On the filtered Smith predictor for MIMO processes with multiple time delays

This paper discusses about a unified implementation structure of the filtered Smith predictor (FSP) for MIMO processes with multiple time delays. Two kinds of dead-time free models are analyzed in order to extend the original properties of the SISO Smith predictor to MIMO processes with multiple time delays. It is demonstrated that FSP strategy can be applied to control open-loop unstable processes with multiple time delays by considering a model without any input, output or internal coupling delays. Moreover, for open-loop stable processes, it is shown that the FSP scheme can be used to speed-up disturbance rejection of processes with multiple time delays by using a nominal model without delay. Different simulation examples are used to illustrate the proposed strategy properties and advantages over other MIMO time-delay compensators. The results may be considered to control either square or non-square processes.     

IMC design for unstable processes with time delays

A modified IMC structure is proposed for unstable processes with time delays. The structure extends the standard IMC structure for stable processes to unstable processes and controllers do not have to be converted to conventional ones for implementation. An advantage of the structure is that setpoint tracking and disturbance rejection can be designed separately. A method is proposed to tune the modified IMC structure with an emphasis on the robustness of the structure. Design for some typical delayed unstable processes shows that the control structure can be tuned easily and achieve good tradeoff between time-domain performance and robustness.     

双输入双输出过程解耦内模控制

针对双输入双输出稳定过程,提出一种新的解耦内模控制设计方法.综合解耦和稳态误差两方面因素,利用对象传递函数模型行列式的静态增益及次对角元素与同行相应主对角元素之商的不合理部分(即不稳定极点和纯超前部分)的逆来设计控制器,简化了多时滞问题的处理.对Wood-Berry蒸馏塔过程设计内模控制器,并将其转化为能在DCS上实施的PID控制器,仿真结果表明了该方法的有效性,控制系统具有较好的解耦能力和较强的鲁棒性.方法简单,易于实现,具有工程应用价值.     

H2 approximation of multiple input/output delay systems

Many physical multivariable processes can be sufficiently described as linear models with multiple input/output delays. To simplify the synthesis and analysis of control problem, a reduced-complexity model is often desired. In this paper, an H₂ model reduction scheme is introduced for stable linear systems with multiple input/output delays. The reduced model can be a finite dimensional linear model, or a linear model with a time delay. In the latter case the approximation can be improved drastically without increasing the order of the finite dimensional part. The stability is preserved in the approximating models by employing a parametrization of linear stable systems. The optimal parameters can be obtained by solving an optimization problem using a gradient-based method. Two chemical numerical examples are used to show the effectiveness of the proposed scheme.     

A self-tuning controller for systems with unknown or varying time delays†

A SISO self-tuning controller with a Smith-predictor type of time delay compensator (STC-TDC) is proposed to handle open-loop stable processes with unknown or varying time delays. Two numerical examples comparing PI control, the standard STC of Clarke and Gawthrop, the self-tuning Dahlin algorithm of Vogel and Edgar, and the STC-TDC show that the new approach performs best for both set-point and load changes when process time delay changes occur. A third example shows that the STC-TDC matches the extended stability characteristics of the alternative approach due to Kurz and Goedecke but is computationally much simpler.     

Global μ -Stability of Delayed Neural Networks With Unbounded Time-Varying Delays

In this letter, dynamical systems with unbounded time-varying delays are investigated. We address the following question: To what extent the time-varying delays can exist while the system is stable? Moreover, a new concept of stability, global mu-stability, is proposed. Under mild conditions, we prove that the dynamical systems with unbounded time-varying delays are globally mu-stable.     

Delay-dependent stability analysis and controller synthesis for Markovian jump systems with state and input delays

This paper focuses on the problem of delay-dependent robust stochastic stability analysis and controller synthesis for Markovian jump systems with state and input delays. It is assumed that the delays are constant and unknown, but their upper bounds are known. By constructing a new Lyapunov-Krasovskii functional and introducing some appropriate slack matrices, new delay-dependent stochastic stability and stabilization conditions are proposed by means of linear matrix inequalities (LMIs). An important feature of the results proposed here is that all the robust stability and stabilization conditions are dependent on the upper bound of the delays. Memoryless state feedback controllers are designed such that the closed-loop system is robustly stochastically stable. Some numerical examples are provided to illustrate the effectiveness of the proposed method.     

Iterative learning control with Smith time delay compensator for batch processes

How to improve the control of batch processes is not an easy task because of modeling errors and time delays. In this work, novel iterative learning control (ILC) strategies, which can fully use previous batch control information and are attached to the existing control systems to improve tracking performance through repetition, are proposed for SISO processes which have uncertainties in modeling and time delays. The dynamics of the process are represented by transfer function plus pure time delay. The stability properties of the proposed strategies for batch processes in the presence of uncertainties in modeling and/or time delays are analyzed in the frequency domain. Sufficient conditions guaranteeing convergence of tracking error are stated and proven. Simulation and experimental examples demonstrating these methods are presented.     

一种改进的Smith预估器研究

在Smith预估器原理与应用的基础上提出了补偿时滞给定 ,解决了大纯滞后系统经改进的Smith预估器补偿后 ,在阶跃给定下 ,有良好的跟随性能 ,而在任意给定函数下 ,系统响应总是滞后于给定的问题     

State Feedback Control of Uncertain Networked Control Systems With Random Time Delays

This note investigates the stabilization problem for a class of linear uncertain networked control systems with random communication time delays. Both sensor-to-controller and controller-to-actuator random-network-induced delays are considered. Markov processes are used to model these random-network-induced delays. Based on the Lyapunov-Razumikhin method a mode-dependent state feedback controller is proposed to stabilize this class of systems. The existence of such a controller is given in terms of the solvability of bilinear matrix inequalities, which are to be solved by a newly proposed algorithm. A numerical example is used to illustrate the validity of the design methodology.     

Exponential stability of nonlinear time-delay systems with delayed impulse effects

The problem of exponential stability for nonlinear time-delay systems with delayed impulses is addressed in this paper. Lyapunov-based sufficient conditions for exponential stability are derived, respectively, for two kinds of delayed impulses (i.e., destabilizing delayed impulses and stabilizing delayed impulses). It is shown that if a nonlinear impulsive time-delay system without impulse input delays is exponentially stable, then under some conditions, its stability is robust with respect to small impulse input delays. Moreover, it is also shown that for a stable nonlinear impulsive time-delay system, if the magnitude of the delayed impulses is sufficiently small, then under some conditions, the delayed impulses do not destroy the stability irrespective of the sizes of the impulse input delays. The efficiency of the proposed results is illustrated by three numerical examples.     

Design of H 2 Controllers for Sampled-Data Systems with Input Time Delays

This paper presents a general framework based on lifting technique for sampled-data systems with input time delays. By analyzing the properties of operator-valued matrices of lifted systems with input time delays, an extended lifting technique is obtained. It is then shown that, with the proposed lifting technique, the complex behavior of the system can be illustrated by two simple lifted systems, which construct the extended lifted system. The extended lifted system has the same induced norm as that of the original system with an input time delay, since the proposed lifting technique is an isometric isomorphism. Through applying the proposed lifting technique to sampled-data systems with input time delays, the time-invariant discrete-time system with infinite-dimensional input and output spaces is obtained. The equivalent discrete-time system, which is derived from the extended lifted system, can satisfy the problem of H ₂ sampled-data control systems with input time delays. Simulation results are given to show that the proposed method can guarantee a more stable system response than the conventional H ₂ sampled-data controller for the sampled-data systems with the various input time delays.     

具有随机通讯时延的离散网络化系统的H∞滤波器设计

由于传感器和滤波器是通过有限带宽的网络连接的,因此系统的测量数据经常会出现时延,而且时延是随机的.本文讨论了具有一步随机通讯时延的离散网络化系统的H∞滤波器设计问题.利用线性矩阵不等式方法设计线性滤波器使得滤波误差系统是均方意义下指数稳定并具有给定的H∞性能.滤波器参数通过凸优化技术求解一个线性矩阵不等式得到.数值仿真表明设计方法的有效性.     

受有线无线异构网络诱导延时和数据丢包约束的分布式网络化H2/H∞滤波研究

针对分布式有线无线异构网络化滤波系统中部署在不同地理空间的多传感器通过无线网络与每个局部融合中心通信, 然后测量数据被传到网关并进行协议转换后通过有线网络传输到对应的分布式滤波器, 会导致数据传输出现分布式有线无线网络诱导延时和数据丢包, 使得H₂/H_∞滤波更加困难的问题, 本文首先采用有向图描述分布式传感器节点的通信拓扑, 然后运用Markov链和伯努利分布分别刻画分布式有线无线网络诱导延时和数据丢包特性, 进而建立了融合分布式滤波器参数、有线无线异构网络通信约束的普适滤波误差动态系统综合模型.理论上证明了在分布式有线无线异构网络通信约束下所设计的滤波器使得滤波误差动态系统随机稳定且满足给定的H₂/H_∞性能指标, 并建立了系统随机稳定性、分布式滤波器参数及最长有线无线网络诱导延时和数据丢包之间的关系.最后, 仿真实例验证了本文所提方法是可行且有效.     

Robust stability analysis of switched uncertain systems with multiple time-varying delays and actuator failures

In this paper,the robust stability issue of switched uncertain multidelay systems resulting from actuator failures is considered.Based on the average dwell time approach,a set of suitable switching signals is designed by using the total activation time ratio between the stable subsystem and the unstable one.It is first proven that the resulting closed-loop system is robustly exponentially stable for some allowable upper bound of delays if the nominal system with zero delay is exponentially stable under these switching laws.Particularly,the maximal upper bound of delays can be obtained from the linear matrix inequalities.At last,the effectiveness of the proposed method is demonstrated by a simulation example.     

Multivariable disturbance observer-based H2 analytical decoupling control design for multivariable systems

In this paper, an H₂ analytical decoupling control scheme with multivariable disturbance observer for both stable and unstable multi-input/multi-output (MIMO) systems with multiple time delays is proposed. Compared with conventional control strategies, the main merit is that the proposed control scheme can improve the system performances effectively when the MIMO processes with severe model mismatches and strong external disturbances. Besides, the design method has three additional advantages. First, the derived controller and observer are given in analytical forms, the design procedure is simple. Second, the orders of the designed controller and observer are low, they can be implemented easily in practice. Finally, the performance and robustness can be adjusted easily by tuning the parameters in the designed controller and observer. It is useful for practical application. Simulations are provided to illustrate the effectiveness of the proposed control scheme.     

Smith predictor with inverted decoupling for square multivariable time delay systems

This paper presents a new methodology to design multivariable Smith predictor for n×n processes with multiple time delays based on the centralised inverted decoupling structure. The controller elements are calculated in order to achieve good reference tracking and decoupling response. Independent of the system size, very simple general expressions for the controller elements are obtained. The realisability conditions are provided and the particular case of processes with all of its elements as first-order plus time delay systems is discussed in more detail. A diagonal filter is added to the proposed control structure in order to improve the disturbance rejection without modifying the nominal set-point response and to obtain a stable output prediction in unstable plants. The effectiveness of the method is illustrated through different simulation examples in comparison with other works.     

Robust stability of uncertain singular time-delay systems via LFT approach

The robust stability problem of continuous-time singular systems with multiple state delays and bounded parametric uncertainties is considered. Both commensurate and non-commensurate delays are investigated. On the basis of the linear fractional transformations (LFTs) framework and μ-analysis, a systematic approach is derived to convert the robustness problem to a robust nonsingularity problem. Some explicit conditions are proposed to guarantee the uncertain singular time-delay system being regular, impulse-free and stable independent of delay. Two illustrative examples are given to show the feasibility of the proposed technique.     

随机时延网络化不确定系统的鲁棒H∞滤波

研究了一类具有随机时延的网络化不确定系统的 H∞ 滤波器设计问题. 这类时延的产生是由于传感器和滤波器通过有限带宽的网络连接而引起的系统测量数据的滞后, 而且它是随机发生的. 本文采用满足 Bernoulli 分布随机变量来描述测量数据的这种随机时延. 利用线性矩阵不等式, 给出了全阶和降阶的滤波器存在的充分条件. 所设计的滤波器使得滤波误差系统是均方指数稳定且具有给定的H∞ 性能. 数值仿真表明设计方法的有效性.