Dynamic real‐time optimization with closed‐loop prediction

Process plants are operating in an increasingly global and dynamic environment, motivating the development of dynamic real‐time optimization (DRTO) systems to account for transient behavior in the determination of economically optimal operating policies. This article considers optimization of closed‐loop response dynamics at the DRTO level in a two‐layer architecture, with constrained model predictive control (MPC) applied at the regulatory control level. A simultaneous solution approach is applied to the multilevel DRTO optimization problem, in which the convex MPC optimization subproblems are replaced by their necessary and sufficient Karush–Kuhn–Tucker optimality conditions, resulting in a single‐level mathematical program with complementarity constraints. The performance of the closed‐loop DRTO strategy is compared to that of the open‐loop prediction counterpart through a multi‐part case study that considers linear dynamic systems with different characteristics. The performance of the proposed strategy is further demonstrated through application to a nonlinear polymerization reactor grade transition problem. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3896–3911, 2017     

基于相角裕度优化的PID参数整定方法研究

针对复杂工业过程的大滞后、参数不确定等特性,提出一种新的鲁棒PID控制器参数整定方法.该方法通过使系统开环传递函数的相角裕度最大化,来求取各个PID参数.由于该方法的稳定裕量是通过取明确依赖于频率的模型来获得,从而避免了陷入保守性.仿真结果表明,使用本文提出的控制器整定方法,在命令输入发生阶跃变化时,控制系统都有很好的动态响应,同时在系统参数发生变化或存在未建模动态时,也能保证系统的稳定鲁棒性.     

Delay‐range‐dependent guaranteed cost control for batch processes with state delay

A guaranteed cost control scheme is proposed for batch processes described by a two‐dimensional (2‐D) system with uncertainties and interval time‐varying delay. First, a 2‐D controller, which includes a robust feedback control to ensure performances over time and an iterative learning control to improve the tracking performance from cycle to cycle, is formulated. The guaranteed cost law concept of the proposed 2‐D controller is then introduced. Subsequently, by introducing the Lyapunov–Krasovskii function and adding a differential inequality to the Lyapunov function for the 2‐D system, sufficient conditions for the existence of the robust guaranteed cost controller are derived in terms of matrix inequalities. A design procedure for the controller is also presented. Furthermore, a convex optimization problem with linear matrix inequality (LMI) constraints is formulated to design the optimal guaranteed cost controller that minimizes the upper bound of the closed‐loop system cost. The proposed control law can stabilize the closed‐loop system as well as guarantee H_∞ performance level and a cost function with upper bounds for all admissible uncertainties. The results can be easily extended to the constant delay case. Finally, an illustrative example is given to demonstrate the effectiveness and advantages of the proposed 2‐D design approach. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2033–2045, 2013     

载人航天器环热控一体化仿真分析

采用系统建模及仿真方法搭建了一种典型载人航天器环热控一体化系统模型，分析了系统的性能。针对3人7天载人飞行工况开展了仿真分析，结果表明，经过合理设计，该系统可将舱内温湿度、压力、氧分压等参数控制在航天医学指标要求范围内。环热控系统仿真结果较好地预测了系统工作过程，显示了主要参数的变化情况，结果合理，验证了仿真方法、系统仿真模型的正确性。通过控制流体回路外回路旁通阀门开度，可准确控制外回路控温点温度，保证舱内温湿度在合理范围之内。此外，外回路控温点的设定会对环热控系统状态带来影响，通过合理设计外回路控温点，可保证舱内温湿度满足航天医学指标要求。     

New parameter tuning method of washout filter-aided controller for dynamic behavior adjustment

Stabilizing unstable operating points is an effectiveway to enhance process benefits and safety, which motivates the development for a variety of advanced control strategies. The washout filter-aided controller (WFC), originally used for electric power system and aircraft, has been introduced to adjust the dynamic behavior of chemical process. However, the parameter tuning method faces two major limitations:the dimension of operating variables must be equal to or greater than that of state variables and only one positive real eigenvalue exists in the open loop system. To overcome the two limitations, this paper proposes a new parameter tuning method, so that theWFC is applicable in most chemical processes. By solving a constrained optimization problem, the controller parameters are determined under the constraint that the reassignment of the eigenvalues of the unstable desired operating point can satisfy the stability condition. Thus parts of the equilibrium manifold including the desired operating point are stabilized without affecting the shape of the equilibrium manifold. Finally, the effectiveness of the WFC improved by the proposed parameter tuning method is illustrated through a case study for propanediol anaerobic fermentation.     

旋壳泵在变频智能控制系统中的应用

描述旋壳泵在变频闭环控制系统中的应用,分析其节能效果.旋壳泵结合变频闭环智能控制能较好地控制和监测泵运行状态,并根据反馈信号自动调节泵的转速,保证系统的可靠运行.本文分析总结系统设计中涉及的相关问题,并给出系统实现各模块功能的电气原理图.     

强制循环蒸发系统线性自抗扰解耦控制的鲁棒设计

针对强制循环蒸发系统液位与出料密度两个回路的非线性耦合问题,提出了一种基于粒子群算法的线性定常自抗扰解耦控制设计。首先通过引入虚拟控制量,将对象解耦配置为两个单输入单输出子系统,并对每个回路设计降维线性扩张状态观测器。随后,对观测器动态线性化得到的近似积分器环节进行比例控制。最后,在可能的大工况内通过粒子群算法优化控制增益耦合矩阵和比例增益。该算法使用观测器估计并补偿动态耦合部分,降低了控制器对数学模型的依赖程度;使用粒子群算法优化定常控制增益矩阵,避免了实时测量出料温度,降低了对传感测量的要求,提高了可靠性并降低了实施难度。数学仿真结果表明该算法能有效地消除液位回路和出料密度回路的耦合作用,在大工况内具有很强的鲁棒性。     

一种改进的热泵供暖系统动态实时优化策略

基于经济性目标的热泵供暖动态优化操作具有重要意义，但在操作区间内环境温度和模型参数变化的不确定性会对实际优化操控带来很大挑战。在完善热泵供暖系统模型的基础上，提出了一种改进的动态实时优化控制策略以改善系统的实际节能效果。该方法首先建立以压缩机和送水泵运行频率为控制变量的热泵供暖系统的非线性动态关系模型，并得到以24 h为周期、以综合性能指标最低为目标的动态实时优化命题。然后，在给定24 h环境温度预测情况下通过求解该优化命题得到热泵压缩机和送水泵的最优运行频率轨线，并以当前时间点的最优控制量对热泵供暖系统进行控制；接着，基于天气逐时预测和模型参数最新校验结果对环境温度轨线或者模型参数进行更新，不断地求解原优化命题以更新最优控制轨线，并不断地采用当前点的最优控制量对热泵供暖系统进行控制，直到当前时间点达到第24 h。实例计算结果表明：采用本文提出的方法可以进一步改善热泵供暖系统的动态优化操控效果，并能够很好地满足给定终端约束要求。本方法对于具有周期性和不确定参数的动态实时优化问题求解具有一定的借鉴意义。     

一种切换参数PI控制器的分析与设计

针对典型化工过程阶跃负载干扰下的期望响应,用两种方法整定PI控制器:相位和增益裕度限制的幅值穿越频率优化法和最大灵敏度约束的积分增益优化法.两种PI控制器有一种互补性,据此提出依响应状态而切换PI控制器参数的方法.仿真表明所提方法对频率响应单调的系统是有效的.     

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。     

含滞后及不确定参数动态过程系统的定量优化方法与应用

许多动态化工系统含有不确定参数。当含不确定参数的过程系统又带有滞后环节时,系统的优化问题就变得非常复杂。对含不确定参数的化工系统的动态过程进行优化,若未考虑滞后环节对动态优化结果的影响,不能保证系统实际操作的优化及安全运行。本文采用改进的有限元正交配置优化算法,较好地解决了含有滞后、不确定参数的化工过程的动态优化问题。最后将一个具有循环返料的反应-分离器系统以及一个绝热反应釜作为案例对该优化方法的应用进行分析,根据案例的研究验证了该优化方法的有效性,从而为含有滞后、不确定参数的动态系统的设计和操作性能优化提供一种有效的定量分析方法和理论依据。     

分布式预测控制全局协调及稳定性分析

实际的化工过程系统维数都较高,对系统进行关联分解并使各子系统进行协调来实现整个大系统全局最优是必要的。对于关联作用存在反馈的化工过程大系统,分散式预测控制算法和基于串联过程推导的邻域优化分布式预测控制算法都不适用,因此在这两个算法的基础上推导出约束条件下基于全局协调的分布式预测控制算法。针对分解后得到的子系统,假设子系统间关联信息的传递存在一个采样时间的滞后,建立每个子系统的预测模型时考虑滞后的关联信息;建立子系统的目标函数时,综合考虑所有关联子系统的输入和输出对本子系统的关联作用;每个子系统滚动优化并行求解各自的最优控制作用。然后,在一定条件下分析了基于全局协调的分布式预测控制算法与集中预测控制算法的一致性,并说明了闭环系统的全局稳定性。最后,通过对Shell公司重油分馏塔和TE过程两个例子进行仿真并与其他算法进行比较,验证了本文提出算法的可行性和有效性。     

Economic model predictive control of nonlinear process systems using empirical models

Economic model predictive control (EMPC) is a feedback control technique that attempts to tightly integrate economic optimization and feedback control since it is a predictive control scheme that is formulated with an objective function representing the process economics. As its name implies, EMPC requires the availability of a dynamic model to compute its control actions and such a model may be obtained either through application of first principles or through system identification techniques. In industrial practice, it may be difficult in general to obtain an accurate first‐principles model of the process. Motivated by this, in the present work, Lyapunov‐based EMPC (LEMPC) is designed with a linear empirical model that allows for closed‐loop stability guarantees in the context of nonlinear chemical processes. Specifically, when the linear model provides a sufficient degree of accuracy in the region where time varying economically optimal operation is considered, conditions for closed‐loop stability under the LEMPC scheme based on the empirical model are derived. The LEMPC scheme is applied to a chemical process example to demonstrate its closed‐loop stability and performance properties as well as significant computational advantages. © 2014 American Institute of Chemical Engineers AIChE J, 61: 816–830, 2015     

催化裂化装置反再系统动态模拟精细化与控制系统“工艺优先”配对设计

催化裂化是目前炼油厂中的核心加工工艺,其反应-再生系统是一个多变量紧密耦合的复杂系统,动态模拟和控制系统设计难度较大。目前,催化裂化装置在进行动态建模时设置了大量假设条件,与实际状况存在诸多不符,另外当前的控制回路配对方法未考虑工艺要求,也不适用于催化裂化这样的开环不稳定系统。基于以上原因,以已建立的反应-再生系统数学模型为基础,建立精细化动态模型,对反应器和再生器模型进行真实逼近,不再忽略气相动态变化,将原模型中气相对时间的导数项恢复,通过离散化的分布参数系统模型,对离散化模型中每段提升管和烧焦罐的时变变量加入时滞。仿真结果表明,精细化动态模型更加接近实际化工生产过程。根据上述模型搭建仿真平台,通过对不稳定的反再系统进行工艺优先的控制系统设计,首先根据化工工艺设计控制回路保证系统的稳定性,然后基于相对增益阵方法设计剩余变量配对,在降低了高维系统设计复杂度的同时保证了生产过程安全。设计结果表明,对于催化裂化装置反再系统,基于工艺特性完成控制回路配对后,剩余变量无须再添加多余的控制回路就能保证控制系统的稳定性和适当的控制性能。     

Real‐time economic model predictive control of nonlinear process systems

Closed‐loop stability of nonlinear systems under real‐time Lyapunov‐based economic model predictive control (LEMPC) with potentially unknown and time‐varying computational delay is considered. To address guaranteed closed‐loop stability (in the sense of boundedness of the closed‐loop state in a compact state‐space set), an implementation strategy is proposed which features a triggered evaluation of the LEMPC optimization problem to compute an input trajectory over a finite‐time prediction horizon in advance. At each sampling period, stability conditions must be satisfied for the precomputed LEMPC control action to be applied to the closed‐loop system. If the stability conditions are not satisfied, a backup explicit stabilizing controller is applied over the sampling period. Closed‐loop stability under the real‐time LEMPC strategy is analyzed and specific stability conditions are derived. The real‐time LEMPC scheme is applied to a chemical process network example to demonstrate closed‐loop stability and closed‐loop economic performance improvement over that achieved for operation at the economically optimal steady state. © 2014 American Institute of Chemical Engineers AIChE J, 61: 555–571, 2015     

Design and control of acetonitrile/N-propanol separation system via extractive distillation using N-methyl pyrrolidone as entrainer

The extractive distillation process for separating a binary azeotrope of acetonitrile and n-propanol is investigated using N-methyl pyrrolidone as entrainer. On the basis of multiparameter optimization, a design with optimized operation conditions for the process is presented. Two dynamic control structures are proposed. Feed disturbances are used to evaluate the dynamic performance. The response results reveal that the control structure CS1 with temperature–composition cascade control loop can handle all the disturbances and maintain product purities, except one large transient deviation, while the improved control structure CS2 with average temperature control loop can overcome this obstacle and handle disturbances effectively.     

在线水质仪在城市污水处理厂精确曝气中的应用

介绍了在污水处理厂应用在线水质分析仪器实施精确曝气的作用,即能够实现水质的连续检测,为精确曝气等各种优化控制提供有效可靠的测量数据,从而提高处理效率,节能降耗。说明了精确曝气的开环控制、闭环控制和复合控制系统的特点及其应用。     

多级汽提分离动态模型及动态模拟

多级汽提分离已广泛应用于CO2-H2S-NH3废水体系,以分离酸性气体和氨为目的。文章以复杂的带侧线加压汽提塔为研究对象,讨论了汽提分离的化学模型和分离动态模型。在此基础上,借助动态模拟工具,研究了在特定控制回路下系统对扰动响应情况。另外,对利用动态模拟工具进行控制回路的PID参数整定方法也给予了讨论。     

An automatic initialization procedure in parameter estimation problems with parameter-affine dynamic models

This paper proposes an initialization approach for parameter estimation problems (PEPs) involving parameter-affine dynamic models. By using the state measurements, the nonconvex PEP is modified such that a convex approximation to the original PEP is obtained. The modified problem is solved by convex optimization methods yielding an approximate solution to the original PEP. The approximate solution can be further refined by linearizing the original problem around the obtained minimum. An assessment of the distance between the real solution and the one provided by the linearization of the problem around the convex approximation is presented. The optimum obtained by the convex approximation is used to subsequently initialize a simultaneous Gauss–Newton (SGN) approach on the original nonconvex PEP. Comparative results for the SGN with arbitrary initialization and with the proposed approach are presented using three benchmark examples in the chemical and biological fields.     

微加压与升压氨合成回路的模拟及优化

根据过程系统工程原理 ,对大型氨合成装置的微加压氨合成 (合成压力 10MPa)回路和升压氨合成 (合成压力 15MPa)回路进行结构分析 ,建立了单元模型。以序贯模块法作为流程模拟方法 ,采用可行路径法对两种流程进行了优化。并根据模拟与优化的结果对两种流程进行了比较 ,结果表明 ,微加压氨合成流程具有良好的经济技术指标。