Multiloop PID controller design using partial least squares decoupling structure

The goal of this paper is to identify and control multi-input multi-output (MIMO) processes by means of the dynamic partial least squares (PLS) model, which consists of a memoryless PLS model connected in series with linear dynamic models. Unlike the traditional decoupling MIMO process, the dynamic PLS model can decompose the MIMO process into a multiloop control system in a reduced subspace. Without the decoupler design, the optimal tuning multiloop PID controller based on the concept of general minimum variance and the constrained criteria can be directly and separately applied to each control loop under the proposed PLS modeling structure. Several potential applications using this technique are demonstrated.     

基于内模控制的Smith反向解耦控制器设计

针对多变量时滞系统提出了一种基于内模控制(Internal Model Control,IMC)的Smith动态解耦控制器设计方法。其中,Smith补偿器被应用在该控制结构中,包含带有时滞项和不带时滞项的补偿结构,以解决不能完全补偿的问题,通过反向解耦设计实现多变量时滞系统动态解耦。多变量系统被解耦成一系列互相独立的单回路对象,通过内模控制原理对Smith控制器进行参数整定,并分析了系统的鲁棒性。仿真实例表明了该方法的有效性,能够较好地克服系统参数扰动导致的干扰,并具有较好的动态性能。     

化工双输入输出时滞过程解耦PID控制器解析设计

基于常规单位反馈控制结构,针对具有时滞特性的化工双输入输出过程提出一种解耦PID控制器的解析设计新方法.该解耦PID控制器的突出优点是控制器设计过程简单直观;控制器可以实现标称系统输出间的显著解耦;系统输出分别使用相应控制器对角元素中的调节参数进行单参数整定.同时,对于实际生产过程中常见的被控过程乘性不确定性,分析了系统保持鲁棒稳定的充要条件.仿真实例验证了该方法优于其它方法.     

TWO-WAY OR ONE-WAY DECOUPLING IN DISTILLATION?†

A systematic simulation study of dual composition control of distillation has been carried out in order to compare different decoupling strategies and contrast them with well-tuned SISO-controllers.

Two column models are studied. One describes the experimental pilot plant used by Wood and Berry (1973) and the other the experimental pilot plant investigated by Luyben and Vinante (1972).

A better control quality-compared to the control quality obtained by SISO-control-may be achieved if suitably chosen decoupling elements are introduced. The best control quality does not, however, necessarily correspond to the best decoupling. In the studied systems, where the controllers of the decoupled systems have been tuned according to the Ziegler-Nichols settings for the effective process transfer functions, there is no incentive to use two decouplers (two-way decoupling): the same or better control quality is obtained with the simpler scheme utilizing only one decoupler (one-way decoupling). Actually, for the Luyben and Vinante system SISO-control is superior to two-way decoupling, whereas one-way decoupling is superior to SISO-control.     

一类多变量系统的自抗扰非线性动态解耦控制

针对一类多变量系统控制中的耦合问题,提出了一种基于自抗扰技术的非线性动态解耦控制(ADRC)方法。该方法不依赖于系统的精确数学模型,分别在控制器耦合矩阵部分已知和未知的情形下,在局部静态解耦的基础上,将各子系统的模型摄动、外扰和包括输入变量相互作用在内的动态耦合视为各通道上的扰动总和,通过引入虚拟控制和状态量,设计扩张状态观测器(ESO)估计总扰动并进行反馈补偿,进而再对各解耦子对象分别设计非线性单输入单输出ADRC以保证闭环系统稳定。最后以蒸馏塔模型的过程控制仿真验证了该方法具有良好的动态解耦效果,对模型不确定性和外部扰动具有较好的鲁棒性和适应能力。     

RECURRENT NEURAL NETWORKS IN DECOUPLING CONTROL OF MULTIVARIABLE NONLINEAR SYSTEMS

In this work we focus on the synergy between modeling with RNNs, and nonlinear controller design for decoupling control. The thesis of the paper is that recurrent neural networks (RNNs) can be conveniently used in an integrated black-box modeling and controller design methodology for decoupling control of multivariable nonlinear systems. A simulation example on a multivariable continuous-stirred-tank-reactor (CSTR) is provided to elucidate related issues. The effects of modeling uncertainty and state reconstruction on decoupling performance are specifically discussed.     

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。     

双容液位系统的动态解耦控制

建立了双容液位系统的计算机监控实验系统的硬件和软件,并通过机理分析方法建立了系统的模型。针对系统的耦合特性,应用对角解耦方法完成模型的动态解耦,并将解耦器在上位机中通过编程实现,从而完成系统的解耦控制。将解耦控制效果分别和常规PID控制、RMPCT控制进行比较。实验结果表明,在这种存在耦合的简单的两入两出系统中,解耦控制的效果较常规PID控制有大幅提高,并且与RMPCT的控制效果相比差别也并不明显,已经可以满足控制的需要,但其成本低廉,与先进控制相比具有巨大的优势。     

SEQUENTIAL LOOP CLOSING IDENTIFICATION OF MULTIVARIABLE PROCESSES USING THE BIASED RELAY FEEDBACK METHOD

Each controller in multiloop control systems for multivariable processes can be tuned sequentially with the ultimate information for the paired input and output while former loops have been closed, and hence, single-input single-output autotuning methods can be applied. In this sequential autotuning for multiloop control systems, several iterations are usually required for better control performances. Especially when pairings are undesirable, the autotuning sequences should be repeated with correct pairings, which result in long field experiments. Here, to avoid this drawback, a simple method to identify process models while loops are being sequentially tuned is proposed. The identified models can be used to correct pairings of multiloop control systems and to improve tuning performances without several field iterations. In addition, they can be used to obtain model-based control systems such as decoupling control systems.     

SEQUENTIAL LOOP CLOSING IDENTIFICATION OF MULTIVARIABLE PROCESSES USING THE BIASED RELAY FEEDBACK METHOD

Each controller in multiloop control systems for multivariable processes can be tuned sequentially with the ultimate information for the paired input and output while former loops have been closed, and hence, single-input single-output autotuning methods can be applied. In this sequential autotuning for multiloop control systems, several iterations are usually required for better control performances. Especially when pairings are undesirable, the autotuning sequences should be repeated with correct pairings, which result in long field experiments. Here, to avoid this drawback, a simple method to identify process models while loops are being sequentially tuned is proposed. The identified models can be used to correct pairings of multiloop control systems and to improve tuning performances without several field iterations. In addition, they can be used to obtain model-based control systems such as decoupling control systems.     

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。     

Decoupling internal model control for multivariable systems with multiple time delays

In this paper, the decoupling internal model control (IMC) with stability is investigated for multivariable stable processes with multiple time delays. All the stabilizing IMC controllers which solve this decoupling problem and the resulting closed-loop systems are characterized in terms of the open-loop system's time delays and non-minimum phase zeros. It shows that the inclusion of some time delays and non-minimum phase zeros might be necessary to make a decoupling solution realizable and stabilizing. Based on this characterization, a control design method for best achievable performance is presented. However, owing to the high complexity of the theoretical controller, a practical controller design procedure is developed with the help of the proposed model reduction algorithm. Examples are given to illustrate our analysis and design. Significant performance improvement over the existing multivariable Smith predictor control has been achieved with the proposed approach.     

工业过程多变量系统的辅助常规控制设计

利用PID控制器对多变量系统进行控制,主要采取分散常规控制或解耦控制的策略。对于存在耦合的系统,分散常规控制无法消除各变量间的相互扰动,而直接设计动态解耦矩阵有时候会存在困难,静态解耦的效果却并不明显。针对已设计好分散常规控制器的方系统,以解耦为目标和原则,设计多变量系统中分散常规控制方案剩余配对的控制器作为辅助控制器,以频域近似的方法整定其PID参数,实现多输入多输出的控制结构,降低了各变量的相互耦合作用,提高了控制性能。通过对Shell公司的典型控制问题的辅助控制器设计与仿真实验,取得了比原有分散常规控制与静态解耦控制更好的控制效果,验证了控制策略的可行性与有效性。     

一类不确定多时滞系统的鲁棒容错控制研究

讨论一类线性不确定多时滞系统的鲁棒容错控制问题.基于Lyapunov稳定性理论和线性矩阵不等式方法（LMI）,针对一类参数有界不确定多时滞系统,给出了状态反馈鲁棒容错控制器设计方法,并且利用该方法得到的闭环控制系统,不仅在执行器失效情况下具有渐进稳定性,对参数不确定也具有良好的鲁棒性.最后,应用设计实例及仿真结果验证该设计方法的可靠性和有效性.     

A two-degrees-of-freedom design methodology for interval process systems

This paper presents a two-degrees-of-freedom design methodology for interval process systems to guarantee both the robust stability and performance. For the robust stability issue, the design technique of Chen and Wang (1997) is utilized for searching a robust stabilizing feedback controller. Subsequently, a pre-filter is constructed based on using a frequency domain method to ensure the desired system performance. For illustration, the proposed design methodology is applied to design a robust control system for a second-order unstable plant in the presence of unknown but bounded parameter uncertainties. Simulation results reveal that the proposed scheme is effective and applicable for interval process systems.     

Multi-agent reinforcement learning for process control: Exploring the intersection between fields of reinforcement learning,control theory,and game theory

The application of reinforcement learning (RL) in process control has garnered increasing research attention. However, much of the current literature is focused on training and deploying a single RL agent. The application of multi-agent reinforcement learning (MARL) has not been fully explored in process control. This work aims to: (i) develop a unique RL agent configuration that is suitable in a MARL control system for multiloop control, (ii) demonstrate the efficacy of MARL systems in controlling multiloop process that even exhibit strong interactions, and (iii) conduct a comparative study of the performance of MARL systems trained with different game-theoretic strategies. First, we propose a design of an RL agent configuration that combines the functionalities of a feedback controller and a decoupler in a control loop. Thereafter, we deploy two such agents to form a MARL system that learns how to control a two-input, two-output system that exhibits strong interactions. After training, the MARL system shows effective control performance on the process. With further simulations, we examine how the MARL control system performs with increasing levels of process interaction and when trained with reward function configurations based on different game-theoretic strategies (i.e., pure cooperation and mixed strategies). The results show that the performance of the MARL system is weakly dependent on the reward function configuration for systems with weak to moderate loop interactions. The MARL system with mixed strategies appears to perform marginally better than MARL under pure cooperation in systems with very strong loop interactions.     

A systematic approach to plant-wide control based on thermodynamics

In this work, a systematic approach to plant-wide control design is proposed. The method combines ingredients from process networks, thermodynamics and systems theory to derive robust decentralized controllers that will ensure complete plant stability. As a first step, the considered process system is decomposed into abstract mass and energy inventory networks. In this framework, conceptual inventory control loops are then designed for the mass and energy layers to guarantee that the states of the plant, both in terms of extensive and intensive properties, will converge to a compact convex region defined by constant inventories. This result by itself does not ensure the convergence of intensive variables to a desired operation point as complex dynamic phenomena such as multiplicities may appear in the invariant set. In order to avoid these phenomena, thermodynamics naturally provides the designer, in these convex regions, with a legitimate storage or Lyapunov function candidate, the entropy, that can be employed to ensure global stability. Based on this, the control structure design procedure is completed with the realization of the conceptual inventory and intensive variable control loops over the available degrees of freedom in the system. To that purpose, both PI and feedback linearization control are employed. The different aspects of the proposed methodology will be illustrated on a non-isothermal chemical reaction network.     

Design of a modern automatic control system for the activated sludge process in wastewater treatment

The Activated Sludge Process (ASP) exhibits highly nonlinear properties. The design of an automatic control system that is robust against disturbance of inlet wastewater flow rate and has short process settling times is a chal enging matter. The proposed control method is an I-P modified controller automatic control system with state variable feedback and control canonical form simulation diagram for the process. A more stable response is achieved with this type of modern control. Settling times of 0.48 days are achieved for the concentration of microorganisms, (reference value step increase of 50 mg·L?1) and 0.01 days for the concentration of oxygen (reference value step increase of 0.1 mg·L?1). Fluctuations of concentrations of oxygen and microorganisms after an inlet disturbance of 5 × 103m3·d?1 are smal . Changes in the reference values of oxygen and microorganisms (increases by 10%, 20%and 30%) show satisfactory response of the system in al cases. Changes in the value of inlet wastewater flow rate disturbance (increases by 10%, 25%, 50%and 100%) are stabilized by the control system in short time. Maximum percent overshoot is also taken in consideration in all cases and the largest value is 25%which is acceptable. The proposed method with I-P controller is better for disturbance rejection and process settling times compared to the same method using PI control er. This method can substitute optimal control systems in ASP.     

基于粒子群优化算法的球磨机制粉系统PID-ANN解耦控制器

球团厂钢球磨煤制粉系统是多变量强耦合、时滞、非线性以及生产工况变化大的复杂对象,其自动控制问题一直是控制界关注的热点。基于粒子群算法具有对整个参数空间进行高效并行搜索的特点以及PID神经网络的自调节和自适应特性,设计了具有PID结构的多变量自适应神经网络控制器。PID神经网络解耦控制方法被用来消除回路之间的耦合,神经网络连接权值由粒子群算法进行学习优化。仿真研究表明所建模型和所提控制方法具有较好的控制品质、良好的自适应解耦能力和自学习功能。该控制策略可在大范围内克服系统的非线性和强耦合问题,具有很高的工程实用价值。     

基于滑模控制的混沌系统在永磁同步电机中的应用研究

将基于滑模控制的方法应用于永磁同步电机（PMSM）混沌系统中。为了在滑动模态中保证系统的同步性能,采用一种新型的比例积分切换面。基于滑动模态的控制器具有鲁棒性,即使在参数不确定和外部干扰存在的情况下,也能保证滑动模态的出现。通过分析高复杂性的动态非线性系统——混沌系统,来研究鲁棒的同步性问题,并在滑动模态下,通过选择适当的反馈阵,采用任意极点配置法来设置系统的动态误差特性。仿真结果表明该控制设计方法实现简单并且性能优良。