基于相角裕度与鲁棒性解析法设计分数阶PI~λ控制器

介绍了一种基于期望相角裕度与提高系统鲁棒性的解析法设计分数阶PIλ控制器。首先,根据相角裕度的定义和提高系统的鲁棒性得到3个非线性方程组,并用图解法得到PIλ控制器的积分阶次λ;然后,由解析法得到控制器的比例增益kP和积分时间常数TI。比较传统Z-N法设计的常规PI控制器,仿真表明解析法得到分数阶PIλ控制器能得到期望的裕度并具有更好的鲁棒性。     

病态对象的鲁棒控制

提出了一种适用于病态对象的鲁棒控制器设计过程.该过程把增益修正法（loop shape design procedure）与频域响应近似法(frequency response approximation)相结合,分两步设计二维自由度（two-degree-of-freedom）控制器：即反馈控制器和前置滤波器.整个设计过程针对一个众所周知的病态系统控制问题进行演示.     

文本分类中特征选择方法的研究与比较

介绍了进行文本分类的关键技术,并着重介绍了常用的文本特征提取方法。选取支持向量机方法作为文本分类器方法,选取不同特征提取方法应用于文本分类,通过实验,比较和分析了由不同的提取方法所构成的分类器的分类性能,确定了信息增益（IG）法和文本证据权（W ET）为两种性能优异的特征提取方法。该结论可为分类性能进一步的优化研究奠定理论和实践基础。     

基于改进粒子群优化的连续系统闭环辨识新方法

将粒子群优化算法(PSO)的全局辨识能力以及无约束多维寻优法--Rosenbrock的局部搜索能力相结合提出一种全新的参数辨识方法.该方法不需要控制器的先验知识,对测试信号无任何要求.仿真实验表明,与PSO-SQP算法及两阶段闭环辨识法相比,该方法对连续系统在响应不充分的情况下有良好的辨识效果.     

CSTR配备的不同类型控制器的参数整定及寻优

以水合法制丙二醇为例,利用Ziegler-Nichols法及经验法考察了CSTR反应器配备的比例控制器(P)、比例积分控制器(PI)及比例积分微分控制器(PID)的控制参数对CSTR反应器控制效果的影响,进而确定其优化的控制参数值。动态模拟结果表明:当配备P型控制器且控制参数kc=2×107时,控制效果最好,但存在控制余差;当配备PI型控制器时,利用Ziegler-Nichols法对控制参数进行调试;当配备PID型控制器时,采用与PI型控制器相同的控制参数整定方法,能够满足对CSTR反应器的控制要求。     

连续搅拌反应釜系统的非线性鲁棒控制

基于非线性鲁棒控制理论,针对一类单输入单输出连续搅拌反应釜（CSTR）模型设计了具有高增益观测器的非线性鲁棒控制器（ONRC）,并提出了一种简单的控制器参数整定方法。与非线性鲁棒控制器（NRC）和滑模控制方法（SMC）的仿真结果比较表明,ONRC对系统不确定性和干扰具有更好的抑制作用,通过Monte-Carlo试验检验显示,ONRC在模型参数摄动时具有更好的性能鲁棒性。     

分数阶控制器在过热汽温控制中的应用研究

在传统串级控制基础上结合分数阶PIλ Dμ控制器,提出过热汽温的分数阶PIλDμ串级控制策略.采用粒子群优化算法对分数阶PIλ Dμ控制器参数进行整定.在Matlab/Simulink仿真环境中对分数阶PIλDμ控制器和整数阶PID控制器的控制效果进行仿真对比,结果表明分数阶pIλ Dμ控制器在设定值跟踪、扰动抑制和鲁...     

基于相对增益分析的换热网络旁路设计

提出一种考虑了可控性的换热网络旁路设计法。基于稳态模型增益的定量计算,推导换热网络稳态数学模型的求解过程,从可控性分析的角度逐一求解换热网络的非方相对增益矩阵,从中确定最优的旁路位置,使被控变量具有较高的可控性。突破相对增益矩阵仅用于控制配对的常规范畴,提出一种通过逐次求解换热网络非方相对增益矩阵优化选取最优旁路设置的方法,并给出了设置旁路的若干准则,以简化求算过程。分析稳态工作点变化后的情况,表明工况变化不影响上述得出的旁路设置。该法适用于大型复杂换热网络,满足生产控制要求,并能保证整个换热网络具有较高的可控性。以某常减压蒸馏装置脱盐前换热网络为例,验证方法的可行性和有效性。     

具有L2增益的陶瓷取坯机械手鲁棒跟踪控制

本文对具有不确定和干扰的二自由度电动陶瓷取坯机械手系统动态模型 ,采用李雅普诺夫函数递推设计方法设计了鲁棒跟踪控制器。所设计的控制器不仅保证跟踪误差系统的稳定性而且使得由力矩干扰到跟踪误差评价信号的L2 增益小于给定的值。同时本文也给出了不用解HJI不等式设计陶瓷取坯机械手H∞ 控制器方法 ,仿真结果表明所设计的控制器具有良好的跟踪性能和较强的鲁棒性     

计算机辅助蒸馏过程模拟及控制(Ⅰ)——多组分复杂蒸馏控制的相对增益矩阵计算研究

本文应用Bristol的相对增益概念,对具有非线性多变量和相关多回路的复杂蒸馏过程,建立起5×5调节和被调参数对的相对增益计算方法,以研究它在设计中的控制策略问题.该方法改进了2×2相对增益子集分析方法的不足,达到了比通常应用的方法更准确和全面地反映出控制回路间存在的相关作用的目的,从而找到在全局意义下的控制策略.     

Tuning PI and fractional order PI controllers with an additional fractional order Pole

The PI controller with an additional pole (PI?+?P) already has been proposed to decrease the noise effect on the control signal. In this paper, a fractional order pole is employed to increase the PI?+?P controller performance. The fractional order is obtained by adjusting the Nyquist plot slope in gain crossover frequency. This condition as well as gain crossover frequency and phase margin specifications are utilized to design the PI controller augmented with an additional fractional order pole (PI?+?FO[P]). To design these two controllers, a first-order plus delay time (FOPDT) model is utilized. For plants that could not be described by this model, its fractional order version (FFOPDT) could be utilized. In this case, a FOPI?+?FO[P] controller is obtained that could improve the transient response of the closed-loop system. The numerical simulations accomplished on various plant models (including chemical plants) demonstrate the effectiveness of the proposed controller comparing with the PI?+?P, PID, FOPI, and fractional order proportional-integral-derivative controllers.     

Controller adjustment for improved nominal performance and robustness—II. Robust geometric control of a distillation column

In Part I of this paper a general frequency domain method to adjust multivariable controllers with respect to both nominal performance and robustness are presented. In Part II this method is used to examine and improve the control of a binary distillation column. The selected control strategies are conventional PI control and geometric control. The PI controller is adjusted in order to obtain satisfactory robustness properties. The basic geometric controller is extended with feedback from state variables which do not alter the nominal disturbance rejection. Both constant gain feedback and integration are examined. The included control parameters are adjusted for improved nominal performance and for robustness. The major result is that the adjusted geometric controller has a robustness which equals that of the adjusted conventional PI controller. However, the nominal performance of the geometric controller is superior to that of conventional PI control. Thus we expect the adjusted geometric controller to have improved performance on a real column compared to that of conventional PI control.     

Constraint handling optimal PI control of open-loop unstable process: Analytical approach

This paper proposes the closed-form analytical design of proportional-integral (PI) controller parameters for the optimal control of an open-loop unstable first order process subject to operational constraints. The main idea of the design process is not only to minimize the control performance index, but also to cope with the constraints in the process variable, controller output, and its rate of change. To derive an analytical design formula, the constrained optimal control problem in the time domain was transformed to an unconstrained optimization in a parameter space associated with closed-loop dynamics. By taking advantage of the proposed analytical approach, a convenient shortcut algorithm was also provided for finding the optimal PI parameters quickly, based on the graphical analysis for the optimal solution of the corresponding optimization problem in the parameter space. The resulting optimal PI controller guarantees the globally optimal closed-loop response and handles the operational constraints precisely.     

Optimization‐Based Nonlinear Centralized Controller Tuning of Liquid‐Liquid Extraction Processes

Abstract

The control problem of an agitated contactor is considered in this work. A Scheibel extraction column is modeled using the non‐equilibrium backflow mixing cell model. Model dynamic analysis shows that this process is highly nonlinear, thus the control problem solution of such a system needs to tackle the process nonlinearity efficiently. The control problem of this process is solved by developing a multivariable nonlinear control system implemented in MATLAB?. In this control methodology, a new controller tuning method is adopted, in which the time‐domain control parameter‐tuning problem is solved as a constrained optimization problem. A MIMO (multi‐input multi‐output) PI controller structure is used in this strategy. The centralized controller uses a 2×2 transfer function and accounts for loops interaction. The controller parameters are tuned using an optimization‐based algorithm with constraints imposed on the process variables reference trajectories. Incremental tuning procedure is performed until the extractor output variables transient response satisfies a preset uncertainty which bounds around the reference trajectory. A decentralized model‐based IMC (internal model control) control strategy is compared with the newly developed centralized MIMO PI control one. Stability and robustness tests are applied to the two algorithms. The performance of the MIMO PI controller is found to be superior to that of the conventional IMC controller in terms of stability, robustness, loops interaction handling, and step‐change tracking characteristics.     

OPTIMALITY CHARACTERISTICS OF PI/PID CONTROLLERS: A COMBINED MIN-MAX/ISE INTERPRETATION

This communication addresses the tuning of PI and PID controllers on the basis of the IMC approach. The tuning is based upon a first order plus time delay (FOPTD) model and aims to achieve a step response specification. Through analysis it has been found that by using the IMC approach we get a PI or a PID depending on the rational approximation used for the time delay term. This article raises the question that the use of a PID instead of a PI controller should be based on another reason more related to the control objectives rather than the use of a better approximation for the time delay. An alternative tuning is presented here, from within the IMC formulation, based on a min-max optimization. From the tuning rule provided by this approach the optimum settings from an integral squared error criterion point of view are derived. The optimal controller results in being a PI controller. From this optimal controller as the starting point, the introduction of the derivative action can be seen as a detuning procedure that can increase the robustness of the controller. This approach provides further insight into the tuning of PI and PID controllers giving the (alternative) parameters a precise engineering meaning.     

Gain scheduling PID control for directed self-assembly of colloidal particles in microfluidic devices

Directed self-assembly provides a promising route to fabricate small-scale structures for various engineering applications. The use of the external fields of variable strength and frequency allows for active controls to be implemented. For assembling specific structural features, precise control over a local particle density is often needed, which can be achieved using feedback control. However, the strong nonlinear behavior of directed self-assembly complicates such control. In this work, a gain-scheduling feedback control strategy for directed self-assembly of colloidal particles is presented. The process gain is described by an empirical steady-state model, which is used for scheduling a proportional-integral feedback controller. The automated controller is implemented experimentally in a microfluidic device for directed self-assembly of colloidal particles. The gain-scheduled controller shows a significantly improved dynamic performance compared with a conventional proportional-integral controller over a broad range of operating parameters.     

A theoretical examination of closed-loop properties and tuning methods of single-loop PI controllers

The dependence of the dominant closed-loop poles on the controller parameters is quantitatively elucidated by a Taylor expansion about the critical (ultimate) gain. The leading expansion coefficients are estimated from the critical (ultimate) gain and frequency and one or two closed-loop measurements of the decay ratio and frequency of system response to set-point/load changes or natural disturbances. An explicit model for the process transfer function is not required. By relating controller performance criteria to the leading poles, optimal gain settings to achieve these criteria can then be determined. In the present work, three tuning methods of increasing accuracy (the modified Ziegler-Nichols rule and Methods A and B) are constructed to satisfy a performance criterion (D.R. = 0.25) and a stability consideration. Method A is presented in a convenient chart and is especially easy to use on line. Stability robustness as measured by the Doyle-Stein index and the estimated closed-loop frequency at the proposed setting are also presented in the same chart.     

NONLINEAR PI CONTROLLER FOR pH PROCESS

The control of pH is one of the most difficult challenges in the process industry because of the severe nonlinearities and high precision required in manipulating the flow rate. The Wiener model, which consists of a linear dynamic element followed by a nonlinear static element, is used for representing such nonlinear processes. Piecewise continuous polynomials are used for mapping the nonlinear static gain accurately. A nonlinear PI controller was designed based on the Wiener model. Simulation results on the nonlinear mathematical model are presented to highlight the superior performance of the Wiener model based nonlinear PI controller in comparison to that of the local linear PI controller. The performance of the nonlinear PI controller was further improved upon by using the method of inequalities to obtain a single set of PI controller settings that takes into account the parametric variations in the linear dynamic element at different operating points. Simulation and experimental results are presented to support the work.     

NONLINEAR PI CONTROLLER FOR pH PROCESS

The control of pH is one of the most difficult challenges in the process industry because of the severe nonlinearities and high precision required in manipulating the flow rate. The Wiener model, which consists of a linear dynamic element followed by a nonlinear static element, is used for representing such nonlinear processes. Piecewise continuous polynomials are used for mapping the nonlinear static gain accurately. A nonlinear PI controller was designed based on the Wiener model. Simulation results on the nonlinear mathematical model are presented to highlight the superior performance of the Wiener model based nonlinear PI controller in comparison to that of the local linear PI controller. The performance of the nonlinear PI controller was further improved upon by using the method of inequalities to obtain a single set of PI controller settings that takes into account the parametric variations in the linear dynamic element at different operating points. Simulation and experimental results are presented to support the work.     

一种新型的浊度控制算法

针对城市供水过程中,待滤水浊度控制过程的大惯性、大滞后、模型参数时变和干扰多等特点,采用一种新型的控制算法来实现对该过程的控制,其具体思想是:分别从对设定值的跟踪性要求和对扰动的抑制性要求出发,采用双控制器分别实现各自的控制,且两个独立的控制器分别采用常规PI和带非线性补偿的PI算法。并将该种新型控制算法和传统PID反馈控制算法、Smith预估控制算法和双PI控制算法进行了仿真比较。最后,还将该种算法实际应用到某水厂的中试实验基地。仿真和实验结果表明:所采用算法能够及时克服扰动,并对模型参数变化不敏感,具有很强的鲁棒性,对设定值具有良好的跟踪能力,确保了供水质量的稳定性。