Performance assessment and robustness analysis using an ARMarkov approach

Application of the ARMarkov model-based formulation offers significant advantages for assessment/monitoring and robustness analysis of process systems. The ARMarkov method does not require a priori specification of the system time delay/interactor matrix, needs only an approximate estimate of model order and can be done using open or closed-loop process data. By appropriate use of standard, linear model estimation techniques, it directly produces statistically consistent estimates of the first few, user-specified number of Markov parameters even in the presence of colored noise. It is shown in this paper that the Markov parameters and the ARMarkov model can be used to calculate the interactor matrix and several process performance metrics including sensitivity/complementary-sensitivity functions and time-domain criteria such as speed of response, minimum variance values etc. In addition it is shown that model-based predictive control (MPC) systems formulated using ARMarkov models have a special state space structure that leads to less conservative robustness bounds for specific types of uncertainties (such as gain mismatch, uncertainty in the fast or slow dynamics, etc.) than applying the Small Gain Theorem directly to the conventional state space model structure.     

Welding current and arc voltage control in a GMAW process using ARMarkov based MPC

A predictive functional controller based on ARMarkov model structure has been designed to control welding current and arc voltage in a GMAW process. The closed loop system performance is investigated through computer simulations and is compared by those achieved from implementing two commonly used controllers i.e. PI and feedback linearization based PID. The local stability of the closed loop system is analyzed in the presence of uncertainties in the linearized model of the process as well as the control parameters. Finally it is shown that the proposed controller performs like a PI controller along with a pre-filter compensator.     

Predictive control based on local linear fuzzy models

This paper deals with predictive control based on fuzzy models. A novel algorithm (LOLIMOT) is proposed for the construction of Takagi-Sugeno fuzzy models. The rule consequents are optimized by a local orthogonal least-squares method that selects the significant regressors. The rule premises are optimized by a tree construction algorithm which partitions the input space in hyper-rectangles. A generalized predictive controller (GPC) and a dynamic matrix controller (DMC) are designed. Both controllers require the extraction of a linear model from the Takagi-Sugeno fuzzy model. For the GPC a new technique called local dynamic linearization is proposed that exploits the special structure of the local linear models. The DMC is based on the evaluation of a step response. The effectiveness of both the identification algorithm and the predictive controllers is shown by application to temperature control of an industrial-scale cross-flow heat exchanger.     

A practical multiple model adaptive strategy for single-loop MPC

This paper details a multiple model adaptive control strategy for model predictive control (MPC). To maintain performance of this linear controller over a wide range of operating levels, a multiple model adaptive control strategy for dynamic matrix control (DMC), the process industry's standard for MPC, is presented. The method of approach is to design multiple linear DMC controllers. The tuning parameters for the linear controllers are obtained using novel analytical expressions. The controller output of the adaptive DMC controller is a weighted average of the multiple linear DMC controllers. The capabilities of the multiple model adaptive strategy for DMC are investigated through computer simulations and an experimental system.     

预测控制的无扰切换技术

提出了关于动态矩阵控制器(DMC)与广义预测控制器(GPC)的改进无扰切换方法．其中 ，前者在DMC控制模式启动初期采用过程的脉冲响应模型实现对过程输出的自由响应预测， 在非DMC控制模式下，只需要存储过程输入/输出数据，而不必在线进行反馈校正．二者都有 一个共同特点，即不必考虑过程的直流工作点，这给预测控制算法的在线实现带来了很大的 方便．最后，通过纸机定量控制系统的仿真研究证明了上述算法的有效性．     

具有串联结构系统的预测控制及并行设计

对具有串联结构的多干扰系统提出了在线ＤＭＣ控制方案，并在已有ＤＭＣ控制的基础上给出并行算法及结构上的设计，这种多闭环的近似模型的扩展ＤＭＣ方法使系统的稳定性、抗扰性及鲁棒性都达到了指标。由于设计中充分利用了系统的冗余信息及并行性，使系统的快速性得到很大提高。     

非线性系统参数自适应直接广义预测控制

针对广义预测控制 (Generalized predictive control, GPC) 计算量大的缺陷, 本文对参数未知非线性系统提出一种直接广义预测控制 (Direct generalized predictive control, DGPC) 方法. 该方法直接辨识广义预测控制器参数, 即基于广义误差估计值对控制器参数 θu 和广义误差估计值中的未知向量 θe 进行自适应辨识. 理论证明了该方法可使广义误差估值收敛到原点的一个小邻域内.     

Design and performance of an intelligent predictive controller for a six-degree-of-freedom robot using the Elman network

The aim of this paper was to propose a recurrent neural network-based predictive controller for robotic manipulators. A neural network controller for a six-joint Stanford robotic manipulator was designed using the generalized predictive control (GPC) and the Elman network. The GPC algorithm, which is a class of digital control method, requires long computational time. This is a disadvantage in real-time robot control; therefore, the Elman network controller was designed to reduce processing time by avoiding the highly mathematical and computational complexity of the GPC. The main reason for choosing the Elman network, amongst several neural network algorithms, was that the presence of feedback loops have a profound impact on the learning capability of the network. The designed neural network controller was able to recover quickly because of its significant generalization capability, which allowed it to adapt very rapidly to changes in inputs. The performance of the controller was also shown graphically using simulation software, including the dynamics and kinematics of the robot model.     

State-space approach to nonlinear predictive generalised minimum variance control

A nonlinear predictive generalised minimum variance control algorithm is introduced for the control of nonlinear discrete-time multivariable systems. The plant model is represented by the combination of a very general nonlinear operator and also a linear subsystem which can be open-loop unstable and is represented in state-space model form. The multi-step predictive control cost index to be minimised involves both weighted error and control signal costing terms. The solution for the control law is derived in the time domain using a general operator representation of the process. The controller includes an internal model of the nonlinear process, but because of the assumed structure of the system, the state observer is only required to be linear. In the asymptotic case, where the plant is linear, the controller reduces to a state-space version of the well-known GPC controller.     

非线性系统多步预测控制的复合神经网络实现

提出一种基于神经网络的非线性多步预测控制,采用由线性网络和动态递归神经网络构成的复合神经网络。在此基础上将线性系统的广义预测控制器扩展为非线性系统的多步预测控制器。通过对非线性过程ＣＳＴＲ的仿真表明,该方法的稳定性和鲁棒性明显优于线性ＤＭＣ预测控制。     

指令跟踪自适应广义预测控制及其应用

现有的广义预测控制系统其闭环性能受可调参数影响较大,它的目标函数无法直接规定 闭环性能.该文提出一种具有独立跟踪和调节目标的新型自适应广义预测控制算法,并将其 应用于快速时变的导弹控制系统设计中.这种算法利用参考模型规定对指令信号的跟踪性 能,减少了可调参数对闭环性能的影响.仿真结果证实了该算法的有效性.     

Predictive LPV control of a liquid–gas separation process

The problem of controlling a liquid–gas separation process is approached by using LPV control techniques. An LPV model is derived from a nonlinear model of the process using differential inclusion techniques. Once an LPV model is available, an LPV controller can be synthesized. The authors present a predictive LPV controller based on the GPC controller [Clarke D, Mohtadi C, Tuffs P. Generalized predictive control – Part I. Automatica 1987;23(2):137–48; Clarke D, Mohtadi C, Tuffs P. Generalized predictive control – Part II. Extensions and interpretations. Automatica 1987;23(2):149–60]. The resulting controller is denoted as GPC–LPV. This one shows the same structure as a general LPV controller [El Gahoui L, Scorletti G. Control of rational systems using linear-fractional representations and linear matrix inequalities. Automatica 1996;32(9):1273–84; Scorletti G, El Ghaoui L. Improved LMI conditions for gain scheduling and related control problems. International Journal of Robust Nonlinear Control 1998;8:845–77; Apkarian P, Tuan HD. Parametrized LMIs in control theory. In: Proceedings of the 37th IEEE conference on decision and control; 1998. p. 152–7; Scherer CW. LPV control and full block multipliers. Automatica 2001;37:361–75], which presents a linear fractional dependence on the process signal measurements. Therefore, this controller has the ability of modifying its dynamics depending on measurements leading to a possibly nonlinear controller. That controller is designed in two steps. First, for a given steady state point is obtained a linear GPC using a linear local model of the nonlinear system around that operating point. And second, using bilinear and linear matrix inequalities (BMIs/LMIs) the remaining matrices of GPC–LPV are selected in order to achieve some closed loop properties: stability in some operation zone, norm bounding of some input/output channels, maximum settling time, maximum overshoot, etc., given some LPV model for the nonlinear system. As an application, a GPC–LPV is designed for the derived LPV model of the liquid–gas separation process. This methodology can be applied to any nonlinear system which can be embedded in an LPV system using differential inclusion techniques.     

广义预测控制器系数直接算法

为了简化广义预测控制算法的分析与设计，提出了广义预测控制器系数直接计算方法．该方法利用过程模型直接递推，把广义预测控制律表达成控制器系数与参考轨迹及过程历史信息乘积的形式．其控制器系数计算只与模型参数及设计参数有关，避免了在线求解Diophantine方程、输出预测表达式及自由响应项，简化了设计思路，减少了在线运算量．在一个DCS控制的非线性液位装置上得到的对比实验结果表明该方法是可行和有效的．     

网络控制系统的自整定PID 控制器设计

结合广义预测控制（GPC）方法和PID反馈结构,设计了一种具有预测功能的PID控制器,PID参数根据未来时刻的预计输出误差进行整定.控制器导出多步控制序列,置于执行器端的延迟补偿器根据网络时延从控制序列中选择控制信息并作用于控制对象,从而对时延进行补偿,使控制性能得到极大改善.控制器结合了PID控制和预测控制的优点,具有较强的鲁棒性和工程意义.最后通过构造Lyapunov函数对闭环系统的稳定性进行了分析,并通过仿真验证了该算法的有效性.     

两种典型预测控制系统的稳定性分析

本文针对两种典型的预测控制──动态矩阵控制和广义预测控制，提出了它们的闭环反馈结构。利用此反馈结构，不仅可以方便地判别预测控制系统的闭环稳定性，而且有效地减少了控制算法的计算量，有利于预测控制算法的在线应用。仿真实例证实了本文的稳定性判别方法是十分有效的。     

一种基于未知模型的广义预测控制算法

研究未知被控对象具有动态调整、参数时变以及受到外界干扰时,采用广义自适应预测控制算法(GPC)对系统进行控制。运用基于CARMA模型的参数在线动态辨识,在线时实算出未知对象的参数模型,再运用预测控制算法,计算出当前的控制量;再滚动优化,使未知系统具有良好的控制性能。并且通过Matlab分析仿真证明了广义预测控制的全局稳定性、收敛性和鲁棒性。     

预测控制算法的内模结构及其统一格式

本文应用内模控制（ＩＭＣ）原理，研究了现有各类预测控制算法ＩＭＣ、ＭＡＣ、ＤＭＣ、ＧＰＣ、ＧＰＰ的控制器方程，闭环系统输入输出和误差方程，归纳出它们的统一算式，为理解各类预测控制算法的内在联系及进一步研究提供了方便．     

A comparative study of three advanced controllers for the regulation of hypnosis

The anesthetic state is a dynamic combination of hypnosis, analgesia and neuromuscular blockade that is maintained by infusing a cocktail of drugs. This work focuses on controlling the hypnosis during a surgical procedure by automatic regulation of isoflurane and employs Bispectral Index (BIS) as the primary controlled variable. A seventh-order nonlinear pharmacokinetic–pharmacodynamic representation has been used for the hypnosis dynamics of patients. This study uses a model predictive control structure for the regulation of BIS. Performance of this controller has been tested for a range of patients and compared with two previously employed control strategies (cascade internal model controller and cascade controller with modeling error compensation). Performance of the three controllers has also been studied for a step change in BIS, measured disturbances and noise in the measured variables. Numerical simulations show that the model predictive controller performed better than the other two controllers.     

基于神经网络的时滞非线性系统的广义预测控制

针对一类时滞非线性被控对象,提出一种基于RBF神经网络的广义预测自校正控制方案,在广义预测控制中,采用RBF神经网络建立被控对象的多步预测模型,并不断修正预测输出,提高预测输出的精度.控制器则采用GPC隐式修正算法,不用辨识对象的模型参数,大大减少了计算量.经过仿真研究,与常规的PID自适应控制方法相比较,证明了该方法的优越性,预测控制误差小,实时性好,动态响应快.     

信息物理环境下不确定系统的随机分布式预测控制

针对信息物理系统环境下可能发生的信息丢包问题,提出一种随机分布式预测控制的分析与设计方法.考虑控制器端到执行器端的传输丢包,采用马尔科夫过程对这一丢包过程进行描述.通过对马尔科夫跳变的线性模型进行增广,研究一种具有随机丢包不确定系统的分布式预测控制方法;将系统分解成多个子系统进行描述,研究基于最小最大化优化的分布式预测控制器设计方法,并提出基于迭代交互的子控制器协调算法.将随机分布式预测控制算法在实际电机系统中进行仿真测试,以验证所提出方法的有效性.