamic security, are illustrated and the methods presently used to solve them are recalled. Special attention is given to significant applications of decomposition by physical decoupling and relaxation or by time-division of decentralized controls, of coordination and hierarchies, with a brief mention of large system analysis areas open to further development.