一种不确定离散时间系统的变结构控制方法

针对离散时间系统变结构控制中存在的问题,利用指数趋近律的趋近特性,提出一种新的离散变结构控制方法.利用递推估计的方法设计变结构控制律,有效地抵消了线性系统中慢变不确定性的影响,实现了对慢变非线性系统的控制.该方法克服了以往控制方法中需已知扰动上界的限制,降低了抖振,加快了趋近速度.仿真结果证明了该方法的有效性.     

Variable structure control for a wheeled mobile robot

This paper is concerned with a robust control for wheeled mobile robots. Mobile robots equipped with undeformable wheels are referred to as 'wheeled mobile robots' and constitute a typical example of non-holonomic systems, where the standard control algorithms developed for robotic manipulators without constraints are no longer applicable. It is shown using the formulation of a dynamic feedback linearization (DFL) methodology that a robust sliding mode controller is an efficient design tool to take into account stabilization and tracking control problems. Compared with previous studies based on DFL, the proposed method shows improvement of the trajectory tracking and stabilization process. The robustness is guaranteed in the presence of parameter uncertainty or unmodeled dynamics by the robust sliding mode control technique. Simulation results along with the conclusions drawn are discussed.     

Variable control scheme in the cascade processes

The article considers the variables process control scheme for cascade processes. We construct variable sample sizes and sampling intervals (VSSI) control charts to effectively monitor the input variable and the output variable produced by a cascade process. The performance of the proposed VSSI control charts is measured by the adjusted average time to signal derived by a Markov chain approach. An example of the metallic film thickness of the computer connectors system shows the application and the performance of the proposed VSSI control charts in detecting shifts in means of the cascade process. Furthermore, the performance of the proposed VSSI control charts and the fixed sample sizes and sampling intervals control charts are compared by numerical analysis results. These demonstrate that the former is much faster in detecting small and medium shifts. The optimum VSSI control charts are also proposed using optimization technique when quality engineers cannot specify the values of the variable sample sizes and sampling intervals. It has been found that the optimum VSSI control charts work and are thus suggested whenever quality engineers cannot specify the values of variable sample sizes and sampling intervals. Furthermore, the impacts of misusing Shewhart charts to monitoring the process means on the cascade process are also investigated.     

Variable structure control design for uncertain discrete-timesystems

The main differences between the designs of discrete-time variable structure systems (VSS) and continuous-time VSS are the determination of the switching hyperplane and the satisfaction of the hitting/sliding condition. These differences yield many difficulties in the design of sliding mode control for the discrete-time VSS. This note tries to overcome these difficulties and design a simple sliding mode control for a single input discrete-time VSS such that not only the discrete-time uncertain system is stabilized robustly, but also the chattering along the sliding mode is reduced explicitly. Instead of the conventional switching hyperplane, in the discrete-time case a “switching region”, which includes the hyperplane S₀ and its neighborhood, is determined and used. The determination of the switching region is to locate the equilibrium point of the nominal subsystem on each hyperplane S_p outside the switching region such that the state motions inside and outside the switching region will occur alternately until the state of the closed-loop system reaches the origin. Moreover, we prove that the robustness property is retained whenever the uncertainty satisfies a standard matching condition     

Variable structure control for three-variable autocatalytic reaction

In this paper, two irreversible exothermic autocatalytic reactions which carry out in continuous stirred tank reactor (CSTR) are considered. A differential-algebraic system is applied to model these chemical reactions. The stability and the dynamic behavior are studied for the differential-algebraic system. The Hopf bifurcation appears when the parameter exceeds a critical value. In order to eliminate this complex behavior, the differential-algebraic system is described by a single-input and single-output system with parameter varying within definite intervals, and then variable structure control with sliding mode based on a special power reaching law is designed to stabilize this chemical system. Numerical simulations are given to illustrate the effectiveness of the method.     

Variable structure model following control for industrial robots

A variable structure model following control (VSMFC) strategy for the control of most types of industrial robots (according to a classification ofCoiffet 1983) has been presented. For 99% of the robots given in the classification of Coiffet (1983), the dynamics of each link can be represented by a simple model with the nonlinearities and coupling dynamics decoupled from the linear part (Stoten 1985). This facilitates the designer to have a modified VSMFC law, which will maintain sliding mode motion of the error and its derivative, referred to as the representative point (RP), on a user chosen switching line and to drive the RP to the origin of the error plane (error is defined as the difference between the states of the reference model and those of the plant). When in sliding mode the system remains insensitive to parameter variations and disturbances     

一种离散时间系统变结构控制的新方法

研究离散时间系统变结构控制问题,提出一种新的离散变结构趋近律.利用该趋近律设计的离散变结构控制器,不仅能大幅度削弱抖振,使系统运动最终趋干原点不存在稳态振荡,而且可使系统的准滑动模态保持步步穿越切换面的基本属性,有效地改善了控制品质,提高了系统的鲁棒性.仿真结果验证了该方法的有效性与合理性.     

基于幂次趋近律的一类离散时间系统的变结构控制

针对一类离散时间系统,提出一种变结构控制设计方法.通过构造幂次趋近律,使得系统的准滑动模态不仅能保持步步穿越切换面的基本属性,而且能大幅度削弱抖振,有效地改善控制品质,提高系统的鲁棒性.采样周期越短,该控制方法的效果越明显.仿真实例表明了所设计控制器的可行性和有效性.     

Variable structure control of a class of uncertain systems

This brief paper proposes a method for tuning the parameters of a variable structure controller. The approach presented extracts the error at the output of the controller and applies a nonlinear tuning law using this error measure. The adaptation mechanism drives the state tracking error vector to the sliding hypersurface and maintains the sliding mode. In the simulations, the approach presented has been tested on the control of Duffing oscillator and the analytical claims have been justified under the existence of measurement noise, uncertainty and large nonzero initial errors.     

基于输出反馈的直升机变结构控制律设计

针对直升机的小扰动模型,设计了静态输出反馈滑模控制器（SOFSMC）。利用参考模型,实现了直升机的相关动态指标。针对滑模面的设计问题,将其等价地转化为一组双线性矩阵不等式（BLMI）,并采用迭代线性矩阵不等式（ILMI）技术来求解。针对控制律的综合问题,给出了一种基于单位向量法的控制律,并通过引入线性反馈来保证系统进入滑动模态后线性控制部分与标称系统的线性控制部分的一致性。仿真结果验证了该方法的有效性。     

随机马尔可夫跳变系统的变结构控制设计

采用滑动扇区方法,研究了不确定随机马尔可夫跳变系统的变结构控制设计问题。首先给出随机马尔可夫跳变系统滑动扇区的定义,然后基于线性矩阵不等式技术,提出一种滑动扇区及变结构控制律设计方法。经过理论证明该控制律能够确保随机马尔可夫跳变不确定系统二次稳定,并有效地抑制抖振。最后数值仿真算例验证了控制方案的有效性。     

Variable structure control of stochastic systems

In this paper, the problem of variable structure control of stochastic (SVSC) systems is proposed and the corresponding variable structure control strategies with complete and incomplete state information are established. The concepts of stochastic sliding mode and sliding motion band are introduced which may be regarded as the basic characteristics of SVSC systems. Robustness of SVSC systems is considered and a general design procedure for SVSC systems is presented. The effectiveness of the proposed control method is shown by simulation results.     

离散交通流的变结构控制

为了得到稳定有序的道路交通流,依据离散趋近律,设计了交通流的速度控制器.考虑到由于匝道的流入和流出使得交通流具有不确定性,设计了动态扰动补偿器.以各路段的密度为控制目标,先通过密度函数的离散趋近律求得目标速度,然后利用速度控制器使得速度在有限步内等于目标速度.当控制器参数满足一定条件时,交通流密度最终稳定在一定的范围内,同时给出了算法步骤和证明.仿真结果显示,速度控制器将有匝道路段的交通流密度稳定在指定值附近,而无匝道路段的交通流密度趋于指定值,从而避免了道路拥挤的发生.     

凸胞型不确定系统的变结构控制

讨论了凸胞型不确定系统的变结构控制,利用LMI方法,给出了滑模面存在的充分条件,并且给出了线性滑模面的显式表达式.所设计的变结构控制律不仅能保证系统在有限时间到达滑模面,并且保证受限在滑模面上的降阶等价系统是D_R稳定的.最后,给出一个设计实例来阐明该控制方法的有效性.     

信息流变结构控制

研究通过信息流变结构控制方法实现对系统的信息结构进行实时切换的问题.提出信息流变结构控制系统所要满足的条件,提出、论证和实现了一种满足信息流变结构控制基本条件的控制系统框架,并对试验结果进行了分析.通过信息流方向的切换可以定义不同的信息处理关系,重组信息处理网络,获得不同的系统功能.     

带前置滤波器的MRAC系统的变结构控制

变结构控制对参数不确定性,外部干扰和未建模动态具有鲁棒性,并被应用到鲁棒模型参考自适应系统.其缺点是易产生抖振.本文设计一种带有前置滤波器的变结构控制器,改善系统动态性能并消除了抖振.前置滤波器使带有符号函数的控制切换产生连续可测信号,实际控制律是光滑的.控制器设计和不确定性估计中引入辅助信号和带有记忆功能的正规化信号,适当选取控制器参数,所设计的控制器保证了闭环系统稳定性和任意小的跟踪误差.仿真结果表明该算法是有效的.     

Variable structure control using system decomposition

An approach to the design of large variable structure systems subject to control bounds is introduced. The method includes a switching hyperplane design based on generalized inverses and system decomposition. To ensure reaching the hyperplane and achieving a sliding condition, the control is switched between local equivalent control and bounded corrective control. The design of the corrective control component is completed using system decomposition into smaller subsystems. An estimate of the domain of attraction corresponding to the bounded control is obtained and used to select the appropriate controller bounds. The method is illustrated using a fifth-order numerical example     

Variable structure surge control for constant speed centrifugal compressors

This paper presents the application of active control of surge in constant speed centrifugal compressors based on the Moore–Greitzer (MG) model. Different controllers are developed for a compression system equipped with a close-coupled valve (CCV) and a throttle control valve (TCV). The combination of the two valves helps suppress surge and assists in overcoming the drawbacks of each valve when it is used individually. The presented controllers are evaluated based on many performance indices. Accordingly, a case-based variable structure controller is developed that succeeds to stabilize the system for various operating conditions and to extend the stable range well beyond the surge line. A flow extension of 76% and a stable throttle level of 0.1, with substantially decreased pressure settling times, are reported. The developed controller performs significantly better compared to other nonlinear controllers, such as the backstepping controller.     

Variable structure output feedback control design for a class of uncertain dynamic systems

In this paper, we consider the problem of designing a variable structure output feedback control (VSOFC) law for a class of uncertain systems with mismatched uncertainty in the state matrix. We derive existence conditions of linear sliding surfaces in terms of constrained linear matrix inequalities (LMIs), and we give VSOFC strategies. We also give a simple design procedure and parameterizations of the linear switching surfaces, together with solvability conditions for the given constrained LMIs. Finally, we give a design example in order to show the effectiveness of our method.     

基于非线性指数趋近律的飞行器纵向姿态控制

基于一种非线性函数构造了新型的非线性指数趋近律,将非线性函数加入传统指数趋近律的等速趋近项系数,使等速趋近项系数随系统运动点到切换面的距离从大到小逐步变化,实现系统运动点到达过程由快到慢的变速控制。通过对到达时间的计算和比较,表明非线性指数趋近律缩短了到达时间,间接增强了系统鲁棒性,进一步降低了系统抖振。四旋翼飞行器纵向姿态控制的仿真结果表明了该控制方法的有效性。