Closed-loop identification with an unstable or nonminimum phase controller

In many practical cases, the identification of a system is done in closed loop with some controller. In this paper, we show that the internal stability of the resulting model, in closed loop with the same controller, is not always guaranteed if this controller is unstable and/or nonminimum phase, and that the classical closed-loop prediction-error identification methods present different properties regarding this stability issue. With some of these methods, closed-loop instability of the identified model is actually guaranteed. This is a serious drawback if this model is to be used for the design of a new controller. We give guidelines to avoid the emergence of this instability problem; these guidelines concern both the experiment design and the choice of the identification method.     

High-performance multi-scale control scheme for stable,integrating and unstable time-delay processes

This paper presents a new multi-scale control scheme which is applicable to both stable and integrating/unstable time-delay processes. The salient feature of the proposed scheme is to decompose a given plant into a sum of basic modes, where an individual sub-controller is specifically designed to control each of these modes. An overall multi-scale controller is then synthesized by combining all the sub-controllers in such a way to achieve good cooperation among the different plant modes as to achieve good nominal performance and performance robustness. Extensive numerical study shows that the proposed multi-scale control scheme provides substantial improvement in control performance/robustness over the classical Smith predictor and some of its well-established variants.     

新加密文件系统的研究与实现

为了解决Windows系统中文件加密存储的难题,分析了Windows EFS系统的不足,深入研究了过滤驱动开发过程中对IRP的处理、文件状态跟踪、避免重入等关键技术,使用文件过滤驱动技术,设计并实现了一个新的加密文件系统.该系统对用户完全透明,可以根据用户的策略对指定文件、文件夹或者某一类型文件进行加密存储,支持NTFS、FAT等多种文件系统,加密算法可以更改.实验结果表明,该系统性能良好且在功能和应用上都扩充了Windows EFS.     

某基地设备综合监控系统网络通讯设计与实现

针对现场现有的监控系统各自封闭,并不兼容的现状,提出了综合监控系统网络通讯方案,构建了集环境温湿度监控、设备监控、变电站监控和风水监控一体的综合监控系统。实际的运行效果证明,该系统设计合理,具有良好的可靠性和实用性。     

Path-following for linear systems with unstable zero dynamics

A constructive solution to the path-following problem for MIMO linear systems with unstable zero dynamics is developed. While the original control variable steers the system output along the path, the path parameter θ is used as an additional control to stabilize zero dynamics with a feedback law which is nonlinear due to the path constraint. A sufficient condition for solvability of the path-following problem is given in terms of the geometric properties of the path. When this condition is satisfied, an arbitrary small L₂ norm of path-following error can be achieved, thus avoiding performance limitations of the standard reference tracking problem imposed by unstable zero dynamics.     

Adaptive suboptimal control of a linear system with bounded disturbance

An adaptive suboptimal control of a linear discrete system with unknown parameters is proposed. An additive disturbance v_t acting on the system is supposed to be uniformly bounded. The criterion is sup_vtI(y^∞₁, u^∞₁), where y_t is the output, u_t is the control. The adaptive control law gives almost the same guaranteed value of the criterion as the optimal linear feedback does for a system with known parameters.     

Stabilization of a distributed system with a stable compensator

It is proved that a multivariable distributed system, that has no poles on the boundary of the half-plane of analyticity of its transfer function, can be stabilized with a stable strictly proper lumped compensator if and only if the standard parity interlacing condition is satisfied. The problem is formulated and solved in a Banach algebra of transfer functions that are Laplace transforms of measures having a finite total variation with respect to some given submultiplicative weight function. In particular, this result can be applied to transfer functions in the Callier-Desoer class, and it seems to be new even for this class. The proofs are closely related to and based on the scalar case solved previously.     

Stabilization of switched continuous-time systems with all modes unstable via dwell time switching

Stabilization of switched systems composed fully of unstable subsystems is one of the most challenging problems in the field of switched systems. In this brief paper, a sufficient condition ensuring the asymptotic stability of switched continuous-time systems with all modes unstable is proposed. The main idea is to exploit the stabilization property of switching behaviors to compensate the state divergence made by unstable modes. Then, by using a discretized Lyapunov function approach, a computable sufficient condition for switched linear systems is proposed in the framework of dwell time; it is shown that the time intervals between two successive switching instants are required to be confined by a pair of upper and lower bounds to guarantee the asymptotic stability. Based on derived results, an algorithm is proposed to compute the stability region of admissible dwell time. A numerical example is proposed to illustrate our approach.     

Proportional stabilization and closed-loop identification of an unstable fractional order process

This paper deals with proportional stabilization and closed-loop step response identification of the fractional order counterparts of the unstable first order plus dead time (FOPDT) processes. At first, the necessary and sufficient condition for stabilizability of such processes by proportional controllers is found. Then, by assuming that a process of this kind has been stabilized by a proportional controller and the step response data of the closed-loop system is available, an algorithm is proposed for estimating the order and the parameters of an unstable fractional order model by using the mentioned data.     

Globally stable adaptive system design for minimum phase SISO plants with input saturation

Model reference adaptive control problem for single-input single-output time-invariant continuous-time plants with input saturation is considered with main attention focused on global properties. A sufficient condition is presented and a new design method of adaptive control systems is proposed. If a priori information about the plant is available to choose the reference model and the reference input so that the sufficient condition holds, the closed-loop adaptive control system designed by the proposed method can have global stability and globally output tracking property. It is shown that the sufficient condition becomes necessary in some cases.     

一类不确定时滞系统的变结构控制

本文针对不确定输入时滞系统,提出了一种具有滑动模态的变结构控制。先把系统变换成形式上不含时滞的系统,再据变换后的系统设计切换函数和控制律。用切换函数使滑动模态渐近稳定,用变化的不连续控制保证滑动模态的存在和削弱抖振。最后,通过一开环不稳定的不确定系统仿真,验证本文的方法是有效的。     

PID controller synthesis for a class of unstable MIMO plants with I/O delays

Conditions are presented for closed-loop stabilizability of linear time-invariant (LTI) multi-input, multi-output (MIMO) plants with I/O delays (time delays in the input and/or output channels) using PID (Proportional+Integral+Derivative) controllers. We show that systems with at most two unstable poles can be stabilized by PID controllers provided a small gain condition is satisfied. For systems with only one unstable pole, this condition is equivalent to having sufficiently small delay-unstable pole product. Our method of synthesis of such controllers identify some free parameters that can be used to satisfy further design criteria than stability.     

锅炉—汽轮机系统的逆系统控制方法

针对非线性锅炉－汽轮机系统各变量间所存在的严重非线性强耦合特征,提出了对其控制的逆系统解耦控制方法,仿真结果表明,采用逆系统控制方法设计的锅炉－汽轮机系统,可在全负荷范围内克服其非线性和严重耦合性,优于其它基于局部工作点所设计的Hx等控制方法。     

Stability analysis of switched positive linear systems with stable and unstable subsystems

This paper addresses the stability problem of switched positive linear systems with stable and unstable subsystems. Based on a multiple linear copositive Lyapunov function, and by using the average dwell time approach, some sufficient stability criteria of global uniform exponential stability are established in both the continuous-time and the discrete-time cases, respectively. Finally, some numerical examples are given to show the effectiveness of the proposed results.     

通用型DRM系统的研究与实现

针对目前DRM系统只对特定类型的文件进行保护的问题,提出了与文件类型无关的通用的DRM系统框架.该框架采用过滤器驱动技术,在操作系统内核文件系统驱动层与I/O管理器问插入一个中层驱动程序--过滤器驱动程序,用来截获I/O请求,并在内核中对文件进行加/解密,解密后的文件由对应的播放器或阅读器来显示.系统框架在设计实现中表明了它的可行性.     

Finite spectrum assignment of unstable time-delay systems with a safe implementation

The instability mechanisms, related to the implementation of distributed delay controllers in the context of finite spectrum assignment, were studied in detail in the past few years. In this note we introduce a distributed delay control law that assigns a finite closed-loop spectrum and whose implementation with a sum of point-wise delays is safe. This property is obtained by implicitly including a low-pass filter in the control loop. This leads to a closed-loop characteristic quasipolynomial of retarded type, and not one of neutral type, which was shown to be a cause of instability in previous schemes.     

Fractional-order unstable pole-zero cancellation in linear feedback systems

As a very well-known classical fact, non-minimum phase zeros of the process put some limitations on the performance of the feedback system. The source of these limitations is that non-minimum phase zeros cannot be cancelled by unstable poles of the controller since such a cancellation leads to internal instability. The aim of this paper is to propose a method for fractional-order cancellation of non-minimum phase zeros of the process and studying its properties. It is specially shown that the proposed cancellation strategy increases the phase and gain margin without leading to internal instability. Since the systems with higher gain and phase margin are easier to control, the proposed method can be used to arrive at more effective controls, which is also verified by the simulation results.     

Stabilization of unstable periodic orbits for a chaotic system

For a switched arrival system with three buffers, assuming that the input rate of work and processing time per unit are constant, it has been proved that the system is chaotic. Now we present a control method to stabilize an unstable periodic orbit by controlling its continuous limit processing time. Our method is based on the geometrical property of the system behavior and sliding-mode approach, and can completely control the chaos. Consequently, an orbit starting from any point will arrive at the periodic orbit within the calculable finite controlled switches.