Distributed Receding Horizon Control of Dynamically Coupled Nonlinear Systems

This paper considers the problem of distributed control of dynamically coupled nonlinear systems that are subject to decoupled constraints. Examples of such systems include certain large scale process control systems, chains of coupled oscillators and supply chain management systems. Receding horizon control (RHC) is a method of choice in these venues as constraints can be explicitly accommodated. In addition, a distributed control approach is sought to enable the autonomy of the individual subsystems and reduce the computational burden of centralized implementations. In this paper, a distributed RHC algorithm is presented for dynamically coupled nonlinear systems that are subject to decoupled input constraints. By this algorithm, each subsystem computes its own control locally. Provided an initially feasible solution can be found, subsequent feasibility of the algorithm is guaranteed at every update, and asymptotic stabilization is established. The theoretical conditions for feasibility and stability are shown to be satisfied for a set of coupled Van der Pol oscillators that model a walking robot experiment. In simulations, distributed and centralized receding horizon controllers are employed for stabilization of the oscillators. The numerical experiments show that the controllers perform comparably, while the computational savings of the distributed implementation over the centralized implementation is clearly demonstrated.     

Distributed LQR control for discrete-time homogeneous systems

This paper investigates the distributed linear quadratic regulation (LQR) controller design method for discrete-time homogeneous scalar systems. Based on the optimal centralised control theory, the existence condition for distributed optimal controller is firstly proposed. It shows that the globally optimal distributed controller is dependent on the structure of the penalty matrix. Such results can be used in consensus problems and used to find under which communication topology (may not be an all-to-all form) the optimal distributed controller exists. When the proposed condition cannot hold, a suboptimal design method with the aid of the decomposition of discrete algebraic Riccati equations and robustness of local controllers is proposed. The computation complexity and communication load for each subsystem are only dependent on the number of its neighbours.     

A Distributed Fault-Tolerant Design for Multiple-Server VOD Systems

Fault tolerance is an important design criterion for reliable and robust video-on-demand systems. Conventional fault-tolerant designs use either a primary backup or an active replication method to provide system fault tolerance. However, these approaches suffer from low utilization of the backup or replication system. In this paper we propose two playback-recovery schemes for distributed video-on-demand systems called the forward playback-recovery scheme and the backward playback-recovery scheme. Unlike conventional fault-tolerant designs, our schemes use existing playback resources to recover faulty playbacks without allocating new resources, significantly reducing recovery overhead. To use the schemes effectively, we developed a distributed algorithm for determining the order and gap information between the playbacks on the distributed video-on-demand servers so that overhead for recovering from a server failure can be minimized. This algorithm achieves N – 1 fault-tolerant resiliency for N-server video-on-demand systems. In addition, three server-recovery policies are also presented to guide surviving servers in applying the proper scheme to recover faulty playbacks, thus reducing overall recovery costs. Simulation results show that the proposed recovery schemes are effective and useful in designing fault-tolerant multiple-server video-on-demand systems.     

Disturbance Decoupled Observers for Systems With Unknown Inputs

This note deals with the design of reduced-order disturbance decoupled scalar functional observers for linear systems with unknown inputs. Based on a parametric approach, existence conditions are derived and a design procedure for finding reduced-order scalar functional observers is given. The derived existence conditions are relaxed and the procedure can find first-order disturbance decoupled scalar functional observers for some cases where the number of unknown inputs is more than the number of outputs. Also, the observer matching condition, which is the necessary requirement for the design of state observers for linear systems with unknown inputs, is not required. Numerical examples are given to illustrate the attractiveness of the proposed design method.      

分布式动态更新支持系统：研究综述

一些服务于关键应用领域、提供持续服务的分布式系统软件需要不断地进化，以修正软件故障、扩展服务功能、提高系统性能，从而产生动态更新的需求，即保证不中断系统服务的同时实现对系统功能的更新。由于分布式系统本身的复杂性，使得其上的动态更新比较复杂，一般需要做的工作包括：在适当的时候自动产生和传递更新消息；透明地实施更新、验证更新的合法性、一致性并处理非法更新下的容错问题；支持多版本节点之间的交互；对更新期间滞留的消息进行处理。本文围绕支持动态更新分布式系统的相关工作，从一般需求、功能目标、需要解决的关键问题、现有的工作成果以及将来的工作五个方面做了较为综合的阐述。     

Event-triggered MPC Design for Distributed Systems With Network Communications

This paper deals with the communication problem in the distributed system, considering the limited battery power in the wireless network and redundant transmission among nodes. We design an event-triggered model predictive control (ET-MPC) strategy to reduce the unnecessary communication while promising the system performance. On one hand, for a linear discrete time-invariant system, a triggering condition is derived based on the Lyapunov stability. Here, in order to further reduce the communication rate, we enforce a triggering condition only when the Lyapunov function will exceed its value at the last triggered time, but an average decrease is guaranteed. On the other hand, the feasibility is ensured by minimizing and optimizing the terminal constrained set between the maximal control invariant set and the target terminal set. Finally, we provide a simulation to verify the theoretical results. It's shown that the proposed strategy achieves a good trade-off between the closed-loop system performance and communication rate.      

存在部分解耦扰动的网络化系统容错控制

针对一类存在执行器故障和部分解耦扰动的离散时间网络化控制系统,研究测量数据随机丢失情况下的主动容错控制问题。首先,通过模型转换将原系统化为一个与之等价的状态增广系统;然后在考虑测量数据发生随机丢失情况下,构造未知输入观测器(unknown input observer, UIO)实现对系统状态与故障的联合估计,再基于状态和故障的在线估计值,设计基于信号补偿的容错控制律实现对原系统的主动容错控制。在该容错控制算法中,观测器与控制器增益的存在性条件均可利用李雅普诺夫稳定性理论对误差系统进行随机分析得到,相应的估计器和控制器参数可通过在线求解具有凸约束的矩阵不等式获得。最后,通过一个喷气式发动机模型的仿真算例验证所提出的故障估计与主动容错控制方法的有效性。     

分布式防火墙系统的安全机制设计

分布式系统因为其物理位置上的松耦合结构具有一定的脆弱性，系统中各成员的动态性和数据传输的不可靠性使得系统自身的安全成为分,布式系统亟待解决的问题。本文就以分布式防火墙系统为例，提出了一个安全模型架构，通过自定义的一套简单，灵活，实用的安全机制来实现系统自身的安全性。     

Agent-Based Design Model of Adaptive Distributed Systems

A next generation distributed system is expected to adapt to various changes of both the users' requirements and the operational conditions of environment where the distributed system operates. The aim of our research is to establish a new design model of an adaptive distributed system (ADS) to deal with various changes occurred in the system environment. In this paper, we propose an agent-based architecture of ADS, based on the agent-based computing paradigm. Then, we implement a prototype of the ADS with respect to videoconferencing applications and also evaluate the adaptive functions of the ADS realized on the basis of the proposed architecture.     

Using Reusable Design Patterns in Distributed Systems

The article revealed the software design issues for the object-oriented distributed system. By surveying several existed design issues, the solution of common design issues is conducted which is compromised by design patterns. Each pattern is described according to its functionality which could be valuable for objected-oriented distributed system developer.     

Timers for Distributed Systems

We deal with temporal aspects of distributed systems, introducing and studying a new model called timed distributed π-calculus. This model extends distributed π-calculus with timers, transforming the communication channels into temporary resources. Distributed π-calculus describes located interactions between processes with restricted access to resources. We introduce time constraints by considering timeout timers for channels. Combining these timers with types and locations, we provide a formal framework able to describe complex systems with constraints on time and on resource access. Its typing system and operational semantics are presented. It is proved that the passage of time does not interfere with the typing system. The new model is proved to be sound by using a method based on subject reduction.     

A Comprehensive Model for the Design of Distributed Computer Systems

The availability of micro-, mini-, and supercomputers has complicated the laws governing the economies of scale in computers. A recent study by Ein-Dor [7] concludes that it is most effective to accomplish any task on the least powerful type of computer capable of performing it. This change in cost/performance, and the promise of increased reliability, modularity, and better response time has resulted in an increased tendency to decentralize and distribute computing power. But some economic factors, such as the communication expenses incurred and increased storage with distributed systems are working against the tendency to decentralize. It is clear that in many instances the optimal solution will be an integration of computers of varying power.     

基于近似模拟的多智能体系统分布式层次控制设计

本文主要探讨基于近似模拟的多智能体系统分布式层次控制的设计问题。为降低问题复杂度,首先建立了一个简单的抽象系统指导各智能体,继而讨论这一抽象系统和多智能体之间的模拟关系。借助于该抽象系统,给出多智能体系统完成一类协调任务的分布式层次控制器。同时利用模拟函数和共同Lyapunov函数,进一步分析了多个体系统在切换拓扑下的集体行为。     

一种互联系统的分布式结构控制器设计方法

研究了一类具有有限耦合连接的分布式互联系统的结构控制器设计问题.与现有的研究不同,在所考虑的分布式网络控制系统中,耦合通信连接的数目是有上界的,而不是固定不变的.利用李亚普诺夫泛函方法,给出闭环系统指数稳定性的充分条件.然后将这种稀疏约束问题转化为势约束问题,并运用一种放松方法来解决这一非线性问题.上述方法不同于传统的...     

基于对角解耦的多变量约束广义预测控制

由于多变量系统各变量之间往往存在严重耦合现象,在对系统进行对角解耦的基础上,设计了带约束输入的广义预测控制算法。该算法保证了系统输出有效跟踪设定值,并且充分考虑了输入信号及其增量均受约束的情况,使其均被控制在允许范围之内,同时避免了求解Diophantine方程,很大程度上减少了计算量。仿真结果表明该算法可以在很大程度上削弱变量之间的耦合程度,且具有良好的控制效果。     

一种嵌入式实时分布计算系统的安全策略设计

本文介绍了一种基于防火墙和安全分布式操作系统的,嵌入式实时分布计算系统的安全策略设计,其中由包过滤路由器和堡垒主机构成的防火墙屏蔽来自系统外部的攻击,防火墙中包含了IPSec协议安全机制。分布计算系统内部的安全保障则源自扩充了安全服务的分布式操作系统。     

Distributed Time-Varying Formation Tracking Analysis and Design for Second-Order Multi-Agent Systems

Distributed time-varying formation tracking analysis and design problems for second-order multi-agent systems with one leader are studied respectively, where the states of followers form a predefined time-varying formation while tracking the state of the leader. Different from the previous results on formation tracking control, the formation for the followers can be described by specified time-varying vectors and the trajectory of the leader can also be time-varying. A distributed formation tracking protocol is constructed using only neighboring relative information. Necessary and sufficient conditions for second-order multi-agent systems with one leader to achieve time-varying formation tracking are proposed by utilizing the properties of the Laplacian matrix, where the formation tracking feasibility constraint is also given. An approach to design the formation tracking protocol is proposed by solving an algebraic Riccati equation. The presented results can be applied to deal with the target enclosing problems and consensus tracking problems for second-order multi-agent systems with one target/leader. An application in the target enclosing of multiple vehicles is provided to demonstrate the effectiveness of the theoretical results.     

一类时滞分布参数系统滑动模控制器的设计

基于变结构控制理论,提出一种用变结构控制方法来消除参数不确定性对系统性能的影响。首先建立延迟为τ的系统模型,鉴于该系统具有稳定与非稳定因素,我们制定一系列标准,从而写出系统的滑动模运动方程,经过证明,确认系统模型在所给的控制律下能顺利进入滑模区域,且处于该滑动切换面之下时,控制状态是稳定的,因此达到了设计要求。经实验征明,该滑动模控制器具有普遍性。