Design of a Robust Optimal Decentralized PI Controller Based on Nonlinear Constraint Optimization For Level Regulation: An Experimental Study

This paper presents the development of a new robust optimal decentralized PI controller based on nonlinear optimization for liquid level control in a coupled tank system. The proposed controller maximizes the closed-loop bandwidth for specified gain and phase margins, with constraints on the overshoot ratio to achieve both closed-loop performance and robustness. In the proposed work, a frequency response fitting model reduction technique is initially employed to obtain a first order plus dead time (FOPDT) model of each higher order subsystem. Furthermore, based on the reduced order model, a proposed controller is designed. The stability and performance of the proposed controller are verified by considering multiplicative input and output uncertainties. The performance of the proposed optimal robust decentralized control scheme has been compared with that of a decentralized PI controller. The proposed controller is implemented in real-time on a coupled tank system. From the obtained results, it is shown that the proposed optimal decentralized PI controller exhibits superior control performance to maintain the desired level, for both the nominal as well as the perturbed case as compared to a decentralized PI controller.      

INFORMATION STRUCTURE CONSIDERATIONS FOR DECENTRALIZED LARGE‐SCALE SYSTEMS

Decentralized control problems are studied in a differential vector space framework. A new notion called the characteristic subspace, which is described by a set of integral chains in the differential vector space of a system is introduced to describe the information structure of a decentralized control system. New criteria are presented for reconfiguring the information structure under decentralized feedback. The new criteria expose certain intrinsic properties of decentralized control systems.     

网络控制系统的网络安全研究

基于网络控制系统(networkedcontrolsystem,NCS)的基本概念,分析了NCS网络安全体系结构和动态需求,讨论了确保NCS网络安全的各种安全机制,提出了自律分散NCS安全体系策略,指出了如何设计具有自律可控性和自律可协调性的NCS安全体系的思想方法,并给出了相应的模型结构。     

Decentralized Observer Design for a Class of Nonlinear Uncertain Large Scale Systems with Lumped Perturbations

Many valuable properties of the state feedback method can not be applied to some class of control systems while some of the system states cannot be measured directly. An attractive alternative approach is to make good use of a state observer. In this paper, a new decentralized sliding mode observer (DSMO) is proposed for a class of nonlinear uncertain large‐scale systems (LSS) with lumped perturbations based on the sliding mode control (SMC) theory. Our main result presented here is that we introduce a new switching term to the traditional LSS observer design for a class of large‐scale system to generate a new decentralized sliding mode observer. The generalized matrix inverse concept is adopted to avoid using the un‐measurable state and the global reaching condition of the sliding mode for each error subsystem is guaranteed. The stability of each equivalent error subsystem is verified based on the strictly positive real concept. It also shows that the investigated uncertain large‐scale systems still possesses the property of insensitivity to the lumped perturbations as does the traditional linear system. Moreover, the state transformation approach is no longer needed as there is no longer concern about the problems of finding a suitable transformation or indirect estimated states, since the proposed DSMO is not based on the transformed system model. Finally, a numerical example with a series of computer simulations is given to demonstrate the validity of the proposed decentralized sliding mode observer.     

Direct decentralized neural control for nonlinear MIMO magnetic levitation system

A direct modified Elman neural networks (MENNs)-based decentralized controller is proposed to control the magnets of a nonlinear and unstable multi-input multi-output (MIMO) levitation system for the tracking of reference trajectories. First, the operating principles of a magnetic levitation system with two moving magnets are introduced. Then, due to the exact dynamic model of the MIMO magnetic levitation system is not clear, two MENNs are combined to be a direct MENN-based decentralized controller to deal with the highly nonlinear and unstable MIMO magnetic levitation system. Moreover, the connective weights of the MENNs are trained online by back-propagation (BP) methodology and the convergence analysis of the tracking error using discrete-type Lyapunov function is provided. Based on the direct and decentralized concepts, the computational burden is reduced and the controller design is simplified. Furthermore, the experimental results show that the proposed control scheme can control the magnets to track various periodic reference trajectories simultaneously in different operating conditions effectively.     

Integrity of systems under decentralized integral control

A decentralized controller that maintains closed loop stability, when the individual controllers fail or are taken out of service, provides fault tolerance and flexibility in operation. Recently, necessary and sufficient conditions [Gündes, Kabuli, 2001. IEEE Transactions on Automatic Control, 46(2), 296-301] for the existence of a block decentralized controller with integral action for a system to possess integrity against controller failures were proposed. In this paper, these conditions are equivalently expressed using the well-known notions of Niederlinski index (NI) and block relative gain (BRG). The alternate representation implies that under minor assumptions, the available necessary conditions based on NI and BRG are actually both necessary and sufficient. We also show that confirming the existence of a block decentralized controller with integral action such that the system has integrity is NP-hard.     

Structural modification of systems using discretization and generalized sampled-data hold functions

This paper investigates the decentralized control of LTI continuous-time plants using generalized sampled-data hold functions (GSHF). GSHFs can be used to modify the structure of the digraph of the resultant discrete plant, by removing certain interconnections in the discrete-time equivalent model to form a hierarchical system model of the plant. This is a new application of discretization and has, as its motivation, the design of decentralized controllers using centralized methods.     

On multivariable stability in the gain space

General existence conditions under which the stability of the individual loops of a multivariable system in a given compact and bounded gain space imply the global asymptotic stability of the multivariable system in the same space are very useful in practice and essentially indicate when in principle it is possible to obtain stable closed-loop performance of a multivariable system by tuning every loop separately. Such conditions are particularly useful for fault tolerant control of multivariable systems. This paper gives the required necessary and sufficient conditions and effectively unifies all previous work on diagonal stabilizability which includes as special cases: the diagonal dominance, the H matrix, the GKK matrix and the decentralized integral controllability (DIC) conditions reported previously in the literature. Some application examples are included.     

Discrete-time control of continuous systems with approximate decentralized fixed modes

In this paper, the discrete-time control of decentralized continuous-time systems, which have approximate decentralized fixed modes, is studied. It is shown that under certain conditions, discrete-time controllers can improve the overall performance of the decentralized control system, when a linear time-invariant continuous-time controller is ineffective. In order to obtain these conditions, a quantitative measure for different types of approximate fixed modes in a decentralized system is given. In this case, it is shown that discrete-time zero-order hold (ZOH) controllers, and in particular, that generalized sampled-data hold functions (GSHF), can significantly improve the overall performance of the resultant closed-loop system. The proposed sampled-data controller is, in fact, a linear time-varying controller for the continuous-time system.     

大规模工业控制系统网络中间件设计

设计一种适用于大规模工业控制系统的网络中间件SCNet。采用面向对象和层次化设计,实现对底层操作系统的封装,提高跨平台的应用能力,为网络应用提供安全易用的对象化接口,并在多路分离、Transport等框架下实现系统化的复用。结合工业应用需求,设计数据整理、会话冗余和故障诊断功能,以解决TCP/IP报文分片问题,提高网络的容错能力和可用性。测试结果证明,SCNet具有较好的复用性和扩展性,能够满足工业控制系统对高性能和高可靠性的要求。     

航天器控制系统的自主诊断重构技术

自主诊断重构是确保航天器控制系统安全可靠自主运行的关键技术之一.本文针对航天器资源严重受限的客观情况,改变传统一味追求华丽算法与豪华配置的设计理念,从航天器的自身特性出发,深入挖掘诊断重构问题的本质,提出基于可诊断性与可重构性评价设计的研究思路.文章首先介绍了航天器自主诊断重构技术的发展现状,分析了当前技术的不足之处并探究了其深层原因;然后,提出了通过可诊断性与可重构性评价设计从根本上提高系统自主诊断重构能力的全新思路,梳理了其研究内容与研究概况;最后,对航天器控制系统自主诊断重构技术的发展趋势进行了展望.     

深空探测航天器控制系统自主管理软件架构研究

深空探测航天器距离远、环境复杂,测控站遥测和遥控操作不能满足控制的实时性和安全性要求,自主管理技术是提高航天器对未知环境的应对能力、提升飞控实效性的主要手段。回顾了深空探测航天器自主管理技术发展的现状,分析了实现自主管理的关键技术,并结合深空探测工程实施和技术发展需求,提出了未来航天器自主管理系统体系结构和软件架构,并进行了仿真实验。     

Coordinated nonlinear robust control of TCSC and excitation for multi-machine systems

An advanced nonlinear robust control scheme is proposed for multi-machine power systems equipped with thyristor-controlled series compensation (TCSC). First, a decentralized nonlinear robust control approach based on the feedback linearization and H∞ theory is introduced to eliminate the nonlinearities and interconnections of the studied system, and to attenuate the exogenous disturbances that enter the system. Then, a system model is built up, which has considered all the generators‘ and TCSC‘s dynamics, and the effects of uncertainties such as disturbances. Next, a decentralized nonlinear robust coordinated control law is developed based on this model. Simulation results on a six-machine power system show that the transient stability of the power system is obviously improved and the power transfer capacity of long distance transmission lines is enhanced regardless of fault locations and system operation points. In addition, the control law has engineering practicality since all the variables in the expression of he control strategy can be measured locally.     

Optimal decentralized control of large scale systems

This paper presents a new optimized decentralized controller design method for solving the tracking and disturbance rejection problems for large-scale linear time-invariant systems, using only low-order decentralized controllers. To illustrate the type of results which can be obtained using the new optimized decentralized control design method, the control of a large flexible space structure is studied and compared with the standard centralized LQR-observer controller. The order of the resultant decentralized controller is much smaller than that of the standard centralized LQR-observer controller. The proposed controller also has certain fail-safe properties and, in addition, it can be five orders of magnitude more robust than the standard LQR-observer controller based on their real stability radii. The new decentralized controller design method is applied to a large flexible space structure system with 5 inputs and 5 outputs and of order 24.     

Advanced multicast class-based bandwidth over-provisioning

Dynamic bandwidth aggregate over-provisioning has been proposed to provide differentiated services with scalable Quality of Service (QoS) control. Previous research showed that efficient over-reservation control allows minimizing QoS control overhead with reduced waste of bandwidth and blocking probability. However, existing over-reservation centric solutions are still inefficient in the face of network dynamics, as they are not able to accommodate the dynamic service demands, thus failing to optimize the bandwidth usage. This paper proposes a new Advanced Class-based resource Over-Reservation (ACOR) solution for multicast sessions, which seeks increased network resources utilization while minimizing QoS control overhead. More specifically, ACOR is able to dynamically update the share of bandwidth between different classes of service, providing improved results with less complexity than current solutions. Our analytical and simulation results prove the cost-effective and scalable QoS control capabilities of ACOR in decentralized networks with multiple distributed ingress routers coordinating the QoS control.     

Robust feedback stabilization of underwater robotic vehicles

The controlled motion of an underwater vehicle is very likely to be affected by arbitrary disturbances with considerable magnitudes. In this paper, we develop a simple approach for optimal robust control design of underwater robotic vehicles having decentralized input-output structure. Our design method is based on an explicit condition on the control input matrix which has been found to be necessary and sufficient for a decentralized control system to be robust against arbitrary, but otherwise, bounded disturbances. That makes it possible to get optimal trade-off relations between the bounds of disturbances, the system output accuracy, and the control force limits. For the robust control design purpose, we apply decentralized sliding-mode control the stability of which can be easily verified using Lyapunov theory. In order to show the effectiveness of the design method, the controlled planar motion of an underwater robotic vehicle is taken as an illustrative example.     

一类具有不确定的互联大系统分散鲁棒输出跟踪控制器设计

针对一类具有不确定的互联大系统，研究了使受控系统鲁棒稳定和渐近跟踪参考输入的分散鲁棒跟踪控制器的设计问题，并对具有分散反馈控制器的闭环大系统，给出了其鲁棒稳定以及渐近跟踪的证明。     

An optimal control based approach to designing plantwide control system architectures

An approach to designing decentralized plantwide control system architectures is presented. The approach is based on splitting the optimal controller gain matrix that results from solving an output optimal control problem into feedback and feedforward parts. These two parts are then used to design and evaluate decentralized control systems. Results for the application of the methodology to a realistic, 4 by 4 reactor with recycle process are given. For this system, the optimal control based approach suggests feedback pairings that are significantly different than those suggested by the steady state RGA. The approach presented can give an indication if MPC is preferred over a decentralized approach to plantwide control. Comparison of the results produced by the best decentralized plantwide system and a model predictive control system are presented.     

分散控制系统结构的综合及其工业应用

本文论述了连续工业过程中分散控制结构的综合问题.首先讨论了一般分散控制结构 的可行性问题,并给出了存在相应的分散控制器使闭环系统具有渐近稳定性、终值无偏性及 鲁棒性的结构要求.其次研究了最经济结构的综合问题,提出了获得最少测量、最少控制与 最简单反馈结构的相应算法以及该综合算法的工业应用实例.     

Linear periodic controller design for decentralized control systems

In the decentralized control of linear time-invariant (LTI) systems, a decentralized fixed mode (DFM) is a system mode which is immoveable using an LTI controller, while a quotient DFM (QDFM) is one which is immoveable using any form of nonlinear time-varying compensation. If a system has no unstable DFMs, there are well-known procedures for designing an LTI stabilizing controller; for systems which have unstable DFMs but no unstable QDFMs, we provide a simple design algorithm which yields a linear periodic sampled-data stabilizing controller.