带前馈的PID控制回路的控制器性能评估

提出一种评估带前馈的PID控制回路的控制器性能的方法.该方法通过求取在最优前馈和反馈控制器作用下的最小过程输出方差,并将其与实际的输出方差比较,以评估控制器的性能,同时可以得到实现该最小方差的最优PID控制器的参数.仿真结果表明,引入前馈作用可以改善PID控制回路的性能,并且采用本文提出的评估方法可以得到一个合理的评估结果.     

PID性能评估与整定软件在常减压装置中的应用

介绍PID控制器原理、PID回路性能评估与整定原理。在常减压装置中的应用结果表明,对所有中和差状态下的问题回路进行性能评估与整定后,各回路均能够投用自动,且回路性能评估达到良级别以上。     

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。     

PLC、PID调节仪表在水温控制装置中的应用

采用PID回路调节仪表和PLC可编程控制器,应用于密炼机循环水温控制装置中,使混炼温差控制在±2.2℃范围内。     

化工过程多回路PID控制系统模式切换参数自整定

化工过程一般为多变量系统,但其主要控制方案为分散多回路PID常规控制。由于多变量系统内部存在不同程度的耦合作用,各控制回路之间存在相互影响,当其他回路进行手动/自动模式切换时,本回路等效被控对象将会发生突变,导致本回路的原有控制参数不能适应等效被控对象的变化,造成控制性能下降,甚至闭环系统不稳定。为避免这种情况的发生,从整个系统的角度研究控制回路模式切换时的稳定性,采用多变量频域Nyquist阵列设计法。基于对角优势下正Nyquist稳定性判据,从Gershgorin圆边界点的角度定量分析各个控制回路在模式切换前后的稳定性变化程度,从而确定各回路控制器增益的调整方向及程度,实现各回路的控制器参数在控制回路模式切换瞬间的自动整定,尽可能抵消控制回路模式切换对整个系统的扰动,保证整个系统的闭环稳定性。以Shell公司重油分馏塔的多回路PID控制系统为例,将3个PID控制回路依次投用时,根据Gershgorin圆边界点进行控制参数的自整定,闭环系统仍能保持一定的控制性能,否则闭环系统将不稳定。     

基于ICA的控制回路故障诊断方法

针对控制回路中各种设备的监测信号之间存在较强的关联性和非高斯分布的特点,首次将独立分量分析法(ICA)用于控制回路的故障诊断中。分别选取回路中控制器输入和输出、执行器输出、变送器输入和输出作为信号观测点,选择控制回路正常运行状况的数据进行ICA建模,获得I2和SPE统计限,当控制回路某个元件发生故障时可以通过统计量的变化对其进行监测。此外,还采用均值贡献率进行故障点定位,有效降低了故障的误诊率。     

串级控制对过程预测控制的影响分析与对策

化工过程控制中普遍设置以流量控制为副回路的串级控制来实现对温度、液位和成分等被控变量的控制。预测控制的操作变量在很多情况下也是流量,其控制作用的实现要靠底层的流量控制回路。本文针对由于现场串级控制结构不允许改变,流量副回路只能接收温度等主控制器的输出作为其给定值,造成上层预测控制的操作变量无法直接下载到流量控制回路的问题,分别提出了一种将上层优化输出通过一阶惯性滤波作用于主回路控制器和一种将串级控制中流量对主被控变量的传递函数嵌入预测控制模型的实施方案,通过Shell标准重油分馏塔的控制问题进行仿真实验证明了两种方案的可行性,并对其控制性能进行了比较分析。两种方法理论上构思简单,实际中易于实现,具有普遍适用性。     

Approach to Control Loop Fault Diagnosis Based on ICA

针对控制回路中各种设备的监测信号之间存在较强的关联性和非高斯分布的特点,首次将独立分量分析法( ICA)用于控制回路的故障诊断中.分别选取回路中控制器输入和输出、执行器输出、变送器输入和输出作为信号观测点,选择控制回路正常运行状况的数据进行ICA建模,获得I2和SPE统计限,当控制回路某个元件发生故障时可以通过统计量的变化对其进行监测.此外,还采用均值贡献率进行故障点定位,有效降低了故障的误诊率.     

双侧送引风机变增益广义预测控制

在分析母管制机组送引风回路控制情况的基础上,提出一种双侧变增益广义预测控制算法。该算法利用回路输入输出数据采用递推最小二乘法对回路对象进行建模,并依此设计了先进的控制系统。该控制方法与原PID控制的对比分析结果表明:该控制方法效果较好,解决了双侧风机不同步的问题。     

倾角及冷却工况对多通路并联回路板式脉动热管传热性能的影响

针对多通路并联回路板式脉动热管建立实验台,采用铜质模块加热和水浴冷却方式作为热工条件,着重考察脉动热管在不同倾角（90°,75°,60°）及冷却工况（4.5 g·s^-1和9.0 g·s^-1）下的传热性能,通过壁面温度的振荡和传热热阻来评价其传热效果。实验结果表明,重力对多通路并联回路板式脉动热管传热性能的影响较大,随着倾角的减少,工质的回流变弱,传热热阻变大,传热极限变低;脉动热管的加热功率与冷却能力是相互匹配的,匹配度越高,脉动热管越不易干烧,传热极限越高,在有倾角的工况下提高传热极限表现得更为明显;脉动热管运行时存在一个最佳水流量,在最佳冷却工况下,脉动热管的运行热阻最低。     

Closed‐loop Fault Detection Using the Local Approach

Fault detection and isolation (FDI) has become a crucial issue for industrial process monitoring in order to increase availability, reliability and production safety. Model‐based FDI methods rely on a mathematical model and input‐output data of a process to perform detection. The local approach is a new model‐based FDI method that aims to detect slight changes of a system's parametric properties. Closed‐loop detection is an important issue for the local approach since all control systems work under closed‐loop conditions. A new algorithm was proposed to revise the original detection algorithm in order to make it work for closed‐loop data. Simulation results show that the proposed method can detect the changes of parameters of a system that can affect closed‐loop performance.     

乳液触变性对流平性的影响研究

乳液的流平性是乳液应用性能中的一个重要项目。目前,评价乳液的流平性主要采用刮涂法、刷涂法和目测法,前者简单、方便和实用,而且还能定量地评定出流平性等级,但耗时较长,且定量比较粗略;而后两种方法虽然简单、方便、快捷,但人为影响因素较大且定量不准。采用流变仪测定乳液的触变环的面积可较好的评价乳液的流平性,且该方法具有准确、方便、快捷等优点。     

SIMULATION OF OSCILLATIONS IN BOILING FLOW IN A NATURAL CIRCULATION EVAPORATOR

This article presents both experimental and theoretical investigations on the nature of oscillations of void fraction and temperature in a boiling natural circulation loop of a short-tube natural circulation evaporator at low pressure and low heat flux conditions. The experimental study includes online measurement of void fraction and temperature in the loop. The proposed moving boundary model equations for boiling channel in the loop have been solved by a finite volume scheme and subsequently nonlinear ODEs have been solved by Gear's method. The proposed model equations have been validated with experimental data and the data taken from literature. The periodic nature of the pulse-variation of both void fraction and temperature has been identified. A comparison has been made on the applicability of homogeneous flow model and nonhomogeneous flow model to predict the void-fraction pulses and the temperature pulses. Measurement uncertainties and model uncertainties have also been discussed.     

基于加权L2-Hausdorff子空间距离的MPC控制回路性能诊断

针对当前MPC控制回路性能评价方法无法准确定位性能下降源的问题,提出一种基于加权L₂-Hausdorff子空间距离的控制回路性能诊断方法.该方法引用恶化性能子空间表征各个性能恶化工况下的回路特征,通过基于模型预测残差的闭环潜能指标实时监测控制回路性能.当发现性能下降时,构造加权L₂-Hausdorff子空间距离来度量当前回路性能模式与已知性能模式的相似度,通过距离聚类来定位回路性能下降的恶化源.最后,通过连续搅拌加热器(continuous stirred tank heater, CSTH)上的仿真实验,验证了所提方法的有效性及可靠性.     

一种改进的锅炉主蒸汽温度多级智能控制系统的应用研究

针对电厂锅炉主蒸汽温度多级控制系统中减温水流量扰动对蒸汽温度的影响,且运行过程中控制系统超调量大、响应速度慢、系统具有非线性,对单回路常规控制系统进行了改进,提出了一种双单内环智能串级控制方法。主控制器采用内模控制方式,根据末级出口主蒸汽温度实测值与设定值之间的偏差经过智能PID在线修正控制参数。仿真结果表明:改进后的控制系统比原单回路控制系统具有更好的鲁棒性和动态特性,并能保持较好的调节性能。     

基于EPI的乙烯行业效率分析

为了有效评价乙烯行业的能效水平,寻找能效改进机会,针对乙烯装置数据特点,结合能源消耗中的活动影响、结构影响与强度影响等因素,提出基于能源绩效指标(EPI)的乙烯行业能源效率评价方法。在能效分析的基础上,结合数据包络分析(DEA)方法,将能效指标与产物收率综合进行分析评价。最后,给出了针对若干装置能源数据的分析评价实例,实验结果验证了该方法的准确性与有效性,为乙烯装置效率评价提供了新思路。     

BP神经网络补偿快速成型系统闭环误差的研究

提出快速成型系统闭环误差反馈的必要性,将BP神经网络引入快速成型技术,建立了快速成型误差补偿模型,探求出一种快速成型系统闭环误差的反馈方法,并通过实例进行了验证。结果表明,基于BP神经网络控制的最大绝对误差和相对误差均比传统误差补偿方法大为降低。     

基于DMC-PID控制的催化剂温控系统设计

通过对动态矩阵控制(DMC)算法和传统PID控制的分析,提出一个基于DMC-PID串级控制的催化剂温控系统。仿真结果表明:DMC-PID控制效果优于PID-PID控制;电流副回路采用PID控制,能够快速有效调节电流进而控制燃烧炉内温度;温度主回路采用DMC控制,克服了传统温控系统存在的超调量大、时延及滞后性等问题,避免了多种不可测扰动的影响。     

Data mining and control loop performance assessment: The multivariate case

Control loop performance assessment (CLPA) techniques assume that the data being analyzed is generated during steady state operation with fixed plant dynamics and controller parameters. However, in industrial settings one often encounters environmental and feedstock variations which can induce significant changes in the plant dynamics. Availability of data sets corresponding to fixed configurations is therefore questionable in industrial scenarios, in which case it becomes imperative to extract the same from routine plant operating data. This article proposes a technique for segmenting multivariate control loop data into portions corresponding to fixed steady state operation of the system. The proposed technique exploits the fact that changes in the operating region of the system lead to changes in variance‐covariance matrix of multivariate control loop data. The univariate interval halving technique is fused with Mahalanobis distance to develop a multivariate tool that accounts for interactions between variables. The resulting data segments can be used for reliable CLPA and/or for user defined benchmarking of control loops. A multivariate control loop performance index is also proposed that requires significantly less data as compared to one of the previously proposed techniques. The proposed technique requires only routine operating data from the plant, and is tested on benchmark systems in the literature with simulations. Experimental validation on a model predictive control system aimed at maintaining the temperature profile of a metal plate demonstrates applicability of the technique to industrial systems. The proposed technique acts as a tool for preprocessing data relevant to CLPA and can be applied to large scale interacting multivariate systems. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3311–3328, 2017     

HYDRODYNAMIC MODELLING IN AN AIR-LIFT LOOP REACTOR

A simple hydrodynamic model is proposed for use in the design, scale-up and characterization of external loop air-lift reactors. The approach is based upon a momentum balance for the flow loop coupled with a drift-flux equation for the reactor riser and establishes a rational basis for a predictive model relating gas throughput to induced liquid flow and gas hold-up in a range of air-lift reactors. The effective resistance of the reactor, k, defined in terms of the total loss coefficients of the reactor and the aerated height of the two-phase riser, was identified to allow for the quantification of the influence of reactor design on the hydrodynamic variables. An extensive body of data for the air-water system, collected on two reactors with active volumes of 0·055 m³ and 0·3 m³, is presented and used, in conjunction with literature data encompassing a wide range of reactor geometries and flow conditions, to define a unique relationship between flow behaviour and reactor configuration. The model, which accounts for the prevailing flow regime in the reactor, provides a direct method of predicting hydrodynamic behaviour in relatively non-viscous systems.