一种在线辨识扰动模型的MPC控制器及其在溶剂脱水塔装置中的应用

提出一种滚动时域伪线性回归（MHPLR）算法,不仅降低了算法对检测噪声的敏感程度,而且无须在线求解优化命题,计算负担小。利用MHPLR在线估计一个时间序列模型来描述DMC控制系统不可测扰动的动态特性。将对扰动的预报应用到DMC算法当中,以改善因原误差校正策略而导致的抗扰性能不佳的情况,并以状态空间形式给出了改进后DMC算法的表达式。将改进的DMC控制器应用到某公司的PTA溶剂脱水塔装置上,提升了控制品质,稳定了生产并降低了酸耗。算法的有效性得到了验证。     

Analysis of different control possibilities for the divided wall column: feedback diagonal and dynamic matrix control

This work addresses the control of the divided wall column (DWC) as a basic issue to be considered when this kind of distillation arrangement is used to take profit of its potential to reduce energy consumption. Different control structures of diagonal feedback control are compared using multiple input multiple output (MIMO) linear analysis tools in the frequency domain. A controllability analysis of the process is done for the separation of different mixtures and for different operating conditions, including optimal operation. As a result, it is seen that a trade off appears between energy minimisation and controllability. As an alternative, application of dynamic matrix control (DMC) to the DWC is also evaluated. Through simulation, the ability of DMC for disturbance rejection and setpoint tracking is studied and compared with that of the feedback diagonal control. Important limitations of using DMC for the composition control of the DWC are finally highlighted.     

Non‐Linear Model Predictive Control: A Personal Retrospective

An overview of non‐linear model predictive control (NMPC) is presented, with an extreme bias towards the author's experiences and published results. Challenges include multiple solutions (from non‐convex optimization problems), and divergence of the model and plant outputs when the constant additive output disturbance (the approach of dynamic matrix control, DMC) is used. Experiences with the use of fundamental models, multiple linear models (MMPC), and neural networks are reviewed. Ongoing work in unmeasured disturbance estimation, prediction and rejection is also discussed.     

Dynamic simulation of cyclic voltammogram on the electrochemical reduction of VO2+ ions

An electrochemical reduction of VO²⁺ ions in a formic acid electrolyte was analyzed by cyclic voltammetry. A new four step reaction mechanism, EECE, was proposed to derive the mass transfer equation, and then it was solved by numerical method, which enabled us to obtain theoretical cyclic voltammograms. Kinetic parameters such as diffusion coefficients, rate constants and transfer coefficients, describing the VO²⁺ ion reduction system, were estimated by fitting the theoretical curve with the experimental data. The parameters obtained were then evaluated on their extended applicability in various concentrations and scan rates. It was shown that the theoretical voltammograms obtained using the above parameters fitted well with the experimental curves for the scan rate variation from 2 to 20 V/sec, while the deviation increased in proportion to the VO²⁺ ion concentration.     

DEVELOPMENT OF A SUPERVISORY CONTROL STRATEGY FOR THE OPTIMAL OPERATION OF GRAIN DRYERS

ABSTRACT

In spite of the importance and especially high energy demands of grain dryers, relatively few studies have been carried out to discover the optimal conditions for their operation. High performance operation can only be achieved if an adequate operating strategy is developed. For its implementation, a reliable control structure is required, and some of the limitations of the conventional control strategies normally used in dryers are observed. These strategies are SISO; the control normally used presents low performance and the disturbance is characterized by several amplitudes and frequencies. A possible way to minimize this difficulty consists of defining the multilevel structure such that each level acts at a given amplitude and frequency. In order to implement this multilevel structure, an optimization problem was developed to function as a supervisory control and a predictive algorithm (DMC) was used for servo or regulatory control. The proposed DMC algorithm presented satisfactory results for the load rejection and set-point variation, only when a small disturbance was applied. For a larger disturbance an optimization procedure was necessary. The routine efficiently maintained the optimal operational conditions of the dryer and could be used in the supervisory control of the system.     

DEVELOPMENT OF A SUPERVISORY CONTROL STRATEGY FOR THE OPTIMAL OPERATION OF GRAIN DRYERS

In spite of the importance and especially high energy demands of grain dryers, relatively few studies have been carried out to discover the optimal conditions for their operation. High performance operation can only be achieved if an adequate operating strategy is developed. For its implementation, a reliable control structure is required, and some of the limitations of the conventional control strategies normally used in dryers are observed. These strategies are SISO; the control normally used presents low performance and the disturbance is characterized by several amplitudes and frequencies. A possible way to minimize this difficulty consists of defining the multilevel structure such that each level acts at a given amplitude and frequency. In order to implement this multilevel structure, an optimization problem was developed to function as a supervisory control and a predictive algorithm (DMC) was used for servo or regulatory control. The proposed DMC algorithm presented satisfactory results for the load rejection and set-point variation, only when a small disturbance was applied. For a larger disturbance an optimization procedure was necessary. The routine efficiently maintained the optimal operational conditions of the dryer and could be used in the supervisory control of the system.     

Fuzzy control of ethanol concentration for emulsan production in a fed-batch cultivation ofAcinetobacter Calcoaceticus RAG-1

A fuzzy control system was organized and applied to the control of ethanol concentration in a fed-batch cultivation process for emulsan production byAcinetobacter calcoaceticus RAG-1. The membership functions and fuzzy rules were determined by sets of data and experiences obtained from the preliminary culture experiments. The input variables, error (the difference between the set point value and the process variable) and the change of the error, were fuzzified by using the membership functions and the output variable, change of the ethanol feed rate, was inferred based on the membership functions and the given fuzzy rules. To obtain the numerical value for the output variable, the center-of-gravity method was used in the defuzzification procedure. The results showed that the ethanol concentration was well regulated around optimal level and the emulsan yield was increased compared with that of the cultivation controlled by the conventional feedback control loop.     

网络化动态矩阵控制及在倒立摆控制中的应用

针对不确定有界长时延网络控制系统,研究动态矩阵控制(DMC)算法及其稳定性问题。首先基于多输入多输出状态空间模型,推导针对长时延网络化控制系统的DMC算法;然后,利用Lyapunov稳定性理论和线性矩阵不等式方法,给出闭环控制系统渐近稳定的充分条件;最后,通过对倒立摆的实时控制验证笔者算法的有效性。     

碳酸二甲酯市场现状及技术进展

目前,全球碳酸二甲酯(DMC)的产量约为12万t/a。生产方法有光气法、酯交换法、甲醇氧化羰基法和二氧化碳-甲醇直接合成法。我国DMC产量不足3万t/a,主要采用酯交换法和甲醇液相氧化羰基法。DMC可作为羰基化试剂代替剧毒物质光气用于合成聚碳酸酯、异氰酸酯、杀虫剂西维因等,用作甲基化试剂代替致癌物硫酸二甲酯合成苯甲醚。     

电厂直接空冷系统汽轮机背压的控制方法

针对传统PID对直接空冷系统背压控制效果差的问题,提出一种基于动态矩阵控制算法的直接空冷系统汽轮机背压控制方法。根据动态矩阵控制算法建立了背压控制器模型,并将它与PID控制的背压控制效果进行了仿真对比,结果表明:与传统PID控制相比,动态矩阵控制算法的响应更快、更稳定。     

GRAPHICS-BASED CONTROL DESIGNS FOR NONMINIMUM-PHASE NONLINEAR SYSTEMS SUBJECT TO INPUT AND OUTPUT CONSTRAINTS

This article deals with the output regulation of nonminimum-phase systems subject to input and output constraints. Through the off-line static data reconciliation algorithm for a class of stable nonlinear bioreactors, the static feedforward control can ensure constant disturbance attenuation in spite of input multiplicities and actuators constraints. Under the pseudo-steady-state error diagnoses and a graphics-based mechanism for disturbance estimation, the proposed error feedback control scheme will induce the piecewise output regulation. Based on the “intelligent” algorithm for tuning improvement, the closed-loop simulation shows that the piecewise control strategy turns out to be robust against the unknown disturbances.     

多变量解耦自抗扰控制在气体流量装置中的应用

针对气体流量装置实验管路流量、压力耦合系统,通过机理法和阶跃响应法建立了其数学模型,并利用自抗扰解耦控制算法实现其解耦控制,以保证气体流量计性能测试过程的稳定性和控制快速性。对于气体流量装置多变量系统,自抗扰控制算法将耦合以及所有的内部不确定性和外部扰动都归结到总扰动中,通过扩张状态观测器和控制律对总扰动进行估计和补偿,使原系统被解耦成两个单输入单输出的子系统并利用PD控制器完成控制。自抗扰控制算法使系统在实现解耦的同时既减弱算法对于模型的依赖,又提高了系统的鲁棒性。仿真和实验结果表明,与PID控制算法相比,自抗扰控制算法调节时间更快,解耦效果更好,对扰动的抑制效果更优,性能鲁棒性更强。     

CFD simulation of paint deposition in an air spray process

This work analyzes the mechanism of spray deposition by means of computational fluid dynamics (CFD) in order to reproduce virtually the spraying of a paint gun adopted for use in the automotive industry and to predict paint drop trajectories and film builds on the target surface. The prediction of the flow of the continuous phase was obtained by solving the time averaged Navier-Stokes equations in connection with suitable closure models for turbulence (RNG and Realizable k-ε). The dispersed phase was treated by a Lagrangian approach, by tracking numerically a large number of representative particles from the gun exit to the target surface. The initial conditions for the droplets were estimated from a detailed simulation of the paint jet at the exit of the nozzle. In this way one could evaluate positions and velocities of droplets at impact and estimate the properties of the deposited layer of paint. The method was validated by comparison with experimental data obtained by phase doppler anemometry and, subsequently, the approach was applied to different geometries and operating conditions.     

Temperature control of highly exothermic batch polymerization reactors

In this article a highly exothermic batch polymerization reactor is considered. The reactor is simplified as a mixing tank with the internal heat generation treated as a disturbance. A fuzzy-hybrid-PID-feedback (FH-PID) control structure is developed in which the output of fuzzy hybrid portion is used to adjust the set point of a PID controller to compensate for the effect of the major disturbance, the heat of reaction. In this way, the hybrid portion of the controller does not influence the stability of the original PID control system. A fuzzy model was constructed to estimate the heat of reaction inside the fuzzy hybrid block. The fuzzy parameters of the hybrid portion do not depend on the process model and can be estimated from the transient response obtained with a conventional PID controller. This FH-PID control strategy has been applied to the temperature control of batch solution and batch inverse emulsion polymerizations of acrylamide in a 1 gallon pilot scale reactor. The results show that this fuzzy hybrid—PID-feedback control strategy improves the control performance of the batch polymerization reactor.     

Inorganic/organic nanocomposite coatings: The next step in coating performance

Inorganic/organic hybrid materials have considerable promise and are beginning to become a major area of research for many coating usages, including abrasion and corrosion resistance. Our primary approach is to prepare the inorganic phase in situ within the film formation process of the organic phase. The inorganic phase is introduced via sol-gel chemistry into a thermosetting organic phase. By this method, the size, periodicity, spatial positioning, and density of the inorganic phase can be controlled. An important aspect of the inorganic/organic hybrid materials is the coupling agent. The initial task of the coupling agent is to provide uniform mixing of the oligomeric organic phase with the sol-gel precursors, which are otherwise immiscible. UV-curable inorganic/organic hybrid systems have the advantages of a rapid cure and the ability to be used on heat sensitive substrates such as molded plastics. Also, it is possible to have better control of the growth of the inorganic phase using UV curing. It is our ultimate goal to completely separate the curing of inorganic and organic phases to gain complete control over the morphology, and hence optimization of “all” the coating properties. Thus far, it has been found that concomitant UV curing of the inorganic and organic phases using titanium sol-gel precursors afforded nanocomposite coatings which completely block the substrate from UV light while maintaining a transparent to visible light. Also, it has been found that the morphology of the inorganic phase is highly dependent on the concentration and reactivity of the coupling agent. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago, IL.     

Kinetics studies of dimethyl carbonate synthesis from urea and methanol over ZnO catalyst

A kinetic experiment of dimethyl carbonate (DMC) synthesis by urea methanol over ZnO catalyst was carried out in an isothermal fixed-bed reactor. A kinetic model based on the mole fraction was proposed and the kinetic parameters were estimated from the experimental results. The model predictions were compared with the experimental data and fair agreements were found. The effects of the reaction temperature (443–473 K), space time (0–4.7 h mol⁻¹ kg _cat ) and urea mass percent (5–9%) in feed on DMC mole fraction were investigated. It was found that the reactions are mainly influenced by the reaction temperature and space time rather than urea mass percent in feed. The experimental and simulated results indicated that the reaction from MC to DMC was the rate-controlling step in the DMC synthesis process from urea and methanol. It is important to remove the DMC and byproduct ammonia to achieve a high selectivity of DMC. This implies that reactive distillation might be used in the DMC synthesis on an industrial scale to achieve a higher selectivity of DMC.     

GRAPHICS-BASED CONTROL DESIGNS FOR NONMINIMUM-PHASE NONLINEAR SYSTEMS SUBJECT TO INPUT AND OUTPUT CONSTRAINTS

This article deals with the output regulation of nonminimum-phase systems subject to input and output constraints. Through the off-line static data reconciliation algorithm for a class of stable nonlinear bioreactors, the static feedforward control can ensure constant disturbance attenuation in spite of input multiplicities and actuators constraints. Under the pseudo-steady-state error diagnoses and a graphics-based mechanism for disturbance estimation, the proposed error feedback control scheme will induce the piecewise output regulation. Based on the “intelligent” algorithm for tuning improvement, the closed-loop simulation shows that the piecewise control strategy turns out to be robust against the unknown disturbances.     

Application of a novel approach for DMC predictive controller design by response surface analysis in a fed-batch bioreactor

This work presents a novel approach for tuning a predictive DMC controller implemented in a fed-batch penicillin bioreactor in order to stabilize the dissolved oxygen concentration by agitation speed manipulation. The operating process variables were calculated by a deterministic and non-structured model solved by a fourth order Runge-Kutta-Gill numerical technique with variable steps. The parameters of the model were obtained from experiments and the literature. The estimated parameters of the DMC controller were model, prediction and control horizons, suppression factor and reference trajectory. The tuning approach employed complete factorial design in order to estimate the influence of these parameters on the integral of the absolute error between the controlled variable and the set point. Response surface analysis provided the optimal parameters. This study showed negligible influence of model, prediction and control horizons while the suppression factor and reference trajectory were very important for the controller. Another important feature of the DMC controller was the that the parameters had negligible influence on each other making design of the controller easier. The performance of the DMC controller was evaluated using several delay times and sample periods of the controlled variable. The behavior of this predictive controller was better than a PID controller tuned by the Modified Simplex method.     

Trail-following pheromones of the rhinotermitidae: Approaches to their authentication and specificity

A method for determining the authenticity of subterranean termite trail pheromones is suggested and utilized to verify the presence of trail pheromones inReticulitermes virginicus, R. flavipes, andR. tibialis. In addition, a possible trail pheromone has been demonstrated forCoptotermes formosanus. A choice bioassay method shows that the above trail pheromones are species specific.     

Nonlinear response of an ideal gas bubble to ambient pressure change in a quiescent fluid

This paper is concerned with the small-amplitude oscillations of a bubble composed of an ideal gas in response to anabrupt change in the ambient pressure field. Specifically, we consider the bubble response to a pressure pulse and a pressure step in an otherwise quiescent fluid. The method of analysis employed in the present study is a standard two-timing expansion to eliminate a secular behavior encountered in the asymptotic expansion. In the impulse response the secularity is self-induced due solely to the nonlinearity of the problem whereas the secularity in the step response arises from the change in the equilibrium bubble volume caused by the ambient pressure change. The two-timing solution for each response shows that the secularity modifies the natural frequency of the radial oscillation. Further, the critical intensity of either the pressure pulse or the pressure step for existence of the steady-state bubble radius is determined from the frequency modulated solution and the stability of the bubble response is also discussed in terms of the bubble compressibility and heat transfer across the interface.