PLC在塑料挤出机温度控制系统中的应用

介绍了SIMATIC S7－300可编程控制器在塑料挤出机温度控制系统中的应用，控制回路采用PID参数自整定和脉宽调功法，控制系统把传统的PID控制和PLC的逻辑判断指令结合起来，使PID控制更为灵活，能满足生产过程的要求。详细描述了系统的工作原理和PLC的硬件组成、软件编制，简单介绍了上位机的组态软件WinCC。     

SOME THEORETICAL INSIGHTS INTO RECENT CONTROL DESIGN ALGORITHMS

Internal Model Control (IMC) design procedure is known to offer valuable advantages over classical control methods, especially for robust controller design. The Perfect Controller is defined using the well-known classical PID algorithm and its equivalence to IMC. After the definition of the Perfect Controller the IMC filter tuning parameter, which is used to maintain robustness, is obtained as a result of reparametrization of the classical PID control algorithm and factorization of the model. Through factorization, invertible part of the model is used directly in defining the perfect controller and the noninvertibility effects of the model are lumped into the new IMC tuning parameter. Closed loop IMC controller design is obtained with appropriate plant parameter uncertainty representation. Theoretical foundation for the transition from classical PID design to IMC design is analyzed using simple common chemical process models.     

单片微处理器在PID调节器中的应用

介绍以MCS-51系列的8031作为中央处理器的智能化PID调节器。该调节器外部接口简单，采用变速积分的PID位置算式，实现了模拟量的直接输入、输出，可方便地与各类模拟的检测及控制仪表相配合，组成不同的过程控制系统。对系统的软硬件设计作了说明。     

Nonlinear control of a batch ester-interchange reactor

Nonlinear control algorithms using feedback input-output linearization and sliding mode control are applied to a lab-scale batch ester-interchange reaction system. Batch ester-interchange reaction requires no overshoot of reaction temperature in earlier stage of reaction and tight temperature control throughout the reaction to keep uniform quality of the final product and to prevent variation of the amount of the byproduct such as diethylene glycol at each batch. Through experimentation we find that the nonlinear controller of input-output linearization algorithm shows better control performance both at setpoint tracking and disturbance rejection than the conventional PID controller. Further, sliding mode control algorithm is supplemented and simulated to show that it improves robustness against plant-model mismatch.     

基于模糊理论的塑料挤出机温度控制系统

提出了一种分段引入积分环节的模糊控制方法，详细介绍了模糊控制器的工作原理、模糊控制规则的确定和量表及温度控制系统的实现方法。生产实践表明，该方法能有效克服普通PID控制器和简单的模糊控制器在塑料挤出机温度控制上的缺点，具有更优良的性能。     

An analytic expression for closed-loop output behavior under multiloop PID control

An analytic expression is derived for closed-loop output behavior under a multiloop PID control. Based on the analytic expression obtained, optimization problems are formulated to assess 1) best achievable quadratic performance using multiloop PID control, 2) best achievable quadratic performance on key process variables while maintaining reasonable performance on other less critical process variables, 3) achievable performance improvement with decouplers, and 4) effects of loop pairing on achievable performance. It is shown through a simulated example that individual loop performance as well as the overall multiloop PID control performance can be assessed by using the proposed method. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

OPTIMAL TEMPERATURE CONTROL IN A BATCH POLYMERIZATION REACTOR USING NONLINEAR GENERALIZED PREDICTIVE CONTROL

The application of Non-Linear Generalized Predictive Control (NLGPC) to the free radical solution polymerization of styrene in a jacketed batch reactor has been realized. The dynamic behavior of polymerization reactor is modelled and simulated for control purposes. The optimal temperature policies for minimum time, desired conversion and molecular chain length were obtained at different initiator concentrations by applying the optimal control theory which is based on the Hamiltonian principle. The polynomial Nonlinear auto Regressive Integrated Moving Average with external input (NARIMAX) model is used to relate the reactor temperature with heat input for nonlinear control algorithm. The linear (ARIMAX) and nonlinear (NARIMAX) models are utilized in the GPC algorithm for comparison. A Pseudo Random Binary Sequence (PRBS) signal was employed to operate the system. The model parameters are evaluated by using Levenberg Marquart Method. The NLGPC, Linear Generalized Predictive Control (LGPC) and standard PID controllers are applied experimentally to the polymerization reactor by using on-line computer control system. The performance of NLGPC control system was compared with LGPC and standard PID controller. It is concluded that the NLGPC control gives much better performance than the other.     

TRACKING PERFORMANCE OF CONTROL METHODS

In this work, the optimal temperature control of a styrene solution polymerization reactor with two different control algorithms is considered. DMC and PFD control mefhods are used to accomplish the optimal temperature control of the polystyrene reactor. Reactor optimal temperature profiles at different initiator initiation concentrations were obtained by applying maximum principle to the mathematical model of the free radical batch polymerization reactor lo produce polystyrene with desired conversion and molecular weight in a minimum lime. The results obtained from the experimental implementation of DMC and PID controller for the control of optimal temperature path of the polymerization reactor were compared.     

TRACKING PERFORMANCE OF CONTROL METHODS

In this work, the optimal temperature control of a styrene solution polymerization reactor with two different control algorithms is considered. DMC and PFD control mefhods are used to accomplish the optimal temperature control of the polystyrene reactor. Reactor optimal temperature profiles at different initiator initiation concentrations were obtained by applying maximum principle to the mathematical model of the free radical batch polymerization reactor lo produce polystyrene with desired conversion and molecular weight in a minimum lime. The results obtained from the experimental implementation of DMC and PID controller for the control of optimal temperature path of the polymerization reactor were compared.     

ADAPTIVE MULTIVARIABLE PID CONTROLOF A DISTILLATION COLUMN WITH UNKNOWN AND VARYING DEAD TIME

A new, reliable, and easy-to-use adaptive control strategy has been developed to overcome the long-existing difficulties in adaptive control practice caused by unknown and varying process dead time. A self-tuning PID control algorithm is adopted to control a distillation column possessing second-order-plus-dead-time dynamics. The self-tuning strategy is based on recursive least-squares estimation of process parameters. U-D factorization is applied to stabilize the parameter estimation calculations. A variable forgetting factor is used to alleviate wind-up in the estimator. A simulation study and an experimental evaluation demonstrate the capability of the adaptive algorithm.     

Changes in cultured arterial smooth muscle cells isolated from chicks upon cholesterol feeding

We have developed cultures of smooth muscle cells (SMC) isolated from arterial hypercholesterolemic chicks (cholesterol-SMC). These cultures are suitable for the study at the molecular level of the changes in arterial SMC induced by a cholesterol diet. By using a strong dose of cholesterol (5%) for 10 d, we obtained very proliferative SMC which became foam cells after 30 d in culture. On the other hand, SMC cultures isolated from control-fed chicks has a lower growth rate than the SMC ones under the same culture conditions. DNA synthesis was fourfold greater in cholesterol-SMC than in control-SMC cultures. Intracellular cholesterol concentrations were the same in both cholesterol and control SMC during the first 14 d of culture but afterward increased in differing ways: after 20 d of culture the cholesterol-SMC increased their cholesterol content to double the control. We give here the results obtained from transmission electron microscopy, lipid analysis, proliferation studies, DNA, RNA and protein synthesis, and then discuss their implications.     

PID最小方差控制在参数整定中的应用

流程工业的控制回路中90%以上都使用PID控制器,在线PID参数整定方法一直是一个有很大意义却比较难解决的工程问题。PID最小方差性能评价常用于评价控制性能,然而其得出的最优PID参数往往并不适用于实际系统,当出现问题时需要重新加阶跃响应整定PID参数。将PID最小方差控制和系统传统的动态性能指针评价方法结合使用,通过系统传统的动态性能指针的要求给出PID参数的取值范围,再根据过程输出方差随PID参数变化而变化的趋势整定PID参数,该方法在实验装置的参数整定中得到了验证。     

基于PLC污水处理厂的pH值自动控制系统设计与研究

采用西门子S7-300 PLC为功能核心,组态王(King View 6.55)软件提供上位监控功能,PID (比例-积分-微分)表和PD (比例?微分)表相结合的控制方式,实现对污水中和池pH在适当范围的控制。所设计系统满足污水厂中和池pH在相应范围控制的要求,监控方便,可靠性好。     

模糊PID控制器在无刷直流电机控制系统中的应用

针对传统PID控制依赖被控对象精确的数学模型,应用于无刷直流电机调速难于达到良好的动态响应的缺点,将模糊PID控制器应用于无刷直流电机的控制中,运用模糊控制原理对PID参数进行在线调整。在分析无刷直流电机数学模型和控制方法的基础上,在MATLAB中应用Fuzzy Toolbox和Simulink对无刷直流电机调速系统进行仿真。实验表明,模糊PID控制相对于传统的PID控制具有更好的动态和静态性能,控制精度也大为提高。     

Honeywell DCS控制回路PID参数整定方法介绍

以honeywell PKS系统PID参数的组成为依据,介绍honeywell PKS系统的PID参数整定方法。     

SMC轻量化初步探究

为实现SMC轻量化,通过模压工艺,从原材料选型、配方设计以及工艺过程控制三个方面对轻质SMC(片状模塑料)进行了探究。首先,通过研究不同类型中空玻璃微珠(HGS)对制品比重、光亮度以及弯曲强度的影响发现,VS5500和H40适合作为轻量化SMC轻质填料,制品的设计密度和真实密度比较接近,且力学性能损失较小。其次,通过配方设计,研究了中空微珠用量、增稠剂类型以及增稠剂用量对制品比重的影响。同时研究了玻纤含量和树脂类型对制品力学性能的影响。研究结果表明,轻质SMC的设计密度不能过低,否则制品中HGS的破损比例将会增加。研究发现EK100作为增稠剂,树脂糊前期粘度可以有效控制,后期粘度快速上升,可以有效防止中空微珠相分离的发生。此外,随着玻纤含量从25%增加到30%,制品力学性能呈现增加趋势,弯曲强度从148 MPa增加到172 MPa,但随着玻纤进一步提高,弯曲强度反而出现大幅度衰减,降到140 MPa。通过研究三种不同类型树脂对制品外观和力学性能的影响,使用P18-03树脂压制的制品外观最好,其弯曲强度为172 MPa,满足汽车外饰件力学性能要求。最后,通过工艺过程控制,研究了微珠处理工艺对制品比重的影响。结果表明,烘干处理的HGS可以有效降低树脂糊的水含量,从而保证树脂糊后期粘度可以达到适合模压的窗口。     

土工格栅生产预热拉伸控制方法的改进

采用了易于软件实现的单参数PID自适应控制算法改善了预热温度控制效果,并根据拉伸过程中温度和速度的关系设计出了一套速度、温度联合双控系统,该系统会根据设定的工艺参数和不同生产阶段的工艺需求自动调整预热温度和拉伸速度,使速度和温度始终处于最佳结合点,很大程度上提高了工艺稳定性和拉伸速度。     

Control strategies for intermittently mixed, forcefully aerated solid-state fermentation bioreactors based on the analysis of a distributed parameter model

This paper tests different control strategies based on classic proportional integral derivative (PID) and advanced dynamic matrix control (DMC) algorithms for an intermittently stirred, forcefully aerated solid-state fermentation bioreactor. The study was done using a distributed parameter model to reproduce the main operating features of this type of bioreactor. There is predicted to be a remarkable improvement in the bioreactor productivity when control strategies are implemented. For this type of bioreactor, the temperature and water content of the substrate bed can be controlled by saturating the air at the air inlet but manipulating its temperature, coupled with a strategy of water replenishment when the water content of the bed falls below a threshold. Dynamic matrix control is superior to PID control; however, a specific convolution matrix for different stages of the fermentation is necessary due to the changing behavior of the system. This work shows the benefit of mathematical modeling, since the many different operating conditions investigated via simulations would not have been economically feasible to undertake experimentally with a large-scale bioreactor. The results obtained provide an excellent starting point for such large-scale experimental work.     

Investigating Control Schemes for an Ideal Thermally Coupled Distillation Column (ITCDIC)

The control schemes of an ITCDIC are addressed. A modified IMC scheme (M‐IMC) is proposed to overcome model/plant mismatch of the Internal Model Control scheme (IMC). Predictive PID control (P‐PID) and Adaptive Predictive control (AP‐PID) schemes are also presented to improve effectively the response speed of the multi‐loop PID control (M‐PID) and eliminate its residual error. A detailed comparative investigation on the above five control schemes was performed. Simulation results demonstrate all the schemes are able to keep two end products within their specifications. M‐IMC is the best one with the fastest response speed. AP‐PID is the second choice since it is better at dealing with sudden set‐point transitions and complex external disturbances than P‐PID. M‐PID cannot compete with AP‐PID and P‐PID due to its slow servo response speed and large residual error. IMC ranks last as it is extremely sensitive to changes in the operating conditions.     

Simulink仿真在PID控制教学中的探索与设计

在“过程控制系统”的教学中,传统的理论教学往往使学生对教学内容缺乏感性认识,感觉枯燥,记忆不深刻。将Simulink仿真应用到PID控制部分教学中,采用建模仿真带动理论教学的方法,让学生对PID控制有更为直观的认识。教学实践表明,该方法增强了学生的学习积极性,提高了他们对过程控制系统的分析与设计能力,取得了良好的课堂教学效果。